Nyegaard M, Borglum AD, Bruun TG, Collier DA, Russ C, Mors O, Ewald H, Kruse TA.
Novel polymorphisms in the somatostatin receptor 5 (SSTR5) gene associated with bipolar affective disorder.
Mol Psychiatry 2002;7(7):745-54
"The somatostatin receptor 5 (SSTR5) gene is a candidate gene for bipolar affective disorder (BPAD) as well as for other neuropsychiatric disorders. The gene is positioned on chromosome 16p13.3, a region that has been implicated by a few linkage studies to potentially harbor a disease susceptibility gene for BPAD. Recent evidence shows that the dopamine D2 receptor (DRD2) and SSTR5 interact physically to form heterodimers with enhanced functional activity. Brain D2 dopamine receptors are one of the major targets of neuroleptic treatments in psychiatric disorders. In this study we systematically screened the promoter and coding region of the SSTR5 gene for genetic variation that could contribute to the development of neuropsychiatric disorders. Eleven novel single nucleotide polymorphisms (SNPs) were identified including four missense SNPs, Leu48Met, Ala52Val, Pro109Ser and Pro335Leu. We carried out an association study of BPAD using 80 Danish cases and 144 control subjects, and replication analysis using 55 British cases and 88 control subjects. For the Danish population, association was suggested between silent SNP G573A and BPAD (P = 0.008). For the British population we found association to BPAD with missense mutation Leu48Met (P = 0.003) and missense mutation Pro335Leu (P = 0.004). The statistical significance of the association was, however, greatly reduced after correcting for multiple testing. When combining genotypes from Leu48Met and Pro335Leu into haplotypes, association to BPAD was found in the British population (P = 0.0007). This haplotype association was not replicated in the Danish population. Our results may indicate that the SSTR5 gene is involved in the etiology of BPAD or may exist in linkage disequilibrium with a susceptibility gene close to SSTR5. However, given the marginal statistical significance and the potential for false-positive results in association studies with candidate genes, further studies are needed to clarify this hypothesis." [Abstract]

Strowski MZ, Dashkevicz MP, Parmar RM, Wilkinson H, Kohler M, Schaeffer JM, Blake AD.
Somatostatin receptor subtypes 2 and 5 inhibit corticotropin-releasing hormone-stimulated adrenocorticotropin secretion from AtT-20 cells.
Neuroendocrinology 2002 Jun;75(6):339-46
"Somatostatin (SRIH) regulates pituitary adrenocorticotropin (ACTH) secretion by interacting with a family of homologous G protein-coupled membrane receptors. The SRIH receptor subtypes (sst(1)-sst(5)) that control ACTH release remain unknown. Using novel, subtype-selective SRIH analogs, we have identified the SRIH receptor subtypes involved in regulating ACTH release from AtT-20 cells, a model for cell line pituitary corticotropes. Radioligand-binding studies with (125)I-SRIH-14 and (125)I-SRIH-28 showed that SRIH-14 and SRIH-28 recognized specific, high-affinity and saturable membrane-binding sites. Nonpeptidyl agonists with selectivity for the sst(2) (L-779,976; compound 2) or sst(1)/sst(5)) (L-817,818; compound 5) receptor subtypes potently displaced (125)I-SRIH-28 from AtT-20 cell membranes, while agonists selective for the sst(1) (L-779,591; compound 1), sst(3) (L-796,778; compound 3) or sst(4) (L-803,087; compound 4) subtypes were inactive. Tyr(11)-SRIH-14, compound 2 (sst(2)) or compound 5 (sst(5)) inhibited forskolin and corticotropin-releasing hormone (CRH)-induced increases in intracellular cAMP. Furthermore, the sst(2) and sst(5) agonists potently inhibited CRH-induced ACTH release from AtT-20 cells. These results provide the first evidence that sst(2) and sst(5) receptor subtypes, but not sst(1), sst(3) or sst(4), inhibit cAMP accumulation and regulate ACTH secretion in the AtT-20 cell model of the rodent corticotrope." [Abstract]

R Day, W Dong, R Panetta, J Kraicer, MT Greenwood, and YC Patel
Expression of mRNA for somatostatin receptor (sstr) types 2 and 5 in individual rat pituitary cells. A double labeling in situ hybridization analysis
Endocrinology 136: 5232-5235, 1995.
"To characterize cell specific expression of sstr subtypes in the pituitary we have analyzed mRNA for sstr1-5 in rat pituitary somatotrophs by reverse transcriptase polymerase chain reaction and determined the pattern and level of expression of mRNA for sstr subtypes 2 and 5 in individual pituitary cell subpopulations by double label in situ hybridization. Purified somatotrophs expressed mRNA for all 5 sstrs. In situ hybridization analysis revealed sstr5 mRNA in 70% of somatotrophs, 57% of thyrotrophs, 38% of corticotrophs, 33% of lactotrophs, and 21% of gonadotrophs. mRNA for sstr2 occurred in 40% of somatotrophs, 36% of thyrotrophs, 26% of lactotrophs, 3% of corticotrophs, and 8% of gonadotrophs. Not only were more cells positive for sstr5 mRNA but the average number of autoradiographic grains/cell was also higher for sstr5 than sstr2. These results show expression of multiple sstr genes in individual pituitary cells. mRNA for sstr2 and 5 occur in each of the 5 major pituitary cell subsets, sstr5 mRNA being more widely and more abundantly expressed than sstr2." [Abstract/Full Text]

