Regulation of glucocorticoids of arginase and argininosuccinate synthetase in cultured rat hepatoma cells

Simultaneous activation of genes encoding urea cycle enzymes and gluconeogenetic enzymes coincides with a corticosterone surge period before metamorphosis in Xenopus laevis

Amphibian tadpoles are postulated to excrete ammonia as nitrogen metabolites but to shift from ammonotelism to ureotelism during metamorphosis. However, it is unknown whether ureagenesis occurs or plays a functional role before metamorphosis. Here, the mRNA-expression levels of two urea cycle enzymes (carbamoyl phosphate synthetase I [CPSI] and ornithine transcarbamylase [OTC]) were measured beginning with stage-47 Xenopus tadpoles at 5 days post-fertilization (dpf), between the onset of feeding (stage 45, 4 dpf) and metamorphosis (stage 55, 32 dpf). CPSI and OTC expression levels increased significantly from stage 49 (12 dpf). Urea excretion was also detected at stage 47. A transient corticosterone surge peaking at stage 48 was previously reported, supporting the hypothesis that corticosterone can induce CPSI expression in tadpoles, as found in adult frogs and mammals. Stage-46 tadpoles were exposed to a synthetic glucocorticoid, dexamethasone (Dex, 10-500 nM) for 3 days. CPSI mRNA expression was significantly higher in tadpoles exposed to Dex than in tadpoles exposed to the vehicle control. Furthermore, glucocorticoid receptor mRNA expression increased during the pre-metamorphic period. In addition to CPSI and OTC mRNA upregulation, the expression levels of three gluconeogenic enzyme genes (glucose 6-phosphatase, phosphoenolpyruvate carboxykinase, and fructose-1,6-bisphosphatase 1) increased with the onset of urea synthesis and excretion. These results suggest that simultaneous induction of the urea cycle and gluconeogenic enzymes coincided with a corticosterone surge occurring prior to metamorphosis. These metabolic changes preceding metamorphosis may be closely related to the onset of feeding and nutrient accumulation required for metamorphosis.

In vivo treatment with progestogens causes immunosuppression of carp Cyprinus carpio leucocytes by affecting nitric oxide production and arginase activity

In this study, carp Cyprinus carpio were injected with various steroid compounds, including synthetic and natural progestogens and the glucocorticoid cortisol, to investigate effects on leucocytes isolated from their kidneys. Injection of cortisol led to an increased spleeno-somatic index (I(S)) on day 21 post-injection (pi) and immunosuppressive effects measured as decreased nitric oxide (NO) production and increased arginase activity in isolated leucocytes on days 14 and 21 pi, respectively. Moreover, reduced NO production was also observed after injection of the synthetic progestogens, levonorgestrel (LEV) and medroxyprogesterone acetate. In addition, LEV influenced arginase activity in head kidney cells on day 14 and day 21 pi. This study is the first demonstration in fishes that the application of these steroid compounds in vivo affects NO production and arginase activity of isolated leucocytes.

Argininosuccinate synthetase from the urea cycle to the citrulline-NO cycle

Argininosuccinate synthetase (ASS, EC 6.3.4.5) catalyses the condensation of citrulline and aspartate to form argininosuccinate, the immediate precursor of arginine. First identified in the liver as the limiting enzyme of the urea cycle, ASS is now recognized as a ubiquitous enzyme in mammalian tissues. Indeed, discovery of the citrulline-NO cycle has increased interest in this enzyme that was found to represent a potential limiting step in NO synthesis. Depending on arginine utilization, location and regulation of ASS are quite different. In the liver, where arginine is hydrolyzed to form urea and ornithine, the ASS gene is highly expressed, and hormones and nutrients constitute the major regulating factors: (a) glucocorticoids, glucagon and insulin, particularly, control the expression of this gene both during development and adult life; (b) dietary protein intake stimulates ASS gene expression, with a particular efficiency of specific amino acids like glutamine. In contrast, in NO-producing cells, where arginine is the direct substrate in the NO synthesis, ASS gene is expressed at a low level and in this way, proinflammatory signals constitute the main factors of regulation of the gene expression. In most cases, regulation of ASS gene expression is exerted at a transcriptional level, but molecular mechanisms are still poorly understood.

