Gynecology_Novak

Gynecology_Novak. Programmed cell death emerged as an important factor in the growth of neoplasms. Historically, neoplastic growth was characterized by uncontrolled cellular proliferation that resulted in a progressive increase in tumor burden. It is recognized that the increase in tumor burden associated with progressive disease reﬂects an imbalance between cell proliferation and cell death. Cancer cells fail to respond to the normal signals to stop proliferating, and they may fail to recognize the physiologic signals that trigger programmed cell death. Modulation of Cell Growth and Function


Gynecology_Novak

Gynecology_Novak. Modulation of Cell Growth and Function The normal cell exhibits an orchestrated response to the changing extracellular environment. The three groups of substances that signal these extracellular changes are steroid hormones, growth factors, and cytokines. The capability to respond to these stimuli requires a cell surface recognition system, intracellular signal transduction, and nuclear responses for the expression of specific genes in a coordinated fashion. Among the genes that participate in control of cell growth and function, proto-oncogenes and tumor suppressor genes are particularly important. More than 100 proto-oncogene products that contribute to growth regulation have been identified (24) (Table 6.1). As a group, proto-oncogenes exert positive effects upon cellular proliferation. In contrast, tumor suppressor genes exert inhibitory regulatory effects on cellular proliferation (Table 6.2).


Gynecology_Novak

Gynecology_Novak. Steroid Hormones Steroid hormones play a crucial role in reproductive biology and in general physiology. Among the various functions, steroid hormones inﬂuence pregnancy, cardiovascular function, bone metabolism, and an individual’s sense of well-being. The action of steroid hormones is mediated via extracellular signals to the nucleus to affect a physiologic response.


Gynecology_Novak

Gynecology_Novak. Estrogens exert a variety of effects on growth and development of different tissues. The effects of estrogens are mediated via estrogen receptors (ER), intracellular proteins that function as ligand-activated transcription factors and belong to the nuclear receptor super-family (25). Two mammalian ERs have been identified: ERα and ERβ. The structure of both receptors is similar and consists of six domains named A through F from the N-to C-terminus, encoded by 8 to 9 exons (26). Domains A and B are located at the N-terminus and contain an agonist-independent transcriptional activation domain (activation function 1, or AF-1). The C domain is a highly conserved central DNA-binding domain composed of two zinc fingers through which ER interacts with the major groove and the phosphate backbone of the DNA helix. The C-terminus of the protein contains domains E and F and functions as ligand-binding domain (LBD–domain E) and AF-2–domain F (Fig. 6.3).


Gynecology_Novak

Gynecology_Novak. Activation of transcription via the ER is a multistep process. The initial step requires activation of the ER via various mechanisms (Fig. 6.4). For example, estrogens such as 17β-estradiol can diffuse into the cell and bind to the LBD of the ER. Upon ligand binding, the ER undergoes conformational changes followed by a dissociation of various bound proteins, mainly heat shock proteins 90 and 70 (Hsp90 and Hsp70). Activation of the ER also requires phosphorylation by several protein kinases, including casein kinase II, protein kinase A, and components of the Ras/Mapk (mitogen-activated protein kinase) pathway (26). Four phosphorylation sites of the ER are clustered in the NH2 terminus with the AF-1 region.


Gynecology_Novak

Gynecology_Novak. The activated ER elicits a number of different genomic as well as nongenomic effects on intracellular signaling pathways. The classical steroid signaling pathway involves binding of the activated estrogen receptor to an estrogen responsive element (ERE) on the genome as homodimers and subsequent stimulation of transcription (27,28). The minimal consensus sequence for Table 6.1 Proto-Oncogenes hst, int-2 Ha-ras, N-ras, N-ras fgr, lck, src, yes cot, plm-1, mos, raf/mil jun, ets-1, ets-2,fos, gil 1,rel, ski, vav lyl-1, maf, myb, myc, L-myc, N-myc, evi-1 the ERE is a 13 bp palindromic inverted repeat (IR) and is defined as 5 -GGTCAnnnTGACC-3 . Genes that are regulated by activated ERs include early gene responses such as c-myc, c-fos, and d-jun, and genes encoding for growth factors such as insulin growth factor (IGF-1 and IGF-2), epidermal growth factor (EGF), transforming growth factor-α, and colony-stimulating factor (CSF-1). Table 6.2 Tumor Suppressor Genes


Gynecology_Novak

Gynecology_Novak. Table 6.2 Tumor Suppressor Genes Figure 6.3 Structure of the two mammalian estrogen receptors. ERα (595 amino acids) and ERβ (530 amino acids) consist of six domains (A–F from the N-to C-terminus). Domains A and B at the N-terminus contain an agonist-independent transcriptional activation domain (activation function 1, or AF-1). The C domain is the central DNA-binding sequence (DBD). Domains E and F function as ligand binding domain (LBD) and activation function 2 (AF-2). Also shown is the structure of the ER ligand 17β-estradiol. In addition to the described genomic effects of estrogens, there is growing evidence for nongenomic effects of estrogens on intracellular signal transduction pathways. These effects include rapid activation of the adenylate cyclase, which results in cyclic adenosine monophosphate (cAMP)–dependent activation of protein kinase A (PKA) (29). Estrogens can stimulate the MAPK pathway and rapidly activate the Erk1/Erk2 proteins.


Gynecology_Novak

Gynecology_Novak. Various ligands with different affinities to the ER were developed and are called selective estrogen receptor modulators (SERMs). Tamoxifen, for example, is a mixed agonist/ antagonist for ERα, but it is a pure antagonist for ERβ. The ERβ receptor is ubiquitously expressed in hormone-responsive tissues, whereas the expression of ERα ﬂuctuates in response to the hormonal milieu. The cellular and tissue effects of an estrogenic compound appear to reﬂect a dynamic interplay between the actions of these estrogen receptor isoforms. These observations underscore the complexity of estrogen interactions with both normal and neoplastic tissue. Mutations of hormone receptors and their functional consequences illustrate their important contributions to normal physiology. For example, absence of ERα in a male human was reported (30). The clinical sequelae attributed to this mutation include incomplete epiphyseal closure, increased bone turnover, tall stature, and impaired glucose tolerance. The


Gynecology_Novak

Gynecology_Novak. in a male human was reported (30). The clinical sequelae attributed to this mutation include incomplete epiphyseal closure, increased bone turnover, tall stature, and impaired glucose tolerance. The androgen insensitivity syndrome is caused by mutations of the androgen receptor (31). Mutations of the receptors for growth hormone and thyroid-stimulating hormone result in a spectrum of phenotypic alterations. Mutations of hormone receptors may also contribute to the progression of neoplastic disease and resistance to hormone therapy (32,33).


Gynecology_Novak

Gynecology_Novak. Growth Factors Growth factors are polypeptides that are produced by a variety of cell types and exhibit a wide range of overlapping biochemical actions. Growth factors bind to high-affinity cell membrane receptors and trigger complex positive and negative signaling pathways that regulate cell proliferation and differentiation (34). In general, growth factors exert positive or negative effects upon the cell cycle by inﬂuencing gene expression related to events that occur at the G1-S cell cycle boundary (35). Because of their short half-life in the extracellular space, growth factors act over limited distances through autocrine or paracrine mechanisms. In the autocrine loop, the growth factor acts on the cell that produced it. The paracrine mechanism of growth control involves the effect of growth factors on another cell in proximity. Growth factors that play an important role in female reproductive physiology are listed in Table 6.3. The biologic response of a cell


Gynecology_Novak

Gynecology_Novak. ERE 5’ GGTCAnnnTGACC 3’ MAPKER A B C PKA IGF EGF c-myc, c-fos, c-jun,IGF, BCL-2 β Figure 6.4 Activation of estrogen receptor mediated transcription. Intracellular estrogen receptor signaling is mediated via different pathways. A: 17β-estrodiol diffuses through the cell membrane and binds to cytoplasmic ER. The ER is subsequently phosphorylated, undergoes dimerization, and binds to the estrogen response element (ERE) on the promoter of an estrogen responsive gene. B: Estrogen ligand binds to membrane-bound ER and activates the mitogenactivated protein kinase (MAPK) pathways that support ER-mediated transcription. C: Binding of cytokines such as insulinlike growth factor (IGF) or epidermal growth factor to their membrane receptor can cause activation of protein kinases like PKA, which subsequently activates ER by phosphorylation. to a specific growth factor depends on a variety of factors, including the cell type, the cellular microenvironment, and the cell cycle status.


Gynecology_Novak

Gynecology_Novak. The regulation of ovarian function occurs through autocrine, paracrine, and endocrine mechanisms (36–42). The growth and differentiation of ovarian cells are particularly inﬂuenced by the insulinlike growth factors (IGF) (Fig. 6.5). IGFs amplify the actions of gonadotropin hormones on autocrine and paracrine growth factors found in the ovary. IGF-1 acts on granulosa cells to cause an increase in cAMP, progesterone, oxytocin, proteoglycans, and inhibin. On theca cells, IGF-1 causes an increase in androgen production. Theca cells produce tumor necrosis factor-α (TNF-α) and EGF, which are regulated by follicle-stimulating hormone (FSH). Epidermal growth factor acts on granulosa cells to stimulate mitogenesis. Follicular ﬂuid contains IGF-1, IGF-2, TNF-α, TNF-β, and EGF. Disruption of these autocrine and paracrine intraovarian pathways may be the basis of polycystic ovarian disease, disorders of ovulation, and ovarian neoplastic disease.


