Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:4.6.1.1 (adenylate cyclase)
19,190 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Many receptors, in response to ligand activation, trigger inositol phospholipid breakdown, which leads to rapid intracellular responses. The sustained activation of this pathway is believed to be at least one of the factors involved in the stimulation of cell growth and there has been much speculation that certain oncogenes use this pathway to effect uncontrolled cellular proliferation. It has been suggested, by analogy with the receptor-mediated control of adenylate cyclase, that the receptor stimulation of inositol phospholipid metabolism is mediated through a guanine nucleotide regulatory protein (G-protein) called Gp (or Np). Although such a species has not been identified, there is now strong experimental evidence that this process is mediated by a G-protein distinct from the stimulatory and inhibitory G-proteins (Gs and Gi, respectively). The ras genes code for a plasma membrane protein, p21, whose only known biochemical property is a high-affinity GTPase activity. We show here that the expression of normal p21N-ras in NIH 3T3 fibroblasts leads to the coupling of certain growth factor receptors to stimulated inositol phosphate production. We propose that the N-ras proto-oncogene encodes a protein which couples the receptors for certain growth factors to the stimulation of phospholipase C. Thus, N-ras p21 may be the putative Gp or a functionally related protein.
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PMID:Normal p21N-ras couples bombesin and other growth factor receptors to inositol phosphate production. 301 91

Thyrotropin-releasing hormone (TRH), vasoactive intestinal polypeptide (VIP) and acetylcholine stimulated high affinity GTPase activity in GH3 cell membrane preparations. The effects of acetylcholine and VIP were blocked by pretreatment of cultured cells with pertussis toxin and cholera toxin respectively. Such pretreatment, which causes covalent modification of the guanine nucleotide-binding proteins (G-proteins) of adenylate cyclase, did not, however, block the effects of TRH on GTPase activity or phosphoinositide breakdown. These data suggest that TRH receptors interact with a G-protein discrete from those associated with regulation of adenylate cyclase activity.
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PMID:Evidence that thyrotropin-releasing hormone-induced increases in GTPase activity and phosphoinositide metabolism in GH3 cells are mediated by a guanine nucleotide-binding protein other than Gs or Gi. 301 44

In membranes from guinea pig cerebellum, a tissue which predominantly contains kappa opioid receptors, exogenous and endogenous kappa-selective opioid agonists stimulated low-km GTPase activity by 11-20% with concentrations for half-maximal stimulation of 3-23 microM. Opioid ligands of the mu and delta type had no effect on GTPase in these membranes. Similar stimulation of GTPase by kappa opiates was obtained in rat and monkey brain membranes pretreated with beta-funaltrexamine (beta-FNA) and cis-(+/-)-3-methylfentanyl isothiocyanate (superfit) to alkylate the mu and delta receptors, respectively. The stimulation of brain GTPase by kappa opiates in both types of membranes was inhibited by naloxone with IC50's of 0.35 microM and 0.40 microM. The results demonstrate the coupling of the kappa opioid receptor to high affinity GTPase, the Ni regulatory protein of the adenylate cyclase complex.
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PMID:Evidence for coupling of the kappa opioid receptor to brain GTPase. 302 93

