Gα11 and Gαq guaninine nucleotide regulatory proteins differentially modulate the response to thyrotropin‐releasing hormone in Xenopus oocytes

Lipinsky, Dafna; Gershengorn, Marvin C.; Oron, Yoram

doi:10.1016/0014-5793(92)80775-c

Cited by 22 publications

(11 citation statements)

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“…There has, however, been some controversy concerning the ability of G proteins of the G␣ q family to activate the PLC cascade in the oocytes. Our earlier study showed that responses are enhanced by injection of cRNA for G␣ q or G␣ 11 (21), but in other reports G␣ q or G␣ 11 injected into the oocyte has reduced Cl Ϫ currents (19,41). The results presented here support the idea that the G␣ subunit of all members of the G␣ q family can couple to GPCRs and activate the oocyte's IP 3 /Ca 2ϩ -induced Cl Ϫ conductance.…”

Section: G␣ 16 Inhibition Of Ligand-induced CLsupporting

confidence: 76%

Desensitization of Inositol 1,4,5-Trisphosphate/Ca2+-induced Cl− Currents by Prolonged Activation of G Proteins in Xenopus Oocytes

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Lester

Davidson

et al. 1996

Journal of Biological Chemistry

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Expression of G protein ␣ subunits of the G q family with various G protein-coupled receptors induces activation of an inositol 1,4,5-trisphosphate (IP 3 )/Ca 2؉ -mediated Cl ؊ conductance in Xenopus oocytes. Our present data show that two members of this family, the human G␣ 16 subunit and the murine homologue G␣ 15 , can induce both activation and inhibition of these agonistinduced currents. Although extremely low amounts (10 -50 pg) of injected G␣ 16 subunit cRNA cause modest (ϳ2-fold) enhancement of ligand-induced Cl ؊ currents in oocytes co-injected with thyrotropin-releasing hormone (TRH) receptor cRNA 48 h postinjection, larger G␣ 16 and G␣ 15 cRNA injections cause >10-fold inhibition of TRH or 5HT2c receptor responses. The inhibition is analyzed in this study. The inhibited currents are recovered if various G␤␥ subunit combinations are also expressed with the G␣ subunits. The constitutively active mutant, G␣ 16 Q212L, also causes a strong attenuation of the ligand-induced Cl ؊ currents, but this inhibition is not recovered by co-expression of G␤␥ subunits. These results indicate that the free G␣ subunit is responsible for the inhibitory signal. Although expression of TRH receptor alone produces maximum responses approximately 48 h after injection, co-expression of TRH receptor with G␣ 16 results in enhanced responses 6 -12 h postinjection, followed by complete attenuation at 36 h. Furthermore, injection of G␣ 16 cRNA alone at comparable levels gives rise to spontaneous Cl ؊ currents within 6 -12 h postinjection, suggesting that the early spontaneous activation underlies the later suppression. Expression of other G protein ␣ subunits of the G q family, at cRNA levels considerably higher than effective for G␣ 16 , produces both analogous spontaneous Cl ؊ currents and, later, inhibition of ligand-induced Cl ؊ currents. Experiments with direct injection of IP 3 and of Ca 2؉ suggest that this inhibition is consistent with the down-regulation of IP 3 receptors. These data indicate that both enhancement and inhibition of signaling through G protein-coupled receptors can be mediated by the expression level and/or activity of an individual G protein.Many hormones, neurotransmitters, and growth factors act via G protein-coupled receptors (GPCRs) 1 in a wide range of transduction processes. The phosphoinositide cascade, which controls calcium-stimulated processes such as secretion, chemotaxis, and fertilization, is regulated by G proteins. Phosphoinositide phospholipase C (PLC) catalyzes the hydrolysis of phosphatidyl 4,5-bisphosphate to generate two second messengers, inositol 1,4,5-trisphosphate (IP 3 ) and diacylglycerol. Diacylglycerol in turn activates protein kinase C; IP 3 binds to an intracellular IP 3 receptor/channel to release Ca 2ϩ stores (Ref.

