The p57(Kip2) cyclin-dependent kinase inhibitor (CDKi) has been implicated in embryogenesis, stem-cell senescence and pathologies, but little is known of its role in cell cycle control. Here, we show that p57(Kip2) is targeted by the p38 stress-activated protein kinase (SAPK). Phosphorylation of p57(Kip2) at T143 by p38 enhances its association with and inhibition of Cdk2, which results in cell-cycle delay upon stress. Genetic inactivation of the SAPK or the CDKi abolishes cell-cycle delay upon osmostress and results in decreased cell viability. Oxidative stress and ionomycin also induce p38-mediated phosphorylation of p57 and cells lacking p38 or p57 display reduced viability to these stresses. Therefore, cell survival to various stresses depends on p57 phosphorylation by p38 that inhibits CDK activity. Together, these findings provide a novel molecular mechanism by which cells can delay cell cycle progression to maximize cell survival upon stress.

This work was supported by the MICINN grant BFU2007-66503 and BFU2010-15839 to M Joaquin and BIO2009-07762, Consolider Ingenio 2010 programme (grant CSD2007-0015) and through contract No. ERAS-CT-2003-980409 of the European Commission, DG Research, FP6 as part of an EURYIscheme award and the Fundación Marcelino Botín to F Posas. F Posas and E de Nadal are recipient of an ICREA Acadèmia (Generalitat de Catalunya)