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ToxSci Advance Access published online on December 20, 2007
Toxicological Sciences, doi:10.1093/toxsci/kfm305
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© The Author 2007. Published by Oxford University Press on behalf of the Society of Toxicology. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org

Mdm2 as a sensitive and mechanistically informative marker for genotoxicity induced by benzo[a]pyrene and dibenzo[a,l]pyrene

Maria Malmlöf, Gerd Pääjärvi, Johan Högberg and Ulla Stenius*

Institute of Environmental Medicine, Karolinska Institutet, S-17177 Stockholm, Sweden

* To whom correspondence should be addressed: Institute of Environmental Medicine, Karolinska Institutet, Box 210, S-171 77 Stockholm, Sweden. Tel.: 46-8-524-878-72; Fax: 46-8-343849; E-mail: ulla.stenius{at}ki.se

Received October 11, 2007; revision received December 7, 2007; accepted December 9, 2007


  Abstract

Mdm2 is an oncoprotein interacting with p53 and maintaining low p53 levels in unstressed cells. Here we investigated the effect of genotoxic compounds on Mdm2 phosphorylation levels. Employing the Mdm2 2A10 antibody and phosphatase treatment we found that Mdm2 accumulated in HepG2 cells when exposed to low concentrations of genotoxic compounds such as mitomycin C, etoposide, 5-fluorouracil and benzo[a]pyrene (BP). The low dose responses were not accompanied by p53 accumulation and the effect of low concentrations of BP on Mdm2 was not affected by siRNA for p53. In human lymphoblasts 10 nM BP induced an Mdm2 response. Low concentrations of BP also induced binding of Mdm2 to chromatin in HepG2 cells, but no p53 binding or H2AX phosphorylation. The more mutagenic dibenzo[a,l]pyrene (DBP) as well as higher BP concentrations instead induced {gamma}H2AX and p53 Ser15 association with chromatin. Acrolein potentiated the effect of BP on p53 stabilisation and chromatin binding. Taken together, these data suggest that 1) Mdm2 is a sensitive biomarker for certain types of genotoxicity, and 2) that PAH-induced Mdm2 binding to chromatin reflects repairable damage, whereas chromatin binding of p53 Ser15 and {gamma}H2AX indicates more persistent DNA damage. The analysis of Mdm2 and related endpoints might be useful for evaluating mutagenic potentials of DNA damages. It is suggested that patterns documented here can be used for separating BP doses that induce readily repaired DNA adducts from doses that overwhelm this capacity.

Key Words: Mdm2; p53; benzo[a]pyrene; dibenzo[a,l]pyrene; PAH.


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