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J Hanoune

Publications and source records attributed to J Hanoune.

175 records · Page 10Linked to original sources
PubMedDate not supplied

Ethanol effects in a rat hepatoma cell line: induction of gamma-glutamyltransferase.

The clone C2 derived from a rat hepatoma cell line was used to investigate the mechanism of the induction of gamma-glutamyltransferase by ethanol. gamma-glutamyltransferase activity was detected in the C2 cell (1.4 mU per mg protein), and its kinetic properties were similar to normal rat liver gamma-glutamyltransferase. Ethanol provoked a dose- and time-dependent increase in gamma-glutamyltransferase activity, the maximum (2- to 3-fold) occurring 48 hr after the addition of ethanol (180 mM). In contrast, the activity of five other enzymes tested were not markedly modified by ethanol. Propanol was more potent than ethanol in inducing gamma-glutamyltransferase (5-fold stimulation), whereas methanol had no effect. The release of the enzyme in the medium was increased by ethanol and propanol. Several observations argue in favor of an increase in the biosynthesis of gamma-glutamyltransferase after ethanol addition: (i) ethanol increased the maximal velocity of the enzyme and did not modify the affinity for its substrates. It did not alter gamma-glutamyltransferase subcellular distribution; (ii) ethanol had no immediate effect when added directly to the assay mixture; (iii) the lag period and the time course of the increase in gamma-glutamyltransferase activity were those expected for an induction process; (iv) the increase in gamma-glutamyltransferase activity was prevented by cycloheximide and actinomycin D suggesting that ethanol acted at the transcriptional level. The effect of ethanol was not mimicked by acetaldehyde. In conclusion, we have demonstrated that ethanol increases the biosynthesis of gamma-glutamyltransferase in a rat hepatoma cell line which provides a new in vitro system.

1-Propanol↗
PubMedDate not supplied

Different chromosomal localization of two adenylyl cyclase genes expressed in human brain.

Recently, we characterized a cDNA clone that encodes a human brain adenylyl cyclase (HBAC1). In the present study, we identified a second population of mRNA suspected to encode a new brain adenylyl cyclase (HBA C2). The amino acid sequence of HBA C2 displays significant homology with HBA C1 in the highly conserved adenylyl cyclase domain (250 aminio acids), found in the 3' cytoplasmic domain of all mammalian adenylyl cyclases. However, outside this domain, the homology is extremely low, suggesting that the corresponding mRNA originates from a different gene. We report here the first chromosomal localization of the adenylyl cyclase genes determined by in situ hybridization of human metaphase chromosomal spreads using human brain cDNA probes specific for each mRNA. The probe corresponding to HBA C1 exhibited a strong specific signal on chromosome 8q24, with a major peak in the band q24.2. In contrast, the HBA C2 probe hybridized to chromosome 5p15, with a major peak in the band p15.3. The two cDNAs hybridized at the two loci without any cross reactivity. Thus, in human brain, a heterogeneous population of adenylyl cyclase mRNAs is expressed, and the corresponding genes might be under the control of independent regulatory mechanisms.

Adenylyl Cyclases↗
PubMedDate not supplied

Forskolin requires more than the catalytic unit to activate adenylate cyclase.

Forskolin, a natural diterpene, is a novel, potent activator of a variety of adenylate cyclase systems; its mechanism and site of action are still disputed. We report here that, while forskolin activates liver adenylate cyclase up to 15-fold, it does not activate cyclase of ram sperm which comprises a pure catalytic subunit. However, forskolin activation of sperm adenylate cyclase activity could be observed after reconstitution with the regulatory component-enriched membrane from human erythrocytes. The diterpene weakly (3-5-fold) activated the cytosolic, soluble cyclase found in rat and ram tests, but this effect was lost when the cyclase was purified by gel chromatography. Our data are not compatible with the hypothesis that forskolin acts directly on the catalytic subunit, but rather suggest that it acts via another regulatory component, part of, or different from, the GTP-binding regulatory complex.

Adenylyl Cyclases↗
PubMedDate not supplied

[Role of guanidylic nucleotides in the adenylate cyclase activity of the rat liver].

Glucagon and adrenaline exert their action upon the liver via the cyclic AMP synthetizing system located in the plasma membrane. The enzyme adenylate cyclase is further regulated by guanyl nucleotides. It has been recently shown that the rat liver plasma membrane system could respond to GTP by simultaneous increase in the cyclase activity in response to glucagon and by the dissociation of this hormone from its binding sites (1). Unambiguous relationship between the activating effect of GTP upon the cyclase and its action upon glucagon binding has not been determined yet (2). This problem was approached using the in vitro action of epinephrine as a model. When 1 to 100 muM GTP or DGP were added to rat liver plasma membranes isolated from adrenalectomized animals, they increased markedly the response of the cyclase system to epinephrine. These effects could be observed in the absence of an ATP-regenerating system and were mimicked by 5'-guanylyl diphosphonate; GTP and GDP were the most active compounds followed by ITP, CTP and by a series of guanyl derivatives. UTP, as well as guanosine, GMP, cyclic GMP and ppGpp were inactive. Guanyl nucleotides did not increase the affinity of the cyclase system for the activating hormones, but enhanced the affinity for ATP-Mg and also the Vmax of the reaction. Finally, GTP, ATP, CTP, UTP but not GDP displaced epinephrine bound to plasma membranes by a mere chelation phenomenon. It is concluded that 1) guanyl nucleotides do not act primarily by influencing the binding of hormones to the membranes; 2) they act directly upon the catalytic subunit of the cyclase; 3) the low concentrations of GTP required for its action strongly suggest that this nucleotide plays a role in the physiological regulation of the intrahepatic cyclic AMP level.

Adenylyl Cyclases↗
PubMedDate not supplied

[Alteration of the catecholamine receptor during hepatic malignancy (author's transl)].

The adenylate cyclase system of a plasma membrane preparation from normal rat liver responds to various catecholamines in the following order: protokylol greater than isoproterenol greater than epinephrine greater than norepinephrine. In the Zadejela ascites hepatoma, the order of sensitivity is modified, indicating a transformation of the receptor from the beta2 to the beta1 type. These observations suggest that the catecholamine receptor might be a single entity, susceptible to secondary, and reversible, modification towards either a beta 1 or a beta 2 type.

Animals↗