Hydrogen Sulfide: A Novel Player in Airway Development, Pathophysiology of Respiratory Diseases, and Antiviral Defenses

Hydrogen sulfide (H2S) is a biologically relevant signaling molecule in mammals. Along with the volatile substances nitric oxide (NO) and carbon monoxide (CO), H2S is defined as a gasotransmitter. It plays a physiological role in a variety of functions, including synaptic transmission, vascular tone, angiogenesis, inflammation, and cellular signaling. The generation of H2S is catalyzed by cystathionine β-synthase (CBS), cystathionine γ-lyase (CSE), and 3-mercaptopyruvate sulfurtransferase (3-MST). The expression of CBS and CSE is tissue specific, with CBS being expressed predominantly in the brain, and CSE in peripheral tissues, including lungs. CSE expression and activity are developmentally regulated, and recent studies suggest that CSE plays an important role in lung alveolarization during fetal development. In the respiratory tract, endogenous H2S has been shown to participate in the regulation of important functions such as airway tone, pulmonary circulation, cell proliferation or apoptosis, fibrosis, oxidative stress, and inflammation. In the past few years, changes in the generation of H2S have been linked to the pathogenesis of a variety of acute and chronic inflammatory lung diseases, including asthma and chronic obstructive pulmonary disease. Recently, our laboratory made the critical discovery that cellular H2S exerts broad-spectrum antiviral activity both in vitro and in vivo, in addition to independent antiinflammatory activity. These findings have important implications for the development of novel therapeutic strategies for viral respiratory infections, as well as other inflammatory lung diseases, especially in light of recent significant efforts to generate controlled-release H2S donors for clinical therapeutic applications.

Human trophoblast-derived hydrogen sulfide stimulates placental artery endothelial cell angiogenesis

Endogenous hydrogen sulfide (H2S), mainly synthesized by cystathionine β-synthase (CBS) and cystathionine γ-lyase (CTH), has been implicated in regulating placental angiogenesis; however, the underlying mechanisms are unknown. This study was to test a hypothesis that trophoblasts synthesize H2S to promote placental angiogenesis. Human choriocarcinoma-derived BeWo cells expressed both CBS and CTH proteins, while the first trimester villous trophoblast-originated HTR-8/SVneo cells expressed CTH protein only. The H2S producing ability of BeWo cells was significantly inhibited by either inhibitors of CBS (carboxymethyl hydroxylamine hemihydrochloride, CHH) or CTH (β-cyano-L-alanine, BCA) and that in HTR-8/SVneo cells was inhibited by CHH only. H2S donors stimulated cell proliferation, migration, and tube formation in ovine placental artery endothelial cells (oFPAECs) as effectively as vascular endothelial growth factor. Co-culture with BeWo and HTR-8/SVneo cells stimulated oFPAEC migration, which was inhibited by CHH or BCA in BeWo but CHH only in HTR-8/SVneo cells. Primary human villous trophoblasts (HVT) were more potent than trophoblast cell lines in stimulating oFPAEC migration that was inhibited by CHH and CHH/BCA combination in accordance with its H2S synthesizing activity linked to CBS and CTH expression patterns. H2S donors activated endothelial nitric oxide synthase (NOS3), v-AKT murine thymoma viral oncogene homolog 1 (AKT1), and extracellular signal-activated kinase 1/2 (mitogen-activated protein kinase 3/1, MAPK3/1) in oFPAECs. H2S donor-induced NOS3 activation was blocked by AKT1 but not MAPK3/1 inhibition. In keeping with our previous studies showing a crucial role of AKT1, MAPK3/1, and NOS3/NO in placental angiogenesis, these data show that trophoblast-derived endogenous H2S stimulates placental angiogenesis, involving activation of AKT1, NOS3/NO, and MAPK3/1.

Effect of Physical Exercise on the Febrigenic Signaling is Modulated by Preoptic Hydrogen Sulfide Production

We tested the hypothesis that the neuromodulator hydrogen sulfide (H₂S) in the preoptic area (POA) of the hypothalamus modulates the febrigenic signaling differently in sedentary and trained rats. Besides H₂S production rate and protein expressions of H₂S-related synthases cystathionine β-synthase (CBS), 3-mercaptopyruvate sulfurtransferase (3-MPST) and cystathionine γ-lyase (CSE) in the POA, we also measured deep body temperature (Tb), circulating plasma levels of cytokines and corticosterone in an animal model of systemic inflammation. Rats run on a treadmill before receiving an intraperitoneal injection of lipopolysaccharide (LPS, 100 μg/kg) or saline. The magnitude of changes of Tb during the LPS-induced fever was found to be similar between sedentary and trained rats. In sedentary rats, H₂S production was not affected by LPS. Conversely, in trained rats LPS caused a sharp increase in H₂S production rate that was accompanied by an increased CBS expression profile, whereas 3-MPST and CSE expressions were kept relatively constant. Sedentary rats showed a significant LPS-induced release of cytokines (IL-1β, IL-6, and TNF-α) which was virtually abolished in the trained animals. Correlation between POA H₂S and IL-6 as well as TNF-α was observed. Corticosterone levels were augmented after LPS injection in both groups. We found correlations between H₂S and corticosterone, and corticosterone and IL-1β. These data are consistent with the notion that the responses to systemic inflammation are tightly regulated through adjustments in POA H₂S production which may play an anti-inflammatory role downmodulating plasma cytokines levels and upregulating corticosterone release.

