New insights into immunomodulation via overexpressing lipoic acid synthase as a therapeutic potential to reduce atherosclerosis

Atherosclerosis is a systemic chronic inflammatory disease. Many antioxidants including alpha-lipoic acid (LA), a product of lipoic acid synthase (Lias), have proven to be effective for treatment of this disease. However, the question remains whether LA regulates the immune response as a protective mechanism against atherosclerosis. We initially investigated whether enhanced endogenous antioxidant can retard the development of atherosclerosis via immunomodulation. To explore the impact of enhanced endogenous antioxidant on the retardation of atherosclerosis via immune regulation, our laboratory has recently created a double mutant mouse model, using apolipoprotein E-deficient (Apoe^-/-) mice crossbred with mice overexpressing lipoic acid synthase gene (Lias^H/H), designated as Lias^H/HApoe^-/- mice. Their littermates, Lias^+/+Apoe^-/- mice, served as a control. Distinct redox environments between the two strains of mice have been established and they can be used to facilitate identification of antioxidant targets in the immune response. At 6 months of age, Lias^H/HApoe^-/- mice had profoundly decreased atherosclerotic lesion size in the aortic sinus compared to their Lias^+/+Apoe^-/- littermates, accompanied by significantly enhanced numbers of regulatory T cells (Tregs) and anti-oxidized LDL autoantibody in the vascular system, and reduced T cell infiltrates in aortic walls. Our results represent a novel exploration into an environment with increased endogenous antioxidant and its ability to alleviate atherosclerosis, likely through regulation of the immune response. These outcomes shed light on a new therapeutic strategy using antioxidants to lessen atherosclerosis.

Biosynthesis of Sulfur-Containing Small Biomolecules in Plants

Sulfur is an essential element required for plant growth. It can be found as a thiol group of proteins or non-protein molecules, and as various sulfur-containing small biomolecules, including iron-sulfur (Fe/S) clusters, molybdenum cofactor (Moco), and sulfur-modified nucleotides. Thiol-mediated redox regulation has been well investigated, whereas biosynthesis pathways of the sulfur-containing small biomolecules have not yet been clearly described. In order to understand overall sulfur transfer processes in plant cells, it is important to elucidate the relationships among various sulfur delivery pathways as well as to investigate their interactions. In this review, we summarize the information from recent studies on the biosynthesis pathways of several sulfur-containing small biomolecules and the proteins participating in these processes. In addition, we show characteristic features of gene expression in Arabidopsis at the early stage of sulfate depletion from the medium, and we provide insights into sulfur transfer processes in plant cells.

Impact of sunflower (Helianthus annuus L.) plastidial lipoyl synthases genes expression in glycerolipids composition of transgenic Arabidopsis plants

Lipoyl synthases are key enzymes in lipoic acid biosynthesis, a co-factor of several enzyme complexes involved in central metabolism. Plant pyruvate dehydrogenase complex (PDH), located in mitochondria and plastids, catalyses the first step of fatty acid biosynthesis in these organelles. Among their different components, the E2 subunit requires the lipoic acid prosthetic group to be active. De novo lipoic acid biosynthesis is achieved by the successive action of two enzymes on octanoyl-ACP: octanoyltransferase (LIP2) and lipoyl synthase (LIP1). In this study, two plastidial lipoyl synthase genes from sunflower (Helianthus annuus L.) were identified (HaLIP1p1 and HaLIP1p2), sequenced and cloned in a heterologous production system (Escherichia coli). Gene expression studies revealed similar expression patterns for both isoforms, with a slight predominance of HaLIP1p1 in vegetative tissues and mature seeds. Tertiary structural models for these enzymes indicate they both have the same theoretical catalytic sites, using lipoyl-lys and 5-deoxyadenosine as docking substrates. The fatty acid profile of E. coli cells overexpressing HaLIP1p1 and HaLIP1p2 did not present major differences, and the in vivo activity of both proteins was confirmed by complementation of an E. coli JW0623 mutant in which lipoyl synthase is defective. Although no significant differences were detected in the total fatty acid composition of transgenic Arabidopsis thaliana seeds overexpressing any of both proteins, a lipidomic analysis revealed a redistribution of the glycerolipid species, accompanied with increased phosphatidylethanolamine (PE) content and a decrease in diacyglycerols (DAG) and phosphatidylcholine (PC). Depletion of the SAM co-factor caused by HaLIP1p1 and HaLIP1p2 overexpression in transgenic plants could explain this remodelling through its effects on PC synthesis.

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.

Expression of 3-Mercaptopyruvate Sulfurtransferase in the Mouse

3-Mercaptopyruvate sulfurtransferase (MST) is one of the principal enzymes for the production of hydrogen sulfide and polysulfides in mammalians, and emerging evidence supports the physiological significance of MST. As a fundamental study of the physiology and pathobiology of MST, it is necessary to establish the tissue distribution of MST in mice. In the present study, the expression of MST in various organs of adult and fetal mice was analyzed by Western blotting and enzyme-immunohistochemistry. Moreover, the histology of MST gene-deficient mice was examined. Western blotting revealed that all organs examined had MST. The brain, liver, kidneys testes, and endocrine organs contained large amounts of MST, but the lungs, spleen, thymus, and small intestine did not. Immunohistochemically, the MST expression pattern varies in a cell-specific manner. In the brain, neural and glial cells are positively stained; in the lung, bronchiolar cells are preferentially stained; in the liver, hepatocytes around central veins are more strongly stained; renal convoluted cells are strongly stained; and pancreatic islets are strongly stained. Fetal tissues were studied, and MST expression was found to be similar before and after birth. Histological observation revealed no remarkable findings in MST gene-deficient mice. The present study revealed fundamental information regarding the MST expression of various organs in adult and fetal mice, and the morphological phenotype of MST gene-deficient mice.

