scholarly journals Platelet adenylate cyclase and phospholipase C are affected differentially by ADP-ribosylation. Effects on thrombin-mediated responses

1988 ◽  
Vol 252 (1) ◽  
pp. 297-300 ◽  
Author(s):  
H S Banga ◽  
R K Walker ◽  
L K Winberry ◽  
S E Rittenhouse
Keyword(s):  
Cyclic Amp ◽  
Adenylate Cyclase ◽  
Phospholipase C ◽  
G Protein ◽  
G Proteins ◽  
Pertussis Toxin ◽  
Marked Decrease ◽  
Human Platelets ◽  
Adp Ribosylation

Thrombin stimulates phospholipase C and inhibits adenylate cyclase in human platelets. We have studied the effect of purified S1 monomer, the ADP-ribosylating subunit of pertussis toxin, on these receptor-coupled G-protein-dependent activities. ADP-ribosylation of a 41 kDa protein is associated with a marked decrease in the ability of thrombin to inhibit cyclic AMP formation, but has little effect on phospholipase C. Therefore adenylate cyclase and phospholipase C appear to be modulated by different G-proteins.

Dual Regulation of Phospolipase C Activity by G Proteins

Physiology ◽  
1993 ◽  
Vol 8 (2) ◽  
pp. 61-63
Author(s):  
H Deckmyn ◽  
C Van Geet ◽  
J Vermylen
Keyword(s):  
Adenylate Cyclase ◽  
Phospholipase C ◽  
G Protein ◽  
G Proteins ◽  
Pertussis Toxin ◽  
Inhibitory Pathway ◽  
Close Parallelism

Some subtypes of phosphatidylinositide-specific phospholipase C (PLC) are activated via pertussis toxin-sensitive or -insensitive G proteins. However, a G protein-dependent PLC inhibitory pathway also may exist. The resultant picture is of dual regulation of PLC, showing a close parallelism with the dual regulation of adenylate cyclase.

THE ROLE OF GTP-BINDING PROTEINS EXHIBITING GTPase ACTIVITY IN PLATELET ACTIVATION

1987 ◽  
Author(s):  
K H Jakobs ◽  
P Gierschik ◽  
R Grandt
Keyword(s):  
Signal Transduction ◽  
Adenylate Cyclase ◽  
Phospholipase C ◽  
G Protein ◽  
G Proteins ◽  
Pertussis Toxin ◽  
Inositol Phosphate ◽  
Adenylate Cyclase Inhibition ◽  
Gi Protein ◽  
Stimulation Of

Activation of platelets by agonists acting via cell surface-located receptors apparently involves as an early event in transmembrane signalling an interaction of the agonist-occupied receptor with a guanine nucleotide-binding regulatory protein (G-protein). The activated G-protein, then, transduces the information to the effector molecule, being responsible for the changes in intracellular second messengers. At least two changes in intracellular signal molecules are often found to be associated with platelet activation by agonists, i.e., increases in inositol trisphosphate and diacylglycerol levels caused by activation of a polyphosphoinositide-specific phospholipase C and decrease in cyclic AMP concentration caused by inhibition of adenylate cyclase.Both actions of platelet-activating agents apparently involve G-proteins as transducing elements. Generally, the function of a G-protein in signal transduction can be measured either by its ability to regulate the activity of the effector molecule (phospholipase C or adenylate cyclase) or the binding affinity of an agonist to its specific receptor or by the abitlity of the G-protein to bind and hydrolyze GTP or one of its analogs in response to agonist-activated receptors. Some platelet-activating agonists (e.g. thrombin) can cause both adenylate cyclase inhibition and phospholipase C activation, whereas others induce either inhibition of adenylate cyclase (e.g. α2-adrenoceptor agonists) or activation of phospholipase C (e.g. stable endoperoxide analogs) . It is not yet known whether the simultaneous activation of two signal transduction systems is due to activation of two separate G-proteins by one receptor, to two distinct receptors activating each a distinct G-protein or to activation of two effector molecules by one G-protein.For some of the G-proteins, rather specific compounds are available causing inactivation of their function. In comparison to Gs, the stimulatory G-protein of the adenylate cyclase system, the adenylate cyclase inhibitory Gi-protein is rather specifically inactivated by ADP-ribosylation of its a-subunit by pertussis toxin, “unfortunately” not acting in intact platelets, and by SH-group reactive agents such as N-ethylmaleimide and diamide, apparently also affecting the Giα-subunit. Both of these treatments completely block α2-adrenoceptor-induced GTPase stimulation and adenylate cyclase inhibition and also thrombin-induced inhibition of adenylate cyclase. In order to know whether the G-protein coupling receptors to phospholipase C is similar to or different from the Gi-protein, high affinity GTPase stimulation by agents known to activate phospholipase C was evaluated in platelet membranes. The data obtained indicated that GTPase stimulation by agents causing both adenylate cyclase inhibition and phospholipase C activation is reduced, but only partially, by the above mentioned Gi-inactivating agents, while stimulation of GTPase by agents stimulating only phospholipase C is not affected by these treatments. These data suggested that the G-protein regulating phospholipase C activity in platelet membranes is different from the Gi-protein and may also not be a substrate for pertussis toxin. Measuring thrombin stimulation of inositol phosphate and diacylglycerol formation in saponin-permeabilized platelets, apparently contradictory data were reported after pertussis toxin treatment, being without effect or causing even an increase in thrombin stimulation of inositol phosphate formation (Lapetina: BBA 884, 219, 1986) or being inhibitory to thrombin stimulation of diacylglycerol formation (Brass et al.: JBC 261, 16838, 1986). These data indicate that the nature of the phospholipase C-related G-protein(s) is not yet defined and that their elucidation requires more specific tools as well as purification and reconstitution experiments. Preliminary data suggest that some antibiotics may serve as useful tools to characterize the phospho-lipase-related G-proteins. The possible role of G-protein phosphorylation by intracellular signal molecule-activated protein kinases in attenuation of signal transduction in platelets will be discussed.