Shimon I.
Somatostatin receptors in pituitary and development of somatostatin receptor subtype-selective analogs.
Endocrine. 2003 Apr;20(3):265-9.
"Somatostatin receptor (SSTR) subtypes 1, 2, and 5 are expressed in the normal human pituitary. SSTR2 and SSTR5 are expressed in almost all growth hormone (GH) cell adenomas, and prolactin (PRL)-secreting tumors express SSTR5 more than SSTR2. SSTR4 is not detected in all pituitary adenoma subtypes, and SSTR1 and SSTR3 are expressed in about 50% of tumors. Human GH is regulated through ligand binding to both SSTR2 and SSTR5, but octreotide and lanreotide, the two clinically available somatostatin analogs, bind to human SSTR2 much better than to SSTR5. Novel SSTR2- and SSTR5- selective analogs with improved binding affinity for these receptor subtypes are highly potent in suppressing GH release from cultures of human fetal pituitaries or GH-cell adenomas. Only SSTR5-selective analogs suppress in vitro PRL secretion from cultured prolactinomas. A new SSTR2+5 bispecific analog with high affinity and selectivity for both SSTR2 and SSTR5, and a somatostatin analog with a unique broad receptor (SSTR1, 2, 3, and 5) binding profile, are both able to inhibit in vitro GH release in GH cell adenomas partially sensitive to octreotide. Recently, a somatostatindopamine hybrid molecule was introduced with potentially functional synergy on GH and PRL release. Using the expanding knowledge on SSTRs and their ligand activation, the development of novel pharmacologic concepts may open new opportunities for effective manipulation of this complex intracellular signaling system. These concepts may achieve better control of pituitary hormone hypersecretion, pituitary size, as well as antitumor effects in patients with SSTR-expressing tumors." [Abstract]

Norman M, Moldovan S, Seghers V, Wang XP, DeMayo FJ, Brunicardi FC.
Sulfonylurea receptor knockout causes glucose intolerance in mice that is not alleviated by concomitant somatostatin subtype receptor 5 knockout.
Ann Surg 2002 Jun;235(6):767-74
"OBJECTIVE: To examine the long-term effects of Sur KO, SSTR5 KO, and double Sur/SSTR5 KO on insulin secretion and glucose regulation. SUMMARY BACKGROUND DATA: The sulfonylurea receptor (Sur) and somatostatin receptor type 5 (SSTR5) play an integral role in the regulatory pathways of the endocrine pancreas. Sur knockout (KO) and SSTR5 KO mice were generated in the authors' laboratories and crossbred to generate Sur/SSTR5 KO mice. All mice were genotyped by Southern blotting and polymerase chain reaction analysis. METHODS: One-year-old Sur KO, Sur/SSTR5 KO, SSTR5 KO, and age-matched wild-type control mice underwent single-pass perfusion of isolated pancreata with low and high glucose concentration (n = 4-6/group). Another group of mice also underwent intraperitoneal glucose tolerance tests with 1.2 g glucose/kg body weight (n = 4/group per time point). RESULTS: Sur1 KO and Sur/SSTR5 KO mice had profoundly decreased insulin secretion in vitro, whereas SSTR5 KO had increased insulin secretion compared with wild-type mice. Sur1 KO and Sur/SSTR5 mice had increased glucose response in vivo compared with wild-type mice. Sur1 KO and Sur/SSTR5 KO mice exhibit glucose intolerance and SSTR5 KO mice show increased insulin response in vitro. CONCLUSIONS: Sur1 KO causes glucose intolerance and SSTR5 KO causes increased insulin secretion. However, Sur/SSTR5 double ablation does not alleviate the diabetic state of the Sur1 KO." [Abstract]

Zambre Y, Ling Z, Chen MC, Hou X, Woon CW, Culler M, Taylor JE, Coy DH, Van Schravendijk C, Schuit F, Pipeleers DG, Eizirik DL.
Inhibition of human pancreatic islet insulin release by receptor-selective somatostatin analogs directed to somatostatin receptor subtype 5.
Biochem Pharmacol 1999 May 15;57(10):1159-64
"In order to identify the subtype responsible for inhibition of insulin release by human B cells, SSTR-selective SS analogs were tested in isolated human islets. Glucose-stimulated insulin secretion in human islets incubated for 1 hr at 20 mM glucose, and in islets cultured for 24 hr at a near-physiological (6.1 mM) glucose concentration, was inhibited (<50% of the control) by SSTR5-specific analogs and by SS14 and SS28. SS14, SS28, and different SSTR5 preferential analogs also inhibited islet amyloid polypeptide release during the 24-hr culture. On the other hand, a group of SSTR2-selective analogs failed to inhibit insulin release. Analysis by reverse transcription-polymerase chain reaction indicated that human islets express similar amounts of SSTR2 and SSTR5 mRNAs, while human pancreatic ductal cells express much lower levels of these mRNAs. In conclusion, our data suggest that SSTR5 is an important mediator of the insulin inhibitory action of SS in cultured human islets." [Abstract]

Cattaneo MG, Taylor JE, Culler MD, Nisoli E, Vicentini LM.
Selective stimulation of somatostatin receptor subtypes: differential effects on Ras/MAP kinase pathway and cell proliferation in human neuroblastoma cells.
FEBS Lett 2000 Sep 22;481(3):271-6
"In previous studies we have showed that somatostatin (SST) inhibits cell division, mitogen-activated protein (MAP) kinase and Ras activity in the human neuroblastoma cell line SY5Y. In the present study, we have assessed the role of a series of SST analogs, three of which were selective for SSTR1, SSTR2 or SSTR5, in these cellular events. All the analogs inhibited forskolin-induced cAMP accumulation. Selective stimulation of SSTR1 or SSTR2 but not of SSTR5 inhibited platelet-derived growth factor (PDGF)-induced [(3)H]thymidine incorporation. The three analogs inhibited PDGF-stimulated MAP kinase activity, at least at an early time. In contrast, none of the analogs used individually was able to inhibit PDGF-stimulated Ras activity. A combined stimulation of SSTR2 and SSTR5 was necessary to obtain a significant inhibitory effect, suggesting the possibility of receptor heterodimerization. These results indicate that SST inhibition of Ras and MAP kinase activities takes place via different pathways and that SST inhibition of PDGF-induced cell proliferation occurs via a Ras-independent pathway." [Abstract]

