title: Rad50 depletion impacts upon ATR-dependent DNA damage responses.
abstract: The Mre11/Rad50/NBS1 (MRN) complex is mutated in inherited genomic instability syndromes featuring cancer predisposition, mental retardation and immunodeficiency. It functions both in DNA double-strand break repair and in controlling the ataxia telangiectasia mutated (ATM) kinase during the response to these lesions. Patients inheriting homozygosity for an NBS1 hypomorphic allele display reduced phosphorylation of signaling factors such as Chk1, but not of chromatin-associated factor H2AX, after stresses that activate the ATM-related kinase, ATR. Therefore, we tested whether MRN has a global controlling role over the ATR kinase through the study of MRN deficiencies generated via RNA interference. We show for the first time that MRN is required for ATR-dependent phosphorylation of structural maintenance of chromosomes 1 (Smc1), which acts within chromatin to ensure sister chromatid cohesion and to effect several DNA damage responses. We have uncovered novel phenotypes caused by MRN deficiency that support a functional link between this complex, ATR and Smc1, including hypersensitivity to UV exposure, a defective UV responsive intra-S phase checkpoint and a specific pattern of genomic instability. In addition, certain ATR-dependent responses do not require MRN. These studies demonstrate that there is indeed a controlling role for MRN over the ATR kinase and have established that the downstream events under this control are broad, including both chromatin-associated and diffuse signaling factors, but may not be universal. These studies contribute to our understanding of the central role that MRN plays in damage detection and signaling, which serve to maintain genomic stability and resist neoplastic transformation.
authors.affiliation: Department of Pathology, University of Michigan, Ann Arbor, MI 48109-0602, USA.
authors.forename: Hui
authors.initials: H
authors.lastname: Zhong
authors.forename: Alyson
authors.initials: A
authors.lastname: Bryson
authors.forename: Mark
authors.initials: M
authors.lastname: Eckersdorff
authors.forename: David O
authors.initials: DO
authors.lastname: Ferguson
mesh_terms: D017766:Acid Anhydride Hydrolases; D064007:Ataxia Telangiectasia Mutated Proteins; D018797:Cell Cycle Proteins / Q000378:metabolism*; D002868:Chromosomal Proteins, Non-Histone / Q000378:metabolism*; D020732:Cytogenetic Analysis; D004249:DNA Damage; D045643:DNA Repair Enzymes / Q000235:genetics / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D005434:Flow Cytometry; D005720:Gamma Rays; D042822:Genomic Instability / Q000235:genetics* / Q000528:radiation effects; D045325:HCT116 Cells; D006801:Humans; D015151:Immunoblotting; D046912:Multiprotein Complexes / Q000235:genetics / Q000378:metabolism*; D010641:Phenotype; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D034622:RNA Interference; D014466:Ultraviolet Rays; D000098550:Structural Maintenance of Chromosome Protein 1
chemical_list: D018797:Cell Cycle Proteins; D002868:Chromosomal Proteins, Non-Histone; D004268:DNA-Binding Proteins; D046912:Multiprotein Complexes; D000098550:Structural Maintenance of Chromosome Protein 1; C576597:ATR protein, human; D064007:Ataxia Telangiectasia Mutated Proteins; D017346:Protein Serine-Threonine Kinases; D017766:Acid Anhydride Hydrolases; C112158:RAD50 protein, human; D045643:DNA Repair Enzymes