RESUMEN

Glutathione transferases (GSTs) are the primary catalysts protecting from reactive electrophile attack. In this review, the quantitative levels and distribution of glutathione transferases in relation to physiological function are discussed. The catalytic properties (random sequential) tell us that these enzymes have evolved to intercept reactive intermediates. High concentrations of enzymes (up to several hundred micromolar) ensure efficient protection. Individual enzyme molecules, however, turn over only rarely (estimated as low as once daily). The protection of intracellular protein and DNA targets is linearly proportional to enzyme levels. Any lowering of enzyme concentration, or inhibition, would thus result in diminished protection. It is well established that GSTs also function as binding proteins, potentially resulting in enzyme inhibition. Here the relevance of ligand inhibition and catalytic mechanisms, such as negative co-operativity, is discussed. There is a lack of knowledge pertaining to relevant ligand levels in vivo, be they exogenous or endogenous (e.g., bile acids and bilirubin). The stoichiometry of active sites in GSTs is well established, cytosolic enzyme dimers have two sites. It is puzzling that a third of the site's reactivity is observed in trimeric microsomal glutathione transferases (MGSTs). From a physiological point of view, such sub-stoichiometric behavior would appear to be wasteful. Over the years, a substantial amount of detailed knowledge on the structure, distribution, and mechanism of purified GSTs has been gathered. We still lack knowledge on exact cell type distribution and levels in vivo however, especially in relation to ligand levels, which need to be determined. Such knowledge must be gathered in order to allow mathematical modeling to be employed in the future, to generate a holistic understanding of reactive intermediate protection.

Asunto(s)

Glutatión Transferasa , Glutatión Transferasa/metabolismo , Humanos , Cinética , Animales

RESUMEN

Microsomal glutathione transferase 1 (MGST1) is a member of the MAPEG family (membrane associated proteins in eicosanoid and glutathione metabolism), defined according to enzymatic activities, sequence motifs, and structural properties. MGST1 is a homotrimer which can bind three molecules of glutathione (GSH), with one modified to a thiolate anion displaying one-third-of-sites-reactivity. MGST1 has both glutathione transferase and peroxidase activities. Each is based on stabilizing the GSH thiolate in the same active site. MGST1 is abundant in the liver and displays a broad subcellular distribution with high levels in endoplasmic reticulum and mitochondrial membranes, consistent with a physiological role in protection from reactive electrophilic intermediates and oxidative stress. In this review paper, we particularly focus on recent advances made in understanding MGST1 activation, induction, broad subcellular distribution, and the role of MGST1 in apoptosis, ferroptosis, cancer progression, and therapeutic responses.

Asunto(s)

Ferroptosis , Neoplasias , Humanos , Apoptosis , Glutatión , Glutatión Transferasa

RESUMEN

While recent targeted and immunotherapies in malignant melanoma are encouraging, most patients acquire resistance, implicating a need to identify additional drug targets to improve outcomes. Recently, attention has been given to pathways that regulate redox homeostasis, especially the lipid peroxidase pathway that protects cells against ferroptosis. Here we identify microsomal glutathione S-transferase 1 (MGST1), a non-selenium-dependent glutathione peroxidase, as highly expressed in malignant and drug resistant melanomas and as a specific determinant of metastatic spread and therapeutic sensitivity. Loss of MGST1 in mouse and human melanoma enhanced cellular oxidative stress, and diminished glycolysis, oxidative phosphorylation, and pentose phosphate pathway. Gp100 activated pmel-1 T cells killed more Mgst1 KD than control melanoma cells and KD cells were more sensitive to cytotoxic anticancer drugs and ferroptotic cell death. When compared to control, mice bearing Mgst1 KD B16 tumors had more CD8+ T cell infiltration with reduced expression of inhibitory receptors and increased cytokine response, large reduction of lung metastases and enhanced survival. Targeting MGST1 alters the redox balance and limits metastases in melanoma, enhancing the therapeutic index for chemo- and immunotherapies.