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.

Brain 3-Mercaptopyruvate Sulfurtransferase (3MST): Cellular Localization and Downregulation after Acute Stroke

3-Mercaptopyruvate sulfurtransferase (3MST) is an important enzyme for the synthesis of hydrogen sulfide (H2S) in the brain. We present here data that indicate an exclusively localization of 3MST in astrocytes. Regional distribution of 3MST activities is even and unremarkable. Following permanent middle cerebral artery occlusion (pMCAO), 3MST was down-regulated in both the cortex and striatum, but not in the corpus collosum. It appears that the down-regulation of astrocytic 3MST persisted in the presence of astrocytic proliferation due to gliosis. Our observations indicate that 3MST is probably not responsible for the increased production of H2S following pMCAO. Therefore, cystathionine β-synthase (CBS), the alternative H2S producing enzyme in the CNS, remains as a more likely potential therapeutic target than 3MST in the treatment of acute stroke through inhibition of H2S production.

The ISC [corrected] proteins Isa1 and Isa2 are required for the function but not for the de novo synthesis of the Fe/S clusters of biotin synthase in Saccharomyces cerevisiae

The yeast Saccharomyces cerevisiae is able to use some biotin precursors for biotin biosynthesis. Insertion of a sulfur atom into desthiobiotin, the final step in the biosynthetic pathway, is catalyzed by biotin synthase (Bio2). This mitochondrial protein contains two iron-sulfur (Fe/S) clusters that catalyze the reaction and are thought to act as a sulfur donor. To identify new components of biotin metabolism, we performed a genetic screen and found that Isa2, a mitochondrial protein involved in the formation of Fe/S proteins, is necessary for the conversion of desthiobiotin to biotin. Depletion of Isa2 or the related Isa1, however, did not prevent the de novo synthesis of any of the two Fe/S centers of Bio2. In contrast, Fe/S cluster assembly on Bio2 strongly depended on the Isu1 and Isu2 proteins. Both isa mutants contained low levels of Bio2. This phenotype was also found in other mutants impaired in mitochondrial Fe/S protein assembly and in wild-type cells grown under iron limitation. Low Bio2 levels, however, did not cause the inability of isa mutants to utilize desthiobiotin, since this defect was not cured by overexpression of BIO2. Thus, the Isa proteins are crucial for the in vivo function of biotin synthase but not for the de novo synthesis of its Fe/S clusters. Our data demonstrate that the Isa proteins are essential for the catalytic activity of Bio2 in vivo.

Biotin synthase is catalytic in vivo, but catalysis engenders destruction of the protein

Biotin synthase is responsible for the synthesis of biotin from dethiobiotin and sulfur. Although the name of the protein implies that it functions as an enzyme, it has been consistently reported that biotin synthase produces <1 molecule of biotin per molecule of protein in vitro. Moreover, the source of the biotin sulfur atom has been reported to be the [2Fe-2S] center of the protein. Biotin synthase has therefore been designated as a substrate or reactant rather than an enzyme. We report in vivo experiments demonstrating that biotin synthase is catalytic but that catalysis puts the protein at risk of proteolytic destruction.

Post-translational regulation of mercaptopyruvate sulfurtransferase via a low redox potential cysteine-sulfenate in the maintenance of redox homeostasis

3-Mercaptopyruvate sulfurtransferase (MST) (EC 2.8.1.2), a multifunctional enzyme, catalyzes a transsulfuration from mercaptopyruvate to pyruvate in the degradation process of cysteine. A stoichiometric concentration of hydrogen peroxide and of tetrathionate (S(4)O(6)(2-)) inhibited rat MST (k(i) = 3.3 min(-1), K(i) = 120.5 microM and k(i) = 2.5 min(-1), K(i) = 178.6 microM, respectively). The activity was completely restored by dithiothreitol or thioredoxin with a reducing system containing thioredoxin reductase and NADPH, but glutathione did not restore the activity. On the other hand, an excess molar ratio dose of hydrogen peroxide inactivated MST. Oxidation with a stoichiometric concentration of hydrogen peroxide protected the enzyme against reaction by iodoacetate, which modifies a catalytic Cys(247), suggesting that Cys(247) is a target of the oxidants. A matrix-assisted laser desorption/ionization-time-of-flight mass spectrometric analysis revealed that hydrogen peroxide- and tetrathionate-inhibited MSTs were increased in molecular mass consistent with the addition of atomic oxygen and with a thiosulfate (S(2)O(3)(-)), respectively. Treatment with dithiothreitol restored modified MST to the original mass. These findings suggested that there was no nearby cysteine with which to form a disulfide, and mild oxidation of MST resulted in formation of a sulfenate (SO(-)) at Cys(247), which exhibited exceptional stability and a lower redox potential than that of glutathione. Oxidative stress decreases MST activity so as to increase the amount of cysteine, a precursor of thioredoxin or glutathione, and furthermore, these cellular reductants restore the activity. Thus the redox state regulates MST activity at the enzymatic level, and on the other hand, MST controls redox to maintain cellular redox homeostasis.

