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)

Functional and specific receptors for vasoactive intestinal peptide (VIP) (determined by their capacity to bind 125I-VIP and activate adenylate cyclase) and cyclic AMP-dependent phosphodiesterase activities were characterized in enterocytes of human fetal small intestine between 18 and 23 weeks of gestation. Half-maximal stimulation of the cyclase and inhibition of 125I-VIP binding in membrane preparations were respectively observed at 1.4 and 5 X 10(-10) M VIP. The peptides structurally related to VIP activated the cyclic AMP generating system at pharmacological doses (10(-7) M and above) in the following order of potency: VIP greater than PHI greater than GRF greater than secretin. Other peptides or test substances, including GIP, pancreatic glucagon, somatostatin-14, gastrin, CCK, neurotensin, pancreatic polypeptide, PYY, substance P, histamine and isoproterenol are inactive in this system, while the ubiquitous adenylate cyclase activators NaF, forskolin and prostaglandins were effective. These results, combined with the appearance of intestinal VIP in nerve fibers at 8 weeks and with the morphological and enzymatic maturation at 9-12 weeks of the intestinal mucosa, indicate that this neuropeptide may regulate either the differentiation or function of enterocytes during the early development of human intestinal mucosa.
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PMID:Vasoactive intestinal peptide receptor activity in human fetal enterocytes. 298 18

Molt 4b lymphoblasts have previously been shown to possess a single class of pharmacologically specific, high affinity receptors for vasoactive intestinal polypeptide (VIP). This study further explores the molecular basis for modulation of human lymphocyte function by VIP. Dose-dependent stimulation of adenylate cyclase was observed in Molt lymphoblasts over the range of 0.1 nM to 1 microM VIP. VIP-mediated by guanine nucleotide. Accumulation of intracellular cAMP was observed in the presence of either VIP or the diterpene, forskolin. The effects of these two agonists were synergistic. Two neuropeptides that share sequence homology with VIP were also studied; both peptide histidine isoleucine (PHI) and human pancreatic growth hormone releasing factor (1-44 GHRF) competed for 125I-VIP binding to Molt cells. PHI stimulated intracellular cAMP accumulation and demonstrated synergism with forskolin, whereas GHRF had no effect on cAMP. Photoaffinity labeling of 100,000 X G soluble proteins with 8-N3-[32P]cAMP followed by SDS gel electrophoresis demonstrated the presence of cAMP-dependent protein kinases I and II. Cyclic AMP-dependent protein kinase II predominated in the soluble fraction and was the only isozyme observed in particulate fractions. Protein phosphorylation was studied in Molt 4b cells preincubated with [32P]PO43- followed by addition of media alone, 1 microM peptide, or 10 microM forskolin. Cells were lysed and subjected to two-dimensional electrophoresis. Increased phosphorylation of a specific 41,000 Mr protein was observed after addition of forskolin, VIP, or PHI. A much lower concentration of VIP (1 nM) also caused a significant net increase in phosphorylation, which was of a lower magnitude. In contrast, no net effect on protein phosphorylation was seen with GHRF. These data demonstrate the presence of a functional VIP receptor that is linked to the G protein-adenylate cyclase complex. The demonstration of cAMP-dependent protein kinase and of VIP- and PHI-mediated protein phosphorylation in Molt 4b lymphoblasts provides evidence on a molecular level for neuropeptide modulation of human lymphocyte function.
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PMID:Cyclic AMP-dependent protein kinase in Molt 4b lymphoblasts: identification by photoaffinity labeling and activation in intact cells by vasoactive intestinal polypeptide (VIP) and peptide histidine isoleucine (PHI). 298 3

The vasoactive intestinal polypeptide (VIP) receptor was characterized on the GH3 rat pituitary tumor cell line using competitive binding studies with peptides having sequence homology with VIP. Further studies investigated receptor coupling to the adenylate cyclase complex by measurement of cAMP levels. Finally, the molecular weight of the receptor was estimated by affinity labeling techniques. Studies using 125I-VIP and unlabeled competing peptides revealed a single class of high affinity binding sites with a dissociation constant (KD) of 17 +/- 2 nM (mean +/- S.E.M.) for VIP, 275 +/- 46 nM for peptide histidine isoleucine (PHI), and 1380 +/- 800 nM for human pancreatic growth hormone releasing factor (GHRF). VIP and PHI each stimulated intracellular cAMP accumulation in a dose-dependent manner; both peptides demonstrated synergism with forskolin. In contrast, GHRF neither stimulated accumulation of cAMP nor demonstrated synergism with forskolin. VIP plus PHI (1 microM each) caused no significant increase in cAMP over either VIP or PHI alone, implying that the two peptides act through the same receptor. Covalent crosslinking of 125I-VIP to its binding site using either disuccinimidyl suberate (DSS) or ethylene glycol bis(succinimidyl succinate) (EGS) was followed by SDS-PAGE and autoradiography. The result is consistent with an Mr 47 000 VIP-binding subunit comprising or being associated with the VIP receptor of GH3 pituitary tumor cells.
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PMID:Vasoactive intestinal peptide effects on GH3 pituitary tumor cells: high affinity binding, affinity labeling, and adenylate cyclase stimulation. Comparison with peptide histidine isoleucine and growth hormone-releasing factor. 300 42

