Overexpression of protein kinase Cζ confers protection against antileukemic drugs by inhibiting the redox-dependent sphingomyelinase activation

Induction of apoptosis by chemotherapeutic drugs involves the sphingomyelin-ceramide (SM-CER) pathway. This signaling is critically dependent on reactive oxygen species (ROS) generation and p53/p56 Lyn activation. In this study, we have investigated the influence of protein kinase C (PKC) zeta overexpression on the SM-CER pathway in U937 human leukemia cell line. We show that PKCzeta overexpression resulted in delayed apoptosis and significant resistance to both 1-beta-D-arabinofuranosylcytosine (ara-C) and daunorubicin (DNR), but there was no significant protection against cell-permeant C-6-CER. Moreover, PKCzeta overexpression abrogated drug-induced neutral sphingomyelinase stimulation and CER generation by inhibiting ROS production. We further investigated p53/p56 Lyn activation in PKCzeta-overexpressing U937 cells treated with ara-C or DNR. We demonstrate that PKCzeta inhibited p53/p56 Lyn phosphorylation and stimulation in drug- or H2O2-treated cells, suggesting that p53/p56 Lyn redox regulation is altered in PKCzeta-overexpressing cells. Finally, we show that PKC-overexpressing U937 cells displayed accelerated H2O2 detoxification. Altogether, our study provides evidence for the role of PKCzeta in the negative regulation of drug-induced SM-CER pathway.