Tumor Suppressor miR-22 Determines p53-Dependent Cellular Fate through Post-transcriptional Regulation of p21

Selective activation of p53 target genes in response to various cellular stresses is a critical step in determining the ability to induce cell-cycle arrest or apoptosis. Here we report the identification of the microRNA miR-22 as a p53 target gene that selectively determines the induction of p53-dependent apoptosis by repressing p21. Combinatorial analyses of the AGO2 immunocomplex and gene expression profiles identified p21 as a direct target of miR-22. Induction of p21 was inhibited by miR-22 after exposure to the genotoxic agent Adriamycin (doxorubicin; Bedford Laboratories), sensitizing cells to p53-dependent apoptosis. Interestingly, the activation of miR-22 depended on the intensity of the stresses that induced cells to undergo apoptosis in the presence of p21 suppression. Our findings define an intrinsic molecular switch that determines p53-dependent cellular fate through post-transcriptional regulation of p21.