TCDD activates Mdm2 and attenuates the p53 response to DNA damaging agents.
In this study we investigated the effect of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on the p53 response to DNA damaging agents. Pre-treatment of rats with TCDD attenuated the p53 liver response to diethylnitrosamine (DEN) and reduced levels of p53 and Ser15 phosphorylated p53. In addition, there were more slowly migrating p53 species, forming a ladder, which suggests an increased ubiquination of p53 in TCDD-pre-treated rats. Terminal deoxynucleotidyl transferase-mediated X-dUTP nick-end labelling analysis indicated decreased apoptosis rates in the livers of these rats. Studies on aryl hydrocarbon receptor (AhR) knockout mice and their wild-type littermates confirmed this effect in AhR +/+ but not in AhR -/- mice, indicating that this effect may be AhR-mediated. Quantitative RT-PCR analysis revealed no increased mRNA levels in TCDD-treated rats, but immunohistological studies indicated that TCDD modulated Mdm2 protein levels, and in particular, increased nuclear levels in rat hepatocytes in situ. In vitro studies employing HepG2 cells confirmed the in vivo data. Thus, TCDD increased basal levels of Mdm2 protein, but not mRNA, and attenuated the p53 response to a variety of genotoxic and cytotoxic agents. The increase in Mdm2 protein levels was accompanied by rapid and highly sensitive phosphorylation of Mdm2 at Ser166, which has been associated to active Mdm2. In summary, TCDD is a potent inhibitor of p53 that may influence the liver's ability to handle genotoxic agents in a safe way, and may play a role in TCDD-induced carcinogenesis.
Institute of Environmental Medicine, Karolinska Institutet, Box 210, 17177 Stockholm, Sweden.
Gerd
G
Pääjärvi
Matti
M
Viluksela
Raimo
R
Pohjanvirta
Ulla
U
Stenius
Johan
J
Högberg
D000477:Alkylating Agents / Q000633:toxicity*; D000818:Animals; D015153:Blotting, Western; D004052:Diethylnitrosamine / Q000633:toxicity*; D004785:Environmental Pollutants / Q000494:pharmacology*; D005260:Female; D022781:Hepatocytes; D007150:Immunohistochemistry; D020287:In Situ Nick-End Labeling; D051379:Mice; D018345:Mice, Knockout; D009687:Nuclear Proteins / Q000187:drug effects / Q000378:metabolism; D000072317:Polychlorinated Dibenzodioxins / Q000494:pharmacology*; D011518:Proto-Oncogene Proteins / Q000187:drug effects / Q000378:metabolism; D051736:Proto-Oncogene Proteins c-mdm2; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D018336:Receptors, Aryl Hydrocarbon / Q000187:drug effects / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D016159:Tumor Suppressor Protein p53 / Q000187:drug effects* / Q000378:metabolism
D000477:Alkylating Agents; D004785:Environmental Pollutants; D009687:Nuclear Proteins; D000072317:Polychlorinated Dibenzodioxins; D011518:Proto-Oncogene Proteins; D012333:RNA, Messenger; D018336:Receptors, Aryl Hydrocarbon; D016159:Tumor Suppressor Protein p53; D004052:Diethylnitrosamine; C497207:Mdm2 protein, mouse; C497208:Mdm2 protein, rat; D051736:Proto-Oncogene Proteins c-mdm2