Gynecology_Novak

Gynecology_Novak. Transforming growth factor-β (TGF-β) activates intracytoplasmic serine threonine kinases and inhibits cells in the late G1 phase of the cell cycle (42). It appears to play an important role in embryonic remodeling. Mullerian-inhibiting substance (MIS), which is responsible for regression of the mullerian duct, is structurally and functionally related to TGF-β (43). TGF-α is an EGF homologue that binds to the EGF receptor and acts as an autocrine factor in normal cells. Table 6.3 Growth Factors that Play Important Roles in Female Reproductive Physiology As with EGF, TGF-α promotes entry of G0 cells into the G1 phase of the cell cycle. The role of growth factors in endometrial growth and function was the subject of several reviews (37–42). Similar to the ovary, autocrine, paracrine, and endocrine mechanisms of control also occur in endometrial tissue.


Gynecology_Novak

Gynecology_Novak. Growth factors trigger intracellular biochemical signals by binding to cell membrane receptors. In general, these membrane-bound receptors are protein kinases that convert an extracellular signal into an intracellular signal. The interaction between growth factor ligand and its receptor results in receptor dimerization, autophosphorylation, and tyrosine kinase activation. Activated receptors in turn phosphorylate substrates in the cytoplasm and trigger the intracellular signal transduction system (Fig. 6.6). The intracellular signal transduction system relies on serine threonine kinases, src-related kinases, and G proteins. Intracellular signals activate nuclear factors that regulate gene expression. Many of the proteins that participate in the intracellular signal transduction system are encoded by proto-oncogenes that are divided into subgroups based on their cellular location or enzymatic function (44,45) (Fig. 6.7).


Gynecology_Novak

Gynecology_Novak. The raf and mos proto-oncogenes encode proteins with serine threonine kinase activity. These kinases integrate signals originating at the cell membrane with those that are forwarded to the nucleus (46,47). Protein kinase C (PKC) is an important component of a second messenger system that exhibits serine threonine kinase activity. This enzyme plays a central role in phosphorylation, which is a general mechanism for activating and deactivating proteins. It also plays an important role in cell metabolism and division (48). The Scr family of tyrosine kinases is related to PKC and includes protein products encoded by the scr, yes, fgr, hck, lyn, fyn, lck, alt, and fps/fes proto-oncogenes. These proteins bind to the inner cell membrane surface.


Gynecology_Novak

Gynecology_Novak. The G proteins are guanyl nucleotide-binding proteins. The heterotrimeric, or large G proteins, link receptor activation with effector proteins such as adenylcyclase, which activates the cAMPdependent, kinase-signaling cascade (49). The monomeric or small G proteins, encoded by the ras proto-oncogene family, are designated p21 and are particularly important regulators of mitogenic signals. The p21 Ras protein exhibits guanyl triphosphate (GTP) binding and GTPase activity. Hydrolysis of GTP to guanyl diphosphate (GDP) terminates p21 Ras activity. The p21 Ras protein inﬂuences the production of deoxyguanosine (dG) and inositol phosphate (IP) 3, arachidonic acid production, and IP turnover. Figure 6.5 The regulation of ovarian function occurs through autocrine, paracrine, and endocrine mechanisms.


Gynecology_Novak

Gynecology_Novak. The phosphoinositide 3 (PI3) kinase can be activated by various growth factors like platelet-derived growth factor (PDGF) or IGF results. Activation of PI3 kinase results in an increase of intracellular, membrane-bound lipids, phosphatidylinositol-(3,4)-diphosphate (PIP2), and phosphatidylinositol-(3,4,5)-triphosphate (PIP3). The Akt protein is subsequently phosphorylated by PIP3-dependent kinases (PDK) for full activation. Activated Akt is released from the membrane and elicits downstream effects that lead to an increase in cell proliferation, prevention of apoptosis, invasiveness, drug resistance, and neoangiogenesis (50). The Pten (phosphatase and chicken tensin homologue deleted on chromosome 10) protein is an important factor in the PI3 kinase pathway, because it counteracts the activation of Akt by dephosphorylating PIP3. Cells with mutated tumor suppressor gene Pten and lack of functional Pten expression display an increased proliferation rate and decreased apoptosis, possibly


Gynecology_Novak

Gynecology_Novak. of Akt by dephosphorylating PIP3. Cells with mutated tumor suppressor gene Pten and lack of functional Pten expression display an increased proliferation rate and decreased apoptosis, possibly supporting the development of a malignant phenotype. Pten frequently is mutated in endometrioid adenocarcinoma. Furthermore, lack of functional Pten expression was described in endometriosis.


Gynecology_Novak

Gynecology_Novak. The mammalian target of rapamycin (mTOR) is regulated by the PI3 kinase pathway. mTOR is a serine/threonine protein kinase that regulates a variety of cellular processes, including proliferation, motility, and translation (51). mTOR integrates the input from various upstream pathways, including insulin and growth factors like IGF proteins. The mTOR pathway provides important survival signals for cancer cells and therefore was one focus of targeted drug development (52). Figure 6.6 Pathways of intracellular signal transduction. For example, rapamycin inhibits mTOR by associating with its intracellular receptor FKBP12. Derivates of rapamycin like everolimus (RAD001) and temsirolimus (CCI779) showed promising results in clinical trials (53).


Gynecology_Novak

Gynecology_Novak. mTOR functions as the catalytic subunit of two different protein complexes. Among the proteins associated with mTOR complex 1 (mTORC1) is mTOR, the regulatory associated protein of mTOR (Raptor), and PRAS40. This complex functions as a nutrient and energy sensor and controls protein synthesis (54). While mTORC1 is activated by insulin, growth factors, amino acids and oxidative stress, low nutrient levels, reductive stress, and growth factor deprivation inhibit its activity. Figure 6.7 Proto-oncogenes are divided into subgroups based on their cellular location or enzymatic function. In contrast, the mTOR complex 2 (mTORC2) contains, among others, mTOR, the rapamycininsensitive protein Rictor, and mammalian stress-activated protein kinase interacting protein 1 (mSIN1). mTORC2 regulates the cytoskeleton and phosphorylates Akt (55). Its regulation is complex, but involves insulin, growth factors, serum, and nutrient levels. Expression of Genes and Proteins


Gynecology_Novak

Gynecology_Novak. Expression of Genes and Proteins Regulation of genetic transcription and replication is crucial to the normal function of the daughter cells, the tissues and ultimately the organism. Transmission of external signals to the nucleus by way of the intracellular signal transduction cascade culminates in the transcription of specific genes and translation of the mRNA into proteins that ultimately affect the structure, function, and proliferation of the cell.


Gynecology_Novak

Gynecology_Novak. The human genome project resulted in the determination of the sequence of DNA of the entire human genome (56). With the completion of this project, it appears that the human haploid genome contains 23,000 protein coding genes. Sequencing the human genome is a major scientific achievement that opens the door for more detailed studies of structural and functional genomics. Structural genomics involves the study of three-dimensional structures of proteins based on their amino acid sequences. Functional genomics provides a way to correlate structure and function. Proteomics involves the identification and cataloging of all proteins used by a cell, and cytomics involves the study of cellular dynamics, including intracellular system regulation and response to external stimuli. The transcriptome is the set of all RNA molecules, including mRNA, rRNA, tRNA, and other noncoding RNA produced in one or a population of cells. The transcriptome varies with external environmental conditions and


Gynecology_Novak

Gynecology_Novak. is the set of all RNA molecules, including mRNA, rRNA, tRNA, and other noncoding RNA produced in one or a population of cells. The transcriptome varies with external environmental conditions and reﬂects the actively expressed genes. The metabolome describes a set of small-molecule metabolites, including hormones and signaling molecules, that are found in a single organism. Similar to the transcriptome and proteome, the metabolome is subject to rapid changes (57). The kinome of an organism describes a set of protein kinases, enzymes that are crucial for phosphorylation reactions.


Gynecology_Novak

Gynecology_Novak. Figure 6.8 Hereditary and sporadic cancer development based on the Knudson “two-hit” genetic model. All cells harbor one mutant tumor suppressor gene allele in hereditary cancer. The loss of the second allele results in the malignant phenotype. Sporadic cancers develop in cells with normal genome, therefore requiring both alleles to be inactivated (two hits). Cancer Genetics Cancer is a genetic disease that results from a series of mutations in various cancer genes. Uncontrolled cell growth occurs because of accumulation of somatic mutations or the inheritance of one or more mutations through the germline, followed by additional somatic mutations. The mutation in genes that are directly involved in normal cellular growth and proliferation can lead to the development of uncontrolled growth, invasion, and metastasis.


Gynecology_Novak

Gynecology_Novak. According to the Knudson hypothesis, which was first described in children with hereditary retinoblastoma, two hits or mutations within the genome of a cell are required for a malignant phenotype to develop (58). In hereditary cancers, the first hit is present in the genome of every cell. Only one additional hit is necessary, therefore, to disrupt the correct function of the second cancer gene allele. In contrast, sporadic cancers develop in cells without hereditary mutations in the cancer predisposing alleles. In this case, both hits must occur in a single somatic cell to disrupt both cancer gene alleles (Fig. 6.8).


Gynecology_Novak

Gynecology_Novak. Most adult solid tumors require 5 to 10 rate-limiting mutations to acquire the malignant phenotype. Among these mutations, some are responsible for causing the cancer phenotype, whereas others might be considered bystander mutations, as with, for example, the amplification of genes that are adjacent to an oncogene. The most compelling evidence for the mutagenic tumor development process is that the age-specific incidence rates for most human epithelial tumors increase at roughly the fourth to eighth power of elapsed time. Gatekeepers and Cancer susceptibility genes are divided into “gatekeepers” and “caretakers” (59). Gate-


Gynecology_Novak

Gynecology_Novak. Gatekeepers and Cancer susceptibility genes are divided into “gatekeepers” and “caretakers” (59). Gate- Caretakers keeper genes control cellular proliferation and are divided into oncogenes and tumor suppressor genes. In general, oncogenes stimulate cell growth and proliferation, and tumor suppressor genes reduce the rate of cell proliferation or induce apoptosis. Gatekeepers prevent the development of tumors by inhibiting growth or promoting cell death. Examples of gatekeeper genes include the tumor suppressor gene p53 and the retinoblastoma gene. Caretaker genes preserve the integrity of the genome and are involved in DNA repair (stability genes). The inactivation of caretakers increases the likelihood of persistent mutations in gatekeeper genes and other cancer-related genes. The DNA mismatch repair genes, MLH1, MSH2, and MSH6, are examples of caretaker genes.


