Steroid hormone-dependent overexpression of cytochromes P450 2A in liver tumors of TGF alpha transgenic male mice

Experimental nonalcoholic fatty liver disease in mice leads to cytochrome p450 2a5 upregulation through nuclear factor erythroid 2-like 2 translocation

Mouse cytochrome P450 2A5 (CYP2A5) is upregulated in various liver diseases and a putative common feature for all of these conditions is altered cellular redox status. Nuclear factor erythroid 2-like 2 (Nrf2) is a transcription factor that is post-translationally regulated by oxidative stress and controls the transcription of protective target genes. In the present study, we have characterized the regulation of CYP2A5 by Nrf2 and evaluated gene expression, protein content and activity of anti-oxidant enzymes in the Nrf2^+/+ and Nrf2^−/− mice model of non-alcoholic fatty liver (NAFLD). After eight weeks of feeding on a high-fat diet, livers from Nrf2^−/− mice showed a substantial increase in macro and microvesicular steatosis and a massive increase in the number of neutrophil polymorphs, compared to livers from wild-type mice treated similarly. Livers of Nrf2^−/− mice on the high-fat diet exhibited more oxidative stress than their wild-type counterparts as assessed by a significant depletion of reduced glutathione that was coupled with increases in malondialdehyde. Furthermore, results in Nrf2-deficient mice showed that CYP2A5 expression was significantly attenuated in the absence of Nrf2, as was found with the conventional target genes of Nrf2. The treatment of wild-type mice with high-fat diet leaded to nuclear accumulation of Nrf2, and co-immunoprecipitation experiments showed that Nrf2 was bound to Cyp2a5. These findings suggest that the high-fat diet induced alteration in cellular redox status and induction of CYP2A5 was modulated through the redox-sensitive transcription Nrf2.

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CYP2A5 up-regulation in response to NAFLD was Nrf2 dependent.

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NAFLD induces oxidant stress.

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A protective role for Nrf2 against hepatic damage by NAFLD was demonstrated.

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NAFLD induces translocation of Nrf2 from the cytoplasm to the nucleus.

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Nrf2 binding to CYP2a5 was shown.

Cytochrome P450 2A5 constitutive expression and induction by heavy metals is dependent on redox-sensitive transcription factor Nrf2 in liver

Mouse cytochrome P450 2A5 (CYP2A5) is upregulated in various pathophysiological liver diseases and induced by structurally variable hepatotoxic chemicals. A putative common feature for all of these conditions is altered cellular redox status. Nuclear factor erythroid 2-like 2 (Nrf2) is a transcription factor that is post-translationally regulated by oxidative stress and controls the transcription of numerous protective target genes. In the present study, we have extensively characterized the regulation of Cyp2a5 by Nrf2 and compared it to a well-characterized target gene Hmox1. The treatment of mouse primary hepatocytes with lead chloride, methylmercury chloride, or phenethyl isothiocyanate all leads to nuclear accumulation of Nrf2. Both CYP2A5 and HMOX1 were induced by all three compounds; however, HMOX1 responded more rapidly and transiently as compared to CYP2A5. Experiments in Nrf2(-/-) primary hepatocytes showed that Nrf2 is crucial for CYP2A5 induction but not for elevation of HMOX1. Both CYP2A5 and HMOX1 were upregulated by Nrf2 overexpression and downregulated by Keap1 or Bach1 overexpression. However, in all cases, CYP2A5 responded much more potently. Results in Nrf2-deficient animals showed that CYP2A5 expression is significantly attenuated in the absence of Nrf2, while expression of HMOX1 was unaffected. Therefore, Cyp2a5 joins the group of genes constitutively regulated by Nrf2. Our current results unequivocally show that expression of CYP2A5 is tightly controlled by Nrf2 in liver. Nrf2 is needed for constitutive expression of CYP2A5, and CYP2A5 is also sensitively upregulated by an increased level of Nrf2 protein. Therefore, CYP2A5 upregulation could be a useful indicator for hepatic activation of the Nrf2 pathway.

Altered gene expression in mouse livers after dichloroacetic acid exposure

Dichloroacetic acid (DCA) is a major by-product of water disinfection by chlorination. Several studies have demonstrated that DCA exhibits hepatocarcinogenic effects in rodents when administered in drinking water. This chemical does not appear to be highly mutagenic, and the mechanism(s) involved in DCA induction of cancer are not clear. The present work was aimed at identifying changes in gene expression which may indicate critical alterations/pathways involved in this chemical's carcinogenic activities. We used cDNA microarray methods for analyses of gene expression in livers of mice treated with the tumorigenic dose of 2 g/l DCA in drinking water for 4 weeks. Total RNA samples obtained from livers of the control and DCA-treated mice were evaluated for gene expression patterns with Clontech Atlas Mouse 1.2 cDNA and Atlas mouse stress/toxicology arrays, and the data analyzed with AtlasImage 2.01 and one-way ANOVA in JMP4 software. From replicate experiments, we identified 24 genes with altered expression, of which 15 were confirmed by Northern blot analysis. Of the 15 genes, 14 revealed expression suppressed two- to five-fold; they included the following: MHR 23A, cytochrome P450 (CYP) 2C29, CYP 3A11, serum paraoxonase/arylesterase 1 (PON 1), liver carboxylesterase, alpha-1 antitrypsin, ER p72, glutathione S-transferase (GST) Pi 1, angiogenin, vitronectin precursor, cathepsin D (CTSD), plasminogen precursor (contains angiostatin), prothrombin precursor and integrin alpha 3 precursor (ITGA 3). An additional gene, CYP 2A4/5, had a two-fold elevation in expression. Further, in ancillary Northern analyses of total RNA isolated from DCA-induced hepatocellular carcinomas (from earlier reported studies of mice treated with 3.5 g/l DCA for 93 weeks), many of the same genes (11 of 15) noted above showed a similar alteration in expression. In summary, we have identified specific genes involved in the functional categories of cell growth, tissue remodeling, apoptosis, cancer progression and xenobiotic metabolism that have altered levels of expression following exposures to DCA. These findings serve to highlight new pathways in which to further probe DCA effects that may be critical to its tumorigenic activity.