scholarly journals The inhibitory GTP-binding protein (Gi) occurs in rat Leydig cells and is differentially modified by lutropin and 12-O-tetradecanoylphorbol 13-acetate

1988 ◽  
Vol 253 (3) ◽  
pp. 895-899 ◽  
Author(s):  
E A Platts ◽  
D Schulster ◽  
B A Cooke
Keyword(s):  
Plasma Membrane ◽  
Luteinizing Hormone ◽  
Cyclic Amp ◽  
Cholera Toxin ◽  
Pertussis Toxin ◽  
Leydig Cells ◽  
Binding Protein ◽  
Gtp Binding Protein ◽  
Gtp Binding ◽  
Subsequent Response

Luteinizing-hormone (LH)-stimulated cyclic AMP production in rat testis Leydig cells was desensitized by both LH and 12-O-tetradecanoylphorbol 13-acetate (TPA). However, TPA, but not LH, enhanced the subsequent response to cholera toxin. Treatment of the cells with pertussis toxin potentiated cyclic AMP production in both control and LH-desensitized cells, but did not potentiate further the responses obtained by TPA pretreatment. The results implicate the presence of an inhibitory GTP-binding protein (Gi), which may be inhibited by TPA. The presence of a Gi-like protein within the plasma membrane of Leydig cells was demonstrated by pertussis-toxin-catalysed [32P]ADP-ribosylation of a Mr-40000-41000 protein.

scholarly journals The inhibitory GTP-binding protein (Gi) regulates the agonistic property of β-adrenergic ligands in isolated rat adipocytes. Evidence for a priming effect of cyclic AMP

1992 ◽  
Vol 288 (1) ◽  
pp. 41-46 ◽  
Author(s):  
C Wesslau ◽  
U Smith
Keyword(s):  
Cyclic Amp ◽  
Adenylate Cyclase ◽  
Pertussis Toxin ◽  
Priming Effect ◽  
Binding Protein ◽  
Gtp Binding Protein ◽  
Rat Adipocytes ◽  
Partial Agonists ◽  
Gtp Binding ◽  
Cellular Sensitivity

Prenalterol, an allegedly beta 1-selective adrenergic agonist with high intrinsic sympathomimetic activity (ISA), was shown to be weakly lipolytic in rat adipocytes. However, in pertussis-toxin-treated adipocytes, the ISA of prenalterol was markedly increased (from 10-20% to approx. 100% of that of isoprenaline). The cellular sensitivity was also increased (EC50 approx. 60 nM and approx. 3 microM in pertussis-toxin-treated and control cells respectively). A similar effect was seen for other partial agonists such as the beta 2-selective agonist terbutaline and for beta-adrenergic antagonists with some intrinsic activity (metoprolol, pindolol). There was no clear change in sensitivity to isoprenaline's ability to stimulate adenylate cyclase in adipocyte membranes from pertussis-toxin-treated animals but the cyclase activity was increased approx. 4-fold in the presence of 1 microM-GTP. Prenalterol stimulated lipolysis by only small increases in intracellular cyclic AMP (cAMP) levels (less than 10% of that seen with isoprenaline). Basal lipolysis was increased in cells from pertussis-toxin-treated rats and the cellular sensitivity to the non-degradable cAMP analogue, N6-monobutyryl-cAMP, was increased. In control cells, a submaximal concentration of prenalterol (0.1 microM) increased the sensitivity to the cAMP analogues, N6-monobutyryl-cAMP and 8-bromo-cAMP. A low concentration (1 mM) of 8-bromo-cAMP also increased the effect of prenalterol. Similar effects were seen when the phosphodiesterase was inhibited. Thus (1) lipolysis is extremely sensitive to small increases in intracellular cAMP; (2) the degree of activation of adenylate cyclase and thus cAMP formation is the rate-limiting step for the biological response of partial agonists; (3) the inhibitory GTP-binding protein, Gi, is an important modulator (‘tissue factor’) of the beta-adrenergic agonistic property; (4) low levels of cAMP exert a priming effect on protein kinase A.

scholarly journals Thrombin exerts a dual effect on stimulated adenylate cyclase in hamster fibroblasts, an inhibition via a GTP-binding protein and a potentiation via activation of protein kinase C

1988 ◽  
Vol 253 (3) ◽  
pp. 711-719 ◽  
Author(s):  
I Magnaldo ◽  
J Pouysségur ◽  
S Paris
Keyword(s):  
Protein Kinase C ◽  
Protein Kinase ◽  
Cyclic Amp ◽  
Adenylate Cyclase ◽  
Phospholipase C ◽  
Pertussis Toxin ◽  
Binding Protein ◽  
Gtp Binding Protein ◽  
Kinase C ◽  
Gtp Binding