Molybdenum Cofactor Biosynthesis in Humans: Identification of a Persulfide Group in the Rhodanese-like Domain of MOCS3 by Mass Spectrometry†

The human MOCS3 protein contains an N-terminal domain similar to the Escherichia coli MoeB protein and a C-terminal segment displaying similarities to the sulfurtransferase rhodanese. MOCS3 is proposed to catalyze both the adenylation and the subsequent generation of a thiocarboxylate group at the C-terminus of the smaller subunit of molybdopterin (MPT) synthase during Moco biosynthesis in humans. Recent studies have shown that the MOCS3 rhodanese-like domain (MOCS3-RLD) catalyzes the transfer of sulfur from thiosulfate to cyanide and is also able to provide the sulfur for the thiocarboxylation of MOCS2A in a defined in vitro system for the generation of MPT from precursor Z. MOCS3-RLD contains four cysteine residues of which only C412 in the six amino acid active loop is conserved in homologous proteins from other organisms. ESI-MS/MS studies gave direct evidence for the formation of a persulfide group that is exclusively formed on C412. Simultaneous mutagenesis of the remaining three cysteine residues showed that none of them is involved in the sulfur transfer reaction in vitro. A disulfide bridge was identified to be formed between C316 and C324, and possible roles of the three noncatalytic cysteine residues are discussed. By ESI-MS/MS a partially gluconoylated N-terminus of the His6-tagged MOCS3-RLD was identified (mass increment of 178 Da) which resulted in a heterogeneity of the protein but did not influence sulfurtransferase activity.

Iron-sulfur clusters of biotin synthase in vivo: a Mössbauer study

Biotin synthase, the enzyme that catalyzes the last step of the biosynthesis of biotin, contains only [2Fe-2S](2+) clusters when isolated under aerobic conditions. Previous results showed that reconstitution with an excess of FeCl(3) and Na(2)S under reducing and anaerobic conditions leads to either [4Fe-4S](2+), [4Fe-4S](+), or a mixture of [4Fe-4S](2+) and [2Fe-2S](2+) clusters. To determine whether any of these possibilities or other different cluster configuration could correspond to the physiological in vivo state, we have used (57)Fe Mössbauer spectroscopy to investigate the clusters of biotin synthase in whole cells. The results show that, in aerobically grown cells, biotin synthase contains a mixture of [4Fe-4S](2+) and [2Fe-2S](2+) clusters. A mixed [4Fe-4S](2+):[2Fe-2S](2+) cluster form has already been observed under certain in vitro conditions, and it has been proposed that both clusters might each play a significant role in the mechanism of biotin synthase. Their presence in vivo is now another argument in favor of this mixed cluster form.

Biotin synthase from Escherichia coli: isolation of an enzyme-generated intermediate and stoichiometry of S-adenosylmethionine use

A cell-free extract from Escherichia coli containing an E. coli biotin synthase that was expressed to approx. 1% of soluble cell protein by cloning the E. coli bioB gene was used to investigate the biotin synthase reaction. The pH optimum was between 8 and 8.5, and the reaction velocity was dependent on the concentrations of dethiobiotin, cysteine, S-adenosylmethionine and asparagine. The catalytic-centre activity of the enzyme in vitro was estimated to be 0.95 h-1, and each molecule of enzyme turned over less than one molecule of dethiobiotin, i.e. the enzyme was not acting catalytically. HPLC analysis of reaction mixtures revealed the presence of a compound with the characteristics of an intermediate: (1) it was labelled with 14C, and therefore derived from the [14C]dethiobiotin substrate; (2) it was present only in reaction mixtures containing biotin synthase; (3) it was not derived from [14C]biotin; (4) 35S from [35S]cystine was incorporated into the intermediate during the reaction; (5) its synthesis was dependent on the presence of S-adenosylmethionine, and was decreased when free cysteine was omitted from the reaction; (6) it could be isolated from the reaction mixture by chromatography and then re-introduced into an assay as the substrate, whereupon it was converted to biotin; (7) this conversion to biotin was S-adenosylmethionine-dependent. During the reaction S-adenosylmethionine was cleaved to methionine and presumably 5'-deoxyadenosine. Observation of the intermediate allowed us to perform experiments to determine the stoichiometry of S-adenosylmethionine use. We propose that two molecules of S-adenosylmethionine are used to synthesize one molecule of biotin, i.e. one from dethiobiotin to the intermediate, and a second from the intermediate to biotin.