Gynecology_Novak

Gynecology_Novak. Hereditary Cancer Most cancers are caused by spontaneous somatic mutations. However, a small percentage of cancers arise on a heritable genomic background. About 12% of all ovarian cancers and about 5% of endometrial cancers are considered to be hereditary (60,61). Germline mutations require additional mutations at one or more loci for tumorigenesis to occur. These Table 6.4 Hereditary Cancer Syndromes Associated with Gynecologic Tumors mutations occur via different mechanisms, for example, via environmental factors such as ionizing radiation or mutations of stability genes. Characteristics of hereditary cancers include diagnosis at a relatively early age and a family history of cancer, usually of a specific cancer syndrome, in two or more relatives. Hereditary cancer syndromes associated with gynecologic tumors are summarized in Table 6.4.


Gynecology_Novak

Gynecology_Novak. Various cancer-causing genetic and epigenetic mechanisms are described. On the genomic level, gain of function gene mutations can lead to a conversion of proto-oncogenes into oncogenes, and loss of function gene mutations can inactivate tumor suppressor genes. Epigenetic changes include DNA methylation, which can cause inactivation of tumor suppressor gene expression by preventing the correct function of the associated promoter sequence. Collectively, these genetic and epigenetic changes are responsible for the development of cancer characterized by the ability of cells to invade and metastasize, grow independently of growth factor support, and escape from antitumor immune responses.


Gynecology_Novak

Gynecology_Novak. Oncogenes Oncogenes comprise a family of genes that result from gain of function mutations of their normal counterparts, proto-oncogenes. The normal function of proto-oncogenes is to stimulate proliferation in a controlled context. Activation of oncogenes can lead to stimulation of cell proliferation and development of a malignant phenotype. Oncogenes were initially discovered through retroviral tumorigenesis. Viral infection of mammalian cells can result in integration of the viral sequences into the proto-oncogene sequence of the host cell. The integrated viral promoter activates transcription from the surrounding DNA sequences, including the proto-oncogene. Enhanced transcription of the proto-oncogene sequences results in the overexpression of growth factors, growth factor receptors, and signal transduction proteins, which results in stimulation of cell proliferation. One of the most important group of viral oncogenes is the family of ras genes, which include c-H(Harvey)-ras,


Gynecology_Novak

Gynecology_Novak. and signal transduction proteins, which results in stimulation of cell proliferation. One of the most important group of viral oncogenes is the family of ras genes, which include c-H(Harvey)-ras, c-K(Kirsten)-ras, and N(Neuroblastoma)-ras.


Gynecology_Novak

Gynecology_Novak. Tumor Suppressor Genes Tumor suppressor genes are involved in the development of most cancers and are usually inactivated in a two-step process in which both copies of the tumor suppressor gene are mutated or inactivated by epigenetic mechanisms like methylation (62). The most commonly mutated tumor suppressor gene in human cancers is p53 (63). The p53 protein regulates transcription of other genes involved in cell cycle arrest such as p21. Up-regulation of p53 expression is induced by DNA damage and contributes to cell cycle arrest, allowing DNA repair to occur. p53 also plays an important role in the initiation of apoptosis. The most common mechanism of inactivation of p53 differs from the classic two-hit model. In most cases, missense mutations that change a single amino acid in the DNA binding domain of p53 results in overexpression of nonfunctional p53 protein in the nucleus of the cell.


Gynecology_Novak

Gynecology_Novak. The identification of tumor suppressor genes was facilitated by positional cloning strategies. The main approaches are cytogenetic studies to identify chromosomal alterations in tumor specimens, DNA linkage techniques to localize genes involved in inherited predisposition to cancer, and examination for loss of heterozygosity or allelic alterations among studies in sporadic tumors. Comparative genomic in situ hybridization (CGH) allows ﬂuorescence identification of chromosome gain and loss in human cancers within a similar experiment.


Gynecology_Novak

Gynecology_Novak. Stability Genes The third class of cancer genes is “stability genes,” which promotes tumorigenesis in a way different from tumor suppressor genes or amplified oncogenes. The main function of stability genes is the preservation of the correct DNA sequence during DNA replication (caretaker function) (64). Mistakes that are made during normal DNA replication or induced by exposure to mutagens can be repaired by a variety of mechanisms that involve mismatch repair genes, nuclear-type excision repair genes, and base excision repair genes. The inactivation of stability genes potentially leads to a higher mutation rate in all genes. However, only mutations in oncogenes and tumor suppressor genes inﬂuence cell proliferation and confer a selective growth advantage to the mutant cell. Similar to tumor suppressor genes, both alleles of stability genes must be activated to cause loss of function.


Gynecology_Novak

Gynecology_Novak. Genetic Aberrations Gene replication, transcription, and translation are imperfect processes, and the fidelity is less than 100%. Genetic errors may result in abnormal structure and function of genes and proteins. Genomic alterations such as gene amplification, point mutations, and deletions or rearrangements were identified in premalignant, malignant, and benign neoplasms of the female genital tract (65) (Fig. 6.9).


Gynecology_Novak

Gynecology_Novak. Amplification Amplification refers to an increase in the copy number of a gene. Amplification results in enhanced gene expression by increasing the amount of template DNA that is available for transcription. Proto-oncogene amplification is a relatively common event in malignancies of the female genital tract. The HER2/neu proto-oncogene, also known as c-erbB-2 and HER2, encodes a 185 kDa transmembrane glycoprotein with intrinsic tyrosine kinase activity. It belongs to a family of transmembrane receptor genes that includes the epidermal growth factor receptors (erbB-1), erbB-3, and erbB-4. HER2/neu interacts with a variety of different cellular proteins that increase cell proliferation. Overexpression of HER2/neu was demonstrated in about 30% of breast cancers, 20% of advanced ovarian cancers, and as many as 50% of endometrial cancers (66). High tissue expression of HER2/neu is correlated with a decreased overall survival, particularly in patients with endometrial cancer.


Gynecology_Novak

Gynecology_Novak. Point Mutations Point mutations of a gene may remain without any consequence for the expression and function of the protein (gene polymorphism). However, point mutations can alter a codon sequence and subsequently disrupt the normal function of a gene product. The ras gene family is an example of oncogene-encoded proteins that disrupt the intracellular signal transduction system following point mutations. Transforming Ras proteins contain point mutations in critical codons (i.e., codons 11, 12, 59, 61) with decrease of GTPase activity and subsequent expression of constitutively active Ras. Point mutations of the p53 gene are the most common genetic mutations described in solid tumors. These mutations occur at preferential “hot spots” that coincide with the most highly conserved regions of the gene. The p53 tumor suppressor gene encodes for a phosphoprotein that is detectable in the nucleus of normal cells. When DNA damage occurs, p53 can arrest cell cycle progression to allow the DNA


Gynecology_Novak

Gynecology_Novak. the gene. The p53 tumor suppressor gene encodes for a phosphoprotein that is detectable in the nucleus of normal cells. When DNA damage occurs, p53 can arrest cell cycle progression to allow the DNA to be repaired or undergo apoptosis. The lack of function of normal p53 within a cancer cell results in a loss of control of cell proliferation with inefficient DNA repair and genetic instability. Mutations of the p53 gene occur in approximately 50% of advanced ovarian cancers and 30% to 40% of endometrial cancers but are uncommon in cervical cancer.


Gynecology_Novak

Gynecology_Novak. Point mutations in the BRCA1 and BRCA2 genes can alter the activity of these genes and predispose to the development of breast and ovarian cancer (67). The frequency of BRCA1 and BRCA2 mutations in the general population in the United States is estimated at 1:250. Specific Figure 6.9 Genes can be amplified or undergo mutation, deletion, or rearrangement. founder mutations were reported for various ethnic groups. For example, two BRCA1 mutations (185delAG and 5382insC) and one BRCA2 mutation (6174delT) are found in 2.5% of Ashkenazi Jews of Central and Eastern European descent. Additional founder mutations were described in other ethnic groups, including from the Netherlands (BRCA1, 2804delAA and several large deletion mutations), Iceland (BRCA2, 995del5), and Sweden (BRCA1, 3171ins5).


Gynecology_Novak

Gynecology_Novak. The BRCA proteins are involved in DNA repair. If DNA is damaged, for example, by ionizing radiation or chemotherapy, the BRCA2 protein binds to the RAD51 protein, which is central for the repair of double-stranded breaks via homologous recombination. BRCA2 regulates the availability and activity of RAD51 in this key reaction. Phosphorylation of the BRCA2/RAD51 complex allows RAD51 to bind to the site of DNA damage and, in conjunction with several other proteins, mediates repair of DNA by homologous recombination. BRCA1 functions within a complex network of protein–protein interactions, mediating DNA repair by homologous recombination and regulating transcription via the BRCA1-associated surveillance complex (BASC).


Gynecology_Novak

Gynecology_Novak. Deletions and rearrangements reﬂect gross changes in the DNA template that may result in the synthesis of a markedly altered protein product. Somatic mutations may involve chromosomal translocations that result in chimeric transcripts with juxtaposition of one gene to the regulatory region of another gene. This mutation type is most commonly reported in leukemias, lymphomas, and mesenchymal tumors. The Philadelphia chromosome in chronic myeloid leukemia, for example, is the result of a reciprocal translocation between one chromosome 9 and one chromosome 22. The DNA sequence removed from chromosome 9 contains the proto-oncogene c-ABL and inserts into the BCR gene sequence on chromosome 22 (Philadelphia chromosome). The resulting chimeric BCR-ABL gene product functions as a constitutively active tyrosine kinase and stimulates cellular proliferation by such mechanisms as an increase of growth factors.


