Induction of gamma-glutamylcysteine synthetase by prostaglandin A2 in L-1210 cells

Bovine in vitro oocyte maturation as a model for manipulation of the γ-glutamyl cycle and intraoocyte glutathione

Glutathione (GSH) is the main non-enzymatic defence against oxidative stress and is a critical intracellular component required for oocyte maturation. In the present study, several modulators of intracellular GSH were assessed for their effect on the in vitro maturation (IVM) and intracellular GSH content of bovine metaphase (MII) oocytes. Of the five GSH modulators tested, only the cell-permeable GSH donor glutathione ethyl ester (GSH-OEt) significantly increased the GSH content of IVM MII oocytes in a concentration-dependent manner without adversely affecting oocyte maturation rate. The GSH level in IVM MII oocytes was greatly influenced by the presence or absence of cumulus cells and severely restricted when oocytes were cultured in the presence of buthionine sulfoximine (BSO), an inhibitor of GSH synthesis. The addition of GSH-OEt to cumulus-denuded or BSO-treated oocytes increased the GSH content of bovine MII oocytes. Supplementation of the maturation medium with bovine serum albumin (BSA) or fetal calf serum (FCS) affected the GSH content of IVM MII oocytes, with greater levels attained under BSA culture conditions. The addition of GSH-OEt to the maturation medium increased the GSH content of IVM MII oocytes, irrespective of protein source. Spindle morphology, as assessed by immunocytochemistry and confocal microscopy, displayed distinct alterations in response to changes in oocyte GSH levels. GSH depletion caused by BSO treatment tended to widen spindle poles and significantly increased spindle area. Supplementation of the IVM medium with GSH-OEt increased spindle length, but did not significantly alter spindle area or spindle morphology. GSH-OEt represents a novel oocyte-permeable and cumulus cell-independent approach for effective elevation of mammalian oocyte GSH levels.

The anti-inflammatory prostaglandin 15d-PGJ2 decreases oxidative/nitrosative mediators in brain after acute stress in rats

RATIONALE

Immobilisation stress is followed by accumulation of oxidative/nitrosative mediators in brain after the release of tumour necrosis factor-alpha (TNFalpha) and other cytokines, nuclear factor kappa B (NFkappaB) activation, nitric oxide synthase-2 (NOS-2) and cyclooxygenase-2 (COX-2) expression in the brain.

OBJECTIVES

This study was conducted to assess if some of the anti-inflammatory products of COX can modify the accumulation of oxidative/nitrosative species seen in brain after stress and to study the mechanisms by which this effect is achieved.

METHODS

Young-adult male Wistar rats were subjected to a single session of immobilisation during 6 h.

RESULTS

In stressed animals, brain levels of the anti-inflammatory 15d-PGJ2 increases concomitantly with COX-2 expression. Inhibition of COX-2 with NS-398 prevents stress-induced 15d-PGJ2 increase. Injection of supraphysiological doses of 15d-PGJ2 (80-120 microg/kg) decreases stress-induced increase in NOS-2 activity as well as the stress-induced increase in NO metabolites. On the other hand, 15d-PGJ2 decreases stress-induced malondialdehyde (an indicator of lipid peroxidation) accumulation in cortex and prevents oxidation of the main anti-oxidant glutathione. The mechanisms involved in the anti-oxidative properties of 15d-PGJ2 in stress involve NFkappaB blockade (by preventing stress-induced IkappaBalpha decrease) as well as inhibition of TNFalpha release in stressed animals. At the doses tested, 15d-PGJ2 decreases COX-2 expression and PGE2 release during stress, suggesting an alternative mechanism for this endogenous compound.

CONCLUSIONS

These findings demonstrate a role for this anti-inflammatory pathway in the brain response to stress and open the possibility for preventing accumulation of oxidative/nitrosative species and subsequent brain damage.

Stable transfection of Chinese hamster ovary cells with glutamate-cysteine ligase catalytic subunit cDNA confers increased resistance to tert-butyl hydroperoxide toxicity

