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

ABSTRACT 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 C 6 -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 H 2 O 2 -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 H 2 O 2 detoxification. Altogether, our study provides evidence for the role of PKC in the negative regulation of drug-induced SM-CER pathway

Rôle des seconds messagers lipidiques impliqués dans la réponse des cellules leucémiques aux médicaments anticancéreux

La simple observation clinique suggère que, si les agents anti-leucémiques sont aptes à éradiquer le compartiment des blastes en division terminale comme le montre le taux élevé de rémission complète (70 %) dans le cas de leucémie aiguë myéloïde ; ces agents sont cependant relativement inaptes à éliminer les cellules des compartiments précoces de la myélopoïèse leucémique comme le suggère le taux élevé de rechutes. Cette interprétation soulève le problème de la chimiorésistance naturelle des cellules composant les compartiments précoces de myélopoïèse leucémique. Au cours des dernières années, une série de travaux ont démontré qu’un même niveau de lésions était susceptible d’induire des effets cellulaires aussi variés qu’une mort rapide par apoptose, une mort reproductive différée ou un effet cytostatique transitoire. L’orientation de la réponse aux lésions est conditionnée par un réseau complexe et hautement régulé de signaux intracellulaire incluant des signaux de mort médiés par le céramide, et des signaux de survie médiés (au moins en partie) par le diacylglycérol et les phosphoinositide-3 phosphates. De la balance entre ces deux types de signalisation dépend la réponse cellulaire et la cytotoxicité. Ce constat ouvre de multiples voies de manipulation pharmacologique visant soit à favoriser la mort, soit à conférer une protection significative vis-à-vis des agents anticancéreux

Implication of Mitochondrial Hydrogen Peroxide Generation in Ceramide-induced Apoptosis

International audienc

Daunorubicin-and Mitoxantrone-Triggered Phosphatidylcholine Hydrolysis: Implication in Drug-Induced Ceramide Generation and Apoptosis

ABSTRACT Several studies have suggested that diacylglycerol can affect the induction of apoptosis induced by toxicants and ceramide. The present study demonstrates that clinically relevant concentrations of the chemotherapeutic drugs daunorubicin and mitoxantrone (0.2-1 M) transiently stimulated concurrently with sphingomyelin-derived ceramide generation and diacylglycerol and phosphorylcholine production within 4 to 10 min via phospholipase C hydrolysis of phosphatidylcholine. Pretreatment of cells with the xanthogenate compound D609, a potent inhibitor of phosphatidylcholine-phospholipase C, led to significant inhibition of drug triggered diacylglycerol and phosphorylcholine production and to a sustained increase in ceramide levels for a period up to 2 h. Moreover, D609 pretreatment induced both cell death and ceramide generation at daunorubicin and mitoxantrone concentrations previously shown to be ineffective (i.e., 0.1 M). These results underline the importance of diacylglycerol in the regulation of programmed cell death and strongly argue for a balance between apoptotic (ceramide) and survival (diacylglycerol) signal transducers

Daunorubicin- and Mitoxantrone-Triggered Phosphatidylcholine Hydrolysis: Implication in Drug-Induced Ceramide Generation and Apoptosis

International audienc

Oxidative stress-induced activation of Lyn recruits sphingomyelinase and is requisite for its stimulation by Ara-C

International audienc