Gynecology_Novak

Gynecology_Novak. Single-nucleotide polymorphism (SNP) describes a variation in the DNA sequence (68). Single nucleotides in the genome differ between paired chromosomes in either one individual or between two individuals. For example, the sequences TGACTA and TCACTA contain one single change in the second nucleotide from guanine (G) to cytosine (C). This results in a G and C allele for this particular gene sequence. SNPs can occur within coding or noncoding sequences of genes or in the intergenic regions. SNPs might not change the amino acid sequence of the protein that is produced (synonymous SNP) or produce a different peptide (nonsynonymous SNPs). If SNPs are located in noncoding regions, various other processes like gene splicing or transcription factor binding might be affected.


Gynecology_Novak

Gynecology_Novak. The frequency of SNPs in a given population is provided by the minor allele frequency. This frequency differs between ethnic groups and geographic locations. SNPs were associated with various human diseases including cancer disease. They also inﬂuence the effect of drug treatment and responses to pathogens and chemicals (69). SNPs are important for the comparison between genomes of different populations for examples providing information about the susceptibility of certain population to develop specific cancers (70). The Cancer Genome Atlas Project In 2006 the National Cancer Institute and the National Human Genome Research Institute initiated the Cancer Genome Atlas (TCGA) project. The goal of the project is to provide a comprehensive genomic characterization and sequence analysis of cancer diseases. The initial phase included glioblastoma multiforme, lung, and ovarian cancer (71,72). Many more tumor types will be added to the analysis.


Gynecology_Novak

Gynecology_Novak. The TCGA is taking advantage of high-throughput genome analysis techniques, including gene expression profiling, SNP genotyping, copy number variation profiling, genome wide methylation profiling, microRNA profiling, and exon sequencing (73). These data are accessible for researchers via the TCGA Web page (74). The immune system plays an essential part in host defense mechanisms, in particular the response to infections and neoplastic transformation. Our increased understanding of immune system regulation provides opportunities for the development of novel immunotherapeutic and immunodiagnostic approaches.


Gynecology_Novak

Gynecology_Novak. The human immune system has the potential to respond to abnormal or tumor cells in various ways. Some of these immune responses occur in an innate or antigen-nonspecific manner, whereas others are adaptive or antigen specific. Adaptive responses are specific to a given antigen. The establishment of a memory response allows a more rapid and vigorous response to the same antigen in future encounters. Various innate and adaptive immune mechanisms are involved in responses to tumors, including cytotoxicity directed to tumor cells mediated by cytotoxic T cells, natural killer (NK) cells, macrophages, and antibody-dependent cytotoxicity mediated by complementation activation (75).


Gynecology_Novak

Gynecology_Novak. Adaptive or specific immune responses include humoral and cellular responses. Humoral immune responses refer to the production of antibodies. Antibodies are bifunctional molecules composed of a variable region with specific antigen-binding sites, combined with a constant region that directs the biologic activities of the antibody, such as binding to phagocytic cells or activation of complement. Cellular immune responses are antigen-specific immune responses mediated directly by activated immune cells rather than by the production of antibodies.


Gynecology_Novak

Gynecology_Novak. The distinction between humoral and cellular responses is historical and originates from the experimental observation that humoral immune function can be transferred by serum, whereas cellular immune function requires the transfer of cells. Most immune responses include both humoral and cellular components. Several types of cells, including cells from both the myeloid and lymphoid lineages, make up the immune system. Specific humoral and cellular immune responses to foreign antigens involve the coordinated action of populations of lymphocytes


Gynecology_Novak

Gynecology_Novak. B Cells, Hormonal Immunity, and Monoclonal Antibodies operating in concert with one another and with phagocytic cells (macrophages). These cellular interactions include both direct cognate interactions involving cell-to-cell contact and cellular interactions involving the secretion of and response to cytokines or lymphokines. Lymphoid cells are found in lymphoid tissues, such as lymph nodes or spleen, or in the peripheral circulation. The cells that make up the immune system originate from stem cells in the bone marrow. B lymphocytes synthesize and secrete antibodies. Mature, antigen-responsive B cells develop from pre-B cells (committed B-cell progenitors) and differentiate to become plasma cells, which produce large quantities of antibodies. Pre-B cells originate from bone marrow stem cells in adults after rearrangement of immunoglobulin genes from their germ cell configuration. Mature B cells express cell surface immunoglobulin molecules that function as receptors for antigen.


Gynecology_Novak

Gynecology_Novak. Upon interaction with antigen, mature B cells respond to become antibody-producing cells.


Gynecology_Novak

Gynecology_Novak. The process requires the presence of appropriate cell–cell stimulatory signals and cytokines. Monoclonal antibodies are directed against a specific antigenic determinant. In contrast, polyclonal antibodies detect multiple epitopes that might be presented by just one or a panel of proteins. The in vitro production of monoclonal antibodies, pioneered by Kohler and Milstein in the 1970s, has become an invaluable diagnostic and therapeutic tool, particularly for the management of malignancies (76). The tumor antigen CA125, for example, was detected in a screen of antibodies generated against ovarian cancer cell lines. A radioimmunoassay is widely used to measure CA125 in the serum of patients with ovarian cancer and guide treatment decisions. Therapeutic approaches utilized immunotoxin-conjugated monoclonal antibodies directed to human ovarian adenocarcinoma antigens. These antibodies induce tumor cell killing and can prolong survival in mice implanted with a human ovarian cancer cell


Gynecology_Novak

Gynecology_Novak. monoclonal antibodies directed to human ovarian adenocarcinoma antigens. These antibodies induce tumor cell killing and can prolong survival in mice implanted with a human ovarian cancer cell line. However, some obstacles limit the clinical use of monoclonal antibodies, including tumor cell antigenic heterogeneity, modulation of tumor-associated antigens, and cross-reactivity of normal host and tumor-associated antigens. No unique tumor-specific antigens were identified. All tumor antigens have to be considered as tumor-related antigens because they are expressed on the malignant as well as the nonmalignant tissues. Because most monoclonal antibodies are murine, the host’s immune system can recognize and respond to these foreign mouse proteins. The use of the genetically engineered monoclonal antibodies composed of human-constant regions with specific antigen-reactive murine variable regions can result in reduced antigenicity.


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Gynecology_Novak. T lymphocytes have a central role in the generation of immune responses by acting as helper cells in both humoral and cellular immune responses and by acting as effector cells in cellular responses. T-cell precursors originate in bone marrow and move to the thymus, where they mature into functional T cells. During their thymic maturation, T cells that can recognize antigen in the context of the major histocompatibility complex (MHC) molecules are selected, while self-responding T cells are removed (75).


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Gynecology_Novak. T cells can be distinguished from other types of lymphocytes by their cell surface phenotype, based on the pattern of expression of various molecules, and by differences in their biologic functions. All mature T cells express certain cell surface molecules, such as the cluster determinant 3 (CD3) molecular complex and the T-cell antigen receptor, which is found in close association with the CD3 complex. T cells recognize antigen through the cell surface T-cell antigen receptor (TCR). The structure and organization of this molecule are similar to those of antibody molecules, which are the B-cell receptors for the antigen. During T-cell development, the T-cell receptor gene undergoes gene arrangements similar to those seen in B cells, but there are important differences between the antigen receptors on B cells and T cells. The T-cell receptor is not secreted, and its structure is somewhat different from that of antibody molecules. The way in which the B-cell and T-cell receptors


Gynecology_Novak

Gynecology_Novak. receptors on B cells and T cells. The T-cell receptor is not secreted, and its structure is somewhat different from that of antibody molecules. The way in which the B-cell and T-cell receptors interact with antigens is quite different. T cells can respond to antigens only when these antigens are presented in association with MHC molecules on antigen-presenting cells. Effective antigen presentation involves the processing of antigen into small fragments of peptide within the antigen-presenting cell and the subsequent presentation of these fragments of antigen in association with MHC molecules expressed on the surface of the antigen-presenting cell. T cells can respond to antigens only when presented in this manner, unlike B cells, which can bind antigens directly, without processing and presentation by antigen-presenting cells (75).


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Gynecology_Novak. There are two major subsets of mature T cells that are phenotypically and functionally distinct: T-helper/inducer cells, which express the CD4 cell surface marker, and the


Gynecology_Novak

Gynecology_Novak. T-cytotoxic cells, which express the CD8 marker. The expression of these markers is acquired during the passage of T cells through the thymus. CD4 T cells can provide help to B cells, resulting in the production of antibodies by B cells, and interact with antigen presented by antigen-presenting cells in association with MHC class II molecules. CD4 T cells can act as helper cells for other T cells. CD8 T cells include cells that are cytotoxic (cells that can kill target cells bearing appropriate antigens), and they interact with antigen presented on target cells in association with MHC class I molecules. These T cells can inhibit the biologic functions of B cells or other T cells (75). Although the primary biologic role of cytotoxic T cells (CTLs) seems to be lysis of virus-infected autologous cells, cytotoxic immune T cells can mediate the lysis of tumor cells directly. Presumably, CTLs recognize antigens associated with MHC class I molecules on tumor cells through their


Gynecology_Novak

Gynecology_Novak. autologous cells, cytotoxic immune T cells can mediate the lysis of tumor cells directly. Presumably, CTLs recognize antigens associated with MHC class I molecules on tumor cells through their antigen-specific T-cell receptor, setting off a series of events that ultimately results in the lysis of the target cell.


Gynecology_Novak

Gynecology_Novak. Monocytes and macrophages, which are myeloid cells, have important roles in both innate and adaptive immune responses; macrophages play a key part in the generation of immune responses. T cells do not respond to foreign antigens unless those antigens are processed and presented by antigen-presenting cells. Macrophages (and B cells and dendritic cells) express MHC class II molecules and are effective antigen-presenting cells for CD4 T cells. Helper-inducer (CD4) T cells that bear a T-cell receptor of appropriate antigen and self-specificity are activated by this antigen-presenting cell to provide help (various factors—lymphokines—that induce the activation of other lymphocytes). In addition to their role as antigen-presenting cells, macrophages play an important part in innate responses by ingesting and killing microorganisms. Activated macrophages, besides their many other functional capabilities, can act as cytotoxic, antitumor killer cells.


