Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Recombinant A' protein could be reconstituted into U2 small nuclear ribonucleoprotein particles (snRNPs) upon addition to HeLa cell extracts as determined by coimmunoprecipitation and particle density; however, direct binding to U2 RNA could not be demonstrated except in the presence of the U2 snRNP B" protein. Mutational analysis indicated that a central core region of A' was required for particle reconstitution. This region consists of five tandem repeats of approximately 24 amino acids each that exhibit a periodicity of leucine and asparagine residues that is distinct from the leucine zipper. Similar leucine-rich (Leu-Leu motif) repeats are characteristic of a diverse array of soluble and membrane-associated proteins from yeasts to humans but have not been reported previously to reside in nuclear proteins. Several of these proteins, including Toll, chaoptin, RNase/angiogenin inhibitors, lutropin-choriogonadotropin receptor, carboxypeptidase N, adenylyl cyclase, CD14, and human immunodeficiency virus type 1 Rev, may be involved in protein-protein interactions. Our findings suggest that in cell extracts the Leu-Leu motif of A' is required for reconstitution with U2 snRNPs and perhaps with other components involved in splicing through protein-protein interactions.
Mol Cell Biol 1991 Mar
PMID:Leucine periodicity of U2 small nuclear ribonucleoprotein particle (snRNP) A' protein is implicated in snRNP assembly via protein-protein interactions. 182 47

An aspartate residue corresponding to aspartate-80 of dopamine D2 receptors is strictly conserved among receptors that couple to guanine nucleotide-binding proteins. Mutation of this residue alters the function of several classes of neurotransmitter receptors. Dopamine D2 receptors couple to the guanine nucleotide-binding protein Gi to inhibit adenylyl cyclase (ATP-pyrophosphate-lyase, cyclizing; EC 4.6.1.1). Like other Gi-coupled receptors, the binding of agonists and some antagonists to D2 receptors is sensitive to pH and sodium. In the present report, we demonstrate that substitution of an alanine or glutamate residue for aspartate-80 severely impairs inhibition of adenylyl cyclase by D2 receptors and also abolishes or decreases the regulation of the affinity of D2 receptors for agonists and substituted benzamide antagonists by sodium and pH. Our data support the hypothesis that the conformation of D2 receptors is maintained by interactions of monovalent cations with aspartate-80. The regulation of D2 receptors by this interaction has important consequences for the affinity of D2 receptors for ligands and for signal transduction by D2 receptors.
Mol Pharmacol 1991 Jun
PMID:Pivotal role for aspartate-80 in the regulation of dopamine D2 receptor affinity for drugs and inhibition of adenylyl cyclase. 182 58

During Dictyostelium discoideum development, cell-cell communication is mediated through cyclic AMP (cAMP)-induced cAMP synthesis and secretion (cAMP signaling) and cell-cell contact. Cell-cell contact elicits cAMP secretion and modulates the magnitude of a subsequent cAMP signaling response (D. R. Fontana and P. L. Price, Differentiation 41:184-192, 1989), demonstrating that cell-cell contact and cAMP signaling are not independent events. To identify components involved in the contact-mediated modulation of cAMP signaling, amoebal membranes were added to aggregation-competent amoebae in suspension. The membranes from aggregation-competent amoebae inhibited cAMP signaling at all concentrations tested, while the membranes from vegetative amoebae exhibited a concentration-dependent enhancement or inhibition of cAMP signaling. Membrane lipids inhibited cAMP signaling at all concentrations tested. The lipids abolished cAMP signaling by blocking cAMP-induced adenylyl cyclase activation. The membrane lipids also inhibited amoeba-amoeba cohesion at concentrations comparable to those which inhibited cAMP signaling. The phospholipids and neutral lipids decreased cohesion and inhibited the cAMP signaling response. The glycolipid/sulfolipid fraction enhanced cohesion and cAMP signaling. Caffeine, a known inhibitor of cAMP-induced adenylyl cyclase activation, inhibited amoeba-amoeba cohesion. These studies demonstrate that endogenous lipids are capable of modulating amoeba-amoeba cohesion and cAMP-induced activation of the adenylyl cyclase. These results suggest that cohesion may modulate cAMP-induced adenylyl cyclase activation. Because the complete elimination of cohesion is accompanied by the complete elimination of cAMP signaling, these results further suggest that cohesion may be necessary for cAMP-induced adenylyl cyclase activation in D. discoideum.
Mol Cell Biol 1991 Jan
PMID:Dictyostelium discoideum lipids modulate cell-cell cohesion and cyclic AMP signaling. 184 24

