Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UMLS:C0043167 (pertussis)
 19,595 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The regulation of pituitary hormone secretion by TRH and GnRH proceeds through similar mechanisms which employ phosphoinositide hydrolysis to generate intracellular signals. Proximal events involve receptor activation of heterotrimeric (alpha beta gamma) GTP-binding (G) proteins which regulate phospholipase (PLC) activity. Since TRH and GnRH actions are not affected by cholera or pertussis toxin, a novel G protein (Gp) was suggested to mediate receptor regulation. The required Gp protein has not been identified and this was the focus of the present study. Recent molecular cloning and biochemical studies have characterized two novel, pertussis toxin-insensitive alpha-subunit proteins of the Gq subfamily (alpha q and alpha 11) which regulate the activity of the beta 1 isoenzyme of PLC. Gq and G11 represent the best candidates for the PLC-activating G proteins which mediate the actions of TRH and GnRH. To test this directly, an antibody to the common Gq/11 alpha-subunit carboxyterminal sequence was generated and shown to react with unique 42-kilodalton Gq alpha and 43-kilodalton G11 alpha proteins in membranes from TRH-responsive GH3 cells and GnRH-responsive alpha T3-1 pituitary cells. The Gq/11 alpha peptide antibody was shown to immunodeplete the Gp activity of GH3 cell membrane extracts measured by reconstitution of the guanine nucleotide regulation of PLC-beta 1. In addition, the immunoglobulin G fraction of Gq/11 alpha peptide immune serum specifically inhibited TRH- and GnRH-stimulated PLC activity measured in the membranes of GH3 and alpha T3-1 cells, respectively. The results indicate that TRH and GnRH activation of PLC requires receptor coupling to a Gp protein(s) which corresponds to Gq, G11 or both.
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PMID:Thyrotropin-releasing hormone and gonadotropin-releasing hormone receptors activate phospholipase C by coupling to the guanosine triphosphate-binding proteins Gq and G11. 133 52

In this study, we investigated the expression of various G proteins in whole sciatic nerves, in myelin and nonmyelin fractions from these nerves, and in membranes of immortalized Schwann cells. In myelin, nonmyelin, and Schwann cell membranes we detected two 39-40-kDa pertussis toxin substrates that were resolved on separation on urea-gradient gels. Two cholera toxin substrates with apparent molecular masses of 42 and 47 kDa were present in nerve and brain myelin and in Schwann cell membranes. In these membranes, a third 45-kDa cholera toxin substrate, which displayed the highest labeling, was also present. Immunoblotting with specific antisera allowed the identification of G(o) alpha, Gi1 alpha, Gi2 alpha, Gi3 alpha, Gq/G11 alpha, and the two isoforms of Gs alpha in nerve homogenates, nerve, and brain myelin fractions. In Schwann cell membranes we identified G(o) alpha, Gi2 alpha, Gi3 alpha, and proteins from the Gq family, but no immunoreactivity toward anti-Gi1 alpha antiserum was detected. In these membranes, anti-Gs alpha antibody recognized the three cholera toxin substrates mentioned above, with the 45-kDa band displaying the highest immunoreactivity. Relative to sciatic nerve myelin, the Schwann cell membranes revealed a significantly higher expression of Gi3 alpha and the absence of Gi1 alpha. The different distribution of G proteins among the different nerve compartments might reflect the very specialized function of Schwann cells and myelin within the nerve.
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PMID:Identification of G protein subtypes in peripheral nerve and cultured Schwann cells. 140 17

An antiserum (13CB) was generated against a synthetic peptide, HDNLKQLMLQ, which is predicted to represent the C-terminal decapeptide of the alpha subunit of the novel G-protein, G13. Competitive ELISA indicated that the antiserum reacted with this peptide but that it showed minimal ability to recognize peptides which represent the equivalent regions of the pertussis toxin-insensitive G-proteins, Gq + G11, G12, G15 + G16, GL1 (also called G14) as Gz, and well as other G-proteins. Immunoblots of human platelet membranes with antiserum 13CB identified a single 43-kDa polypeptide, and while this immunoreactivity was abolished by the presence of the cognate peptide it was not modified by the presence of peptides corresponding to the equivalent region of other G-proteins. Immunoreactivity corresponding to G13 alpha was detected in a range of cell types with human platelets having the highest levels of this polypeptide.
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PMID:Immunological identification of the alpha subunit of G13, a novel guanine nucleotide binding protein. 155 27

Platelet activation begins with the binding of an agonist to the cell surface and culminates in the events of platelet aggregation, secretion and clot formation. Recent studies have identified two large families of GTP-binding proteins in platelets that are thought to participate in the events of platelet activation. The first of these are the G proteins, heterotrimeric proteins which are best known for their ability to mediate the interaction between agonist receptors and intracellular enzymes such as adenylyl cyclase, phospholipase C and phospholipase A2. To date, at least six G proteins have been identified in platelets: Gs, Gz, three variants of Gi and either Gq or G11 (or both). An additional, pertussis toxin-resistant G protein, Gq, may also be present. The second group of GTP-binding proteins present in platelets is substantially smaller than the heterotrimeric G proteins, ranging in size from 21 to 28 kDa. At least 15 such low molecular weight GTP-binding proteins have been identified in platelets, many of which are homologous to the products of the ras proto-oncogenes. In cells other than platelets, low molecular weight GTP-binding proteins have been implicated in protein transport, cell activation events and malignant transformation. Their role in platelets is unknown.
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PMID:The role of GTP-binding proteins in platelet activation. 166 93