Glutathione (GSH) plays vital roles in antioxidant defense mechanisms. To determine whether gene transfection strategies could be used to enhance GSH synthetic capacities and protect mammalian cells against oxidant stresses, we used liposome-mediated transfer of the cDNA for rat glutamate-cysteine ligase (GLCL) catalytic subunit (GLCLC) to transfect Chinese hamster ovary (CHO) cells. CHO cell lines (CHOhi) with stably enhanced GLCL activities (14.61+/-0.82 mU/mg protein) and greater GSH contents (45.7+/-1.37 nmol/mg protein) than observed in wild-type CHO K1 cells (0.26+/-0.01 mU/mg protein and 20.7+/-1.15 nmol/mg protein, respectively) were developed and were confirmed to have integrated the GLCLC cDNA into their genomic DNA and to exhibit increased GLCLC mRNA levels, by Southern and northern analyses, respectively. Similarly treated and selected CHO cell lines that showed no increases in GLCL activities (CHOun) were studied as controls for the effects of GLCLC transgene expression. CHOhi cells showed significantly greater resistance to oxidant stress caused by exposure to tert-butyl hydroperoxide (tBuOOH) than did CHO or CHOun cells. Twenty-four hours after exposure to 400 or 800 microM tBuOOH, wild-type CHO cells had released more cellular lactate dehydrogenase (67.3+/-14.5% and 94.4+/-2%) than had CHOhi cells (5.11+/-0.5% and 46.0+/-5.4%, n=4, P<0.05). The present data demonstrate improved resistance to oxidant injury of CHO cells stably transfected with the GLCLC cDNA. Although additional enhancements in GLCL activities are possible by transfection with cDNAs for both catalytic and regulatory GLCL subunits, our results demonstrate that the increases in GLCL activities that can be attained by transfection of the GLCLC cDNA alone can enhance cellular antioxidant defense function.

Biphasic effects of 15-deoxy-delta(12,14)-prostaglandin J(2) on glutathione induction and apoptosis in human endothelial cells

The lipid products derived from the cyclooxygenase pathway can have diverse and often contrasting effects on vascular cell function. Cyclopentenone prostaglandins (cyPGs), such as 15-deoxy-Delta(12,14)-prostaglandin-J(2) (15d-PGJ(2)), a peroxisome proliferator-activated receptor-gamma (PPARgamma) agonist, have been reported to cause endothelial cell apoptosis, yet in other cell types, cyPGs induce cytoprotective mediators, such as heat shock proteins, heme oxygenase-1, and glutathione (GSH). Herein, we show in human endothelial cells that low micromolar concentrations of 15d-PGJ(2) enhance GSH-dependent cytoprotection through the upregulation of glutamate-cysteine ligase, the rate-limiting enzyme of GSH synthesis, as well as GSH reductase. The effect of 15d-PGJ(2) on GSH synthesis is attributable to the cyPG structure but is independent of PPAR, inasmuch as the other cyPGs, but not PPARgamma or PPARalpha agonists, are able to increase GSH. The increase in cellular GSH is accompanied by abrogation of the proapoptotic effects of 4-hydroxynonenal, a product of lipid peroxidation present in atherosclerotic lesions. However, higher concentrations of 15d-PGJ(2) (10 micromol/L) cause endothelial cell apoptosis, which is further enhanced by depletion of cellular GSH by buthionine sulfoximine. We propose that the GSH-dependent cytoprotective pathways induced by 15d-PGJ(2) contribute to its antiatherogenic effects and that these pathways are distinct from those leading to apoptosis.

Cyclopentenone prostaglandins: new insights on biological activities and cellular targets

The cyclopentenone prostaglandins PGA2, PGA1, and PGJ2 are formed by dehydration within the cyclopentane ring of PGE2, PGE1, and PGD2. PGJ2 is metabolized further to yield Delta(12)-PGJ(2) and 15-deoxy-Delta(12,14)-PGJ(2) (15d-PGJ(2)). Various compounds within the cyclopentenone prostaglandin family possess potent anti-inflammatory, anti-neoplastic, and anti-viral activity. Most actions of the cyclopentenone prostaglandins do not appear to be mediated by binding to G-protein coupled prostanoid receptors. Rather, the bioactivity of these compounds results from their interaction with other cellular target proteins. 15-deoxy-Delta(12,14)-PGJ(2) is a high affinity ligand for the nuclear receptor PPARgamma and modulates gene transcription by binding to this receptor. Other activities of the cyclopentenone prostaglandins are mediated by the reactive alpha,beta-unsaturated carbonyl group located in the cyclopentenone ring. The transcription factor NF-kappaB and its activating kinase are key targets for the anti-inflammatory activity of 15d-PGJ2, which inhibits NF-kappaB-mediated transcriptional activation by PPARgamma-dependent and independent molecular mechanisms. Other cyclopentenone prostaglandins, such as Delta(7)-PGA1 and Delta(12)-PGJ2, have strong anti-tumor activity. These compounds induce cell cycle arrest or apoptosis of tumor cells depending on the cell type and treatment conditions. We review here recent progress in understanding the mechanisms of action of the cyclopentenone prostaglandins and their possible use as therapeutic agents.