Effects of dietary vitamin E and selenium on arginase activity in the liver, kidneys, and heart of rats treated with high doses of glucocorticoid

The effects of dietary intake of vitamin E and selenium on arginase activity in the liver, kidneys, and heart of rats treated with high doses of prednisolone were investigated. Rats were divided into five groups. Groups 3, 4, and 5 received a daily supplement in their drinking water of vitamin E, Se, and a combination of vitamin E and Se, respectively, for 30 days. For 3 days subsequently, the control group (group 1) was given a placebo, and the remaining four groups were injected intramuscularly with prednisolone. The tissue samples were collected from each group at 4, 8, 12, 24, and 48 h after the last administration of prednisolone. In the group treated with prednisolone alone, arginase activity in the liver was found to have increased at all the time periods, whereas it had decreased significantly in the heart at 48 h. Arginase activity in the kidneys was not affected by prednisolone. Compared to the control and prednisolone groups, arginase activity in the kidneys and heart of the vitamin E- and Se-supplemented groups was found to be significantly increased at all time periods, however, no difference was seen in the combination group. Arginase activity in the liver of the vitamin E-supplemented group was found to have decreased at all time periods, however, in the Se group compared to the prednisolone group it had reduced at 24 and 48 h only. In the combination group compared to the prednisolone group, liver arginase activity increased constantly up to 12 h returning to normal values at 48 h. Vitamin E and Se in combination may prevent the changes in arginase activity in various tissues caused by prednisolone.

Induction of arginase II in livers of bile duct-ligated rats

Nitric oxide (NO) has been implicated in playing a role in liver cirrhosis, but the regulatory mechanisms are still unclear. As arginase shares a common substrate with NO synthase (NOS), the aim of this study was to investigate the expression of arginase I and II in cirrhotic liver. Liver cirrhosis was induced in rats by chronic bile duct ligation (BDL). Controls were sham-operated. Competitive polymerase chain reaction was performed to assay the expression of messenger RNA of arginase I and II. Protein expression was detected by immunohistochemistry and western-blotting. The level of arginine in plasma was lower in BDL rats, while the ornithine level in plasma was correspondingly higher (r= -0.96, P<0.0001). Arginase I messenger RNA was reduced significantly in BDL rats (3.34+/-0.32 vs. 1.32+/-0.21 x 10(4) attomole/microg of total RNA, sham vs. BDL, P<0.001), as well as arginase I protein. In contrast, arginase II mRNA was induced in the livers of BDL rats, with negligible expression in controls (0.35+/-0.11 vs. 3.64+/-0.54 attomole/microg of total RNA, sham vs. BDL, P<0.001). Arginase II protein was localized in some hepatocytes and hyperplastic bile ductular epithelial cells of cirrhotic livers but not in control livers. In conclusion, arginase II was induced in BDL livers, while the expression of arginase I was down-regulated. These data suggest that arginase I and II are regulated differently and may have different functions in the livers of BDL rats. Reduction of arginase I in BDL livers may be responsible for the lowering of arginine levels in the plasma, while induction of arginase II could be important in regulating NO synthesis as well as other important mechanisms involved in liver cirrhosis.

Glucocorticoids inhibit lipopolysaccharide-induced up-regulation of arginase in rat alveolar macrophages