Immunoprecipitation of a pertussis toxin substrate of the Go family from rat islets of Langerhans

1992 ◽  
Vol 12 (2) ◽  
pp. 95-100 ◽  
Author(s):  
Nicholas S. Berrow ◽  
Roger D. Hurst ◽  
Susan L. F. Chan ◽  
Noel G. Morgan
Keyword(s):  
Molecular Weight ◽  
Insulin Secretion ◽  
Adenylate Cyclase ◽  
G Protein ◽  
G Proteins ◽  
Islets Of Langerhans ◽  
Pertussis Toxin ◽  
Inhibitory Receptors ◽  
Rat Islets ◽  
Rat Islets Of Langerhans

Rat islets express a pertussis toxin sensitive G-protein involved in receptor-mediated inhibition of insulin secretion. This has been assumed previously to represent “Gi” which couples inhibitory receptors to adenylate cyclase. Incubation of islet G-proteins with32P-NAD and pertussis toxin resulted in the labelling of a band of molecular weight 40,000. This band was very broad and did not allow resolution of individual components. Incubation of the radiolabelled proteins with an anti-Go antiserum resulted in specific immunoprecipitation of a32P-labelled band. These results demonstrate that the complement of pertussis toxin sensitive G-proteins in rat islets includes Go.

Stimulation by G Protein βγ Subunits of Phospholipase C β Isoforms in Human Platelets

1998 ◽  
Vol 79 (05) ◽  
pp. 1008-1013 ◽  
Author(s):  
Yoshiko Banno ◽  
Tomiko Asano ◽  
Yoshinori Nozawa
Keyword(s):  
Phospholipase C ◽  
G Protein ◽  
G Proteins ◽  
Human Platelet ◽  
Minor Component ◽  
Similar Efficacy ◽  
Human Platelets ◽  
Bovine Brain ◽  
Γ Subunit ◽  
A Minor

SummaryDifferent phospholipase C (PLC) isoforms were located in human platelet cytosol and membranes. PLCγ2 and PLCβ3b were mainly located in the cytosol and PLCβ2 and PLCβ3a were in both cytosol and membranes by using specific antibodies against PLC isozymes (Banno Y, Nakashima S, Ohzawa M, Nozawa Y. J Biol Chem 1996; 271: 14989-94). Three PLC fractions activated by G protein βγ subunits were purified from human platelet cytosol and membrane fractions. Two PLC fractions from membranes were identified as PLCβ2 and PLCβ3a, and one from cytosol was PLCβ3b. These PLCβ isoforms were activated by the purified βγ subunits of brain G proteins in the order PLCβ3b > PLCβ3a > PLCβ2. Western blot analysis of γ subunits of the purified platelet G proteins with antibodies against various standard γ subunits revealed that the major component of the γ subunit of Gi2 and Gq was γ5, and that γ7 was a minor component. Studies using various subtypes of βγ subunits, βγ2, βγ3, and βγ7 purified from bovine brain, βγ5 from bovine lung, or βγ12 from bovine spleen, failed to show differences in their ability to stimulate the isolated platelet PLCβ isoforms. These results suggest that the βγ subunits of Gi2 and Gq have similar efficacy in regulation of effectors in human platelets.