In order to determine species specificity in growth hormone-releasing factor (GRF) interaction with vasoactive intestinal polypeptide (VIP) receptors, we have tested rat (r) GRF (with a His1 such as in VIP), human (h) GRF and position 1 substituted analogs of hGRF (Ala1, Ac-Tyr1, His1, Phe1, and Trp1 in the place of Tyr1) for their ability to inhibit 125I-VIP binding and to stimulate adenylate cyclase activity in human and rat intestinal epithelial membranes. We show that rGRF has a much higher affinity than hGRF for both human and rat VIP receptors. In humans, the Ki values for inhibiting 125I-VIP binding are 0.5 (VIP), 26 (rGRF), and 830 nM (hGRF). In rats the values are 0.6 (VIP), 46 (rGRF), and 1100 nM (hGRF). This is due in part to the presence of His1 in rGRF since the analog His1 hGRF has a higher affinity than hGRF in man and rat, i.e., Ki = 320 nM and 460 nM, respectively. Studies of adenylate cyclase stimulation reveal that rGRF and His1 hGRF are full VIP agonists in man and rat, whereas hGRF and its other analogs behave as partial agonists in both species. One of the hGRF analogs tested (Ac-Tyr1hGRF) is of great interest since it inhibits 125I-VIP binding to rat intestinal membranes with a Ki = 430 nM but has a negligible intrinsic activity in stimulating adenylate cyclase activity (about 6% of the efficacy of VIP). This analog does inhibit the VIP-stimulated adenylate cyclase activity in a dose-dependent manner, complete inhibition of the VIP (0.01-1 nM) effect being obtained with 30 microM analog. The Schild plot of the inhibitory effect further indicates competitive antagonism. In contrast, Ac-Tyr1hGRF is a partial VIP agonist in humans (about 20% of the efficacy of VIP). These results evidence the important role of His1 for peptide interaction with VIP receptors and provide the first example of a competitive VIP antagonist.
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PMID:Study of species specificity in growth hormone-releasing factor (GRF) interaction with vasoactive intestinal peptide (VIP) receptors using GRF and intestinal VIP receptors from rat and human: evidence that Ac-Tyr1hGRF is a competitive VIP antagonist in the rat. 300 61

Anterior pituitaries from the dwarf mouse strain "little" did not release growth hormone or accumulate adenosine 3',5'-monophosphate (cyclic AMP) in response to human and rat growth hormone-releasing factor (GRF). Dibutyryl cyclic AMP, as well as the adenylate cyclase stimulators forskolin and cholera toxin, markedly stimulated growth hormone (GH) release. The basis of the GH deficiency in the little mouse may therefore be a defect in an early stage of GRF-stimulated GH release related either to receptor binding or to the function of the hormone-receptor complex.
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PMID:Receptor-associated resistance to growth hormone-releasing factor in dwarf "little" mice. 300 29

The present review is focused on the exocrine pancreas and liver where the only known effector mechanism of VIP is the activation of adenylate cyclase in plasma membranes. A two-state model of activation-deactivation of the enzyme visualizes the participation of VIP receptors and Ns, the guanyl nucleotide stimulatory protein of adenylate cyclase. In the rat pancreas, VIP and GRF receptors are indistinguishable and disulfide bridges influence their functional integrity. The antagonism of VIP and somatostatin perhaps requires, at the adenylate cyclase level, the contribution of Ni, the guanyl nucleotide inhibitory protein. The potentiation of VIP by various stimulants acting on Ca2+ movements may rely on later events, e.g., on a concerted activation of protein kinases. When comparing quantitatively peptide binding to receptors with adenylate cyclase activation, cyclic AMP levels and amylase secretion, a tool is at hand to tailor synthetic agonists and antagonists of VIP, with appropriate changes in the N-terminal moiety of the peptide (a good agonist allows efficient coupling of receptors to the adenylate cyclase system). Apart from stimulus-secretion coupling, VIP may influence protein synthesis in the rat pancreas, through the phosphorylation of ribosomal protein S6, and may alter the activity of the endoplasmic reticulum via the phosphorylation of Mr = 21 kDa and Mr = 25 kDa proteins. In rat liver membranes, high affinity VIP receptors are specifically labelled with 125I-helodermin and are coupled to adenylate cyclase (at variance with low affinity VIP receptors). These receptors are highly responsive to divalent cations and to guanyl nucleotides.
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PMID:Effector mechanisms of peptides of the VIP family. 301 87

