Induction of Drug Metabolism-Related Enzymes by Methylcholanthrene and Phenobarbital in Transgenic Mice Carrying Human Prototype c-Ha-ras Gene and Their Wild Type Littermates.

Abstract

Transgenic mice hemizygously carrying human c-Ha-ras proto-oncogene, TgrasH2 show very sensitive and facilitated carcinogenicity to various carcinogens. In this study, activities of certain enzymes related to drug metabolism and energy metabolism were measured in microsome and cytosol fractions of livers of Tg-rasH2 mice and their wild type littermates with both sexes treated with 3-methylcholanthrene (MC) and phenobarbital (PB). Aminopyrine N-demethylase activities increased significantly in livers of all mice treated with PB. MC and PB treatments induced significant increases in activities of UDP-glucuronosyltransferase and S-adenosyl homocysteinase compared to those in the non-treated groups in microsome fractions from all mice. In cytosol fractions of livers of all mice, glutathione S-transferase activity was significantly induced in the PB treated groups. There were no significant differences in activities of lactate dehydrogenase, glucose 6-phosphate dehydrogenase, pyruvate kinase and glucose 6-phosphatase related to energy metabolism in livers and kidneys among all mice. TgrasH2 mice showed stable activities of enzymes related to drug detoxication and energy metabolism similar to those of non-transgenic mice. These results suggest that the human c-Ha-ras transgene may not affect drug metabolism-related enzymes, and the facilitated carcinogenic response in the Tg-rasH2 mouse is not due to these enzymatic disorders.

Regulation of Cytochrome P450 Expression by Ras- and β-Catenin-Dependent Signaling

“…No significant differences between the transgenic animals and their wild-type littermates were found for total hepatic CYP content, protein levels of distinct CYP isoforms, and for different CYP-related enzyme activities [42]. Accordingly, CYP activities were comparable between both male and female RasH2 transgenics and the respective wildtype controls [43]. These results were largely confirmed by a subsequent study in which no significant differences in CYP expression between RasH2 mice and wild-type controls were found.…”

“…Moreover, striking analogies in the transcriptome profiles of periportal hepatocytes and Ha-Ras-mutated mouse hepatoma cells indicate an important role of Ras signaling in the regulation of the periportal hepatocyte phenotype [4]. However, transgenic expression of Ha-ras or HGF led to conflicting results: whereas over-expression of HGF or mutant Ha-Ras (in the Tg lox(pA)H-ras* mouse) was effective in blocking basal CYP expression [5,49], two other Ha-Ras-transgenic mice (tg.AC and RasH2) did not show altered CYP expression [42][43][44]46]. In tg.AC mice, expression of the mutant Ha-Ras transgene is under control of the embryo-specific -globin promoter, and, as a consequence, expression of the transgene is lost in adult liver [45].…”

“…Decreased expression of several CYPs, especially Cyp2e1, in response to insulin in cultured rat hepatocytes and Fao rat hepatoma cells, as well as enhanced Cyp2e1 mRNA levels after glucagon treatment of hepatocytes have been reported in several articles, in 2b ---HGF activity: testosterone 16 -hydroxylase [49] 2b/2c ---HGF activity: testosterone 6 -hydroxylase [49] 2b9 ---HGF mRNA [49] 2b10 ---HGF mRNA [49] 2c/3a RasH2 human c-Ha-Ras activity: aminopyrine N-demethylase [42] 2c/3a RasH2 human c-Ha-Ras activity: aminopyrine N-demethylase [43] 2c29 ---HGF mRNA, Western blot 1 [49] 2c39 ---HGF mRNA, Western blot 1 [49] 2c50 ---HGF mRNA, Western blot 1 [49] 2c70 ---HGF mRNA, Western blot 1 [49] 2d9 ---HGF mRNA [49] 2d13 ---c-Met knockout mRNA [50] 2d22 ---c-Met knockout mRNA [50] 2e RasH2 human c-Ha-Ras Western blot, activity: aniline hydroxylase [42] 2e RasH2 human c-Ha-Ras Western blot [44] 2e RasH2 human c-Ha-Ras activity: aniline hydroxylase [43] 2e tg.AC v-Ha-Ras Western blot [44] 2e1 tg.AC v-Ha-Ras Western blot [46] 2e1 Tg lox(pA)H-ras* human c-Ha-Ras immunohistochemistry [5] 2g1 ---HGF mRNA [49] 3a RasH2 human c-Ha-Ras Western blot [42] 3a RasH2 human c-Ha-Ras Western blot [44] 3a tg.AC v-Ha-Ras Western blot [44] 3a tg.AC v-Ha-Ras Western blot [46] 3a ---HGF Western blot, activity: testosterone 6 -hydroxylase [49] 3a11 ---HGF mRNA [49] 3a13 ---c-Met knockout mRNA [50] 3a44 ---c-Met knockout mRNA [50] total CYP RasH2 human c-Ha-Ras CO difference spectra [42] total CYP RasH2 human c-Ha-Ras (males only) CO difference spectra [44] total CYP tg.AC v-Ha-Ras CO difference spectra [44] 1 Total Cyp2c protein content was determined by Western blotting without provision for distinct isoforms. Organ: liver, if not otherwise identified.…”

Identification of novel dioxin-responsive genes by representational difference analysis

“…It is shown here that Sahh is induced by dioxin. Previous work has shown that liver Sahh activity is increased in mice exposed to 3-methylcolanthrene, another ligand for the AhR (Ohnishi et al 2001). Up-regulation of Sahh by dioxin might facilitate the collective activities of all methylation reactions in the cell by removing feedback inhibition, thereby affecting an array of biological processes.…”

Changes in Hepatic Enzyme Activities in Transgenic Mice Carrying Human Prototype c-Ha-ras Gene Treated with Diethylnitrosamine.

“…The major target organs of DEN are the liver, lung, forestomach and hematopoietic system [12]. In our previous reports, Tg-rasH2 mice were characterized by stable activities of some enzymes related to drug detoxication and energy metabolism in their livers and kidneys compared to those in the non-transgenic control [18]. On the other hand, it has been reported that activities of enzymes in the glycolysis and the pentose phosphate pathway are significantly increased in developed tumor cells [1,7,17].…”