The regulation of cellular responsiveness to dopamine via the D2 dopamine receptor was investigated in mouse fibroblast Ltk-cells stably expressing the rat D2-short receptor [Nature (Lond.) 336:783-787 (1988)]. Dopamine inhibited forskolin-stimulated cAMP levels in these cells (half-maximal inhibition at 3.9 +/- 1.1 nM), and the inhibition by dopamine was blocked by D2 antagonists and was pertussis toxin sensitive. Treatment of these cells with the D2 agonist quinpirole (1 microM) resulted in desensitization of dopaminergic inhibition of forskolin-stimulated cAMP accumulation, with a approximately 4-fold decrease in the potency of dopamine after 1 hr of treatment. No significant changes in total cellular D2 receptor concentrations were observed, even after prolonged agonist treatment. At longer time points, basal and forskolin-stimulated cellular cAMP levels were increased in treated cells. The effect of D2 agonist treatment on membrane adenylyl cyclase (EC 4.6.1.1) activity was examined. Basal and forskolin- and prostaglandin E1-stimulated adenylyl cyclase activities were increased by quinpirole treatment for 24 hr. This sensitization of adenylyl cyclase was blocked by the presence of a D2 antagonist. Pertussis toxin pretreatment blocked the sensitization of adenylyl cyclase by quinpirole, although pertussis toxin also caused increased adenylyl cyclase activity on its own. Sensitization was not dependent upon dopaminergic inhibition of intracellular cAMP levels, because quinpirole treatment in the presence of membrane-permeable cAMP analogs or 3-isobutyl-1-methylxanthine (an inhibitor of cAMP phosphodiesterase) resulted in greater sensitization of adenylyl cyclase activity than quinpirole treatment alone. These results suggest that, in this model system, responsiveness to dopamine via the D2 receptor is regulated by both desensitization of receptor function and sensitization of the stimulatory adenylyl cyclase pathway.
Mol Pharmacol 1991 Jan
PMID:Regulation of responsiveness at D2 dopamine receptors by receptor desensitization and adenylyl cyclase sensitization. 184 20

A rat D2L dopamine receptor, a splice variant of the D2 receptor, has recently been cloned. When transfected into and stably expressed in Chinese hamster ovary cells, these receptors mediate the inhibition of both basal and forskolin-stimulated cAMP production, as previously described. We examined what role this receptor might play in the production of the second messenger arachidonic acid. The calcium ionophore A23187 stimulated the release of arachidonic acid, and this release of arachidonic acid was potentiated by dopamine in a concentration-dependent manner. Dopamine alone, however, had no effect on arachidonic acid release. Quinpirole, a D2-selective agonist, augmented A23187-stimulated arachidonic acid release, and sulpiride, a D2-selective antagonist, blocked this augmentation. cAMP analogs and agents that activate adenylyl cyclase were utilized in an attempt to overcome this dopamine effect. Forskolin, prostaglandin E2, dibutyryl-cAMP, 8-(4-chlorophenylthio)-cAMP, and pertussis toxin all had no appreciable effect on either A23187-stimulated arachidonic acid release or the dopamine enhancement. Inhibition of protein kinase C using long term phorbol ester desensitization and pharmacological inhibitors diminished the dopamine potentiation of arachidonic acid release. These results suggest that the D2 receptor may be increasing the release of arachidonic acid by a mechanism involving protein kinase C but independent of the D2 receptor's inhibition of adenylyl cyclase.
Mol Pharmacol 1991 Mar
PMID:Transfected D2 dopamine receptors mediate the potentiation of arachidonic acid release in Chinese hamster ovary cells. 184 57

