Patterns of microRNA (miRNA) expression are correlated to the degrees of tumor cell differentiation in human prostate cancer. MiRNAs can complementarily bind to either oncogenes or tumor suppressor genes, resulting in targeted gene silencing and thus changes of cellular tumorigenecity. Using miRNA microarray analysis, 8 down-regulated and 3 up-regulated known miRNAs in androgen-independent human prostate cancer cell lines, such as LNCaP C4-2B and PC3, compared to those androgen-dependent cell lines, such as LNCaP and PC3-AR9 were consistently detected. Fluorescent in-situ hybridization assays in human prostate cancer tissue arrays containing sixty patients at different stages also showed the same miRNA expression patterns in hormone-refractory prostate carcinomas (HRPC) compared to androgen-sensitive non-cancerous prostate epithelium. In-vitro tumorigenecity assays using one of the identified miRNAs, mir-146a, were performed to provide validation of its function in prostate cancer. Gain-of-function transfection of mir-146a markedly suppressed its targeted ROCK1 gene expression in androgen-independent PC3 cells, consequently resulting in reduced cancer cell proliferation, invasion and metastasis to human bone marrow endothelial cell monolayers. Since ROCK1 is the key kinase for activating hyaluronan-mediated HRPC transformation in vivo and in PC3 cells, mir-146a should function as a tumor-suppressor gene in modulating the ROCK1-associated tumorigenecity.
