Contact inhibition controls miR-223 stabilization via p27kip1 expression

The control of cell cycle progression mostly relays on the concerted activity of cyclins, CDKs and CDKs inhibitor. Recent data demonstrated that microRNAs, by regulating the expression of these proteins, contribute to the control of cell cycle progression. Here we provide evidences that the CDK inhibitor p27Kip1 directly regulates microRNAs stability thereby influencing cell cycle exit following contact inhibition. By the use of wild type and p27 knock-out cells we uncovered several microRNAs whose expression is linked to the cell cycle exit in a p27-dependent manner. By studying one of this microRNA, miR-223, we provide evidence that p27 is an RNA binding protein able to bind miR-223 to stabilize its expression. High miR-223 levels participate in the control of cell proliferation. Overall, we identify a previously completely unknown and conserved function of p27Kip1 that contributes to the proper regulation of cell cycle progression impinging on microRNA expression.