Asunto(s)

Antineoplásicos , Neoplasias Pulmonares , Melanoma , Humanos , Ratones , Animales , Glutatión Transferasa/metabolismo , Antineoplásicos/farmacología , Antineoplásicos/uso terapéutico , Estrés Oxidativo , Neoplasias Pulmonares/tratamiento farmacológico , Melanoma/tratamiento farmacológico , Glutatión/metabolismo

RESUMEN

Recent advancements in the treatment of melanoma are encouraging, but there remains a need to identify additional therapeutic targets. We identify a role for microsomal glutathione transferase 1 (MGST1) in biosynthetic pathways for melanin and as a determinant of tumor progression. Knockdown (KD) of MGST1 depleted midline-localized, pigmented melanocytes in zebrafish embryos, while in both mouse and human melanoma cells, loss of MGST1 resulted in a catalytically dependent, quantitative, and linear depigmentation, associated with diminished conversion of L-dopa to dopachrome (eumelanin precursor). Melanin, especially eumelanin, has antioxidant properties, and MGST1 KD melanoma cells are under higher oxidative stress, with increased reactive oxygen species, decreased antioxidant capacities, reduced energy metabolism and ATP production, and lower proliferation rates in 3D culture. In mice, when compared to nontarget control, Mgst1 KD B16 cells had less melanin, more active CD8+ T cell infiltration, slower growing tumors, and enhanced animal survival. Thus, MGST1 is an integral enzyme in melanin synthesis and its inhibition adversely influences tumor growth.

Asunto(s)

Glutatión Transferasa , Melaninas , Melanoma , Animales , Humanos , Ratones , Glutatión Transferasa/genética , Glutatión Transferasa/metabolismo , Melaninas/biosíntesis , Melanoma/genética , Melanoma/inmunología , Melanoma/fisiopatología , Pez Cebra/metabolismo , Oxidación-Reducción , Ratones Endogámicos C57BL , Línea Celular Tumoral , Proliferación Celular/genética

RESUMEN

Glutathione transferases (GSTs) are a class of phase II detoxifying enzymes catalysing the conjugation of glutathione (GSH) to endogenous and exogenous electrophilic molecules, with microsomal glutathione transferase 1 (MGST1) being one of its key members. MGST1 forms a homotrimer displaying third-of-the-sites-reactivity and up to 30-fold activation through modification of its Cys-49 residue. It has been shown that the steady-state behaviour of the enzyme at 5 °C can be accounted for by its pre-steady-state behaviour if the presence of a natively activated subpopulation (~ 10%) is assumed. Low temperature was used as the ligand-free enzyme is unstable at higher temperatures. Here, we overcame enzyme lability through stop-flow limited turnover analysis, whereby kinetic parameters at 30 °C were obtained. The acquired data are more physiologically relevant and enable confirmation of the previously established enzyme mechanism (at 5 °C), yielding parameters relevant for in vivo modelling. Interestingly, the kinetic parameter defining toxicant metabolism, kcat /KM , is strongly dependent on substrate reactivity (Hammett value 4.2), underscoring that glutathione transferases function as efficient and responsive interception catalysts. The temperature behaviour of the enzyme was also analysed. Both the KM and KD values decreased with increasing temperature, while the chemical step k3 displayed modest temperature dependence (Q10 : 1.1-1.2), mirrored in that of the nonenzymatic reaction (Q10 : 1.1-1.7). Unusually high Q10 values for GSH thiolate anion formation (k2 : 3.9), kcat (2.7-5.6) and kcat /KM (3.4-5.9) support that large structural transitions govern GSH binding and deprotonation, which limits steady-state catalysis.

Asunto(s)

Glutatión Transferasa , Proteínas de la Membrana , Catálisis , Glutatión/metabolismo , Glutatión Transferasa/genética , Glutatión Transferasa/metabolismo , Cinética , Temperatura , Animales , Ratas

RESUMEN

Prostaglandin E2 (PGE2) is a lipid mediator of inflammation and cancer progression. It is mainly formed via metabolism of arachidonic acid by cyclooxygenases (COX) and the terminal enzyme microsomal prostaglandin E synthase-1 (mPGES-1). Widely used non-steroidal anti-inflammatory drugs (NSAIDs) inhibit COX activity, resulting in decreased PGE2 production and symptomatic relief. However, NSAIDs block the production of many other lipid mediators that have important physiological and resolving actions, and these drugs cause gastrointestinal bleeding and/or increase the risk for severe cardiovascular events. Selective inhibition of downstream mPGES-1 for reduction in only PGE2 biosynthesis is suggested as a safer therapeutic strategy. This review covers the recent advances in characterization of new mPGES-1 inhibitors in preclinical models and their future clinical applications.