Pertussis toxin sensitive G-protein coupling of HDL receptor to phospholipase C in human platelets

1992 ◽  
Vol 67 (5) ◽  
pp. 559-567 ◽  
Author(s):  
H. Nazih ◽  
D. Devred ◽  
F. Martin-Nizard ◽  
V. Clavey ◽  
J.C. Fruchart ◽  
...  
Keyword(s):  
Phospholipase C ◽  
G Protein ◽  
Pertussis Toxin ◽  
Human Platelets ◽  
G Protein Coupling ◽  
Protein Coupling

G PROTEIN REGULATORS OF PHOSPHOLIPASE C AND ADENYLATE CYCLASE IN PLATELETS

1987 ◽  
Author(s):  
L F Brass ◽  
D R Manning ◽  
M J Woolkalis
Keyword(s):  
Adenylate Cyclase ◽  
Phospholipase C ◽  
G Protein ◽  
Pertussis Toxin ◽  
Platelet Activating Factor ◽  
Protein Band ◽  
2D Electrophoresis ◽  
Guanine Nucleotide Binding Protein ◽  
Pi Hydrolysis ◽  
Camp Formation

The hydrolysis of polyphosphoinositides (PI) by phospholipase C during platelet activation produces two key intracellular messengers, inositol triphosphate and diacylglycerol. This process is thought to be regulated by a guanine nucleotide binding protein referred to as Gp. Although the evidence that Gp exists is compelling, to date it has not been isolated. Uncertainty about its identity has been compounded by variations between tissues in the susceptibility of Gp to pertussis toxin and by reconstitution studies which show that pertussis toxin-inhibited PI hydrolysis can be restored by purified Gi, the pertussis toxin-sensitive G protein which inhibits adenylate cyclase. Therefore, it remains unclear whether Gp represents a new G protein or a second role for Gj. When platelets permeabilized with saponin were incubated with pertussis toxin and 32P-NAD, a single 42 kDa protein was 32P-ADP-ribosylated which co-migrated with the purified a subunit of Gi. Preincubating the platelets with an agonist inhibited labeling of this protein by dissociating the G protein into subunits. The extent of inhibition correlated with the number of toxin-sensitive functions caused by the agonist. Labeling was abolished by thrombin, which inhibited cAMP formation and caused toxin-inhibitable PI hydrolysis. Labeling was partially inhibited by vasopressin and platelet activating factor, which caused toxin-inhibitable PI hydrolysis, but had no effect on cAMP formation and by epinephrine, which inhibited cAMP formation, but did not cause PI hydrolysis. Labeling was unaffected by the TxA2 analog U46619, which neither caused toxin-sensitive PI hydrolysis nor inhibited cAMP formation. These observations suggest that the 42 kDa band may contain a subunits from both Gp and Gi and, in fact, 2D electrophoresis resolved the 42 kDa protein band into two proteins with distinct pi. However, those agonists linked functionally only to Gp or only to Gi decreased the labeling of both proteins. Therefore, our data suggest (1) that Gj and Gp are the same protein and (2) that whether a aiven platelet agonist affects adenylate cyclase or phospholipase C or both depends upon factors extrinsic to the G protein.

scholarly journals Phospholipase C-β1 is regulated by a pertussis toxin-insensitive G-protein

1991 ◽  
Vol 280 (3) ◽  
pp. 753-760 ◽  
Author(s):  
T F J Martin ◽  
J E Lewis ◽  
J A Kowalchyk
Keyword(s):  
Phospholipase C ◽  
G Protein ◽  
G Proteins ◽  
Pertussis Toxin ◽  
Gh3 Cells ◽  
Phospholipid Vesicles ◽  
Protein Tyrosine Phosphorylation ◽  
Gtp Binding ◽  
Gamma Subunits ◽  
Gh3 Cell

Regulation of phospholipase C (PLC) by receptors is mediated either through protein tyrosine phosphorylation or by activation of GTP-binding proteins (Gp). For the latter, pertussis toxin (PT)-sensitive and -insensitive pathways have been described, indicating PLC regulation by at least two types of G-proteins. The identity of PLC isoenzymes which are regulated by either type of Gp remains to be determined. Thyrotropin-releasing hormone stimulates a PLC in GH3 cells via a PT-insensitive Gp. Reconstitution methods for the assay of the GH3-cell Gp were developed. Previously, the membrane PLC was found to be reversibly extracted from membranes by high salt and to be activated by guanosine 5′-[gamma-thio]triphosphate (GTP[S]) only when membrane-associated, suggesting that Gp was retained in salt-extracted membranes. In the present work, Gp was cholate-solubilized from PLC-deficient membranes and incorporated into phospholipid vesicles, which were found to confer GTP[S]- and AlF4(-)-stimulated activity on a solubilized membrane PLC. The reconstitution provided a direct assay for the GH3-cell Gp which was shown to be distinct from Gi, Go and Gs proteins by immunodepletion studies. Incorporation of G-protein beta-gamma subunits into phospholipid vesicles with Gp inhibited GTP[S]-stimulated activity in the reconstitution. The results indicated that Gp is a heterotrimeric G-protein with the properties expected for the PT-insensitive GH3-cell Gp protein. PLC-beta 1 was fully purified and shown to be regulated by Gp in the reconstitution. In contrast, PT-sensitive G-proteins failed to affect the activity of PLC-beta 1. The results indicate (1) that a PT-insensitive Gp regulates PLC-beta 1 and (2) that PT-sensitive and -insensitive pathways of PLC regulation employ different PLC isoenzymes as well as different G-proteins.

