Sensing of intermediates in V(D)J recombination by ATM

Abstract

Ataxia-telangiectasia mutated (ATM) is required for resistance to radiation-induced DNA breaks. Here we use chromatin immunoprecipitation to show that ATM also localizes to breaks associated with V(D)J recombination. ATM recruitment to the recombining locus correlates approximately with recruitment of the break-initiating factor RAG1 and precedes efficient break repair, consistent with localization of ATM to normal recombination intermediates. A product of ATM kinase activity, Ser 18-phosphorylated p53, was detected similarly at these breaks, arguing that ATM phosphorylates target proteins in situ. We suggest routine surveillance of intermediates in V(D)J recombination by ATM helps suppress potentially oncogenic translocations when repair fails. Ataxia-telangiectasia is characterized by cerebellar degeneration, immunodeficiency, and a high frequency of malignancy, usually lymphoid in origin (Morrell et al. 1986). The gene mutated in this disease (ataxia-telangiectasia mutated, or ATM) is required for resistance to DNA double-strand break (DSB) inducing agents such as ionizing radiation, and is an important trigger for the cellular response to DSBs (for review, see Rotman and Shiloh 1999). ATM may act as a primary sensor of DSBs, first binding directly to DSBs and consequently activating through phosphorylation several downstream effectors of the DNA damage response, including Nbs1, BRCA1, Chk2, and p53 (for review, see Durocher and Jackson 2001). For example, after treatment with ionizing radiation, phosphorylation of p53 at Ser 15 (Ser 18 in mice) in cells is largely ATM dependent (for review, see Giaccia and Kastan 1998) and is required for effective p53-dependent responses to this stimulus (Chao et al. 2000).In contrast to its important role in mediating resistance to exogenous DSB-inducing agents, genetic evidence for a role for ATM in repair of DSB intermediates in V(D)J recombination is less clear. V(D)J recombination is an essential step in the generation of a diverse repertoire of immunoglobulins and T-cell receptors (for review, see Gellert 1997). RAG1 and RAG2 proteins initiate V(D)J recombination by introducing DSBs precisely adjacent to recombination-targeting signals that flank segments of immunoglobulin and T-cell receptor coding sequence. Efficient resolution of broken species requires factors implicated in end-joining DSB repair, including Ku, XRCC4, ligase IV, and the ATM-related kinase DNA-PKcs, but not ATM. Cells from patients with AT support normal levels of V(D)J recombination using an extra-chromosomal substrate assay (Hsieh et al. 1993), and mature antigen receptor-bearing lymphocytes are readily observed in ATM-deficient mice (Barlow et al. 1996;Elson et al. 1996;Xu et al. 1996).Are V(D)J recombination intermediates recognized by ATM as DNA damage? The lack of requirement for ATM in V(D)J recombination might suggest that ATM is excluded from breaks associated with this pathway, possibly through masking of ends by RAG1 and RAG2, to avoid counter-productive apoptotic responses during this n...

ATM deficiency impairs thymocyte maturation because of defective resolution of T cell receptor α locus coding end breaks

“…Translocations involving the TCR␣/␦ locus were also observed at high frequency in nonlymphoma peripheral T cells of ATM mice (9). Consistent with a role of the ATM protein in V(D)J recombination, chromatin immunoprecipitation has also indicated that ATM localizes to the Ig locus in pre-B cell lines and to TCR␣ in mouse thymocytes (12). Most recently, elegant experiments have provided evidence that ATM can function in vitro in the resolution of DNA double-strand breaks generated during V(D)J recombination (13).…”

Programmed DNA breaks in lymphoid cells: repair mechanisms and consequences in human disease

“…ATM (for ataxia telangiectasia mutated) is a serine/threonine protein kinase that functions in the repair of DNA lesions. It acts in concert with the MRN complex (comprising the exonuclease MRE11, RAD50 and NBS1, which is formed stably only when all three proteins are present) 10, 11. Whereas DNA‐PKcs contributes to signalling DSBs at signal ends, the kinase activity of ATM, which belongs within the same family of kinases as DNA‐PKcs, can partially compensate for its function at signal ends 12, 13…”

Variable Diversity Joining Recombination: Nonhairpin Coding Ends in Thymocytes of SCID and Wild-Type Mice

“…Alternatively, a protein kinase related to DNA-PKcs may have limited ability to phosphorylate and recruit Artemis to the postcleavage complex in the absence of DNA-PKcs. Relevant to this possibility, the protein kinase ataxi-telangiectasia mutated has been shown to localize to broken DNA intermediates of V(D)J recombination (62). Another possible explanation is that RAG proteins and/or the Mre11, RAD50, and Nsb1 complex may be responsible for some hairpin opening, when DNA-PKcs activity is low or absent.…”