Asunto(s)

Antiinflamatorios no Esteroideos/farmacología , Evaluación Preclínica de Medicamentos/métodos , Prostaglandina-E Sintasas/antagonistas & inhibidores , Animales , Ensayos Clínicos como Asunto , Humanos , Prostaglandina-E Sintasas/metabolismo

RESUMEN

BACKGROUND AND PURPOSE: Microsomal PGE synthase-1 (mPGES-1), the inducible synthase that catalyses the terminal step in PGE2 biosynthesis, is of high interest as therapeutic target to treat inflammation. Inhibition of mPGES-1 is suggested to be safer than traditional NSAIDs, and recent data demonstrate anti-constrictive effects on vascular tone, indicating new therapeutic opportunities. However, there is a lack of potent mPGES-1 inhibitors lacking interspecies differences for conducting in vivo studies in relevant preclinical disease models. EXPERIMENTAL APPROACH: Potency was determined based on the reduction of PGE2 formation in recombinant enzyme assays, cellular assay, human whole blood assay, and air pouch mouse model. Anti-inflammatory properties were assessed by acute paw swelling in a paw oedema rat model. Effect on vascular tone was determined with human ex vivo wire myography. KEY RESULTS: We report five new mPGES-1 inhibitors (named 934, 117, 118, 322, and 323) that selectively inhibit recombinant human and rat mPGES-1 with IC50 values of 10-29 and 67-250 nM respectively. The compounds inhibited PGE2 production in a cellular assay (IC50 values 0.15-0.82 µM) and in a human whole blood assay (IC50 values 3.3-8.7 µM). Moreover, the compounds blocked PGE2 formation in an air pouch mouse model and reduced acute paw swelling in a paw oedema rat model. Human ex vivo wire myography analysis showed reduced adrenergic vasoconstriction after incubation with the compounds. CONCLUSION AND IMPLICATIONS: These mPGES-1 inhibitors can be used as refined tools in further investigations of the role of mPGES-1 in inflammation and microvascular disease.

Asunto(s)

Antiinflamatorios/farmacología , Arterias/efectos de los fármacos , Dinoprostona/biosíntesis , Edema/tratamiento farmacológico , Inhibidores Enzimáticos/farmacología , Tono Muscular/efectos de los fármacos , Prostaglandina-E Sintasas/antagonistas & inhibidores , Células A549 , Animales , Antiinflamatorios/química , Antiinflamatorios/farmacocinética , Arterias/enzimología , Modelos Animales de Enfermedad , Relación Dosis-Respuesta a Droga , Edema/inmunología , Inhibidores Enzimáticos/química , Inhibidores Enzimáticos/farmacocinética , Escherichia coli/genética , Humanos , Técnicas In Vitro , Masculino , Ratones , Ratones Endogámicos C57BL , Estructura Molecular , Contracción Muscular/efectos de los fármacos , Músculo Liso Vascular/efectos de los fármacos , Músculo Liso Vascular/enzimología , Miografía , Prostaglandina-E Sintasas/sangre , Prostaglandina-E Sintasas/genética

RESUMEN

We show for the first time that, in contrast to other glutathione transferases and peroxidases, deletion of microsomal glutathione transferase 1 (MGST1) in mice is embryonic lethal. To elucidate why, we used zebrafish development as a model system and found that knockdown of MGST1 produced impaired hematopoiesis. We show that MGST1 is expressed early during zebrafish development and plays an important role in hematopoiesis. High expression of MGST1 was detected in regions of active hematopoiesis and co-expressed with markers for hematopoietic stem cells. Further, morpholino-mediated knock-down of MGST1 led to a significant reduction of differentiated hematopoietic cells both from the myeloid and the lymphoid lineages. In fact, hemoglobin was virtually absent in the knock-down fish as revealed by diaminofluorene staining. The impact of MGST1 on hematopoiesis was also shown in hematopoietic stem/progenitor cells (HSPC) isolated from mice, where it was expressed at high levels. Upon promoting HSPC differentiation, lentiviral shRNA MGST1 knockdown significantly reduced differentiated, dedicated cells of the hematopoietic system. Further, MGST1 knockdown resulted in a significant lowering of mitochondrial metabolism and an induction of glycolytic enzymes, energetic states closely coupled to HSPC dynamics. Thus, the non-selenium, glutathione dependent redox regulatory enzyme MGST1 is crucial for embryonic development and for hematopoiesis in vertebrates.