Up Regulation of cystathione γ lyase and Hydrogen Sulphide in the Myocardium Inhibits the Progression of Isoproterenol-Caffeine Induced Left Ventricular Hypertrophy in Wistar Kyoto Rats

Hydrogen sulphide (H2S) is an emerging molecule in many cardiovascular complications but its role in left ventricular hypertrophy (LVH) is unknown. The present study explored the effect of exogenous H2S administration in the regression of LVH by modulating oxidative stress, arterial stiffness and expression of cystathione γ lyase (CSE) in the myocardium. Animals were divided into four groups: Control, LVH, Control-H2S and LVH-H2S. LVH was induced by administering isoprenaline (5mg/kg, every 72 hours, S/C) and caffeine in drinking water (62mg/L) for 2 weeks. Intraperitoneal NaHS, 56μM/kg/day for 5 weeks, was given as an H2S donor. Myocardial expression of Cystathione γ lyase (CSE) mRNA was quantified using real time polymerase chain reaction (qPCR).There was a 3 fold reduction in the expression of myocardial CSE mRNA in LVH but it was up regulated by 7 and 4 fold in the Control-H2S and LVH-H2S myocardium, respectively. Systolic blood pressure, mean arterial pressure, pulse wave velocity were reduced (all P<0.05) in LVH-H2S when compared to the LVH group. Heart, LV weight, myocardial thickness were reduced while LV internal diameter was increased (all P<0.05) in the LVH-H2S when compared to the LVH group. Exogenous administration of H2S in LVH increased superoxide dismutase, glutathione and total antioxidant capacity but significantly reduced (all P<0.05) plasma malanodialdehyde in the LVH-H2S compared to the LVH group. The renal cortical blood perfusion increased by 40% in LVH-H2S as compared to the LVH group. Exogenous administration of H2S suppressed the progression of LVH which was associated with an up regulation of myocardial CSE mRNA/ H2S and a reduction in pulse wave velocity with a blunting of systemic hemodynamic. This CSE/H2S pathway exhibits an antihypertrophic role by antagonizing the hypertrophic actions of angiotensin II(Ang II) and noradrenaline (NA) but attenuates oxidative stress and improves pulse wave velocity which helps to suppress LVH. Exogenous administration of H2S augmented the reduced renal cortical blood perfusion in the LVH state.

Expression profile of hydrogen sulfide and its synthases correlates with tumor stage and grade in urothelial cell carcinoma of bladder

BACKGROUND

Hydrogen sulfide (H2S) is a newly discovered gas transmitter. It is synthesized by cystathionine β-synthase (CBS), cystathionine γ-lyase (CSE), and 3-mercaptopyruvate sulfurtransferase (MPST). Endogenous hydrogen sulfide has never been studied in bladder cancer.

PURPOSE

We evaluated H2S production and its synthases expression levels in transitional cell carcinoma (urothelial cell carcinoma of bladder [UCB]) of human bladder tissue and cell lines.

MATERIALS AND METHODS

Immunostaining was performed in urothelial cell lines and bladder specimens from 94 patients with UCB of different stages/grades. The expression levels/activities of CBS, CSE, and MPST of specimens and cell lines were analyzed by image semiquantity assay, western blot, and a sulfur-sensitive electrode. We tried to find the correlation between hydrogen sulfide and its synthases with tumor stage in UCB. All experiments were repeated at least 3 times.

RESULTS

Immunoreactivity for CBS, CSE, and MPST was detected in malignant uroepithelium and muscular layer of all tissues examined and cultured cells. The expression levels of CBS, CSE, and MPST were associated with UCB stage/grade. Muscle-invasive bladder cancer samples showed the highest production of H2S (52.6±2.91 nmol/[mg·min]) among all tested samples and EJ cells (transitional cell carcinoma, grade IIIshowed the highest production of H2S among all tested cell lines (53.3±7.02nmol/[mg·min]).

CONCLUSIONS

Protein levels and catalytic activities of CBS, CSE, and MPST increased with the increase of malignant degrees in human bladder tissues and human UCB cell lines. Our findings may promote the application of these novel enzymes to UCB diagnosis or treatment.

