miR-133b regulates the MET proto-oncogene and inhibits the growth of colorectal cancer cells in vitro and in vivo.

Colorectal cancer (CRC) is one of the leading causes of cancer-related mortality worldwide. MicroRNAs (miRs) are single-stranded, noncoding RNAs that are important in many biological processes. Although the oncogenic and tumor-suppressive functions of several miRs have been characterized, their precise biological roles remain largely unexplored. In the present study, the role of miR-133b was identified in the regulation of CRC cell proliferation and apoptosis. miR-133b expression was shown to be greatly downregulated in human CRC cells compared to normal colon cells. Downregulation of miR-133b expression was also significant in six of eight human CRC tissues compared with adjacent normal tissues. In the CRC cell lines SW-620 and HT-29, ectopic expression of miR-133b potently affected tumor cell proliferation and apoptosis in vitro and in vivo by direct targeting of the receptor tyrosine kinase MET. Transfection of SW-620 and HT-29 cells with miR-133b significantly suppressed a luciferase-reporter containing the MET-3'-untranslated region. Taken together, these results provide evidence that miR-133b regulated tumor cell proliferation and apoptosis through modulation of the MET signaling pathway.