Asunto(s)

Diferenciación Celular/genética , Glutatión Transferasa/genética , Hematopoyesis/genética , Hemoglobinas/biosíntesis , Animales , Linaje de la Célula/genética , Técnicas de Silenciamiento del Gen , Glutatión Transferasa/antagonistas & inhibidores , Células Madre Hematopoyéticas/metabolismo , Hemoglobinas/genética , Ratones , Mitocondrias/genética , Mitocondrias/metabolismo , ARN Interferente Pequeño/genética , Pez Cebra/genética , Pez Cebra/crecimiento & desarrollo

RESUMEN

Previous studies that have investigated the association between B-vitamin supplement use and risk for cataract yield conflicting results. The aim of this study was to examine the association between use of high-dose B-vitamin supplements (approximately 10 times recommended daily intake) and risk for age-related cataract in a population-based prospective study of 13 757 women from the Swedish Mammography Cohort and 22 823 men from the Cohort of Swedish Men. Dietary supplement use and potential confounders were assessed using a questionnaire at baseline. Information on cataract diagnosis and extraction was obtained through linkage to registers. During the follow-up period between January 1998 and December 2011, we identified 8395 cataract cases (3851 for women and 4544 for men). The use of B vitamins plus other supplements and B vitamins only was associated with 9 % (95 % CI 2, 17) and 27 % (95 % CI 12, 43) increased risk for cataract, respectively. The hazard ratios for use of B vitamins only and risk for cataract stratified by different age groups were as follows: <60 years: 1·88 (95 % CI 1·47, 2·39); 60-69 years: 1·21 (95 % CI 0·96, 1·53); and ≥70 years: 1·09 (95 % CI 0·91, 1·31) (P interaction=0·002). Our results suggest that the use of high-dose B-vitamin supplements was associated with an increased risk for cataract. This association might be confined to younger participants.

Asunto(s)

Envejecimiento , Catarata/inducido químicamente , Catarata/epidemiología , Complejo Vitamínico B/administración & dosificación , Complejo Vitamínico B/efectos adversos , Anciano , Estudios de Cohortes , Dieta , Suplementos Dietéticos , Femenino , Humanos , Estilo de Vida , Masculino , Persona de Mediana Edad , Fenómenos Fisiológicos de la Nutrición , Estudios Prospectivos , Ingesta Diaria Recomendada , Factores de Riesgo , Encuestas y Cuestionarios , Suecia

RESUMEN

Microsomal glutathione transferase 1 (MGST1) is a detoxification enzyme belonging to the Membrane Associated Proteins in Eicosanoid and Glutathione Metabolism (MAPEG) superfamily. Here we have used electron crystallography of two-dimensional crystals in order to determine an atomic model of rat MGST1 in a lipid environment. The model comprises 123 of the 155 amino acid residues, two structured phospholipid molecules, two aliphatic chains and one glutathione (GSH) molecule. The functional unit is a homotrimer centered on the crystallographic three-fold axes of the unit cell. The GSH substrate binds in an extended conformation at the interface between two subunits of the trimer supported by new in vitro mutagenesis data. Mutation of Arginine 130 to alanine resulted in complete loss of activity consistent with a role for Arginine 130 in stabilizing the strongly nucleophilic GSH thiolate required for catalysis. Based on the new model and an electron diffraction data set from crystals soaked with trinitrobenzene, that forms a dead-end Meisenheimer complex with GSH, a difference map was calculated. The map reveals side chain movements opening a cavity that defines the second substrate site.

Asunto(s)

Glutatión Transferasa/química , Glutatión Transferasa/metabolismo , Proteínas Mutantes/química , Proteínas Mutantes/metabolismo , Animales , Sitios de Unión , Cristalografía , Glutatión/química , Glutatión/metabolismo , Glutatión Transferasa/genética , Microscopía Electrónica de Transmisión , Modelos Moleculares , Mutagénesis , Proteínas Mutantes/genética , Unión Proteica , Conformación Proteica , Multimerización de Proteína , Ratas

RESUMEN

Microsomal glutathione transferase 1 (MGST1) has a unique ability to be activated, ≤30-fold, by modification with sulfhydryl reagents. MGST1 exhibits one-third-of-the-sites reactivity toward glutathione and hence heterogeneous binding to different active sites in the homotrimer. Limited turnover stopped-flow kinetic measurements of the activated enzyme allowed us to more accurately determine the KD for the "third" low-affinity GSH binding site (1.4 ± 0.3 mM). The rate of thiolate formation, k2 (0.77 ± 0.06 s-1), relevant to turnover, could also be determined. By deriving the steady-state rate equation for a random sequential mechanism for MGST1, we can predict KM, kcat, and kcat/KM values from these and previously determined pre-steady-state rate constants (all determined at 5 °C). To assess whether the pre-steady-state behavior can account for the steady-state kinetic behavior, we have determined experimental values for kinetic parameters at 5 °C. For reactive substrates and the activated enzyme, data for the microscopic steps account for the global mechanism of MGST1. For the unactivated enzyme and more reactive electrophilic substrates, pre-steady-state and steady-state data can be reconciled only if a more active subpopulation of MGST1 is assumed. We suggest that unactivated MGST1 can be partially activated in its unmodified form. The existence of an activated subpopulation (approximately 10%) could be demonstrated in limited turnover experiments. We therefore suggest that MSGT1 displays a preexisting dynamic equilibrium between high- and low-activity forms.

