Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:2.5.1.18 (glutathione S-transferase)
22,582 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Much progress has been made in elucidating the biochemical and molecular mechanisms that underlie aflatoxin carcinogenesis. In humans, biotransformation of AFB1 to the putative carcinogenic intermediate. AFB-8,9-exo-epoxide, occurs predominantly by cytochromes P450 1A2 and 3A4, with the relative importance of each dependent upon the relative magnitude of expression of the respective enzymes in liver. Genetic variability in the expression of these and other cytochromes P450 may result in substantial interindividual differences in susceptibility to the carcinogenic effects of aflatoxins. Detoxification of AFB-8,9-epoxide by a specific alpha class glutathione S-transferase is an important protective mechanism in mice, and it accounts for the resistance of this species to the carcinogenic effects of AFB. This particular form of GST is expressed constitutively only at low levels in rats, but it is inducible by antioxidants such as ethoxyquin, and it accounts for much of the chemoprotective effects of a variety of substances, including natural dietary components that putatively act via an "antioxidant response element" (ARE). In humans, the constitutively expressed GSTs have very little activity toward AFB1-8,9-exo-epoxide, suggesting that--on a biochemical basis--humans should be quite sensitive to the genotoxic effects of aflatoxins. If a gene encoding a high aflatoxin-active form of GST is present in the human genome, but is not constitutively expressed, and is inducible by dietary antioxidants (as occurs in rats), then chemo- and/or dietary intervention measures aimed at inducing this enzyme could be highly effective. However, as it is possible that human CYP 1A2 may also be inducible by these same chemicals (because of the possible presence of an ARE in this gene), the ultimate consequence of dietary treatment with chemicals that induce biotransformation enzymes via an ARE is uncertain. The balance of the rate of activation (exo-epoxide production) to inactivation (GST conjugation plus other P450-mediated non-epoxide oxidations) may be a strong indicator of individual and species susceptibility to aflatoxin carcinogenesis, if the experimental conditions are reflective of true dietary exposures. There is strong evidence that AFB-8,9-exo-epoxide binds to G:C rich regions of DNA, forming an adduct at the N7-position of guanine. Substantial evidence demonstrates that AFB1-8,9-epoxide can induce activating mutations in the ras oncogene in experimental animals, primarily at codon 12.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Mechanisms of aflatoxin carcinogenesis. 804 48

We have performed comparative studies on the E7 proteins from malignant and non-malignant Human Papillomavirus types HPV 1, 6, 11, 16, 18, 33). GST/E7 fusion proteins from all these HPV types associate with Rb1, p107 and the cyclin A/CDK2 complex. As has been shown for Rb1, the association with p107 and Cyclin A was weaker for the 'low risk' HPV6 and 11 E7 proteins as compared to 'high risk' HPV16, 18 and 33 E7 proteins. In contrast the E7 protein of the benign type HPV1 bound Rb1, p107 and cyclin A with the same affinity as the 'high risk' E7 proteins. The affinities of the E7/Rb1 interaction have been confirmed in vivo by the 'two hybrid' method in the yeast Saccharomyces cerevisiae. Although HPV1 E7 showed the same affinity in vitro and in vivo for Rb1 as the high risk HPV E7s, it did not have the ability to activate the E2F-1 transcription factor inhibited by Rb1, nor did it have any transforming activity when coexpressed with activated ras in primary rodent cells.
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PMID:Functional studies of E7 proteins from different HPV types. 805 27

