p53-Independent ceramide formation in human glioma cells during gamma-radiation-induced apoptosis.

虽然p53抑癌基因产物在DNA损伤性化疗药物诱导的细胞凋亡中起着关键作用，但携带功能性p53的人胶质瘤细胞比携带突变型p53的人胶质瘤细胞对伽玛射线的抗性更强。携带野生型P53基因的U-87 MG细胞对伽玛射线耐受。通过表达16型人乳头瘤病毒E6癌蛋白而失去功能性P53的U87-W E6细胞对辐射诱导的细胞凋亡变得敏感。酸性鞘磷脂酶(A-sMase)形成神经酰胺，而不是中性神经鞘磷脂酶形成神经酰胺，与P53非依赖性的细胞凋亡有关，A-sMase的抑制剂((2-isopropyl-1-(4-[3-N-methyl-N-(3，4-dimethoxybphenethyl)氨基-苯磺酰基)吲哚嗪抑制辐射诱导的细胞死亡。相反，在具有内源性功能性p53的胶质瘤细胞中，辐射诱导的A-sMase激活被阻断。γ射线可诱导酸性神经酰胺酶的表达，且在具有功能性P53的细胞中表达更为明显。已知的抑制神经酰胺酶活性的N-油酰乙醇胺，意外地下调了U87-W E6细胞的酸性神经酰胺酶，并加速了辐射诱导的细胞凋亡。此外，N-油酰乙醇胺可以抑制辐射诱导的酸性神经酰胺酶的表达，从而促进神经酰胺的形成，从而使具有功能的P53的细胞对伽马射线敏感。小干扰RNA逆转录病毒表达缺失功能性P53的U87-MG细胞也观察到对伽马辐射的增敏作用。这些结果表明神经酰胺可能是伽玛射线对人胶质瘤细胞P53非依赖性凋亡的中介，提示依赖于P53的酸性神经酰胺酶的表达和阻断A-sMase的激活在内源性功能性P53细胞的伽玛射线辐射防护中起着关键作用。

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.