Shimokawa I, Yanagihara K, Higami Y, Okimoto T, Tomita M, Ikeda T, Lee S.
Effects of aging and dietary restriction on mRNA levels of receptors for growth hormone-releasing hormone and somatostatin in the rat pituitary.
J Gerontol A Biol Sci Med Sci 2000 Jun;55(6):B274-9
"Aging impairs and dietary restriction may modulate pituitary response to growth hormone (GH)-releasing hormone (GHRH) and somatostatin (SRIH) for GH secretion. Using the semiquantitative reverse-transcription polymerase chain reaction method, we analyzed the mRNA levels of the GHRH receptor (grfr) and SRIH receptor subtype 2 (sstr2) and subtype 5 (sstr5) in anterior pituitaries of male rats fed ad libitum or 30% dietary restricted. Aging reduced the mRNA levels of these receptors in a slightly different manner. The levels of grfr progressively decreased between 6 and 24 months, whereas those of sstr2 and sstr5 declined after 16 months. Dietary restriction did not diminish the aging-dependent changes, although it slightly augmented the levels of grfr, but not sstr2 and sstr5. The present results suggest that the aging-dependent impairment in pituitary response for GH secretion could result mostly from a decline in grfr rather than relative increase of sstrs. Although DR could slightly enhance the pituitary sensitivity to GHRH, the antiaging action may be minor at the level of gene expression." [Abstract]

Pierre Cordelier, Jean-Pierre Estève, Corinne Bousquet, Nathalie Delesque, Anne-Marie O'Carroll, Andrew V. Schally, Nicole Vaysse, Christiane Susini, and Louis Buscail
Characterization of the antiproliferative signal mediated by the somatostatin receptor subtype sst5
PNAS 94: 9343-9348, August 1997.
"We conclude that, in CHO cells, CCK and somatostatin modulate cell proliferation and MAP kinase signaling cascade through a cGMP-dependent pathway. These effects are positively regulated through CCKA receptors and negatively controlled through sst5 receptors." [Full Text]

L Buscail, J Esteve, N Saint-Laurent, V Bertrand, T Reisine, A O'Carroll, GI Bell, AV Schally, N Vaysse, and C Susini
Inhibition of Cell Proliferation by the Somatostatin Analogue RC-160 is Mediated by Somatostatin Receptor Subtypes SSTR2 and SSTR5 Through Different Mechanisms
PNAS 92: 1580-1584.
"Cell proliferation was induced in CHO cells by 10% (vol/vol) fetal calf serum, 1 µM insulin, or 0.1 µM cholecystokinin (CCK)-8; RC-160 inhibited serum-induced proliferation of CHO cells expressing SSTR2 and SSTR5 (EC50, 53 and 150 pM, respectively) but had no effect on growth of cells expressing SSTR1, -3, or -4. In SSTR2-expressing cells, orthovanadate suppressed the growth inhibitory effect of RC-160. This analogue inhibited insulin-induced proliferation and rapidly stimulated the activity of a tyrosine phosphatase in only this cellular clone. This latter effect was observed at doses of RC-160 (EC50, 4.6 pM) similar to those required to inhibit growth (EC50, 53 pM) and binding to the receptor (IC50, 170 pM), implicating tyrosine phosphatase as a transducer of the growth inhibition signal in SSTR2-expressing cells. In SSTR5-expressing cells, the phosphatase pathway was not involved in the inhibitory effect of RC-160 on cell growth, since this action was not influenced by tyrosine and serine/threonine phosphatase inhibitors. In addition, in SSTR5-expressing cells, RC-160 inhibited CCK-stimulated intracellular calcium mobilization at doses (EC50, 0.35 nM) similar to those necessary to inhibit somatostatin-14 binding (IC50, 21 nM) and CCK-induced cell proliferation (EC50, 1.1 nM). This suggests that the inositol phospholipid/calcium pathway could be involved in the antiproliferative effect of RC-160 mediated by SSTR5 in these cells. RC-160 had no effect on the basal or carbachol-stimulated calcium concentration in cells expressing SSTR1 to -4. Thus, we conclude that SSTR2 and SSTR5 bind RC-160 with high affinity and mediate the RC-160-induced inhibition of cell growth by distinct mechanisms." [Abstract/Full Text]

Kamal Sharma, Yogesh C. Patel, and Coimbatore B. Srikant
C-Terminal Region of Human Somatostatin Receptor 5 Is Required for Induction of Rb and G1 Cell Cycle Arrest
Mol. Endocrinol. 13: 82-90, 1999.
"To determine whether the antiproliferative signaling via these hSSTRs causes cell cycle arrest and to identify the molecular mediators involved in this process, we evaluated the effect of SST in CHO-K1 cells expressing hSSTRs 1, 2, 4, and 5 on cell cycle progression and induction of Rb and p21. We report here that SST-induced G1 cell cycle arrest in these cells is due mainly to the induction of Rb. Maximal effect was exerted via hSSTR5 followed by hSSTR 2, 4, and 1. In hSSTR5-expressing cells, a major portion of SST-induced Rb was hypophosphorylated. SST-induced G1 arrest and induction of Rb were pertussis toxin sensitive, G protein dependent, and protein tyrosine phosphatase (PTP) dependent. In octreotide (OCT)-treated cells there was a redistribution of PTP activity from the cytosol to the membrane. Mutational analysis of the C tail of this receptor revealed that the C tail of the receptor is essential for PTP-dependent cytostatic signaling." [Full Text]

Seungjoon Park, Jun Kamegai, Todd A. Johnson, Lawrence A. Frohman, and Rhonda D. Kineman
Modulation of Pituitary Somatostatin Receptor Subtype (sst1–5) Messenger Ribonucleic Acid Levels by Changes in the Growth Hormone Axis
Endocrinology 141: 3556-3563, 2000. [Full Text]

