Inhibition of ubiquitin‑specific protease�14 promotes connexin�32 internalization and counteracts cisplatin cytotoxicity in human ovarian cancer cells

Although cisplatin is one of the most accepted therapies for ovarian cancer, recurrence and drug resistance remain problematic. Both the ubiquitin‑proteasome system (UPS) and connexin (Cx) are closely related to tumor progression. However, the role of ubiquitin‑specific protease 14 (USP14) and Cx in mediating drug resistance remains unclear. In the present study, we aimed to determine whether USP14 is involved in cisplatin resistance and modulates the internalization of connexin 32 (Cx32) in ovarian cancer. The results of the deubiquitinase (DUB) trap assay and western blot analysis revealed that the expression and activity levels of USP14 were downregulated in A2780 cisplatin‑resistant cells (A2780‑CDDP) relative to these levels in A2780 cisplatin‑sensitive cells (A2780). CCK‑8 assay results showed that inhibition of USP14 by a specific inhibitor or siRNA decreased cisplatin cytotoxicity in A2780 cells. Additionally, USP14 inhibition increased the expression of Cx32 without changing its mRNA and ubiquitination levels, as showed by Real‑time qPCR and immunoprecipitation assay respectively. Cisplatin resistance induced by USP14 inhibition was counteracted by Cx32 knockdown. Moreover, USP14 inhibition contributed to Cx32 internalization, as determined by western blot analysis and a reduction in gap junction intercellular communication (GJIC), as showed by parachute dye‑coupling assay. Collectively, these data suggest that Cx32 internalization by USP14 inhibition modulates the cisplatin resistance in ovarian cancer cells, thus serving as a potential drug target to challenge chemotherapy failure. In addition, USP14 can also be used as a marker to monitor the development of cisplatin resistance in ovarian cancer treatment.