Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P61278 (somatostatin)
 22,083 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Specific somatostatin (SRIH) receptors on human pituitary adenoma cell membranes were characterized using [125I]Tyr11-SRIH as the radioligand. Specific binding of [125I] Tyr11-SRIH to adenoma cell membranes reached a steady state within 30 min at 25 C, and semilogarithmic analysis of the data revealed that the rate of the binding was linear at 25 C with a t1/2 of 13.2 min. Specific binding increased linearly with 5-160 micrograms plasma membrane protein. SRIH-14 and SRIH-28 inhibited [125I]Tyr11-SRIH binding to adenoma cell membranes with ID50S of 0.32 and 0.50 nM, respectively, while secretin, glucagon, gastrin, cholecystokinin-8, bombesin, TRH, LHRH, human GH-releasing factor-(1-44)-NH2, D-Ala2-met-enkephalin, gamma-aminobutyric acid and taurine did not significantly inhibit binding. All of 13 GH-secreting adenomas investigated had specific and high affinity SRIH receptors, with a dissociation constant (Kd) of 0.80 +/- 0.15 nM (mean +/- SEM) and a maximal binding capacity (Bmax) of 234.2 +/- 86.9 fmol/mg protein (mean +/- SEM). Among five of the nonsecreting pituitary adenomas examined, two had SRIH receptors with Kd values of 0.18 and 0.32 nM and Bmax values of 17.2 and 48.0 fmol/mg protein, respectively. In the remaining three, SRIH receptors were not detected. These results indicate that GH-secreting adenomas as well as some nonfunctioning adenomas have specific SRIH receptors, and hence, the function of the adenomas could be altered by SRIH.
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PMID:Specific somatostatin receptors on human pituitary adenoma cell membranes. 286 81

It was shown that somatostatin (SRIF) inhibited cAMP-dependent vasoactive intestinal peptide (VIP)-stimulated prolactin (PRL) release by a GH3 clonal strain of rat pituitary tumor cells and decreased basal PRL secretion and inhibited PRL release in response to thyrotropin releasing hormone (TRH) whose action was independent of prior synthesis of cAMP. Pretreatment of these cells with pertussis toxin prevented SRIF's inhibitory effects on basal and TRH-stimulated hormone secretion as well as its VIP-stimulated responses. The blockade of SRIF's inhibitory effect on the actions of TRH or VIP was dependent on both the duration of preincubation and concentration of the toxin and was correlated with the ability of the toxin to catalyze the ADP-ribosylation of the 39,000-Da membrane protein. It is likely that this pertussis toxin substrate is involved in signal transduction of SRIF on cAMP-dependent actions of VIP and cAMP-independent action of TRH. However, the mechanism of SRIF's action on TRH is not clear, since SRIF did not affect the intracellular responses by TRH, neither intracellular Ca2+ mobilization nor the increase of 1,2-diacylglycerol formation following the breakdown of polyphosphoinositides.
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PMID:Pertussis toxin blocks the inhibitory effects of somatostatin on cAMP-dependent vasoactive intestinal peptide and cAMP-independent thyrotropin releasing hormone-stimulated prolactin secretion of GH3 cells. 286 31

Somatostatin binding to its receptors on rat pancreatic acinar membranes was characterized with [125I-Tyr1]somatostatin. The COOH-terminal octapeptide of cholecystokinin (CCK8), when present at various concentrations in the reaction mixture for the binding study, reduced labeled somatostatin binding in a dose-dependent manner, whereas carbachol or Ca2+ ionophore did not affect the binding. By contrast, when pancreatic acini were first treated with carbachol and thereafter [125I-Tyr1]somatostatin binding to membranes prepared from these acini was examined, carbachol reduced subsequent somatostatin binding in a dose-dependent manner. Scatchard analysis of the labeled somatostatin binding revealed that carbachol pretreatment decreased the maximum binding capacity from 142 +/- 20 fmol/mg of membrane protein to 63.5 +/- 3.5 fmol/mg of membrane protein without significantly affecting the binding affinity. To test for the possibility that CCK8 also may affect labeled somatostatin binding through an intracellular process, pancreatic acini were first treated with CCK8 and then the membrane bound CCK8 was washed out. Subsequent labeled somatostatin binding to membranes from these acini was also decreased. When 1 mM EDTA was present in the pretreatment medium, the inhibitory effect of carbachol or CCK8 was partially abolished, suggesting that an intracellular process to modulate somatostatin binding is dependent on Ca2+. On the other hand, pretreatment of acini with Ca2+ ionophore almost failed to affect subsequent labeled somatostatin binding. Results therefore suggest that CCK8 can modulate labeled somatostatin binding to pancreatic acinar membranes not only acting through an intracellular process but also at membrane sites and carbachol- or CCK8-activated intracellular process to modulate somatostatin binding is dependent on Ca2+, but Ca2+ mobilization itself is not sufficient to affect subsequent somatostatin binding.
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PMID:[CCK and carbachol differently modulate somatostatin binding to rat pancreatic acinar membranes]. 287 7