1. As arginase by limiting nitric oxide (NO) synthesis may play a role in airway hyperresponsiveness and glucocorticoids are known to induce the expression of arginase I in hepatic cells, glucocorticoid effects on arginase in alveolar macrophages (AM Phi) were studied. 2. Rat AM Phi were cultured in absence or presence of test substances. Thereafter, nitrite accumulation, arginase activity, and the expression pattern of inducible NO synthase, arginase I and II mRNA (RT - PCR) and proteins (immunoblotting) were determined. 3. Lipopolyssacharides (LPS, 20 h) caused an about 2 fold increase in arginase activity, whereas interferon-gamma (IFN-gamma), like LPS a strong inducer of NO synthesis, had no effect. 4. Dexamethasone decreased arginase activity by about 25% and prevented the LPS-induced increase. Mifepristone (RU-486) as partial glucocorticoid receptor agonist inhibited LPS-induced increase by 45% and antagonized the inhibitory effect of dexamethasone. 5. Two different inhibitors of the NF-kappa B-pathway also prevented LPS-induced increase in arginase activity. 6. Rat AM Phi expressed mRNA and protein of arginase I and II, but arginase I expression was stronger. Arginase I mRNA and protein was not affected by IFN-gamma, but increased by LPS and this effect was prevented by dexamethasone. Both, LPS and IFN-gamma enhanced the levels of arginase II mRNA and protein, effects also inhibited by dexamethasone. As IFN-gamma did not affect total arginase activity, arginase II may represent only a minor fraction of total arginase activity. 7. In rat AM Phi glucocorticoids inhibit LPS-induced up-regulation of arginase activity, an effect which may contribute to the beneficial effects of glucocorticoids in the treatment of inflammatory airway diseases.

IL-4 and IL-13 upregulate arginase I expression by cAMP and JAK/STAT6 pathways in vascular smooth muscle cells

The objectives of this study were to determine whether rat aortic smooth muscle cells (RASMC) express arginase and to elucidate the possible mechanisms involved in the regulation of arginase expression. The results show that RASMC contain basal arginase I (AI) activity, which is significantly enhanced by stimulating the cells with either interleukin (IL)-4 or IL-13, but arginase II (AII) expression was not detected under any condition studied here. We further investigated the signal transduction pathways responsible for AI induction. AI mRNA and protein levels were enhanced by addition of forskolin (1 microM) and inhibited by H-89 (30 microM), suggesting positive regulation of AI by a protein kinase A pathway. Genistein (10 microgramg/ml) and sodium orthovanadate (Na(3)VO(4); 10 microM) were used to investigate the role of tyrosine phosphorylation in the control of AI expression. Genistein inhibited, whereas Na(3)VO(4) enhanced the induction of AI by IL-4 or IL-13. Along with immunoprecipitation and immunoblot analyses, these data implicate the JAK/STAT6 pathway in AI regulation. Dexamethasone (Dex) and interferon (IFN)-gamma were investigated for their effects on AI induction. Dex (1 microM) and IFN-gamma (100 U/ml) alone had no effect on basal AI expression in RASMC, but both reduced AI induction by IL-4 and IL-13. In combination, Dex and IFN-gamma abolished AI induction by IL-4 and IL-13. Finally, both IL-4 and IL-13 significantly increased RASMC DNA synthesis as monitored by [(3)H]thymidine incorporation, demonstrating that upregulation of AI is correlated with an increase in cell proliferation. Blockade of AI induction by IFN-gamma, H-89, or genistein also blocked the increase in cell proliferation. These observations are consistent with the possibility that upregulation of AI might play an important role in the pathophysiology of vascular disorders characterized by excessive smooth muscle growth.

Differential regulation of arginases and inducible nitric oxide synthase in murine macrophage cells

Activated macrophages avidly consume arginine via the action of inducible nitric oxide synthase (iNOS) and/or arginase. In contrast to our knowledge regarding macrophage iNOS expression, the stimuli and mechanisms that regulate expression of the cytosolic type I (arginase I) or mitochondrial type II (arginase II) isoforms of arginase in macrophages are poorly defined. We show that one or both arginase isoforms may be induced in the RAW 264.7 murine macrophage cell line and that arginase expression is regulated independently of iNOS expression. For example, 8-bromo-cAMP strongly induced both arginase I and II mRNAs but not iNOS. Whereas interferon-gamma induced iNOS but not arginase, 8-bromo-cAMP and interferon-gamma mutually antagonized induction of iNOS and arginase I mRNAs. Dexamethasone, which did not induce either arginase or iNOS, almost completely abolished induction of arginase I mRNA by 8-bromo-cAMP but enhanced induction of arginase II mRNA. Lipopolysaccharide (LPS) induced arginase II mRNA, but 8-bromo-cAMP plus LPS resulted in synergistic induction of both arginase I and II mRNAs. In all cases, increases in arginase mRNAs were sufficient to account for the increases in arginase activity. These complex patterns of expression suggest that the arginase isoforms may play distinct, although partially overlapping, functional roles in macrophage arginine metabolism.