15-Deoxy-Delta(12,14)-prostaglandin J(2) facilitates thyroglobulin production by cultured human thyrocytes

A cyclopentenone-type prostaglandin, 15-deoxy-Delta(12, 14)-prostaglandin J(2) (15-d-PGJ(2)), has been shown to induce the cellular stress response and to be a ligand for the peroxisome proliferator-activated receptor (PPAR)-gamma. We studied its effect on the basal and thyrotropin (TSH)-induced production of thyroglobulin (TG) by human thyrocytes cultured in the presence of 10% FBS. In 15-d-PGJ(2)-treated cells in which the agent itself did not stimulate cAMP production, both the basal production of TG and the response to TSH were facilitated, including the production of TG and cAMP, whereas such production was decreased in untreated cells according to duration of culture. PGD(2) and PGJ(2), which are precursors to 15-d-PGJ(2), exhibited an effect similar to 15-d-PGJ(2). However, the antidiabetic thiazolidinediones known to be specific ligands for PPAR-gamma, and WY-14643, a specific PPAR-alpha ligand, lacked this effect. 15-d-PGJ(2) and its precursors, but not the thiazolidinediones, induced gene expression for heme oxygenase-1 (HO-1), a stress-related protein, and strongly inhibited interleukin-1 (IL-1)-induced nitric oxide (NO) production. Cyclopentenone-type PGs have been recently shown to inhibit nuclear factor-kappaB (NF-kappaB) activation via a direct and PPAR-independent inhibition of inhibitor-kappaB kinase, suggesting that, in human thyrocytes, such PGs may inhibit IL-1-induced NO production, possibly via an inhibition of NF-kappaB activation. On the other hand, sodium arsenite, a known activator of the stress response pathway, induced HO-1 mRNA expression but lacked a promoting effect on TG production. Thus 15-d-PGJ(2) and its precursors appear to facilitate TG production via a PPAR-independent mechanism and through a different pathway from the cellular stress response that is available to cyclopentenone-type PGs. Our findings reveal a novel role of these PGs associated with thyrocyte differentiation.

Cyclopentenone prostaglandin 15-deoxy-Delta(12,14)-prostaglandin J(2) acts as a general inhibitor of inflammatory responses in activated BV-2 microglial cells

15-deoxy-Delta(12,14)-PGJ(2), a cyclopentenone derivative of PGD(2), was recently reported [Petrova et al., Proc. Natl. Acad. Sci. USA 96 (1999) 4668-4673] to suppress inducible nitric oxide synthase (iNOS) production in microglia and mixed glial cultures stimulated with lipopolysaccharide (LPS). We report here that in addition to suppressing iNOS production, 15d-PGJ(2) also decreases the production of tumor necrosis factor alpha (TNFalpha), interleukin-1 beta (IL-1beta) and cyclooxygenase-2 (COX-2) in LPS-stimulated BV-2 microglial cells, thereby acting as a general inhibitor of microglial activation. Concomitantly, 15d-PGJ(2) itself up-regulates the production of the antioxidant enzyme heme oxygenase-1 (HO-1) and increases intracellular total glutathione levels. To test if increased HO-1 levels were involved in the ability of 15d-PGJ(2) to block microglial activation, we used a HO-1 inhibitor that could block the activity of HO-1. The presence of the HO-1 inhibitor did not alter the 15d-PGJ(2)-induced inhibition of LPS-stimulated iNOS and TNFalpha protein levels, and led to only a partial reduction in the protection offered by 15d-PGJ(2) against LPS-induced nitrite production. These results suggest that HO-1 upregulation by 15d-PGJ(2) is not the primary pathway responsible for the anti-inflammatory action of 15d-PGJ(2) in microglial cells.

Regulation of gamma-glutamylcysteine synthetase subunit gene expression: insights into transcriptional control of antioxidant defenses

Gamma-glutamylcysteine synthetase (GCS; also referred to as glutamate-cysteine ligase, GLCL) catalyzes the rate-limiting reaction in glutathione (GSH) biosynthesis. The GCS holoenzyme is composed of a catalytic and regulatory subunit, each encoded by a unique gene. In addition to some conditions which specifically upregulate the catalytic subunit gene, expression of both genes is increased in response to many Phase II enzyme inducers including oxidants, heavy metals, phenolic antioxidants and GSH-conjugating agents. Electrophile Response Elements (EpREs), located in 5'-flanking sequences of both the GCSh and GCSl subunit genes, are hypothesized to at least partially mediate gene induction following xenobiotic exposure. Recent experiments indicate that the bZip transcription factor Nrf2 participates in EpRE-mediated GCS subunit gene activation in combination with other bZip proteins. An AP-1-like binding sequence and an NF-kappaB site have also been implicated in regulation of the catalytic subunit gene following exposure to certain pro-oxidants. Potential signaling mechanisms mediating GCS gene induction by the diverse families of Phase II enzyme inducers include thiol modification of critical regulatory sensor protein(s) and the generation of the reactive oxygen species. This review summarizes recent progress in defining the molecular mechanisms operative in transcriptional control of the genes encoding the two GCS subunits, identifying areas of agreement and controversy. The mechanisms involved in GCS regulation might also be relevant to the transcriptional control of other components of the antioxidant defense battery.

