title: Blockage of transcription as a trigger for p53 accumulation by 2-acetylaminofluorene DNA-adducts.
abstract: The hepatocarcinogen 2-acetylaminofluorene is one of the most studied experimental carcinogens. We have shown previously that normal rat hepatocytes accumulate the tumour suppressor p53 after exposure to this compound while preneoplastic rat hepatocytes do not. We suggested that the lack of p53 response may confer a growth advantage on preneoplastic hepatocytes and may be an important factor in hepatic tumor promotion by 2-acetylaminofluorene and other genotoxic compounds. Inhibition of RNA polymerase II driven transcription by DNA lesions may constitute one of the mechanisms leading to accumulation of the tumour suppressor p53. We have investigated the accumulation of p53 by structurally different DNA lesions of 2-acetylaminofluorene for which the rate of nucleotide excision repair (NER) and inhibition of transcription are known. Experiments were performed with NER proficient human fibroblasts as well as repair deficient xeroderma pigmentosum group A (XPA) cells, XPC cells [only transcription coupled repair (TCR)] and Cockayne syndrome (CS)B cells [only global genome repair (GGR)]. The cells were exposed to N-acetoxy-acetylaminofluorene (NAAAF) in the presence or absence of paraoxon inducing dG-C8-AAF or dG-C8-AF adducts respectively. Both treatments led to accumulation of p53 in all cells. However, dG-C8-AAF adducts produced greater p53 induction than dG-C8-AF adducts. The percentage p53-positive cells was highest and the threshold for p53 accumulation was lowest in XPA and CSB cells. Our results further demonstrate that both the potency of a lesion to inhibit transcription as well as the restoration of RNA synthesis determines the magnitude of p53 induction.
authors.affiliation: Division of Toxicology, Leiden/Amsterdam Center for Drug Research, Leiden University, Leiden, The Netherlands.
authors.forename: Hilde E
authors.initials: HE
authors.lastname: van Gijssel
authors.forename: Leon H F
authors.initials: LH
authors.lastname: Mullenders
authors.forename: Michiel F
authors.initials: MF
authors.lastname: van Oosterwijk
authors.forename: John H N
authors.initials: JH
authors.lastname: Meerman
mesh_terms: D000099:Acetoxyacetylaminofluorene / Q000633:toxicity*; D002460:Cell Line; D003057:Cockayne Syndrome / Q000235:genetics / Q000378:metabolism; D018736:DNA Adducts / Q000235:genetics / Q000378:metabolism*; D004249:DNA Damage; D004260:DNA Repair; D005347:Fibroblasts / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D014158:Transcription, Genetic; D016159:Tumor Suppressor Protein p53 / Q000096:biosynthesis* / Q000235:genetics; D014983:Xeroderma Pigmentosum / Q000235:genetics / Q000378:metabolism
chemical_list: D018736:DNA Adducts; D016159:Tumor Suppressor Protein p53; D000099:Acetoxyacetylaminofluorene