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TCDD activates Mdm2 and attenuates the p53 response to DNA damaging agents

Gerd Pääjärvi1, Matti Viluksela, Raimo Pohjanvirta

  • 1Institute of Environmental Medicine, Karolinska Institutet, Box 210, 17177 Stockholm, Sweden.

Carcinogenesis
|October 2, 2004
PubMed

Insights

2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) exposure inhibits the p53 response to DNA damage in the liver, potentially increasing cancer risk. This TCDD effect appears mediated by the aryl hydrocarbon receptor (AhR) and involves increased Mdm2 protein levels.

Area of Science:

  • Toxicology
  • Molecular Biology
  • Carcinogenesis

Background:

  • The p53 protein is a critical tumor suppressor that responds to DNA damage.
  • 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is a potent environmental toxicant with known carcinogenic potential.
  • The interaction between TCDD and the p53 pathway in the liver is not fully understood.

Purpose of the Study:

  • To investigate the impact of TCDD pre-treatment on the p53 response to DNA damaging agents in the liver.
  • To elucidate the role of the aryl hydrocarbon receptor (AhR) in mediating TCDD's effects on p53.
  • To determine the molecular mechanisms by which TCDD affects p53 signaling and liver cell apoptosis.

Main Methods:

  • Animal studies involving TCDD pre-treatment in rats and AhR knockout mice.
  • Assessment of p53 and phosphorylated p53 levels via Western blotting and immunohistochemistry.
  • Analysis of p53 ubiquitination and apoptosis rates using laddering assays and TUNEL staining.
  • In vitro studies using HepG2 cells to confirm in vivo findings.

Main Results:

  • TCDD pre-treatment attenuated the p53 response to diethylnitrosamine (DEN), reducing p53 and Ser15 phosphorylated p53 levels.
  • Increased p53 ubiquitination and decreased apoptosis rates were observed in TCDD-exposed livers.
  • The observed effects were dependent on the aryl hydrocarbon receptor (AhR), as they occurred in AhR +/+ mice but not in AhR -/- mice.
  • TCDD modulated Mdm2 protein levels, increasing nuclear Mdm2 in hepatocytes, and this was associated with Mdm2 phosphorylation at Ser166.

Conclusions:

  • TCDD acts as a potent inhibitor of the p53 response in the liver, potentially by increasing Mdm2 protein levels.
  • This inhibition of p53 may impair the liver's ability to manage genotoxic insults, contributing to TCDD-induced carcinogenesis.
  • The aryl hydrocarbon receptor (AhR) plays a key role in mediating TCDD's suppressive effects on the p53 pathway.

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