Mutant clones resistant to ACTH-induced desensitization of adenylyl cyclase (Y1DR) were previously isolated from the Y1 mouse adrenocortical tumor cell line. In this study, both parental Y1 cells (Y1DS) and a Y1DR mutant were transfected with a gene encoding the mouse beta 2-adrenergic receptor, and transfectants isolated from both Y1DS and Y1DR cells were shown to express beta 2-adrenergic receptors. These transfectants responded to the beta-adrenergic agonist isoproterenol with increases in adenylyl cyclase activity and steroidogenesis and changes in cell shape. The transfectants were analyzed to determine whether the Y1DR mutation was specific for ACTH-induced desensitization of adenylyl cyclase or also affected desensitization of adenylyl cyclase via the beta 2-adrenergic receptor. Treatment of intact Y1DS transfectants with isoproterenol caused a rapid desensitization of the adenylyl cyclase system to further stimulation by the beta-adrenergic agonist. Treatment of intact cells with isoproterenol did not affect ACTH-stimulated adenylyl cyclase activity, indicating that desensitization was agonist specific or homologous. Y1DR transfectants were resistant to the desensitizing effects of isoproterenol in intact cells as well as in cell homogenates. These results indicate that the mutation in Y1DR transfectants affects a component that is common to the pathways of isoproterenol-induced desensitization and ACTH-induced desensitization of adenylyl cyclase. As determined using the hydrophilic beta-receptor antagonist CGP-12177, isoproterenol caused a rapid sequestration of cell surface receptors in both Y1DS and Y1DR transfectants. From these results we infer that the DR phenotype does not arise from mutations affecting receptor sequestration and that receptor number does not limit the response to isoproterenol in these transfectants.
Mol Endocrinol 1991 Jan
PMID:Regulation of adenylyl cyclase activity by beta-adrenergic agonists in a desensitization-resistant mutant cell line. 185 Jan 9

We have used the polymerase chain reaction technique to selectively amplify guanine nucleotide-binding regulatory protein (G protein)-coupled receptor cDNA sequences from rat striatal mRNA, using sets of highly degenerate primers derived from transmembrane sequences of previously cloned G protein-coupled receptors. A novel cDNA fragment was identified, which exhibits considerable homology to various members of the G protein-coupled receptor family. This fragment was used to isolate a full-length cDNA from a rat striatal library. A 2.2-kilobase clone was obtained that encodes a protein of 326 amino acids with seven transmembrane domains, as predicted by hydropathy analysis. Stably transfected mouse A9-L cells and Chinese hamster ovary cells that expressed mRNA for this clone were screened with putative receptor ligands. Saturable and specific binding sites for the A1 adenosine antagonist [3H]-1,3-dipropyl-8-cyclopentylxanthine were identified on membranes from transfected cells. The rank order of potency and affinities of various adenosine agonist and antagonist ligands confirmed the identity of this cDNA clone as an A1 adenosine receptor. The high affinity binding of A1 adenosine agonists was shown to be sensitive to the nonhydrolyzable GTP analog guanylyl-5'-imidodiphosphate. In adenylyl cyclase assays, adenosine agonists inhibited forskolin-stimulated cAMP production by greater than 50%, in a pharmacologically specific fashion. Northern blot and in situ hybridization analyses of receptor mRNA in brain tissues revealed two transcripts of 5.6 and 3.1 kilobases, both of which were abundant in cortex, cerebellum, hippocampus, and thalamus, with lower levels in olfactory bulb, striatum, mesencephalon, and retina. These regional distribution data are in good agreement with previous receptor autoradiographic studies involving the A1 adenosine receptor. We conclude that we have cloned a cDNA encoding an A1 adenosine receptor linked to the inhibition of adenylyl cyclase activity.
Mol Pharmacol 1991 Jul
PMID:Cloning and expression of an A1 adenosine receptor from rat brain. 185 34

We have previously demonstrated that monooleylphosphatidate (MOPA) and phosphatidate inhibit adenylyl cyclase in cultured fibroblasts. In this study, the specificity of the phospholipid effect was probed by analysis of the effect of phosphonate analogs of these phospholipids on adenylyl cyclase in C6 glioma cells. The MOPA phosphonate analog inhibited adenylyl cyclase, but the comparable phosphonate analog of phosphatidate was ineffective. The IC50 for inhibition of adenylyl cyclase by the MOPA phosphonate analog was similar to that of MOPA, the maximal inhibitions were comparable (approximately 45% inhibition of hormone-stimulated adenylyl cyclase), and the effects of both appeared to be mediated by Gi, because treatment with islet-activating protein reduced the inhibition to 5-10%.
Mol Pharmacol 1991 Jun
PMID:Potent Gi-mediated inhibition of adenylyl cyclase by a phosphonate analog of monooleylphosphatidate. 190 81