Multi-faceted regulation of gamma-glutamylcysteine synthetase

Glutathione is an important antioxidant that is involved in numerous cellular activities. gamma-Glutamylcysteine synthetase (gammaGCS) is a key regulatory enzyme in the synthesis of glutathione. It is a heterodimeric zinc metalloprotein that belongs to a unique class of proteins that gain activity due to formation of a reversible disulfide bond. The two subunits of gammaGCS exhibit differential and coordinate transcription regulation. In addition, the subunits are regulated at the posttranscriptional and posttranslational levels. These various levels of regulation allow numerous stimuli to induce or inhibit activity.

Biologic and pharmacologic regulation of mammalian glutathione synthesis

Glutathione (L-gamma-glutamyl-L-cysteinylglycine, GSH) is synthesized from its constituent amino acids by the sequential action of gamma-glutamylcysteine synthetase (gamma-GCS) and GSH synthetase. The intracellular GSH concentration, typically 1-8 mM, reflects a dynamic balance between the rate of GSH synthesis and the combined rate of GSH consumption within the cell and loss through efflux. The gamma-GCS reaction is rate limiting for GSH synthesis, and regulation of gamma-GCS expression and activity is critical for GSH homeostasis. Transcription of the gamma-GCS subunit genes is controlled by a variety of factors through mechanisms that are not yet fully elucidated. Glutathione synthesis is also modulated by the availability of gamma-GCS substrates, primarily L-cysteine, by feedback inhibition of gamma-GCS by GSH, and by covalent inhibition of gamma-GCS by phosphorylation or nitrosation. Because GSH plays a critical role in cellular defenses against electrophiles, oxidative stress and nitrosating species, pharmacologic manipulation of GSH synthesis has received much attention. Administration of L-cysteine precursors and other strategies allow GSH levels to be maintained under conditions that would otherwise result in GSH depletion and cytotoxicity. Conversely, inhibitors of gamma-GCS have been used to deplete GSH as a strategy for increasing the sensitivity of tumors and parasites to certain therapeutic interventions.

Interactions of prostaglandin A2 with the glutathione-mediated biotransformation system

The cyclopentenone prostaglandin A2 (PGA2) is known to inhibit cell proliferation, and metabolism of this compound thus might be important in controlling its ultimate function. The glutathione-related metabolism of PGA2 was therefore investigated both with purified glutathione S-transferase P1-1 (GSTP1-1) and with IGR-39 human melanoma cells. Firstly, the irreversible inhibition of human GSTP1-1 and its mutants C47S, C101S, and C47S/C101S was studied. PGA2 appeared to inhibit GSTP1-1 mainly by binding to the cysteine 47 moiety of the enzyme. This binding was reversed by a molar excess of GSH, indicating that retro-Michael cleavage occurs. Secondly, after exposing IGR-39 human melanoma cells to PGA2, both diastereoisomers of the PGA2-glutathione conjugate are excreted into the medium, although with a clear excess of the S-form, due to its preferential formation by the GSTP1-1 present in the cells. Thirdly, the effect of PGA2 on intracellular GST activity was determined by quantification of the excreted glutathione conjugate S-(2,4-dinitrophenyl)glutathione (DNPSG) after exposure to 1-chloro-2,4-dinitrobenzene. DNPSG excretion was inhibited after incubation with 10 or 20 microM PGA2 for 1 or 4 hr, as a result of glutathione depletion, reversible GST inhibition, and covalent modification of intracellular GST. Furthermore, PGA2 also inhibited transport of DNPSG by the multidrug resistance-associated protein, an effect that was reversible and competitive. In conclusion, PGA2 modulates all three aspects of the glutathione-mediated biotransformation system, i.e. GSH levels, GSTP1-1 activity, and transport of GSH conjugates. A role for GSTP1-1 as a specific transport protein inside the cell is indicated.

gamma-glutamylcysteine synthetase: mRNA stabilization and independent subunit transcription by 4-hydroxy-2-nonenal

gamma-Glutamylcysteine synthetase (GCS), the rate-limiting enzyme in de novo glutathione (GSH) synthesis, is composed of one catalytic (heavy) and one regulatory (light) subunit. Although both subunits are increased at the mRNA level by oxidants, it is not clear whether they are regulated through the same mechanism. 4-Hydroxy-2-nonenal (4HNE), a lipid peroxidation product, may act as a mediator for the induction of gene expression by oxidants. In the present study, 4HNE was used to study the mechanism of induction of the two GCS subunits in rat lung epithelial L2 cells. 4HNE increased both the transcription rates and the stability of mRNA for both GCS subunits, resulting in an increased mRNA content for both subunits. Both GCS subunit proteins and enzymatic activities also increased. Emetine, a protein synthesis inhibitor, blocked the increase in GCS light subunit mRNA but not the increase in GCS heavy subunit mRNA. This suggested that although 4HNE increased transcription and stabilization of both GCS subunit mRNAs, the signaling pathways involved in the induction of the two GCS subunits differed.

