Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UMLS:C0043167 (pertussis)
 19,595 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We have reported previously that the widespread inhibitory actions of somatostatin might be mediated by its ability to inhibit the expression of the immediate early genes c-fos and c-jun. The products of these genes form a heterodimeric transcription factor complex [activator protein 1 (AP-1)], which is known to be induced by treatment with phorbol esters. In the present study, we sought to investigate the mechanisms by which somatostatin inhibits immediate early gene expression. For our experiments, we used a rat pituitary adenoma cell line (GH3), which is known to express multiple subclasses of somatostatin receptors. The phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) stimulated both AP-1 binding and transcriptional activity in GH3 cells and the somatostatin analogue octreotide inhibited this response by 40-70%. In the presence of two different phosphatase inhibitors, sodium orthovanadate or okadaic acid, the ability of somatostatin to inhibit AP-1 binding and transcriptional activity was abolished. This effect of octreotide, which appears to be mediated by the SSTR2 and SSTR5 subtypes of somatostatin receptors, was paralleled by its ability to inhibit TPA-stimulated GH3 cell proliferation. Pretreatment of the GH3 cells with pertussis toxin (200 ng/ml) reversed the inhibitory effect of octreotide on both AP-1 function and cellular proliferation. Our observations lead us to conclude that somatostatin not only inhibits immediate early gene expression but also inhibits AP-1 binding and transcriptional activity via the action of several classes of protein phosphatases. This effect, which is pertussis toxin sensitive, might be one mechanism by which somatostatin inhibits cellular proliferation.
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PMID:Somatostatin inhibits AP-1 function via multiple protein phosphatases. 763 95

Using a combination of polymerase chain reaction and genomic library screening we have cloned a human gene for a subtype of the somatostatin (SST) receptor (SSTR) termed human SSTR5 (hSSTR5), which is located on chromosome 16. The predicted amino acid sequence of hSSTR5 displays 75% sequence identity with a recently identified rat SSTR [Mol. Pharmacol. 42:939-946 (1992)], suggesting that it is the human homologue of this receptor. hSSTR5 consists of a 363-residue polypeptide exhibiting a putative seven-transmembrane domain topology typical of G protein-coupled receptors. The receptor displays considerable sequence identity to hSSTR1 (42%), hSSTR2 (48%), hSSTR3 (47%), and hSSTR4 (46%). Membranes prepared from COS-7 cells transiently expressing the hSSTR5 gene bound 125I-Leu8,D-Trp22,Tyr25-SST-28 (125I-LTT-SST-28) with high affinity and in a saturable manner. SST-14, SST-28, and various synthetic SST peptide agonists produced dose-dependent inhibition of radioligand binding with the following rank order of potency: LTT-SST-28 > SST-28 > D-Trp8-SST-14 > SST-14 approximately RC-160 approximately BIM 23014 > MK-678 > SMS 201-995. hSSTR5 bound SST-28 with a 12.6-fold greater affinity (Ki = 0.19 nM), compared with SST-14 (Ki = 2.24 nM), indicating that the receptor is SST-28 selective. Addition of GTP, guanosine-5'-O-(3-thio)triphosphate, Na+ ions, or pertusis toxin greatly reduced 125I-LTT-SST-28 binding, thereby indicating that hSSTR5 is coupled to pertussis toxin-sensitive G proteins. Both SST-14 and SST-28 displayed dose-dependent inhibition of forskolin-stimulated cAMP accumulation, consistent with functional coupling of the receptor to adenylyl cyclase inhibition. Northern blot analysis of SSTR5 mRNA revealed a 2.4-kilobase transcript in normal rat pituitary and GH3 rat pituitary tumor cells and a 4.0-kilobase transcript in normal human pituitary. Reverse transcriptase polymerase chain reaction revealed expression of the hSSTR gene in fetal human pituitary and hypothalamus but not in human cerebral cortex. In situ hybridization of the rat pituitary showed that SSTR5 mRNA is selectively localized in the anterior lobe. SSTR5 mRNA was not expressed in four human pituitary tumors (somatotroph adenoma, prolactinoma, and chromophobe adenomas) or in a human insulinoma. Although hSSTR5 displays approximately 75% sequence identity with rat SSTR5, the two receptors display significantly different pharmacological profiles, especially with respect to their binding affinities for the SST analogue SMS 201-995.
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PMID:Molecular cloning, functional characterization, and chromosomal localization of a human somatostatin receptor (somatostatin receptor type 5) with preferential affinity for somatostatin-28. 790 5