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Section: G␣ 16 Inhibition Of Ligand-induced CLsupporting

confidence: 76%

Desensitization of Inositol 1,4,5-Trisphosphate/Ca2+-induced Cl− Currents by Prolonged Activation of G Proteins in Xenopus Oocytes

Quick

Lester

Davidson

et al. 1996

Journal of Biological Chemistry

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“…pear to have distinctly different f unctions after thyrotropinreleasing hormone or ␣ 1 -adrenergic receptor activation (Lipinsky et al, 1992;Macrez-Leprêtre et al, 1997). These studies, and our results, suggest that the coupling preferences suggested by in vitro and overexpression studies may not reflect those found in native cells.…”

Section: Discussioncontrasting

confidence: 39%

The α Subunit of G_qContributes to Muscarinic Inhibition of the M-Type Potassium Current in Sympathetic Neurons

et al. 1998

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Rat superior cervical ganglion (SCG) neurons express lowthreshold noninactivating M-type potassium channels (I K(M) ), which can be inhibited by activation of M1 muscarinic receptors. This inhibition occurs via pertussis toxin-insensitive G-proteins belonging to the G␣ q family (Caulfield et al., 1994). We have used DNA plasmids encoding antisense sequences against the 3Ј untranslated regions of G␣ subunits (antisense plasmids) to investigate the specific G-protein subunits involved in muscarinic inhibition of I K(M) . These antisense plasmids specifically reduced levels of the target G-protein 48 hr after intranuclear injection. In cells depleted of G␣ q , muscarinic inhibition of I K(M) was attenuated compared both with uninjected neurons and with neurons injected with an inappropriate G␣ oA antisense plasmid. In contrast, depletion of G␣ 11 protein did not alter I K(M) inhibition. To determine whether the ␣ or ␤␥ subunits of the G-protein mediated this inhibition, we have overexpressed the C terminus of ␤ adrenergic receptor kinase 1 (␤ARK1), which binds free ␤␥ subunits. ␤ARK1 did not reduce muscarinic inhibition of I K(M) at a concentration of plasmid that can reduce ␤␥-mediated inhibition of calcium current (Delmas et al., 1998a). Also, expression of ␤ 1 ␥ 2 dimers did not alter the I K(M) density in SCG neurons. In contrast, I K(M) was virtually abolished in cells expressing GTPase-deficient, constitutively active forms of G␣ q and G␣ 11 . These data suggest that G␣ q is the principal mediator of muscarinic I K(M) inhibition in rat SCG neurons and that this more likely results from an effect of the ␣ subunit than the ␤␥ subunits of the G q heterotrimer.

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“…To address this question, we have used the Xenopus oocytes system to study receptor-G protein specificity in vivo. Coexpression of thyrotropin-releasing hormone receptors with either mouse G␣ q or G␣ 11 demonstrated different modulation of the response to thyrotropin-releasing hormone by each one of these G proteins (22). Applying the antisense approach, we demonstrated for the first time different coupling preferences of neuromedin B receptor for G␣ q and G␣ 11 (1).…”