Role of amino acid residues in the active site of rat liver mercaptopyruvate sulfurtransferase. CDNA cloning, overexpression, and site-directed mutagenesis

A complete amino acid structure of rat liver mercaptopyruvate sulfurtransferase (MST, EC 2.8.1.2) was determined by sequence analysis of cDNA and purified enzyme. The enzyme consists of 296 amino acid residues with a calculated molecular mass of 32,808 Da. Sequence identity in cDNA and the deduced amino acid sequence are 65 and 60% respectively, between rat MST and rhodanese. By their entire sequence similarity MST and rhodanese are confirmed to be evolutionarily related enzymes (Nagahara, N., Okazaki, T., and Nishino, T. (1995) J. Biol. Chem. 270, 16230-16235). The conversion of MST to rhodanese was attempted, and the role of amino acid residues was studied by site-directed mutagenesis with the isolated cDNA of rat liver MST. There is a strong possibility that Cys247 is a catalytic site of MST. Arg187 is suggested to be a binding site of both mercaptopyruvate and thiosulfate in MST. Arg196, which is missed in rhodanese, is important for catalysis in MST. On the other hand, the substitution of Arg for Gly248 or Lys for Ser249 facilitates catalysis of thiosulfate in MST. It is concluded that Arg187 and Arg196 of rat MST are critical residues in determining substrate specificity for mercaptopyruvate. On the other hand, Arg185, Arg247, and Lys248 of rat rhodanese are critical residues in determining substrate specificity for thiosulfate.

Biotin synthase from Arabidopsis thaliana. cDNA isolation and characterization of gene expression

The full-length BIO2 cDNA from Arabidopsis thaliana was isolated using an expressed sequence tag that was homologous to the Escherichia coli biotin synthase gene (BioB). Comparisons of the deduced amino acid sequence from BIO2 with bacterial and yeast biotin synthase homologs revealed a high degree of sequence similarity. The amino terminus of the predicted BIO2 protein contains a stretch of hydrophobic residues similar in composition to transit peptide sequences. BIO2 is a single-copy nuclear gene in Arabidopsis that is expressed at high levels in the tissues of immature plants. Expression of BIO2 was higher in the light relative to dark and was induced 5-fold during biotin-limited conditions. These results demonstrate that expression of at least one gene in this pathway is regulated in response to developmental, environmental, and bio-chemical stimuli.

Cloning and sequence analysis of the 5'-flanking region of the estrogen sulfotransferase gene: steroid response elements and cell-specific nuclear DNA-binding proteins

A 2954 bp region of the guinea pig estrogen sulfotransferase gene was cloned and sequenced including 2888 nt upstream of the cap site. This represents the first cloning of the promoter region of a steroid sulfotransferase gene. The 5'-flanking region was found to contain a conventional TATA box variant and sequences homologous to estrogen and glucocorticoid response elements. Gel mobility shift assays detected the presence of nuclear proteins in adrenocortical SW-13 and Y-1 cells that bind specifically to 30 mer DNA sequences containing either estrogen or glucocorticoid response elements. In contrast, gel shift experiments using 3T3 fibroblast cells failed to demonstrate similarly upshifted bands. Block deletion studies indicated that regulation of basal estrogen sulfotransferase promoter activity was located within the first 1000 bp upstream of the transcription initiation site.

Inconsistent expression of glycolipid sulfotransferase activity between hepatoma and serum

Glycolipid sulfotransferase activity in human and rat hepatocellular carcinoma tissues was studied, since an elevated level of the enzyme activity in serum had been demonstrated in cancer patients. The level of the enzyme activity in carcinoma tissues, however, could not be distinguished from that of normal controls. Similar observations were made for rat hepatoma. A higher level of enzyme activity was observed in the female than in the male. Inconsistent expression between hepatoma tissue and serum suggests that humoral factor(s) derived from hepatoma tissue stimulates production of the sulfotransferase, which is released into the blood-stream in the host.

Synthesis of rhodanese in Hep 3B cells

The biosynthesis of rhodanese was studied in human hepatoma cell lines by immunoblotting and pulse-labeling experiments using polyclonal antibodies raised against the bovine liver enzyme. Rhodanese, partially purified from human liver, showed an apparent molecular weight of 33,000 daltons, coincident with that of rhodanese from Hep 3B cells. After pulse labeling of Hep 3B cells both at 37 degrees C and 25 degrees C, rhodanese in the cytosol fraction exhibited the same molecular weight as the enzyme isolated from the particulate fraction containing mitochondria. Moreover, newly synthesized rhodanese from total Hep 3B RNA translation products showed the same electrophoretic mobility as rhodanese from Hep 3B cells. These results suggest that rhodanese, unlike most mitochondrial proteins, is not synthesized as a higher molecular weight precursor.

Comparison of the mechanisms of action of insulin and triiodothyronine on the synthesis of cerebroside sulfotransferase in cultures of cells dissociated from brains of embryonic mice

