 Ero1-α is mainly induced by hypoxia (HIF-1), whereas Ero1-β is mainly induced by the unfolded protein response (UPR).During endoplasmic reticulum stress (such as occurs in beta cells of the pancreas or in macrophages causing atherosclerosis), CHOP can induce activation of Ero1, causing calcium release from the endoplasmic reticulum into the cytoplasm, resulting in apoptosis.Homologues of the Saccharomyces cerevisiae Ero1 proteins have been found in all eukaryotic organisms examined, and contain seven cysteine residues that are absolutely conserved, including three that form the sequence Cys–X–X–Cys–X–X–Cys (where X can be any residue).