Glutathione S-transferase in chemotherapy resistance and in carcinogenesis.

Cytosolic glutathione S-transferases are composed of two monomeric subunits. These monomers are the products of different gene families designated alpha, mu, and pi. Dimerization yields either homodimeric or heterodimeric holoenzymes within the same family. The members of this complex group of proteins have been linked to the detoxification of environmental chemicals and carcinogens, and have been shown to be overexpressed in normal and tumor cells following exposure to cytotoxic drugs. They also are overexpressed in carcinogen-induced rat liver preneoplastic nodules in rat liver. In all of these cases, the changes in expression of glutathione S-transferases are paralleled by increased resistance to cytotoxic chemicals. The degree of resistance is related to the substrate specificity of the isozyme. The relationship of the glutathione S-transferase genes to drug resistance has been directly demonstrated by gene transfer studies, where cDNAs encoding the various subunits of glutathione S-transferase have been transfected into a variety of cell types. This review discusses the results of numerous studies that associate resistance to alkylating agents with overexpression of protective detoxifying glutathione S-transferase enzymes.     

Molecular characterization of corn glutathione S-transferase isozymes involved in herbicide detoxication

Corn ( Zea mays L.) glutathione S-transferases (EC 2.5.1.18) have attracted interest, in part, due to their involvement in the metabolism of several herbicides, including atrazine and alachlor. Three corn, glutathione S-transferases have been purified, and cDNA clones have been isolated and sequenced for two of these, GST I and GST III. In addition to showing some amino acid sequence similarity to each other, the two sequenced corn glutathione S-transferases also show some similarity to rat and human enzymes. The corn glutathione S-transferases responsible for atrazine tolerance have not yet been purified or cloned, but purification attempts indicate that corn has two glutathione S-transferases with activity towards atrazine. While many glutathione S-transferases from various organisms have been detected by using 1-chloro-2,4-dinitrobenzene as a substrate, the atrazine-specific glutathione S-transferases have very little or no activity with 1-chloro-2,4-dinitrobenzene. This shows the importance of assaying with a variety of substrates when characterizing glutathione S-transferases.     

The role of gene splicing, gene amplification and regulation in mosquito insecticide resistance

The primary routes of insecticide resistance in all insects are alterations in the insecticide target sites or changes in the rate at which the insecticide is detoxified. Three enzyme systems, glutathione S-transferases, esterases and monooxygenases, are involved in the detoxification of the four major insecticide classes. These enzymes act by rapidly metabolizing the insecticide to non-toxic products, or by rapidly binding and very slowly turning over the insecticide (sequestration). In Culex mosquitoes, the most common organophosphate insecticide resistance mechanism is caused by co-amplification of two esterases. The amplified esterases are differentially regulated, with three times more Est beta 2(1) being produced than Est alpha 2(1). Cis-acting regulatory sequences associated with these esterases are under investigation. All the amplified esterases in different Culex species act through sequestration. The rates at which they bind with insecticides are more rapid than those for their non-amplified counterparts in the insecticide-susceptible insects. In contrast, esterase-based organophosphate resistance in Anopheles is invariably based on changes in substrate specificities and increased turnover rates of a small subset of insecticides. The up-regulation of both glutathione S-transferases and monooxygenases in resistant mosquitoes is due to the effects of a single major gene in each case. The products of these major genes up-regulate a broad range of enzymes. The diversity of glutathione S-transferases produced by Anopheles mosquitoes is increased by the splicing of different 5' ends of genes, with a single 3' end, within one class of this enzyme family. The trans-acting regulatory factors responsible for the up-regulation of both the monooxygenase and glutathione S-transferases still need to be identified, but the recent development of molecular tools for positional cloning in Anopheles gambiae now makes this possible.     