Cloning and characterization of the mouse and rat type II arginase genes

Two forms of arginase, both catalyzing the hydrolysis of arginine to ornithine and urea, are found in animals ranging from amphibians to mammals. In humans, inherited deficiency of hepatic or type I arginase results in hyperargininemia, a syndrome characterized by periodic episodes of hyperammonemia, spasticity, and neurological deterioration. In these patients, a second extrahepatic or type II arginase activity is significantly increased, an induction that may partially compensate for the lack of AI activity and apparently mitigates some of the clinical effects of the condition. Cloning and characterization of the human AII cDNA was recently accomplished. The cloning, sequencing, and partial characterization of the mouse and rat AII cDNAs are reported herein. The DNA sequences predicted polypeptides of 354 amino acids, including a N-terminal mitochondrial import signal. Sequence homology to the human type II arginase, arginase activity data, and immunoprecipitation with an anti-AII antibody confirm the identity of these cloned genes as rodent extrahepatic type II arginases.

Menstrual cycle and gonadal steroid effects on symptomatic hyperammonaemia of urea-cycle-based and idiopathic aetiologies

We report two female patients, one with a known inborn error of ureagenesis and the other of unknown cause, in whom recurrent, transient episodes of severe hyperammonaemia increased in frequency and severity with sexual maturity and parturition. Both responded to ovarian steroids administered continuously to suppress ovulation and menstruation, and ultimately to simple hysterectomy. These studies suggest a new therapeutic approach to defective ureagenesis in female patients and a relationship between ammonia production or disposal and the menstrual cycle.

Regulation of arginase production by glucocorticoid in three human gastric cancer cell lines

Gastric cancer tissues have high levels of glucocorticoid receptors (GR) and arginase. To investigate the interrelation of glucocorticoid, GR and arginase, three human gastric cancer cell lines (AZ-521, NUGC-3, KATO-III) were treated with hydrocortisone in the presence or absence of a glucocorticoid antagonist RU38486. GR were found to be present in all three lines, and hydrocortisone significantly increased the production of total arginase in all 3 lines. The induction of arginase production by hydrocortisone was inhibited by RU38486. These findings suggest that the regulation of arginase production by hydrocortisone in gastric cancer cells is mediated through GR.

Content of glucocorticoid receptor and arginase in gastric cancer and normal gastric mucosal tissues

The content of glucocorticoid receptor (GR) and arginase in human gastric cancer and the corresponding normal gastric mucosal tissues was determined. Among the 25 patients studied, the GR content in gastric cancer tissues was 33.2 +/- 10.2 fmol/mg protein versus 7.6 +/- 3.4 fmol/mg protein in gastric mucosal tissues. This difference is statistically significant (P less than 0.005). Of the 25 paired samples, 19 cancer tissues contained GR, whereas only seven of the normal mucosal tissues had GR. The level of arginase in gastric cancer tissues in 19 patients was assayed, it was 26.6 +/- 4.2 ng/mg protein which is also significantly higher than that in normal gastric mucosal tissues (13.5 +/- 1.8 ng/mg protein) (P less than 0.005). Since glucocorticoids and arginase are potent immune suppressive agents, the increased level of GR and arginase in gastric cancer tissue suggest that these glucocorticoid-related factors in gastric cancer tissue may play a partial role in regulating cellular immunity.