Three separate sets of receptors sensitive to VIP, GIP and pancreatic/entero-glucagons, have been characterized in HGT-1 cells. The order of relative potencies of VIP receptor agonists was VIP greater than rh GRF-43, rh GRF-29 greater than PHI greater than hp GRF-40, secretin. G-37 was about 4 times less potent than G-29 in HGT-1 cells (G-29 greater than G-37), whereas it was about 20 times more potent than G-29 in rat fundic glands (G-37 greater than G-29). Adenylate cyclase in HGT-1 cells was stimulated by VIP, G-29, G-37 and GIP, over a concentration from 3.16 X 10(-9) to 3.16 X 10(-7) M GIP. The experimental data: (1) support the enterogastrone activity of GIP, via adenylate cyclase activation and somatostatin release by gastric D cells; (2) demonstrate that HGT-1 cells originating from a human fundic tumor are sensitive to the glucagon-like peptides G-29 and -37, as rat fundic glands; (3) indicate that the pharmacological properties of the VIP receptor in this human gastric cell line are similar to those characterized in normal human gastric glands.
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PMID:Functional receptors for VIP, GIP, glucagon-29 and -37 in the HGT-1 human gastric cancer cell line. 301 90

The ability of 30 synthetic GRF(1-29)-NH2 analogs to stimulate adenylate cyclase activity was investigated in membranes from rat adenopituitary, rat liver and rat pancreas. In adenopituitary membranes, GRF and GRF analogs interacted with specific GRF receptors, whereas in liver and pancreatic membranes, they interacted with VIP receptors. The C-terminal moiety of GRF was responsible for GRF receptor recognition as the hybrid analog (His1, D-Ala2)-GRF(1-9), VIP(10-28) stimulated pituitary adenylate cyclase through the occupancy of VIP receptors only. When GRF or VIP receptors were occupied by GRF analogs, the N-terminal part of the ligand appeared critical for adenylate cyclase activation. This was established by testing 30 GRF analogs mono-, bi- or tri-substituted in positions 1 to 10. Major observations included: (a) the characterization of (N-Ac-Tyr1, D-Arg2)-GRF(1-29)-NH2 as an antagonist of GRF-stimulated pituitary adenylate cyclase; (b) the discovery of the (N-Ac-Tyr1, D-Phe2)-, (His1, D-Ala2, D-Ser3, NLeu27)-, and (His1, D-Ala2, D-Thr7, NLeu27)-derivatives of GRF(1-29)-NH2 as specific antagonists of VIP receptors in rat pancreatic membranes; (c) the importance of the free NH2 function of amino acid residue 1 for pancreatic adenylate cyclase activation, and (d) the decreased efficiency of iodinated (Tyr1)-GRF(1-29)-NH2 as opposed to the non iodinated form, in all systems tested.
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PMID:Comparative structural requirements of thirty GRF analogs for interaction with GRF- and VIP receptors and coupling to adenylate cyclase in rat adenopituitary, liver and pancreas. 301 3

It has been reported that rat growth hormone releasing factor (rat GRF-43), similarly to the two human GRFs (GRF-40 and 44) stimulates adenylate cyclase activity in pituitary cells. Controversial findings have been presented by two different groups on the action of GRF on phosphoinositides (PI) metabolism, a phenomenon linked to Ca-- mediated intracellular mechanisms. In the work to be reported, we evaluated the accumulation of inositol phosphates induced by GRF exposure in primary cultures of rat and human pituitary cells. Addition of rat GRF-43 to rat pituitary cells at doses up to 1 microM had no effect on inositol phosphates accumulation, while already at a dose as low as 0.05 nM it increased growth hormone secretion in the incubation medium significantly. In the same cell system, TRH, a known activator of PI breakdown, significantly increased [3H]inositol phosphates. In primary cultures of human somatotrophs from acromegalic subjects as in rats, addition of hpGRF-40 and also of TRH did not elicit any modification in the accumulation of [3H]inositol phosphates. Consistent with in vivo findings, both peptides induced a significant release of GH in the medium. Our results show that the GH releasing effect of GRF does not involve the hydrolysis of phosphatidylinositol in normal rat as well as in tumoral human somatotrophs. In addition it appears that the anomalous response of TRH on adenomatous cells from acromegalic patients is differently mediated in respect to the action of the tripeptide on normal lactotrophs and thyrotrophs.
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PMID:Growth hormone-releasing factor does not stimulate phosphoinositides breakdown in primary cultures of rat and human pituitary cells. 301 52

Adenylate cyclase activity was studied in anterior pituitary homogenates from young adult (6 months) and old (20 and 24 months) male rats. Basal, NaF-, GTP-, 5'-guanylimidodiphosphate (Gpp(NH)p)- and forskolin-stimulated activities were similar in the three groups, implying that the stimulatory guanyl nucleotide regulatory binding site (NS) and the catalytical unit were unaffected by aging. Vasoactive intestinal peptide (VIP)-stimulated adenylate cyclase activity was also identical in the three groups. The efficacy (i.e., the maximum effect) of growth hormone-releasing factor [GRF(1-29)-NH2] on adenylate activity was reduced by 45-49% in old and senescent rats with no change in peptide potency (i.e., the concentration required for half-maximal enzyme stimulation). These results suggest that aging induced a selective loss of functional GRF receptors but influenced neither the coupling between receptors, NS and the catalytic unit nor the efficacy of the catalytic unit per se.
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PMID:Decreased stimulation of adenylate cyclase by growth hormone-releasing factor in the anterior pituitary of old rats. 310 90


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