Gynecology_Novak

Gynecology_Novak. Natural Killer Cells Natural killer cells are effector cells in an innate type of immune response: the nonspecific killing of tumor cells and virus-infected cells. Therefore, NK activity represents an innate form of immunity that does not require an adaptive, memory response for optimal biologic function, but the antitumor activity can be increased by exposure to several agents, particularly cytokines such as interleukin-2 (IL-2). Characteristically, NK cells have a large granular lymphocyte morphology. NK cells display a pattern of cell surface markers that differs from those characteristic of T or B cells. NK cells can express a receptor for the crystallizable fragment (Fc) portion of antibodies, and other NK-associated markers. NK cells appear to be functionally and phenotypically heterogeneous, when compared with T or B cells. The cells that can carry out antibody-dependent cellular cytotoxicity, or antibody-targeted cytotoxicity, are NK-like cells. Antibody-dependent cellular


Gynecology_Novak

Gynecology_Novak. when compared with T or B cells. The cells that can carry out antibody-dependent cellular cytotoxicity, or antibody-targeted cytotoxicity, are NK-like cells. Antibody-dependent cellular cytotoxicity by NK-like cells resulted in the lysis of tumor cells in vitro. The mechanisms of this tumor cell killing are not clearly understood, although close cellular contact between the effector cell and the target cell seems to be required.


Gynecology_Novak

Gynecology_Novak. Cytokines, Lymphokines, and Immune Mediators


Gynecology_Novak

Gynecology_Novak. Many events in the generation of immune responses (as well as during the effector phase of immune responses) require or are enhanced by cytokines, which are soluble mediator molecules (Table 6.5) (77–92). Cytokines are pleiotropic in that they have multiple biologic functions that depend on the type of target cell or its maturational state. Cytokines are heterogeneous in the sense that most cytokines share little structural or amino acid homology. Cytokines are called monokines if they are derived from monocytes, lymphokines if they are derived from lymphocytes, interleukins if they exert their actions on leukocytes, or interferons (IFNs) if they have antiviral effects. They are produced by a wide variety of cell types and seem to have important roles in many biologic responses outside the immune response, such as inﬂammation or hematopoiesis. They may also be involved in the pathophysiology of a wide range of diseases and show great potential as therapeutic agents in immunotherapy


Gynecology_Novak

Gynecology_Novak. the immune response, such as inﬂammation or hematopoiesis. They may also be involved in the pathophysiology of a wide range of diseases and show great potential as therapeutic agents in immunotherapy for cancer. Although cytokines are a heterogeneous group of proteins, they share some characteristics. For instance, most cytokines are low-to intermediate-molecular weight (10–60 kd) glycosylatedsecreted proteins. They are involved in immunity and inﬂammation, are produced transiently and locally (they act in an autocrine and paracrine rather than an endocrine manner), are extremely potent in small concentrations, and interact with high-affinity cellular receptors that are specific for each cytokine. The cell surface binding of cytokines by specific receptors results in signal transduction followed by changes in gene expression and, ultimately, by changes in cellular proliferation or altered cell behavior, or both. Their biologic actions overlap, and exposure of responsive cells to


Gynecology_Novak

Gynecology_Novak. followed by changes in gene expression and, ultimately, by changes in cellular proliferation or altered cell behavior, or both. Their biologic actions overlap, and exposure of responsive cells to multiple cytokines can result in synergistic or antagonistic biologic effects.


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Gynecology_Novak. Table 6.5 Sources, Target Cells, and Biological Activities of Cytokines Involved in Immune Responses IL-1, interleukin-1; TH1, type 1 T-helper lymphocyte; NK cells, natural killer cells; TH2, type 2 T-helper lymphocyte; IgE, immunoglobulin E; MHCII, major histocompatibility complex class II; Ag, antigen; IFN, interferon; TNF, tumor necrosis factor. Modified from Berek JS, Martinez-Maza O. Immunology and immunotherapy. In: Lawton FG, Neijt JP, Swenerton KD. Epithelial cancer of the ovary. London, Engl.: BMJ, 1995:224, with permission. T-cell subsets characterized by the secretion of distinct patterns of cytokines were identified.


Gynecology_Novak

Gynecology_Novak. TH1 and TH2 are two helper T-cell subpopulations that control the nature of an immune response by secreting a characteristic and mutually antagonistic set of cytokines: Clones of TH1 produce IL-2 and IFN-γ, whereas TH2 clones produce IL-4, IL-5, and IL-10 (86). A similar dichotomy between TH1-and TH2-type responses was reported in humans (87,88). Human IL-10 inhibits the production of IFN-γ and other cytokines by human peripheral blood mononuclear cells and by suppressing the release of cytokines (IL-1, IL-6, IL-8, and TNF-α) by activated monocytes (89–92). IL-10 down-regulates class II MHC expression on monocytes, resulting in a strong reduction in the antigen-presenting capacity of these cells (92). Together, these observations support the concept that IL-10 has an important role as an immune-inhibitory cytokine. Additional T-cell subsets were identified, including Th17 cells and regulatory T cells (Treg). Th17 cells are a distinct, pro-inﬂammatory T-cell subset, which is


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Gynecology_Novak. as an immune-inhibitory cytokine. Additional T-cell subsets were identified, including Th17 cells and regulatory T cells (Treg). Th17 cells are a distinct, pro-inﬂammatory T-cell subset, which is functionally characterized by mediating protection against extracellular bacteria and by its pathogenic role in autoimmune disorders (93–98). Th17 cells characteristically produce IL-17, CXCL13 (a B-cell stimulatory chemokine), IL-6, and TNF-α, in contrast to Th2 cells, which characteristically produce IL-4, IL-5, IL-9 and IL-13, or Th1 cells, which produce IFN-γ (Fig. 6.2). Treg cells constitute another subset of CD4-positive T cells that participates in the maintenance of immunologic self-tolerance by actively suppressing the activation and expansion of self-reactive lymphocytes. Treg cells are characterized by the expression of CD25 (the IL-2 receptor chain) and the transcription factor FoxP3 (99,100). Treg cell activity is thought to be important in preventing the development of


Gynecology_Novak

Gynecology_Novak. cells are characterized by the expression of CD25 (the IL-2 receptor chain) and the transcription factor FoxP3 (99,100). Treg cell activity is thought to be important in preventing the development of autoimmune diseases. Removal of Treg may enhance immune responses against infectious agents or cancer. Although much remains to be learned about the role of Treg activity in antitumor immunity, it is clear that such cells may play a role in modulating host responses to cancer.


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Gynecology_Novak. Because epithelial cancers of the ovary usually remain confined to the peritoneal cavity, even in the advanced stages of the disease, it was suggested that the growth of ovarian cancer intraperitoneally could be related to a local deficiency of antitumor immune effector mechanisms (102,103). Studies showed that ascitic ﬂuid from patients with ovarian cancer contained increased concentrations of IL-10 (102). Various other cytokines are seen in ascitic ﬂuid obtained from women with ovarian cancer, including IL-6, IL-10, TNF-α, granulocyte colony-stimulating factor (G-CSF), and granulocyte-macrophage colony-stimulating factor (GM-CSF) (103). A similar pattern was seen in serum samples from women with ovarian cancer with elevations of IL-6 and IL-10.


Gynecology_Novak

Gynecology_Novak. TNF-α is a cytokine that can be directly cytotoxic for tumor cells, can increase immune cell–mediated cellular cytotoxicity, and can activate macrophages and induce secretion of monokines. Other biologic activities of TNF-α include the induction of cachexia, inﬂammation, and fever; it is an important mediator of endotoxic shock. Cytokines are extraordinarily pleiotropic with a bewildering array of biologic activities, including some outside the immune system (55,56,77,83). Because some cytokines have direct or indirect antitumor and immune-enhancing effects, several of these factors are used in the experimental treatment of cancer.


Gynecology_Novak

Gynecology_Novak. The precise roles of cytokines in antitumor responses have not been elucidated. Cytokines can exert antitumor effects by many different direct or indirect activities. It is possible that a single cytokine could increase tumor growth directly by acting as a growth factor while at the same time increasing immune responses directed toward the tumor. The potential of cytokines to increase antitumor immune responses was tested in experimental adoptive immunotherapy by exposing the patient’s peripheral blood cells or tumor-infiltrating lymphocytes to cytokines such as IL-2 in vitro, thus generating activated cells with antitumor effects that can be given back to the patient (104–106). Some cytokines can exert direct antitumor effects. Tumor necrosis factor can induce cell death in sensitive tumor cells.


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Gynecology_Novak. The effects of cytokines on patients with cancer might be modulated by soluble receptors or blocking factors. For instance, blocking factors for TNF and for lymphotoxin were found in ascitic ﬂuid from patients with ovarian cancer (106). Such factors could inhibit the cytolytic effects of TNF or lymphotoxin and should be taken into account in the design of clinical trials of intraperitoneal infusion of these cytokines. Cytokines have growth-increasing effects on tumor cells in addition to inducing antitumor effects. They can act as autocrine or paracrine growth factors for human tumor cells, including those of nonlymphoid origin. For instance, IL-6 (which is produced by various types of human tumor cells) can act as a growth factor for human myeloma, Kaposi’s sarcoma, renal carcinoma, and epithelial ovarian cancer cells (77–83).


