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)

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

The diverse biological actions of somatostatin (SRIF) are mediated by a family of receptors, of which five have been cloned and characterized. One of the SRIF receptor subtypes, SSTR2, has been shown to exist in two forms. SSTR2A and SSTR2B are 369 and 346 amino acids in size, respectively, and differ in length and amino acid sequence in their intracellularly located carboxyl termini. SSTR2A and SSTR2B are generated by alternative splicing of SSTR2 mRNA. We previously characterized mouse SSTR2A and showed that it could be distinguished from other cloned SRIF receptor subtypes by its high affinity for MK-678 and its lack of coupling to adenylyl cyclase. To determine whether the properties of mouse SSTR2A and SSTR2B differ, we have expressed both in COS-7 cells and characterized their ligand-binding properties and ability to couple to adenylyl cyclase. The two receptors exhibited similar affinities for a number of SSTR2-selective agonists such as MK-678. Pretreatment with SRIF of COS-7 cells expressing each receptor reduced high affinity agonist binding to both SSTR2A and SSTR2B, indicating that both receptors can be regulated. Furthermore, agonist binding to both receptors was reduced by GTP analogs and Na+, indicating that they both associate with G proteins. As shown previously, SSTR2A could not mediate SRIF inhibition of forskolin-stimulated cAMP formation. In contrast, SSTR2B was coupled to adenylyl cyclase and was able to mediate SRIF inhibition of forskolin-stimulated cAMP formation. Thus, SSTR2A and SSTR2B differ in their ability to couple to adenylyl cyclase. Because SSTR2A and SSTR2B differ only in the length and amino acid sequence of their carboxyl termini, these findings imply that the carboxyl-terminal 15 residues of SSTR2B may be involved in coupling this receptor to adenylyl cyclase.
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PMID:Splice variant of the somatostatin receptor 2 subtype, somatostatin receptor 2B, couples to adenylyl cyclase. 1021 90

The effects of somatostatin analogues RC-160 and SMS-201-995 on tyrosine phosphatase and cell proliferation were investigated in COS-7 and NIH 3T3 cells expressing human somatostatin receptor subtype 1 or 2 (SSTR1 or SSTR2). Binding experiments were performed on membranes from COS-7 cells expressing human SSTR1 or SSTR2 using 125I-labeled [Tyr11]S-14 or [Tyr3]SMS-201-995, respectively. The somatostatin analogues RC-160 and SMS-201-995 exhibited low affinity for SSTR1 (IC50 of 0.43 and 1.5 microM, respectively) and high affinity for SSTR2 (IC50 of 0.27 and 0.19 nM). Addition of these analogues to cells expressing either SSTR1 or SSTR2 did not result in an inhibition of adenylate cyclase activity. In SSTR2-expressing cells, both analogues induced a rapid stimulation of a tyrosine phosphatase activity (EC50: RC-160, 2 pM; SMS-201-995, 6 pM) and an inhibition of serum-stimulated proliferation (EC50: RC-160, 6.3 pM; SMS-201-995, 12 pM). In SSTR1-expressing cells, only RC-160 induced stimulation of a tyrosine phosphatase activity. Both analogues caused an inhibition of cell proliferation at a concentration higher than 10 nM in accordance with their affinities for the SSTR1 receptor subtype. A good correlation between the affinities of RC-160 and SMS-201-995 for each receptor subtype and their potencies to inhibit cell proliferation suggests the involvement of these receptors in cell growth regulation. Tyrosine phosphatase was stimulated by both these analogues in SSTR2 and by RC-160 in SSTR1 at affinities similar to their ability to inhibit growth and bind to receptors, implicating tyrosine phosphatase as a transducer of the growth inhibition signal. We also found that mRNAs of receptor subtypes were variably expressed in different pancreatic and colon cancer cell lines, indicating the necessity of a precise analysis of receptor subtypes in target tissues before therapy with analogues.
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PMID:Stimulation of tyrosine phosphatase and inhibition of cell proliferation by somatostatin analogues: mediation by human somatostatin receptor subtypes SSTR1 and SSTR2. 790 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