Screening, morphological and molecular characterization of fungi producing cystathionine γ-lyase

The potency for production of cystathionine γ-lyase (CGL) by the fungal isolates was screened. Among the tested twenty-two isolates, Aspergillus carneus was the potent CGL producer (6.29 U/mg), followed by A. ochraceous (6.03 U/mg), A. versicolor (2.51 U/mg), A. candidus (2.12 U/mg), A. niveus and Penicillium notatum (2.0 U/mg). The potent six isolates producing CGL was characterized morphologically, A. carneus KF723837 was further molecularly characterized based on the sequence of 18S-28S rDNA. Upon sulfur starvation, the yield of A. carneus extracellular CGL was increased by about 1.7- and 4.1-fold comparing to non-sulfur starved and L-methionine free medium, respectively. Also, the uptake of L-methionine was duplicated upon sulfur starvation, assuming the activation of specific transporters for L-methionine and efflux of CGL. Also, the intracellular thiols and GDH activity of A. carneus was strongly increased by S starvation, revealing the activation of in vivo metabolic antioxidant systems. Upon irradiation of A. carneus by 2.0 kGy of γ-rays, the activity of CGL was increased by two-fold, regarding to control, with an obvious decreases on its yield upon further doses. Practically, CGL activity from the solid A. carneus cultures, using rice bran as substrate, was increased by 1.2-fold, comparing to submerged cultures, under optimum conditions.

Cystathionase mediates senescence evasion in melanocytes and melanoma cells

The development of malignant melanoma is a highly complex process, which is still poorly understood. A majority of human melanomas are found to express a few oncogenic proteins, such as mutant RAS and BRAF variants. However, these oncogenes are also found in nevi, and it is now a well-accepted fact that their expression alone leads to senescence. This renders the understanding of senescence escape mechanisms an important point to understand tumor development. Here, we approached the question of senescence evasion by expressing the transcription factor v-myc myelocytomatosis viral oncogene homolog (c-MYC), which is known to act synergistically with many oncogenes, in melanocytes. We observed that MYC drives the evasion of reactive-oxygen stress-induced melanocyte senescence, caused by activated receptor tyrosine kinase signaling. Conversely, MIZ1, the growth suppressing interaction partner of MYC, is involved in mediating melanocyte senescence. Both, MYC overexpression and Miz1 knockdown led to a strong reduction of endogenous reactive-oxygen species (ROS), DNA damage and senescence. We identified the cystathionase (CTH) gene product as mediator of the ROS-related MYC and MIZ1 effects. Blocking CTH enzymatic activity in MYC-overexpressing and Miz1 knockdown cells increased intracellular stress and senescence. Importantly, pharmacological inhibition of CTH in human melanoma cells also reconstituted senescence in the majority of cell lines, and CTH knockdown reduced tumorigenic effects such as proliferation, H2O2 resistance and soft agar growth. Thus, we identified CTH as new MYC target gene with an important function in senescence evasion.

Down-regulation of hydrogen sulfide biosynthesis accompanies murine interstitial cells of Cajal dysfunction in partial ileal obstruction

Purpose

To investigate the role of endogenous hydrogen sulfide (H₂S) in partial obstruction-induced dysfunction of the interstitial cells of Cajal (ICC) in mice ileum.

Materials and Methods

Partial intestinal obstruction was induced surgically in male imprinting control region (ICR) mice. ICC networks were studied by Immunohistochemistry. Electrical activity was recorded by intracellular recording techniques. The expression of ICC phenotype marker c-kit receptor tyrosine kinase (c-kit), membrane binding stem cell factor (mSCF), the endogenous H₂S biosynthesis enzymes cystathionine-β-synthase (CBS) and cystathionine-γ-lyase (CSE) was studied by Western blotting. The expression of tumor necrosis factor-α (TNF-α) mRNA was observed by using real-time polymerase chain reaction.

Results

Partial intestinal obstruction resulted in ICC networks were disrupted above obstruction 14 days after the operation. The slow waves of intestinal smooth muscles in the dilated region were significantly suppressed and their amplitude and frequency were reduced, whilst the resting membrane potentials were depolarized. The expression of c-kit and mSCF was significantly decreased, also suggesting the disruption of the ICC network. The expression of TNF-α was significantly increased in the tunica muscularis of the obstructed intestine. Treatment of cultured intestinal smooth muscle cells with TNF-α caused dramatic down regulation of mSCF. The expression of CBS and CSE was significantly decreased in the tunica muscularis of the obstructed intestine. Intraperitoneal injection (i.p) of DL-propargylglycine, an irreversible inhibitor of CSE, and aminooxyacetic acid, an inhibitor of CBS, elevated the expression of TNF-α mRNA in the tunica muscularis of the ileum. Obstruction-induced over expression of TNF-α was significantly improved by supplementation of NaHS, but not the expressions of mSCF and c-kit.