Whitney W. Woodmansee, Rhonda L. Mouser, David F. Gordon, Janet M. Dowding, William M. Wood, and E. Chester Ridgway
Mutational Analysis of the Mouse Somatostatin Receptor Type 5 Gene Promoter
Endocrinology 143: 2268-2276, 2002.
"We have previously characterized the structure of the murine somatostatin receptor type 5 gene (sst5). Initial transient transfection studies in pituitary somatolactotropes (GH3) mapped the promoter activity of this gene to a region 290 bp upstream of the transcription start site. The current study identifies the sst5 promoter region critical for basal activity. A series of deletions was generated, and promoter activity was localized to a region between -83 and -19. Similar promoter deletion patterns were evident in five pituitary cell types. Seven 10-bp transversion mutations encompassing the region between -83 and -19 were generated, and functional activity was assessed. Promoter activity was reduced by the mutations spanning -67 to -47 compared with the wild-type construct. Another mutation between -26 and -17 resulted in promoter activity reduction in GH3 cells, but not TtT-97 thyrotropes. Deoxyribonuclease I protection analysis of the sst5 promoter region between -208/+47 was performed using GH3 and TtT-97 nuclear extracts. The most striking protected regions, located between -61 and -41 and -25 and -3, correlated with functionally important regions identified by transfection studies. In summary, the mouse sst5 gene promoter has been characterized, and functional activity and nuclear factor interactions were mapped to two specific promoter regions. The region between -67 and -47 appears to contain a nucleotide sequence critical for basal transcriptional regulation of the mouse sst5 gene in pituitary cells." [Abstract]

Ujendra Kumar, Dale Laird, Coimbatore B. Srikant, Emanuel Escher, and Yogesh C. Patel
Expression of the Five Somatostatin Receptor (SSTR1-5) Subtypes in Rat Pituitary Somatotrophes: Quantitative Analysis by Double-Label Immunofluorescence Confocal Microscopy
Endocrinology 138: 4473-4476, 1997.
"Using quantitative double-label fluorescence immunocytochemistry and confocal microscopy, we have analysed the pattern of expression of SSTR1-5 in normal rat pituitary somatotrophes. Antipeptide rabbit polyclonal antibodies were produced against the extracellular domains of SSTR1-5. SSTR antigens were colocalized in GH positive cells using rhodamine conjugated secondary antibody for SSTRs and FITC-conjugated secondary antibody for GH. SSTR5 was the predominant subtype which was expressed in 86 ± 9.7% of GH cells followed by SSTR2 in 42 ± 6.4% of GH positive cells. SSTR4 and SSTR3 were modestly expressed in 23 ± 4.7% and 18 ± 3.2% of somatotrophes respectively whereas SSTR1 was the least expressed subtype occurring in only 5 ± 1.2% of somatotrophes. These results demonstrate variable expression of the 5 SSTRs in somatotrophes. The preponderance of the SST-28 preferring SSTR5 subtype correlates with the reported higher potency of SST-28 than SST-14 for inhibiting GH secretion." [Abstract]

Stroh T, Kreienkamp HJ, Beaudet A.
Immunohistochemical distribution of the somatostatin receptor subtype 5 in the adult rat brain: predominant expression in the basal forebrain.
J Comp Neurol 1999 Sep 13;412(1):69-82
"Somatostatin exerts its actions by means of a family of G protein-coupled receptors, five of which have so far been cloned. Whereas mRNAs for receptor subtypes sst(1)-sst(4) have been unequivocally localized in the brain, the data concerning the fifth subtype, sst(5), are contradictory. Moreover, whereas sst(1) and sst(2A) receptor proteins have been localized by immunohistochemistry, the distribution of sst(3)-sst(5) receptor proteins and/or subtype-specific binding remains to be determined in the central nervous system. In the present study, we investigated the distribution of immunoreactive sst(5) in adult rat brain and pituitary and demonstrated the presence of this receptor protein in the central nervous system by using an affinity-purified antibody generated against the C-terminus of the receptor. The specificity of the antibody for sst(5) was established by immunoblotting experiments on membranes prepared from cells transfected with cDNA encoding different somatotropin release inhibiting (SRIF) receptor subtypes as well as from anterior pituitary. In both systems, the antibody specifically recognized a band at approximately 50 kDa molecular mass, corresponding well to the reported size of the cloned receptor (48 kDa). Immunofluorescence in COS-7 cells transfected with individual SRIF receptor subtypes as well as in sections of rat pituitary demonstrated the antibody's applicability to the immunohistochemical detection of sst(5) receptors. In rat brain sections, sst(5) immunoreactivity was predominantly associated with neuronal perikarya and primary dendrites. Immunolabeling was most prominent in the olfactory tubercle, islands of Calleja, diagonal band of Broca, substantia innominata, and magnocellular preoptic nucleus of the basal forebrain as well as in the reticular nucleus of the thalamus. Other, less intensely labeled areas included the cerebral cortex, hippocampus, amygdala, preoptic area as well as the lateroanterior nucleus of the hypothalamus. The present findings provide the first characterization of the anatomic distribution of sst(5) receptors in the rat brain. They demonstrate a prominent expression of these receptors in the basal forebrain, suggesting that they may be involved in the mediation of somatostatin effects on the sleep-wake cycle through their association with cortically projecting subcortical systems. Copyright 1999 Wiley-Liss, Inc." [Abstract]

Akbar M, Okajima F, Tomura H, Majid MA, Yamada Y, Seino S, Kondo Y.
Phospholipase C activation and Ca2+ mobilization by cloned human somatostatin receptor subtypes 1-5, in transfected COS-7 cells.
FEBS Lett 1994 Jul 11;348(2):192-6
"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." [Abstract]