scholarly journals Extracellular ATP stimulates three different receptor-signal transduction systems in FRTL-5 thyroid cells. Activation of phospholipase C, and inhibition and activation of adenylate cyclase

1992 ◽  
Vol 283 (1) ◽  
pp. 281-287 ◽  
Author(s):  
K Sato ◽  
F Okajima ◽  
Y Kondo
Keyword(s):  
Signal Transduction ◽  
Cyclic Amp ◽  
Adenylate Cyclase ◽  
Phospholipase C ◽  
Pertussis Toxin ◽  
Extracellular Atp ◽  
Thyroid Cells ◽  
Receptor Signal ◽  
Atp Analogues ◽  
Signal Transduction Systems

In FRTL-5 thyroid cells, extracellular ATP, a P2-agonist, not only stimulates phospholipase C but also inhibits forskolin- or thyrotropin (TSH)-induced stimulation of adenylate cyclase in a pertussis toxin-sensitive manner [Okajima, Sato, Nazarea, Sho, & Kondo (1989) J. Biol. Chem. 264, 13029-13037]. We have now found that, in pertussis toxin-treated cells, ATP can directly stimulate adenylate cyclase. Although adenylate cyclase modulation occurs through ATP metabolites such as AMP and adenosine, we show that extracellular ATP itself also regulates cyclic AMP production, based on the following: (1) the actions of ATP were imitated by hydrolysis-resistant ATP analogues, (2) the elimination of adenosine by adenosine deaminase decreased the effect of ATP only partially, at least at concentrations greater than 10 microM-ATP, and (3) the amount of AMP produced from ATP was too low to account for the ATP effects. To identify the respective receptors for the three different actions of ATP, we established an antagonist profile. Suramin, which has been reported to be a P2-receptor antagonist, inhibited ATP-induced phospholipase C activation in a competitive fashion, but did not affect ATP-induced adenylate cyclase modulation. On the other hand, 8-cyclopentyl-1,3-diphenylxanthine competitively antagonized both the stimulatory and inhibitory ATP actions on cyclic AMP levels, but did not influence the activation of phospholipase C by ATP. The order of potency for various xanthine derivatives was clearly different with respect to their antagonistic effects on the stimulation and inhibition of adenylate cyclase induced by ATP. We conclude that ATP activates three receptors, each of which is coupled to a different signal transduction system in FRTL-5 cells, i.e. phospholipase C activation, and adenylate cyclase activation and inhibition.

Use of pertussis toxin to investigate the mechanism of action of prostaglandin F2α on the corpus luteum in sheep

1993 ◽  
Vol 10 (1) ◽  
pp. 79-85 ◽  
Author(s):  
T J McCann ◽  
A P F Flint
Keyword(s):  
Cyclic Amp ◽  
Adenylate Cyclase ◽  
Corpus Luteum ◽  
G Protein ◽  
Mechanism Of Action ◽  
Pertussis Toxin ◽  
Prostaglandin F2α ◽  
Inhibitory Effect ◽  
Luteal Tissue ◽  
Hydrolysis Of

ABSTRACT Pertussis toxin catalysed the ADP-ribosylation of a protein of Mr 40 000 in ovine luteal tissue. Ribosylation of 45% of this protein in whole cell incubations (as judged by subsequent ribosylation of cell-free preparations in the presence of [32P]NAD) attenuated the prostaglandin (PG)F2α-stimulated hydrolysis of [3H]inositol-labelled phosphatidylinositol-4,5-bisphosphate into inositol trisphosphate by 60%, but did not affect the inhibition by PGF2α of LH-stimulated accumulation of cyclic AMP. It is concluded that activation of phospholipase C by PGF2α involves a pertussis toxin-sensitive protein, probably a G protein, and that the inhibitory effect of PGF2α on LH-stimulated adenylate cyclase is unlikely to be directly mediated by such a protein.

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