Conclusions

The down regulation of endogenous H₂S biosynthesis is related to over expression of TNF-α in obstructed small intestine. TNF-α-mediated mSCF down-regulation is not the only reason of partial intestinal obstruction-induced loss of ICC.

Comparative proteomic analysis of the esophageal squamous carcinoma cell line EC109 and its multi-drug resistant subline EC109/CDDP

To gain insights into the mechanisms of drug resistance in esophageal squamous cell carcinoma (ESCC), we employed proteomic techniques to study the global protein change of the multi-drug resistant ESCC cell line EC109/CDDP, which was established in our previous work, in comparison with its parental drug sensitive cell line EC109. By two-dimensional electrophoresis and mass spectrometry, we successfully identified 44 proteins with altered expression levels. These proteins are involved in endoplasmic reticulum stress response, metabolic process, DNA replication and repair, nucleotide binding, calcium binding, and cytoskeletal proteins. Among them, the differential expression levels of thioredoxin domain-containing protein 4 precursor and cystathionine gamma-lyase were further validated by Western blot and RT-PCR. Our present results lay foundation for future in-depth work on molecular mechanism of ESCC drug resistance, and aid in the identification and use of novel markers in clinical practice.

Oxidative stress as a signal to up-regulate gamma-cystathionase in the fetal-to-neonatal transition in rats

Hepatic gamma-cystathionase, a rate-limiting enzyme for the synthesis of L-cysteine from L-methionine in the trans-sulphuration pathway, exhibits significantly higher activity in the newly born infant as compared to the fetus. The aim of this work was: 1) To determine whether the increase in gamma-cystathionase activity occurring in the fetal-to-neonatal transition is due to up-regulation of its mRNA and protein, 2) To elucidate the mechanisms responsible for this increase in gamma-cystathionase activity. Our results show that expression of gamma-cystathionase at both the mRNA and protein levels was higher in newborn than in fetal liver. gamma-Cystathionase activity in fetal hepatocytes in vitro increased when incubated with tert-butyl-hydroperoxide at low concentration (0.01 mM). Hence, moderate oxidative stress would act as a signal to up-regulate gamma-cystathionase in the fetal to neonatal transition. Stress hormones, such as phenylephrine or glucagon also increased gamma-cystathionase activity in fetal hepatocytes. We also report a competitive inhibition of purified gamma-cystathionase by L-cysteine, which would help to maintain physiological low L-cysteine levels in hepatocytes. In conclusion, our results show that increased hepatic gamma-cystathionase activity in the fetal-to-neonatal transition is due to up-regulation of its gene expression mediated by stress hormones together with the physiological oxidative stress that occurs at birth.

H2S, Endoplasmic Reticulum Stress, and Apoptosis of Insulin-secreting Beta Cells

Cystathionine gamma-lyase (CSE) is a key enzyme in the trans-sulfuration pathway, which uses L-cysteine to produce hydrogen sulfide (H2S). Functional changes of pancreatic beta cells induced by endogenous H2S have been reported, but the effect of the CSE/H2S system on pancreatic beta cell survival has not been known. In this study, we demonstrate that H2Sat physiologically relevant concentrations induced apoptosis of INS-1E cells, an insulin-secreting beta cell line. Transfection of INS-1E cells with a recombinant defective adenovirus containing the CSE gene (Ad-CSE) resulted in a significant increase in CSE expression and H2S production. Ad-CSE transfection also stimulated apoptosis. The other two end products of CSE-catalyzed enzymatic reaction, ammonium and pyruvate, had no effects on INS-1E cell apoptosis, indicating that overexpression of CSE may stimulate INS-1E cell apoptosis via increased endogenous production of H2S. Both exogenous H2S (100 microM) and Ad-CSE transfection inhibited ERK1/2 but activated p38 MAPK. Interestingly, BiP and CHOP, two indicators of endoplasmic reticulum (ER) stress, were up-regulated in H2S-and CSE-mediated apoptosis in INS-1E cells. After suppressing CHOP mRNA expression, H2S-induced apoptosis of INS-1E cells was significantly decreased. Inhibition of p38 MAPK, but not of ERK1/2, inhibited the expression of BiP and CHOP and decreased H2S-stimulated apoptosis, suggesting that p38 MAPK activation functions upstream of ER stress to initiate H2S-induced apoptosis. It is concluded that H2S induces apoptosis of insulin-secreting beta cells by enhancing ER stress via p38 MAPK activation. Our findings may help unmask a novel role of CSE/H2S system in regulating pancreatic functions under physiological condition and in diabetes.

