UBE2C-mediated Autophagy Inhibition via Ubiquitination of SIRT1 Contributes to Endometrial Cancer Progression

Abstract Recent studies have shown that autophagy plays an important role in gynecologic tumors, and ubiquitin modification of autophagy regulatory components is essential to regulate autophagic flux. In this study, we found that the ubiquitin-conjugating enzyme E2C (UBE2C) affects endometrial cancer cell apoptosis and proliferation by inhibiting autophagy. Electron microscopy observation of cell ultrastructure and experimental biochemical analysis showed that endometrial cancer cells with UBE2C expression knocked down display typical autophagic characteristics. Cells were cotreated with the autophagy pharmacologic inhibitors chloroquine and/or bafilomycin A1, and mRFP-GFP-LC3 assays were performed to monitor autophagic flux and determine whether UBE2C suppresses the autophagy program. Investigation of the corresponding mechanism by which UBE2C inhibits autophagy revealed that UBE2C induces K48-linked SIRT1 ubiquitination and promotes ubiquitination-dependent degradation of SIRT1, subsequently reducing H4K16 deacetylation levels and epigenetically inhibiting the expression of autophagy-related genes. The results of cell counting kit-8, Hoechst staining, and immunofluorescence assays further indicated that deletion of the autophagy-related gene BECN1 significantly attenuates UBE2C knockdown–induced cell apoptosis. Moreover, overexpression of UBE2C promoted tumor growth in the xenograft mice model. While, the introduction of rapamycin, an agonist of autophagy, successfully reversed tumor growth and apoptosis inhibition mediated by UBE2C overexpression in vitro and in vivo. Taken together, our results suggested that UBE2C-mediated ubiquitination and degradation of SIRT1 contribute to the malignant progression of endometrial cancer through epigenetic inhibition of autophagy. Implications: Our study highlights the tumorigenic role and regulatory mechanism of UBE2C in endometrial cancer; UBE2C inhibits endometrial cancer cell apoptosis through autophagy-related mechanisms and our findings provide new insights into the treatment of endometrial cancer.