title: Repression of BRCA1 through a feedback loop involving p53.
abstract: The BRCA1 and p53 tumor suppressors have been shown to interact and cooperate to activate transcription of p53-responsive genes. In this study, we show that BRCA1 is initially up-regulated, followed by a reduction to below basal levels in response to treatment with the DNA-damaging agents adriamycin and mitomycin C, and that the reduction of BRCA1 expression is dependent on the presence of wild-type p53. Elimination of p53 by expression of human papilloma virus E6 resulted in an inability to down-regulate BRCA1 in response to adriamycin. Ectopic expression of p53 resulted in a rapid decrease in BRCA1 protein and RNA levels and BRCA1 promoter-driven luciferase activity even in null p21 cells deficient in p53-dependent G(1) arrest. ATM(-)(/-) lymphoblastoid cells were deficient in their ability to reduce BRCA1 protein in response to DNA damage, whereas the wild-type counterparts reduced BRCA1 protein levels after exposure to adriamycin. These results, in conjunction with others, suggest a loop wherein BRCA1 initially participates in accumulation of p53 protein, whereas later p53 acts to reduce BRCA1 expression.
authors.affiliation: Laboratory of Molecular Oncology and Cell Cycle Regulation, Howard Hughes Medical Institute, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104, USA.
authors.forename: T K
authors.initials: TK
authors.lastname: MacLachlan
authors.forename: B C
authors.initials: BC
authors.lastname: Dash
authors.forename: D T
authors.initials: DT
authors.lastname: Dicker
authors.forename: W S
authors.initials: WS
authors.lastname: El-Deiry
mesh_terms: D064007:Ataxia Telangiectasia Mutated Proteins; D019313:BRCA1 Protein / Q000235:genetics* / Q000378:metabolism; D018797:Cell Cycle Proteins; D004249:DNA Damage / Q000187:drug effects; D004268:DNA-Binding Proteins; D015536:Down-Regulation / Q000187:drug effects; D004317:Doxorubicin / Q000494:pharmacology; D005246:Feedback; D005434:Flow Cytometry; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D019398:Genes, BRCA1 / Q000235:genetics*; D017930:Genes, Reporter; D006801:Humans; D016685:Mitomycin / Q000494:pharmacology; D009856:Oncogene Proteins, Viral / Q000235:genetics / Q000378:metabolism; D011401:Promoter Regions, Genetic / Q000235:genetics; D017346:Protein Serine-Threonine Kinases / Q000235:genetics; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*; D014162:Transfection; D014407:Tumor Cells, Cultured; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism*; D025521:Tumor Suppressor Proteins
chemical_list: D019313:BRCA1 Protein; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; C118860:E6 protein, Human papillomavirus type 6; D009856:Oncogene Proteins, Viral; D012333:RNA, Messenger; D012097:Repressor Proteins; D016159:Tumor Suppressor Protein p53; D025521:Tumor Suppressor Proteins; D016685:Mitomycin; D004317:Doxorubicin; C576324:ATM protein, human; D064007:Ataxia Telangiectasia Mutated Proteins; D017346:Protein Serine-Threonine Kinases