title: Caspase-dependent and -independent activation of acid sphingomyelinase signaling.
abstract: Recent evidence suggests clustering of plasma membrane rafts into ceramide-enriched platforms serves as a transmembrane signaling mechanism for a subset of cell surface receptors and environmental stresses (Grassme, H., Jekle, A., Riehle, A., Schwarz, H., Berger, J., Sandhoff, K., Kolesnick, R., and Gulbins, E. (2001) J. Biol. Chem. 276, 20589-20596; Cremesti, A., Paris, F., Grassme, H., Holler, N., Tschopp, J., Fuks, Z., Gulbins, E., and Kolesnick, R. (2001) J. Biol. Chem. 276, 23954-23961). Translocation of the secretory form of acid sphingomyelinase (ASMase) into microscopic rafts generates therein the ceramide that drives raft coalescence. This process serves to feed forward Fas activation, with approximately 2% of full caspase 8 activation sufficient for maximal ASMase translocation, leading to death-inducing signaling complex formation within ceramide-rich platforms, and apoptosis. Here we report that treatment of Jurkat T cells with UV-C also induces ASMase translocation into rafts within 1 min, catalyzing sphingomyelin hydrolysis to ceramide and raft clustering. In contrast to Fas, UV-induced ASMase translocation and activation were caspase-independent. Nonetheless, ceramide-rich platforms promoted UV-C-induced death signaling, because ASMase inhibition or raft disruption inhibited apoptosis, improving clonogenic cell survival. These studies thus define two distinct mechanisms for biologically relevant ASMase activation within rafts; a Fas-mediated mechanism dependent upon caspase 8 and FADD, and a UV-induced mechanism independent of caspase activation. Consistent with this notion, genetic depletion or pharmacologic inhibition of caspase 8 or FADD, which render Jurkat cells incapable of sphingolipid signaling and apoptosis upon Fas ligation, did not impair these events upon UV-C stimulation.
authors.affiliation: Laboratory of Signal Transduction and Department of Radiation Oncology, Memorial Sloan-Kettering Cancer Center, New York, New York 10021, USA.
authors.forename: Jimmy A
authors.initials: JA
authors.lastname: Rotolo
authors.forename: Jianjun
authors.initials: J
authors.lastname: Zhang
authors.forename: Manjula
authors.initials: M
authors.lastname: Donepudi
authors.forename: Hyunmi
authors.initials: H
authors.lastname: Lee
authors.forename: Zvi
authors.initials: Z
authors.lastname: Fuks
authors.forename: Richard
authors.initials: R
authors.lastname: Kolesnick
mesh_terms: D000590:Amino Acid Chloromethyl Ketones / Q000494:pharmacology; D017209:Apoptosis; D029681:Arabidopsis Proteins / Q000378:metabolism*; D015153:Blotting, Western; D053181:Caspase 8; D020169:Caspases / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D002469:Cell Separation; D002470:Cell Survival; D002518:Ceramides / Q000378:metabolism; D019852:Diacylglycerol Kinase / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004307:Dose-Response Relationship, Radiation; D004789:Enzyme Activation; D044943:Fatty Acid Desaturases / Q000378:metabolism*; D005434:Flow Cytometry; D006801:Humans; D019169:Jurkat Cells; D021962:Membrane Microdomains / Q000528:radiation effects; D011485:Protein Binding; D021381:Protein Transport; D015398:Signal Transduction; D013107:Sphingolipids / Q000378:metabolism; D013108:Sphingomyelin Phosphodiesterase / Q000378:metabolism*; D013997:Time Factors; D014466:Ultraviolet Rays
chemical_list: D000590:Amino Acid Chloromethyl Ketones; D029681:Arabidopsis Proteins; D002518:Ceramides; D013107:Sphingolipids; C096713:benzyloxycarbonylvalyl-alanyl-aspartyl fluoromethyl ketone; D044943:Fatty Acid Desaturases; C084083:Fad7 protein, Arabidopsis; D019852:Diacylglycerol Kinase; C112980:acid sphingomyelinase-1; D013108:Sphingomyelin Phosphodiesterase; C505530:CASP8 protein, human; D053181:Caspase 8; D020169:Caspases