Abstract
The tumor suppressor protein p53 is a transcription factor that regulates apoptotic responses produced by genotoxic agents. Previous studies have reported that 7,12-dimethylbenz[a]anthracene (DMBA)-induced bone marrow toxicity is p53-dependent in vivo. Our laboratory has shown that DMBA-induced splenic immunosuppression is CYP1B1- and microsomal epoxide hydrolase (mEH)-dependent, demonstrating that the DMBA-3,4-dihydrodiol-1,2-epoxide metabolite (DMBA-DE) is probably responsible for DMBA-induced immunosuppression. DMBA-DE is known to bind to DNA leading to strand breaks. Therefore, we postulated that a p53 pathway is required for DBMA-induced immunosuppression. In the present studies, our data show that activated p53 accumulated in the nuclei of spleen cells in WT and AhR-null mice after DMBA treatment, but not in CYP1B1-null or mEH-null mice. These results suggest that DMBA activates p53 in a CYP1B1- and mEH-dependent manner in vivo but is not AhR-dependent. Ataxia telangiectasia mutated (ATM) and ATM and Rad3-related protein (ATR) are sensors for DNA damage that signal p53 activation. Increased ATM, phospho-ATM (Ser1987), and ATR levels were observed after DMBA treatment in WT, p53-null, and AhR-null mice but not in CYP1B1-null or mEH-null mice. Therefore, ATM and ATR seem to act upstream of p53 as sensors of DNA damage. Ex vivo immune function studies demonstrated that DMBA-induced splenic immunosuppression is p53-dependent at doses of DMBA that produce immunosuppression in the absence of cytotoxicity. High-dose DMBA cytotoxicity may be associated with p53-independent pathways. This study provides new insights into the requirement of genotoxicity for DMBA-induced immunosuppression in vivo and highlights the roles of ATM/ATR in signaling p53.
Footnotes
-
This work was supported by National Institutes of Health grant R01-ES05495, and the New Mexico Center for Environmental Health Sciences was supported by center grant P30-ES012072 from the National Institute of Environmental Health Sciences.
-
ABBREVIATIONS: PAH, polycyclic aromatic hydrocarbon; DMBA, 7,12-Dimethylbenz[a]anthracene; mEH, microsomal epoxide hydrolase; DMBA-DE, DMBA-3,4-dihydrodiol-1,2-epoxide; AhR, aryl hydrocarbon receptor; ATM, ataxia telangiectasia mutated; ATR, ATM and Rad3-related; Con A, Concanavalin A; LPS, lipopolysaccharide; WT, wild-type; CO, corn oil; TBS/T, Tris-buffered saline containing Tween 20; HRP, horseradish peroxidase; NK, natural killer cells; FITC, fluorescein isothiocyanate; APC, allophycocyanin; PE, phycoerythrin; PFC, plaque-forming cell; SRBC, sheep red blood cell.
- Received June 22, 2007.
- Accepted October 9, 2007.
- The American Society for Pharmacology and Experimental Therapeutics
MolPharm articles become freely available 12 months after publication, and remain freely available for 5 years.Non-open access articles that fall outside this five year window are available only to institutional subscribers and current ASPET members, or through the article purchase feature at the bottom of the page.
|