PubMed Health⌕ Search

Biomedical subjects

J Hanoune

Publications and source records attributed to J Hanoune.

At least 91 records · Page 5Linked to original sources
PubMed1983

The hormonal induction of gamma glutamyltransferase in rat liver and in a hepatoma cell line.

Gamma glutamyltransferase (GGT) is a membrane-bound enzyme that is involved in glutathione metabolism and aminoacids uptake. GGT activity is stimulated by a number of hormones and pharmacological agents in certain animal tissues. In rat liver, adrenalectomy causes a 2-fold decrease in GGT activity and hydrocortisone treatment of adrenalectomized animals specifically stimulates this enzyme activity. In a highly differentiated hepatoma cell line, Fao, GGT activity is similar to rat liver and is under glucocorticoids control. These hormones specifically stimulate GGT activity (2- to 3-fold). Translation and transcription inhibitors prevent the hormonal effect. The stimulation of GGT activity is therefore probably due to an increase in GGT mRNA synthesis. The results reported suggest that the Fao cell line is a very convenient system for the study of the molecular mechanisms of both the glucocorticoid effects on differentiated cells as well as the modulation of membrane-bound enzymes biosynthesis.

5'-Nucleotidase↗
PubMed1983

Binding of yohimbine stereoisomers to alpha-adrenoceptors in rat liver and human platelets.

1--Displacement of tritiated prazosin binding to rat liver plasma membranes and tritiated yohimbine human platelet membranes shows that (+)-yohimbine, alloyohimbine and alpha-yohimbine (rauwolscine) are selective alpha 2-adrenoceptor antagonists (KD alpha 1/KD alpha 2:635, 46.6 and 112 respectively) whereas corynanthine is more alpha 1-selective (KD alpha 1/KD alpha 2:0.036). 2--11-Methoxy derivatives of alpha-yohimbine and epi-alpha-yohimbine are very weak alpha-adrenoceptor blockers. 3--It is concluded that the aromatic A ring, the Nb atom, and the carboxymethyl moiety are important for the binding of yohimbine to the alpha-adrenoceptor, the carboxymethyl group being important for the alpha 1/alpha 2 specificity of the molecule.

Animals↗
PubMed1983

Adrenergic regulation of glycogenolysis in rat liver after cholestasis. Modulation of the balance between alpha 1 and beta 2 receptors.

The effects of extrahepatic cholestasis upon adrenergic regulation of glycogenolysis and upon the numbers of adrenoceptors in rat liver were studied using isolated hepatocytes and plasma membranes, respectively. A 60% decrease in the number of alpha 1 adrenoceptors (285 vs. 680 fmol/mg protein) and a simultaneous 2.7-fold increase in the number of beta adrenergic sites (67 vs. 25 fmol/mg protein) were observed beginning 36 h after bile flow obstruction and persisted for at least 68 h. The reciprocal modification of the numbers of alpha 1 and beta adrenoceptors was accompanied by a change in the manner of stimulation of glycogen phosphorylase by catecholamines in hepatocytes; originally alpha 1 adrenergic in normal rats (phenylephrine Ka = 0.9 microM, isoproterenol Ka = 7.1 microM), the stimulation became predominantly beta adrenergic in cholestatic animals (phenylephrine Ka = 3.7 microM, isoproterenol Ka = 0.06 microM). In normal rats, activation of the enzyme by epinephrine was inhibited by the alpha blocker phentolamine, without inhibition by the beta blocker propranolol. In contrast, propranolol was more effective than phentolamine in cholestatic rat hepatocytes. Modification of the regulation of glycogenolysis after cholestasis did not seem to be secondary to an alteration in the metabolism of thyroid hormones or in the action of glucocorticoids. However, cholestasis provoked a 10-fold increase in the number of hepatic mitoses and in the incorporation of thymidine into liver DNA of cholestatic animals. Similar changes were observed in regenerating livers, following two-thirds hepatectomy. We propose that the changes following extrahepatic cholestasis might, as well, be explained by a regenerative process.

Animals↗
PubMed1983

[The adenylate cyclase system of human platelets].

This review summarizes current knowledge on the adenylate cyclase system of human platelets. In the first part, the main molecular entities of this system are described, emphasis being layed on coupling proteins (Ns, Ni) which transduce the hormonal message from receptors to the catalytic unit. The mechanisms by which regulation of adenylate cyclase occurs is discussed and a comprehensive model is proposed. In the second part, are reviewed the hormonal and non hormonal regulators of the adenylate cyclase system. The role of the platelet adenylate cyclase system is discussed in relation to pathology and the action of certain drugs on platelet activity.

Adenosine↗
PubMed1982

Guanine nucleotide inhibition of cyc- S49 mouse lymphoma cell membrane adenylyl cyclase.

