The CDK inhibitor Purvalanol A Induces Neutrophil Apoptosis and Increases the Turnover Rate of Mcl-1: Potential role of p38-MAPK in Regulation of Mcl-1 Turnover

Abstract

Human neutrophils are terminally-differentiated cells that do not replicate and yet express a number of enzymes, notably cell cycle-dependent kinases (CDKs) that are normally associated with control of DNA synthesis and cell cycle progression. In neutrophils, CDKs appear to function mostly to regulate apoptosis, although the mechanisms by which they regulate this process are largely unknown. Here we show that the CDK2 inhibitor, Purvalanol A induces a rapid decrease in Mcl-1 levels in human neutrophils and peripheral blood mononuclear cells (PBMCs), but only induces apoptosis in neutrophils which are dependent on expression on this protein for survival. This rapid decrease in cellular Mcl-1 protein levels was due to a Purvalanol A-induced decrease in stability, with the half-life of the protein decreasing from approximately 2h in control cells to just over 1h after addition of the CDK2 inhibitor: it also blocked the GM-CSF dependent stabilisation of Mcl-1. Purvanalol A blocked GM-CSF stimulated activation of Erk and STAT3, and stimulated an additive activation of Akt with GM-CSF. Purvalanol A alone stimulated a rapid and sustained activation of p38-MAPK and the pan p38-MAPK inhibitor, BIRB796 partly blocked the Purvalanol A-induced apoptosis and Mcl-1 loss. These novel effects Purvalanol A may result, at least in part, from blocking GM-CSF mediated Erk activation. In addition, we propose that Purvalanol A-induced activation of p38-MAPK is, at least in part, responsible for its rapid effects on Mcl-1 turnover and acceleration of neutrophil apoptosis. This article is protected by copyright. All rights reserved.