title: p53-Independent ceramide formation in human glioma cells during gamma-radiation-induced apoptosis.
abstract: Although the p53 tumor-suppressor gene product plays a critical role in apoptotic cell death induced by DNA-damaging chemotherapeutic agents, human glioma cells with functional p53 were more resistant to gamma-radiation than those with mutant p53. U-87 MG cells with wild-type p53 were resistant to gamma-radiation. U87-W E6 cells that lost functional p53, by the expression of type 16 human papillomavirus E6 oncoprotein, became susceptible to radiation-induced apoptosis. The formation of ceramide by acid sphingomyelinase (A-SMase), but not by neutral sphingomyelinase, was associated with p53-independent apoptosis. SR33557 (2-isopropyl-1-(4-[3-N-methyl-N-(3,4-dimethoxybphenethyl)amino]propyloxy)benzene-sulfonyl) indolizine, an inhibitor of A-SMase, suppressed radiation-induced apoptotic cell death. In contrast, radiation-induced A-SMase activation was blocked in glioma cells with endogenous functional p53. The expression of acid ceramidase was induced by gamma-radiation, and was more evident in cells with functional p53. N-oleoylethanolamine, which is known to inhibit ceramidase activity, unexpectedly downregulated acid ceramidase and accelerated radiation-induced apoptosis in U87-W E6 cells. Moreover, cells with functional p53 could be sensitized to gamma-radiation by N-oleoylethanolamine, which suppressed radiation-induced acid ceramidase expression and then enhanced ceramide formation. Sensitization to gamma-radiation was also observed in U87-MG cells depleted of functional p53 by retroviral expression of small interfering RNA. These results indicate that ceramide may function as a mediator of p53-independent apoptosis in human glioma cells in response to gamma-radiation, and suggest that p53-dependent expression of acid ceramidase and blockage of A-SMase activation play pivotal roles in protection from gamma-radiation of cells with endogenous functional p53.
authors.affiliation: Department of Neurosurgery, Gifu University School of Medicine, Tsukasamachi-40, Gifu 500-8705, Japan. f2105013@guedu.cc.gifu-u.ac.jp
authors.forename: S
authors.initials: S
authors.lastname: Hara
authors.forename: S
authors.initials: S
authors.lastname: Nakashima
authors.forename: T
authors.initials: T
authors.lastname: Kiyono
authors.forename: M
authors.initials: M
authors.lastname: Sawada
authors.forename: S
authors.initials: S
authors.lastname: Yoshimura
authors.forename: T
authors.initials: T
authors.lastname: Iwama
authors.forename: Y
authors.initials: Y
authors.lastname: Banno
authors.forename: J
authors.initials: J
authors.lastname: Shinoda
authors.forename: N
authors.initials: N
authors.lastname: Sakai
mesh_terms: D017209:Apoptosis / Q000502:physiology* / Q000528:radiation effects; D002518:Ceramides / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000378:metabolism; D063388:Endocannabinoids; D004789:Enzyme Activation / Q000187:drug effects / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004983:Ethanolamines / Q000494:pharmacology; D002517:Galactosylgalactosylglucosylceramidase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D005720:Gamma Rays; D005909:Glioblastoma / Q000378:metabolism; D006801:Humans; D009829:Oleic Acids; D009856:Oncogene Proteins, Viral / Q000378:metabolism; D034741:RNA, Small Interfering / Q000378:metabolism; D013108:Sphingomyelin Phosphodiesterase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D014407:Tumor Cells, Cultured; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism*
chemical_list: D002518:Ceramides; D004268:DNA-Binding Proteins; C052603:E6 protein, Human papillomavirus type 18; D063388:Endocannabinoids; D004791:Enzyme Inhibitors; D004983:Ethanolamines; D009829:Oleic Acids; D009856:Oncogene Proteins, Viral; D034741:RNA, Small Interfering; D016159:Tumor Suppressor Protein p53; C033595:N-oleoylethanolamine; D013108:Sphingomyelin Phosphodiesterase; D002517:Galactosylgalactosylglucosylceramidase