The role of a novel copper complex in overcoming doxorubicin resistance in Ehrlich ascites carcinoma cells in vivo

One of the important pathways of resistance to anthracyclines is governed by elevated levels of glutathione (GSH) in cancer cells. Resistant cells having elevated levels of GSH show higher expression of multidrug-resistant protein (MRP); the activity of glutathione S-transferases (GSTs) group of enzymes have also been found to be higher in some drug-resistant cells. The general mechanism in this type of resistance seems to be the formation of conjugates enzymatically by GSTs, and subsequent efflux by active transport through MRP (MRP1-MRP9). MRPs act as drug efflux pump and can also co-transport drugs like doxorubicin (Dox) with GSH. Depletion of GSH in resistant neoplastic cells may possibly sensitize such cells, and thus overcome multidrug resistance (MDR). A number of resistance modifying agents (RMA) like DL-buthionine (S, R) sulfoxamine (BSO) and ethacrynic acid (EA) moderately modulate resistance by acting as a GSH-depleting agent. As most of the GSH-depleting agents have dose-related toxicity, development of non-toxic GSH-depleting agent has immense importance in overcoming MDR. The present study describes the resistance reversal potentiality of novel copper complex, viz., copper N-(2-hydroxy acetophenone) glycinate (CuNG) developed by us in Dox-resistant Ehrlich ascites carcinoma (EAC/Dox) cells. CuNG depletes GSH in resistant (EAC/Dox) cells possibly by forming conjugate with it. Depletion of GSH results in higher Dox accumulation that may lead to enhanced rate of apoptosis in EAC/Dox cells. In vivo studies with male Swiss albino mice bearing ascitic growth of EAC/Dox showed tremendous increase in life span (treated/control, T/C = 453%) for the treated group with apparent regression of tumor. Resistance to Dox in EAC/Dox cells is associated with over expression of GST-P1, GST-M1 (enzymes involved in phase II detoxification) and MRP1 (a transmembrane ATPase efflux pump for monoglutathionyl conjugates of xenobiotics). CuNG causes down regulation of all these three proteins in EAC/Dox cells. The effect of CuNG as RMA is better than BSO in many aspects.     

P-glycoprotein, glutathione and glutathione S-transferase increase in a colon carcinoma

The acquisition of resistance to anticancer agents used in chemotherapy is the main cause of treatment failure in malignant disorders, provoking tumours to become resistant during treatment, although they initially respond to it. The main multidrug resistance (MDR) mechanism in tumour cells is the expression of P-gly-coprotein (P-gly), that acts as an ATP-dependent active efflux pump of chemotherapeutic agents. Furthermore, an increased detoxification of compounds mediated by high levels of glutathione (GSH) and glutathione S-transferase (GST), has been found in resistant cells. We developed a study aiming to evaluate the evolution of the main drug resistance markers in tumour cells: P-gly, GSH and GST, during the acquisition of resistance to colchicine, for the purpose of studying the adaptation process and its contribution to the MDR phenomenon. A human colon adenocarcinoma cell line was exposed to colchicine during 82 days, being P-gly, GSH levels and GST activity evaluated by flow cytometry, spectrofluorimetry and spectrophotometry, during exposure time. P-gly and GSH levels increased gradually during the exposure to colchicine, reaching 2.35 and 3.21 fold each. On day 82, GST activity increased 1.84 fold at the end of the exposure period. Moreover, an increment in drug cross-resistance was obtained that ranges from 2.62 to 5.22 fold for colchicine, vinblastine, vincristine and mitomycin C. The increments obtained in P-gly, GSH and GST could probably contribute to the MDR phenomenon in this human colon adenocarcinoma cell line.     

Green tea catechins in chemoprevention of cancer: A molecular docking investigation into their interaction with glutathione S-transferase (GST P1-1)

The anti- and pro-oxidant effects of green tea catechins have been implicated in the alterations of cellular functions determining their chemoprotective and therapeutic potentials in toxiCIT000y and diseases. The glutathione S-transferases (GSTs; EC 2.5.1.18) family is a widely distributed phase-II detoxifying enzymes and the GST P1-1 isoenzyme has been shown to catalyze the conjugation of GSH with some alkylating anti-cancer agents, suggesting that over-expression of GST P1-1 would result in tumor cell resistance. Here we report the docking study of four green tea catechins and four alkylating anticancer drugs into the GST P1-1 model, as GSTs were found to be affected by tea catechins. The EGCG ligands exhibit higher docking potential with respect to the anticancer agents, with a ligand-receptor interaction pattern indicating an high conformational stability. Consequently, the competition mechanisms favourable for the green tea catechins could lead to enzyme(s) desensitisation with a reduction of the alkylating drugs metabolism. The results provide a useful theoretical contribution in understanding the biochemical mechanisms implicated in the chemotherapeutic use of green tea catechins in oxidative stress-related diseases.     