The effect of low (physiological) concentrations of insulin (2 and 20 ng/ml) and L-triiodothyronine (T3) were studied on two myelin-related enzymes: (1) the 3'-phosphoadenosine-5'-phosphosulfate:cerebroside sulfotransferase (CST, EC 2.8.2.11) catalyzing the production of sulfatide, and (2) the myelin enzyme, 2',3'-cyclic nucleotide 3'-phosphohydrolase (CNP, EC 3.1.4.3.7) in myelinogenic cultures of cells dissociated from embryonic mouse brain. Insulin treatment (20 ng/ml) of the cells in the presence of serum increased CST activity at 18 and 25 days in vitro (DIV) by 86 and 211%, respectively. At 18 DIV and under the same conditions, CNP was significantly stimulated (95%) by high doses of insulin (2,000 ng/ml) only, while arylsulfatase A (EC 3.1.6.1) or cerebroside sulfatase activities, both of which are involved in sulfatide degradation, were unchanged. Thus, it can be assumed that the observed increase of the incorporation of [35S]O4 into sulfatide after insulin treatment of mixed cell cultures is the result of CST induction rather than a decreased catabolism. The level of CST activity in insulin-treated cells (20 ng/ml) in serum-free medium was also increased at 18 and 25 DIV by about 50 and 70%, respectively. Conversely, none of the insulin concentrations used in the absence of serum (even at high doses) had any effect, either at 18 or 25 DIV on CNP and ASA activities. The involvement of insulin in the regulation of sulfatide synthesis was further confirmed by dose-response curves relating the activity of CST to hormone concentration in the medium. The increase in the activity of CST in insulin-treated cells was due only to the increase in the Vmax of this enzyme, suggesting that it may be attributed to enzyme induction. A study of kinetic parameters of CST indicated that there were no differences in pH optimum and Km values between control and induced enzyme. Further experiments using cycloheximide point to a direct effect of insulin on oligodendrocyte CST induction. Data similar to those described above for insulin were also obtained with T3. As for insulin, T3 stimulated the induction of CST but in serum-free medium only. This effect was prevented by cycloheximide. In addition, the induction of CST by T3 was blocked by actinomycin D. This was not the case for insulin. These results suggest that T3 and insulin act on CST by different mechanisms, i.e. at transcriptional and post-translational levels, respectively. Apart from this, the insulin effect on CST activity was additive to that of T3.(ABSTRACT TRUNCATED AT 400 WORDS)

Expression of hydroxysteroid sulphotransferase is related to estrogen receptor status in human mammary cancer

A positive correlation between the expression of estrogen sulphotransferase (EC 2.8: 2.4) and the estrogen receptor (ER) in human breast cancer tissues was previously demonstrated. We have now established that a similar correlation exists between the expression of hydroxysteroid sulphotransferase (EC 2.8: 2.2) and ER in such tissues. Enzyme activity was present in 93% of the ER + tumor cytosols (mean 59 +/- 44 (SD) pmol dehydroepiandrosterone sulphate formed per mg protein per 2 h (n = 42). Activity was detected in 68% of ER - tumors and this was significantly lower (mean 21 +/- 26 (SD) (n = 19), P less than 0.001) than the former group. Metabolism of estradiol-17 beta (E2) and the adrenal-derived estrogen 5-androstene-3 beta, 17 beta-diol (ADIOL), which is a substrate for hydroxysteroid sulphotransferase but not estrogen sulphotransferase, was studied in four ER + human mammary cancer cell lines (MCF-7, T47-D, MDA-MB-361 and ZR-75-1) and four ER-human mammary cell lines (BT-20, MDA-MB-231, MDA-MB-330 and HBL-100), employing steroid concentrations of 1 nM. At this concentration, formation of ester sulphates was a major route of metabolism in the ER + cell lines; E2 yielding a mean of 6.5 pmol estrogen monosulphates/mg DNA in 16 h and ADIOL yielding a mean of 9.4 pmol C19-5-ene steroid monosulphates/mg DNA in 16 h. In three of the four ER - cell lines, formation of sulphates from E2 occurred at an eight-fold lower rate (mean 0.8 pmol estrogen sulphates/mg DNA in 16 h), whereas MDA-MB-330 cells did not form estrogen sulphates. Only one of the four ER- cell lines (BT-20) sulphurylated ADIOL and this was at a 12-fold lower rate compared to the mean value for the ER + cel lines. Oxidation of E2 and ADIOL occurred in all cell lines and was generally the major route of metabolism in the ER - cells. A significant correlation between formation of estrone and dehydroepiandrosterone occurred for all cell lines (r = 0.98, P less than 0.001) indicating that the same 17 beta-hydroxysteroid dehydrogenase was probably involved. Since ADIOL is estrogenic in a number of systems at the concentration found in the blood of Western women (approximately 2 nM), the coordinated expression of hydroxysteroid sulphotransferase, estrogen sulphotransferase, and ER, supports the concept of a functional relationship between estrogen action via ER and sulphurylation reactions.

Cloning of the biotin synthetase gene from Bacillus sphaericus and expression in Escherichia coli and Bacilli

Biotin synthetase (BS) catalyses the biotransformation of dethiobiotin (DTB) to biotin. Here we report the cloning, characterization and expression of the gene encoding BS of Bacillus sphaericus. A recombinant plasmid pSB01, containing an 8.2-kb DNA fragment from B. sphaericus, was isolated by phenotypic complementation of an Escherichia coli bioB strain. Nucleotide sequence analysis of this fragment and N-terminal sequence determination of the recombinant protein product revealed that the bioB gene of B. sphaericus consists of a 996-bp open reading frame which is closely associated with at least one other gene. E. coli cells transformed with a bioB expression vector performed efficient bioconversion of DTB to biotin under defined culture conditions. Biotin production from transformed Bacillus subtilis and B. sphaericus recombinant strains was also demonstrated. Comparison of the amino acid sequences of BS from E. coli and B. sphaericus revealed extensive similarity.

