title: p38alpha, but not p38beta, inhibits the phosphorylation and presence of c-FLIPS in DISC to potentiate Fas-mediated caspase-8 activation and type I apoptotic signaling.
abstract: Pharmacological inhibitors of JNK (SP600125) and p38 (PD169316) sensitize tumor cells to Fas-mediated apoptosis. PD169316 is less potent than SP600125 and diminishes its effect when present together. Because the p38 isoforms that promote (p38alpha) or inhibit (p38beta) apoptosis are both suppressed by PD169316, we investigated their regulatory involvement in Fas-signaling. We report here, that p38alpha, but not p38beta, exerts its proapoptotic effect by inhibiting the phosphorylation and presence of c-FLIPS, but not c-FLIPL, in the DISC to promote caspase-8 activation and type I signaling in Fas-activated Jurkat cells. Its effect was enhanced by enforced expression of Flag-tagged p38alpha and was attenuated by its inactive mutant (p38alpha-AGF) or by translational silencing. By contrast, type II signaling was facilitated by p38alpha-dependent mitochondrial presence of tBid and inhibition of Bcl-2 (Ser70) phosphorylation as well as by p38alpha/beta-dependent mitochondrial localization of Bax and inhibition of phosphorylation of Bad (Ser112/Ser155). Potentiation of Fas-mediated apoptosis by the inhibition of JNK1/2 correlated with the loss of Bad (Ser136) phosphorylation and was dependent on the stimulatory effect of p38alpha on DISC and the downstream effects of both p38alpha and p38beta. These data underscore the need to reassess the findings obtained with pan-p38 inhibitors and suggest that activation of p38alpha coupled with targeted inhibition of p38beta and JNK1/2 should optimally sensitize tumor cells to Fas-mediated apoptosis.
authors.affiliation: Fraser Laboratories, Department of Medicine, McGill University Health Centre and Royal Victoria Hospital, Montreal, Quebec, H3A 1A1, Canada.
authors.forename: Leon
authors.initials: L
authors.lastname: Tourian
authors.forename: Hong
authors.initials: H
authors.lastname: Zhao
authors.forename: Coimbatore B
authors.initials: CB
authors.lastname: Srikant
mesh_terms: D000873:Anthracenes / Q000494:pharmacology; D000911:Antibodies, Monoclonal / Q000378:metabolism; D017209:Apoptosis / Q000187:drug effects*; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; D002352:Carrier Proteins / Q000378:metabolism; D053181:Caspase 8; D020169:Caspases / Q000032:analysis / Q000378:metabolism*; D053418:Death Domain Receptor Signaling Adaptor Proteins; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D007093:Imidazoles / Q000494:pharmacology; D015151:Immunoblotting; D047908:Intracellular Signaling Peptides and Proteins / Q000037:antagonists & inhibitors*; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism; D019169:Jurkat Cells; D008564:Membrane Potentials / Q000187:drug effects; D008928:Mitochondria / Q000378:metabolism; D010766:Phosphorylation; D011233:Precipitin Tests; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D016755:Proto-Oncogene Proteins c-jun / Q000037:antagonists & inhibitors; D018124:Receptors, Tumor Necrosis Factor / Q000737:chemistry; D051028:bcl-2-Associated X Protein; D051025:bcl-Associated Death Protein; D019014:fas Receptor / Q000235:genetics / Q000378:metabolism*; D048051:p38 Mitogen-Activated Protein Kinases / Q000235:genetics / Q000378:metabolism*
chemical_list: D000873:Anthracenes; D000911:Antibodies, Monoclonal; C494819:BAD protein, human; C494826:BAX protein, human; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; C506386:CFLAR protein, human; D002352:Carrier Proteins; D053418:Death Domain Receptor Signaling Adaptor Proteins; D004791:Enzyme Inhibitors; D007093:Imidazoles; D047908:Intracellular Signaling Peptides and Proteins; D007527:Isoenzymes; D019253:Proto-Oncogene Proteins c-bcl-2; D016755:Proto-Oncogene Proteins c-jun; D018124:Receptors, Tumor Necrosis Factor; D051028:bcl-2-Associated X Protein; D051025:bcl-Associated Death Protein; D019014:fas Receptor; C432165:pyrazolanthrone; D048051:p38 Mitogen-Activated Protein Kinases; C505530:CASP8 protein, human; D053181:Caspase 8; D020169:Caspases; C408604:2-(4-nitrophenyl)-4-(4-fluorophenyl)-5-(4-pyridinyl)-1H-imidazole