Prolonged exposure of cells or tissues to drugs or hormones such as catecholamines leads to a state of refractoriness to further stimulation by that agent, known as homologous desensitization. In the case of the beta-adrenergic receptor coupled to adenylate cyclase, this process has been shown to be intimately associated with the sequestration of the receptors from the cell surface through a cAMP-independent process. Recently, we have shown that homologous desensitization in the frog erythrocyte model system is also associated with increased phosphorylation of the beta-adrenergic receptor. We now provide evidence that the phosphorylation state of the beta-adrenergic receptor regulates its functional coupling to adenylate cyclase, subcellular translocation, and recycling to the cell surface during the process of agonist-induced homologous desensitization. Moreover, we show that the receptor phosphorylation is reversed by a phosphatase specifically associated with the sequestered subcellular compartment. At 23 degrees C, the time courses of beta-adrenergic receptor phosphorylation, sequestration, and adenylate cyclase desensitization are identical, occurring without a lag, exhibiting a t1/2 of 30 min, and reaching a maximum at approximately 3 hr. Upon cell lysis, the sequestered beta-adrenergic receptors can be partially recovered in a light membrane vesicle fraction that is separable from the plasma membranes by differential centrifugation. The increased beta-adrenergic receptor phosphorylation is apparently reversed in the sequestered vesicle fraction as the sequestered receptors exhibit a phosphate/receptor stoichiometry that is similar to that observed under basal conditions. High levels of a beta-adrenergic receptor phosphatase activity appear to be associated with the sequestered vesicle membranes. The functional activity of the phosphorylated beta-adrenergic receptor was examined by reconstituting purified receptor with its biochemical effector the guanine nucleotide regulatory protein (Ns) in phospholipid vesicles and assessing the receptor-stimulated GTPase activity of Ns. Compared to controls, phosphorylated beta-adrenergic receptors, purified from desensitized cells, were less efficacious in activating the Ns GTPase activity. These results suggest that phosphorylation of the beta-adrenergic receptor leads to its functional uncoupling and physical translocation away from the cell surface into a sequestered membrane domain. In the sequestered compartment, the phosphorylation is reversed thus enabling the receptor to recycle back to the cell surface and recouple with adenylate cyclase.
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PMID:Phosphorylation/dephosphorylation of the beta-adrenergic receptor regulates its functional coupling to adenylate cyclase and subcellular distribution. 302 43

Thrombin inhibits adenylate cyclase and stimulates GTP hydrolysis by high-affinity GTPase(s) in membranes of human platelets at almost identical concentrations. Both of these thrombin actions are similar to those observed with agonist-activated alpha 2-adrenoceptors coupling to the inhibitory guanine nucleotide-binding protein N1. However, stimulation of GTP hydrolysis caused by adrenaline (alpha 2-adrenoceptor agonist) and by thrombin at maximally effective concentrations was partially additive, whereas with regard to adenylate cyclase inhibition no additive response was observed. Furthermore, treatment of platelet membranes with pertussis toxin, which inactivates Ni and largely abolishes thrombin- and adrenaline-induced adenylate cyclase inhibition and adrenaline-induced GTPase stimulation, decreased the thrombin-induced stimulation of GTP hydrolysis by only about 30%. Additionally, the thiol reagent N-ethylmalemide (NEM) at rather low concentrations abolished thrombin- and adrenaline-induced stimulation of GTP hydrolysis was decreased by only 30-40% by treatment of platelet membranes with even high concentrations of NEM. Treatment with cholera toxin, which inhibits GTPase activity of the Ns (stimulatory guanine nucleotide-binding) protein, has no effect on thrombin-stimulated GTP hydrolysis. The data suggest that thrombin interaction with its receptor sites in platelet membranes leads to stimulation of two GTP-hydrolysing enzymes. One of these enzymes is apparently Ni and is also activated by agonist-activated alpha 2-adrenoceptors and is inactivated by pertussis toxin and NEM treatment. The other GTP-hydrolysing enzyme activated by thrombin may represent a guanine nucleotide-binding protein apparently involved in the coupling of thrombin receptors to the phosphoinositide phosphodiesterase.
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PMID:Evidence for two GTPases activated by thrombin in membranes of human platelets. 302 30

