Liao W C, Haimovitz-Friedman A, Persaud R S, McLoughlin M, Ehleiter D, Zhang N, Gatei M, Lavin M, Kolesnick R, Fuks Z
Department of Radiation Oncology, Memorial Sloan-Kettering Cancer Center, New York, New York 10021, USA.
J Biol Chem. 1999 Jun 18;274(25):17908-17. doi: 10.1074/jbc.274.25.17908.
DNA double-stranded breaks (dsb) activate surveillance systems that identify DNA damage and either initiate repair or signal cell death. Failure of cells to undergo appropriate death in response to DNA damage leads to misrepair, mutations, and neoplastic transformation. Pathways linking DNA dsb to reproductive or apoptotic death are virtually unknown. Here we report that metabolic incorporation of 125I-labeled 5-iodo-2'deoxyuridine, which produces DNA dsb, signaled de novo ceramide synthesis by post-translational activation of ceramide synthase (CS) and apoptosis. CS activation was obligatory, since fumonisin B1, a fungal pathogen that acts as a specific CS inhibitor, abrogated DNA damage-induced death. X-irradiation yielded similar results. Furthermore, inhibition of apoptosis using the peptide caspase inhibitor benzyloxycarbonyl-Val-Ala-Asp fluoromethylketone did not affect CS activation, indicating this event is not a consequence of induction of apoptosis. ATM, the gene mutated in ataxia telangiectasia, is a member of the phosphatidylinositol 3-kinase family that constitutes the DNA damage surveillance/repair system. Epstein-Barr virus-immortalized B cell lines from six ataxia telangiectasia patients with different mutations exhibited radiation-induced CS activation, ceramide generation, and apoptosis, whereas three lines from normal patients failed to manifest these responses. Stable transfection of wild type ATM cDNA reversed these events, whereas antisense inactivation of ataxia telangiectasia-mutated gene product in normal B cells conferred the ataxia telangiectasia phenotype. We propose that one of the functions of ataxia telangiectasia-mutated gene product is to constrain activation of CS, thereby regulating DNA damage-induced apoptosis.
DNA双链断裂（dsb）会激活监测系统，该系统可识别DNA损伤并启动修复或发出细胞死亡信号。细胞在DNA损伤时未能进行适当的死亡会导致错误修复、突变和肿瘤转化。将DNA双链断裂与生殖或凋亡性死亡联系起来的途径实际上还不清楚。在这里，我们报告称，产生DNA双链断裂的125I标记的5-碘-2'-脱氧尿苷的代谢掺入，通过神经酰胺合酶（CS）的翻译后激活发出了从头合成神经酰胺和凋亡的信号。CS激活是必不可少的，因为作为特定CS抑制剂的真菌病原体伏马菌素B1消除了DNA损伤诱导的死亡。X射线照射产生了类似的结果。此外，使用肽半胱天冬酶抑制剂苄氧羰基-Val-Ala-Asp氟甲基酮抑制凋亡并不影响CS激活，表明这一事件不是凋亡诱导的结果。共济失调毛细血管扩张症中发生突变的基因ATM是磷脂酰肌醇3激酶家族的成员，该家族构成了DNA损伤监测/修复系统。来自六名患有不同突变的共济失调毛细血管扩张症患者的爱泼斯坦-巴尔病毒永生化B细胞系表现出辐射诱导的CS激活、神经酰胺生成和凋亡，而来自正常患者的三个细胞系未能表现出这些反应。野生型ATM cDNA的稳定转染逆转了这些事件，而正常B细胞中共济失调毛细血管扩张症突变基因产物的反义失活赋予了共济失调毛细血管扩张症表型。我们提出，共济失调毛细血管扩张症突变基因产物的功能之一是限制CS的激活，从而调节DNA损伤诱导的凋亡。