COS-7 cells were transfected with human somatostatin (SRIF) receptor type 1 and 2 (human SSTR1 and SSTR2, respectively) cDNAs. In human SSTR2-expressing cells, SRIF not only inhibited forskolin-induced cAMP accumulation but also stimulated phospholipase C and Ca2+ mobilization. While the inhibition of cAMP accumulation was completely reversed by pertussis toxin (PTX) treatment of the cells, SRIF-induced activation of phospholipase C and Ca2+ mobilization was partially but not completely inhibited by the toxin treatment. In human SSTR1-expressing cells, however, SRIF induced only slight inhibition of cAMP accumulation and stimulation of phospholipase C-Ca2+ system. We conclude that the transfected SSTR2 can couple to phospholipase C as well as adenylate cyclase in a stimulatory and inhibitory manner, respectively. Both PTX-sensitive and -insensitive GTP-binding proteins may be involved in the SSTR2 signal transduction mechanisms.
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PMID:Transfected human somatostatin receptor type 2, SSTR2, not only inhibits adenylate cyclase but also stimulates phospholipase C and Ca2+ mobilization. 791 18

We transfected the COS-7 cells with cDNAs encoding different human somatostatin receptor (hSSTR) subtypes, and found that hSSTR subtypes mediate not only the inhibition of forskolin-induced cAMP accumulation but also the stimulation of phospholipase C (PLC) and Ca2+ mobilization. Activation of PLC by 1 microM somatostatin (SRIF) was in the order of: hSSTR5 > hSSTR2 > hSSTR3 > hSSTR4 >> hSSTR1. Pertussis toxin (PTX) treatment completely or partially reversed the PLC activation. 1 nM SRIF was equally effective for adenylate cyclase (AC) inhibition in a PTX-sensitive manner, in all the cells expressing different hSSTRs, except for hSSTR1. Nevertheless, SRIF stimulated AC even in the presence of forskolin at higher doses of SRIF in PTX-treated hSSTR5-expressing cells. We conclude that the cloned hSSTRs differentially couple to PTX-sensitive and -insensitive G-proteins to modulate PLC, Ca2+ mobilization and AC.
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PMID:Phospholipase C activation and Ca2+ mobilization by cloned human somatostatin receptor subtypes 1-5, in transfected COS-7 cells. 803 40

We report here on the cloning of a human intronless gene encoding a member of the G-protein linked somatostatin (SST) receptor subfamily, termed SSTR3. Based on the deduced amino acid sequence, this gene encodes a 418 amino acid protein displaying sequence similarity, particularly within putative transmembrane domains, with the recently cloned human SSTR1 (62%), SSTR2 (64%) and SSTR4 (58%) receptors. Membranes prepared from COS-7 cells transiently expressing the human SSTR3 gene bound [125I]Leu8,D-Trp22,Tyr25 SST-28 in a saturable manner with high affinity (approximately 200 pM) and with rank order of potency (D-Trp8 SST-14 > SST-14 > SMS-201-995 > SST-28) indicative of a somatostatin-14 selective receptor. The pharmacological profile of the expressed human SSTR3 receptor is similar but not identical to that reported for the rat homolog [(1992) J. Biol. Chem. 267, 20422] where the peptide selectivity is SST-28 > or = SST-14 >>> SMS-201-995. Northern blot analysis reveals the presence of an SSTR3 mRNA species of approximately 5 kb in various regions of the monkey brain, including the frontal cortex, cerebellum, medulla, amygdala, with little or no SSTR3 mRNA detectable in brain regions such as the striatum, hippocampus, and olfactory tubercle. The SSTR3 receptor gene maps to human chromosome 22. The existence of at least four distinct human genes encoding somatostatin-14 selective receptors with diverse pharmacological specificities may help to account for some of the multiple biological actions of somatostatin under normal and pathological conditions.
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PMID:A human somatostatin receptor (SSTR3), located on chromosome 22, displays preferential affinity for somatostatin-14 like peptides. 809 79