Asunto(s)

Glutatión Transferasa/metabolismo , Biocatálisis , Activación Enzimática , Glutatión Transferasa/química , Humanos , Cinética , Modelos Moleculares , Estructura Molecular

RESUMEN

Microsomal glutathione transferase 1 (MGST1) is a membrane bound enzyme involved in the detoxification of reactive electrophiles and protection of membranes from oxidative stress. The enzyme displays an unusual and broad subcellular distribution with especially high levels in the endoplasmic reticulum (ER) and outer mitochondrial membrane (OMM). Here we examined the molecular basis for this dual distribution. We hypothesized that the amphipathic properties of the first transmembrane segment (TMS), that contains a positively charged lysine (K25), is a central feature guiding dual targeting. The lysine-25 was substituted to alanine by site directed mutagenesis. We also increased the amphipathic character of the helix by inserting an additional lysine either one turn above or below K25. Expressing these constructs in simian COS cells, and analyzing subcellular distribution by immunocytochemistry, we observed an increased ER targeting of K25A-MGST1. In contrast I22K-MGST1 and F28K-MGST1 displayed pronounced mitochondrial targeting. By using in vitro transcription-translation we examined whether insertion of WT-MGST1 into ER is co- or post-translational and provide evidence for the former. In the same experimental set-up, mitochondrial insertion was shown to depend on the positive charge. Together these results show that removing the positive charge of lysine-25 promotes ER incorporation, but counteracts mitochondrial insertion. In contrast, introducing an extra lysine in the first TMS of MGST1 had opposite effects. The amphipathic character of the first TMS thus constitutes a molecular determinant for the dual targeting of MGST1. Broad subcellular distribution is consistent with a physiological role in protection from reactive intermediates and oxidative stress.

Asunto(s)

Glutatión Transferasa/metabolismo , Microsomas Hepáticos/metabolismo , Secuencia de Aminoácidos , Animales , Células COS , Línea Celular , Chlorocebus aethiops , Retículo Endoplásmico/metabolismo , Mitocondrias/metabolismo , Membranas Mitocondriales/metabolismo , Estrés Oxidativo/fisiología

RESUMEN

Both soluble and membrane-bound enzymes can catalyze the conversion of lipophilic substrates. The precise substrate access path, with regard to phase, has however, until now relied on conjecture from enzyme structural data only (certainly giving credible and valuable hypotheses). Alternative methods have been missing. To obtain the first experimental evidence directly determining the access paths (of lipophilic substrates) to phase constrained enzymes we here describe the application of a BODIPY-derived substrate (PS1). Using this tool, which is not accessible to cytosolic enzymes in the presence of detergent and, by contrast, not accessible to membrane embedded enzymes in the absence of detergent, we demonstrate that cytosolic and microsomal glutathione transferases (GSTs), both catalyzing the activation of PS1, do so only within their respective phases. This approach can serve as a guideline to experimentally validate substrate access paths, a fundamental property of phase restricted enzymes. Examples of other enzyme classes with members in both phases are xenobiotic-metabolizing sulphotransferases/UDP-glucuronosyl transferases or epoxide hydrolases. Since specific GSTs have been suggested to contribute to tumor drug resistance, PS1 can also be utilized as a tool to discriminate between phase constrained members of these enzymes by analyzing samples in the absence and presence of Triton X-100.

