UNIPROT:P61278 - FACTA Search

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Query: UNIPROT:P61278 (somatostatin)
22,083 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Adrenaline and somatostatin inhibit insulin secretion via pertussis toxin (PTX)-sensitive mechanisms. Since glucose-stimulated release involves inhibition of ATP-sensitive K+ (K+ATP) channels and activation of Ca2+ influx, we took advantage of the glucose-sensitive, insulin-secreting cell line INS-1 to investigate whether inhibitors of insulin release modulate membrane voltage and K+ATP channel activity in cell-attached patch-clamp experiments. We found that adrenaline, through alpha2-adrenoceptors, and somatostatin counteracted glucose-induced depolarization and action potentials. As expected, these effects were mediated via PTX-sensitive G proteins since PTX pretreatment of the cells eliminated the effects of adrenaline and somatostatin on membrane voltage. When INS-1 cells were activated by adding both the K+ATP channel inhibitor tolbutamide and the adenylyl cyclase activator forskolin, adrenaline and somatostatin still repolarized the plasma membrane. Single-channel measurements in the cell-attached mode revealed that tolbutamide closed a 40 to 70 pS K+ channel which was neither reopened by adrenaline nor by somatostatin. In parallel cell preparations, insulin secretion was measured by radioimmunoassay. Insulin release induced by glucose, forskolin and tolbutamide was abolished by adrenaline. In contrast, somatostatin attenuated insulin secretion by only 30%. After comparing the potency of adrenaline and somatostatin on membrane voltage and on insulin secretion, it is concluded that the repolarizing effect of adrenaline on membrane voltage is not sufficient to explain its potent inhibitory effect on insulin secretion.
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PMID:Adrenaline-, not somatostatin-induced hyperpolarization is accompanied by a sustained inhibition of insulin secretion in INS-1 cells. Activation of sulphonylurea K+ATP channels is not involved. 866 72

The use of primary beta-cells in biochemical and molecular research is limited by the availability of pancreatic endocrine tissue. Numerous investigators have attempted to establish an insulin-secreting cell line that retains normal regulation of insulin secretion. Different approaches have been used, including induction of pancreatic tumors by irradiation or viral infection, immortalization of beta-cells in vitro, and development of transgenic mice with targeted expression of a recombinant oncogene in the beta-cell. Few of these attempts have proven successful, because cell differentiation and proliferation capacities are mutually exclusive. The most widely used insulin-secreting cell lines are RIN, HIT, beta TC, MIN6 and INS-1 cells. These cells contain mainly insulin and small amounts of glucagon and somatostatin. RIN cells, except for the subclone RIN-38, are not glucose-responsive. HIT cells and beta TC cells secrete insulin in response to glucose, but their dose-response curve is markedly shifted to the left MIN6, INS-1 and a newly available subclone of beta TC cells (beta TC-6 F7) are reported to retain normal regulation of glucose-induced insulin secretion. Although the behaviour of none of these cell lines perfectly mimics primary beta-cell physiology, they are extremely valuable tools for the study of molecular events underlying beta-cell function and dysfunction. In addition, insulin-secreting cell lines represent a potential source of transplantable tissue to overcome the limited availability of primary islets for this procedure.
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PMID:Insulin-secreting cell lines: classification, characteristics and potential applications. 869 99

