Increased Constitutive c-Jun N-terminal Kinase Signaling in Mice Lacking Glutathione S-Transferase Pi
ABSTRACT Glutathione S-transferase Pi (GSTP) detoxifies electrophiles by catalyzing their conjugation with reduced glutathione. A second function of this protein in cell defense has recently been proposed that is related to its ability to interact with c-Jun N-terminal kinase (JNK). The present study aimed to determine whether this interaction results in increased constitutive JNK activity in the absence of GSTP in GstP1/P2(-/-) mice and whether such a phenomenon leads to the up-regulation of genes that are relevant to cell defense. We found a significant increase in constitutive JNK activity in the liver and lung of GstP1/P2-/- compared with GstP1/P2(+/+) mice. The greatest increase in constitutive JNK activity was observed in null liver and was accompanied by a significant increase in activator protein-1 DNA binding activity (8-fold) and in the mRNA levels for the antioxidant protein heme oxygenase-1 compared with wild type. Furthermore UDP-glucuronosyltransferase 1A6 mRNA levels were significantly higher in the livers of GstP1/P2(-/-) compared with GstP1/P2(+/+) mice, which correlated to a 2-fold increase in constitutive activity both in vitro and in vivo. There was no difference in the gene expression of other UDP-glucuronosyltransferase isoforms, manganese superoxide dismutase, microsomal epoxide hydrolase, or GSTA1 between GstP1/P2(-/-) and GstP1/P2(+/+) mice. Additionally there was no phenotypic difference in the induction of heme oxygenase-1 mRNA after acetaminophen administration. This study not only demonstrates the role of GSTP as a direct inhibitor of JNK in vivo but also its role in regulating the constitutive expression of specific downstream molecular targets of the JNK signaling pathway.
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ABSTRACT: High drug attrition rates due to toxicity, the controversy of experimental animal usage, and the EU REACH regulation demanding toxicity profiles of a high number of chemicals demonstrate the need for new, in vitro toxicity models with high predictivity and throughput. Metabolism by cytochrome P450s (P450s) is one of the main causes of drug toxicity. As some of these enzymes are highly polymorphic leading to large differences is metabolic capacity, isotype-specific test systems are needed. In this review, we will discuss the use of "yeast" expressing (mammalian) P450s as a powerful, additional model system in drug safety. We will discuss the various cellular model systems for bioactivation-related toxicity and subsequently describe the properties of yeast as a model system, including the endogenous bioactivation enzymes present, the heterologous expression of (mammalian) P450s and the application of yeasts expressing heterologous P450s and/or other biotransformation enzymes in toxicity studies. All major human drug-metabolizing P450s have been successfully expressed in yeast and various mutagenicity tests have been performed with these humanized yeast strains. The few examples of non-mutagenic toxicity studies with these strains and of the combination of P450s with phase II or other human enzymes show the potential of yeast as a model system in metabolism-related toxicity studies. The wide variety of genome-wide screens available in yeast, combined with its well-annotated genome, also facilitate follow-up studies on the genes involved in toxicity. Unless indicated otherwise yeast will refer to baker's yeast Saccharomyces cerevisiae.Current Drug Metabolism 08/2012; DOI:10.2174/138920012803762783 · 3.49 Impact Factor
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ABSTRACT: Glutathione-S-transferase of the Pi class (GSTP1) is frequently overexpressed in a variety of solid tumors and has been identified as a potential therapeutic target for cancer therapy. GSTP1 is a phase II detoxification enzyme and conjugates the tripeptide glutathione to endogenous metabolites and xenobiotics, thereby limiting the efficacy of antitumor chemotherapeutic treatments. In addition, GSTP1 regulates cellular stress responses and apoptosis by sequestering and inactivating c-Jun N-terminal kinase (JNK). Thiazolides are a novel class of antibiotics for the treatment of intestinal pathogens with no apparent side effects on the host cells and tissue. Here we show that thiazolides induce a GSTP1-dependent and glutathione-enhanced cell death in colorectal tumor cell lines. Downregulation of GSTP1 reduced the apoptotic activity of thiazolides, whereas overexpression enhanced it. Thiazolide treatment caused strong Jun kinase activation and Jun kinase-dependent apoptosis. As a critical downstream target of Jun kinase we identified the pro-apoptotic Bcl-2 homolog Bim. Thiazolides induced Bim expression and activation in a JNK-dependent manner. Downregulation of Bim in turn significantly blocked thiazolide-induced apoptosis. Whereas low concentrations of thiazolides failed to induce apoptosis directly, they potently sensitized colon cancer cells to TNF-related apoptosis-inducing ligand- and chemotherapeutic drug-induced cell death. Although GSTP1 overexpression generally limits chemotherapy and thus antitumor treatment, our study identifies GSTP1 as Achilles' heel and thiazolides as novel interesting apoptosis sensitizer for the treatment of colorectal tumors.Oncogene 12/2011; 31(37):4095-106. DOI:10.1038/onc.2011.575 · 8.56 Impact Factor