title: The role of the Ah receptor and p38 in benzo[a]pyrene-7,8-dihydrodiol and benzo[a]pyrene-7,8-dihydrodiol-9,10-epoxide-induced apoptosis.
abstract: Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous contaminants in the environment. Benzo[a]pyrene (B[a]P), a prototypical member of this class of chemicals, affects cellular signal transduction pathways and induces apoptosis. In this study, the proximate carcinogen of B[a]P metabolism, trans-7,8-dihydroxy-7,8-dihydrobenzo[a]pyrene (B[a]P-7,8-dihydrodiol) and the ultimate carcinogen, B[a]P-r-7,t-8-dihydrodiol-t-9,10-epoxide(+/-) (BPDE-2) were found to induce apoptosis in human HepG2 cells. Apoptosis initiated by B[a]P-7,8-dihydrodiol was linked to activation of the Ah receptor and induction of CYP1A1, an event that can lead to the formation of BPDE-2. With both B[a]P-7,8-dihydrodiol and BPDE-2 treatment, changes in anti- and pro-apoptotic events in the Bcl-2 family of proteins correlated with the release of mitochondrial cytochrome c and caspase activation. The onset of apoptosis as monitored by caspase activation was linked to mitogen-activated protein (MAP) kinases. Utilizing mouse hepa1c1c7 cells and the Arnt-deficient BPRc1 cells, activation of MAP kinase p38 by B[a]P-7,8-dihydrodiol was shown to be Ah receptor-dependent, indicating that metabolic activation by CYP1A1 was required. This was in contrast to p38 activation by BPDE-2, an event that was independent of Ah receptor function. Confirmation that MAP kinases play a critical role in BPDE-2-induced apoptosis was shown by inhibiting caspase activation of poly(ADP-ribose)polymerase 1 (PARP-1) by chemical inhibitors of p38 and ERK1/2. Furthermore, mouse embryo p38-/- fibroblasts were shown to be resistant to the actions of BPDE-2-induced apoptosis as determined by annexin V analysis, cytochrome c release, and cleavage of PARP-1. These results confirm that the Ah receptor plays a critical role in B[a]P-7,8-dihydrodiol-induced apoptosis while p38 MAP kinase links the actions of an electrophilic metabolite like BPDE-2 to the regulation of programmed cell death.
authors.affiliation: Laboratory of Environmental Toxicology, Department of Pharmacology, University of California, San Diego, La Jolla, California 92093-0636, USA.
authors.forename: Shujuan
authors.initials: S
authors.lastname: Chen
authors.forename: Nghia
authors.initials: N
authors.lastname: Nguyen
authors.forename: Kumiko
authors.initials: K
authors.lastname: Tamura
authors.forename: Michael
authors.initials: M
authors.lastname: Karin
authors.forename: Robert H
authors.initials: RH
authors.lastname: Tukey
mesh_terms: D015123:7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide / Q000494:pharmacology*; D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D051784:Aryl Hydrocarbon Receptor Nuclear Translocator; D002273:Carcinogens / Q000494:pharmacology*; D006528:Carcinoma, Hepatocellular; D020169:Caspases / Q000378:metabolism; D019363:Cytochrome P-450 CYP1A1 / Q000235:genetics / Q000378:metabolism; D003574:Cytochrome c Group / Q000378:metabolism / Q000494:pharmacology; D004249:DNA Damage; D004268:DNA-Binding Proteins; D004101:Dihydroxydihydrobenzopyrenes / Q000494:pharmacology*; D004789:Enzyme Activation / Q000187:drug effects; D005347:Fibroblasts; D006801:Humans; D008113:Liver Neoplasms; D008156:Luciferases / Q000235:genetics; D051379:Mice; D018345:Mice, Knockout; D020928:Mitogen-Activated Protein Kinases / Q000172:deficiency / Q000502:physiology*; D011065:Poly(ADP-ribose) Polymerases / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000032:analysis; D018336:Receptors, Aryl Hydrocarbon / Q000502:physiology*; D011993:Recombinant Fusion Proteins; D014157:Transcription Factors / Q000235:genetics; D014162:Transfection; D014407:Tumor Cells, Cultured; D051020:bcl-X Protein; D048051:p38 Mitogen-Activated Protein Kinases
chemical_list: C497396:ARNT protein, human; C497397:Arnt protein, mouse; C494811:BCL2L1 protein, human; C494812:Bcl2l1 protein, mouse; D002273:Carcinogens; D003574:Cytochrome c Group; D004268:DNA-Binding Proteins; D004101:Dihydroxydihydrobenzopyrenes; D019253:Proto-Oncogene Proteins c-bcl-2; D018336:Receptors, Aryl Hydrocarbon; D011993:Recombinant Fusion Proteins; D014157:Transcription Factors; D051020:bcl-X Protein; C017228:benzo(a)pyrene 7,8-dihydrodiol; D051784:Aryl Hydrocarbon Receptor Nuclear Translocator; D015123:7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide; D008156:Luciferases; D019363:Cytochrome P-450 CYP1A1; D011065:Poly(ADP-ribose) Polymerases; D020928:Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D020169:Caspases