Gynecology_Novak

Gynecology_Novak. Cytokines are of great potential value in the treatment of cancer, but because of their multiple— even conﬂicting—biologic effects, a thorough understanding of cytokine biology is essential for their successful use (104–117). Cell biology is characterized by considerable redundancy and functional overlap, so a defect in one mechanism does not invariably jeopardize the function of the cell. When a sufficient number of abnormalities in structure and function occur, normal cell activity is jeopardized, and uncontrolled cell growth or cell death results. Either end point may result from accumulated genetic mutations over time. Factors are identified that enhance the likelihood of genetic mutations, jeopardize normal cell biology, and may increase the risk of cancer.


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Gynecology_Novak. high-dose chemotherapy with stem cell support may be at increased risk of developing a variety of solid neoplasms. These examples illustrate the importance of immune function in host surveillance for transformed cells. Another example of altered immune function that may be related to the development of cervical dysplasia is the alteration in mucosal immune function that occurs in women who smoke cigarettes (60). The Langerhans cell population of the cervix is decreased in women who smoke. Langerhans cells are responsible for antigen processing. It is postulated that a reduction in these cells increases the likelihood of successful HPV infection of the cervix.


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Gynecology_Novak. Diet The role of diet in disease prevention and predisposition is widely recognized but poorly understood (116,121). Dietary fat intake is correlated with the risk of colon and breast cancer. Fiber is considered protective against colon cancer. With respect to the female reproductive system, epidemiologic studies provide conﬂicting results. Deficiencies of folic acid and vitamins A and C were associated with the development of cervical dysplasia and cervical cancer. Considerable research must be performed to clarify the impact of diet on cancer prevention and development. 1. Taylor AM, McConville CM, Byrd PJ. Cancer and DNA processing disorders. Br Med Bull 1994;50:708–717. 2. Kraemer KH, Levy DD, Parris CN, et al. Xerodermapigmentosum and related disorders: examining the linkage between defective DNA repair and cancer. J Invest Dermatol 1994;103[Suppl 5]:96S–101S. 3. Jacobs T. Control of the cell cycle. Dev Biol 1992;153:1–15. 4.


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Gynecology_Novak. 69. Goode EL, Maurer MJ, Sellers TA, et al. Inherited determinants of ovarian cancer survival. Clin Cancer Res 2010;16:995–1007. 70. Notaridou M, Quaye L, Dafou D, et al. The Australian Ovarian Cancer Study Group/Australian Cancer Study (Ovarian Cancer). Common alleles in candidate susceptibility genes associated with risk and development of epithelial ovarian cancer. Int J Cancer 2011;128: 2063–2074. 71. The Cancer Genome Atlas. Available at: http://en.wikipedia.org/ wiki/The Cancer Genome Atlas. Accessed April 28, 2011. 72. Cancer Genome Atlas Research Network. Comprehensive genomic characterization defines human glioblastoma genes and core pathways. Nature 2008;455:1061–1068. 73. Verhaak RG, Hoadley KA, Purdom E, et al. Integrated genomic analysis identifies clinically relevant subtypes of glioblastoma characterized by abnormalities in PDGFRA, IDH1, EGFR, and NF1. Cancer Cell 2010;17:98–110 74.


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Gynecology_Novak. National Cancer Institute. The Cancer Genome Atlas. Available at: http://cancergenome.nih.gov./ Accessed April 28, 2011. 75. Boyer CM, Knapp RC, Bast RC Jr. Biology and immunology. In: Berek JS, Hacker NF, eds. Practical gynecologic oncology, 2nd ed. Baltimore, MD: Williams & Wilkins, 1994:75–115. 76. Kohler G, Milstein C. Continuous cultures of fused cells secreting antibody of predefined specificity. Nature 1978;256:495–497. 77. Di Giovine FS, Duff GW. Interleukin 1: the first interleukin. Immunol Today 1990;11:13–20. 78. Hirano T, Akira S, Taga T, et al. Biological and clinical aspects of interleukin 6. Immunol Today 1990;11:443–449. 79. Watson JM, Sensintaffar JL, Berek JS, et al. Epithelial ovarian cancer cells constitutively produce interleukin-6 (IL-6). Cancer Res 1990;50:6959–6965. 80. Berek JS, Chang C, Kaldi K, et al. Serum interleukin-6 levels correlate with disease status in patients with epithelial ovarian cancer. Am J Obstet Gynecol 1991;164:1038–1043. 81.


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Gynecology_Novak. 80. Berek JS, Chang C, Kaldi K, et al. Serum interleukin-6 levels correlate with disease status in patients with epithelial ovarian cancer. Am J Obstet Gynecol 1991;164:1038–1043. 81. Miki S, Iwano M, Miki Y, et al. Interleukin-6 (IL-6) functions as an in vitro autocrine growth factor in renal cell carcinomas. FEBS Lett 1989;250:607–610. 82. Wu S, Rodabaugh K, Mart´ez-Maza O, et al. Stimulation of ovarian tumor cell proliferation with monocyte products including interleukin-1, interleukin-6 and tumor necrosis factor-α. Am J Obstet Gynecol 1992;166:997–1007. 83. Mart´ez-Maza O, Berek JS. Interkeukin-6 and cancer treatment. In Vivo 1991;5:583. 84. Mule JJ, McIntosh JK, Jablons DM, et al. Antitumor activity of recombinant interleukin-6 in mice. J Exp Med 1990;171:629– 636. 85. Fiorentino DF, Bond MW, Mosmann TR. Two types of mouse helper T cells. IV. TH2 clones secrete a factor that inhibits cytokine production by TH1 clones. J Exp Med 1989;170:2081–2095. 86.


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Gynecology_Novak. 85. Fiorentino DF, Bond MW, Mosmann TR. Two types of mouse helper T cells. IV. TH2 clones secrete a factor that inhibits cytokine production by TH1 clones. J Exp Med 1989;170:2081–2095. 86. Mosmann TR, Moore KW. The role IL-10 in cross regulation of TH1 and TH2 responses. Immunol Today 1991;12:A49–53. 87. Del Prete GF, De Carli M, Ricci M, et al. Helper activity for immunoglobulin synthesis of T helper type 1 (TH1) and TH2 human T cell clones: the help of TH1 clones is limited by their cytolytic capacity. J Exp Med 1991;174:809–813. 88. Romagnani S. Human TH1 and TH2 subsets: doubt no more. Immunol Today 1991;12:256–257. 89. Zlotnik A, Moore KW. Interleukin-10. Cytokine 1991;3:366–371. 90. Fiorentino DF, Zlotnik A, Mosmann TR, et al. IL-10 inhibits cytokine production by activated macrophages. J Immunol 1991;147: 3815–3822. 91. Bogdan C, Vodovotz Y, Nathan C. Macrophage deactivation by IL-10. J Exp Med 1991;174:1549–1555. 92.


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Gynecology_Novak. 91. Bogdan C, Vodovotz Y, Nathan C. Macrophage deactivation by IL-10. J Exp Med 1991;174:1549–1555. 92. de Waal Malefyt R, Abrams J, Bennett B, et al. Interleukin10 (IL-10) inhibits cytokine synthesis by human monocytes: an autoregulatory role of IL-10 produced by monocytes. J Exp Med 1991;174:1209–1220. 93. Weaver CT, Harrington LE, Mangan PR, et al. Th17: an effector CD4 T cell lineage with regulatory T cell ties. Immunity 2006;24: 677–688. 94. Katsifis GE, Moutsopoulos NM, Wahl SM. (2007) T lymphocytes in Sjogren’s syndrome: contributors to and regulators of pathophysiology. Clin Rev Allergy Immunol 2007;32:252–264. 95. Korn T, Oukka M, Kuchroo V, et al. Th17 cells: effector T cells with inﬂammatory properties. Semin Immunol 2007;19:362–371. 96. Stockinger B, Veldhoen M. Differentiation and function of Th17 T cells. Curr Opin Immunol 2007;19:281–286. 97.


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Gynecology_Novak. 96. Stockinger B, Veldhoen M. Differentiation and function of Th17 T cells. Curr Opin Immunol 2007;19:281–286. 97. Ouyang M, Garnett AT, Han TM, et al. A web based resource characterizing the zebrafish developmental profile of over 16,000 transcripts. Gene Expr Patterns 2008;8:171–180. 98. Romagnani S. Human Th17 cells. Arthritis Res Ther 2008;10: 206. 99. Sakaguchi S, Sakaguchi N, Shimizu J, et al. Immunologic tolerance maintained by CD25+ CD4+ regulatory T cells: their common role in controlling autoimmunity, tumor immunity, and transplantation tolerance. Immunol Rev 2001;182:18–32. 100. Shevach EM. CD4+ CD25+ suppressor T cells: more questions than answers. Nat Rev Immunol 2002;2:389–400. 101. Berek JS. Epithelial ovarian cancer. In: Berek JS, Hacker NF, eds. Practical gynecologic oncology, 2nd ed. Baltimore, MD: Williams & Wilkins, 1994:327–375. 102.


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Gynecology_Novak. 101. Berek JS. Epithelial ovarian cancer. In: Berek JS, Hacker NF, eds. Practical gynecologic oncology, 2nd ed. Baltimore, MD: Williams & Wilkins, 1994:327–375. 102. Gotlieb WH, Abrams JS, Watson JM, et al. Presence of IL-10 in the ascites of patients with ovarian and other intraabdominal cancers. Cytokine 1992;4:385–390. 103. Watson JM, Gotlieb WH, Abrams JH, et al. Cytokine profiles in ascitic ﬂuid from patients with ovarian cancer: relationship to levels of acute phase proteins and immunoglobulins, immunosuppression and tumor classification. J Soc Gynecol Invest 1993;186:8. 104. Rosenberg SA. Immunotherapy of cancer by systemic administration of lymphoid cells plus interleukin-2. J Biol Response Mod 1984;3:501–511. 105. Rosenberg SA, Lotze MT. Cancer immunotherapy using interleukin-2 and interleukin-2–activated lymphocytes. Annu Rev Immunol 1986;4:681–709. 106.