Green tea catechins in chemoprevention of cancer: a molecular docking investigation into their interaction with glutathione S-transferase (GST P1-1)

The anti- and pro-oxidant effects of green tea catechins have been implicated in the alterations of cellular functions determining their chemoprotective and therapeutic potentials in toxicity and diseases. The glutathione S-transferases (GSTs; EC 2.5.1.18) family is a widely distributed phase-II detoxifying enzymes and the GST P1-1 isoenzyme has been shown to catalyze the conjugation of GSH with some alkylating anti-cancer agents, suggesting that over-expression of GST P1-1 would result in tumor cell resistance. Here we report the docking study of four green tea catechins and four alkylating anticancer drugs into the GST P1-1 model, as GSTs were found to be affected by tea catechins. The EGCG ligands exhibit higher docking potential with respect to the anticancer agents, with a ligand-receptor interaction pattern indicating an high conformational stability. Consequently, the competition mechanisms favourable for the green tea catechins could lead to enzyme(s) desensitisation with a reduction of the alkylating drugs metabolism. The results provide a useful theoretical contribution in understanding the biochemical mechanisms implicated in the chemotherapeutic use of green tea catechins in oxidative stress-related diseases.     

The elusive roles of bacterial glutathione<Emphasis Type="Italic"> S-</Emphasis>transferases: new lessons from genomes

Glutathione S-transferases constitute a large family of enzymes which catalyze the addition of glutathione to endogenous or xenobiotic, often toxic electrophilic chemicals. Eukaryotic glutathione S-transferases usually promote the inactivation, degradation or excretion of a wide range of compounds by formation of the corresponding glutathione conjugates. In bacteria, by contrast, the few glutathione S-transferases for which substrates are known, such as dichloromethane dehalogenase, 1,2-dichloroepoxyethane epoxidase and tetrachlorohydroquinone reductase, are catabolic enzymes with an essential role for growth on recalcitrant chemicals. Glutathione S-transferase genes have also been found in bacterial operons and gene clusters involved in the degradation of aromatic compounds. Information from bacterial genome sequencing projects now suggests that glutathione S-transferases are present in large numbers in proteobacteria. In particular, the genomes of three Pseudomonas species each include at least ten different glutathione S-transferase genes. Several of the corresponding proteins define new classes of the glutathione S-transferase family and may also have novel functions that remain to be elucidated.     

Glutathione-related enzymes,glutathione and multidrug resistance

This review examines the hypothesis that glutathione and its associated enzymes contribute to the overall drug-resistance seen in multidrug resistant cell lines. Reports of 34 cell lines independently selected for resistance to MDR drugs are compared for evidence of consistent changes in activity of glutathione-related enzymes as well as for changes in glutathione content. The role of glutathione S-transferases in MDR is further analyzed by comparing changes in sensitivity to MDR drugs in cell lines selected for resistance to non-MDR drugs that have resulting increases in glutathione S-transferase activity. In addition, results of studies in which genes for glutathione S-transferase isozymes were transfected into drug-sensitive cells are reviewed. The role of the glutathione redox cycle is examined by comparing changes in elements of this cycle in MDR cell lines as well as by analyzing reports of the effects of glutathione depletion on MDR drug sensitivity. Overall, there is no consistent or compelling evidence that glutathione and its associated enzymes augment resistance in multidrug resistant cell lines.     

Purification and characterization of a new form of glutathione S-transferase from human erythrocytes

Presence of a new form of glutathione S-transferase has been demonstrated in human erythrocytes. using two different affinity ligands this enzyme has been separated from the previously characterized glutathione S-transferases ?. The new enzyme is highly basic with a pI of > 10. The new enzyme which represents less than 5 percent of glutathione-S-transferase activity towards 1-chloro-2,4-dinitrobenzene as substrate and about 10 percent of total glutathione S-transferase protein of erythrocytes has different amino acid composition, substrate specificities, and immunological characteristics from those of the major erythrocyte glutathione S-transferase ?. Immunological properties of the new enzyme indicate that this form may be different from other glutathione S-transferases of human tissues.     