Philippe Sarret, Dominique Nouel, Claude Dal Farra, Jean-Pierre Vincent, Alain Beaudet, and Jean Mazella
Receptor-mediated Internalization Is Critical for the Inhibition of the Expression of Growth Hormone by Somatostatin in the Pituitary Cell Line AtT-20
J. Biol. Chem. 274: 19294-19300, July 1999.
"The inhibitory effect of the neuropeptide somatostatin on the expression of growth hormone was measured by quantitative polymerase chain reaction in the pituitary cell line AtT-20. We demonstrate that this effect is dependent on the internalization of somatostatin-receptor complexes and that it is totally independent from the peptide-induced inhibition of adenylate cyclase. Indeed, the inhibitory effect of the peptide on growth hormone mRNA levels was totally insensitive to pertussis toxin treatment but was totally abolished under conditions which block somatostatin receptor internalization. Comparative confocal microscopic imaging of fluorescent somatostatin sequestration and fluorescence immunolabeling of sst1, sst2A, and sst5 receptors suggests that sst2A is most probably responsible of the inhibitory effect of somatostatin on growth hormone expression." [Full Text]

Lamberts, Steven W.J., van der Lely, Aart-Jan, de Herder, Wouter W., Hofland, Leo J.
Octreotide
N Engl J Med 1996 334: 246-254
"The clinical introduction of somatostatin analogues has resulted in new insights into the physiology of a number of organ systems. Despite the broad range of physiologic actions of somatostatin, its analogues control hormonal hypersecretion by somatostatin-receptor–positive endocrine tumors without serious side effects. The subtypes of somatostatin receptors on these tumors may turn over at a different rate from those on normal tissue. Therefore, the inhibitory effects of octreotide on hormonal hypersecretion by endocrine tumors persist, whereas adaptation occurs in most normal somatostatin target tissues, thus preventing serious side effects." [Full Text]

Rocheville M, Lange DC, Kumar U, Patel SC, Patel RC, Patel YC.
Receptors for dopamine and somatostatin: formation of hetero-oligomers with enhanced functional activity.
Science 2000 Apr 7;288(5463):154-7
"Somatostatin and dopamine are two major neurotransmitter systems that share a number of structural and functional characteristics. Somatostatin receptors and dopamine receptors are colocalized in neuronal subgroups, and somatostatin is involved in modulating dopamine-mediated control of motor activity. However, the molecular basis for such interaction between the two systems is unclear. Here, we show that dopamine receptor D2R and somatostatin receptor SSTR5 interact physically through hetero-oligomerization to create a novel receptor with enhanced functional activity. Our results provide evidence that receptors from different G protein (heterotrimeric guanine nucleotide binding protein)-coupled receptor families interact through oligomerization. Such direct intramembrane association defines a new level of molecular crosstalk between related G protein-coupled receptor subfamilies." [Abstract]

Jeffrey C. Liu, Ross E. Baker, Clement Sun, Valdine C. Sundmark, and Harry P. Elsholtz
Activation of Go-coupled Dopamine D2 Receptors Inhibits ERK1/ERK2 in Pituitary Cells. A KEY STEP IN THE TRANSCRIPTIONAL SUPPRESSION OF THE PROLACTIN GENE
J. Biol. Chem. 277: 35819-35825, September 2002.
"In pituitary lactotrophs the prolactin gene is stimulated by neuropeptides and estrogen and is suppressed by dopamine via D2-type receptors. Stimulatory signals converge on activation of the mitogen-activated protein kinases ERK1/2, but dopamine regulation of this pathway is not well defined. Paradoxically, D2 agonists activate ERK1/2 in many cell types. Here we show that in prolactin-secreting GH4ZR7 cells and primary pituitary cells, dopamine treatment leads to a rapid, pronounced, and specific decrease in activated ERK1/2. The response is blocked by D2-specific antagonists and pertussis toxin. Interestingly, in stable lines expressing specific pertussis toxin-resistant G subunits, toxin treatment blocks dopamine suppression of MAPK in Gi2- but not Go-expressing cells, demonstrating that Go-dependent pathways can effect the inhibitory MAPK response. At the nuclear level, the MEK1 inhibitor U0126 mimics the D2-agonist bromocryptine in suppressing levels of endogenous prolactin transcripts. Moreover, a good correlation is seen between the IC50 values for inhibition of MEK1 and suppression of prolactin promoter function (PD184352 > U0126 > U0125). Both dopamine and U0126 enhance the nuclear localization of ERF, a MAPK-sensitive ETS repressor that inhibits prolactin promoter activity. In addition, U0126 suppression is transferred by tandem copies of the Pit-1-binding site, consistent with mapping experiments for dopamine responsiveness. Our data suggest that ERK1/2 suppression is an obligatory step in the dopaminergic control of prolactin gene transcription and that bidirectional control of ERK1/2 function in the pituitary may provide a key mechanism for endocrine gene control." [Abstract]

Ramesh C. Patel, Ujendra Kumar, Don C. Lamb, John S. Eid, Magalie Rocheville, Michael Grant, Aruna Rani, Theodore Hazlett, Shutish C. Patel, Enrico Gratton, and Yogesh C. Patel
Ligand binding to somatostatin receptors induces receptor-specific oligomer formation in live cells
PNAS 99: 3294-3299, March 2002.
"Heptahelical receptors (HHRs) are generally thought to function as monomeric entities. Several HHRs such as somatostatin receptors (SSTRs), however, form homo- and heterooligomers when activated by ligand binding. By using dual fluorescent ligands simultaneously applied to live cells monotransfected with SSTR5 (R5) or SSTR1 (R1), or cotransfected with R5 and R1, we have analyzed the ligand receptor stoichiometry and aggregation states for the three receptor systems by fluorescence resonance energy transfer and fluorescence correlation spectroscopy. Both homo- and heterooligomeric receptors are occupied by two ligand molecules. We find that monomeric, homooligomeric, and heterooligomeric receptor species occur in the same cell cotransfected with two SSTRs, and that oligomerization of SSTRs is regulated by ligand binding by a selective process that is restricted to some (R5) but not other (R1) SSTR subtypes. We propose that induction by ligand of different oligomeric states of SSTRs represents a unique mechanism for generating signaling specificity not only within the SSTR family but more generally in the HHR family." [Full Text]