Asunto(s)

Enzimas Inmovilizadas/química , Epóxido Hidrolasas/química , Glucuronosiltransferasa/química , Glutatión Transferasa/química , Sulfotransferasas/química , Animales , Biocatálisis , Compuestos de Boro/química , Citosol/enzimología , Enzimas Inmovilizadas/metabolismo , Epóxido Hidrolasas/metabolismo , Células Eucariotas/enzimología , Colorantes Fluorescentes/química , Glucuronosiltransferasa/metabolismo , Glutatión Transferasa/metabolismo , Humanos , Interacciones Hidrofóbicas e Hidrofílicas , Inactivación Metabólica , Cinética , Microsomas/enzimología , Modelos Moleculares , Octoxinol/química , Especificidad por Sustrato , Sulfotransferasas/metabolismo , Xenobióticos/química , Xenobióticos/metabolismo

RESUMEN

INTRODUCTION: Prostaglandins are signaling molecules that regulate different physiological processes, involving allergic and inflammatory responses and cardiovascular control. They are involved in several pathophysiological processes, including inflammation and cancer. The inducible terminal enzyme, microsomal prostaglandin E synthase 1 (MPGES1), catalyses prostaglandin E2 production during inflammation. MPGES1 has therefore been intensively studied as a pharmaceutical target and many competitive inhibitors targeting its active site have been developed. However, little is known about its catalytic mechanism. AIM: The objective of this study was to investigate which amino acids play a key role in the catalytic mechanism of MPGES1. MATERIALS AND METHODS: Based on results and predictions from previous structural studies, the amino acid residues Asp49, Arg73, Arg126, and Ser127 were chosen and altered by site-directed mutagenesis. The mutated enzyme variants were cloned and expressed in both the E. coli and the Baculovirus expression systems. Their catalytic significance was evaluated by activity measurements with prostanoid profiling. RESULTS AND CONCLUSIONS: Our study shows that Arg126 and Asp49 are absolutely required for the catalytic activity of MPGES1, as when exchanged, the enzyme variants loose activity. Ser127 and Arg73 on the other hand, don't seem to be central to the catalytic mechanism because when exchanged, their variants retain considerable activity. Our finding that the Ser127Ala variant retains activity was surprising since high-resolution structural data supported a role in glutathione activation. The close proximity of Ser127 to the active site is, however, supported since the Ser127Cys variant displays 80% lowered activity.

RESUMEN

Glutathione transferases (GSTs) are often overexpressed in tumors and frequently correlated to bad prognosis and resistance against a number of different anticancer drugs. To selectively target these cells and to overcome this resistance we previously have developed prodrugs that are derivatives of existing anticancer drugs (e.g., doxorubicin) incorporating a sulfonamide moiety. When cleaved by GSTs, the prodrug releases the cytostatic moiety predominantly in GST overexpressing cells, thus sparing normal cells with moderate enzyme levels. By modifying the sulfonamide it is possible to control the rate of drug release and specifically target different GSTs. Here we show that the newly synthesized compounds, 4-acetyl-2-nitro-benzenesulfonyl etoposide (ANS-etoposide) and 4-acetyl-2-nitro-benzenesulfonyl doxorubicin (ANS-DOX), function as prodrugs for GSTA1 and MGST1 overexpressing cell lines. ANS-DOX, in particular, showed a desirable cytotoxic profile by inducing toxicity and DNA damage in a GST-dependent manner compared to control cells. Its moderate conversion of 500 nmol/min/mg, as catalyzed by GSTA1, seems hereby essential since the more reactive 2,4-dinitrobenzenesulfonyl doxorubicin (DNS-DOX) (14000 nmol/min/mg) did not display a preference for GSTA1 overexpressing cells. DNS-DOX, however, effectively killed GSTP1 (20 nmol/min/mg) and MGST1 (450 nmol/min/mg) overexpressing cells as did the less reactive 4-mononitrobenzenesulfonyl doxorubicin (MNS-DOX) in a MGST1-dependent manner (1.5 nmol/min/mg) as shown previously. Furthermore, we show that the mechanism of these prodrugs involves a reduction in GSH levels as well as inhibition of the redox regulatory enzyme thioredoxin reductase 1 (TrxR1) by virtue of their electrophilic sulfonamide moiety. TrxR1 is upregulated in many tumors and associated with resistance to chemotherapy and poor patient prognosis. Additionally, the prodrugs potentially acted as a general shuttle system for DOX, by overcoming resistance mechanisms in cells. Here we propose that GST-dependent prodrugs require a conversion rate "window" in order to selectively target GST overexpressing cells, while limiting their effects on normal cells. Prodrugs are furthermore a suitable system to specifically target GSTs and to overcome various drug resistance mechanisms that apply to the parental drug.