Quantitative analysis of DNA binding by the Escherichia coli arginine repressor

The cis-trans isomerisation of maleylacetoacetate to fumarylacetoacetate is the penultimate step in the tyrosine/phenylalanine catabolic pathway and has recently been shown to be catalysed by glutathione S-transferase enzymes belonging to the zeta class. Given this primary metabolic role it is unsurprising that zeta class glutathione S-transferases are well conserved over a considerable period of evolution, being found in vertebrates, plants, insects and fungi. The structure of this glutathione S-transferase, cloned from Arabidopsis thaliana, has been solved by single isomorphous replacement with anomalous scattering and refined to a final crystallographic R-factor of 19.6% using data from 25.0 A to 1.65 A. The zeta class enzyme adopts the canonical glutathione S-transferase fold and forms a homodimer with each subunit consisting of 221 residues. In agreement with structures of glutathione S-transferases from the theta and phi classes, a serine residue (Ser17) is present in the active site, at a position that would allow it to stabilise the thiolate anion of glutathione. Site-directed mutagenesis of this residue confirms its importance in catalysis. In addition, the role of a highly conserved cysteine residue (Cys19) present in the active site of the zeta class glutathione S-transferase enzymes is discussed.     

Irreversible inhibition of hepatic glutathione S-transferase by ciprofibrate, a peroxisome proliferator

Ciprofibrate (2-[4-(2,2-dichlorocyclopropyl) phenoxy]2-methyl propionic acid) which is a hypolipidemic agent and has been shown to cause peroxisome proliferation, non-competitively inhibits glutathione S-transferase activity of rat liver, both in vivo and in vitro. Among all the glutathione S-transferases of rat liver, ligandin is maximally inhibited by ciprofibrate. Studies with the purified glutathione S-transferases of rat liver indicate that the affinities of different subunits of liver enzymes for ciprofibrate are in the order Ya greater than Yb, Yb' greater than Yc.     

Rat lung glutathione S-transferases. Evidence for two distinct types of 22000-Mr subunits.

Two immunologically distinct types of 22000-Mr subunits are present in rat lung glutathione S-transferases. One of these subunits is probably similar to Ya subunits of rat liver glutathione S-transferases, whereas the other subunit Ya' is immunologically distinct. Glutathione S-transferase II (pI7.2) of rat lung is a heterodimer (YaYa') of these subunits, and glutathione S-transferase VI (pI4.8) of rat lung is a homodimer of Ya' subunits. On hybridization in vitro of the subunits of glutathione S-transferase II of rat lung three active dimers having pI values 9.4, 7.2 and 4.8 are obtained. Immunological properties and substrate specificities indicate that the hybridized enzymes having pI7.2 and 4.8 correspond to glutathione S-transferases II and VI of rat lung respectively.     

Conjugation of isoprene monoepoxides with glutathione, catalyzed by alpha, mu, pi and theta-class glutathione S-transferases of rat and man

In the present study, the enzymatic conjugation of the isoprene monoepoxides 3,4 epoxy-3-methyl-1-butene (EPOX-I) and 3,4-epoxy-2-methyl-1-butene (EPOX-II) with glutathione was investigated, using purified glutathione S-transferases (GSTs) of the alpha, mu, pi and theta-class of rat and man. HPLC analysis of incubations of EPOX-I and EPOX-II with [35S]glutathione (GSH) showed the formation of two radioactive fractions for each isoprene monoepoxide. The structures of the EPOX-I and EPOX-II GSH conjugates were elucidated with 1H-NMR analysis. As expected, two sites of conjugation were found for both isoprene epoxides. EPOX-II was conjugated more efficiently than EPOX-I. In addition, the mu and theta class glutathione S-transferases were much more efficient than the alpha and pi class glutathione S-transferases, both for rat and man. Because the mu- and theta-class glutathione S-transferases are expressed in about 50 and 40-90% of the human population, respectively, this may have significant consequences for the detoxification of isoprene monoepoxides in individuals who lack these enzymes. Rat glutathione S-transferases were more efficient than human glu tathione S-transferases: rat GST T1-1 showed about 2.1-6.5-fold higher activities than human GST T1-1 for the conjugation of both EPOX-I and EPOX-II, while rat GST M1-1 and GST M2-2 showed about 5.2-14-fold higher activities than human GST M1a-1a. Most of the glutathione S-transferases showed first order kinetics at the concentration range used (50-2000 microM). In addition to differences in activities between GST-classes, differences between sites of conjugation were found. EPOX-I was almost exclusively conjugated with glutathione at the C4-position by all glutathione S-transferases, with exception of rat GST M1-1, which also showed significant conjugation at the C3-position. This selectivity was not observed for the conjugation of EPOX-II. Incubations with EPOX-I and EPOX-II and hepatic S9 fractions of mouse, rat and man, showed similar rates of GSH conjugation for mouse and rat. Compared to mouse and rat, human liver S9 showed a 25-50-fold lower rate of GSH conjugation.     