Somatostatin has been shown to exert diverse biological effects in various tissues. Recently, the human genes encoding five subtypes of somatostatin receptor (SSTR1-SSTR5) were cloned. Among these subtypes SSTR2 is present in many endocrine tumors as well as normal tissues and may mediate the effects of somatostatin analog, SMS201-995. In this study, we have investigated the intracellular effect of SSTR2 stably expressed in Chinese hamster ovary cells. Somatostatin-14 does not affect the forskolin stimulated cAMP formation when human SSTR2 is expressed in CHO cells, which lack internal Gi alpha 1 protein. However, somatostatin-14 inhibits the adenylyl cyclase in a dose dependent and pertussis toxin-sensitive manner when human SSTR2 is co-expressed with Gi alpha 1 in CHO cells. These results indicate that human SSTR2 is functionally coupled to Gi alpha 1 protein but not to Gi alpha 2 or Gi alpha 3 when expressed in CHO cells.
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PMID:Human somatostatin receptor, SSTR2, is coupled to adenylyl cyclase in the presence of Gi alpha 1 protein. 791 78

The recent molecular cloning of the genes and cDNAs encoding multiple somatostatin (SRIF) receptor subtypes has allowed for the individual expression of these receptors in mammalian cells and characterization of their respective pharmacological profiles. Previously, we fully described and compared the pharmacological properties of the first three SRIF receptor subtypes, SRIF receptor type (SSTR)1, SSTR2, and SSTR3. In the present study, we have investigated the properties of the newly cloned SRIF receptor subtypes SSTR4 and SSTR5 with regard to pharmacological profiles, the regulation of high affinity agonist binding to these receptors by stable GTP analogues, Na+, or prior exposure to agonists, and the inhibition of forskolin-stimulated cAMP accumulation mediated by these receptors. We labeled SSTR4 and SSTR5 expressed in Chinese hamster ovary (CHO-K1) and COS-1 cells, respectively, with the metabolically stable SRIF analogue 125I-CGP 23996. Radioligand binding competition studies were performed using SRIF analogues of differing structures, including hexapeptide analogues similar to MK-678, octapeptide analogues similar to SMS 201-995, pentapeptide analogues similar to c[Ahep-Phe-D-Trp-Lys-Thr(Bzl)], and linear SRIF analogues. SSTR4 bound compounds in all structural classes with high to moderate affinities, and several compounds were identified that are > 100-fold selective for SSTR4, compared with the other cloned SRIF receptors, including the linear SRIF analogue BIM-23052 and the CGP 23996-like SRIF analogue L-362,855. In contrast, SSTR5 bound very few SRIF analogues with high affinity. Both receptors could be regulated by prior exposure to agonist. In addition, agonist binding to SSTR4 was reduced by stable GTP analogues, Na+, and pertussis toxin, but agonist binding to SSTR5 was not affected by these treatments. SSTR4 is efficiently coupled to the inhibition of adenylyl cyclase activity, whereas SSTR5 appears not to couple to this cellular effector system. Such differences between the cloned SRIF receptors provide useful strategies for identifying regions of these receptor subtypes that may be involved in ligand-binding specificities and G protein and cellular effector system coupling. The identification of subtype-selective SRIF analogues may lead to more specific therapeutic interventions.
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PMID:Characterization of cloned somatostatin receptors SSTR4 and SSTR5. 810 85