Comparison of biochemical properties of liver arginase from streptozocin-induced diabetic and control mice

Arginase activity is elevated in livers of diabetic animals compared to controls and there is evidence that this is due in part to increased specific activity (activity/mg arginase protein). To investigate the molecular basis of this increased activity, the physicochemical and kinetic properties of hepatic arginase from diabetic and control mice were compared. Two types of arginase subunits with molecular weights of 35,000 and 38,000 were found in both the diabetic and control animals and the subunits in these animals had similar, multiple ionic forms. Kinetic parameters of purified preparations of arginase for arginine (apparent Km and Vmax values) and the thermal stability of these preparations from diabetics and controls were also similar. Furthermore, no difference was found in the distribution of arginase activity among different subcellular liver fractions. Separation of basic and acidic oligomeric forms of arginase by fast-protein liquid chromatography resulted in a slightly different distribution of activity among the forms in the normal and diabetic group. The apparent Km values for Mn2+ of the basic form of the enzyme were 25 and 33 microM for the enzyme from normal and diabetic animals, respectively; for acidic forms, for which two apparent Km values were measured, the values were 8 and 197 microM for arginase from controls and 35 and 537 microM from diabetics. These results indicate that in diabetes, while no marked changes in the physicochemical characteristics of arginase are obvious, some changes are found in the interaction of arginase with its cofactor Mn.

Induction of the five urea-cycle enzymes by glucagon in cultured foetal rat hepatocytes

Foetal hepatocytes obtained from rats at different stages were cultured in order to investigate the inducibility of the five urea-cycle enzymes by glucagon and dibutyryl cyclic AMP (Bt2cAMP). When 18.5-day-old hepatocytes were cultured for 3 days with 10(-7) M glucagon, the activities of carbamoyl phosphate synthetase (CPS), argininosuccinase (ASL) and arginase were increased by 1.4-, 1.8- and 1.9-fold, respectively, as compared to controls. These effects were mimicked by 10(-4) M Bt2cAMP, but the activities of ornithine transcarbamylase (OTC) and argininosuccinate synthetase (ASS) were never changed by the addition of these compounds. Hepatocytes cultured at earlier stages were not responsive to glucagon unless dexamethasone was added simultaneously, suggesting that this steroid might induce some steps necessary for glucagon action. Bt2cAMP was effective as early as day 16.5 without requiring the presence of steroids. In addition, the effect of the cyclic nucleotide appeared additive or synergistic with that of dexamethasone. The simultaneous addition of actinomycin D did not affect the glucagon-induced increase in enzyme levels, thus suggesting a post-transcriptional effect of the hormone on the foetal enzyme activities. Insulin itself did not have any effect on the basal level of the enzyme activities and had only a moderate inhibitory effect on glucagon-induced ASL activity. This slight effect of insulin is in contrast with the marked inhibitory effect of dexamethasone on this enzyme activity that we described previously.

Regulation of mRNA levels for five urea cycle enzymes in rat liver by diet, cyclic AMP, and glucocorticoids

Adaptive changes in levels of urea cycle enzymes are largely coordinate in both direction and magnitude. In order to determine the extent to which these adaptive responses reflect coordinate regulatory events at the pretranslational level, measurements of hybridizable mRNA levels for all five urea cycle enzymes were carried out for rats subjected to various dietary regimens and hormone treatments. Changes in relative abundance of the mRNAs in rats with varying dietary protein intakes are comparable to reported changes in enzyme activities, indicating that the major response to diet occurs at the pretranslational level for all five enzymes and that this response is largely coordinate. In contrast to the dietary changes, variable responses of mRNA levels were observed following intraperitoneal injections of dibutyryl cAMP and dexamethasone. mRNAs for only three urea cycle enzymes increased in response to dexamethasone. Levels of all five mRNAs increased severalfold in response to dibutyryl cAMP at both 1 and 5 h after injection, except for ornithine transcarbamylase mRNA which showed a response at 1 h but no response at 5 h. Combined effects of dexamethasone and dibutyryl cAMP were additive for only two urea cycle enzyme mRNAs, suggesting independent regulatory pathways for these two hormones. Transcription run-on assays revealed that transcription of at least two of the urea cycle enzyme genes--carbamylphosphate synthetase I and argininosuccinate synthetase--is stimulated approximately four- to fivefold by dibutyryl cAMP within 30 min. The varied hormonal responses indicate that regulatory mechanisms for modulating enzyme concentration are not identical for each of the enzymes in the pathway.

