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J M Mato

Publications and source records attributed to J M Mato.

At least 73 records · Page 4Linked to original sources
PubMed1993

Changes in the insulin-sensitive glycosyl-phosphatidyl-inositol signalling system with aging in rat hepatocytes.

An inositol-phosphate glycan (InsP glycan), which is the polar head group of an insulin-sensitive glycosyl-phosphatidylinositol (glycosyl-PtdIns), has been reported to mimic some insulin actions when added to different types of cells. In connection with this, a specific, time-dependent and energy-dependent transport system for this InsP glycan has been identified in isolated rat hepatocytes [Alvarez, J. F., Sánchez-Arias, J. A., Guadaño, A., Estevez, F., Varela, I., Felíu, J. E. & Mato, J.M. (1991) Biochem. J. 274, 369-374]. Here we have investigated the glycosyl-PtdIns-dependent insulin-signalling system in hepatocytes isolated from either 3-month-old or 24-month-old rats. Aging reduced the stimulatory effect of insulin on [U-14C]glucose incorporation into glycogen, caused a significant decrease in basal glycosyl-PtdIns levels and blocked the insulin-mediated hydrolysis of this lipid. In 24-month-old rats, we also observed a diminution in the rate of hepatocyte InsP-glycan uptake and a marked reduction of the stimulatory effect of this compound on glycogen synthesis. These results support the hypothesis that insulin resistance associated with aging is accompanied by an impairment of the glycosyl-PtdIns-dependent cellular signalling system.

Aging↗
PubMed1993

Brain-derived neurotrophic factor and neurotrophin-3 induce cell proliferation in the cochleovestibular ganglion through a glycosyl-phosphatidylinositol signaling system.

We have investigated the role of brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3) in the regulation of cell proliferation in the early developing cochleovestibular ganglion (CVG). Ganglia were isolated from 72-hr chick embryos and cultured for 24 hr. Both BDNF and NT-3 had a powerful mitogenic effect, at doses of 1-5 ng/ml, consistent with an involvement of the high-affinity receptor. Evidence for the participation of the glycosyl-phosphatidylinositol (GPI)/inositol phosphoglycan (IPG) signaling system in the mediation of proliferative effects of BDNF and NT-3 is presented. Both of these neurotrophins elicited a fast and transient hydrolysis of labeled GPI, approximately 60% in 30 sec. The dose-response profile of GPI hydrolysis overlaps the neurotrophin-induced cell proliferation response profile. Anti-IPG antibodies were able to block the growth-promoting effects of BDNF and NT-3. Anti-IPG antibodies immunoprecipitated a CVG-endogenous IPG, induced upon BDNF treatment, which exhibited proliferative stimulating properties. Both BDNF and NT-3 are proposed as potential candidates for regulation of growth during CVG development, with this mitogenic effect being mediated by the GPI/IPG signaling system.

Animals↗
PubMed1993

Brain-derived neurotrophic factor and neurotrophin-3 support the survival and neuritogenesis response of developing cochleovestibular ganglion neurons.

The effects of brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3) on the differentiation of avian cochleovestibular ganglion and their possible association with the hydrolysis of glycosyl-phosphatidylinositol (GPI) were studied. BDNF and NT-3 (2 ng/ml) promoted neurite outgrowth in explants of both cochlear and vestibular ganglia. This effect on neuritogenesis was stage-dependent, reaching a maximum at E7 for NT-3 and at E9 for BDNF. The magnitude of the response of the vestibular ganglion to BDNF was always smaller than that of the cochlear ganglion of an equivalent stage. BDNF and NT-3 stimulation of neuronal survival and neurite extension was also demonstrated in dissociated neuronal cell cultures. The effect was concentration-dependent with saturation of the response occurring at 4 ng/ml for BDNF and at 2 ng/ml for NT-3, the half-maximal effect occurring at 2 and 1 ng/ml, respectively, for the most sensitive stages of the chick cochlear ganglion. Inositol phosphoglycan (IPG) did not mimic the effects of BDNF or NT-3 on neuronal survival and neurite outgrowth, nor was it able to potentiate their responses. Antibodies raised against IPG did not block the effects of these neurotrophins. The results suggest that BDNF and NT-3 may act in cooperation to establish the innervation pattern of the inner ear. Unlike their early proliferative effects, neurotrophic effects are uncoupled from the GPI/IPG signal transduction system.