Antisera were raised to a synthetic peptide which represents the predicted C-terminal decapeptide of the alpha subunit of the G-proteins Gq and G11. Competitive ELISA indicated that antiserum CQ2 displayed strong reactivity against this peptide. Antiserum CQ2 identified an apparently single polypeptide of 42 kDa which was expressed widely. The mobility of this polypeptide in SDS-PAGE was not modified by pretreatment of cells with pertussis toxin, indicating that it was not a substrate for this toxin. Furthermore, the levels and mobility of this polypeptide were unaltered by treatment of cells with cholera toxin, defining that it was not related to Gs alpha.
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PMID:Widespread distribution of Gq alpha/G11 alpha detected immunologically by an antipeptide antiserum directed against the predicted C-terminal decapeptide. 190 88

The human leukaemic cell line K562 is a pluripotent stem cell with the potential to mature along a megakaryocytic or erythroid line. In these cells, thrombin and U46619 (9,11-dideoxy-9 alpha, 11 alpha-methanoepoxy prostaglandin F2 alpha), a thromboxane A2 analogue, increased intracellular Ca2+ in a rapid and concentration-dependent manner. The peak transient observed with both thrombin and U46619 was preserved upon stimulation in the absence of extracellular calcium and blunted with phorbol myristate acetate, suggestive of activation of phospholipase C. Short-term treatment with leupeptin abolished the calcium response to thrombin, but did not alter that to U46619. Both pertussis toxin (PT) and DMSO pretreatment inhibited thrombin- but not U46619-stimulated intracellular calcium elevation, indicating that these agonists signal through different G-proteins. Western blot analysis of crude membranes from K562 cells revealed the presence of G12 alpha and G13 alpha; the other known PT-substrates, Gi1 alpha and G0 alpha, were not detected. Consistent with this observation, ADP-ribosylation experiments revealed the presence of two PT substrates which co-migrated with human erythrocyte G12 alpha and G13 alpha. An antibody raised against Gq/11 alpha, a subfamily of G-protein alpha subunits unmodified by PT, specifically recognized 42 kDa protein(s) in K562 cells. PCR amplification of reverse-transcribed K562 RNA followed by DNA sequencing showed that these cells express messages for both Gq alpha and G11 alpha. Treatment of K562 cells with DMSO reduced the levels of thrombin receptor mRNA, without simultaneous changes in the expression of G12 alpha and G13 alpha. We have thus identified Ca(2+)-mobilizing agonists and related G-proteins in K562 cells, together with changes induced by DMSO in this signalling pathway.
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PMID:Ca2+ signalling in K562 human erythroleukaemia cells: effect of dimethyl sulphoxide and role of G-proteins in thrombin- and thromboxane A2-activated pathways. 749 5

The key event in receptor-catalyzed activation of heterotrimer G proteins is binding of GTP, which leads to subunit dissociation generating GTP-bound alpha subunits and free beta gamma complexes. We have previously identified a mutation that abolished GTP binding in G alpha o (S47C) and demonstrated that the mutant retained the ability to bind beta gamma and could act in a dominant negative fashion when expressed in Xenopus oocytes (Slepak, V.Z., Quick, M.W., Aragay, A.M., Davidson, N., Lester, H.A., and Simon, M.I. (1993) J. Biol. Chem. 268, 21889-21894). In the current work, we investigated the effects of the homologous mutant of G alpha i2 (S48C) upon signaling pathways reconstituted in transiently transfected COS-7 cells. We found that expression of the G alpha i2 S48C mutant prevented stimulation of phospholipase C (PLC) beta 2 by free beta gamma subunit complexes. This effect of G alpha i S48C was not readily reversible in contrast to the inhibitory effect of wild-type G alpha i2, which could be reversed upon activation of the cotransfected muscarinic M2 receptor, presumably by release of beta gamma from the G protein heterotrimer. Coexpression of G alpha i S48C or the wild-type G alpha i2 also dramatically decreased G16-mediated stimulation of PLC by C5a in the cells transfected with cDNAs encoding C5a receptor and G alpha 16. Activation of PLC via endogenous Gq or G11 in the presence of alpha 1C adrenergic receptors was similarly attenuated by coexpression of G alpha i or G alpha i S48C. Pertussis toxin treatment of the transfected cells enhanced the inhibition of the receptor-stimulated PLC by wild-type G alpha i subunits but did not influence the effects of the dominant negative mutant. The enhancement of the wild-type G alpha i inhibitory effect by pertussis toxin can be explained by stabilization of G alpha i binding to beta gamma as a result of ADP-ribosylation, while G alpha i S48C mutant binds beta gamma irreversibly even without pertussis toxin treatment. Therefore, a feasible mechanism to rationalize the attenuation of the G alpha 16 and Gq/11-mediated activation of PLC by cotransfected G alpha i is the competition between G alpha i and G alpha 16 or Gq/11 for the beta gamma complexes, which are necessary for the G protein coupling with receptors. These experiments provide new evidence for the role of beta gamma in the integration of signals controlling phosphoinositide release through different G alpha families.
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PMID:Functional analysis of a dominant negative mutant of G alpha i2. 787 52