Levels of cystathionine γ lyase production by Geotrichum candidum in synthetic media and correlation with the presence of sulphur flavours in cheese

Geotrichum candidum is a cheese-ripening agent with the potential to produce sulphur flavour compounds in soft cheeses. We aimed to develop an alternative test for predicting the aromatic (sulphur flavours) potential of G. candidum strains in soft cheese. Twelve strains of G. candidum with different levels of demethiolase activity (determined by a chemical method) in YEL-met (yeast extract, lactate methionine) medium were studied. We investigated cgl (cystathionine gamma lyase) gene expression after culture in three media - YEL-met, casamino acid and curd media - and then carried out sensory analysis on a Camembert cheese matrix. We found no correlation between demethiolase activity in vitro and cgl gene expression. Sensory analysis (detection of sulphur flavours) identified different aromatic profiles linked to cgl expression, but not to demethiolase activity. The RT-PCR technique described here is potentially useful for predicting the tendency of a given strain of G. candidum to develop sulphur flavours in cheese matrix. This is the first demonstration that an in vitro molecular approach could be used as a predictive test for evaluating the potential of G. candidum strains to generate sulphur compounds in situ (Camembert cheese matrix).

Differential induction of cystathionine gamma-lyase in the livers and kidneys of mouse dams during gestation and lactation

Cystathionine gamma-lyase (CSE) is the last key enzyme in the transsulfuration pathway for the biosynthesis of cysteine from methionine in mammals, and catalyzes the hydrolysis of cystathionine into cysteine. Cysteine can be provided through diet; however, several investigators have suggested that infants may require dietary supplements of cysteine because of very low or undetectable CSE activity in their livers. We have previously shown that CSE levels are much lower in the livers and kidneys of fetal and infant mice than in those of adult mice, suggesting that the maternal supply of cysteine is important for the early development of mice. Here we examined changes of CSE expression in the livers and kidneys of dams during gestation and lactation. Hepatic enlargement was observed as early as gestational day 12.5 (G12.5) and thereafter became more prominent, whereas expression of CSE in the livers was found after postpartum day 1 (P1) and reached a peak at P14. The maintenance of lactation was essential for both hepatic enlargement and CSE expression. In contrast, kidneys gained weight only slightly during lactation while CSE expression in kidneys was markedly induced at G15.5 and then gradually declined through to P28. Serum concentrations of homocysteine (the precursor of cystathionine) were significantly lower in G18.5 dams than in virgins or G15.5 dams, suggesting that the expression of CSE in the kidneys contributes to the effective clearance of homocysteine during the late gestational stage.

Hydrogen sulfide ameliorates vascular calcification induced by vitamin D3 plus nicotine in rats

AIM

To investigate the role of the endogenous cystathionine gamma-synthase (CSE)/hydrogen sulfide (H2S) pathway in vascular calcification in vivo.

METHODS

A rat vascular calcification model was established by administration of vitamin D3 plus nicotine (VDN). The amount of CSE and osteopontin (OPN) mRNA was determined by using semi-quantitative reverse-transcription polymerase chain reaction. The calcium content, 45Ca2+ accumulation and alkaline phosphatase (ALP) activity were measured. H2S production and CSE activity were measured.

RESULTS

von Kossa staining produced strong positive black/brown staining in areas among the elastic fibers of the medial layer in the calcified aorta. The calcium content, 45Ca2+ accumulation and ALP activity in calcified arteries increased by 6.77-, 1.42-, and 1.87-fold, respectively, compared with controls. The expression of the OPN gene was upregulated (P<0.01). Expression of the CSE gene was downregulated. However, calcium content, 45Ca2+ uptake and ALP activity in the VDN plus NaHS group was lower than that in the VDN group. The content of calcium and 45Ca2+ accumulation and activity of ALP in the aorta were 34.8%, 40.75% and 63.5% lower in the low-dosage NaHS group than in the VDN group, respectively (P<0.01), and the calcium content and deposition of 45Ca2+ and activity of ALP was 83.9%, 37.8 % and 46.2% lower in the aorta in the high-dosage NaHS group than in the VDN group, respectively (P<0.01). The expression of the OPN gene was downregulated.

CONCLUSION

The production of H2S, and CSE activity were decreased and CSE gene expression was downregulated in rats with vascular calcification. H2S can ameliorate vascular calcification, suggesting that the H2S/CSE pathway plays a regulatory role in the pathogenesis of vascular calcification.

Pro‐apoptotic effect of endogenous H2S on human aorta smooth muscle cells

Cystathionine gamma-lyase (CSE) is a key enzyme in the trans-sulfuration pathway, which uses L-cysteine to produce hydrogen sulfide (H2S). The CSE/H2S system has been shown to play an important role in regulating cellular functions in different systems. In the present study, we overexpressed CSE in human aorta smooth muscle cells (HASMCs) using a recombinant defective adenovirus containing CSE gene (Ad-CSE). Infection of HASMCs with Ad-CSE resulted in a significant increase in the expression of CSE protein and H2S production. Ad-CSE transfection inhibited cell growth and stimulated apoptosis, as evidenced by cell viability assay, Hoechst 33258 staining, TUNEL, and caspase 3 activation. CSE-mediated apoptosis was associated with an increased ERK and p38 MAPK activation, up-regulation of p21(Cip/WAK-1), and down-regulation of cyclin D1 expression. After inhibiting endogenous background CSE gene expression, direct administration of H2S at 100 microM induced apoptosis of HASMCs. The other two endproducts of CSE-catalyzed enzymatic reaction, ammonium and pyruvate, failed to do so. These results demonstrate that overexpression of CSE stimulates SMC apoptosis due to an increased endogenous production of H2S. Adenovirus-mediated transfer of CSE gene may provide a novel therapeutic approach in treating vascular diseases linked to abnormal cellular proliferation and vascular remodeling.