Guanine nucleotides and pertussis toxin were used to investigate whether somatostatin receptors interact with the guanine nucleotide inhibitory protein (Ni) on pancreatic acinar membranes in the rat. Guanine nucleotides reduced 125I-[Tyr1]somatostatin binding to acinar membranes up to 80%, with rank order of potency being 5'-guanylyl imidodiphosphate [Gpp(NH)p] greater than GTP greater than GDP greater than GMP. Scatchard analysis revealed that the decrease in somatostatin binding caused by Gpp(NH)p was due to the decrease in the maximum binding capacity without a significant change in the binding affinity. The inhibitory effect of Gpp(NH)p was partially abolished in the absence of Mg2+. When pancreatic acini were treated with 1 microgram/ml pertussis toxin for 4 h, subsequent 125I-[Tyr1]somatostatin binding to acinar membranes was reduced. Gpp(NH)p further decreased somatostatin binding to islet-activating protein (IAP)-treated acinar membranes. Pertussis toxin treatment also abolished the inhibitory effect of somatostatin on vasoactive intestinal peptide-stimulated increase in cellular content of adenosine 3',5'-cyclic monophosphate (cAMP) in the acini. Furthermore, exposure of acini to IAP caused ADP ribosylation of a membrane protein with Mr = 41,000 in parallel to the inhibition of cAMP accumulation in acini. The present results suggest, therefore, that 1) somatostatin probably functions in the pancreas to regulate adenylate cyclase enzyme system via Ni, 2) the extent of modification of Ni is correlated with the ability of somatostatin to inhibit cAMP accumulation in acini, and 3) guanine nucleotides also inhibit somatostatin binding to its receptor.
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PMID:Coupling of guanine nucleotide inhibitory protein to somatostatin receptors on pancreatic acinar membranes. 288 15

CRF stimulates the synthesis and secretion of proopiomelanocortin-derived peptides from AtT-20 mouse pituitary tumor cells. This study has shown that there is a specific binding site for CRF located on the plasma membrane of these cells. Both [125I]iodo-Tyr0CRF and noniodinated CRF (10(-11)-10(-7) M) stimulated, in a dose-dependent manner, the secretion of equimolar amounts of beta-endorphin-like immunoactivity from AtT-20 cells. Disuccinimidyl suberate, a cross-linking agent, was used to demonstrate specific binding of [125I]iodo-Tyr0CRF to plasma membranes from these cells. After cross-linking [125I] iodo-Tyr0CRF, the membrane proteins were solubilized with sodium dodecyl sulfate and electrophoresed on a 10% polyacrylamide gel. A single radioactively labeled band, corresponding to a mol wt of 66,000, was identified by autoradiography. [125I]Iodo-Tyr0CRF binding to these membranes was inhibited by 10(-7) M unlabeled CRF or an equimolar concentration of the CRF analog sauvagine. Similar concentrations (10(-7) M) of TRH, GnRH, insulin, [Arg8]vasopressin, somatostatin, and ACTH did not inhibit [125I]iodo-Tyr0CRF binding to the plasma membranes. Incubation of AtT-20 cells for 24 h in the presence of 10 nM dexamethasone reduced [125I]iodo-Tyr0CRF binding by 80% compared to that in untreated cells. Dexamethasone also inhibited the CRF-stimulated beta-endorphin-like immunoactivity secretory response. These data indicate that binding of CRF to a specific membrane protein is an integral component in the stimulation of AtT-20 cells by CRF.
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PMID:Identification of a corticotropin-releasing factor-binding protein in the plasma membrane of AtT-20 mouse pituitary tumor cells and its regulation by dexamethasone. 303 86

We have demonstrated the presence of specific receptors for somatostatin (SRIF) in normal rat pituitary membranes using ([125I]Tyr11]SRIF) as the radioligand. These receptors bind SRIF with high affinity (Ka approximately 0.47 X 10(10) M-1) and have a maximal binding capacity of 0.095 pmol/mg membrane protein. Two other radioiodinated SRIF analogs which contain N-terminally situated radiolabel, [125I-Tyr1]SRIF and [125I-N-Tyr] SRIF, were found unsuitable for receptor binding studies due to loss of the radiolabel from the ligand molecule under the experimental conditions employed. Binding of [125I]Tyr11]SRIF to these receptors was specific and was not influenced by a variety of other neuropeptides. The specificity of SRIF receptors was also examined using 10 synthetic SRIF analogs as well as catfish somatostatin I. Catfish somatostatin I was 8.3 times less potent than SRIF in binding to SRIF receptors, although it has been reported to be equipotent in terms of in vitro GH inhibition. Analogs which exhibit greater potency for GH inhibition in vitro bound to these receptors with greater affinities than SRIF, whereas biologically inactive analogs showed markedly reduced binding, suggesting that the in vitro GH inhibitory actions of SRIF analogs are related to their ability to interact with SRIF receptors.
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PMID:Characterization of pituitary membrane receptors for somatostatin in the rat. 612 62

