Regulation of RAP1B by miR-139 suppresses human colorectal carcinoma cell proliferation

Background: MicroRNAs (miRNAs) are strongly implicated in carcinogenesis, but their specific roles in the major cancers have yet to be fully elucidated. Methods: The expression levels of miR-139 in colorectal carcinoma and paired normal tissues were examined using real-time PCR assays. Potential functions of miR-139 were evaluated in colorectal carcinoma cell lines (SW480, SW620, LS174T, and HCT116) using miR-139 mimics, anti-miR-139, and siRNA RAP1B. Results: In this study, we determined that miR-139 is down-regulated in colorectal carcinoma (CRC) tissues. Lower miR-139 expression correlates with more advanced CRC and lower overall survival of patients with CRC. The ectopic expression of miR-139 in human CRC cells decreased cell growth and tumorigenicity, whereas the silencing of miR-139 promoted cell growth. Mechanistic studies revealed that miR-139 repressed the activity of a reporter gene fused to the 3'-untranslated region of RAP1B, whereas miR-139 silencing up-regulated the expression of the reporter gene. RNAi-mediated knockdown of RAP1B phenocopied the antiproliferative effect of miR-139, whereas the overexpression of RAP1B blocked miR-139-mediated antiproliferative effects in CRC cells. Conclusions: Taken together, these results demonstrated that miR-139 decreases proliferation by directly targeting RAP1B, defining miR-139 as a new putative tumour suppressor miRNA in CRC. (C) 2012 Elsevier Ltd. All rights reserved.