Murine cystathionine gamma-lyase: complete cDNA and genomic sequences, promoter activity, tissue distribution and developmental expression

Cystathionine gamma-lyase (CSE) is the last key enzyme in the trans-sulphuration pathway for biosynthesis of cysteine from methionine. Cysteine could be provided through diet; however, CSE has been shown to be important for the adequate supply of cysteine to synthesize glutathione, a major intracellular antioxidant. With a view to determining physiological roles of CSE in mice, we report the sequence of a complete mouse CSE cDNA along with its associated genomic structure, generation of specific polyclonal antibodies, and the tissue distribution and developmental expression patterns of CSE in mice. A 1.8 kb full-length cDNA containing an open reading frame of 1197 bp, which encodes a 43.6 kDa protein, was isolated from adult mouse kidney. A 35 kb mouse genomic fragment was obtained by lambda genomic library screening. It contained promoter regions, 12 exons, ranging in size from 53 to 579 bp, spanning over 30 kb, and exon/intron boundaries that were conserved with rat and human CSE. The GC-rich core promoter contained canonical TATA and CAAT motifs, and several transcription factor-binding consensus sequences. The CSE transcript, protein and enzymic activity were detected in liver, kidney, and, at much lower levels, in small intestine and stomach of both rats and mice. In developing mouse liver and kidney, the expression levels of CSE protein and activity gradually increased with age until reaching their peak value at 3 weeks of age, following which the expression levels in liver remained constant, whereas those in kidney decreased significantly. Immunohistochemical analyses revealed predominant CSE expression in hepatocytes and kidney cortical tubuli. These results suggest important physiological roles for CSE in mice.

Role of hydrogen sulphide in haemorrhagic shock in the rat: protective effect of inhibitors of hydrogen sulphide biosynthesis

Haemorrhagic shock (60 min) in the anaesthetized rat resulted in a prolonged fall in the mean arterial blood pressure (MAP) and heart rate (HR). Pre-treatment (30 min before shock) or post-treatment (60 min after shock) with inhibitors of cystathionine gamma lyase (CSE; converts cysteine into hydrogen sulphide (H(2)S)), dl-propargylglycine or beta-cyanoalanine (50 mg kg(-1), i.v.), or glibenclamide (40 mg kg(-1), i.p.), produced a rapid, partial restoration in MAP and HR. Neither saline nor DMSO affected MAP or HR. Plasma H(2)S concentration was elevated 60 min after blood withdrawal (37.5+/-1.3 microM, n=18 c.f. 28.9+/-1.4 microM, n=15, P<0.05). The conversion of cysteine to H(2)S by liver (but not kidney) homogenates prepared from animals killed 60 min after withdrawal of blood was significantly increased (52.1+/-1.6 c.f. 39.8+/-4.1 nmol mg protein(-1), n=8, P<0.05), as was liver CSE mRNA (2.7 x). Both PAG (IC(50), 55.0+/-3.2 microM) and BCA (IC(50), 6.5+/-1.2 microM) inhibited liver H(2)S synthesizing activity in vitro. Pre-treatment of animals with PAG or BCA (50 mg kg(-1), i.p.) but not glibenclamide (40 mg kg(-1), i.p., K(ATP) channel inhibitor) abolished the rise in plasma H(2)S in animals exposed to 60 min haemorrhagic shock and prevented the augmented biosynthesis of H(2)S from cysteine in liver. These results demonstrate that H(2)S plays a role in haemorrhagic shock in the rat. CSE inhibitors may provide a novel approach to the treatment of haemorrhagic shock.