The coupling of two endothelin receptor subtypes (ET(A) and ETB) to several types of guanine-nucleotide-binding regulatory protein (G protein) was examined. Two subtypes of receptor cDNAs were transfected alone or together with four different G protein alpha subunit cDNAs in COS-7 cells. In ET(A) receptor-transfected cells, endothelin-1 (ET-1) activated phosphatidylinositol-specific phospholipase C as measured by the production of phosphatidylinositol 1,4,5-trisphosphate [Ins(1,4,5)P3]. ETB-receptor-transfected cells also produced Ins(1,4,5)P3 on stimulation by ET-1. The ET-1-induced production of Ins(1,4,5)P3 was markedly higher in G alpha q-cotransfected or G alpha 11-cotransfected cells than in cells transfected with each receptor alone. ET-1 also stimulated production of cAMP in ET(A) or ETB receptor-transfected cells. The production of cAMP was synergistically amplified by G alpha s co-transfection with each receptor. In contrast, when G alpha i2 was co-transfected with the ET(A) or ETB receptor, ET-1 displayed an inhibitory action on forskolin-stimulated cAMP accumulation. Pertussis-toxin treatment of the G alpha i2-transfected cells resulted in abolition of the endothelin-induced inhibition of cAMP accumulation. These observations indicate that both ET(A) and ETB receptors are able to couple to Gq, G11, Gs and Gi2, and suggest that endothelin receptors stimulate multiple effectors via several types of G protein simultaneously. The overall effects induced by endothelin may differ in cell types depending on the level of expression of each G-protein subtype in the cell.
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PMID:Molecular identification of guanine-nucleotide-binding regulatory proteins which couple to endothelin receptors. 788 89

Prolonged exposure of alpha T3-1 pituitary gonadotrophs to a gonadotrophin-releasing hormone receptor agonist results in marked down-regulation of the pertussis toxin-insensitive G proteins Gq alpha and G11 alpha. The turnover of Gq alpha/G11 alpha was substantially accelerated in the presence of agonist. By contrast, the rate of degradation of the G protein Gi2 alpha was unaffected by agonist treatment. Analysis of Gq alpha/G11 alpha mRNA levels by reverse transcription-PCR demonstrated no detectable differences between control and agonist-treated cells. These studies indicate that gonadotrophin-releasing hormone receptor agonist-mediated down-regulation of Gq alpha/G11 alpha is a reflection of enhanced proteolysis of the activated G proteins.
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PMID:Gonadotrophin-releasing hormone receptor agonist-mediated down-regulation of Gq alpha/G11 alpha (pertussis toxin-insensitive) G proteins in alpha T3-1 gonadotroph cells reflects increased G protein turnover but not alterations in mRNA levels. 789 95

In estradiol-dominated rat myometrium, endothelin (ET)-1 caused contraction and increased the accumulation of [3H]inositol phosphates (EC50 = 70 nM), with the sequential generation of inositol trisphosphate, inositol bisphosphate, and inositol monophosphate. There was a coincident early decrease in phosphatidyl-inositol bisphosphate. The ET-1 stimulatory effect was pertussis toxin insensitive, suggesting an activation of phospholipase C via Gq/G11 proteins. ET-1 also inhibited the generation of cAMP induced by forskolin (EC50 = 30 nM). The inhibition was maintained in Ca(2+)-depleted medium and was prevented by pertussis toxin, suggesting G(i)-mediated inhibition of adenylyl cyclase. The rank order of potency for these various ET-1 effects [ET-1 > (Thr2)-sarafotoxin-b >> ET-3], as well as the inhibitory effect displayed by BQ123, a specific ETA receptor antagonist, provided evidence for the involvement of the ETA receptor subtype. Exposure to ET-1 (15 min) resulted in concentration-dependent and homologous desensitization (40%) of the inositol phosphate response triggered by ET-1. There was virtually no recovery of ET-1-mediated inositol phosphate responses in the desensitized tissue even after 180 min of incubation. In contrast, the persistent low level of ET-1 activity that was observed in spite of several washings and in the absence of rechallenge with ET-1 was progressively revsersed and totally eliminated by BQ123. The ET-1 inhibitory effect on cAMP was also desensitized, as evidenced by the attenuation of the inhibitory effect of ET-1 after 15 min of ET-1 pretreatment. The data indicate that in rat myometrium the ETA receptor is coupled, via two distinct G proteins, to two main signal transduction cascades, which both undergo rapid desensitization.
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PMID:Endothelin receptor type A signals both the accumulation of inositol phosphates and the inhibition of cyclic AMP generation in rat myometrium: stimulation and desensitization. 793 29


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