There are conflicting reports about the involvement of single nucleotide polymorphisms (SNPs) of the ataxia telangiectasia mutated (ATM) gene with cancer, and the consequences of these SNPs for ATM function remain unclear. We therefore sought to identify SNPs of the ATM gene in pediatric Hodgkin disease (HD) and to analyze ATM function in cells from patients with these SNPs. We have identified SNPs of the ATM gene in 5 of 14 children (S1455R, n ؍ 1; H1380Y, n ؍ 1; N1650S, n ؍ 2; and I709I, n ؍ 1). One patient had nonsense-associated altered splicing of the ATM gene. Lymphoblastoid cell lines expressing the S1455R and N1650S exhibited defective ATM-mediated p53 phosphorylation and Chk2 activation; cells expressing the H1380Y exhibited defective c-Abl activation after X-irradiation. Expression of the N1650S in ATM-null fibroblasts conferred only partial hyperradiosensitivity. Furthermore, the introduction of N1650S ATM into U2OS cells, which express wild-type ATM, showed reduced p53-Ser15 phosphorylation, suggesting a dominant-negative effect of the N1650S over the wild-type ATM protein. We conclude that the rare polymorphic variants of the ATM gene that we identified in children with HD encode functionally abnormal proteins, and we discuss the possible genetic risk factors for childhood HD.
IntroductionIt is estimated that 0.5% to 1% of the general population are heterozygous carriers of mutations in the ataxia telangiectasia mutated (ATM) gene that is responsible for ataxia telangiectasia (AT), an autosomal recessive, multisystem disorder associated with progressive cerebellar ataxia, bulbar telangiectasia, immunologic deficiency, chromosomal instability, radiation sensitivity, and predisposition to lymphoreticular cancers. 1 The heterozygous carriers of the ATM gene, who are clinically normal, have an increased susceptibility to cancer, 2-4 particularly breast cancer, 4-6 and patients with AT are at high risk of malignancies such as leukemia and malignant lymphoma, including Hodgkin disease (HD). 2,7-10 Although most cases of HD occur sporadically, there may be inheritable factors involved in the development of HD, [11][12][13][14][15] and a subset of HD is associated with an increased incidence of secondary malignancies, especially in patients who were younger at the time of treatment. [16][17][18][19] Survivors of HD, like AT carriers, are at increased risk of radiation-induced breast cancer. 18,20,21 The 13-kb transcript of the ATM gene encodes a 350-kDa protein kinase whose carboxy-terminal region exhibits homology to the catalytic domain of phosphoinositide-3-kinases 22,23 and that plays key roles in intracellular signaling, cell-cycle control, and DNA repair and recombination. 24 In response to DNA damage, increased ATM protein kinase activity mediates the activation and stabilization of p53 and results in cell-cycle arrest. p53 is stabilized by ATM-mediated phosphorylation at Ser15 25,26 and Ser20. The ATM-dependent phosphorylation of p53 at Ser20 is mediated by the checkpoint kinases Cds1/Chk2...