Induction of apoptosis, p53 and heme oxygenase-1 by cytotoxic prostaglandin delta12-PGJ2 in transformed endothelial cells

Delta12-prostaglandin (PG)J2, which has been reported to have potent growth inhibitory activity in various tumor cells, induced apoptosis at 5 microg/ml culture medium in transformed mouse endothelial (F2) cells. Immunoblot analysis using anti-p53 or anti-WAF1 antibodies demonstrated that these two proteins had increased following delta12-PGJ2 treatment in F2 cells. Western blotting analysis using anti-heme oxygenase-1 (heat shock protein (HSP)32) antibody also revealed that delta12-PGJ2 induced HSP32 formation in F2 cells. HSP32 was also induced by heat shock treatment at 43 degrees C for 90 min. In contrast, HSP72 was not induced by heat shock or by delta12-PGJ2 treatment. In agreement with these findings, HSP32 immunofluorescence in the cytoplasm of F2 cells was intensified by delta12-PGJ2 treatment. More intense HSP32 immunoreactivity was similarly observed after heat shock treatment. These results suggest that delta12-PGJ2 caused the apoptotic cell death of F2 cells, which involved a certain process required for p53 or HSP32 induction.

Cytosolic phospholipase A2 (PLA2), but not secretory PLA2, potentiates hydrogen peroxide cytotoxicity in kidney epithelial cells

Phospholipase A2 (PLA2) and reactive oxygen species have been implicated both individually and synergistically in various forms of cellular injury. The form(s) of PLA2 important for cell injury and the implications of enhanced activity of the enzyme, however, have not been discerned. Previous studies reveal an increase in PLA2 activity associated with cell injury, but this association does not establish a causal relationship between the increase in activity and the injury. LLC-PK1 cell lines were created that express either the cytosolic PLA2 or a group II PLA2. The susceptibility of these cells to hydrogen peroxide toxicity was determined in order to evaluate the relative importance of these two forms of PLA2 in oxidant injury. Expression of cytosolic PLA2 in the LLC-cPLA2 cell line was associated with a 50-fold increase in PLA2 activity in the cytosolic fraction, an increase in agonist-stimulated arachidonate release, and immunodetection of the cytosolic PLA2 protein that was undetectable in control cells. Exposure to hydrogen peroxide or menadione, but not mercuric chloride, resulted in significantly greater lactate dehydrogenase release in LLC-cPLA2 cells when compared with control cells. Exogenous arachidonic acid (150 microM) did not enhance hydrogen peroxide-induced injury. The intracellular calcium chelator, 1,2-bis-(o-aminophenoxy)ethane-N,N,N', N'-tetraacetic acid/tetra(acetoxymethyl) ester, protected the cells against injury, but the calcium ionophore, A23187, did not increase injury. Glycine conferred no protective effect against hydrogen peroxide toxicity. By contrast to these results with cytosolic PLA2-expressing cells, secretory PLA2 expression to very high levels did not increase susceptibility to hydrogen peroxide. Thus, cytosolic PLA2 may an be an important mediator of oxidant damage to renal epithelial cells.

Involvement of protein kinase in delta 12-prostaglandin J2-induced expression of rat heme oxygenase-1 gene

We recently identified the cis-regulatory element and its specific nuclear binding factors for delta 12-prostaglandin (PG) J2-induced expression of the rat heme oxygenase, HO-1 [Koizumi, T., Odani, N., Okuyama, T., Ichikawa, A. and Negishi, M. (1995) J. Biol. Chem. 270, in press]. Here we further examined the molecular mechanism underlying the delta 12-PGJ2-induced HO-1 gene expression. Protein kinase inhibitors, 2-aminopurine and staurosporine, suppressed the delta 12-PGJ2-induced HO-1 mRNA and the nuclear protein binding to the delta 12-PGJ2-responsive cis-regulatory element in rat basophilic leukemia cells. Furthermore, the nuclear protein binding to the element was suppressed by in vitro phosphatase treatment of the nuclear proteins from delta 12-PGJ2-treated cells. These findings suggest that delta 12-PGJ2 induces the expression of the HO-1 gene through phosphorylation of the nuclear proteins which bind to the delta 12-PGJ2-responsive element.