The effects of Al3+ and F- on the catecholamine-stimulated GTPase cycle were studied by using reconstituted phospholipid vesicles that contained purified beta-adrenergic receptor and the stimulatory GTP-binding protein of the adenylate cyclase system, Gs. Al3+/F- activated reconstituted Gs to levels previously reported for detergent-solubilized, purified Gs, although both activation and deactivation were faster in the reconstituted preparation. Under these conditions, Al3+/F- did not inhibit by more than 15% the beta-adrenergic agonist-stimulated GTPase activity of the vesicles nor did it significantly inhibit the rates of GTP binding, GTP hydrolysis, or GDP release. When Mg2+ (50 mM) was used instead of agonist to promote GTP hydrolysis in the receptor-Gs vesicles, Al3+/F- was found to inhibit GTP gamma S binding, GDP release, and steady-state GTPase activity to unstimulated levels. These data can be interpreted as indicating that the receptor catalyzes nucleotide exchange by Gs faster or more efficiently than does Mg2+.
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PMID:Effect of Al3+ plus F- on the catecholamine-stimulated GTPase activity of purified and reconstituted Gs. 302 41

The time course of opioid receptor binding disappearance and loss of responsiveness of the opioid-controlled GTPase and adenylate cyclase were compared in membranes derived from NG108-15 cells pretreated with the opioid peptide agonist [D-Ala2,D-Leu5]enkephalin (DADLE). Upon pretreatment with DADLE, a rapid desensitization of the opioid-stimulated GTPase occurred with a time course distinguishable as two exponential components having respective half-lives of 5-9 and 60-80 min. Opioid receptor binding activity, as assessed using [3H]diprenorphine, also decayed as two exponential components whose half-lives were similar to those for GTPase desensitization (7 and 120 min). However, when [3H]diprenorphine binding was measured in the presence of sodium and GTP, only the second, slow component was apparent. In contrast, desensitization of the opioid-controlled adenylate cyclase occurred as only one exponential decaying process, displaying a half-life of 57 min. Whereas the loss of responsiveness of GTPase to DADLE was entirely accounted for by a reduction in the maximal stimulation produced acutely by DADLE, desensitization of adenylate cyclase was characterized by both a decrease in maximal inhibition and a shift to the right of the EC50 of the agonist in inhibiting acutely the enzyme. In addition, after 1 hr of pretreatment with DADLE, the opioid-stimulated GTPase was desensitized by 65%, whereas 80% of maximal inhibition of adenylate cyclase could still be achieved. We suggest that: the rapid loss of responsiveness of the opioid-GTPase system results from an uncoupling between the receptor and the nucleotide-binding regulatory protein (N); the fast decaying GTPase activity appears to be not directly related to the opioid-mediated inhibition of adenylate cyclase; and the slow decaying GTPase activity, as well as the desensitization of the opioid-adenylate cyclase, is most likely accounted for by down-regulation of the opioid receptor. These findings may indicate that part of the opioid-stimulated GTPase in the membrane is not involved in inhibition of the cyclase and could reflect the activity of a regulatory protein which couples opioid receptors to another membrane effector. Alternatively, they might be interpreted on the basis of a model which involves a tight coupling between receptor activation and N protein and a large amplification mechanism between N protein and adenylate cyclase.
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PMID:GTPase and adenylate cyclase desensitize at different rates in NG108-15 cells. 302 28

The properties of a reconstituted signal transmission chain using purified beta 1-adrenoceptor (R), G-protein subunits (G) and adenylate cyclase (C) in lipid vesicles are described. This assay system was used to test beta, gamma-subunits of different origin with respect to their effects on R X G and R X G X C coupling and on the functional properties of GS alpha and Gi alpha. The findings reported here point to large differences in the efficacy of beta, gamma-subunits from different sources assessed by deactivation of [ALF4]-activated rabbit liver GS and pertussis toxin-catalyzed ADP-ribosylation of bovine neutrophil G alpha. This is explained by differences in the interaction domains of the interacting subunits. Furthermore, the sensitivity of R X G and R X G X C coupling to inhibition by beta, gamma-subunits was greater than the effects of beta, gamma-subunits on hormonally activated GTPase activity of GS. One of the consequences of differential inhibition of R X G X C coupling is an amplified response of the signal transmission chain to hormonal activation. This is in agreement with observations reported by Cerione et al.
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PMID:The role of beta, gamma-subunits of guanine nucleotide binding proteins in control of a reconstituted signal transmission chain containing purified components of the adenylate cyclase system. 304 Sep 77