Detection of time-dependent and oxidatively induced antigens of bovine liver rhodanese with monoclonal antibodies

Rhodanese has been extensively utilized as a model protein for the study of enzyme structure-function relationships. An immunological study of conformational changes occurring in rhodanese as a result of oxidation or thermal inactivation was conducted. Three monoclonal antibodies (MABs) to rhodanese were produced. Each MAB recognized a unique epitope as demonstrated by binding of the MABs to different proteolytic fragments of rhodanese. While none of the MABs significantly bound native, soluble, sulfur-substituted bovine rhodanese, as indicated in indirect enzyme-linked immunosorbent assay experiments, each MAB was immunoadsorbed from solution by soluble rhodanese as a function of the time rhodanese was incubated at 37 degrees C. Thus, as rhodanese was thermally inactivated, conformational changes resulted in the expression of three new epitopes. Catalytic conformers demonstrated different rates of thermally induced antigen expression. Each MAB also recognized epitopes expressed when rhodanese was immobilized on microtiter plates at 37 degrees C. Two conformers resulting from oxidation of rhodanese by hydrogen peroxide were identified immunologically. All MABs recognized rhodanese that was oxidized with peroxide and allowed to undergo a secondary cyanide-dependent reaction which also resulted in a fluorescence shift and increased proteolytic susceptibility. Only one MAB was capable of recognizing an epitope expressed when rhodanese was oxidized with peroxide and then separated from the reactants to prevent induction of the secondary conformational changes.

Dual regulation of 3 beta-hydroxysteroid dehydrogenase, 17 alpha-hydroxylase, and dehydroepiandrosterone sulfotransferase by adenosine 3',5'-monophosphate and activators of protein kinase C in cultured human adrenocortical cells

The relationship between cAMP and protein kinase C in the regulation of 3 beta-hydroxysteroid dehydrogenase (3 beta HSD), 17 alpha-hydroxylase, and sulfotransferase was examined in human fetal adrenocortical cells under defined serum-free conditions in culture. Forskolin induced 3 beta HSD and 17 alpha-hydroxylase in a dose-dependent manner, with maximal effects at 10 microM. 12-O-Tetradecanoyl phorbol 13-acetate (TPA) at 1 nM depressed the induction of 17 alpha-hydroxylase activity by forskolin by more than 95% and increased the stimulation of 3 beta HSD activity by forskolin by 4- to 5-fold. Increases were maximal at 48-72 h of incubation. Dehydroepiandrosterone sulfotransferase activity increased over 48 h when cells were transferred to serum-free defined medium. Addition of 10 microM forskolin stimulated sulfotransferase activity only when cells remained in 10% serum. TPA at 1 nM inhibited the increase in sulfotransferase activity. The concentration of TPA required for inhibition of forskolin-stimulated 17 alpha-hydroxylase and sulfotransferase activity was similar to that required for enhancement of forskolin-induced 3 beta HSD activity, suggesting that comparable levels of C kinase activation are involved in these events. Angiotensin II, carbachol, epidermal growth factor, and fibroblast growth factor had actions similar to those of TPA on one or more of these enzyme activities. TPA also had similar actions on enzyme activities when they were stimulated by cAMP analogs rather than by forskolin. These studies suggest that adrenal steroid biosynthesis is under dual regulation by cAMP and protein kinase C. cAMP induces enzymes required for synthesis of 17 alpha-hydroxylated steroids, including the adrenal androgens. Activation of protein kinase C may play a complementary role by enhancing the induction of enzymes required for non-17 alpha-hydroxylated steroid biosynthesis and inhibiting those involved in the synthesis of androgens.

Oestrogen sulfotransferase: isolation of a high specific activity species from bovine placenta

During the course of a study of the control of expression of steroid-binding proteins in human mammary cancer oestrogen sulfotransferase was isolated from bovine placenta. By a combination of salt precipitation and ion-exchange and gel-permeation chromatography two forms of the enzyme were isolated. The forms, which apparently differ only in charge, have specific activities 100-300 times greater than has previously been reported for the enzyme. Partial peptide sequences of these enzymes are presented.

Species differences of glucuronidation and sulfation in relation to hepatocarcinogenesis

The role of glucuronidation and sulfation in the control of proximal and ultimate carcinogens is briefly reviewed. In accordance with the adopted practice of tumor risk assessment, data from two rodent species (rat, mouse) and man have been compared. Sulfate esters have been established as ultimate carcinogens in 2-acetylaminofluorene, safrole and estragole induced hepatocarcinogenesis. In interspecies comparisons the tumor incidence paralleled sulfotransferase activity (Miller and Miller 1981). Glucuronides are often stable transport forms of carcinogens and in this way determine their organ specificity, for example in 2-naphthylamine-induced bladder carcinogenesis and in colon carcinogenesis produced by 2',3-dimethyl-4-aminobiphenyl. In contrast to sulfotransferase activity certain UDP-glucuronyltransferase activities are differentially inducible by xenobiotics. A 3-methylcholanthrene-inducible phenol-glucuronyltransferase (GT1), present in rat, mouse and man, appears to be part of an adaptive program to detoxify aromatic hydrocarbons. After initiation of hepatocarcinogenesis permanent alterations of these enzymes occur; GT1 is markedly increased whereas sulfotransferase is decreased. Together with changes of other drug metabolizing enzymes these alterations often lead to toxin-resistance of initiated hepatocytes. This phenomenon may facilitate selective growth of initiated hepatocytes and may enhance the probability of multiple hits in their genome.