Cyc- S49 mouse lymphoma cell membranes contain an adenylyl cyclase system which is deficient in the regulatory properties characteristic of a stimulatory guanine nucleotide-binding regulatory component (Ns), such as enhancement of activity in the presence of GTP, GTP analogues, and NaF. Detailed kinetic analysis of cycl- adenylyl cyclase showed, however, that it is not unresponsive to these agents, for their addition to assays elicited inhibitory effects. Inhibition of cyc- activity was seen in 11 different membrane preparations obtained from two different strains and was observable both in the absence and presence of the strongly stimulatory diterpene forskolin. The GTP analogues GTP gamma S and guanyl-5'-yl imidodiphosphate caused a maximum of 60% inhibition with IC50 values of 2 and 12 nM, respectively. GTP itself was less potent than its analogues, with an IC50 of 100 mM, and elicited less inhibition as well (a maximum of 25%). Cholera toxin treatment of cyc- S49 cell membranes, under conditions which appeared to maximally activate the adenylyl cyclase system of wild type S49 cell membranes, had no effect on inhibition of catalytic activity. Our results indicate the presence in cyc- S49 cell membranes of a guanine nucleotide-binding component which is inhibitory to adenylyl cyclase activity (Ni). This suggests (a) that these membranes cannot be considered as completely deficient of adenylyl cyclase guanine nucleotide-binding regulatory components, and (b) that these membranes offer a unique opportunity to study Ni-mediated effects of guanine nucleotides and fluoride in the functional absence of Ns-mediated effects of these agents.

Adenylyl Cyclase Inhibitors↗
PubMed1982

Glucocorticoid hormones increase the activity of gamma-glutamyltransferase in a highly differentiated hepatoma cell line.

Gamma-Glutamyltransferase activity was detected in the plasma membrane of the highly differentiated hepatoma cell line Fao, (0.93 mU/mg cell protein). Dexamethasone (1 microM) provoked a 2-3-fold increase in the activity of the enzyme in the presence of fetal calf serum. Maximal induction occurred 48-72 h after addition of the glucocorticoid to the cell culture medium. The hormonal specificity was demonstrated by the relative potencies of several glucocorticoids and sex steroids: hydrocortisone and corticosterone increased gamma-glutamyltransferase activity while tetrahydrocorticosterone and all sex steroids tested were ineffective. The effect of dexamethasone on gamma-glutamyltransferase activity wa specific since the activities of several other plasma membrane enzymes were not modified. The mechanism of the dexamethasone-induced increase in gamma-glutamyltransferase activity was neither by modification of the affinity of the enzyme for its substrates nor by alteration of the subcellular distribution of the enzyme. This increase was prevented by cycloheximide and actinomycin D. The data presented are consistent with a specific glucocorticoid receptor-mediated induction of gamma-glutamyltransferase activity in Fao cells. The kinetic parameters of the induction process by glucocorticoids are very similar to those found in adult rat liver. These results suggest that the Fao cell line is a very convenient system for the study of the molecular mechanisms of glucocorticoid effects on differentiated cells.

Acyltransferases↗
PubMed1982

Adenylate cyclase in Xenopus laevis oocytes: characterization of the progesterone-sensitive, membrane-bound form.

Progesterone-induced reinitiation of meiosis in Xenopus laevis oocytes involves a decrease in cAMP level. In these cells, adenylate cyclase is compartmentalized, with 25-30% in the plasma membrane fraction P-10000 (sedimenting at 10000 X g) and greater than 50% in the cytosol. Soluble adenylate cyclase appears not to be regulated via a GTP-binding regulatory protein (G/F) and is insensitive to progesterone. In contrast, membrane-bound adenylate cyclase seems to be linked to G/F, since it is stimulated by sodium fluoride, guanyl-5'-imidodiphosphate (Gpp(NH)p) and by cholera toxin; it is also inhibited by progesterone. The steroid inhibition is displayed towards basal and stimulated activities. The extent of progesterone inhibition of basal activity is dependent on Mg2+ and Mn2+ concentrations. The hormonal effect is independent of GTP concentration and is observed even in the presence of the non-hydrolysable analogue of GTP, Gpp(NH)p. The progesterone effect is not mediated by adenosine. Exposure of the P-10000 fraction to 5'-deoxy-5'-S-isobutylthioadenosine (a methyltransferase inhibitor) increases adenylate cyclase activity.

5'-Nucleotidase↗
PubMed1982

Physiological and physiopathological modulations of the balance between alpha- and beta-adrenoreceptors.

Adrenergic receptors exist as two subtypes, alpha, and beta, in various tissues. In rat liver, catecholamines exert the same effect on glycogenolysis and neoglucogenesis via either alpha or beta control. In this review we report on the modification in the balance between alpha- and beta-adrenoreceptors induced as the result of adrenalectomy and extrahepatic cholestasis. Following adrenalectomy, the number of beta-adrenergic receptors in rat liver, measured using specific radioligands, increases two-fold, with no change in the alpha-adrenoreceptors. In extrahepatic cholestasis we measured a fourfold increase in the number of beta-sites and a two- to threefold decrease in the number of alpha-sites. Moreover, this modification in the balance between alpha- and beta-adrenoreceptors was concomitant with the apparition of a mixed beta- and alpha-adrenergic regulation of glycogenolysis in cholestatic rats, whereas this process is purely or almost purely alpha-adrenergic in normal rats.

