Stabilization Of Histone Demethylase PHF8 By USP7 Promotes Breast Carcinogenesis

PHF8 is a histone demethylase implicated in multiple pathological disorders including X-linked mental retardation and tumorigenesis. However, how the abundance and function of PHF8 areregulated is not understood. We report here that PHF8 is physically associated with deubiquitinase USP7. We demonstrated that USP7 promotes deubiquitination and stabilization of PHF8, leading to the up-regulation of a group of genes including cyclin A2 that are critically implemented in cell growth and proliferation. Interestingly, USP7 itself is transcriptionally regulated, via positive feedback, by PHF8. Significantly, USP7 is overexpressed in breast carcinomas, and its level of expression is positively correlated with that of PHF8 and cyclin A2 and with histologic grades of breast cancer. We showed that USP7, through stabilizing PHF8 and up-regulating cyclin A2, promotes breast carcinogenesis. Importantly, the interaction between USP7 with PHF8 is augmented during DNA damage. Furthermore, we demonstrated that USP7-promoted PHF8 stabilization confers cellular resistance to genotoxic insults and is required for HR and NHEJ thus efficient break repair. Our study provides a mechanistic link of USP7 to epigenetic regulation and DNA repair, and supports the pursuit of USP7 and PHF8 as potential targets for breast cancer intervention, especially when combined with chemo-or radio-therapies.Objective:Explore the mechanism of how the abundance and function of PHF8 are regulated.Results:A. Physically, PHF8 and USP7 have direct interaction in vivo.The N-terminal MATH domain of USP7 interacts with PHF8 directly, while C terminus of PHF8 directly interacts with USP7.B. USP7 stabilize PHF8 via itsdeubiquitin conjugating enzyme activity towards PHF8. USP7is able to remove ubiquitin chains on PHF8, thus stablizing PHF8.C. The USP7/PHF8 axis co-regulates downstream target genes including cyclin A2, and plays an important role in promoting the proliferation of breast cancer cells.D. USP7 is highly expressed in tumors, and its expression level is related to that of PHF8 and cyclin A2, as well as the pathological grading of breast cancer.E. In the process of DNA damage repair, the interaction between USP7 and PHF8 was obviously enforced.F. During DNA damage repair,USP7/PHF8 complex regulates both HR and NHEJ thus effectively confers cellular resistance to genotoxic insults.Conclusion:Our study provides a mechanistic link of USP7 to epigenetic regulation of PHF8, and show that USP7/PHF8 axis not only promotes tumorigenesis of breast cancer, but also confers cellular resistance to genotoxic insults, suggesting that the pursuit of USP7 and PHF8 as potential targets for breast cancer intervention, especially when combined with chemo- or radio-therapies.