Effect of culture age on drug metabolizing enzymes and their induction in primary cultures of rat hepatocytes

In order to further establish optimal and reproducible conditions for the use of primary hepatocyte cultures in studies of drug metabolism, the effect of culture age on the basal and induced activities of ethoxycoumarin O-deethylase (ECDE), UDP-glucuronyltransferase (GT) [methylumbelliferone (MU) and p-nitrophenol (pNP) as substrates] and sulfotransferase (MU) were measured. In contrast to the monooxygenase activity conjugating activities were maintained for 2-3 weeks in culture, although especially sulfate conjugation showed a transient decline during the first days, and GT activity increased later on during culture. Low induction of ECDE with both phenobarbital (PB) and 3-methylcholanthrene (MC) was seen during the first day in culture, and maximum induction was obtained when inducer was added on the second or third day. The MC inducible GT (pNP) exhibited a similar behaviour indicating that the coordinated induction of the MC inducible activities is preserved in culture. The results show that primary cultures of hepatocytes can be used to study conjugating enzymes and their regulation. However, each functional parameter that is to be investigated in hepatocyte cultures should first be studied as a function of culture age to establish the optimum time.

Turnover of succinyl-CoA:3-oxoacid CoA-transferase in glioma and neuroblastoma cells. Specific influence of acetoacetate in neuroblastoma cells

The specific activity of succinyl-CoA:3-oxo-acid CoA-transferase (3-oxoacid CoA-transferase, EC 2.8.3.5) increases significantly during growth in culture in both mouse neuroblastoma N2a and rat glioma C6 cells. To investigate the mechanism(s) responsible for this, antibody specific for rat brain 3-oxoacid CoA-transferase was raised in rabbits. Immunotitrations of 3-oxoacid CoA-transferase from neuroblastoma and glioma cells on days 3 and 7 of growth after subculture showed that the ratio of 3-oxoacid CoA-transferase activity to immunoprecipitable enzyme protein remained constant, indicating that differences in specific activity of the enzyme at these times in both cell types reflect differences in concentration of enzyme protein. In glioma cells, the relative rate of 3-oxoacid CoA-transferase synthesis was about 0.04-0.05% throughout 9 days in culture. In contrast, the relative rate of synthesis of 3-oxo-acid CoA-transferase in neuroblastoma cells was about 0.07-0.08% on days 3, 5 and 7 after subculture, but fell to 0.052% on day 9. The degradation rates of total cellular protein (t1/2 = 28 h) and 3-oxoacid CoA-transferase (t1/2 = 46-50 h) were similar in both cell lines. The rise in specific activity of the enzyme in both cell lines from days 3 to 7 without a significant increase in the relative rate of synthesis reflects a slow approach to steady-state conditions for the enzyme secondary to its slow degradation. Differences in 3-oxoacid CoA-transferase specific activity between the two cell lines are apparently due to a difference of about 60% in relative rates of enzyme synthesis. The presence of 0.5 mM-acetoacetate in the medium significantly increased the specific activity of 3-oxoacid CoA-transferase in neuroblastoma cells during the early exponential growth phase. This treatment increased the relative rate of synthesis of 3-oxoacid CoA-transferase by 23% (P less than 0.025) in these cells on day 3, suggesting that substrate-mediated induction of enzyme synthesis is a mechanism of regulation of 3-oxoacid CoA-transferase.

Bile salt sulfotransferase: alterations during maturation and non-inducibility during substrate ingestion

Development of the capacity for hepatic biotransformation of potentially toxic, endogenous compounds such as lithocholate may be dependent on induction by substrate or hormonal modulation. Our aim was to observe the ontogeny of hepatic sulfotransferase (ST) activity, a presumed detoxification pathway, and to determine the effect of substrate ingestion and cortisone administration on ST activity. Pregnant rats were fed a standard chow diet containing lithocholate; the maternal diet was continued during the suckling and weaning phase of the pups. Liver cytosol and serum were obtained from dams and from pups at weekly intervals from fetal life through 4 weeks of age. In controls, there was a progressive increase in hepatic ST activity from 6.2 +/- 2.9 pmol/mg protein per min, (mean +/- SEM) in fetal liver, 18.1 +/- 3.9 at 1 week, an 33.6 +/- 7.2 at 2 weeks to a peak of 56.4 +/- 11.8 at 3 weeks of age. In female rats older than 4 weeks of age, ST activity in hepatic cytosol was threefold higher than in males. There was a decline to adult levels (9.2 +/- 2.4 in males and 39.4 +/- 4.3 in females) at 56 days of life. Cortisone acetate administration had no effect on enzyme activity in pups except those 3 weeks old or older in which there was a precocious decrease in enzyme activity to adult levels. The administration of lithocholate caused a dose-related postnatal alteration of intrahepatic bile ducts manifest as cholangitis with ductular proliferation; hepatocytes were spared.(ABSTRACT TRUNCATED AT 250 WORDS)

Induction by carrot allelochemicals of insecticide-metabolising enzymes in the southern armyworm (Spodoptera eridania)

Carrot foliage monoterpenes induce cytochrome P-450 up to 2.9-fold, NADPH cytochrome c (P-450) reductase up to 1.6-fold, NADPH-oxidation up to 3.8-fold, aldrin epoxidation up to 1.5-fold in southern armyworm larval midgut tissues when incorporated in their diet at 0.2% for 3 days. Stigmasterol and ergosterol did not substantially induce microsomal oxidase activities and significantly inhibited GSH S-aryltransferase activity and sulfotransferase activity. Coumarin did not substantially affect microsomal oxidase and sulfotransferase activity but is the most potent inducer of GSH S-aryltransferase activity, increasing this activity 7-fold. None of the chemicals is acutely toxic to the sixth instar larvae or affect the larval weight gain except coumarin which significantly depressed the maximal body weight attained.

