title: p53 regulates cellular responses to environmental carcinogen benzo[a]pyrene-7,8-diol-9,10-epoxide in human lung cancer cells.
abstract: The p53 tumor suppressor is a mutational target of environmental carcinogen anti-benzo[a]pyrene-7,8-diol-9,10-epoxide (BPDE). We now demonstrate that p53 plays an important role in regulation of cellular responses to BPDE. Exposure of p53-null H1299 human lung cancer cells to BPDE resulted in S and G(2) phase cell cycle arrest, but not mitotic block, which correlated with induction of cyclin B1 protein expression, down-modulation of cell division cycle 25C (Cdc25C) and Cdc25B protein levels, and hyperphosphorylation of Cdc25C (S216), cyclin-dependent kinase 1 (Cdk1; Y15), checkpoint kinase 1 (Chk1; S317 and S345) and Chk2 (T68). The BPDE-induced S phase block, but not the G(2)/M phase arrest, was significantly attenuated by knockdown of Chk1 protein level. The BPDE-mediated accumulation of sub-diploid fraction (apoptotic cells) was significantly decreased in H1299 cells transiently transfected with both Chk1 and Chk2 specific siRNAs. The H460 human lung cancer cell line (wild-type p53) was relatively more sensitive to BPDE-mediated growth inhibition and enrichment of sub-diploid apoptotic fraction compared with H1299 cells. The BPDE exposure failed to activate either S or G(2) phase checkpoint in H460 cells. Instead, the BPDE-treated H460 cells exhibited a nearly 8-fold increase in sub-diploid apoptotic cells that was accompanied by phosphorylation of p53 at multiple sites. Knockdown of p53 protein level in H460 cells attenuated BPDE-induced apoptosis but enforced activation of S and G(2) phase checkpoints. In conclusion, the present study points towards an important role of p53 in regulation of cellular responses to BPDE in human lung cancer cells.
authors.affiliation: Department of Pharmacology, University of Pittsburgh Cancer Institute, Pittsburgh, Pennsylvania 15213, USA.
authors.forename: Hui
authors.initials: H
authors.lastname: Xiao
authors.forename: Shivendra V
authors.initials: SV
authors.lastname: Singh
mesh_terms: D000818:Animals; D064007:Ataxia Telangiectasia Mutated Proteins; D001564:Benzo(a)pyrene / Q000494:pharmacology*; D002274:Carcinogens, Environmental / Q000494:pharmacology*; D002453:Cell Cycle / Q000187:drug effects* / Q000502:physiology; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism; D045744:Cell Line, Tumor; D000071877:Checkpoint Kinase 1; D064447:Checkpoint Kinase 2; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D004789:Enzyme Activation; D004852:Epoxy Compounds / Q000378:metabolism*; D006801:Humans; D008175:Lung Neoplasms / Q000378:metabolism*; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism; D034622:RNA Interference; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism*; D025521:Tumor Suppressor Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D002274:Carcinogens, Environmental; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D004852:Epoxy Compounds; D016159:Tumor Suppressor Protein p53; D025521:Tumor Suppressor Proteins; D001564:Benzo(a)pyrene; D011494:Protein Kinases; D064447:Checkpoint Kinase 2; C576324:ATM protein, human; C576597:ATR protein, human; D064007:Ataxia Telangiectasia Mutated Proteins; C000605867:CHEK1 protein, human; C578634:CHEK2 protein, human; D000071877:Checkpoint Kinase 1; D017346:Protein Serine-Threonine Kinases