Animals↗
PubMed1992

Modulation of rat liver S-adenosylmethionine synthetase activity by glutathione.

Rat liver S-adenosylmethionine (AdoMet) synthetase appears as high-M(r) (tetramer) and low-M(r) (dimer) forms. Both are inhibited in the presence of GSSG at pH 8. The calculated Ki values are 2.14 and 4.03 mM for the high- and low-M(r) forms, respectively. No effect on enzyme activity was observed in the presence of GSH, but modulation of inhibition by GSSG can be obtained by addition of GSH. At a total glutathione concentration (GSH + GSSG) of 10 mM, a KOX of 1.74 was calculated for the high-M(r) form, whereas this constant was 2.85 for the low-M(r) AdoMet synthetase. No incorporation of [35S]GSSG was observed in either of the enzyme forms, and inhibition of enzyme activity was correlated with dissociation of both AdoMet synthetases to a monomer. The data obtained in the presence of GSSG seem to suggest that oxidation leads to the formation of an intrasubunit disulfide. The possible regulation of AdoMet synthetase activity by the GSH/GSSG ratio is discussed, as well as its in vivo significance.

Animals↗
PubMed1992

How is rat liver S-adenosylmethionine synthetase regulated?

The in vivo regulation of S-adenosylmethionine synthetase, a key enzyme in methionine metabolism, is so far unknown. The enzyme activity has been shown to be modulated by glutathione and the oxidation state of its sulfhydryl groups. Analysis of the protein sequence has revealed the presence of putative phosphorylation sites. A mixed regulatory mechanism combining phosphorylation and the oxido/reduction of sulfhydryl groups is proposed. The role of glutathione in this mechanism is also discussed.

Animals↗
PubMed1992

S-adenosylmethionine treatment prevents carbon tetrachloride-induced S-adenosylmethionine synthetase inactivation and attenuates liver injury.

Administration of carbon tetrachloride to rats resulted in induction of hepatic fibrosis and a 60% reduction of hepatic S-adenosylmethionine synthetase activity without producing any significant modification of hepatic levels of S-adenosylmethionine synthetase messenger RNA. The reduction of S-adenosylmethionine synthetase activity was corrected by treatment with S-adenosylmethionine (3 mg/kg/day, intramuscularly). Administration of carbon tetrachloride also produced a 45% depletion of liver glutathione (reduced form) that was corrected by S-adenosylmethionine treatment. After the rats received carbon tetrachloride, a 2.3-fold increase in liver collagen was observed; prolyl hydroxylase activity was 2.5 times greater than that seen in controls. These increases were attenuated in animals treated with carbon tetrachloride and S-adenosylmethionine. The attenuation by S-adenosylmethionine treatment of the fibrogenic effect of carbon tetrachloride was associated with a decrease in the number of rats in which cirrhosis developed.

Animals↗
PubMed1992

Impairment of glycosyl-phosphatidylinositol-dependent insulin signaling system in isolated rat hepatocytes by streptozotocin-induced diabetes.

The addition to different types of cells of an inositol-phosphate glycan, generated by the phospholipase C-catalyzed hydrolysis of a insulin-sensitive glycosyl-phosphatidylinositol (glycosyl-PI), mimics some of the biological effects of this hormone. Recently, a specific, time-, dose-, and energy-dependent transport system for this inositol-phosphate glycan has been identified in isolated rat hepatocytes. Here, we show that streptozotocin-induced diabetes mellitus reduced (by about 60%) the basal content of the insulin-sensitive glycosyl-PI in isolated rat hepatocytes. Moreover, streptozotocin-induced diabetes blocked the hydrolysis of the glycosyl-PI in response to insulin, diminished inositol phosphate-glycan uptake by the hepatocytes, and abolished the stimulatory effect of this compound on glycogen synthesis. All these metabolic changes caused by streptozotocin administration were reversed by treatment of the animals with insulin. Our results support the hypothesis that insulin resistance in streptozotocin-induced diabetic rats is related to the impairment of glycosyl-PI metabolism.