Significance of increased secretion of glucocorticoids in mice and rats injected with bacterial endotoxin

Injection of mice or rats with lipopolysaccharide (LPS) is associated with an increased secretion of glucocorticoids. The high level of mortality following injection of LPS that is noted in adrenalectomized rats can be reversed by dexamethasone or corticosterone. That histamine may be an endogenous mediator of the release of corticosterone caused by LPS is suggested by an attenuation of this corticosterone response by promethazine, an H1 antihistamine. Additional support that LPS-dependent glucocorticoid secretion is mediated, in part, by histamine, is suggested by spleen cell transfer studies revealing differences in the induction of histidine decarboxylase (HDC) synthesis and corticosterone release by the C3H/HeN and C3H/HeJ strains of mice that are differentially sensitive to LPS effects. These and other data on increased levels of histamine and HDC during mitogen-induced lymphocyte blastogenesis, as well as experiments revealing immunomodulatory effects of histamine and histamine agonists and antagonists on lymphocyte blastogenesis, are consistent with the hypothesis that following infection with gram-negative bacteria, the histamine-induced increase in glucocorticoid secretion results in inhibition of HDC in splenocytes, a concomitant attenuation of histamine production, and a resulting return to immune homeostasis.

Isolation of human liver arginase cDNA and demonstration of nonhomology between the two human arginase genes

A human liver cDNA library was screened by colony hybridization with a rat liver arginase cDNA. The number of positive clones detected was in agreement with the estimated abundance of arginase message in liver, and the identities of several of these clones were verified by hybrid-select translation, immunoprecipitation, and competition by purified arginase. The largest of these human liver arginase cDNAs was then used to detect arginase message on northern blots at levels consistent with the activities of liver arginase in the tissues and cells studied. The absence of a hybridization signal with mRNA from a cell line expressing only human kidney arginase demonstrated the lack of homology between the two human arginase genes and indicated considerable evolutionary divergence between these two loci.

Cloning of rat liver arginase cDNA and elucidation of regulation of arginase gene expression in H4 rat hepatoma cells

In order to study the regulation of expression of the two arginase genes in mammalian tissues, we undertook to clone cDNA specific for rat liver arginase. mRNA was isolated from rat liver polysomes enriched for the arginase message by immunopurification and was used to produce an 800-member cDNA library carried in pBR322. Four arginase clones were identified by hybrid selection, and one was used to find two others following colony hybridization. Clonal identity was verified by its enrichment in the cDNA made from immunopurified mRNA; by hybrid selection, immunoprecipitation, and competition by purified arginase; hybridization on Northern analysis with liver-derived RNA (high in arginase) and its absence with mRNA from tissues low in arginase; and independent identification by hybrid selection and colony hybridization. Northern analysis of mRNA from H4-II-E-C3 (H4) rat hepatoma cells in which arginase activity was induced by hydrocortisone demonstrated equal, eightfold augmentation of both arginase activity and arginase mRNA levels. Southern blot analysis of DNA from these cells indicated that no change in arrangement or copy number accompanied induction. Southern analysis also suggested that the gene for rat liver arginase is present in a single copy, without pseudogenes, and that a high degree of homology exists between it and its mouse counterpart.