The activity of several proteins involved in the development of antitumor drug resistance is regulated by protein phosphorylation. These proteins include the mdr-1-encoded P-glycoprotein (Pgp) and topoisomerase II (topo II). The corresponding evidence is reviewed and attempts to modulate multidrug resistance (MDR) by protein kinase C inhibitors are described. The expression of several proteins which are essential in drug resistance is regulated at the transcriptional level, involving protein phosphorylation by members of the protein kinase C (PKC) family, casein kinase II (CKII), and others. These proteins include mdr-1-encoded P-glycoprotein, metallothionein, glutathione S-transferase (GST), dTMP synthase, and the proteins Fos and Jun. The corresponding genes are under positive regulation of ras, which in turn requires the activation of a protein kinase cascade for its function. Protein kinases are therefore potentially useful targets in reducing the expression of proteins involved in the development of multifactorial drug resistance caused by the expression of transforming ras-genes. Attempts to inhibit the ras-induced fos expression by an inhibitor of protein kinase C (ilmofosine) are described. Protein kinase inhibitors are also able to synergistically enhance the cytotoxicity of cis-platinum, which is discussed as resulting from a reduction of PKC-dependent fos expression.
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PMID:Role of protein kinases in antitumor drug resistance. 806 Nov 7

Different domains of the serine/threonine kinase, raf-1, were expressed as fusion proteins with glutathione S-transferase (GST) in Escherichia coli and purified to near homogeneity by affinity chromatography. A cysteine-rich domain of raf-1 was found to contain 2 mol of zinc (molar basis), similar to analogous cysteine-rich domains of protein kinase C. GST-fusion proteins, containing the cysteine-rich domain of raf-1, bound to liposomes in a phosphatidylserine-dependent manner. In contrast to protein kinase C, the translocation of raf-1 was not dependent upon diacylglycerol, phorbol ester, or calcium, nor did raf-1 bind phorbol esters. A GST-fusion protein encoding residues 1-147 of raf-1 bound to normal GTP-ras with high affinity, but not to mutant GTP-Ala35 ras; no binding was detected to GDP-ras. The binding of a smaller fusion protein (residues 1-130 of raf-1) was about 10-fold weaker, inferring that a 17-amino acid sequence represents a critical binding determinant in intact raf-1. These residues are adjacent to the amino-terminal end of, and partially extend into, the cysteine-rich domain (amino acids 139-184). A synthetic peptide corresponding to this 17-amino acid sequence blocked the interaction of raf-1 with ras. The function of the cysteine-rich region of raf-1 homologous to protein kinase C is to promote translocation of raf-1 kinase to membranes and to form part of the high affinity binding site for GTP-ras.
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PMID:The cysteine-rich region of raf-1 kinase contains zinc, translocates to liposomes, and is adjacent to a segment that binds GTP-ras. 814 97

The Bem2 and Bem3 proteins, which appear to play roles in the regulation of bud site formation in Saccharomyces cerevisiae, show striking homology to a number of proteins that compose a family of GTPase-activating proteins (GAPs) for the rho-subgroup of ras-related GTP-binding proteins. These members include human platelet GAP for Cdc42Hs (the human homolog of a S. cerevisiae GTP-binding protein that regulates bud site assembly), the break point cluster region protein, the brain protein chimerin, the 85-kDa regulatory subunit (p85) of the phosphatidylinositol 3-kinase, and the ras-GAP-binding protein (p190). A fusion protein composed of the glutathione S-transferase protein and the rho-GAP homology region of Bem3 (designated GST-Bem3) stimulates the GTPase activity of the wild-type Cdc42Hs protein (Cdc42HsGly-12), but has no stimulatory effect on a GTPase-defective mutant (Cdc42HsVal-12), whereas a GST-Bem2 fusion protein does not stimulate the GTPase activity of either form of Cdc42Hs. We have compared the ability of GST-Bem3 to serve as a GAP for Cdc42Hs relative to other members of the rho-GAP subfamily and found the following order of potency: human platelet Cdc42Hs GAP > p190 > Bem3 > break point cluster region protein, whereas p85, like Bem2, shows no GAP activity or any ability to bind to the GTP-bound form of Cdc42Hs. We have taken advantage of the functional specificity exhibited by Bem3 (versus Bem2) in using Bem2/Bem3 chimeras, as well as different deletion mutant versions of the Bem3 protein, to delineate the limits of a functional Cdc42 GAP domain. The results of this study indicate that the carboxyl-terminal approximately 224 amino acids (which contain three regions of homology to the other members of the rho-GAP family) represent a "limit GAP." The first two appear to be important for binding to Cdc42Hs and for partial GAP activity.
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PMID:Biochemical comparisons of the Saccharomyces cerevisiae Bem2 and Bem3 proteins. Delineation of a limit Cdc42 GTPase-activating protein domain. 822 21