Animals↗
PubMed1991

Analysis of the 5' non-coding region of rat liver S-adenosylmethionine synthetase mRNA and comparison of the Mr deduced from the cDNA sequence and the purified enzyme.

A 3 kb cDNA coding for rat liver S-adenosylmethionine (AdoMet) synthetase has been isolated. The Mr of the protein has been unequivocally determined by cDNA sequencing and enzyme purification on a thiopropyl-Sepharose column. The length of the mRNA 5' non-coding region has been defined by primer-extension analysis. The rat liver cloned cDNA has been also used to detect S-adenosylmethionine synthetase mRNA in human liver.

Animals↗
PubMed1991

Glycosyl-phosphatidylinositol/inositol phosphoglycan: a signaling system for the low-affinity nerve growth factor receptor.

Nerve growth factor (NGF) exerts a variety of actions during embryonic development. At the early stages of inner ear development, NGF stimulates cell proliferation, an effect mediated through low-affinity receptors. We have studied the possibility that the glycosyl-phosphatidylinositol/inositol phosphoglycan (glycosyl-PtdIns/IPG) system is involved in transmitting this NGF signal. Endogenous glycosyl-PtdIns was characterized in extracts of cochleovestibular ganglia (CVGs) that incorporated [3H]glucosamine, [3H]galactose, [3H]myristic acid, and [3H]palmitic acid. Incubation of CVG with NGF produced a rapid and transient hydrolysis of glycosyl-PtdIns. Hydrolysis was complete at 100 ng/ml, and the half-maximal effect occurred at 25 ng/ml, overlapping with the concentration dependence of the mitogenic effect of NGF. An IPG was isolated from embryonic extracts. It had biological effects similar to those reported for the insulin-induced IPG in other tissues. It exerted a powerful mitogenic effect on CVG, comparable to that of NGF. Both the IPG- and NGF-induced cell proliferation were blocked by anti-IPG antibodies that recognized the endogenous IPG on a silica plate immunoassay. These results show that CVG possesses a fully active glycosyl-PtdIns/IPG signal transduction system and that the proliferative effects associated with NGF binding to low-affinity receptors require IPG generation.

Animals↗
PubMed1991

Transport in isolated rat hepatocytes of the phospho-oligosaccharide that mimics insulin action. Effects of adrenalectomy and glucocorticoid treatment.

The addition to intact cells of an inositol phospho-oligosaccharide (POS), which is the polar head-group of an insulin-sensitive glycosylphosphatidylinositol, mimics and may mediate some of the biological effects of this hormone. Here we report the existence of a POS transport system in hepatocytes. This POS transport system is specific and time- and dose-dependent. Insulin-resistance caused by dexamethasone administration to rats was accompanied by a decrease in the hepatocyte POS transport system. In contrast, bilateral adrenalectomy provoked a significant increase in the transport of POS. Both the temporal uptake of POS and the regulation of this process by conditions known to modify the sensitivity to insulin suggest that this novel transport system might be involved in the insulin signalling mechanism.

Adrenalectomy↗
PubMed1991

The role of cysteine-150 in the structure and activity of rat liver S-adenosyl-L-methionine synthetase.

The present paper reports the tryptic digestion of N-ethylmaleimide-treated S-adenosyl-L-methionine synthetase (high- and low-Mr forms) and the isolation of the modified peptides by h.p.l.c. There is only one site modified after 5 min incubation, and the modification at this site correlates with the main activity decrease. The amino acid composition of this peptide was determined, and its localization in the sequence shows the modified residue as cysteine-150, which is located close to the putative ATP-binding site. Modification of the enzyme for 20 min led to the appearance of a second labelled peptide, which seems to be responsible for about a further 10% of the activity loss. The modification by N-ethylmaleimide of the enzyme was partially prevented in the presence of adenosine 5'-[beta gamma-imido]triphosphate and methionine, further supporting the hypothesis that the modified residues lie within the active site. Urea treatment of the enzyme, followed by modification with N-ethylmaleimide, produces the modification of 7 of the 10 cysteine residues present in the sequence. The results obtained were the same for either of the isoforms.

