Suppression of cisplatin induced ATF3 expression and apoptosis by BK polyomavirus and its encoded microRNA in bladder cancer cells.

Recent evidence links BK polyomavirus (BKPyV) infection to an increased risk of bladder cancer. This study investigates the role of BKPyV and its microRNA, miR-B1, in cisplatin-induced apoptosis. PCR analysis detected BKPyV DNA in 3 of 22 urothelial carcinoma (UC) samples from a non-transplant population. Bladder cancer cells infected with BKPyV showed increased proliferation and miR-B1-3p and -5p expression. Bioinformatics analysis identified a miR-B1-5p target site in the 3'-UTR of activating transcription factor 3 (ATF3), confirmed by a luciferase assay. The inhibitory effect was further validated by reduced ATF3 mRNA levels following overexpression of miR-B1 vectors or 5p mimics. Cisplatin treatment upregulated ATF3 expression, as shown by qPCR and immunoblotting. Overexpression of ATF3 mitigated the cisplatin-induced reduction in cell viability and elevated apoptotic markers, including cleaved caspase-3 and cleaved poly(ADP-ribose) polymerase (PARP). BKPyV infection or large T antigen (TAg) overexpression suppressed cisplatin-induced ATF3 expression, reducing its cytotoxicity and apoptotic marker expression. However, overexpression of ATF3 in BKPyV-infected bladder cancer cells attenuated BKPyV's inhibitory effects, restoring cisplatin-induced cytotoxicity and apoptotic marker expression, suggesting BKPyV infection promotes resistance to cisplatin cytotoxicity. Transfection with miR-B1 vectors or miR-B1-5p mimics decreased cisplatin-induced annexin V-positive cells, caspase-3 activity, and apoptotic marker expression, indicating that miR-B1 suppresses cisplatin-induced apoptosis. In conclusion, this study demonstrates that BKPyV promotes bladder cancer cell growth and impairs cisplatin-induced apoptosis, with miR-B1 targeting ATF3 as a key mechanism. Targeting BKPyV replication or regulating miR-B1 expression could offer potential therapeutic strategies for managing BKPyV-positive and cisplatin-resistant urothelial carcinoma.