RNA‐binding motif protein 5 (RBM5) acts as a tumor suppressor in various human cancers and presents with several important characteristics, such as the potentiation of apoptosis, inhibition of the cell cycle, and alternative splicing of Fas and caspase‐2 precursor mRNA. However, its role in bladder urothelial carcinoma (BUC) remains unknown. In this study, we found that RBM5 expression was significantly down‐regulated in BUC tissues when compared with the adjacent nontumor tissues. The down‐regulation of RBM5 activates ²‐catenin, which binds to the T‐cell factor/lymphocyte enhancer factor element of the miR‐432‐5p promoter and elevates the expression of miR‐432‐5p in bladder cancer cells. The up‐regulated miR‐432‐5p directly targets 3′‐UTR and depresses RBM5 expression. Thus, RBM5–miR‐432‐5p–²‐catenin forms a feedback loop in regulating bladder cancer cell apoptosis. Our findings provide evidence that the regulatory feedback loop among RBM5, miR‐432‐5p, and Wnt–²‐catenin is responsible for the progress of bladder cancer cells.—Zhang, Y.‐P., Liu, K.‐L., Wang, Y.‐X., Yang, Z., Han, Z.‐W., Lu, B.‐S., Qi, J.‐C, Yin, Y.‐W., Teng, Z.‐H., Chang, X.‐L., Li, J.‐D., Xin, H., Li, W. Down‐regulated RBM5 inhibits bladder cancer cell apoptosis by initiating an miR‐432‐5p/²‐catenin feedback loop. FASEB J. 33, 10973–10985 (2019). http://www.fasebj.org

RNA–binding motif protein 24 (RBM24) acts as a multifunctional determinant of cell fate, proliferation, apoptosis, and differentiation during development by regulating premRNA splicing and mRNA stability. It is also implicated in carcinogenesis, but the functions of RBM24 in bladder cancer (BC) remain unclear. In the present study, we revealed that RBM24 was upregulated in BC tissues. Importantly, we found that a higher level of RBM24 was correlated with poor prognosis in BC patients. Overexpression of RBM24 promoted BC cell proliferation, while depletion of RBM24 inhibited BC cell proliferation in vivo and in vitro. Mechanistically, RBM24 positively regulated Runx1t1 expression in BC cells by binding to and enhancing Runx1t1 mRNA stability. Furthermore, Runx1t1 in turn promoted RBM24 expression by interacting with the transcription factor TCF4 and suppressing the transcription of miR-625-5p, which directly targets RBM24 and suppresses RBM24 expression. RBM24-regulated BC cell proliferation was moderated via the Runx1t1/TCF4/miR-625-5p feedback loop. These results indicate that the RBM24/Runx1t1/TCF4/miR-625-5p positive feedback loop participates in BC progression. Disruption of this pathway may be a potential therapeutic strategy for BC treatment.

The transcription factor E2F1 regulates the expression of the miR-20b-5p precursor and is involved in epithelial-to-mesenchymal transition (EMT). Transforming growth factor-β1 (TGF-β1) induces EMT in prostate cancer (PCa) by binding to TGF-beta receptor 2 (TGFBR2) to activate TGF-β signaling. However, the relationship between TGFBR2, E2F1, and miR-20b-5p in the modulation of EMT in PCa cells remains unknown. In this study, we found that the level of miR-20b-5p expression was significantly lower in PC3 and DU145 cells than that in prostate epithelial (RWPE-1) cells, and TGF-β1 treatment further down-regulated miR-20b-5p expression in these two cell lines. Functional studies showed that miR-20b-5p suppressed TGF-β1-induced migration and invasion of PC3 and DU145 cells by up-regulating E-cadherin and down-regulating vimentin, leading to TGF-β1-induced inhibition of EMT. Using gain and loss of function experiments, it was shown that E2F1 mediated TGF-β1 regulation of miR-20b-5p expression. Further, a luciferase activity assay showed that TGFBR2 was a direct target of miR-20b-5p in PCa cells. These results suggest that miR-20b-5p, TGFBR2, and E2F1 form a regulatory loop to modulate EMT induced by TGF-β1. A novel regulatory mechanism underlying the miR-20b-5p/TGFBR2/E2F1 axis is involved in TGF-β1-induced EMT of PCa cells, and miR-20b-5p may be a potential therapeutic target for PCa.

Prostate cancer (PCa) is a frequently occurring malignancy in males, and epithelial mesenchymal transition (EMT) plays a critical role in PCa metastasis. Thus, developing biomarkers inhibiting EMT may provide significance for treatment of PCa. Hence, the aim of the current study was to investigate the mechanism by which FBP1 gene silencing influences PCa cell EMT, invasion and metastasis by mediating the MAPK pathway. PCa cell lines exhibiting the highest FBP1 expression were selected and treated with plasmids of siRNA-FBP1 sequence 1 and 2, pcDNA3.1-Flag-FBP1 (over-expression plasmid of FBP1), U0126 (an inhibitor of the ERK signaling pathway) and PD98059 (an inhibitor of the MEK signaling pathway). Cell proliferation, migration and invasion were detected by MTT assay, wound healing assay and Transwell assay, respectively. The mRNA and protein expression of related factors of EMT and MAPK signaling were determined by RT-qPCR and western blot analysis, respectively. Xenograft tumor growth after inoculation of DU145 cells was regularly analyzed in the nude mice. The positive expression of EMT markers was determined by immunohistochemistry. DU-145 and PC-3 cells displaying the highest FBP1 expression were selected for further analysis. The PCa cells treated with siRNA-FBP1 exhibited increased proliferation, migration rate and invasion, in addition to facilitated xenograft tumor growth. Notably, siRNA-FBP1 was identified to accelerate PCa cell EMT by elevating the expression of Vimentin and N-cadherin while diminishing E-cadherin expression via activation of the MAPK signaling pathway. The aforementioned results were reversed in PCa cells treated by pcDNA3.1-Flag-FBP1. Evidence has been provided in this study that FBP1 gene silencing activates the MAPK pathway, which ultimately promotes cell EMT, invasion and metastasis in PCa.

Nicotinic acetylcholine receptor (nAChR) subunit α5 (α5-nAChR) is involved in tumor cell proliferation, inhibition of apoptosis, progression of metastasis, and induction of angiogenesis in certain solid tumors. However, the role of α5-nAChR in prostate cancer cell growth and metastasis is unclear. In the present study, the role of α5-nAChR in cell proliferation, migration, invasion and apoptosis was investigated by silencing the expression levels of α5-nAChR in the prostate cancer cell lines DU145 and PC3. A siRNA oligonucleotide targeting α5-nAChR was designed. The cell proliferation of DU145 and PC3 cell lines was analyzed by the Cell Counting Kit-8 (CCK-8) assay. Cell migratory and invasive activities were determined using wound healing and Transwell assays, respectively. Western blot analysis was used to quantify α5-nAChR, p-AKT and p-ERK1/2 levels in DU145 and PC3 cells. Knockdown of α5-nAChR was associated with decreased cell proliferation, migration, invasion and increased apoptosis. In addition, decreased phosphorylation levels of AKT and ERK1/2 were revealed following α5-nAChR knockdown in DU145 and PC3 cells compared with those observed in the scramble control samples. The expression levels of the apoptosis-related proteins were altered following silencing of α5-nAChR. In summary, the data indicated that α5-nAChR was involved in the proliferation and invasion of human prostate cancer cells.