Reversal of MRP-mediated multidrug resistance in human lung cancer cells by the antiprogestatin drug RU486.

Multidrug resistance-associated protein (MRP) and P-glycoprotein (P-gp) are drug efflux pumps conferring multidrug resistance to tumor cells. RU486, an antiprogestatin drug known to inhibit P-gp function, was examined for its effect on MRP activity in MRP-overexpressing lung tumor GLC4/Sb30 cells. In such cells, the antihormone compound was found to increase intracellular accumulation of calcein, a fluorescent compound transported by MRP, in a dose-dependent manner, through inhibition of cellular export of the dye; in contrast, it did not alter calcein levels in parental GLC4 cells. RU486, when used at 10 microM, a concentration close to plasma concentrations achievable in humans, strongly enhanced the sensitivity of GLC4/Sb30 cells towards two known cytotoxic substrates of MRP, the anticancer drug vincristine and the heavy metal salt potassium antimonyl tartrate. Vincristine accumulation levels were moreover up-regulated in RU486-treated GLC4/Sb30 cells. In addition, such cells were demonstrated to display reduced cellular levels of glutathione which is required for MRP-mediated transport of some anticancer drugs. These findings therefore demonstrate that RU486 can down-modulate MRP-mediated drug resistance, in addition to that linked to P-gp, through inhibition of MRP function.     

Trialkyl phosphorothioates and glutathione S-transferases

Using a rat liver cytosol source of enzyme trialkyl phosphorothioates have been shown to be substrates of glutathione S-transferases. Using OSS-trimethyl phosphorodithioate (OSS-Me(O] and OOS-trimethyl phosphorothioate (OOS-Me(O] the methyl transferred to the sulphydryl of glutathione is that attached to phosphorus via an oxygen atom. Fractionation of liver cytosol has shown that although the bulk activity is due to the three isozymes (1-1; 3-4; 1.2), OSS-Me(O) is a general substrate for glutathione S-transferases. The specific activity is low compared with the substrates 1-chloro-2,4-dinitrobenzene and 1,2-dichloro-4-nitrobenzene.     

A comparison of the glutathione S-transferases of trout and rat liver.

1. Cytosol from trout liver, gills and intestinal caeca has substantial glutathione S-transferase activity. 2. Gel-exclusion and ion-exchange chromatography suggest that trout liver has several glutathione S-transferases with different molecular weights and ionic charges. 3. A component capable of binding lithocholic acid eluted together with glutathione S-transferase activity. Some of the transferase activity did not elute together with binding activity. 4. The enzymic activity from trout liver was less stable at 37 degrees C than that from rat liver. 5. The glutathione S-transferases of fish liver have a similar specific activity to those of rat liver but different molecular properties.     

东亚飞蝗谷胱甘肽S-转移酶RNA干扰效率研究

东亚飞蝗Locusta migratoria manilensis(Meyen)是我国主要的农业害虫之一,已发现东亚飞蝗对某些农药产生了抗性,其抗性机制可能与谷胱甘肽硫转移酶(GST)代谢解毒相关.本研究利用特异性引物合成东亚飞蝗GST 4个不同家族基因的双链RNA(dsRNA),将dsRNA注射到东亚飞蝗幼虫体内,采...