Adrenalectomy↗
PubMed1982

Recent advances in the purification of the alpha 1-adrenoceptor.

In order to purify the alpha-adrenergic receptor labeled with [3H]POB, antibodies against the irreversible alpha-adrenergic antagonist, phenoxybenzamine (POB), have been raised in rabbits immunized with POB conjugated to immunoglobulin. The antigen was prepared by first reacting POB with the sulfhydryl group of cysteine, after which the POB complex was coupled to thyroglobulin in the presence of water soluble carbodimide. POB-specific antibodies were first detected 10 days after the first booster injection. These antibodies display a high degree of specificity. Slight cross-reactivity occurred only with compounds structurally related to POB, such as dibenamine and nitrogen mustards, while catecholamines and alpha-adrenergic compounds not structurally related to POB did not cross-react, even when present in 100,000-fold excess. Moreover, the antibodies are still capable of recognizing POB once bound to alpha-adrenergic receptor. When membranes, prelabeled with [3H]POB, are solubilized with digitonin and incubated with anti-POB antiserum, the radioactivity can be specifically precipitated upon addition of goat anti-rabbit gamma-globulin serum. Thus these antibodies may be a useful tool in the purification of the alpha-adrenergic receptor of rat liver covalently linked to POB.

Animals↗
PubMed1981

A high affinity calcium-stimulated magnesium-dependent ATPase in rat liver plasma membranes. Dependence of an endogenous protein activator distinct from calmodulin.

A Mg-dependent adenosine triphosphatase (ATPase) activated by submicromolar free Ca2+ was identified in detergent-dispersed rat liver plasma membranes after fractionation by concanavalin A-Ultrogel chromatography. Further resolution by DE-52 chromatography resulted in the separation of an activator from the enzyme. The activator, although sensitive to trypsin hydrolysis, was distinct from calmodulin for it was degraded by boiling for 2 min, and its action was not sensitive to trifluoperazine; in addition, calmodulin at concentrations ranging from 0.25 ng-25 micrograms/assay had no effect on enzyme activity. Ca2+ activation followed a cooperative mechanism (nH = 1.4), half-maximal activation occurring at 13 +/- 5 nM free Ca2+. ATP, ITP, GTP, CTP, UPT, and ADP displayed similar affinities for the enzyme; K0.5 for ATP was 21+/- 9 microM. However, the highest hydrolysis rate (20 mumol of Pi/mg of protein/10 min) was observed at 0.25 mM ATP. For all the substrates tested kinetic studies indicated that two interacting catalytic sites were involved. Half-maximal activity of the enzyme required less than 12 microM total Mg2+. This low requirement for Mg2+ of the high affinity (Ca2+-Mg2+)ATPase was probably the major kinetic difference between this activity and the nonspecific (Ca2+ or Mg2+)ATPase. In fact, definition of new assay conditions, i.e. a low ATP concentration (0.25 mM) and the absence of added Mg2+, allowed us to reveal the (Ca2+-Mg2+)ATPase activity in native rat liver plasma membranes. This enzyme belongs to the class of plasma membrane (Ca2+-Mg2+)ATPases dependent on submicromolar free Ca2+ probably responsible for extrusion of intracellular Ca2+.

Adenosine Triphosphatases↗
PubMed1981

Progesterone inhibits membrane-bound adenylate cyclase in Xenopus laevis oocytes.

Recent experimental evidence indicates that progesterone acts at the cell surface to trigger protein synthesis and to reinitiate the first meiotic division in Xenopus laevis oocytes. The steroid hormone is physiologically released by follicle cells surrounding oocytes in the ovaries, and this naturally occurring event can be reproduced in vitro by adding progesterone to the incubation medium. Recently, cyclic AMP has been implicated in the mechanism of progesterone action in oocytes; there was an almost immediate decrease in cyclic AMP concentration in oocytes after addition of progesterone in vitro, whether or not the oocytes were pretreated with cholera toxin. Adenylate cyclase in X. laevis oocytes is compartmentalized, greater than 50% soluble and approximately 30% is found in the plasma membrane-containing fraction. We report here that physiological concentrations of progesterone selectively inhibit membrane-bound adenylate cyclase activity, after addition in intact oocytes or in cell-free experiments; this specificity confirms the proposed membrane site of action for the hormone when reinitiating meiosis and is the first example of a 'direct' enzymatic action of a steroid (not by protein synthesis) related to a physiological function.

Adenylyl Cyclase Inhibitors↗