Somatostatin is a known inhibitor of hormone secretion and of nutrient transport. Because somatostatin-like immunoreactivity has been detected in amniotic fluid and the placenta has both hormone secretory and nutrient transport functions, we investigated the possible existence of somatostatin receptors on placenta cell membranes. Binding of 125I-Tyr1- and 125I-Tyr11-somatostatin (5-21%) to solubilized placenta cell membranes was observed. Binding was time-, temperature-, and pH-dependent and occurred maximally with incubation at concentrations of 25 micrograms of membrane protein. Displacement of binding of 125I-Tyr1 and Tyr11 somatostatin by cold cyclic and linear somatostatin and somatostatin analogs Ala-5, Ala-8, and Ala-11 was observed. Scatchard analysis of data revealed high capacity of (Ro 0.44 mol/micrograms X 10(-12) but low affinity (Kd 1.8 M X 10(-7) binding sites similar to that reported in other tissues. Binding was not reversible under our experimental conditions. The significance of this low affinity binding of somatostatin to placenta cell membranes remains to be determined.
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PMID:Characterization of somatostatin specific binding in plasma cell membranes of human placenta. 614 16

Specific binding sites for secretin have been identified in rat fundic membranes, using 125I-secretin. The binding was saturable, reversible, time and temperature dependent. Optimal pH for binding was around 7-7.5. Scatchard plots were compatible with the existence of 2 classes of receptors; the first class with a high affinity for secretin (apparent Kd of 4 x 10(-10) M) and a low binding capacity (150 fmol per mg membrane protein, i.e., 4,500 high affinity sites/cell) and a class of receptors with a lower affinity (Kd of 3 x 10(-9) M) and a higher binding capacity (580 fmol per mg membrane protein i.e., 17,400 sites/cell). Glucagon, gastric inhibitory polypeptide and somatostatin had no-effect on secretin binding. In contrast, VIP inhibited 125I-secretin binding and stimulated adenylate cyclase activity, in both cases at a 200-times lower potency than secretin (ID50 and Ka = 2 x 10(-7) M VIP). The properties of these secretin receptors strongly support the concept that secretin acts as a regulatory peptide on the rat gastric epithelium.
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PMID:Secretin binding sites coupled with adenylate cyclase in rat fundic membranes. 628 94

Regulation of tyrosine phosphorylation is thought to be an essential step in signal transduction mechanisms that mediate cellular responses. In pancreatic tumour cells we demonstrated that somatostatin analogues inhibited cell proliferation and stimulated a membrane protein tyrosine phosphatase (PTP) activity at concentrations at which they bind to the somatostatin receptor. To elucidate the role of PTP in the signal transduction pathway activated by somatostatin receptors we first studied the interaction of PTP with the somatostatin receptor at the membrane. We purified somatostatin receptors by immunoaffinity from pancreatic membranes that strongly expressed the type 2 somatostatin receptor sstr2. We identified the receptor as an 87 kDa protein. We demonstrated that a PTP activity co-purified with somatostatin receptors. The PTP was identified as a 66 kDa protein immunoreactive to antibodies against SHPTP1. These antibodies immunoprecipitated somatostatin receptors either occupied or unoccupied by ligand indicating that SHPTP1 is associated with somatostatin receptors. We then expressed sstr2A in monkey kidney COS-7 cells and mouse NIH/3T3 fibroblasts and demonstrated that somatostatin analogues (RC 160, octreotide and BIM 23014) which exhibited high affinity for sstr2 stimulated a PTP activity and inhibited cell proliferation in proportion to their affinities for sstr2. Under the same conditions these analogues have no effect on the growth of cells expressing sstr1. All these results suggest that a PTP related to SHPTP1 is associated with somatostatin receptors and may be involved in the negative growth signal promoted by sstr2.
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PMID:A tyrosine phosphatase is associated with the somatostatin receptor. 758 47

A binding assay for growth hormone releasing factor (GRF) has been developed using scintillation proximity assay (SPA) technology. Binding conditions were validated by several criteria. Equilibrium binding was attained within three hours at 22 degrees C in crude membrane fractions of HEK293 (293-P2) and GH4C1 (GH4-P1) cells transfected with the porcine GRF receptor. Saturation binding isotherms produced a KD of 296 pM and a Bmax of 4.7 pmols/mg membrane protein in 293-P2 cells. Cells not expressing the GRF receptor displayed no specific binding for the ligand. Competition binding curves produced the following rank order of potency for tested peptides: GRF analogs D-Ala2 = D-Arg2 (IC50 approximately 1 nM) >> PACAP > secretin, VIP (EC50 > 100 nM). Somatostatin (SRIF) binding was also adapted to the SPA format in a GH4C1 cell line transfected with the SRIF receptor subtype 2 (SSTR2) and in HEK293 cells transfected with the SRIF receptor subtype 5 (SSTR5). This assay represents a major improvement for binding measurements of these and potentially many other ligands for G-protein linked receptors, requiring no separation of bound from free hormone, allowing detailed pharmacological evaluations and enabling measurement of equilibrium binding in real time. In the 96-well format, it is suitable for high throughput screening.
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PMID:A rapid and sensitive binding assay for growth hormone releasing factor. 766 92


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