Cystathionine gamma-lyase overexpression inhibits cell proliferation via a H2S-dependent modulation of ERK1/2 phosphorylation and p21Cip/WAK-1

Cystathionine gamma-lyase (CSE) is a key enzyme in the trans-sulfuration pathway. CSE uses L-cysteine as a substrate to produce hydrogen sulfide (H2S). The CSE/H2S system has been shown to play an important role in regulating cellular functions in different systems. In the present study, we used CSE stably overexpressed HEK-293 cells to explore the effect of the CSE/H2S system on cell growth and proliferation. The overexpression of CSE resulted in increases in CSE mRNA levels, CSE proteins, and intracellular H2S production rates, as well as the inhibition of cell proliferation and DNA synthesis. These effects were accompanied by a sustained ERK activation and up-regulation of the cyclin-dependent kinase inhibitor p21Cip/WAK-1. Blocking the action of ERK with U0126 inhibited the induction of p21Cip/WAK-1, suggesting that ERK activation functions upstream of p21Cip/WAK-1 activation to initiate the CSE overexpression-induced cell growth inhibition. The antiproliferative effect of CSE is likely mediated by endogenously produced H2S because the H2S scavenger methemoglobin (10 microm) significantly decreased the H2S production rate and reversed the antiproliferative effect afforded by CSE. Exogenous H2S (100 microm) also inhibited cell proliferation. However, the other CSE-catalyzed products, ammonium and pyruvate, failed to inhibit cell proliferation. Methemoglobin also abolished the inhibitory effect of exogenous H2S on cell proliferation. Moreover, exogenous H2S induced a sustained ERK and p21Cip/WAK-1 activation. These findings support the hypothesis that endogenously produced H2S may play a fundamental role in cell proliferation and survival.

H2S generated by heart in rat and its effects on cardiac function

Hydrogen sulfide (H2S), which was considered as a novel gasotransmitter, is produced endogenously from L-cysteine in mammalian brain and vessels, and might be a physiological function regulator to these organs. Here, we showed that mRNA for H2S producing enzyme, cystathionine gamma-lyase, was expressed in myocardial tissues and H2S could endogenously be produced in myocardial tissues. Negative inotropic effect of H2S was proved in present study in vitro and in vivo experiments, and the effect could partly be blocked by glibenclamide, a KATP channel blocker. An intravenous bolus injection of NaHS provoked a decrease in central venous pressure. The present findings suggested that H2S could be endogenously produced by heart tissues, as a physiological cardiac function regulator, mediated by KATP channel pathway.

Negative transcriptional regulation of a positive regulator: the expression of malT, encoding the transcriptional activator of the maltose regulon of Escherichia coli, is negatively controlled by Mlc

The maltose regulon consists of 10 genes encoding a multicomponent and binding protein-dependent ABC transporter for maltose and maltodextrins as well as enzymes necessary for the degradation of these sugars. MalT, the transcriptional activator of the system, is necessary for the transcription of all mal genes. MalK, the energy-transducing subunit of the transport system, acts phenotypically as repressor, particularly when overproduced. We isolated an insertion mutation that strongly reduced the repressing effect of overproduced MalK. The affected gene was sequenced and identified as mlc, a known gene encoding a protein of unknown function with homology to the Escherichia coli NagC protein. The loss of Mlc function led to a threefold increase in malT expression, and the presence of mlc on a multicopy plasmid reduced malT expression. By DNasel protection assay, we found that Mlc protected a DNA region comprising positions +1 to +23 of the malT transcriptional start point. Using a mlc-lacZ fusion in a mlc and mlc+ background, we found that Mlc represses its own expression. As Mlc also regulates another operon (manXYZ, see pages 369-379 of this issue), it may very well constitute a new global regulator of carbohydrate utilization.

The possible role of hydrogen sulfide as an endogenous smooth muscle relaxant in synergy with nitric oxide

Hydrogen sulfide (H2S), which is well known as a toxic gas, is produced endogenously in mammalian tissues from L-cysteine mainly by two pyridoxal-5'-phosphate-dependent enzymes, cystathionine beta-synthetase and cystathionine gamma-lyase. Recently, we showed that cystathionine beta-synthetase in the brain produces H2S, and that H2S facilitates the induction of hippocampal long-term potentiation by enhancing NMDA receptor activity. Here we show that mRNA for another H2S producing enzyme, cystathionine gamma-lyase, is expressed in the ileum, portal vein, and thoracic aorta. The ileum also expresses cystathionine beta-synthetase mRNA. These tissues produce H2S, and this production is blocked by cystathionine beta-synthetase and cystathionine gamma-lyase specific inhibitors. Although exogenously applied H2S alone relaxed these smooth muscles, much lower concentrations of H2S greatly enhanced the smooth muscle relaxation induced by NO in the thoracic aorta. These observations suggest that the endogenous H2S may regulate smooth muscle tone in synergy with NO.