Previous studies in Chinese-hamster fibroblasts (CCL39 line) indicate that an important signalling pathway involved in thrombin's mitogenicity is the activation of a phosphoinositide-specific phospholipase C, mediated by a pertussis-toxin-sensitive GTP-binding protein (Gp). The present studies examine the effects of thrombin on the adenylate cyclase system and the interactions between the two signal transduction pathways. We report that thrombin exerts two opposite effects on cyclic AMP accumulation stimulated by cholera toxin, forskolin or prostaglandin E1. (1) Low thrombin concentrations (below 0.1 nM) decrease cyclic AMP formation. A similar inhibition is induced by A1F4-, and both thrombin- and A1F4- –induced inhibitions are abolished by pertussis toxin. (2) Increasing thrombin concentration from 0.1 to 10 nM results in a progressive suppression of adenylate cyclase inhibition and in a marked enhancement of cyclic AMP formation in pertussis-toxin-treated cells. A similar stimulation is induced by an active phorbol ester, and thrombin-induced potentiation of adenylate cyclase is suppressed by down-regulation of protein kinase C. Therefore, we conclude that (1) the inhibitory effect of thrombin on adenylate cyclase is the direct consequence of the activation of a pertussis-toxin-sensitive inhibitory GTP-binding protein (Gi) possibly identical with Gp, and (2) the potentiating effect of thrombin on cyclic AMP formation is due to stimulation of protein kinase C, as an indirect consequence of Gp activation. Our results suggest that the target of protein kinase C is an element of the adenylate cyclase-stimulatory GTP-binding protein (Gs) complex. At low thrombin concentrations, activation of phospholipase C is greatly attenuated by increased cyclic AMP, leading to predominance of the Gi-mediated inhibition.

scholarly journals Redistribution of a rab3-like GTP-binding protein from secretory granules to the Golgi complex in pancreatic acinar cells during regulated exocytosis

1994 ◽  
Vol 124 (1) ◽  
pp. 43-53 ◽  
Author(s):  
BP Jena ◽  
FD Gumkowski ◽  
EM Konieczko ◽  
GF von Mollard ◽  
R Jahn ◽  
...  
Keyword(s):  
Plasma Membrane ◽  
Golgi Complex ◽  
Binding Protein ◽  
Secretory Granules ◽  
Acinar Cells ◽  
Pancreatic Acinar Cells ◽  
Apical Plasma Membrane ◽  
Gtp Binding Protein ◽  
Regulated Exocytosis ◽  
Gtp Binding

Regulated secretion from pancreatic acinar cells occurs by exocytosis of zymogen granules (ZG) at the apical plasmalemma. ZGs originate from the TGN and undergo prolonged maturation and condensation. After exocytosis, the zymogen granule membrane (ZGM) is retrieved from the plasma membrane and ultimately reaches the TGN. In this study, we analyzed the fate of a low M(r) GTP-binding protein during induced exocytosis and membrane retrieval using immunoblots as well as light and electron microscopic immunocytochemistry. This 27-kD protein, identified by a monoclonal antibody that recognizes rab3A and B, may be a novel rab3 isoform. In resting acinar cells, the rab3-like protein was detected primarily on the cytoplasmic face of ZGs, with little labeling of the Golgi complex and no significant labeling of the apical plasmalemma or any other intracellular membranes. Stimulation of pancreatic lobules in vitro by carbamylcholine for 15 min, resulted in massive exocytosis that led to a near doubling of the area of the apical plasma membrane. However, no relocation of the rab3-like protein to the apical plasmalemma was seen. After 3 h of induced exocytosis, during which time approximately 90% of the ZGs is released, the rab3-like protein appeared to translocate to small vesicles and newly forming secretory granules in the TGN. No significant increase of the rab3-like protein was found in the cytosolic fraction at any time during stimulation. Since the protein is not detected on the apical plasmalemma after stimulation, we conclude that recycling may involve a membrane dissociation-association cycle that accompanies regulated exocytosis.

GTP analogues cause release of the alpha subunit of the GTP binding protein, GO, from the plasma membrane of NG108-15 cells

1988 ◽  
Vol 152 (1) ◽  
pp. 243-251 ◽  
Author(s):  
Hayley McArdle ◽  
Ian Mullaney ◽  
Anthony Magee ◽  
Cecilia Unson ◽  
Graeme Milligan
Keyword(s):  
Plasma Membrane ◽  
Binding Protein ◽  
Alpha Subunit ◽  
Gtp Binding Protein ◽  
Gtp Binding

Effects of lithium ion on ADP ribosylation of inhibitory GTP-binding protein by pertussis toxin, islet-activating protein

1991 ◽  
Vol 206 (1) ◽  
pp. 33-37 ◽  
Author(s):  
Hideo Kawamoto ◽  
Yasuhiro Watanabe ◽  
Taro Imaizumi ◽  
Tadaaki Iwasaki ◽  
Hiroshi Yoshida
Keyword(s):  
Pertussis Toxin ◽  
Binding Protein ◽  
Lithium Ion ◽  
Gtp Binding Protein ◽  
Adp Ribosylation ◽  
Gtp Binding
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