Amino Acids↗
PubMed1991

Metabolic labelling and partial characterization of glycophospholipids in pancreatic islet cells.

Insulin action is thought to be mediated by an inositol-, glucosamine- and galactose-containing oligosaccharide liberated by phosphodiesterase hydrolysis of a glycosyl-phosphatidylinositol. This oligosaccharide inhibits insulin biosynthesis and secretion in pancreatic islets. In the present study, two main glycolipids (peak I and II) were resolved by sequential TLC of lipids extracted from islet cells labelled with tritiated glucosamine, galactose or myristate. The two glycolipids displayed comparable sensitivity to beta-galactosidase but differed from one another by their sensitivity to phosphatidylinositol-specific phospholipase C. Moreover, structural heterogeneity within each peak was suggested by their partial resistance to nitrous acid deamination. These findings support the presence in islet cells of glycolipids similar to those currently considered as a possible postreceptor target for insulin in other cell types.

Animals↗
PubMed1991

Inositol phospho-oligosaccharide stimulates cell proliferation in the early developing inner ear.

The ability of an inositol phospho-oligosaccharide (POS) to mimic the mitogenic effects of nerve growth factor (NGF) and insulin on the early development of the inner ear was investigated. POS (10 microM) stimulated the incorporation of [3H]thymidine into the cochleovestibular ganglion by 3.9-fold. NGF (50 ng/ml) stimulation was 4.7-fold. POS and NGF showed no additivity. Cells induced to proliferate by POS overlapped with those expressing NGF receptors. POS, like insulin, potentiated the mitogenic effect of bombesin on the otic vesicle epithelium. DNA synthesis in the presence of bombesin (100 nM) plus POS (10 microM) was increased by 6.4-fold. POS stimulation was not additive with insulin. The results suggest that POS may play a role in growth factor regulation of cell proliferation during embryonic development.

Animals↗
PubMed1991

Insulin-like effects of inositol phosphate-glycan on messenger RNA expression in rat hepatocytes.

The ability of an inositol phosphate-glycan (IPG) to mimic the effects of insulin on regulation of the expression of specific mRNAs was studied in isolated hepatocytes from normal and diabetic rats. Incubation of normal liver cells with IPG (10 microM) during 90 min produced a 5-fold decrease in phosphoenolpyruvate carboxykinase (PEPCK) mRNA levels, which had been previously increased about 10-fold by incubation with 8-bromo-cAMP (0.1 mM). The effect of IPG was dose dependent and could not be reproduced by galactose, glucosamine, or myo-inositol. IPG reduction of PEPCK mRNA is primarily due to a decrease in the rate of transcription of the gene, as judged by nuclear run-on transcription experiments performed in rat hepatoma H4IIE cells. In hepatocytes isolated from diabetic rats, treatment with 5 microM IPG for 15 min caused a 4-fold induction in the expression of alpha 2-microglobulin mRNA concomitantly with a 2.5-fold decrease in the level of PEPCK mRNA. Cleavage of IPG with nitrous acid abolished both the increase and the decrease in specific mRNAs levels. Glycosyl-phosphatidylinositol, the lipid precursor of IPG, did not modify either PEPCK or alpha 2-microglobulin mRNA levels. These data indicate that both positive and negative effects of insulin on the regulation of gene expression are mimicked by IPG.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1991

Inhibition of glutathione synthesis in the liver leads to S-adenosyl-L-methionine synthetase reduction.

