Background: A growing body of studies have demonstrated the aberrant expression of microRNAs (miRNAs) contributes to human tumor metastasis. MicroRNA-124-3p (miR-124-3p), which is down-regulated in various cancers, has been found to be involved in several signaling pathways relevant to tumor cell migration and invasion. However, the roles of miR-124-3p in human bladder cancer remain unclear. This study aims to investigate the functional significance of miR-124-3p and to understand how it targets the integrin receptor, and thus affects the progression of human bladder cancer.
Methods: Clinical specimens from 36 patients and three human bladder cancer cell lines were analyzed for miR-124-3p and integrin α3 (ITGA3) . To investigate the effects of miR-124-3p and ITGA3 on proliferation of bladder cancer cells, the MTT assay, colon-formation assay and flow cytometry were performed. In addition, wound healing assay and transwell assay were carried out to examine the migration and invasion of the bladder cancer cells transfected with miR-124-3p mimics or si-ITGA3. The luciferase reporter assay, quantitative real-time polymerase chain reaction (qRT-PCR) and western blot were applied to validate the miR-124-3p directly binding with ITGA3. Finally, western blot was used to examine the expression level of the proteins involved in FAK/PI3K/AKT and FAK/Src signal pathway as well as epithelial-mesenchymal transition (EMT) process.
Results: The down-regulation of miR-124-3p and up-regulation of ITGA3 were observed in clinical specimens and bladder cancer cell lines. Overexpression of miR-124-3p or silencing ITGA3 inhibited tumor cell migration and invasion. Luciferase assay confirmed miR-124-3p directly targets ITGA3, and western blot suggested that miR-124-3p plays a crucial role in the EMT and metastasis of human bladder cancer through FAK/PI3K/AKT and FAK/Src signaling mechanism. Also, by targeting ITGA3, miR-124-3p can modulate the expression of N- and E-cadherin, and thus inhibit the EMT.
Conclusions: By targeting ITGA3 and downstream FAK/PI3K/AKT and FAK/Src signaling pathways, miR-124-3p suppresses cell migration and invasion in bladder cancer. Our study reasonably speculates that miR-124-3p can be potentially developed as a therapeutic target and prognostic biomarker for bladder cancer.
Keywords: Bladder cancer; EMT; FAK/PI3K/AKT; ITGA3; miR-124-3p.