Raf-1 is a serine/threonine kinase which is essential in cell growth and differentiation. Tyrosine kinase oncogenes and receptors and p21ras can activate Raf-1, and recent studies have suggested that Raf-1 functions upstream of MEK (MAP/ERK kinase), which phosphorylates and activates ERK. To determine whether or not Raf-1 directly activates MEK, we developed an in vitro assay with purified recombinant proteins. Epitope-tagged versions of Raf-1 and MEK and kinase-inactive mutants of each protein were expressed in Sf9 cells, and ERK1 was purified as a glutathione S-transferase fusion protein from bacteria. Raf-1 purified from Sf9 cells which had been coinfected with v-src or v-ras was able to phosphorylate kinase-active and kinase-inactive MEK. A kinase-inactive version of Raf-1 purified from cells that had been coinfected with v-src or v-ras was not able to phosphorylate MEK. Raf-1 phosphorylation of MEK activated it, as judged by its ability to stimulate the phosphorylation of myelin basic protein by glutathione S-transferase-ERK1. We conclude that MEK is a direct substrate of Raf-1 and that the activation of MEK by Raf-1 is due to phosphorylation by Raf-1, which is sufficient for MEK activation. We also tested the ability of protein kinase C to activate Raf-1 and found that, although protein kinase C phosphorylation of Raf-1 was able to stimulate its autokinase activity, it did not stimulate its ability to phosphorylate MEK.
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PMID:Reconstitution of the Raf-1-MEK-ERK signal transduction pathway in vitro. 841 57

Xenopus oocytes from unprimed frogs possess insulin-like growth factor I (IGF-I) receptors but lack insulin and IGF-I receptor substrate 1 (IRS-1), the endogenous substrate of this kinase, and fail to show downstream responses to hormonal stimulation. Microinjection of recombinant IRS-1 protein enhances insulin-stimulated phosphatidylinositol (PtdIns) 3-kinase activity and restores the germinal vesicle breakdown response. Activation of PtdIns 3-kinase results from formation of a complex between phosphorylated IRS-1 and the p85 subunit of PtdIns 3-kinase. Microinjection of a phosphonopeptide containing a pYMXM motif with high affinity for the src homology 2 (SH2) domain of PtdIns 3-kinase p85 inhibits IRS-1 association with and activation of the PtdIns 3-kinase. Formation of the IRS-1-PtdIns 3-kinase complex and insulin-stimulated PtdIns 3-kinase activation are also inhibited by microinjection of a glutathione S-transferase fusion protein containing the SH2 domain of p85. This effect occurs in a concentration-dependent fashion and results in a parallel loss of hormone-stimulated oocyte maturation. These inhibitory effects are specific and are not mimicked by glutathione S-transferase fusion proteins expressing the SH2 domains of ras-GAP or phospholipase C gamma. Moreover, injection of the SH2 domains of p85, ras-GAP, and phospholipase C gamma do not interfere with progesterone-induced oocyte maturation. These data demonstrate that phosphorylation of IRS-1 plays an essential role in IGF-I and insulin signaling in oocyte maturation and that this effect occurs through interactions of the phosphorylated YMXM/YXXM motifs of IRS-1 with SH2 domains of PtdIns 3-kinase or some related molecules.
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PMID:Insulin-stimulated oocyte maturation requires insulin receptor substrate 1 and interaction with the SH2 domains of phosphatidylinositol 3-kinase. 841 61