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Gynecology_Novak. 105. Rosenberg SA, Lotze MT. Cancer immunotherapy using interleukin-2 and interleukin-2–activated lymphocytes. Annu Rev Immunol 1986;4:681–709. 106. Rosenberg SA, Lotze MT, Muul LM, et al. Observations on the systemic administration of autologous lymphokine-activated killer cells and recombinant interleukin-2 to patients with metastatic cancer. N Engl J Med 1985;313:1485–1492. 107. Cappuccini F, Yamamoto RS, DiSaia PJ, et al. Identification of tumor necrosis factor and lymphotoxin blocking factor(s) in the ascites of patients with advanced and recurrent ovarian cancer. Lymphokine Cytokine Res 1991;10:225–229. 108. Rosenberg SA, Lotze MT, Muul LM, et al. A progress report on the David L. Olive Steven F. Palter The female reproductive process involves the central nervous system (primarily hypothalamus), the pituitary gland, the ovary, and the uterus (endometrium). All must function appropriately for normal reproduction to occur.


Gynecology_Novak

Gynecology_Novak. Hypothalamic gonadotropin-releasing hormone (GnRH) simultaneously regulates both luteinizing hormone (LH) and follicle-stimulating hormone (FSH) in the pituitary by being secreted in a pulsatile manner. The pulse frequency determines the relative amounts of LH and FSH secretion. The ovary responds to FSH and LH in a defined, sequential manner to produce follicular growth, ovulation, and corpus luteum formation. The cycle is designed to produce an optimal environment for pregnancy; if pregnancy does not occur, the cycle begins again. In the early menstrual cycle the ovary produces estrogen, which is responsible for endometrial growth. Following ovulation, progesterone is also produced in significant quantities, which transforms the endometrium into a form ideal for implantation of the embryo. If no pregnancy occurs, the ovary ceases to produce estrogen and progesterone, the endometrium is sloughed, and the cycle begins again.


Gynecology_Novak

Gynecology_Novak. The reproductive process in women is a complex and highly evolved interaction of many components. The carefully orchestrated series of events that contributes to a normal ovulatory menstrual cycle requires precise timing and regulation of hormonal input from the central nervous system, the pituitary gland, and the ovary. This delicately balanced process can be disrupted easily and result in reproductive failure, which is a major clinical issue confronting gynecologists. To manage effectively such conditions, it is critical that gynecologists understand the normal physiology of the menstrual cycle. The anatomic structures, hormonal components, and interactions between the two play a vital role in the function of the reproductive system. Fitting together the various pieces of this intricate puzzle will provide “the big picture”: an overview of how the reproductive system of women is designed to function.


Gynecology_Novak

Gynecology_Novak. Neuroendocrinology represents facets of two traditional fields of medicine: endocrinology, which is the study of hormones (i.e., substances secreted into the bloodstream that have diverse actions at sites remote from the point of secretion), and neuroscience, which is the study of the action of neurons. The discovery of neurons that transmit impulses and secrete their products into the vascular system to function as hormones, a process known as neurosecretion, demonstrates that the two systems are intimately linked. For instance, the menstrual cycle is regulated through the feedback of hormones on the neural tissue of the central nervous system (CNS).


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Gynecology_Novak. Hypothalamus The hypothalamus is a small neural structure situated at the base of the brain above the optic chiasm and below the third ventricle (Fig. 7.1). It is connected directly to the pituitary gland and is the part of the brain that is the source of many pituitary secretions. Anatomically, the hypothalamus is divided into three zones: periventricular (adjacent to the third ventricle), medial (primarily cell bodies), and lateral (primarily axonal). Each zone is further subdivided into structures known as nuclei, which represent locations of concentrations of similar types of neuronal cell bodies (Fig. 7.2).


Gynecology_Novak

Gynecology_Novak. The hypothalamus is not an isolated structure within the CNS; instead, it has multiple interconnections with other regions in the brain. In addition to the well-known pathways of hypothalamic output to the pituitary, there are numerous less well-characterized pathways of output to diverse regions of the brain, including the limbic system (amygdala and hippocampus), the thalamus, and the pons (1). Many of these pathways form feedback loops to areas supplying neural input to the hypothalamus. Several levels of feedback to the hypothalamus exist and are known as the long, short, and ultrashort feedback loops. The long feedback loop is composed of endocrine input from Figure 7.1 The hypothalamus and its neurologic connections to the pituitary. Figure 7.2 The neuronal cell bodies of the hypothalamus.


Gynecology_Novak

Gynecology_Novak. Figure 7.1 The hypothalamus and its neurologic connections to the pituitary. Figure 7.2 The neuronal cell bodies of the hypothalamus. circulating hormones, just as feedback of androgens and estrogens onto steroid receptors is present in the hypothalamus (2,3). Similarly, pituitary hormones may feed back to the hypothalamus and serve important regulatory functions in short-loop feedback. Finally, hypothalamic secretions may directly feed back to the hypothalamus itself in an ultrashort feedback loop. The major secretory products of the hypothalamus are the pituitary-releasing factors (Fig. 7.3): 1. Gonadotropin-releasing hormone (GnRH), which controls the secretion of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) 2. Corticotropin-releasing hormone (CRH), which controls the release of adrenocorticotrophic hormone (ACTH) 3. Growth hormone–releasing hormone (GHRH), which regulates the release of growth hormone (GH) 4.


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Gynecology_Novak. Growth hormone–releasing hormone (GHRH), which regulates the release of growth hormone (GH) 4. Thyrotropin-releasing hormone (TRH), which regulates the secretion of thyroid-stimulating hormone (TSH) The hypothalamus is the source of all neurohypophyseal hormone production. The neural posterior pituitary can be viewed as a direct extension of the hypothalamus connected by the fingerlike infundibular stalk. The capillaries in the median eminence differ from those in other regions of the brain. Unlike the usual tight junctions that exist between adjacent capillary endothelial lining cells, the capillaries in this region are fenestrated in the same manner as capillaries outside the CNS. As a result, there is no blood–brain barrier in the median eminence.


Gynecology_Novak

Gynecology_Novak. Pituitary The pituitary is divided into three regions or lobes: anterior, intermediate, and posterior. The anterior pituitary (adenohypophysis) is quite different structurally from the posterior neural pituitary (neurohypophysis), which is a direct physical extension of the hypothalamus. The adenohypophysis is derived embryologically from epidermal ectoderm from an infolding of Rathke’s pouch. Therefore, it is not composed of neural tissue, as is the posterior pituitary, and does not have direct neural connections to the hypothalamus. Instead, a unique anatomic relationship exists that combines elements of neural production and endocrine secretion. The adenohypophysis itself has no direct arterial blood supply. Its major source of blood ﬂow is also its source of hypothalamic input—the portal vessels. Blood ﬂow in these portal vessels is primarily from the hypothalamus to the pituitary. Blood is supplied to the posterior pituitary via the superior, middle, and inferior hypophyseal


Gynecology_Novak

Gynecology_Novak. portal vessels. Blood ﬂow in these portal vessels is primarily from the hypothalamus to the pituitary. Blood is supplied to the posterior pituitary via the superior, middle, and inferior hypophyseal arteries. In contrast, the anterior pituitary has no direct arterial blood supply. Instead, it receives blood via a rich capillary plexus of the portal vessels that originates in the median eminence of the hypothalamus and descends along the pituitary stalk. This pattern is not absolute, however, and retrograde blood ﬂow has occurred (4). This blood ﬂow, combined with the location of the median eminence outside the blood–brain barrier, permits bidirectional feedback control between the two structures.


Gynecology_Novak

Gynecology_Novak. Figure 7.3 The hypothalamic secretory products function as pituitary-releasing factors that control the endocrine function of the ovaries, the thyroid, and the adrenal glands. The specific secretory cells of the anterior pituitary are classified based on their hematoxylin-and eosin-staining patterns. Acidophilic-staining cells primarily secrete GH and prolactin and, to a variable degree, ACTH (5). The gonadotropins are secreted by basophilic cells, and TSH is secreted by the neutral-staining chromophobes.


Gynecology_Novak

Gynecology_Novak. GnRH (also called luteinizing hormone–releasing hormone, or LHRH) is the controlling factor for gonadotropin secretion (6). It is a decapeptide produced by neurons with cell bodies primarily in the arcuate nucleus of the hypothalamus (7–9) (Fig. 7.4). Embryologically, these neurons originate in the olfactory pit and then migrate to their adult locations (10). These GnRHsecreting neurons project axons that terminate on the portal vessels at the median eminence where GnRH is secreted for delivery to the anterior pituitary. Less clear in function are multiple other secondary projections of GnRH neurons to locations within the CNS. The gene that encodes GnRH produces a 92 amino acid precursor protein, which contains the GnRH decapeptide and a 56 amino acid peptide known as GnRH-associated peptide (GAP). The GAP is a potent inhibitor of prolactin secretion and a stimulator of gonadotropin release.


Gynecology_Novak

Gynecology_Novak. GnRH is unique among releasing hormones in that it simultaneously regulates the secretion of two hormones—FSH and LH. It also is unique among the body’s hormones because it must be secreted in a pulsatile fashion to be effective, and the pulsatile release of GnRH inﬂuences the release of the two gonadotropins (11–13). Using animals that had undergone electrical destruction of the arcuate nucleus and had no detectable levels of gonadotropins, a series of experiments were performed with varying dosages and intervals of GnRH infusion (13,14). Continual infusions did not result in gonadotropin secretion, whereas a pulsatile pattern led to physiologic secretion patterns and follicular growth. Continual exposure of the pituitary gonadotroph to GnRH results in a phenomenon called down-regulation, through which the number of gonadotroph cell surface GnRH receptors is decreased (15). Similarly, intermittent exposure to GnRH will “up-regulate” or “autoprime” the gonadotroph to increase its


Gynecology_Novak

Gynecology_Novak. through which the number of gonadotroph cell surface GnRH receptors is decreased (15). Similarly, intermittent exposure to GnRH will “up-regulate” or “autoprime” the gonadotroph to increase its number of GnRH receptors (16). This allows the cell to have a greater response to subsequent GnRH exposure. Similar to the intrinsic electrical pacemaker cells of the heart, this action most likely represents an intrinsic property of the GnRH-secreting neuron, although it is subject to modulation by various neuronal and hormonal inputs to the hypothalamus.