Glucagon is insulinotropic, but it remains uncertain whether the insulinotropic action is mediated directly by glucagon receptors expressed on beta-cells or by cross-binding to the insulinotropic glucagon-like peptide-1 (GLP-1) receptor known to be expressed on beta-cells. Binding of [125I]glucagon to GLP-1 receptors and not to glucagon receptors has been reported in tumor-derived beta-cells (15). The objectives of the current study were to use receptor-binding techniques and a glucagon receptor-specific antiserum to determine whether glucagon receptors are present on beta-cells. Specific binding (7.2 +/- 0.8%) of [125I]GLP-1 to beta TC-3 cells was displaced equivalently with GLP-1 and exendin-(9-39) )Kd = 0.9 and 0.4 nM. respectively), whereas approximately 700-fold higher concentrations of glucagon were required for equal displacement (Kd = 400 nM). Binding of [125I]glucagon to beta TC-3 cells (approximately 1%) was displaced equivalently with 1 microM glucagon, GLP-1, or exendin-(9-39). These observations support earlier findings that beta TC-3 cells do not express functional glucagon receptors. However, specific binding of [125I]glucagon was observed on INS-1 cells (2.3 +/- 0.2%); this was displaced with glucagon (Kd = 1 nM), but not 1 microM GLP-1 or exendin-(9-39). To examine the distribution of glucagon receptors on native beta-cells, dispersed cultured rat islets were immunostained for glucagon, somatostatin, or insulin in combination with a polyclonal rabbit antiserum raised to an extracellular portion of the glucagon receptor (KD-14). The glucagon receptor antiserum colocalized staining with approximately 97% of immunoreactive insulin cells, 9% of immunoreactive glucagon cells, and 11% of immunoreactive somatostatin cells. Perfusion of the rat pancreas with concentrations of glucagon as low as 10(-12) M resulted in significant insulin release. These results suggest that whereas the tumor-derived beta-cell line beta TC-3 does not express functional glucagon receptors, INS-1 cells and isolated rat pancreatic beta-cells have specific glucagon receptors, as do a subpopulation of alpha- and delta-cells. A model is proposed for the role of glucagon in islet hormone secretion during feeding and fasting.
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PMID:Distribution of glucagon receptors on hormone-specific endocrine cells of rat pancreatic islets. 889 86

The peptide hormone glucagon is expressed in A cells of the pancreatic islets due to an interaction between multiple regulatory elements within the 5'-flanking region of its gene directing glucagon gene transcription. An A-cell-specific enhancer-like element in the rat glucagon gene, G3, contains two domains, both of which are necessary for G3 activity. Domain A of the G3 element comprises a sequence motif, PISCES, that is also found in control elements of the rat insulin I and somatostatin genes exhibiting cell-specific transcriptional activities distinct from G3. In this study, the nuclear proteins binding to domain B of G3 were characterized. In electrophoretic mobility shift assays using nuclear extracts from a glucagon-producing islet cell line, it was observed that the binding specificity of G3-domain-B-binding proteins is related to that of winged helix proteins supporting the hypothesis that the proteins binding to domain B of G3 may belong to the winged helix protein family of transcription factors. The overexpression of a dominant-negative winged helix protein mutant (derived from HNF-3) virtually abolished the transcriptional activity of G3 in a glucagon-expressing islet cell line. These results suggest that the unique A-cell-specific basal transcriptional activity of the glucagon G3 element depends on a combination of at least two proteins, the islet specific PISCES-binding protein and a more widely expressed winged helix protein.
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PMID:Glucagon gene G3 enhancer: evidence that activity depends on combination of an islet-specific factor and a winged helix protein. 908 37

To study the regulation of growth and differentiated function of insulin-secreting cells, the rat insulinoma cell line INS-1 was cultured in a defined serum-free medium containing prolactin, IGF-I, and triiodothyronine, which was originally reported to maintain insulin secretion of islet cells. Growth and viability, as well as cellular insulin content of INS-1 cells in the defined medium, were comparable to the control cells cultured in the complete medium containing 10% fetal calf serum. However, after a 3-day culture in this medium, insulin secretion in response to glucose, pyruvate, and leucine was markedly blunted compared with the control cells (-78, -68, and -56%, respectively), whereas the response to 30 mmol/l K+ was only slightly decreased. In these cells: 1) nutrient metabolism assessed by tetrazolium salt reduction was reduced in response to pyruvate and leucine, which are mainly metabolized in the mitochondria; 2) oxidation of both [3,4-(14)C]glucose and [1-(14)C]pyruvate was decreased (-22 and -32%, respectively); 3) glucose failed to depolarize the membrane potential, whereas tolbutamide was fully active; 4) video imaging analysis of cytosolic Ca2+ showed a decrease in the population of glucose-responsive cells, while the response to 30 mmol/l K+ was preserved; 5) serum replenishment for 3 days restored glucose-induced insulin secretion. Interestingly, conditioned serum-free medium from rat islets maintained the insulin secretory function of INS-1 cells, although glucagon, somatostatin, and some other factors failed to restore the function. In contrast, conditioned media from HepG2, PC12, and human umbilical vein endothelial cells did not substitute for serum. Thus, the impaired insulin secretion of the cells cultured in the defined medium is best explained by defective mitochondrial metabolism. Islet cells, but not INS-1 cells, produce factors required for normal signal generation by nutrient secretagogues.
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PMID:Glucose-induced insulin secretion in INS-1 cells depends on factors present in fetal calf serum and rat islet-conditioned medium. 928 42