The recent molecular cloning of the genes encoding three somatostatin (SRIF) receptor subtypes has allowed for the individual expression of these receptors in mammalian cells and characterization of their respective pharmacological profiles. In the present study, we have investigated the affinities of a battery of SRIF analogues to bind to SRIF receptor subtypes SSTR1 (cloned somatostatin complex), SSTR2, and SSTR3, as well as their abilities to inhibit the release of growth hormone from anterior pituitary cells in vitro. We labeled SSTR1 and SSTR3 receptors expressed in Chinese hamster ovary and COS-1 cells, respectively, with the metabolically stable SRIF analogue 125I-CGP 23996. SSTR2 receptors expressed in Chinese hamster ovary cells were labeled with the SSTR2-specific radioligand 125I-MK-678. Inhibition 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)] (SA), and linear SRIF analogues. SSTR1 bound SRIF and SRIF-28 with high affinity and the peptide SA and its structural analogues with low affinity. The hexapeptides did not interact with SSTR1 at concentrations as high as 1 microM, and only a few of the octapeptides or linear peptides bound, with very low affinities. In contrast, 125I-MK-678 binding to SSTR2 was potently inhibited by the hexapeptides, octapeptides, and some of the linear compounds, whereas SA and its analogues did not bind to SSTR2. The potencies of the various SRIF agonists to inhibit growth hormone release in vitro was highly correlated with their potencies to inhibit radioligand binding to SSTR2, but not to SSTR1 or SSTR3. SSTR3 bound analogues of each class but with moderate to low affinities, with the exception of several linear peptides and one of the octapeptides. We report for the first time the binding affinities of linear analogues of SRIF, some of which display subnanomolar affinities and are highly selective for SRIF receptor subtypes. Most importantly, these studies identify several peptide analogues that are highly potent, specific, and selective for individual subtypes of SRIF receptors. Such information, coupled with the knowledge of the distribution of these receptor subtypes in normal and pathological tissues, will be critical for more specific experimental and therapeutic interventions.
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PMID:Cloned somatostatin receptors: identification of subtype-selective peptides and demonstration of high affinity binding of linear peptides. 810 Mar 50

Based on pharmacological, biochemical, and molecular criteria, multiple somatostatin receptor (SSTR) subtypes selective for somatostatin (SST)-14 and -28 have been postulated to exist in both the brain and periphery. We report here on the cloning and characterization of a human gene encoding a new member of the guanine nucleotide-binding protein-linked SSTR family, termed human (h)SSTR4. The 388-amino acid protein, with a predicted molecular mass of approximately 42 kDa, displays sequence similarity, particularly within putative transmembrane domains, with the recently cloned hSSTR1 (69%), hSSTR2 (56%), and hSSTR3 (58%). Membranes prepared from COS-7 cells transiently expressing the hSSTR4 gene bound 125I-[Leu8,D-Trp22,Tyr25]SST-28 in a saturable manner with high affinity (approximately 60 pM) and with a pharmacological profile and rank order of potency ([D-Trp8]SST-14 > SST-14 > SMS 201-995 > SST-28 > MK-678) indicative of a SST-14-selective receptor. Ki values for the inhibition of 125I-[Leu8,D-Trp22,Tyr25]SST-28 binding to the expressed receptor by these somatostatinergic peptides were 0.3, 1.1, 1.4, 2.2, and 6.5 nM, respectively. High affinity agonist binding to hSSTR4 was significantly reduced by GTP and pertussis toxin, indicating association of the expressed receptor with pertussis toxin-sensitive guanine nucleotide-binding proteins. Northern blot analysis revealed the presence of an SSTR4 mRNA species of approximately 4 kilobases in select regions of the monkey brain, including the hippocampus, hypothalamus, cortex, and striatum, with little or no receptor mRNA detected in either the olfactory tubercle, medulla, cerebellum, or amygdala. The SSTR4 gene maps to human chromosome 20. These findings document the existence of a novel human SSTR gene. Although the hSSTR4 displays an overall deduced amino acid homology of 86% with the recently reported rat homolog [Proc. Natl. Acad. Sci. USA 89:11151-11155 (1992)], the two gene products possess distinctive pharmacological profiles and affinities for the SST agonists SMS 201-995 and MK-678.
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PMID:Cloning and expression of a human somatostatin-14-selective receptor variant (somatostatin receptor 4) located on chromosome 20. 810 Mar 52

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


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