The hepatic levels of glutathione in rats treated with buthionine sulfoximine (4 mmol/kg), an inhibitor of glutathione synthesis, were 72.5% +/- 4.9% of those determined in control animals. This decrease in glutathione concentration was prevented by the administration of glutathione monoethyl ester (7.5 mmol/kg). S-Adenosyl-L-methionine-synthetase activity in the liver of rats treated with buthionine sulfoximine was 39.4% +/- 6.5% of that determined in control animals. Again, glutathione monoethyl ester prevented the effect of buthionine sulfoximine on S-adenosyl-L-methionine-synthetase activity. There was a close correlation (r = 0.936) between the hepatic levels of glutathione and S-adenosyl-L-methionine-synthetase activity. The hepatic concentration of S-adenosyl-L-methionine in buthionine sulfoximine-treated animals was 59.7% +/- 3.7% of that measured in control rats. Contrasting with the protective effects mentioned above, glutathione monoester had no preventive action on buthionine sulfoximine-induced S-adenosyl-L-methionine depletion. Electron microscopic examination of liver samples of rats after buthionine sulfoximine administration showed evidence of liver degeneration, which was attenuated by glutathione monoethyl ester treatment. Glutathione (7.5 mmol/kg) treatment was less effective than glutathione monoethyl ester in attenuating buthionine sulfoximine effects on hepatic S-adenosyl-L-methionine metabolism and morphology. The reduction of S-adenosyl-L-methionine-synthetase activity observed after treatment with buthionine sulfoximine and its prevention by glutathione monoethyl ester, as well as the correlation between the activity of this enzyme and glutathione levels, indicate that glutathione plays an important role in maintaining S-adenosyl-L-methionine-synthetase activity in the liver.

Acetaminophen↗
PubMed1990

Insulin-induced phospho-oligosaccharide stimulates amino acid transport in isolated rat hepatocytes.

The ability of the insulin-induced phospho-oligosaccharide to stimulate amino acid transport was studied in isolated rat hepatocytes. At low alpha-aminoisobutyric acid concentrations (0.1 mM), both 100 nM-insulin and 10 microM-phospho-oligosaccharide doubled amino acid uptake after 2 h of incubation. This stimulation was prevented by 0.1 mM-cycloheximide or 5 micrograms of actinomycin D/ml, indicating that the phospho-oligosaccharide, like insulin, was acting via the synthesis of a high-affinity transport component. The effects of the phospho-oligosaccharide and of insulin were blocked by Ins2P (2.5 mM), but not by myo-inositol, inositol hexaphosphoric acid or several monosaccharides such as mannose, glucosamine and galactose. Both the temporal effect on amino acid entry and the extent of stimulation of this process by the phospho-oligosaccharide indicate that this molecule mimics, and may mediate, some of the long-term actions of insulin. However, the effects of phospho-oligosaccharide and insulin were not exactly the same, since the effect of insulin, but not of the phospho-oligosaccharide, was additive with that of glucagon.

Amino Acids↗
PubMed1990

Modulation of casein kinase II activity by the polar head group of an insulin-sensitive glycosyl-phosphatidylinositol.

A phospho-oligosaccharide, whose production is stimulated by insulin, modulated the activity of partially purified casein kinase II. Whereas at 2 microM the phospho-oligosaccharide stimulated casein kinase II 1.3-fold, higher concentrations of this molecule were inhibitory. 50% inhibition of the enzyme was obtained at 15 microM phospho-oligosaccharide. This biphasic effect of the phospho-oligosaccharide on casein kinase II activity was observed using as substrate both casein or the specific peptide for casein kinase II, Arg-Arg-Arg-Glu-Glu-Glu-Thr-Glu-Glu-Glu. The effect of the phospho-oligosaccharide on casein kinase II was still observed after gel filtration. Deamination of the phospho-oligosaccharide with nitrous acid abolished both the activation and the inhibition of casein kinase II. The glycophospholipid precursor of the phospho-oligosaccharide did not affect casein kinase II activity. Moreover, modulation of casein kinase II activity was not observed with other compounds structurally related to the phospho-oligosaccharide, when used in the micro-molar range. In conclusion, the present results indicate that the phospho-oligosaccharide that mimics and might mediate some of the actions of insulin modulates casein kinase II activity in vitro.

Amino Acid Sequence↗