The common cytogenetic finding characteristic of human malignant testicular germ-cell tumors is the presence of an isochromosome of the short arm of chromosome 12, i(12p), suggesting alterations in the proto-oncogenes (e.g., c-Ki-ras2) or putative tumor suppressor genes (TSG) that are localized here. However, to date there is no proof for such alterations. Conversely, alterations in expression of the retinoblastoma gene, a classical TSG, have been reported for the majority of testicular tumors. Other molecular genetic alterations have been described, affecting genes that are involved in the normal regulation of spermiogenesis, such as the c-kit gene product and its ligand SCF, as well as hst1, which is normally expressed in embryonal tissues only. The well-documented sensitivity of testicular tumors to chemotherapeutic agents may be caused by decreased activity of the glutathione S-transferase detoxification enzymes, as well as alterations of the expression of this gene family.
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PMID:[Malignant testicular tumors: cytogenetic and molecular biology principles]. 851 33

A Caenorhabditis elegans cDNA encoding a homologue of the p21 ras-related CDC42, designated as CDC42Ce, was isolated from a nematode mixed stage cDNA library. The encoded protein of 188 amino acid residues has 85% identity to both human G25K and CDC42Hs and 79 and 76% identity to the yeast CDC42Sp and CDC42Sc proteins, respectively. The CDC42Ce cDNA maps to a position on C. elegans chromosome II in close proximity to lin-26, a cell lineage gene. The CDC42Ce cDNA hybridizes to 2- and 1.5-kilobase mRNAs. Their expression is developmentally regulated with highest levels at the embryonic stage, decreasing progressively during development except for an increase of the more abundant 1.5-kilobase mRNA at the L3 stage. The glutathione S-transferase/CDC42Ce fusion protein expressed in Escherichia coli displays both GTP binding and intrinsic GTPase activities. The GTPase activity of CDC42Ce is moderately stimulated by human n-chimaerin, a GTPase-activating protein for the related p21 rac1. The CDC42Ce protein complements the temperature-sensitive lethal mutation cdc42-1 in yeast Saccharomyces cerevisiae. These data suggest that CDC42Ce is the C. elegans homologue of the yeast CDC42. The developmental expression pattern of mRNA and is biochemical properties of its encoded protein which are closely related to CErac1 suggest that the two p21s might be involved in related biological processes.
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PMID:The CDC42 homologue from Caenorhabditis elegans. Complementation of yeast mutation. 851 66

Ras (Ha-Ras, Ki-Ras, N-Ras) is implicated in the regulation of various cell functions such as gene expression and cell proliferation downstream from specific extracellular signals. Here, we partially purified a Ras-interacting protein with molecular mass of about 180 kDa (p180) from bovine brain membrane extract by glutathione S-transferase (GST)-Ha-Ras affinity column chromatography. This protein bound to the GTP gamma S (guanosine 5'-(3-O-thio)triphosphate, a nonhydrolyzable GTP analog).GST-Ha-Ras affinity column but not to those containing GDP.GST-Ha-Ras or GTP gamma S.GST-Ha-Ras with a mutation in the effector domain (Ha-RasA38). The amino acid sequences of the peptides derived from p180 were almost identical to those of human AF-6 that is identified as the fusion partner of the ALL-1 protein. The ALL-1/AF-6 chimeric protein is the critical product of the t (6:11) abnormality associated with some human leukemia. AF-6 has a GLGF/Dlg homology repeat (DHR) motif and shows a high degree of sequence similarity with Drosophila Canoe, which is assumed to function downstream from Notch in a common developmental pathway. The recombinant N-terminal domain of AF-6 and Canoe specifically interacted with GTP gamma S.GST-Ha-Ras. The known Ras target c-Raf-1 inhibited the interaction of AF-6 with GTP gamma S.GST-Ha-Ras. These results indicate that AF-6 and Canoe are putative targets for Ras.
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PMID:Identification of AF-6 and canoe as putative targets for Ras. 855 59


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