Inhibition of miR-193a expression by Max and RXRα activates K-Ras and PLAU to mediate distinct aspects of cellular transformation.

MicroRNA profiling in isogenic models of cellular transformation involving either breast epithelial cells or fibroblasts reveals that expression of miR-193a is lower in transformed cells than in nontransformed cells. The transcription factors Max and RXRα bind directly to the miR-193a promoter and inhibit miR-193a expression during transformation. miR-193a inhibits cellular transformation by directly targeting the 3' untranslated regions of PLAU and K-Ras. Interestingly, miR-193a controls anchorage-independent growth in soft agar through K-Ras, whereas it affects invasive growth through PLAU. miR-193a overexpression inhibits the tumorigenicity of developmentally diverse but not all cancer cell types, and it inhibits tumor growth in colon- and breast-derived xenografts. Finally, expression of miR-193a is inversely correlated with PLAU and K-Ras in human colon adenocarcinomas. Thus, a pathway in which Max and RXRα inhibit miR-193a expression, thereby activating the PLAU and K-Ras oncogenes is important for distinct aspects of cellular transformation, as well as tumor growth and colon (and perhaps other types of) cancer.