Komatsuzaki K, Terashita K, Kinane TB, Nishimoto I.
Somatostatin type V receptor activates c-Jun N-terminal kinases via Galpha(12) family G proteins.
Biochem Biophys Res Commun 2001 Dec 21;289(5):1211-7
"Somatostatin is a neurotransmitter with diverse effects including anti-proliferation in a wide range of normal and neoplastic cells, and occasionally growth stimulatory and neurotrophic actions. Stress-activated protein kinase or c-Jun N-terminal kinase (SAPK/JNK) can also induce growth arrest and occasionally growth stimulation. However, the relationship between somatostatin and SAPK/JNK is less clear. Here we report that the binding of somatostatin to the somatostatin receptor type V (SSTR5) upregulates SAPK/JNK activity. We also show that this activation is mediated by Galpha(12) and Galpha(13). This study demonstrates that SSTR5 is the heptahelical receptor that activates SAPK/JNK via the G(12) family G proteins." [Abstract]

Saveanu A, Morange-Ramos I, Gunz G, Dufour H, Enjalbert A, Jaquet P.
A luteinizing hormone-, alpha-subunit- and prolactin-secreting pituitary adenoma responsive to somatostatin analogs: in vivo and in vitro studies.
Eur J Endocrinol 2001 Jul;145(1):35-41
"RESULTS: This adenoma presented with high levels of SSTR2, SSTR3 and SSTR5 mRNAs, as compared with a series of gonadotroph adenomas. In cell culture studies, PRL, LH and alpha-subunit were inhibited by 60%, 47% and 33% respectively by SRIF-14 at a concentration of 10 nmol/l. The SSTR2 (BIM-23197, lanreotide) and SSTR5 (BIM-23268) preferential analogues both produced a partial 21-38% inhibition of PRL, LH, and alpha-subunit release. DISCUSSION: In this plurihormonal-secreting adenoma, the high efficacy of somatostatin analogues to inhibit PRL, LH and alpha-subunit secretion in vivo may be explained by the unusually high level of expression and by the functionality of both SSTR2 and SSTR5 receptor subtypes." [Abstract]

Patel YC.
Somatostatin and its receptor family.
Front Neuroendocrinol 1999 Jul;20(3):157-98
"Somatostatin (SST), a regulatory peptide, is produced by neuroendocrine, inflammatory, and immune cells in response to ions, nutrients, neuropeptides, neurotransmitters, thyroid and steroid hormones, growth factors, and cytokines. The peptide is released in large amounts from storage pools of secretory cells, or in small amounts from activated immune and inflammatory cells, and acts as an endogenous inhibitory regulator of the secretory and proliferative responses of target cells that are widely distributed in the brain and periphery. These actions are mediated by a family of seven transmembrane (TM) domain G-protein-coupled receptors that comprise five distinct subtypes (termed SSTR1-5) that are endoded by separate genes segregated on different chromosomes. The five receptor subtypes bind the natural SST peptides, SST-14 and SST-28, with low nanomolar affinity. Short synthetic octapeptide and hexapeptide analogs bind well to only three of the subtypes, 2, 3, and 5. Selective nonpeptide agonists with nanomolar affinity have been developed for four of the subtypes (SSTR1, 2, 3, and 4) and putative peptide antagonists for SSTR2 and SSTR5 have been identified. The ligand binding domain for SST ligands is made up of residues in TMs III-VII with a potential contribution by the second extracellular loop. SSTRs are widely expressed in many tissues, frequently as multiple subtypes that coexist in the same cell. The five receptors share common signaling pathways such as the inhibition of adenylyl cyclase, activation of phosphotyrosine phosphatase (PTP), and modulation of mitogen-activated protein kinase (MAPK) through G-protein-dependent mechanisms. Some of the subtypes are also coupled to inward rectifying K(+) channels (SSTR2, 3, 4, 5), to voltage-dependent Ca(2+) channels (SSTR1, 2), a Na(+)/H(+) exchanger (SSTR1), AMPA/kainate glutamate channels (SSTR1, 2), phospholipase C (SSTR2, 5), and phospholipase A(2) (SSTR4). SSTRs block cell secretion by inhibiting intracellular cAMP and Ca(2+) and by a receptor-linked distal effect on exocytosis. Four of the receptors (SSTR1, 2, 4, and 5) induce cell cycle arrest via PTP-dependent modulation of MAPK, associated with induction of the retinoblastoma tumor suppressor protein and p21. In contrast, SSTR3 uniquely triggers PTP-dependent apoptosis accompanied by activation of p53 and the pro-apoptotic protein Bax. SSTR1, 2, 3, and 5 display acute desensitization of adenylyl cyclase coupling. Four of the subtypes (SSTR2, 3, 4, and 5) undergo rapid agonist-dependent endocytosis. SSTR1 fails to be internalized but is instead upregulated at the membrane in response to continued agonist exposure. Among the wide spectrum of SST effects, several biological responses have been identified that display absolute or relative subtype selectivity. These include GH secretion (SSTR2 and 5), insulin secretion (SSTR5), glucagon secretion (SSTR2), and immune responses (SSTR2). Copyright 1999 Academic Press." [Abstract]

Tulipano G, Bonfanti C, Milani G, Billeci B, Bollati A, Cozzi R, Maira G, Murphy WA, Poiesi C, Turazzi S, Giustina A.
Differential inhibition of growth hormone secretion by analogs selective for somatostatin receptor subtypes 2 and 5 in human growth-hormone-secreting adenoma cells in vitro.
Neuroendocrinology 2001 May;73(5):344-51
"We conclude that the availability of somatostatin analogs selective for SSTR5 will enhance the treatment potency and spectrum in acromegaly." [Abstract]