The addition of bradykinin to NG108-15 cells results in a transient hyperpolarization followed by prolonged cell depolarization. Injection of inositol 1,4,5-trisphosphate or Ca2+ into the cytoplasm of NG108-15 cells also elicits cell hyperpolarization followed by depolarization. Tetraethylammonium ions inhibit the hyperpolarizing response of cells to bradykinin or inositol 1,4,5-trisphosphate. Thus, the hyperpolarizing phase of the cell response may be due to inositol 1,4,5-trisphosphate-dependent release of stored Ca2+ into the cytoplasm, which activates Ca2+-dependent K+ channels. The depolarizing phase of the cell response to bradykinin is due largely to inhibition of M channels, thereby decreasing the rate of K+ efflux from cells and, to a lesser extent, to activation of Ca2+-dependent ion channels and Ca2+ channels. In contrast, injection of inositol 1,4,5-trisphosphate or Ca2+ into the cytosol did not alter M channel activity. Incubation of NG108-15 cells with pertussis toxin inhibits bradykinin-dependent cell hyperpolarization and depolarization. Bradykinin stimulates low Km GTPase activity and inhibits adenylate cyclase in NG108-15 membrane preparations but not in membranes prepared from cells treated with pertussis toxin. Reconstitution of NG108-15 membranes from cells treated with pertussis toxin with nanomolar concentrations of a mixture of highly purified No and Ni [guanine nucleotide-binding proteins that have no known function (No) or inhibit adenylate cyclase (Ni)] restores bradykinin-dependent activation of GTPase and inhibition of adenylate cyclase. These results show that [bradykinin . receptor] complexes interact with No or Ni and suggest that No and/or Ni mediate the transduction of signals from bradykinin receptors to phospholipase C and adenylate cyclase.
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PMID:Bradykinin-activated transmembrane signals are coupled via No or Ni to production of inositol 1,4,5-trisphosphate, a second messenger in NG108-15 neuroblastoma-glioma hybrid cells. 308 91

The GTP binding regulatory protein (Ni involved in adenylate cyclase inhibition was purified from rat brain and reconstituted, together with muscarinic cholinergic receptors purified from porcine brain, into phospholipid vesicles. Guanosine 5'-O-(3-[35S]thio)-triphosphate ([35S]GTP gamma S) binding and GTP hydrolyzing activities of reconstituted Ni were stimulated by the addition of a muscarinic agonist, carbachol. The effect of carbachol was to increase the Vmax values of these activities, but the Km values were also increased slightly in most cases. Carbachol bound to vesicles with the same order of magnitude of Km as that for stimulation of GTPase. The affinity of this binding was reduced by GTP gamma S, indicating that the high-affinity receptor-Ni complex was formed in a GTP-dependent manner in reconstituted vesicles. Incubation of Ni with NAD and islet-activating protein (IAP), pertussis toxin, caused ADP-ribosylation of the alpha-subunit of Ni. The criteria for the receptor-Ni interaction, i.e. carbachol stimulation of the activities of Ni and the GTP gamma S effect on carbachol binding, were no longer observed, when this IAP-treated Ni, instead of the nontreated Ni, was reconstituted into vesicles, though there was no difference between IAP-treated and nontreated Ni in their basal activities observable without carbachol. No, the protein with a character very similar to Ni in rat brain, was also coupled to muscarinic receptors when they were reconstituted into vesicles under the same conditions. Thus, GTP-binding proteins serving as the substrate of IAP-catalyzed ADP-ribosylation are capable of interaction functionally with muscarinic receptors in phospholipid vesicles.
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PMID:Functional interaction of purified muscarinic receptors with purified inhibitory guanine nucleotide regulatory proteins reconstituted in phospholipid vesicles. 308 83


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