Overexpression of protein kinase Czeta 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) ζ overexpression on the SM-CER pathway in U937 human leukemia cell line. We show that PKCζ overexpression resulted in delayed apoptosis and significant resistance to both 1-β-d-arabinofuranosylcytosine (ara-C) and daunorubicin (DNR), but there was no significant protection against cell-permeant C 6 -CER. Moreover, PKCζ overexpression abrogated drug-induced neutral sphingomyelinase stimulation and CER generation by inhibiting ROS production. We further investigated p53/p56 Lyn activation in PKCζ-overexpressing U937 cells treated with ara-C or DNR. We demonstrate that PKCζ inhibited p53/p56 Lyn phosphorylation and stimulation in drug- or H 2 O 2 -treated cells, suggesting that p53/p56 Lyn redox regulation is altered in PKCζ-overexpressing cells. Finally, we show that PKCζ-overexpressing U937 cells displayed accelerated H 2 O 2 detoxification. Altogether, our study provides evidence for the role of PKCζ in the negative regulation of drug-induced SM-CER pathway.