The somatostatin receptor subtypes SSTR2 and SSTR5 mediate distinct endocrine and exocrine functions of somatostatin and may also be involved in mediating the neuromodulatory actions of somatostatin in the brain. To investigate whether these receptors couple to voltage-sensitive Ca2+ channels, SSTR2 and SSTR5 selective agonists were tested for their effects on AtT-20 cells using whole cell patch clamp techniques. The SSTR2 selective agonist MK 678 inhibited Ca2+ currents in AtT-20 cells. The effects of MK 678 were reversible and blocked by pertussis toxin pretreatment, suggesting that SSTR2 couples to the L-type Ca2+ channels via G proteins. Other SSTR2-selective agonists, including BIM 23027 and NC8-12, were able to inhibit the Ca2+ currents in these cells. The SSTR5 selective agonist BIM 23052 also inhibited the Ca2+ currents in these cells and this effect was reversible and blocked by pertussis toxin treatment. The ability of SSTR5 to mediate inhibition of the Ca2+ current was greatly attenuated by pretreatment with the SSTR5-selective agonist BIM 23052, whereas SSTR2-mediated inhibition of the Ca2+ current was not altered by pretreatment with the SSTR2-selective agonist MK 678. Thus, the SSTR2 and SSTR5 couplings to the Ca2+ current are differentially regulated. The peptide L362,855, which we previously have shown to have high affinity for the cloned SSTR5, had minimal effects on Ca2+ currents in AtT-20 cells at concentrations up to 100 nM and did not alter the ability of MK 678 to inhibit Ca2+ currents. However, it completely antagonized the effects of the SSTR5-selective agonist BIM 23052 on the Ca2+ currents. L362,855 is an antagonist/partial agonist at SSTR5 since it can reduce Ca2+ currents in these cells at concentrations above 100 nM. L362,855 is also an antagonist/partial agonist at the cloned rat SSTR5 expressed in CHO cells since it is able to block the inhibition of cAMP accumulation induced by somatostatin at concentrations below 100 nM but at higher concentrations can inhibit cAMP formation itself. Structural analysis of L362,855 reveals that only a single hydroxyl group at residue seven in the peptide is needed to convert the compound from an antagonist/partial agonist to a full agonist at SSTR5. These studies reveal that two different somatostatin receptor subtypes, SSTR2 and SSTR5, can mediate the inhibition of an L-type Ca2+ channel in AtT-20 cells by somatostatin. The receptor subtype responses can be distinguished by selective agonists and antagonists and are regulated differently by agonist pretreatment. The inhibition of Ca2+ influx into endocrine cells and neurons may be a major cellular mechanism by which somatostatin modulates hormone and neurotransmitter release. Our results reveal that at least two receptor subtypes can mediate this cellular response.
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PMID:Somatostatin receptor subtypes SSTR2 and SSTR5 couple negatively to an L-type Ca2+ current in the pituitary cell line AtT-20. 868 11

Somatostatin (SRIF) induces its biological actions by interacting with a family of five recently cloned receptors. SRIF receptor subtype, SSTR1, has high affinity for SRIF, but no ligand has been available that selectively binds to this receptor. Desamino acid(1,2,5) [DTryptophan8, N-p-isopropl-4-aminomethyl-l-phenylalanine9]SRIF(des-AA1,2,5 [DT rp8, IAmp9]SRIF inhibits the binding of [125ITyr11]SRIF to the cloned human SSTR1 with an affinity of 1.8+0.7nM, but does not bind to the other cloned SRIF receptors. des-AA1,5[125ITyr2,DTrp8,IAmp9]SRIF bound selectively, potently and saturably to SSTR1 with a Kd of 0.5 + 0.1 nM and a maximal binding density of 226 +/- 56 fmol/mg of protein. The binding of des-AA1,5[125ITyr2,DTrp8,IAmp9]SRIF to SSTR1 was potently inhibited by SRIF, [DTrp8]SRIF, des-AA1,2,5[DTrp8,IAmp9,DSer13]SRIF and SRIF 28 with K, values of 0.7+0.3, 0.2+0.2, 4.3+0.7 and 0.6+0.1 nM, respectively. SRIF analogs that selectively bind to SSTR2 and SSTR5 were impotent in displacing des-AA1,5[125ITyr2,DTrp8,IAmp9]SRIF from human SSTR1. des-AA1,5[125ITyr2,DTrp8,IAmp9]SRIF binding to SSTR1 expressed in COS-7 cells was reduced by GTPgS, and this effect was prevented by pertussis toxin treatment. In contrast, the binding of[125ITyr11]SRIF to SSTR1 was not affected by these treatments. These findings indicate that des-AA1,5[125ITyr2,DTrp8,IAmp9]SRIF may bind to SSTR1 in a defferent manner than SRIF. des-AA1,2,5[DTrp8,IAmp9]SRIF and its tyrosine analog are the first ligands that selectively bind to SSTR1 with high affinity and should be useful in localizing and determining the functional properties of this receptor.
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PMID:Development of a selective agonist at the somatostatin receptor subtype sstr1. 878 39