The aim of the present study was to investigate whether mechanisms distal to the regulation of Ca2-influx are involved in tolbutamide-induced stimulation and adrenaline- and somatostatin- induced inhibition of insulin secretion in INS-1 cells. Using the patch clamp method, the membrane voltage was either kept constant at -70 mV, or Ca2+-influx was activated by short depolarising pulses to 0 my. These pulses induced an increase in cellular capacitance (Cm) caused by fusion of secretory granules with the plasma membrane. Tolbutamide did not alter, neither Cm under voltage clamp at -70 mV nor increases of Cm due to voltage pulses. The inhibitors of secretion, adrenaline and somatostatin, counteracted the augmentation of [Ca2+]i which was induced by glucose, tolbutamide and forskolin. In the voltage clamp mode, however, where no changes of [Ca2]i. were observed, adrenaline but not somatostatin inhibited the increase of Cm caused by depolarizing voltage pulses. The adrenaline effect on Cm was dependent on the addition of GTP to the pipette solution. When GTP was replaced by GDPbetaS or GTPgammaS, the effect of adrenaline on Cm was abolished. The blockade of calcineurin, by the addition of calcineurin inhibitory peptide (CIP) to the pipette solution, did not affect the adrenaline-induced inhibition of Cm. Moreover. After incubation of the cells with deltamethrin, a calcineurin inhibitor, the stimulation of secretion was attenuated, but the adrenaline-induced inhibition was not affected. Our results suggest that adrenaline-induced inhibition of insulin secretion involves a site of action directly related to the exocytotic membrane fusion. In contrast, the stimulator tolbutamide and the inhibitor somatostatin had no direct effect on exocytosis in INS-1 cells.
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PMID:Effects of adrenaline and tolbutamide on insulin secretion in INS-1 cells under voltage control. 1084 99

AR42J is an exocrine pancreatic cell line that has been reported to differentiate towards an endocrine phenotype when stimulated with various growth factors, such as activin A, hepatocyte growth factor (HGF), betacellulin or glucagon-like peptide 1. In our experiments, AR42J-B13 cells differentiated morphologically in response to the growth factor treatment as reported previously. However, they failed to express the insulin gene. We found that the cells did not express several transcription factors known to be found in the beta-cell, including Nkx6.1, isl-1, Pax4 and Pax6. In addition, the mRNA level for pdx-1 and Nkx2.2 were very low in comparison to the insulinoma cell lines INS-1 and RINm5F. However, some transcription factors typically found in beta-cells and neuroendocrine cells were expressed also in the AR42J-B13 cells. These included BETA2/NeuroD, HNF1alpha, C/EBPbeta and IA-1. Unlike the insulinoma cells, AR42J cells expressed the exocrine transcription factor p48. In order to induce endocrine differentiation, we transfected the AR42J-B13 cells with the full length cDNAs of isl-1, Nkx6.1, Nkx2.2 and pdx-1 under the control of the CMV promoter, both separately and in combinations. The expression of Nkx2.2 led consistently to the appearance of pancreatic polypeptide but not insulin, glucagon or somatostatin mRNA. The PP mRNA expression in Nkx2.2 cDNA transfected cells was independent of the growth factor treatment used for differentiating AR42J cells. In conclusion, the AR42J-B13 line possesses some features of a pancreatic neuroendocrine cell. However, we were unable to confirm the capacity of these cells to differentiate into insulin-producing cells. Our results indicate that Nkx2.2 plays a role in the transcriptional regulation of PP expression.
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PMID:Transcription factor expression and hormone production in pancreatic AR42J cells. 1094 Apr 82

