In the sentence extracted from biomedical literature, identify all the disease entities. The required answer format is the same sentence with HTML <span> tags to mark up specific entities. 
### Entity Markup Guides:
Use <span class="disease"> to denote a disease.

### Input Text: We next demonstrated in coimmunoprecipitates that VHL and Sp1 were part of the same complex and , by using a glutathione - S - transferase - VHL fusion protein and purified Sp1 , that VHL and Sp1 directly interact .
### Output Text:
We next demonstrated in coimmunoprecipitates that VHL and Sp1 were part of the same complex and , by using a glutathione - S - transferase - VHL fusion protein and purified Sp1 , that VHL and Sp1 directly interact . 