miR-129 regulates cell proliferation by downregulating Cdk6 expression

Abstract

Reduced expression of miR-129 has been reported in multiple tumor cell lines and in primary tumors including medulloblastoma, undifferentiated gastric cancers, lung adenocarcinoma, endometrial cancer and colorectal carcinoma. There is also recent evidence of an antiproliferative activity of miR-129 in tumor cell lines. Still, little is known about how miR-129 regulates cell proliferation. Here we found that lentiviral-mediated over-expression of miR-129 in mouse lung epithelial cells (E10 cells) results in significant G1 phase arrest that eventually leads to cell death. miR-129 induce G1 phase arrest in multiple human lung adenocarcinoma cell lines, suggesting miR-129 targeting of G1/S phase-specific regulators. Interestingly, we show that Cdk6, a kinase involved in G1-S transition, is a direct target of miR-129. We also found the down-regulation of three other cell cycle-related novel targets of miR-129, including Erk1, Erk2 and protein kinase C epsilon (Prkce). We further show that among these targets, only Cdk6 is functionally relevant. Restoring expression of Cdk6, but not Prkce partially rescues the cell growth arrest and cell death phenotype that results from miR-129 over-expression. Together, our data indicate that miR-129 plays an important role in regulating cell proliferation by downregulation of Cdk6.