Identification of a cis-regulatory element for delta 12-prostaglandin J2-induced expression of the rat heme oxygenase gene

We recently reported that delta 12-prostaglandin (PG) J2 caused various cells to synthesize heme oxygenase, HO-1 (Koizumi, T., Negishi, M., and Ichikawa, A. (1992) Prostaglandins 43, 121-131). Here we examined the molecular mechanism underlying the delta 12-PGJ2-induced HO-1 synthesis. delta 12-PGJ2 markedly stimulated the promoter activity of the 5'-flanking region of the rat HO-1 gene from -810 to +101 in rat basophilic leukemia cells. From functional analysis of various deletion mutant genes we found that the delta 12-PGJ2-responsive element was localized in a region from -690 to -660, containing an E-box motif, which was essential for the delta 12-PGJ2-stimulated promoter activity. When the region containing the delta 12-PGJ2-responsive element was combined with a heterologous promoter, SV40 promoter, in the sense and antisense direction, the element showed an enhancer activity in response to delta 12-PGJ2. Gel mobility shift assays demonstrated that delta 12-PGJ2 specifically stimulated the binding of two nuclear proteins to the E-box motif of this region. These results indicate that delta 12-PGJ2 induces the expression of the rat HO-1 gene through nuclear protein binding to a specific element having an E-box motif.

Induction by prostaglandin A1 of haem oxygenase in myoblastic cells: an effect independent of expression of the 70 kDa heat shock protein

Prostaglandins of the A type (PGA) induce the synthesis of 70 kDa heat shock proteins (hsp70) in a large variety of mammalian cells. Induction of hsp70 has been associated with a cytoprotective effect of PGA1 after virus infection or thermal injury. In the present report we provide evidence that, in murine myoblasts, PGA1 is not able to induce hsp70 expression, whereas it increases the synthesis of the constitutive protein, hsc70, and dramatically induces the synthesis of a 32 kDa protein (p32). The p32 protein has been identified as haem oxygenase. PGA1 acts at the transcriptional level by inducing haem oxygenase mRNA synthesis, and the signal for induction appears to be associated with decreased intracellular GSH levels. Haem oxygenase, a low-molecular-mass stress protein induced in mammalian cells by oxidant stress, is known to be part of a general inducible antioxidant defence pathway. The fact that prostaglandin synthesis is stimulated in muscle during contraction and in the heart in response to ischaemia raises the possibility that induction of haem oxygenase by PGA in myoblasts could be part of a protective mechanisms in operation during stress and hypoxia.

Antiviral effect of cyclopentenone prostaglandins on vesicular stomatitis virus replication

Prostaglandins are potentially useful antiviral agents, however their mechanism of action is unclear. Recent evidence suggests that RNA transcription of vesicular stomatitis virus (VSV) is inhibited by prostaglandins (Bader and Ankel, J. Gen. Virol. 71, 2823-2832, 1990). Prostaglandins are known to have multiple effects on cells which may or may not be related to their antiviral action. We examined the effects of prostaglandins on cells and on VSV RNA polymerase in vitro to seek the mechanism of antiviral action. Actinomycin D inhibited cellular RNA synthesis but failed to block the antiviral activity of prostaglandins on VSV. Thus induction of host cell RNA transcription is not involved in the antiviral action. Neither modulation of the cellular glutathione level by prostaglandins nor formation of prostaglandin-glutathione conjugates was required for the antiviral action. The relative inhibition of VSV RNA polymerase in vitro by prostaglandins with different structures correlated to inhibition of VSV replication in infected cells. This result indicates that the same step in VSV replication is inhibited by prostaglandins both in the in vitro RNA polymerase assay and in the infected cell.

Characterization of the transport system of prostaglandin A2 in L-1210 murine leukemia cells

Prostaglandin (PG) A2 has been shown to be actively incorporated into mammalian cells and transferred to the cell nucleus. To characterize the properties of the PGA2 transfer system, we examined the status of PGA2 in L-1210 cells with modified cellular glutathione (GSH) levels. PGA2 in the cytosol fraction of the cells existed in its free-form, the GSH conjugate-form and a macromolecule associate-form (protein bound-form). When the GSH level was lowered under culture conditions, the amount of free-form increased while that of the protein bound-form was unchanged. When PGA2-loaded cells were incubated in a salt solution, free- and conjugate-forms were emitted from the cells. A concomitant decrease and increase of protein bound PGA2 in cytosol and nuclei, respectively, were observed. Subsequent studies with isolated cellular fractions revealed that PGA2 bound to cytosolic protein was transported into the nuclear interior in a temperature-dependent manner. The binding of PGA2 to the protein and subsequent transport to the nuclei were inhibited by PGJ2 and 4-hydroxy-cyclopentenone, but not by PGB2, PGD2, PGE2, PGF2 alpha, arachidonic acid or oleic acid. N-Ethylmaleimide (NEM) and p-chloromercuribenzoate (PCMB) strongly interfered with these transfer processes, suggesting that sulfhydryl components are involved in the transport of PGA2. Subfractionation of cytosol by gel chromatography proved the presence of two proteins (100-150 kDa and 25-35 kDa) that are capable of transporting PGA2 to cell nuclei. Though 40-45 kDa proteins, which correspond to GSH S-transferases, bound to PGA2, they lacked the nuclear transport activities.

