Functional link between ataxia-telangiectasia and Nijmegen breakage syndrome gene products

Abstract

Ataxia-telangiectasia (A-T) and Nijmegen breakage syndrome (NBS) are recessive genetic disorders with susceptibility to cancer and similar cellular phenotypes. The protein product of the gene responsible for A-T, designated ATM, is a member of a family of kinases characterized by a carboxy-terminal phosphatidylinositol 3-kinase-like domain. The NBS1 protein is specifically mutated in patients with Nijmegen breakage syndrome and forms a complex with the DNA repair proteins Rad50 and Mrel1. Here we show that phosphorylation of NBS1, induced by ionizing radiation, requires catalytically active ATM. Complexes containing ATM and NBS1 exist in vivo in both untreated cells and cells treated with ionizing radiation. We have identified two residues of NBS1, Ser 278 and Ser 343 that are phosphorylated in vitro by ATM and whose modification in vivo is essential for the cellular response to DNA damage. This response includes S-phase checkpoint activation, formation of the NBS1/Mrel1/Rad50 nuclear foci and rescue of hypersensitivity to ionizing radiation. Together, these results demonstrate a biochemical link between cell-cycle checkpoints activated by DNA damage and DNA repair in two genetic diseases with overlapping phenotypes.

Cleavage of the BRCT tandem domains of nibrin by the 657del5 mutation affects the DNA damage response less than the Arg215Trp mutation

“…In particular, after IR treatment, ATM phosphorylates NBN at Ser278 and Ser343 (21)(22)(23)(24). These two Ser residues are crucial for the proper activation of the intra-S phase checkpoint in response to the DNA damage (46).…”

“…Although ATM responds to the presence of DSBs, ATR appears to be activated by single-stranded DNA, arising at stalled replication forks or generated during processing of bulky lesions (53,54). ATR phosphorylates many of the same damage response proteins as ATM, including NBN (21)(22)(23)(24), which localizes to stalled replication forks (55).…”

“…Notably, the BRCT domains are the major mediators of phosphorylation-dependent protein-protein interactions in cell cycle checkpoint and DNA repair mechanisms (14)(15)(16)(17)(18)(19)(20). The central region of NBN contains a consensus sequence encompassing the Ser343 residue that, together with the Ser278 residue located within the BRCT2 domain, is phosphorylated by ATM kinase in response to IR (21)(22)(23)(24). Lastly, the C-terminal region of NBN contains the MRE11-binding domain and the ATM-binding motif (12,25).…”

SV40 T antigen interacts with Nbs1 to disrupt DNA replication control

“…The expression of myc-tagged Nbs1 fragments and T was examined by Western blot analysis (anti-myc and anti-T) performed on transfected cell lysate (Lysate). (FHA) The forkhead-associated domain; (BRCT) the breast cancer C-terminal domain (Carney et al 1998;Varon et al 1998). by ATM after DNA damage, and this phosphorylation is important for certain subsequent cellular responses, such as S-phase checkpoint control and cellular radiation sensitivity (Gatei et al 2000;Lim et al 2000;Wu et al 2000;Zhao et al 2000). To test whether the presence of T impairs DNA damage-driven Nbs1 phosphorylation, we compared SDS-gel mobility of Nbs1 before and after ionizing radiation (IR) of IMR 90 primary fibroblasts and a derivative that synthesizes T [IMR90(T)].…”

“…Both the ATM gene product and Nbs1 are active in this process. Nbs1 is phosphorylated by ATM at several serine residues after S-phase ionizing radiation, and these ATM-mediated phosphorylation events are essential for activating the intra-S-phase checkpoint in response to DNA damage (Gatei et al 2000;Lim et al 2000;Wu et al 2000;Zhao et al 2000). Nbs1 forms a tight complex with two repair proteins, Mre11 and Rad50 (Carney et al 1998).…”