Asunto(s)

Glutatión Transferasa/metabolismo , Profármacos/farmacología , Antineoplásicos/farmacología , Línea Celular Tumoral , Citostáticos/farmacología , Doxorrubicina/farmacología , Resistencia a Antineoplásicos/efectos de los fármacos , Etopósido/farmacología , Glutatión/metabolismo , Humanos , Células MCF-7 , Sulfonamidas/farmacología , Regulación hacia Arriba/efectos de los fármacos

RESUMEN

Microsomal prostaglandin E2 synthase type 1 (mPGES-1) is responsible for the formation of the potent lipid mediator prostaglandin E2 under proinflammatory conditions, and this enzyme has received considerable attention as a drug target. Recently, a high-resolution crystal structure of human mPGES-1 was presented, with Ser-127 being proposed as the hydrogen-bond donor stabilizing thiolate anion formation within the cofactor, glutathione (GSH). We have combined site-directed mutagenesis and activity assays with a structural dynamics analysis to probe the functional roles of such putative catalytic residues. We found that Ser-127 is not required for activity, whereas an interaction between Arg-126 and Asp-49 is essential for catalysis. We postulate that both residues, in addition to a crystallographic water, serve critical roles within the enzymatic mechanism. After characterizing the size or charge conservative mutations Arg-126-Gln, Asp-49-Asn, and Arg-126-Lys, we inferred that a crystallographic water acts as a general base during GSH thiolate formation, stabilized by interaction with Arg-126, which is itself modulated by its respective interaction with Asp-49. We subsequently found hidden conformational ensembles within the crystal structure that correlate well with our biochemical data. The resulting contact signaling network connects Asp-49 to distal residues involved in GSH binding and is ligand dependent. Our work has broad implications for development of efficient mPGES-1 inhibitors, potential anti-inflammatory and anticancer agents.

Asunto(s)

Dipéptidos/química , Oxidorreductasas Intramoleculares/química , Microsomas/enzimología , Catálisis , Dominio Catalítico , Cristalografía por Rayos X , Glutatión/metabolismo , Oxidorreductasas Intramoleculares/metabolismo , Ligandos , Mutagénesis Sitio-Dirigida , Prostaglandina-E Sintasas , Conformación Proteica

RESUMEN

Human microsomal glutathione transferase 2 (MGST2) is a trimeric integral membrane protein that belongs to the membrane-associated proteins in eicosanoid and glutathione metabolism (MAPEG) family. The mammalian MAPEG family consists of six members where four have been structurally determined. MGST2 activates glutathione to form a thiolate that is crucial for GSH peroxidase activity and GSH conjugation reactions with electrophilic substrates, such as 1-chloro-2,4-dinitrobenzene (CDNB). Several studies have shown that MGST2 is able to catalyze a GSH conjugation reaction with the epoxide LTA4 forming the pro-inflammatory LTC4. Unlike its closest homologue leukotriene C4 synthase (LTC4S), MGST2 appears to activate its substrate GSH using only one of the three potential active sites [Ahmad S, et al. (2013) Biochemistry. 52, 1755-1764]. In order to demonstrate and detail the mechanism of one-third of the sites reactivity of MGST2, we have determined the enzyme oligomeric state, by Blue native PAGE and Differential Scanning Calorimetry, as well as the stoichiometry of substrate and substrate analog inhibitor binding to MGST2, using equilibrium dialysis and Isothermal Titration Calorimetry, respectively. Global simulations were used to fit kinetic data to determine the catalytic mechanism of MGST2 with GSH and CDNB (1-chloro-2,4-dinitrobenzene) as substrates. The best fit was observed with 1/3 of the sites catalysis as compared with a simulation where all three sites were active. In contrast to LTC4S, MGST2 displays a 1/3 the sites reactivity, a mechanism shared with the more distant family member MGST1 and recently suggested also for microsomal prostaglandin E synthase-1.

Asunto(s)

Dinitroclorobenceno/química , Glutatión Transferasa/química , Glutatión Transferasa/metabolismo , Glutatión/química , Secuencia de Aminoácidos , Calorimetría , Dominio Catalítico , Dinitroclorobenceno/metabolismo , Electroforesis en Gel de Poliacrilamida , Expresión Génica , Glutatión/metabolismo , Glutatión Transferasa/genética , Humanos , Cinética , Microsomas/enzimología , Simulación de Dinámica Molecular , Datos de Secuencia Molecular , Pichia/genética , Pichia/metabolismo , Multimerización de Proteína , Proteínas Recombinantes/química , Proteínas Recombinantes/genética , Proteínas Recombinantes/metabolismo , Alineación de Secuencia , Homología de Secuencia de Aminoácido