Interaction between glucocorticoids, 8-bromoadenosine 3',5'-monophosphate, and insulin in regulation of synthesis of carbamoyl-phosphate synthetase I in Reuber hepatoma H-35

Regulation of synthesis of carbamoyl-phosphate synthetase I by glucocorticoids, 8-bromoadenosine 3',5'-monophosphate (8-bromo-cAMP), and insulin was investigated in Reuber hepatoma H-35. By measuring the incorporation of [35S]methionine into carbamoyl-phosphate synthetase I and its precursor, we showed that dexamethasone stimulates the enzyme synthesis approximately fivefold. A detectable stimulation was observed at 1 nM of dexamethasone, half-maximal stimulation at 4 nM, and maximal stimulation above 40 nM. Corticosterone was more effective than dexamethasone both for the minimal concentration needed and for the extent of the stimulation. Hydrocortisone was less effective than dexamethasone. 8-Bromo-cAMP also stimulated the enzyme synthesis at a concentration of 3 mM. The effect of 8-bromo-cAMP was suggested to be additive to the effect of dexamethasone. Physiological concentrations of insulin strongly suppressed the stimulatory effect of dexamethasone on the enzyme synthesis but could not completely counteract the effect of dexamethasone. The half-maximal and maximal effects of insulin were observed at 0.5 nM and 5 nM, respectively. Insulin also counteracted the effect of 8-bromo-cAMP on the enzyme synthesis.

Expression of carbamoyl-phosphate synthetase I mRNA in Reuber hepatoma H-35 cells. Regulation by glucocorticoid and insulin

Reuber hepatoma H-35 cells actively synthesize the urea cycle enzyme, carbamoyl-phosphate synthetase I. Treatment of H-35 cells with dexamethasone (0.14 microM), however, enhanced synthesis of the enzyme (as measured by incorporation of [35S]methionine) by 4-5-fold. Insulin (0.18 microM) completely inhibited dexamethasone-dependent stimulation of enzyme synthesis. In vitro translation and cDNA hybridization assays were employed to measure effects of dexamethasone plus or minus insulin on levels of mRNA encoding the biosynthetic precursor of carbamoyl-phosphate synthetase I (pCPS) in Reuber H-35 cells. Both measurements yielded similar results: dexamethasone increased pCPS mRNA levels by 4-5-fold and insulin suppressed this response, but only by 50%. Specific cDNA hybridization assays also demonstrated that Reuber H-35 cells, even after hormone treatments, contain only very low levels of albumin mRNA, and no detectable ornithine carbamoyl-transferase mRNA.

Regulation by glucocorticoids of rat-liver phenylalanine hydroxylase in vivo

Phenylalanine hydroxylase, a liver-associated enzyme, is induced markedly by glucocorticoids in two permanent rat-hepatoma cell lines. In order to gain evidence that this phenomenon also occurs in vivo, we examined the effect of adrenalectomy and/or hormone supplementation on the levels of phenylalanine hydroxylase in the livers of adult rats: glucocorticoid administration increases, and adrenal ablation reduces, the activity of the hepatic enzyme, and the diminution occurring in the latter instance is entirely prevented by concurrent hormone replacement. These results thus corroborate earlier findings from a single experiment and are consistent with the hypothesis that adrenal corticosteroid hormones participate in modulating phenylalanine-hydroxylase levels within the diploid hepatocyte.

Induction of carbamoyl-phosphate synthetase I in Reuber hepatoma H-35 by dexamethasone

Reuber hepatoma H-35 was found to retain the activity of carbamoyl-phosphate synthetase I. The content of this enzyme in H-35 grown in Eagle's minimal essential medium was about half that in rat liver. The enzyme from H-35 was the same as that from rat liver in molecular weight estimated by SDS-polyacrylamide gel electrophoresis, specific enzyme activity, kinetic parameters for ATP and N-acetyl-L-glutamate, and immunological crossreactivity. The enzyme in H-35 was induced by dexamethasone (1.4-fold) but not by glucagon or dibutyryl cAMP. Incorporation of [35S] methionine into the enzyme indicated that the effect of dexamethasone was due to increased synthesis of the enzyme protein (2.1-fold). By labeling with [35S]methionine, the precursor and the mature forms of carbamoyl-phosphate synthetase I were observed in the post-mitochondrial and mitochondrial fractions, respectively. By chasing the labeled cells with unlabeled methionine and cycloheximide, it was observed that the rate of translocation of the precursor into mitochondria is not affected by dexamethasone.