title: Role of ceramide in mediating apoptosis of irradiated LNCaP prostate cancer cells.
abstract: The sphingomyelin metabolites ceramide and sphingosine are mediators of cell death induced by gamma-irradiation. We studied the production of ceramide and the effects of exogenous ceramide on apoptosis in LNCaP prostate cancer cells that are highly resistant to gamma-irradiation-induced cell death. LNCaP cells can be sensitized to gamma-irradiation by tumor necrosis factor alpha (TNF-alpha) and, to a lesser degree, by the agonistic FAS antibody CH-11. TNF-alpha activated intrinsic and extrinsic apoptosis pathways and increased ceramide and sphingosine levels in irradiated LNCaP cells. CH-11 activated only the extrinsic apoptosis pathways and had a negligible effect on ceramide and sphingosine levels in irradiated LNCaP cells. Exogenous ceramide and bacterial sphingomyelinase sensitized LNCaP cells to radiation-induced apoptosis and had a synergistic effect on cell death after irradiation with TNF-alpha, but not with CH-11. Cell death effects after exposure to ceramide and irradiation were blocked by the serine protease inhibitor TLCK (Na-p-tosyl-L-lysine-chloromethylketone), but not by the caspase inhibitor z-VAD (2-val-Ala-Asp(oMe)-CH(2)F). During LNCaP cell apoptosis induced by exogenous ceramide, we observed activation of caspase-9, but not caspases-8, -3, or -7. The effect of ceramide occurred largely via the intrinsic mitochondrial apoptosis pathway and enhanced TNF-alpha, but not CH-11 effects on irradiated cells. The data show that ceramide enhanced activation of the intrinsic apoptotic pathway and enhanced cell death induced by TNF-alpha with or without gamma-irradiation. TNF-alpha and gamma-irradiation elevated levels of endogenous ceramide and activated the intrinsic cell death pathway.
authors.affiliation: Department of Oncology, Georgetown University, Washington, DC 20007-2197, USA.
authors.forename: K
authors.initials: K
authors.lastname: Kimura
authors.forename: M
authors.initials: M
authors.lastname: Markowski
authors.forename: L C
authors.initials: LC
authors.lastname: Edsall
authors.forename: S
authors.initials: S
authors.lastname: Spiegel
authors.forename: E P
authors.initials: EP
authors.lastname: Gelmann
mesh_terms: D000230:Adenocarcinoma / Q000473:pathology; D000970:Antineoplastic Agents / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects*; D020169:Caspases / Q000502:physiology; D045744:Cell Line, Tumor; D002518:Ceramides / Q000378:metabolism* / Q000494:pharmacology; D004357:Drug Synergism; D004789:Enzyme Activation; D006801:Humans; D008297:Male; D011471:Prostatic Neoplasms / Q000473:pathology*; D015842:Serine Proteinase Inhibitors / Q000494:pharmacology; D013108:Sphingomyelin Phosphodiesterase / Q000494:pharmacology; D013110:Sphingosine / Q000378:metabolism; D014107:Tosyllysine Chloromethyl Ketone / Q000494:pharmacology; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology
chemical_list: D000970:Antineoplastic Agents; D002518:Ceramides; D015842:Serine Proteinase Inhibitors; D014409:Tumor Necrosis Factor-alpha; D014107:Tosyllysine Chloromethyl Ketone; D013108:Sphingomyelin Phosphodiesterase; D020169:Caspases; D013110:Sphingosine