Vol. 62, Issue 6, 1446-1455, December 2002

Overexpression of Protein Kinase C Confers Protection Against Antileukemic Drugs by Inhibiting the Redox-Dependent Sphingomyelinase Activation

Christine Bezombes, Aurélie de Thonel, Andriana Apostolou, Thierry Louat, Jean-Pierre Jaffrézou, Guy Laurent, and Anne Quillet-Mary

Institut National de la Santé et de la Recherche Médicale U563, Institut Claudius Regaud, Toulouse, France (C.B., A.d.T., A.A., T.L., J.-P.J, G.L., A.Q.-M.); and Service d'Hématologie, Centre Hospitalier Universitaire Purpan, Toulouse, France (G.L.)

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)  overexpression on the SM-CER pathway in U937 human leukemia cell line. We show that PKC overexpression resulted in delayed apoptosis and significant resistance to both 1--D-arabinofuranosylcytosine (ara-C) and daunorubicin (DNR), but there was no significant protection against cell-permeant C₆-CER. Moreover, PKC overexpression abrogated drug-induced neutral sphingomyelinase stimulation and CER generation by inhibiting ROS production. We further investigated p53/p56 Lyn activation in PKC-overexpressing U937 cells treated with ara-C or DNR. We demonstrate that PKC inhibited p53/p56 Lyn phosphorylation and stimulation in drug- or H₂O₂-treated cells, suggesting that p53/p56 Lyn redox regulation is altered in PKC-overexpressing cells. Finally, we show that PKC-overexpressing U937 cells displayed accelerated H₂O₂ detoxification. Altogether, our study provides evidence for the role of PKC in the negative regulation of drug-induced SM-CER pathway.