Proteomic analysis of the murine liver in response to a combined exposure to psychological stress and 7,12-dimethylbenz(a)anthracene

Polycyclic aromatic hydrocarbons (PAHs) are environmental carcinogens implicated to underlie development of several types of cancers. Cytochrome P450 (CYP) enzymes play key roles in the conversion of PAHs to highly potent carcinogens, namely diol epoxides. 7,12-Dimethylbenz(a)anthracene (DMBA), a PAH, is highly carcinogenic, where in mouse models it is known to be responsible for initiating tumor formation in many organs including mammary tissues, ovaries, and skin. Psychological stress, via release of biochemical mediators, can greatly impact carcinogenesis. The present investigation examined the hypothesis that psychological stress modulates metabolism and carcinogenicity of DMBA through alteration of key drug metabolizing enzyme abundance levels in the liver utilizing mass spectrometry-based proteomics. To test this hypothesis, four groups of mice were treated as follows: nonstressed, stressed, nonstressed/DMBA-exposed, and stressed/DMBA-exposed, where the stressor was a well-accepted model of restraint. Liver proteins were extracted, resolved by one-dimensional gel electrophoresis, digested in-gel with trypsin, and analyzed by liquid chromatography-tandem mass spectrometry. This investigation resulted in the unique identification of 59 isoforms of CYP enzymes. Changes in protein abundances derived from spectral counting indicates that stress alone results in increases in the abundance of proteins responsive to oxidative stress, along with Phase I and II metabolizing enzymes, such as CYP2J5 and UDP glucoronytransferases. The proteomic results further indicate that exposure to DMBA induces increases in the abundance of CYP1A2 and serine protease inhibitors and decreases the abundance of CYP4 V3. Finally, significant changes in the abundance of proteins such as CYP1A2, CYP3A11, and Topoisomerase-2 were found between nonstressed and stressed/DMBA-treated mice. These data support the hypothesis that psychological stress modulates DMBA-induced regulation of drug metabolizing proteins in the liver.