Gynecology_Novak

Gynecology_Novak. The continual pulsatile secretion of GnRH is necessary because GnRH has an extremely short half-life (only 2–4 minutes) as a result of rapid proteolytic cleavage. The pulsatile secretion of GnRH varies in both frequency and amplitude throughout the menstrual cycle and is tightly regulated (17,18) (Fig. 7.5). The follicular phase is characterized by frequent, small-amplitude pulses of GnRH secretion. In the late follicular phase, there is an increase in both frequency and amplitude of pulses. During the luteal phase, however, there is a progressive lengthening of the interval between pulses. The amplitude in the luteal phase is higher than that in the follicular phase, but it declines progressively over the 2 weeks. This variation in pulse frequency allows for variation in both LH and FSH throughout the menstrual cycle. For example, decreasing the pulse frequency of GnRH decreases LH secretion but increases FSH, an important aspect of enhancing FSH availability in the late luteal


Gynecology_Novak

Gynecology_Novak. FSH throughout the menstrual cycle. For example, decreasing the pulse frequency of GnRH decreases LH secretion but increases FSH, an important aspect of enhancing FSH availability in the late luteal phase. The pulse frequency is not the sole determinant of pituitary response; additional hormonal inﬂuences, such as those exerted by ovarian peptides and sex steroids, can modulate the GnRH effect.


Gynecology_Novak

Gynecology_Novak. Although GnRH is primarily involved in endocrine regulation of gonadotropin secretion from the pituitary, it is apparent that this molecule has autocrine and paracrine functions throughout the body. The decapeptide is found in both neural and nonneural tissues; receptors are present in many extrapituitary structures, including the ovary and placenta. Data suggest that GnRH may be involved in regulating human chorionic gonadotropin (hCG) secretion and implantation, as well as in decreasing cell proliferation and mediating apoptosis in tumor cells (19). The role of GnRH in the extrapituitary sites remains to be fully elucidated. Figure 7.4 Gonadotropin-releasing hormone is a decapeptide. Figure 7.5 The pulsatile secretion of gonadotropin-releasing hormone in the follicular and luteal phases of the cycle.


Gynecology_Novak

Gynecology_Novak. Figure 7.5 The pulsatile secretion of gonadotropin-releasing hormone in the follicular and luteal phases of the cycle. Mechanism of Action Used clinically, GnRH agonists are modifications of the native molecule to either increase receptor affinity or decrease degradation (20). Their use leads to a persistent activation of GnRH receptors, as if continuous GnRH exposure existed. As would be predicted by the constant GnRH infusion experiments, this leads to suppression of gonadotropin secretion. An initial release of gonadotropins is followed by a profound suppression of secretion. The initial release of gonadotropins represents the secretion of pituitary stores in response to receptor binding and activation. With continued activation of the gonadotroph GnRH receptor, however, there is a down-regulation effect and a decrease in the concentration of GnRH receptors. As a result, gonadotropin secretion decreases and sex steroid production falls to castrate levels (21).


Gynecology_Novak

Gynecology_Novak. Additional modification of the GnRH molecule results in an analogue that has no intrinsic activity but competes with GnRH for the same receptor site (22). These GnRH antagonists produce a competitive blockade of GnRH receptors, preventing stimulation by endogenous GnRH and causing an immediate fall in gonadotropin and sex steroid secretion (23). The clinical effect is observed within 24 to 72 hours. Moreover, antagonists may not function solely as competitive inhibitors; evidence suggests they may also produce down-regulation of GnRH receptors, further contributing to the loss of gonadotropin activity (24).


Gynecology_Novak

Gynecology_Novak. Structure—Agonists and Antagonists As a peptide hormone, GnRH is degraded by enzymatic cleavage of bonds between its amino acids. Pharmacologic alterations of the structure of GnRH led to the creation of agonists and antagonists (Fig. 7.4). The primary sites of enzymatic cleavage are between amino acids 5 and 6, 6 and 7, and 9 and 10. Substitution of the position-6 amino acid glycine with large bulky amino acid analogues makes degradation more difficult and creates a form of GnRH with a relatively long half-life. Substitution at the carboxyl terminus produces a form of GnRH with increased receptor affinity. The resulting high affinity and slow degradation produces a molecule that mimics continuous exposure to native GnRH (20). Thus, as with constant GnRH exposure, down-regulation occurs. GnRH agonists are widely used to treat disorders that are dependent on ovarian hormones (21). They are used to control ovulation induction cycles and to treat precocious puberty, ovarian


Gynecology_Novak

Gynecology_Novak. occurs. GnRH agonists are widely used to treat disorders that are dependent on ovarian hormones (21). They are used to control ovulation induction cycles and to treat precocious puberty, ovarian hyperandrogenism, leiomyomas, endometriosis, and hormonally dependent cancers. The development of GnRH antagonists proved more difficult because a molecule was needed that maintained the binding and degradation resistance of agonists but failed to activate the receptor. Early attempts involved modification of amino acids 1 and 2, as well as those previously utilized for agonists. Commercial antagonists have structural modifications at amino acids 1, 2, 3, 6, 8, and 10. The treatment spectrum is expected to be similar to that of GnRH agonists, but with more rapid onset of action.


Gynecology_Novak

Gynecology_Novak. Nonpeptide, small molecule structures with high affinity for the GnRH receptor were developed (25). These compounds demonstrated the ability to suppress the reproductive axis in a dose-related manner via oral administration, unlike the parenteral approach required with traditional peptide analogues (26). Investigation may elucidate an expanded therapeutic role for these antagonists. Endogenous Opioids and Effects on GnRH The endogenous opioids are three related families of naturally occurring substances produced in the CNS that represent the natural ligands for the opioid receptors (27–29). There are three major classes of endogenous opioids, each derived from precursor molecules: 1. Endorphins are named for their endogenous morphinelike activity. These substances are produced in the hypothalamus from the precursor proopiomelanocortin (POMC) and have diverse activities, including regulation of temperature, appetite, mood, and behavior (30). 2.


Gynecology_Novak

Gynecology_Novak. 2. Enkephalins are the most widely distributed opioid peptides in the brain, and they function primarily in regulation of the autonomic nervous system. Proenkephalin A is the precursor for the two enkephalins of primary importance: methionine–enkephalin and leucine–enkephalin. 3. Dynorphins are endogenous opioids produced from the precursor proenkephalin B that serve a function similar to that of the endorphins, producing behavioral effects and exhibiting a high analgesic potency. The endogenous opioids play a significant role in the regulation of hypothalamic–pituitary function. Endorphins appear to inhibit GnRH release within the hypothalamus, resulting in inhibition of gonadotropin secretion (31). Ovarian sex steroids can increase the secretion of central endorphins, further depressing gonadotropin levels (32).


Gynecology_Novak

Gynecology_Novak. Endorphin levels vary significantly throughout the menstrual cycle, with peak levels in the luteal phase and a nadir during menses (33). This inherent variability, although helping to regulate gonadotropin levels, may contribute to cycle-specific symptoms experienced by ovulatory women. For example, the dysphoria experienced by some women in the premenstrual phase of the cycle may be related to a withdrawal of endogenous opiates (34). Anterior Pituitary The anterior pituitary is responsible for the secretion of the major hormone-releasing factors—FSH, LH, TSH, and ACTH—as well as GH and prolactin. Each hormone is released by a specific pituitary cell type. The gonadotropins FSH and LH are produced by the anterior pituitary gonadotroph cells and are responsible for ovarian follicular stimulation. Structurally, there is great similarity between FSH and LH (Fig. 7.6). They are both glycoproteins that share identical α subunits


Gynecology_Novak

Gynecology_Novak. Figure 7.6 The structural similarity between follicle-stimulating hormone (FSH), luteinizing hormone (LH), and thyroid-stimulating hormone (TSH). The α subunits are identical, and the β subunits differ. and differ only in the structure of their β subunits, which confer receptor specificity (35,36). The synthesis of the β subunits is the rate-regulating step in gonadotropin biosynthesis (37). Thyroid-stimulating hormone and placental hCG also share identical α subunits with the gonadotropins. There are several forms of each gonadotropin, which differ in carbohydrate content as a result of posttranslation modification. The degree of modification varies with steroid levels and is an important regulator of gonadotropin bioactivity.


Gynecology_Novak

Gynecology_Novak. Prolactin, a 198–amino acid polypeptide secreted by the anterior pituitary lactotroph, is the primary trophic factor responsible for the synthesis of milk by the breast (38). Several forms of this hormone, which are named according to their size and bioactivity, are normally secreted (39). Prolactin gene transcription is principally stimulated by estrogen; other hormones promoting transcription are TRH and a variety of growth factors.


Gynecology_Novak

Gynecology_Novak. Prolactin secretion is under tonic inhibitory control by the hypothalamic secretion of dopamine (40). Therefore, disease states characterized by decreased dopamine secretion or any condition that interrupts transport of dopamine down the infundibular stalk to the pituitary gland will result in increased synthesis of prolactin. In this respect, prolactin is unique in comparison with all other pituitary hormones: It is predominantly under tonic inhibition, and release of control produces an increase in secretion. Clinically, increased prolactin levels are associated with amenorrhea and galactorrhea, and hyperprolactinemia should be suspected in any individual with symptoms of either of these conditions. Although prolactin appears to be primarily under inhibitory control, many stimuli can elicit its release, including breast manipulation, drugs, stress, exercise, and certain foods.