Increased skin tumorigenesis in mice lacking pi class glutathione S -transferases

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Abstract
The activity of chemical carcinogens is a complex balance between metabolic activation by cytochrome P450 monooxygenases and detoxification by enzymes such as glutathione S -transferase (GST). Regulation of these proteins may have profound effects on carcinogenic activity, although it has proved impossible to ascribe the observed effects to the activity of a single protein. GstP appears to play a very important role in carcinogenesis, although the precise nature of its involvement is unclear. We have deleted the murine GstP gene cluster and established the effects on skin tumorigenesis induced by the polycyclic aromatic hydrocarbon 7,12-dimethylbenz anthracene and the tumor promoting agent 12- O -tetradecanoylphorbol-13-acetate. After 20 weeks, a highly significant increase in the number of papillomas was found in the GstP1/P2 null mice [ GstP1/P2 (−/−) mice, 179 papillomas, mean 9.94 per animal vs. GstP1/P2 (+/+) mice, 55 papillomas, mean 2.89 per animal, ( P < 0.001)]. This difference in tumor incidence provides direct evidence that a single gene involved in drug metabolism can have a profound effect on tumorigenicity, and demonstrates that GstP may be an important determinant in cancer susceptibility, particularly in diseases where exposure to polycyclic aromatic hydrocarbons is involved, for instance in cigarette smoke-induced lung cancer.

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