Angiotensin II can inhibit hormone-stimulated adenylyl cyclase in intact hepatocytes or in hepatic membrane preparations. Because the response can be blocked by pertussis toxin, the object of the present study was to determine which of the known variants of Gi can couple angiotensin II receptors to inhibition of adenylyl cyclase. The potential candidates were identified by probing RNA isolated from rat hepatocytes with cDNAs specific for the alpha subunits of known toxin-sensitive guanine nucleotide-binding regulatory proteins (G proteins). Hepatocytes contained no detectable RNA for the Go or Gi1 alpha subunits and similar levels of RNA coding for the Gi2 and Gi3 alpha subunits. To determine whether Gi3 could couple angiotensin receptors to inhibition of cyclase, membranes were prepared from hepatocytes whose G proteins were fully ADP-ribosylated with pertussis toxin, and the Gi3 holoprotein purified from rabbit liver was reconstituted into the membranes. The nature of the Gi3 reconstituted into the membrane was assessed by immunoblotting with antibodies specific for the Gi alpha subunits. Reconstitution of 6-10 pmol of Gi3/mg of membrane protein into the toxin-treated membranes restored the ability of 10 nM angiotensin II to inhibit adenylyl cyclase. Because pertussis toxin has nonspecific effects, an assay was developed to measure the interaction of the angiotensin receptor with reconstituted G proteins in normal membranes. In the presence of Mg2+, guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S) caused a reduction of the affinity of the angiotensin II receptor for 125I-angiotensin II that was stable to washing and the detergents used to reconstitute G proteins into the membranes. Using this protocol to activate G proteins and "uncouple" receptors, the ability of the GDP-liganded form of Gi to restore high affinity binding was examined. Reconstitution of about 10-15 pmol of oligomeric Gi3/mg of membrane protein restored both the high affinity state of the angiotensin II receptor and the ability of GTP gamma S to shift the affinity to a lower state. The same shift in receptor affinity could be accomplished by reconstituting the Gi3 alpha subunit, resolved free of beta gamma subunits, into the membranes. Reconstitution of up to 50 pmol of Gs/mg of membrane protein had no effect on angiotensin II receptor affinity. The results suggest that a major form of Gi in hepatocytes is Gi3 and that it can couple angiotensin receptors to inhibition of adenylyl cyclase.
Mol Pharmacol 1991 Aug
PMID:Inhibitory GTP-binding regulatory protein Gi3 can couple angiotensin II receptors to inhibition of adenylyl cyclase in hepatocytes. 190 48

Many hormones have been shown to activate phospholipase C, which results in the hydrolysis of membrane polyphosphoinositides, such as phosphatidylinositol 4,5-bisphosphate (PIP2). Two second messengers are known to be produced by PIP2 hydrolysis, 1,2-diacylglycerol, an endogenous activator of a family of enzymes called protein kinase C (PKCs), and inositol 1,4,5-trisphosphate, which raises free levels of intracellular Ca2+. Treatment of various cells with 4 beta-phorbol 12-myristate 13-acetate (PMA), a specific exogenous activator of PKCs, causes an enhancement or sensitization of adenylyl cyclase activities. This finding prompted us to examine the effects of direct hormonal activation of PIP2 hydrolysis on the sensitization of adenylyl cyclase. Liao et al. [J. Biol. Chem. 265:11273-11284 (1990)] have shown that P2 purinergic receptor agonists such as ATP and muscarinic receptor agonists such as carbachol stimulate PIP2 hydrolysis in L cells expressing the M5 muscarinic acetylcholine receptor. We investigated the effects of these hormones on adenylyl cyclase and contrasted these effects with the sensitizing effects of PMA. We found that ATP pretreatment of two different types of L cells resulted in a rapid 50-150% sensitization of prostaglandin E1-, epinephrine-, and forskolin-stimulated adenylyl cyclase activity, with an EC50 of 3 microM ATP. This effect was qualitatively similar to that caused by 10 nM PMA. The enhancement of adenylyl cyclase activity was associated with an increase in the Vmax for hormonal stimulation and with a lack of significant effects of ATP on the EC50. The effect was completely eliminated when adenylyl cyclase was assayed in the presence of high free Mg2+ levels (10 mM). Down-regulation of PKCs with long term PMA treatment did not affect the ATP-induced sensitization of adenylyl cyclase, although the PMA-induced sensitization of adenylyl cyclase was eliminated. In contrast to the effects of ATP and PMA, treatment of the cells with carbachol alone had no effect on adenylyl cyclase; however, in combination with nanomolar concentrations of PMA, synergism of the sensitization of adenylyl cyclase was observed. These data indicate that the activation of P2 purinergic receptors by ATP, and possibly activation of M5 muscarinic receptors by carbachol, may be important in the signal transduction pathways leading to the increases in the responsiveness of hormone-stimulated adenylyl cyclase.
Mol Pharmacol 1991 Oct
PMID:Sensitization of adenylyl cyclase by P2 purinergic and M5 muscarinic receptor agonists in L cells. 192 86


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