A free-radical hypothesis for the instability and evolution of genotype and phenotype in vitro

It has been known for several decades that cultured murine cells undergo a defined series of changes, i.e., an in vitro evolution, which includes crisis, spontaneous transformation ('immortalization'), aneuploidy, and spontaneous neoplastic transformation. These changes have been shown to be caused by the in vitro environment rather than an inherent instability of the murine phenotype or genotype. Serum amine oxidases were recently identified as a predominant cause of crisis. These enzymes generate hydrogen peroxide from polyamine substrates that enter the extracellular milieu. This finding implicates free-radical toxicity as the underlying cause of in vitro evolution. We propose an oxyradical hypothesis to explain each of the stages of in vitro evolution and discuss its significance for cytotechnology and long-term cultivation of mammalian cell types.

Glutathione inhibits replication and expression of viral proteins in cultured cells infected with Sendai virus

Addition of reduced glutathione inhibited the production of Sendai virus in African green monkey kidney (AGMK) cells. This result could be accounted for by a direct action of GSH on viral replication. The inhibitory action was associated to an increase of the GSH intracellular level, while the host cell metabolism was unaffected. The antiviral effect was related to decrease and inactivation of the hemagglutinin-neuraminidase (HN) virus glycoprotein.

Modulation of thioacetamide-induced hepatocellular necrosis by prostaglandins is associated with novel histologic changes

Cytoprotective effects of the prostaglandins 16,16-dimethyl PGE2 (dmPGE2) and PGF2 alpha tromethamine (PGF2 alpha) were evaluated in the rat model of acute hepatocellular necrosis induced by thioacetamide (TAA). dmPGE2 (100 micrograms/kg SC 8 hourly) did not induce a significant increase in survival when started after the onset of TAA-induced fulminant hepatic failure. However, priming with dmPGE2 (100 micrograms/kg SC 30 min before TAA) reduced TAA-induced elevations in serum ALT (684 +/- 68 (SEM) vs 274 +/- 135 IU/1, p less than 0.01). This phenomenon did not occur if dmPGE2 was administered after TAA or by the IP route. Modulation of TAA-induced centrizonal hepatocellular necrosis by dmPGE2 was associated with a striking increase in centrizonal ballooning of hepatocytes (p less than 0.01), and, as assessed by stereology, less hepatocellular necrosis and degenerative changes. PGF2 alpha, which in contrast to dmPGE2 does not act via cAMP, had no effect on TAA-induced changes in serum ALT or hepatic histology. These findings suggest that dmPGE2 decreases hepatocellular necrosis by activating surface membrane adenylate cyclase and consequently stimulating cAMP. Ballooning of hepatocytes could occur secondary to these membrane events and appears to be a marker of dmPGE2-induced cytoprotection in this model.

Cloning and nucleotide sequence of a full-length cDNA for human liver gamma-glutamylcysteine synthetase

We have cloned and sequenced a full-length cDNA for human liver gamma-glutamylcysteine synthetase (GCS), the rate-limiting enzyme in glutathione biosynthesis. The cDNA consists of 2634 bp containing an open reading frame encoding a protein of 367 amino acids and having a calculated M(r) = 72,773. The nucleotide sequence of the cDNA for human liver GCS shares an 84% overall similarity with the composite rat GCS sequence deduced from three overlapping partial cDNAs (Yan and Meister, JBC 265: 1588-1593, 1990). The deduced amino acid sequences are 94% similar. Comparison of Northern blots of total RNA isolated from rat kidney or liver with that from human kidney revealed the GCS mRNA to be larger in the human tissue (approximately 4.0 kb vs. approximately 3.7 kb). (The sequence for the human liver GCS cDNA has been assigned accession number M90656 in GenBank/EMBL databases.

Formation of a prostaglandin A2-glutathione conjugate in L1210 mouse leukemia cells

