Ataxia Telangiectasia-mutated Gene Product Inhibits DNA Damage-induced Apoptosis via Ceramide Synthase

Abstract

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 125 I-labeled 5-iodo-2de-oxyuridine, 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.

Neutral Sphingomyelinase-3 Is a DNA Damage and Nongenotoxic Stress-Regulated Gene That Is Deregulated in Human Malignancies

“…The blot was sequentially probed with 32 P-labeled nSMase3 and p21 WAF1 probes; ethidium bromide staining of the 28S and 18S rRNA is also shown for RNA loading and integrity. prolonged ceramide production (11,51), suggesting that de novo ceramide synthesis rather than a sphingomyelinasemediated mechanism may be involved. Alternatively, it has been proposed that elevated ceramide levels following DNA damage is partly the result of the p53-mediated down-regulation of sphingosine-kinase-1, which is involved in the catabolism of ceramide to sphingosine-1-phosphate (52).…”

Implications of galactocerebrosidase and galactosylcerebroside metabolism in cancer cells

“…2). 40 Therefore, the suppression of GALC in HNSCC appears to be not only an indicator but also a factor that contributes to the process of carcinogenesis. This finding might further explain the increased expression of glycosphingolipids in other cancers and offer a target for antineoplastic treatment as well.…”

“…49 However, this finding remains controversial, and many authors still attribute the induction of the apoptosis to the applied ceramide molecule. 16,40,50 Scarlatti et al postulate a pathway due to inactivation of proteinkinase B and activation of becelin1 by ceramide leading to apoptosis. 50 …”

Role of the ceramide-signaling pathways in ionizing radiation-induced apoptosis

“…Moreover, loss of ceramide generation from neutral SMase (NSMase) confers resistance to IR-induced apoptosis (Chmura et al, 1997). In addition, DNA-damaging agents exposure might produce ceramide by de novo synthesis via ceramide synthase (CS) activity (Bose et al, 1995;Dbaibo et al, 1998;Liao et al, 1999). Like for growth factor-deprived cells, TNFa, vincristine or anti-Fastreated cells (Hannun, 1996), a biphasic model of ceramide production was also proposed in response to IR (Haimovitz-Friedman, 1998;Lin et al, 2000).…”