Induction of porcine uterine estrogen sulfotransferase activity by progesterone

Studies have been carried out which were designed to examine the hormonal requirement for the appearance of estrogen sulfotransferase activity in porcine uteri. Mature, ovariectomized (OVX) gilts were housed for 3 weeks before being treated with various regimens of estradiol-17 beta (E2) and progesterone (P). Uteri were then removed, minced, incubated for 2 h with [3H] E2 (10(-8) M) and Na2 35SO4 (10(-4) M) and the labeled metabolic products were extracted and analyzed. Endometrial samples were also taken for the determination of E2 and P cytoplasmic and nuclear receptors (R). It was found that 4 daily injections of 250 micrograms of E2 was sufficient to bring plasma E2 concentrations to that representative of a normal estrous cycle (approx. 30 pg/ml) and to induce cytoplasmic PR to high levels (7000--19000 fmol/mg DNA). Estrogen sulfotransferase activity, which was negligible in OVX and E2-treated pigs, increased to near normal secretory levels (4 pmol product/h per 0.4 g tissue) only in pigs primed with E2 and subsequently treated with E2 and P (25--250 mg/day, 3 days). This treatment also brought about the translocation of PR to the nuclear compartment. The steroid alcohol sulfotransferase activity in these tissues decreased upon ovariectomy and remained unaffected by the hormone treatments. Endometria from treated and untreated pigs were cultured for a period up to 7 days. During this time E2 (10(-8) M) induced and/or maintained PR and P (10(-6) M) was shown to stimulate estrogen sulfurylation concomitant with the translocation of PR to the nucleus. These studies have demonstrated that, in OVX pigs and endometrial cultures, P stimulated uterine estrogen sulfotransferase activity to a level normally found in secretory uteri. In order for P to bring about elevated levels of estrogen sulfurylation it was necessary that the endometrium contain adequate concentrations of cytoplasmic PR (which required E2 priming of the system) and the P receptor complex must display nuclear translocation.

Induction of estrogen sulfotransferase in the human endometrium by progesterone in organ culture

It has been established that progesterone will induce 17 beta-estradiol (E2) dehydrogenase in the human endometrium. Whether it plays a similar role in the induction of estrogen sulfotransferase is not known, although this is likely, since estrone sulfate is the main metabolite of E2 when incubated with secretory, but not proliferative, human endometrium. We have now examined the influence of progesterone on both enzymes in endometrial tissue in organ culture. Estrogen sulfotransferase activity was not detectable in the cytosol of proliferative tissue when cultured in the absence of hormone, but was induced by culture in the presence of progesterone to a value (mean +/- SEM) of 19.7 +/- 5.3 pmol E2-3-sulfate h-1 mg cytosol protein-1. A significant (P less than 0.05) induction of E2 dehydrogenase activity was also observed in the same tissues [from 3.7 +/- 1.9 to 10.4 +/- 2.7 (mean +/- SEM) nmol estrone h-1 mg microsomal protein-1]. Corresponding values for secretory endometrium, when cultured under identical conditions in the absence of progesterone, were 20.3 +/- 11.6 pmole h-1 mg-1 and 31.1 +/- 25.1 nmol h-1 mg-1 for estrogen sulfotransferase and E2 dehydrogenase, respectively. Values not significantly different from these were obtained when progesterone was present in the cultures. These data indicate that progesterone secretion during the luteal phase is responsible for the induction of both E2 dehydrogenase and sulfotransferase activities in the endometrium. It is likely that these enzymes are closely coupled, resulting in the rapid metabolism of E2 by formation and excretion of estrone sulfate.

Thiosulfate oxidase from an Alcaligenes grown on mercaptosuccinate

The soil isolate Alcaligenes sp. (M1) was able to use mercaptosuccinate (MS) as a sole source of carbon, sulfur, and energy. Resting cells oxidized the sulfur moiety of MS completely to sulfate. Thiosulfate oxidase, rhodanese, sulfite oxidase, and adenosine-5-phosphosulfate reductase were all detected in crude extracts. However, only thiosulfate oxidase appeared to be induced by growth of the organism on mercaptosuccinate. The intracellular thiosulfate oxidase was purified 139 to 170-fold by a procedure which included MnCl2 precipitation, treatment with calcium phosphate gel, and successive column chromatography on diethylaminoethyl (DEAE) Sephadex and Sephadex G-150, respectively. The resultant enzyme had a pH optimum which appeared to be below 5.0 and an optimum temperature of 40 °C using ferricyanide as electron acceptor. However, with cytochrome c as electron acceptor the pH optimum was 7.2 to 7.6. No activity was observed with other electron acceptors such as methylene blue, nicotinamide-adenine dinucleotide, 2,6-dichlorophenol-indophenol, and flavine-adenine dinucleotide. Enzymatic activity was inhibited 100% by 10−3 M mercuric chloride and 90% by 10−3 M p-chloromercuribenzoate (p-CMB). The molecular weight of the enzyme was found to be about 90 000. Resting cells and thiosulfate oxidase converted thiosulfate labeled in the inner sulfur atom to tetrathionate as the only detectable product, thereby suggesting that thiosulfate oxidase does not play a direct role in sulfate formation from mercaptosuccinate.