NFBD1/MDC1, 53BP1 and BRCA1 have both redundant and unique roles in the ATM pathway.
NFBD1/MDC1, 53BP1 and BRCA1 are DNA damage checkpoint proteins with twin BRCT domains. In order to determine if they have redundant roles in responses to ionizing radiation, we used siRNA and shRNA to deplete NFBD1, 53BP1 and BRCA1 in single, double and triple combinations. These analyses were performed in early passage human foreskin fibroblasts so that checkpoint responses could be assessed in a normal genetic background. We report that NFBD1, 53BP1 and BRCA1 have both unique and redundant functions in radiation-induced phosphorylation and localization events in the ATM-Chk2 pathway. 53BP1, but not NFBD1 and BRCA1, mediates ionizing radiation-induced ATM S1981 autophosphorylation. In contrast, all three mediators collaborate to promote IR-induced Chk2 T68 phosphorylation. NFBD1 and 53BP1, but not BRCA1, work together to mediate pATMS1981, pChk2T68 and NBS1 ionizing radiation induced foci (IRIF). However, the relative importance of NFBD1 and 53BP1 in IRIF formation differ. We also determined the interdependence among mediators in IRIF recruitment. We extend previous findings in cancer cells and mouse cells that NFBD1 is upstream of 53BP1 and BRCA1 to primary human cells. Furthermore, NFBD1 promotes BRCA1 IRIF through both 53BP1-dependent and 53BP1-independent mechanisms.
Wilson
Kathleen A
KA
Department of Pathology and Graduate Program in Genetics, Yale University School of Medicine, New Haven, Connecticut 06510, USA. kathleen.a.wilson@yale.edu
Stern
David F
DF
D048868:Adaptor Proteins, Signal Transducing; D064007:Ataxia Telangiectasia Mutated Proteins; D019313:BRCA1 Protein / Q000502:physiology*; D018797:Cell Cycle Proteins / Q000378:metabolism / Q000502:physiology*; D002460:Cell Line; D064447:Checkpoint Kinase 2; D004268:DNA-Binding Proteins / Q000378:metabolism / Q000502:physiology*; D005347:Fibroblasts / Q000166:cytology / Q000378:metabolism; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000502:physiology*; D009687:Nuclear Proteins / Q000502:physiology*; D010766:Phosphorylation / Q000528:radiation effects; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism / Q000502:physiology*; D034741:RNA, Small Interfering / Q000494:pharmacology; D011839:Radiation, Ionizing; D015534:Trans-Activators / Q000502:physiology*; D025521:Tumor Suppressor Proteins / Q000378:metabolism / Q000502:physiology*; D000071857:Tumor Suppressor p53-Binding Protein 1
D048868:Adaptor Proteins, Signal Transducing; D019313:BRCA1 Protein; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D047908:Intracellular Signaling Peptides and Proteins; C413163:MDC1 protein, human; D009687:Nuclear Proteins; D034741:RNA, Small Interfering; C498301:TP53BP1 protein, human; D015534:Trans-Activators; D025521:Tumor Suppressor Proteins; D000071857:Tumor Suppressor p53-Binding Protein 1; D064447:Checkpoint Kinase 2; C576324:ATM protein, human; D064007:Ataxia Telangiectasia Mutated Proteins; C576325:Atm protein, mouse; C578634:CHEK2 protein, human; C578633:Chek2 protein, mouse; D017346:Protein Serine-Threonine Kinases