Rohrer SP, Schaeffer JM.
Identification and characterization of subtype selective somatostatin receptor agonists.
J Physiol Paris 2000 May-Aug;94(3-4):211-5
"High affinity, subtype selective non-peptide agonists of somatostatin receptor subtypes 1-5 were identified in combinatorial libraries constructed based on molecular modeling of known peptide agonists. Simultaneous traditional chemical synthesis yielded an additional series of somatostatin subtype-2 receptor (SSTR2) selective agonists. These compounds have been used to further define the physiological functions of the individual somatostatin receptor subtypes. In vitro experiments demonstrated the role of the SSTR2 in inhibition of glucagon release from mouse pancreatic alpha-cells and the somatostatin subtype-5 receptor (SSTR5) as a mediator of insulin secretion from pancreatic beta-cells. Both SSTR2 and SSTR5 regulated growth hormone release from the rat anterior pituitary gland. In vivo studies performed with SSTR2 receptor selective compounds demonstrated effective inhibition of pulsatile growth hormone release in rats. The SSTR2 selective compounds also lowered plasma glucose levels in normal and diabetic animal models. The availability of high affinity, subtype selective non-peptide agonists for each of the somatostatin receptors provides a direct approach to defining their physiological function both peripherally and in the central nervous system." [Abstract]

Suich DJ, Mousa SA, Singh G, Liapakis G, Reisine T, DeGrado WF.
Template-constrained cyclic peptide analogues of somatostatin: subtype-selective binding to somatostatin receptors and antiangiogenic activity.
Bioorg Med Chem 2000 Sep;8(9):2229-41
"Template-constrained cyclic peptides in which the ends of the -Tyr-D-Trp-Lys-Val-tetrapeptide were linked by scaffolds based on either an N,N'-dimethyl-N,N'-diphenylurea or a substituted biphenyl system (DJS631 and DJS811, respectively), bound selectively to mouse SSTR2B and rat and human SSTR5 with affinities as high as 1 nM. DJS811, at a dose of 3 mg/kg/day, was shown in a mouse Matrigel model to inhibit angiogenesis to a level of 79%. The development of structured turn scaffolds allows beta-turn sequences to be contained in the context of a compact structure, with less peptidic nature and potentially greater bioavailability than cyclic hexapeptides. These systems can be used to study the determinants of beta-turn formation, as well as to probe the importance of turn sequences occurring in molecular recognition interactions. The antiangiogenic activity of DJS811 suggests that it may have antitumor activity as well. In addition, because SSTR2 is overexpressed on many types of tumors, DJS631 and DJS811 may be useful in the development of agents for tumor imaging or the radiotherapy of cancer." [Abstract]

Emilia Ballarè, Luca Persani, Andrea G. Lania, Marcello Filopanti, Enza Giammona, Sabrina Corbetta, Simona Mantovani, Maura Arosio, Paolo Beck-Peccoz, Giovanni Faglia, and Anna Spada
Mutation of Somatostatin Receptor Type 5 in an Acromegalic Patient Resistant to Somatostatin Analog Treatment
J. Clin. Endocrinol. Metab. 86: 3809-3814, 2001.
"Introduction of somatostatin analogs has greatly contributed to improving the prognosis of acromegaly. Although the majority of patients are effectively treated by these agents, resistance occurs in a subset of patients. So far, resistance to somatostatin has never been associated with mutations of the somatostatin receptor subtypes (sst2 and sst5) that inhibit GH secretion. Molecular analysis of genomic DNA from pituitary tumor and peripheral blood obtained from an acromegalic resistant to octreotide showed a somatic activating mutation of Gs (Arg201Cys), no mutation in sst2, and one polymorphism (Pro109Ser) and one germ line mutation (Arg240Trp) in sst5. Wild-type (WT) and mutant sst5 PCR products were cloned and transfected into Chinese hamster ovary K1 cells. In Chinese hamster ovary K1 cells stably expressing mutant sst5, somatostatin-28 was less potent in inhibiting cyclic AMP levels than in WT cells. Proliferation of mutant cells exceeded that of WT by 50%. Moreover, somatostatin reduced cell growth and MAPK activity in WT but not in mutant cells in which the peptide even increased MAPK activity. We suggest that this mutation that abrogates the antiproliferative action of somatostatin and activates mitogenic pathways may be involved in the resistance to somatostatin treatment." [Full Text]

S. Petersenn, A. C. Rasch, C. Böhnke, and H. M. Schulte
Identification of an Upstream Pituitary-Active Promoter of Human Somatostatin Receptor Subtype 5
Endocrinology 143: 2626-2634, 2002.
"Somatostatin receptor subtype 5 (sst5) has been linked to inhibition of PRL and insulin secretion. We characterized the genomic structure of the human sst5. The transcription start site was located 94 nucleotides upstream of the initiator ATG codon. Sequence analysis of 5'-inverse PCR products revealed the presence of a 6.1-kb intron in the 5'-untranslated region. RT-PCR analysis indicated tissue-specific activation of the newly identified upstream promoter in pituitary, but not in small intestine, lung, or placenta. A -1741 promoter directed significant levels of luciferase expression in GH4 rat pituitary cells, Skut-1B endometrium cells, and JEG3 chorion carcinoma cells, which was absent in COS-7 monkey kidney cells. A minimal -101 promoter was sufficient to allow tissue-specific expression. Its activity in COS-7 cells was not enhanced by cotransfection of the pituitary-specific transcription factor Pit-1. Analysis of deletion constructs revealed a GC-rich region immediately upstream of the transcription start site, which is necessary for promoter activity. Somatostatin led to a significant inhibition, and forskolin and thyroid hormone to a significant stimulation of pituitary-specific promoter activity. Further mapping suggested a cAMP-responsive element located between -101 and the transcription start site, and thyroid hormone-responsive elements between -1741 and -1269 and between -317 and -101. These studies identified an upstream promoter of the sst5 gene with tissue-specific activity." [Abstract]

Freeman, Marc E., Kanyicska, Bela, Lerant, Anna, Nagy, Gyorgy
Prolactin: Structure, Function, and Regulation of Secretion
Physiol. Rev. 2000 80: 1523-1631 [Full Text]