Ca(2+)/calmodulin-dependent protein kinase II is a member of a broad family of ubiquitously expressed Ca(2+) sensing serine/threonine-kinases. Ca(2+)/calmodulin-dependent protein kinase II is highly expressed in insulin secreting cells and is associated with insulin secretory granules and has been proposed to play an important role in exocytosis or in insulin granule transport to release sites. To elucidate its function the antisense sequence of the major beta-cell subtype, Ca(2+)/calmodulin-dependent protein kinase II delta(2), was stably expressed in INS-1 rat insulinoma cells. This caused a loss of Ca(2+)/calmodulin-dependent protein kinase II delta(2) expression at the mRNA and protein level, while the expression of the 95% homologous Ca(2+)/calmodulin-dependent protein kinase II gamma and of beta-cell specific proteins such as the homeodomain factor pancreatic-duodenal homeobox factor-1 (PDX-1, also referred to as islet/duodenum homeobox-1, IDX-1, insulin promoter factor-1, IPF-1 and somatostatin transactivating factor-1, STF-1), the glucagon-like peptide-1 (GLP-1) receptor and K(ATP)-channels K(IR)6.2/SUR-1 (sulfonylurea receptor-1) was not altered. Unexpectedly, the cells showed a large reduction of insulin gene expression, which was due to reduced insulin gene transcription. Electrophoretic mobility shift assays of PDX-1 binding to the insulin promoter A1 and E2/A3A4 elements showed additional bands indicating alterations of PDX-1 complex formation. Stable over expression of Ca(2+)/calmodulin-dependent protein kinase II delta(2), by contrast, was associated with elevated expression of insulin mRNA. Therefore, we conclude that Ca(2+)/calmodulin-dependent protein kinase II delta(2) links fuel-dependent increases in intracellular Ca(2+) concentrations to transcriptional regulation of genes related to the metabolic control of insulin secretion.
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PMID:Ca2+/calmodulin-dependent protein kinase II delta2 regulates gene expression of insulin in INS-1 rat insulinoma cells. 1260 Aug 4

Cocaine- and amphetamine-regulated transcript (CART) is an anorexigenic peptide widely expressed in the central and peripheral, including the enteric, nervous systems. CART is also expressed in pituitary endocrine cells, adrenomedullary cells, islet somatostatin cells, and in rat antral gastrin cells. We used immunocytochemistry (IHC) and in situ hybridization (ISH) to study CART expression in developing rat pancreas. We also examined co-expression of CART and islet hormones and developmental markers and the effect of CART on proliferation using clonal insulin cells (INS-1 832/13). A major portion of each of the islet cell types, except the ghrelin cells, expressed CART during a period before and around birth. Two weeks postnatally, CART expression was restricted to somatostatin cells. Pre- and early postnatally, many of the CART-expressing cells co-expressed cytokeratin 20 (CK20), a marker of duct cells and islet precursor cells, the trophic hormone gastrin, and a smaller subpopulation also harbored the proliferation marker Ki67. CART was also expressed in pancreatic nerve fibers, both sensory and autonomic, and in ganglion nerve cell bodies. Although highly expressed in the developing islets, CART did not affect proliferation of INS-1 cells. We have demonstrated that CART is expressed in several islet cell types during rat development but is restricted to somatostatin cells and neurons in the adult rat.
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PMID:Cocaine- and amphetamine-regulated transcript (CART) is expressed in several islet cell types during rat development. 1472 68

Cocaine- and amphetamine-regulated transcript (CART) is an anorexigenic peptide widely expressed in the central, peripheral, and enteric nervous systems. CART is also expressed in endocrine cells, including beta-cells during rat development and delta-cells of adult rats. We examined the effect of CART 55-102 on islet hormone secretion, using INS-1(832/13) cells and isolated rat islets. In addition, islet CART expression was examined in two rat models of type 2 diabetes: Goto-Kakizaki (GK) rats and dexamethasone (DEX)-treated rats. At high glucose, CART potentiated cAMP-enhanced insulin secretion via the cAMP/protein kinase A-dependent pathway. In the absence of cAMP-elevating agents, CART was without effect on INS-1 cells but modestly inhibited secretion of insulin, glucagon, and somatostatin from isolated islets. CART was markedly upregulated in the beta-cells of both diabetes models. Thus, in DEX-treated rats, islet CART mRNA expression, and the number of CART-immunoreactive beta-cells were 10-fold higher than in control rats. In GK rats, the relative number of CART-expressing beta-cells was 30-fold higher than in control rats. We conclude that CART is a regulator of islet hormone secretion and that CART is upregulated in the beta-cells of type 2 diabetic rats.
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PMID:CART regulates islet hormone secretion and is expressed in the beta-cells of type 2 diabetic rats. 1644 61

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