title: The Mre11-Rad50-Nbs1 complex mediates activation of TopBP1 by ATM.
abstract: The activation of ATR-ATRIP in response to double-stranded DNA breaks (DSBs) depends upon ATM in human cells and Xenopus egg extracts. One important aspect of this dependency involves regulation of TopBP1 by ATM. In Xenopus egg extracts, ATM associates with TopBP1 and thereupon phosphorylates it on S1131. This phosphorylation enhances the capacity of TopBP1 to activate the ATR-ATRIP complex. We show that TopBP1 also interacts with the Mre11-Rad50-Nbs1 (MRN) complex in egg extracts in a checkpoint-regulated manner. This interaction involves the Nbs1 subunit of the complex. ATM can no longer interact with TopBP1 in Nbs1-depleted egg extracts, which suggests that the MRN complex helps to bridge ATM and TopBP1 together. The association between TopBP1 and Nbs1 involves the first pair of BRCT repeats in TopBP1. In addition, the two tandem BRCT repeats of Nbs1 are required for this binding. Functional studies with mutated forms of TopBP1 and Nbs1 suggested that the BRCT-dependent association of these proteins is critical for a normal checkpoint response to DSBs. These findings suggest that the MRN complex is a crucial mediator in the process whereby ATM promotes the TopBP1-dependent activation of ATR-ATRIP in response to DSBs.
authors.affiliation: Division of Biology 147-75, California Institute of Technology, Pasadena, CA 91125, USA.
authors.forename: Hae Yong
authors.initials: HY
authors.lastname: Yoo
authors.forename: Akiko
authors.initials: A
authors.lastname: Kumagai
authors.forename: Anna
authors.initials: A
authors.lastname: Shevchenko
authors.forename: Andrej
authors.initials: A
authors.lastname: Shevchenko
authors.forename: William G
authors.initials: WG
authors.lastname: Dunphy
mesh_terms: D000818:Animals; D064007:Ataxia Telangiectasia Mutated Proteins; D002352:Carrier Proteins / Q000737:chemistry / Q000378:metabolism*; D002453:Cell Cycle / Q000528:radiation effects; D018797:Cell Cycle Proteins / Q000378:metabolism*; D002457:Cell Extracts; D002460:Cell Line; D000071877:Checkpoint Kinase 1; D053903:DNA Breaks, Double-Stranded / Q000528:radiation effects; D045643:DNA Repair Enzymes; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004789:Enzyme Activation / Q000528:radiation effects; D006801:Humans; D000076228:MRE11 Homologue Protein; D008954:Models, Biological; D050505:Mutant Proteins / Q000378:metabolism; D010063:Ovum / Q000166:cytology / Q000201:enzymology / Q000528:radiation effects; D011485:Protein Binding / Q000528:radiation effects; D011494:Protein Kinases / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D011839:Radiation, Ionizing; D020449:Repetitive Sequences, Amino Acid; D025521:Tumor Suppressor Proteins / Q000378:metabolism*; D014981:Xenopus / Q000378:metabolism*; D029867:Xenopus Proteins / Q000378:metabolism*
chemical_list: D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D002457:Cell Extracts; D004268:DNA-Binding Proteins; C510917:Mre11 protein, Xenopus; D050505:Mutant Proteins; C511600:NBN protein, Xenopus; C542167:Rad50 protein, Xenopus; C509993:TopBP1 protein, Xenopus; D025521:Tumor Suppressor Proteins; D029867:Xenopus Proteins; D011494:Protein Kinases; C576324:ATM protein, human; D064007:Ataxia Telangiectasia Mutated Proteins; D000071877:Checkpoint Kinase 1; D017346:Protein Serine-Threonine Kinases; D000076228:MRE11 Homologue Protein; D045643:DNA Repair Enzymes