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dc.contributor.authorSchreck, Ilona
dc.contributor.authorChudziak, Doreen
dc.contributor.authorSchneider, Sandra
dc.contributor.authorSeidel, Albrecht
dc.contributor.authorPlatt, Karl L.
dc.contributor.authorOesch, Franz
dc.contributor.authorWeiss, Carsten
dc.date.accessioned2009-10-06T10:52:23Z
dc.date.available2009-10-06T10:52:23Z
dc.date.issued2009-05-17
dc.identifier.citationToxicology 2009, 259 (3):91-96en
dc.identifier.issn0300-483X
dc.identifier.pmid19428948
dc.identifier.doi10.1016/j.tox.2009.02.006
dc.identifier.urihttp://hdl.handle.net/10146/83595
dc.description.abstractThe aryl hydrocarbon receptor (AhR) mediates toxicity of a variety of environmental pollutants such as polycyclic aromatic hydrocarbons (PAHs) and dioxins. However, the underlying mechanisms and genetic programmes regulated by AhR to cause adverse effects but also to counteract poisoning are still poorly understood. Here we analysed the effects of two AhR ligands, benzo[a]pyrene (B[a]P), a DNA damaging tumour initiator and promotor and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), a pure tumour promoter, on cell survival and on nucleotide excision repair (NER) gene expression. NER deals with so called "bulky" DNA adducts including those generated by enzymatically activated B[a]P. Therefore, the hypothesis that AhR may enhance NER gene expression to trigger DNA repair in the presence of genotoxic AhR ligands was tested. Furthermore, we investigated a potential cytoprotective effect of AhR activation by the non-genotoxic ligand TCDD against cell death induced by various genotoxins. Finally, the actions of genotoxins themselves on NER gene expression were studied. As a cell culture model we used mouse hepatoma cells (Hepa-c7) proficient for AhR and its partner protein ARNT as well as subclones deficient in AhR (Hepa-c12) or ARNT (Hepa-c4) to study involvement of AhR and ARNT in response to B[a]P and TCDD. Indeed, the mRNA levels of the two NER genes XP-C and DNA polymerase kappa were increased by B[a]P and TCDD, however, this was not accompanied by an increase in the amount of the respective proteins. Pretreatment of cells with TCDD did not reduce cytotoxicity induced by various genotoxins. Thus, in Hepa-c7 cells AhR has no major effects on the expression of these crucial NER proteins and does not prevent genotoxin-provoked cell death. As expected, the genotoxins B[a]P and cis-platin led to p53 accumulation and induction of its target p21. Interestingly, however, NER gene expression was not enhanced but rather decreased. As two NER genes, XP-C and DNA damage binding protein ddb2, are up-regulated by p53 and ultraviolet radiation in human cells these findings suggest cell type, species or lesion specific actions of p53 on DNA repair gene expression. Importantly, in cells with damaged DNA up-regulation of p53 may not suffice to enhance DNA repair gene expression.
dc.description.sponsorshipThis work was supported by ECNIS (Environmental Cancer Risk, Nutrition and Individual Susceptibility), a network of excellence operating within the European Union 6th Framework Program, Priority 5: “Food Quality and Safety” (Contract No. 513943).en
dc.language.isoenen
dc.relation.urlhttp://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TCN-4VR24B9-2&_user=1843694&_rdoc=1&_fmt=&_orig=search&_sort=d&_docanchor=&view=c&_acct=C000055040&_version=1&_urlVersion=0&_userid=1843694&md5=87626e928d5a9c3fc6e680f726340df7en
dc.subjectAryl hydrocarbon receptoren
dc.subjectNucleotide excision repairen
dc.subjectBenzo[a]pyreneen
dc.subject2,3,7,8-Tetrachlorodibenzo-p-dioxinen
dc.subjectcis-Platinen
dc.subjectp53en
dc.subject.meshAnimals
dc.subject.meshAryl Hydrocarbon Receptor Nuclear Translocator
dc.subject.meshBlotting, Western
dc.subject.meshCell Line, Tumor
dc.subject.meshCell Survival
dc.subject.meshDNA Repair
dc.subject.meshDNA-Directed DNA Polymerase
dc.subject.meshEnvironmental Pollutants
dc.subject.meshGene Expression Profiling
dc.subject.meshGene Expression Regulation
dc.subject.meshGenes, p53
dc.subject.meshLiver Neoplasms, Experimental
dc.subject.meshMice
dc.subject.meshMutagens
dc.subject.meshReceptors, Aryl Hydrocarbon
dc.titleInfluence of aryl hydrocarbon- (Ah) receptor and genotoxins on DNA repair gene expression and cell survival of mouse hepatoma cells.en
dc.typeArticleen
dc.identifier.journalToxicologyen
html.description.abstractThe aryl hydrocarbon receptor (AhR) mediates toxicity of a variety of environmental pollutants such as polycyclic aromatic hydrocarbons (PAHs) and dioxins. However, the underlying mechanisms and genetic programmes regulated by AhR to cause adverse effects but also to counteract poisoning are still poorly understood. Here we analysed the effects of two AhR ligands, benzo[a]pyrene (B[a]P), a DNA damaging tumour initiator and promotor and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), a pure tumour promoter, on cell survival and on nucleotide excision repair (NER) gene expression. NER deals with so called "bulky" DNA adducts including those generated by enzymatically activated B[a]P. Therefore, the hypothesis that AhR may enhance NER gene expression to trigger DNA repair in the presence of genotoxic AhR ligands was tested. Furthermore, we investigated a potential cytoprotective effect of AhR activation by the non-genotoxic ligand TCDD against cell death induced by various genotoxins. Finally, the actions of genotoxins themselves on NER gene expression were studied. As a cell culture model we used mouse hepatoma cells (Hepa-c7) proficient for AhR and its partner protein ARNT as well as subclones deficient in AhR (Hepa-c12) or ARNT (Hepa-c4) to study involvement of AhR and ARNT in response to B[a]P and TCDD. Indeed, the mRNA levels of the two NER genes XP-C and DNA polymerase kappa were increased by B[a]P and TCDD, however, this was not accompanied by an increase in the amount of the respective proteins. Pretreatment of cells with TCDD did not reduce cytotoxicity induced by various genotoxins. Thus, in Hepa-c7 cells AhR has no major effects on the expression of these crucial NER proteins and does not prevent genotoxin-provoked cell death. As expected, the genotoxins B[a]P and cis-platin led to p53 accumulation and induction of its target p21. Interestingly, however, NER gene expression was not enhanced but rather decreased. As two NER genes, XP-C and DNA damage binding protein ddb2, are up-regulated by p53 and ultraviolet radiation in human cells these findings suggest cell type, species or lesion specific actions of p53 on DNA repair gene expression. Importantly, in cells with damaged DNA up-regulation of p53 may not suffice to enhance DNA repair gene expression.


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