Vitamin B6 deficiency accelerates metabolic turnover of cystathionase in rat liver

Although most of cystathionase was found to exist as an inactive apoenzyme in the liver of vitamin B6-deficient rats, the concentrations of the immunoreactive enzyme protein were virtually the same for control and vitamin B6-deficient livers. Under vitamin B6 deficiency, however, the rate of synthesis of cystathionase, measured by incorporation of labeled amino acid into the immunoprecipitated enzyme, was increased severalfold due to an increased level of cystathionase mRNA. Western blot analysis of lysosomal proteins showed that the amount of cystathionase in the lysosomes from the liver of vitamin B6-deficient rats was also increased severalfold. This observation suggests that lysosomes specifically recognize the apocystathionase for sequestration in preference to the holoenzyme. The present study provides the molecular basis for dual roles of vitamin B6 in controlling the metabolic turnover of cystathionase; it regulates synthesis of the enzyme by modulating the expression of cystathionase gene, and it regulates degradation of the enzyme by different susceptibilities of apo- and holoenzymes to lysosomal proteolysis.

MalY of Escherichia coli is an enzyme with the activity of a beta C-S lyase (cystathionase)

The Escherichia coli maltose system consists of a number of genes whose products are involved in the uptake and metabolism of maltose and maltodextrins. MalT is the central positive gene activator of the regulon and is, together with the cyclic AMP-catabolite gene activator protein system, necessary for the expression of the maltose genes. Expression of malY, a MalT-independent gene, leads to the repression of all MalT-dependent genes. We have purified MalY to homogeneity and found it to be a pyridoxal-5-phosphate-containing enzyme with the enzymatic activity of a beta C-S lyase (cystathionase). MalY is a monomeric protein of 42,000 to 44,000 Da. Strains expressing MalY constitutively abolish the methionine requirement of metC mutants. The enzymatic activity of MetC, the cleavage of cystathionine to homocysteine, ammonia, and pyruvate, can be catalyzed by MalY. However, the cystathionase activity is not required for the function of MalY in repressing the maltose system. By site-directed mutagenesis, we changed the conserved lysine residue at the pyridoxal phosphate binding site (position 233) of MalY to isoleucine. This abolished beta C-S lyase activity but not the ability of the protein to repress the maltose system. Also, the overexpression of plasmid-encoded metC did not affect mal gene expression, nor did the deduced amino acid sequence of MetC show homology to that of MalY.

Regulation of L-cystine transport in Salmonella typhimurium

A kinetic analysis of L-cystine uptake in wild-type Salmonella typhimurium indicates the presence of at least two, and possibly three, separate transport systems. CTS-1 accounts for the majority of uptake at 20 muM L-cystine, with a Vmax of 9.5 nmol/min per mg and a Km of 2.0 muM; CTS-2 is a low-capacity, higher-affinity system with a Vmax of 0.22 nmol/min per mg and a Km of 0.05 muM; a third, nonsaturable process has been designated CTS-3. We find that wild-type CTS-1 levels are at least 11 times higher in sulfur-limited cells than in L-cystine-grown cells. Pleiotropic cysteine auxotrophs of the types cysE (lacking serine transacetylase) and cysB- (lacking a regulatory element of positive control) have very low levels of CTS-1 even when grown under conditions of sulfur limitation, which response is analogous to that previously observed for cysteine biosynthetic enzymes (N . M. Kredich, J. Biol. Chem. 246:3474-3484, 1971). CTS-1 is induced in cysE mutants by growth in the presence of O-acetyl-L-serine (the product of serine transacetylase), again paralleling the behavior of the cysteine biosynthetic pathway. Strain DW25, a prototrophic cysBc mutant, which is constitutive for cysteine biosynthesis, is also derepressed for CTS-1 when grown on L-cystine. Since CTS-1 is regulated by sulfur limitation, O-acetyl-L-serine, and the cysB gene product, the same three conditions controlling cysteine biosynthesis, we propose that this transport system is a part of the cysteine regulon.

Induction of cystathionase in foetal rat liver explants. Effects of dexamethasone, N-6, O-2 -dibutyryladenosine 3,5 -monophosphate and glucagon in vitro

At the 18th day of gestation and thereafter foetal rat liver explants in organ culture showed the competence to respond to dexamethasone by increased cystathionase activity, whereas the ability to respond to dibutyryl cyclic AMP or glucagon became evident at a later developmental stage (during the last 2 days prior to term). Simultaneous incubation with cycloheximide inhibited the stimulatory effect of these agents on foetal rat liver cystathionase activity in vitro. Dexamethasone and glucagon were both capable of increasing liver cystathionase activity both in newborn and 3-day-old animals in vivo.

Genetic characterization of the metK locus in Escherichia coli K-12

Three independently isolated metK mutants have been shown to have leisions lying between speB and glc near 57 min on the Escherichia coli chromosome. Two deletions result in a lack of the metC gene product but neither extends into the metK glc region. The three metK mutations are recessive to the wild-type allele carried on the KLF16 episome.

Induction of cystathionase in human foetal liver

Incubation of liver explants from second-trimester human foetuses with dexamethasone, glucagon or dibutyryl cyclic AMP (plus theophylline) increased the activity of liver cystathionase from unmeasurable or trace values to adult values. Simultaneous incubation with cycloheximide or actinomycin D inhibited this effect.