HSPA8-mediated stability of the CLPP protein regulates mitochondrial autophagy in cisplatin-resistant ovarian cancer cells

Abstract

Background: Currently, platinum agents remain the mainstay of chemotherapy for ovarian cancer (OC). However, cisplatin (DDP) resistance is a major reason for chemotherapy failure. Thus, it is extremely important to elucidate the mechanism of resistance to DDP. Methods: We establish 2 DDP-resistant ovarian cancer cell lines and find that caseinolytic protease P (CLPP) is significantly downregulated in the DDP-resistant cell lines when compared to wild-type ovarian cancer cell lines (SK-OV-3 and OVcar3). Next, we investigate the functions of CLPP in the DDP-resistant and wild-type ovarian cancer cells using various assays including cell counting kit-8 assays, western blotting, immunofluorescent staining, and reactive oxygen species (ROS) and apoptosis detection. Results: Our experiments show that CLPP knockdown significantly increase the half maximal inhibitory concentration (IC50) and mitophagy of wild-type SK-OV-3 and OVcar3 cells, while CLPP overexpression reduces the IC50 values and mitophagy of DDP-resistant SK-OV-3 and OVcar3 cells. Next, we perform database predictions and experiments to show that heat shock protein family A member 8 (HSPA8) regulates CLPP protein stability. The dynamic effects of the HSPA8/CLPP axis in the ovarian cancer cells were also examined. HSPA8 increases mitophagy and the IC50 values of SK-OV-3 and OVcar3 cells, but inhibits their ROS production and apoptosis. In addition, CLPP partly reverses the effects induced by HSPA8 in the SK-OV-3 and OVcar3 cells. Conclusions: CLPP increases the DDP resistance of ovarian cancer by inhibiting mitophagy and promoting cellular stress. Meanwhile, HSPA8 promotes the degradation of CLPP protein by inducing its stability.