title: Regulation of p53 by TopBP1: a potential mechanism for p53 inactivation in cancer.
abstract: Proper control of the G(1)/S checkpoint is essential for normal proliferation. The activity of p53 must be kept at a very low level under unstressed conditions to allow growth. Here we provide evidence supporting a crucial role for TopBP1 in actively repressing p53. Depletion of TopBP1 upregulates p53 target genes involved in cell cycle arrest and apoptosis and enhances DNA damage-induced apoptosis. The regulation is mediated by an interaction between the seventh and eighth BRCT domains of TopBP1 and the DNA-binding domain of p53, leading to inhibition of p53 promoter binding activity. Importantly, TopBP1 overexpression is found in 46 of 79 primary breast cancer tissues and is associated with high tumor grade and shorter patient survival time. Overexpression of TopBP1 to a level comparable to that seen in breast tumors leads to inhibition of p53 target gene expression and DNA damage-induced apoptosis and G(1) arrest. Thus, a physiological level of TopBP1 is essential for normal G(1)/S transition, but a pathological level of TopBP1 in cancer may perturb p53 function and contribute to an aggressive tumor behavior.
authors.affiliation: Division of Hematology and Oncology, Department of Medicine, University of Alabama at Birmingham, Birmingham, AL 35294-3300, USA.
authors.forename: Kang
authors.initials: K
authors.lastname: Liu
authors.forename: Naresh
authors.initials: N
authors.lastname: Bellam
authors.forename: Hui-Yi
authors.initials: HY
authors.lastname: Lin
authors.forename: Bing
authors.initials: B
authors.lastname: Wang
authors.forename: Cecil R
authors.initials: CR
authors.lastname: Stockard
authors.forename: William E
authors.initials: WE
authors.lastname: Grizzle
authors.forename: Weei-Chin
authors.initials: WC
authors.lastname: Lin
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000502:physiology; D001943:Breast Neoplasms / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D002453:Cell Cycle / Q000502:physiology; D002460:Cell Line; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D005260:Female; D005786:Gene Expression Regulation; D006801:Humans; D051379:Mice; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D034741:RNA, Small Interfering / Q000235:genetics / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D015996:Survival Rate; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism*
chemical_list: D002352:Carrier Proteins; D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; D034741:RNA, Small Interfering; D011993:Recombinant Fusion Proteins; C110513:TOPBP1 protein, human; D016159:Tumor Suppressor Protein p53