Identifying Novel Substrates of Ubiquitin-Specific Protease 7 (USP7) And Speckle-Type POZ (Pox Virus and Zinc Finger) Protein (SPOP)

Speckle-type POZ protein (SPOP), an E3 ubiquitin ligase adaptor protein, and ubiquitin-specific protease 7 (USP7), a deubiquitinating enzyme, have previously been implicated in prostate cancer pathogenesis. The objective of this project was to identify novel substrates of SPOP and USP7 to provide insight on the molecular mechanisms contributing to prostate cancer. Employing biochemical and cellular biology techniques, we identified, murine double minute 2 (MDM2), an E3 ubiquitin ligase, as a potential substrate of SPOP. We demonstrated that SPOP interacts with MDM2 through its MATH domain in vitro and negatively regulates its stability in vivo. Moreover, we identified sirtuin 2 (SIRT2), an NAD+-dependent deacetylase, as a novel substrate of USP7. We demonstrated that USP7 interacts and regulates the stability of SIRT2 in vivo. Collectively, our results suggest that SPOP and USP7 through the regulation of MDM2 and SIRT2, may contribute to prostate cancer, however further studies are required to verify this.