miR-186 downregulates protein phosphatase PPM1B in bladder cancer and mediates G1-S phase transition

Nuclear factor-κB (NF-κB) is a core regulator in multiple tumorigenic pathways. Its activation is mediated by IκB kinase β (IKKβ). Protein phosphatase PPM1B is reported to dephosphorylate IKKβ, thereby terminating IKKβ-mediated NF-κB activation. However, the role of PPM1B in bladder cancer is unclear. The aim of this study was to determine the expression patterns and molecular mechanisms of PPM1B in bladder cancer. Comparative analyses were conducted in six bladder cancer cell lines, a normal urinary epithelial cell line, and adjacent non-tumorous bladder epithelia. Searches were conducted through publicly available algorithms and The Cancer Genome Atlas. HT-1376 and RT4 cells were transduced to stably overexpress PPM1B and its predicted regulator miR-186. Subsequent in vitro studies included 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT), colony formation, anchorage-independent growth ability, luciferase reporter assays, and flow cytometric cell cycle analyses. A xenograft model was established in nude mice to evaluate the effect of PPM1B in bladder tumors in vivo. The results revealed that PPM1B was frequently downregulated in bladder cancer cells at both protein and messenger RNA (mRNA) levels, whereas miR-186 was upregulated. Further analyses showed that miR-186 promoted G1-S transition by targeting PPM1B at its 3'-untranslated region (3'UTR). Conversely, ectopic expression of PPM1B significantly suppressed proliferation and tumorigenicity in bladder cancer cells in vitro and in vivo, thereby neutralizing the oncogenic effect of miR-186. This study has identified PPM1B and miR-186 as potential diagnostic markers in bladder cancer. Promotion of PPM1B and suppression of miR-186 may offer effective therapeutic strategies in the treatment of bladder cancer.