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confidence: 89%

Gα14 and Gαq Mediate the Response to Trypsin in Xenopus Oocytes

Shapira

Amit

Revach

et al. 1998

Journal of Biological Chemistry

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Xenopus oocytes respond to trypsin with a characteristic chloride current, virtually indistinguishable from responses mediated by a large number of native and expressed G protein-coupled receptors. We studied the involvement of G proteins of the G␣ q family as possible mediators of this and other G protein-coupled receptormediated responses in Xenopus oocytes. We have cloned the third member of the G␣ q family, Xenopus G␣ 14 , in addition to the previously cloned Xenopus G␣ q and G␣ 11 (Shapira, H., Way, J., Lipinsky, D., Oron, Y., and Battey, J. F. (1994) FEBS Lett. 348, 89 -92). Amphibian G␣ 14 is 354 amino acids long and is 93% identical to its mammalian counterpart. Based on the G␣ 14 cDNA sequence, we designed a specific antisense DNA oligonucleotide (antiG␣ 14 ) that, together with antiG␣ q and antiG␣ 11 , was used in antisense depletion experiments. 24 h after injection into oocytes, either antiG␣ q or antiG␣ 14 reduced the response to 1 g/ml trypsin by 70%, whereas antiG␣ 11 had no effect. A mixture of antiG␣ q and antiG␣ 14 virtually abolished the response. These data strongly suggest that G␣ q and G␣ 14 are the exclusive mediators of the trypsin-evoked response in Xenopus oocytes. Similar experiments with the expressed gastrin-releasing peptide receptor and muscarinic m1 receptor revealed the coupling of G␣ q and G␣ 11 , but not G␣ 14 , to these receptors in oocytes. These results confirm the hypothesis that endogenous members of the G␣q family discriminate among different native receptors in vivo.Heterotrimeric GTP-binding proteins (G proteins) of the G␣ q family activate the phosphatidylinositol-bisphosphate-inositoltrisphosphate-calcium pathway in a pertussis toxin-insensitive manner. Among G␣ q family members, G␣ q and G␣ 11 share 88% homology and are expressed ubiquitously (2-4). G␣ 14 is 81% identical to G␣ q and is restricted in its tissue distribution mainly to spleen, lung, kidney, and testes (5). G␣ 15 and its human counterpart, G␣ 16 , show only 58 and 57% amino acid identity, respectively, to mouse G␣ q and are restricted to a subset of hematopoietic cells (5, 6). Upon activation, all G proteins of the G␣ q family activate ␤ isomers of phospholipase C.The coexistence of closely related G proteins in the same cell suggests different functions or different interactions between individual G proteins and either receptors or phospholipases. However, in reconstitution systems and transfected cells, G␣ q and G␣ 11 have been shown to couple indiscriminately to a wide range of receptors, e.g. muscarinic m1 receptor (m1-R) 1 (7, 8) and m3-R (9), thyrotropin-releasing hormone (10, 11), parathyroid hormone (12), gastrin-releasing peptide (GRP) and vasopressin (13), gonadotrophin-releasing hormone (14), angiotensin II and bradykinin (15), histamine (16), and ␣ 1 -adrenergic receptors (17). G␣ 15/16 , despite restricted distribution, are capable of coupling many serpentine receptors tested, including those natively coupled to G␣ s and G␣ i (for review, see Ref. 18). Similarly, an attempt to assign differ...

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Gα₁₁ and Gα_q guaninine nucleotide regulatory proteins differentially modulate the response to thyrotropin‐releasing hormone in Xenopus oocytes

Cited by 22 publications

References 27 publications

Desensitization of Inositol 1,4,5-Trisphosphate/Ca2+-induced Cl− Currents by Prolonged Activation of G Proteins in Xenopus Oocytes

Desensitization of Inositol 1,4,5-Trisphosphate/Ca2+-induced Cl− Currents by Prolonged Activation of G Proteins in Xenopus Oocytes

The α Subunit of G_qContributes to Muscarinic Inhibition of the M-Type Potassium Current in Sympathetic Neurons

Gα14 and Gαq Mediate the Response to Trypsin in Xenopus Oocytes

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Gα11 and Gαq guaninine nucleotide regulatory proteins differentially modulate the response to thyrotropin‐releasing hormone in Xenopus oocytes

Cited by 22 publications

References 27 publications

Desensitization of Inositol 1,4,5-Trisphosphate/Ca2+-induced Cl− Currents by Prolonged Activation of G Proteins in Xenopus Oocytes

Desensitization of Inositol 1,4,5-Trisphosphate/Ca2+-induced Cl− Currents by Prolonged Activation of G Proteins in Xenopus Oocytes

The α Subunit of GqContributes to Muscarinic Inhibition of the M-Type Potassium Current in Sympathetic Neurons

Gα14 and Gαq Mediate the Response to Trypsin in Xenopus Oocytes

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Gα₁₁ and Gα_q guaninine nucleotide regulatory proteins differentially modulate the response to thyrotropin‐releasing hormone in Xenopus oocytes

The α Subunit of G_qContributes to Muscarinic Inhibition of the M-Type Potassium Current in Sympathetic Neurons