Prostaglandins containing a cyclopentenone moiety are potent antiviral and antigrowth compounds. Some evidence indicates that these prostaglandins are conjugated to glutathione by cells. However, the metabolism of one group, the prostaglandins of the A type, is unclear due to conflicting reports. We studied the uptake and metabolism of prostaglandin A2 (PGA2) in mouse L1210 leukemia and L929 fibroblast cell lines in which this prostaglandin has antiviral and antigrowth effects. Both cell types took up the PGA2 and then metabolized it to a more polar compound. Inside L1210 cells, PGA2 was initially conjugated to glutathione and then reduced at the 9-keto position to form 9-OH-PGA2-GSH. The 9-OH-PGA2-GSH was then secreted from the cells and apparently degraded to form the CysGly and Cys derivatives. Intracellular glutathione was decreased markedly by the addition of the PGA2 in L1210 and L929 cells. This result confirms that conjugation of PGA2 to glutathione occurs in both cell types. Formation of the 9-OH-PGA2-GSH and other glutathione-related conjugates was prevented when glutathione was depleted by growth in buthionine sulfoximine. The glutathione-depleted cells were insensitive to the cytotoxicity of the PGA2, suggesting that one of the glutathione-related conjugates may be involved in the cytotoxicity of PGA2. These results end the controversy over the metabolism of PGA2 and suggest mechanisms for its antiviral and antigrowth actions.

Studies on Se incorporation in selenoproteins; effects of peroxisome proliferators and hydrogen peroxide generating system

The objective of this study was to characterize the influence of peroxisome proliferation on the metabolism of physiological concentrations of Se. In an initial series of experiments hepatocytes in primary cultures and isolated from ordinary-fed rats, were used. The cells were exposed to 75Se-selenite (30 nM) and after 24 h the labelling of selenoproteins was analysed with SDS-PAGE. Treatments with mono(2-ethylhexyl)phthalate (MEHP; a metabolite of di(2-ethylhexyl)phthalate (DEHP)), nafenopin, decreased oxygen tension and a H2O2 generating system decreased the labelling of a 23-kDa and a 15-kDa protein. The decreased labelling of the 23- and the 15-kDa proteins was usually accompanied by an increased labelling of a 58-kDa protein. Increased oxygen tension induced uncertain effects, possibly due to toxicity. In order to further evaluate the validity of the model, the labelling was also studied in hepatocytes isolated from Se-deficient and torula yeast-fed rats. In these cells there was a decreased labelling of the 23-kDa protein as compared to cells from Se-supplemented controls when 100 nM selenite was used. In in vivo experiments it was found that a DEHP-induced decrease in glutathione peroxidase (GSH-Px) activity was potentiated by high doses of selenite. To a large extent, the labelling data are compatible with enzyme activity data and in vivo data. For example, the decreased labelling of the 23-kDa protein may reflect the decreased GSH-Px activity. It is concluded that the effects induced by MEHP on Se-labelling can be explained by an increase in the steady state level of H2O2.

Protective effect of prostaglandin A2 against menadione-induced cell injury in cultured porcine aorta endothelial cells

Prostaglandin A2 (PGA2) stimulates the biosynthesis of gamma-glutamylcysteine synthetase and elevates glutathione (GSH) contents in cultured mammalian cells. To clarify the importance of gamma-glutamylcysteine synthetase induction in the defence of endothelial cells against oxidative stress, the effect of PGA2 on menadione (2-methyl-1,4-naphthoquinone)-induced cell injury was examined. Incubation of porcine aorta endothelial cells with menadione produced marked loss of cellular GSH and protein sulfhydryl groups, followed by leakage of lactic dehydrogenase (LDH) into the culture medium. The LDH leakage and modification of protein thiol was, however, completely prevented by pretreatment of the cells with PGA2. The protective effect of PGA2 was more potent than that of cysteine delivery agents such as methionine, N-acetylcysteine or 2-oxo-4-thiazolidine carboxylic acid (OTC). The results suggest that cellular GSH plays an important role in the defence against oxidative stress, and induction of gamma-glutamylcysteine synthetase is effective for protecting vascular endothelial cells.

Specific role of an alpha,beta-unsaturated carbonyl group in gamma-glutamylcysteine synthetase induction by prostaglandin A2

The effects of prostaglandins (PGs) on cellular glutathione (GSH) status in L-1210 cells were examined. PGA2 and J2, which have an alpha,beta-unsaturated carbonyl group in the cyclopentane ring, elevated the GSH content, but PGB2, D2, E2 and F2 alpha did not show the effect. When L-1210 cells were incubated with various 2-cyclopentenone derivatives, 4-hydroxy-2-cyclopentenone and some of related compounds elevated cellular GSH levels. Subsequent study with cell-free extract of cultured L-1210 cells revealed that PGA2 and 4-hydroxy-2-cyclopentenone induced gamma-glutamycysteine synthetase activity at the transcriptional level. This induction was also found in other cultured mammalian cells such as HeLa S3, NIH/3T3 and porcine aorta endothelial cells. When L-1210 cells were incubated with PGA2 in the presence of 4-hydroxy-2-cyclopentenone and its analogues, they inhibited the accumulation of PGA2 in cell nuclei. Our findings thus suggest that an alpha,beta-unsaturated carbonyl moiety is responsible for enhancing the biosynthesis of gamma-glutamylcysteine synthetase in cultured cells.