RESUMEN

Thioredoxin reductase 1 (TRXR1) and microsomal glutathione transferase 1 (MGST1) are important redox and detoxifying enzymes in adult life. The aim of this study was to investigate the expression of these enzymes during fetal life. In addition, the role of gene methylation was studied since this might play an important role in the on-and-off switch of gene expression between fetal and adult life. To this end, the expression of the TRXR1-encoding gene TXNRD1 and the MGST1-encoding gene MGST1 was studied in fetal tissues. The mean mRNA expression of TXNRD1 in fetal livers were seven times higher compared to the mean expression in adult livers (p < 0.001). Of the six studied splice variants of TXNRD1, four had a significantly higher expression in the fetal livers as compared to adult livers. The mean expression of MGST1 was twofold higher in adult compared to fetal liver tissue (p = 0.01). For MGST1 the alternative first exon 1B was the predominant splice variant in both fetal and adult liver samples. The highest mRNA expression of both TXNRD1 and MGST1 was found in fetal adrenals, whereas expression was lower in fetal liver, lungs and kidneys. There was a significant correlation between the hepatic expression of TXNRD1 and MGST1. Treatment with the demethylating agent 5-AZA resulted in decreased levels of TXNRD1 in human liver HepG2 cells but did not affect the expression of MGST1. In conclusion, the expression of TXNRD1 is higher in fetuses than in adults and might be of importance during fetal life. Hepatic TXNRD1 and MGST1 are co-expressed in both fetuses and adults suggesting common regulatory mechanisms.

RESUMEN

A recent study identified a haplotype on a small region of chromosome 12, between markers D12S1725 and D12S1596, shared by all patients with familial neuroblastoma (NB). We previously localized the human MGST1 gene, whose gene product protects against oxidative stress, to this very same chromosomal region (12p112.1-p13.33). Owing to the chromosomal location of MGST1; its roles in tumorigenesis, drug resistance, and oxidative stress; and the known sensitivity of NB cell lines to oxidative stress, we considered a role for MGST1 in NB development. Surprisingly there was no detectable MGST1 mRNA or protein in either NB cell lines or NB primary tumor tissue, although all other human tissues, cell lines, and primary tumor tissue examined to date express MGST1 at high levels. The mechanism behind the failure of NB cells and tissue to express MGST1 mRNA is unknown and involves the failure of MGST1 pre-mRNA expression, but does not involve chromosomal rearrangement or nucleotide variation in the promoter, exons, or 3' untranslated region of MGST1. MGST1 provides significant protection against oxidative stress and constitutes 4 to 6% of all protein in the outer membrane of the mitochondria. As NB cells are extremely sensitive to oxidative stress, and often used as a model system to investigate mitochondrial response to endogenous and exogenous stress, these findings may be due to the lack of expression MGST1 protein in NB. The significance of this finding to the development of neuroblastoma (familial or otherwise), however, is unknown and may even be incidental. Although our studies provide a molecular basis for previous work on the sensitivity of NB cells to oxidative stress, and possibly marked variations in NB mitochondrial homeostasis, they also imply that the results of these earlier studies using NB cells are not transferable to other tumor and cell types that express MGST1 at high concentrations.

Asunto(s)

Glutatión Transferasa/biosíntesis , Neuroblastoma/genética , Estrés Oxidativo/genética , ARN Mensajero/biosíntesis , Carcinogénesis/genética , Línea Celular Tumoral , Exones , Regulación Neoplásica de la Expresión Génica , Humanos , Mitocondrias/genética , Neuroblastoma/patología , Regiones Promotoras Genéticas

RESUMEN

Oxidative stress and inflammation may be involved in the etiology of age-related cataract. This study is the first to investigate the association between urinary levels of 8-iso-prostaglandin F2α (PGF2α; as a biomarker for systemic oxidative stress in vivo) and 15-keto-dihydro-PGF2α (as a biomarker for systemic inflammation in vivo) and risk of age-related cataract. We observed in a nested case-control study, including 258 women with incident cataract diagnosis and/or cataract extraction and 258 women without cataract, matched on age and date of urine sample collection that, women with higher levels of urinary 8-iso-PGF2α as compared with lower levels had an increased risk of age-related cataract. There was no difference in 15-keto-dihydro-PGF2α levels between cases and controls. Our observations lead to the hypothesis that higher systemic oxidative stress increases the risk of developing age-related cataract.

Asunto(s)

Envejecimiento/metabolismo , Envejecimiento/patología , Catarata/metabolismo , Inflamación/metabolismo , Estrés Oxidativo , Anciano , Estudios de Casos y Controles , Catarata/patología , Catarata/orina , Dinoprost/análogos & derivados , Dinoprost/orina , Femenino , Humanos