Somatostatin (SST) controls the proliferation of a variety of cell types. Its effects are mediated by five G protein-coupled receptors (SSTR1-SSTR5), variably expressed in normal and cancer tissues. SST inhibition of cell proliferation can be exploited by both direct and indirect mechanisms: the main direct pathway involves the modulation of phosphotyrosine phosphatase (PTP) activity. Here we show that SST cytostatic activity is mediated by the activation of a receptor-like PTP, named PTPeta. The role of this PTP in the antiproliferative activity of SST in five glioma cell lines (C6, U87MG, U373MG, DBTRG05MG, and CAS1) and in four postsurgical human glioblastoma specimens, has been studied. SST inhibited growth only in C6 and U87MG that express PTPeta. In C6 cells, SST antiproliferative effects were reverted by pretreatment with pertussis toxin and vanadate, indicating the involvement of G proteins and PTPs. The role of PTPeta in the SST inhibitory effects was demonstrated by testing the PTPeta activity: it was increased by SST treatment and paralleled by inhibition of ERK1/2 activation. Since basic fibroblast growth factor-dependent MEK phosphorylation was not affected by SST, we propose a direct effect of SST-activated PTPeta on ERK1/2 phosphorylation. Finally, the SSTR mRNAs were identified in all of the 36 gliomas analyzed, whereas PTPeta expression was found in 33% of cases. Culturing four gliomas, a precise correlation between the expression of PTPeta and the SST antiproliferative effects was identified. In conclusion, in glioma cells, SST antiproliferative activity requires the expression and activation of PTPeta, which directly dephosphorylates ERK1/2.
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PMID:The phosphotyrosine phosphatase eta mediates somatostatin inhibition of glioma proliferation via the dephosphorylation of ERK1/2. 1565 6

Somatostatin (SST) is a peptide hormone that acts through a family of heptahelical receptors belonging to the G-protein coupled receptor (GPCR) superfamily. There are five known SST receptor subtypes termed SSTR1-5 and all couple to G alpha(i/o) G-proteins. It has been previously demonstrated that these receptors can form both homo- and heterodimers within their family or with other GPCR family members. Although agonist was demonstrated as a factor in modulating certain dimeric pairs, the molecular mechanism(s) underlying this regulation remains undetermined. Here, we demonstrate the coupling of G-protein as a contributing factor in the homo- and heterodimerisation of human (h) SSTR2 and SSTR5. When cells stably expressing hSSTR2 are pretreated with pertussis toxin (PTX), dissociation of hSSTR2 dimers occurs. Interestingly, although dimerisation of hSSTR5 was unaffected following PTX treatment, heterodimerisation between hSSTR2 and hSSTR5 is potentiated in the absence of receptor-stimulation. These results demonstrate the importance of G-protein in the maintenance and regulation of hSSTR dimers.
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PMID:The role of G-proteins in the dimerisation of human somatostatin receptor types 2 and 5. 1974 26