miR-185 targets RhoA and Cdc42 expression and inhibits the proliferation potential of human colorectal cells.

Increasing evidence in the past few years has shown that miRNAs could serve functionally as "oncogenes" or "tumor suppressor genes" and regulate multiple cellular processes relevant to carcinogenesis and cancer progression. Both RhoA and Cdc42, two members of the Rho GTPase family, are found to be upregulated in several types of human tumors including colorectal cancer, and have been implicated in cancer initiation and progression. In the present studies, we found that miR-185 expression greatly inhibited the proliferation potential of Hela cells. An examination of the predicted targets of miR-185 revealed RhoA and Cdc42 among the putative targets that are crucial for cell proliferation. A genomic sequence analysis indicated that nt 1844-1852 of the RhoA 3'UTR and nt 1382-1396 of the cdc42 3'UTR encode for miR-185 target matching sequences and they are highly conserved across different species. Using a luciferase-reporter assay, we show that miR-185 expression significantly suppressed the RhoA and Cdc42 3'UTR activities, and the inhibitory effect was lost when the putative target sites for miR-185 were mutated. Consistent with these results, ectopic expression of miR-185 reduced protein levels of RhoA and Cdc42 in cells, indicating miR-185 functionally regulates RhoA and Cdc42 abundance. Similar to the effects of knocking down RhoA and/or Cdc42 expression, miR-185 effectively inhibited proliferation, induced G1 cell cycle arrest and apoptosis, and blocked invasion of colorectal cancer cells. Thus, miR-185 is a negative regulator of RhoA and Cdc42 and their cellular activities, and could inhibit proliferation and invasion of colorectal cancer cells.