Nedim Hukovic, Rosemarie Panetta, Ujendra Kumar, Magalie Rocheville, and Yogesh C. Patel
The Cytoplasmic Tail of the Human Somatostatin Receptor Type 5 Is Crucial for Interaction with Adenylyl Cyclase and in Mediating Desensitization and Internalization
J. Biol. Chem. 273: 21416-21422, August 1998. [Full Text]

Thomas Stroh, Alexander C. Jackson, Philippe Sarret, Claude Dal Farra, Jean-Pierre Vincent, Hans-Jürgen Kreienkamp, Jean Mazella, and Alain Beaudet
Intracellular Dynamics of sst5 Receptors in Transfected COS-7 Cells: Maintenance of Cell Surface Receptors during Ligand-Induced Endocytosis
Endocrinology 141: 354-365, 2000. [Full Text]

Martinez V, Coy DH, Lloyd KC, Tache Y.
Intracerebroventricular injection of somatostatin sst5 receptor agonist inhibits gastric acid secretion in rats.
Eur J Pharmacol 1996 Jan 25;296(2):153-60
"Somatostatin and its analogs act in the brain to influence gastric acid secretion. Five different somatostatin receptor subtypes have been characterized (sst1 to sst5). We studied the influence of somatostatin (0.18-0.6 nmol/rat) and selective sst2, sst3 and sst5 receptor ligands on basal gastric acid secretion in conscious rats equipped with chronic gastric and intracerebroventricular (i.c.v.) cannulae. Somatostatin-14 (0.36 nmol/rat), the sst2, sst3 and sst5 receptor agonist, Des-AA1,2,4,5,12,13-[D-Tryp8,D-Cys14]somatostatin (SMS 201-995) (0.18-0.36 nmol/rat) and the sst5 receptor agonist, BIM-23052, (0.8-1.2 nmol/rat) injected i.c.v. inhibited gastric acid secretion. Maximal inhibition reaching 42%, 60% and 42% was induced by somatostatin-14 (0.36 nmol/rat), SMS 201-995 (0.18 nmol/rat) and BIM-23052 (0.8 nmol/rat) respectively. The sst2 receptor agonist, DC 32-87 (0.2-0.8 nmol/rat) and sst3 receptor agonist, BIM-23056 (0.2-1.2 nmol/rat), did not modify gastric acid secretion, except the sst3 receptor agonist at 0.4 nmol/rat which increased acid output at 20 min post-injection. The sst2 receptor agonists (0.4 nmol/rat) co-injected i.c.v. with a subthreshold dose of sst5 (0.4 nmol/rat) inhibited gastric acid secretion. These results show that i.c.v. injection of somatostatin-14 inhibits basal gastric acid secretion in conscious rats through an action on sst5 receptor subtype which can be potentiated by sst2 receptor subtype." [Abstract]

Fagan SP, Azizzadeh A, Moldovan S, Ray MK, Adrian TE, Ding X, Coy DH, Brunicardi FC.
Insulin secretion is inhibited by subtype five somatostatin receptor in the mouse.
Surgery 1998 Aug;124(2):254-8; discussion 258-9
"BACKGROUND: Recently five somatostatin receptor subtypes (SSTRs) were cloned, allowing the development of highly specific agonists to these SSTRs. Previous studies have shown a species specificity phenomenon with respect to the inhibition of insulin secretion by these selective agonists. This study was undertaken to determine which SSTR (2 or 5) is responsible for the inhibitory effect of somatostatin on glucose-stimulated mouse insulin secretion. METHODS: Intact mouse islets (n = 10) were stimulated with D-glucose in the presence or absence of receptor-specific somatostatin agonists. RESULTS: D-glucose (16.7 mmol/L) augmented insulin secretion by 158% above that seen with 3.9 mmol/L D-glucose. In the presence of DC 32-92 (SSTR5) selective agonist, D-glucose (16.7 mmol/L) augmented insulin secretion by 64% above that seen with 3.9 mmol/L D-glucose. The presence of SSTR 5 selective agonist resulted in a significant (P < .05) inhibition of glucose-stimulated insulin secretion. The identification of SSTR5 within the mouse pancreas was established by reverse transcriptase polymerase chain reaction and confirmed by Southern blot analysis. CONCLUSIONS: These results suggest that the inhibitory effect of somatostatin on insulin secretion is mediated through the subtype 5 receptor within the mouse islet." [Abstract]

Chisholm C, Greenberg GR.
Somatostatin-28 regulates GLP-1 secretion via somatostatin receptor subtype 5 in rat intestinal cultures.
Am J Physiol Endocrinol Metab 2002 Aug;283(2):E311-7
"Five somatostatin receptors (SSTRs) bind somatostatin-14 (S-14) and somatostatin-28 (S-28), but SSTR5 has the highest affinity for S-28. To determine whether S-28 acting through SSTR5 mediates inhibition of glucagon-like peptide-1 (GLP-1), fetal rat intestinal cell cultures were treated with somatostatin analogs with relatively high specificity for SSTRs 2-5. S-28 dose-dependently inhibited GLP-1 secretion stimulated by gastrin-releasing peptide more potently than S-14 (EC50 0.01 vs. 5.8 nM). GLP-1 secretion was inhibited by an SSTR5 analog, BIM-23268, more potently than S-14 and nearly as effectively as S-28. The SSTR5 analog L-372,588 also suppressed GLP-1 secretion equivalent to S-28, but a structurally similar peptide, L-362,855 (Tyr to Phe at position 7), was ineffective. An SSTR2-selective analog was less effective than S-28, and an SSTR3 analog was inactive. Separate treatment with GLP-1-(7-36)-NH2 increased S-28 and S-14 secretion by three- and fivefold; BIM-23268 abolished S-28 without altering S-14, whereas the SSTR2 analog was inactive. The results indicate that somatostatin regulation of GLP-1 secretion occurs via S-28 through activation of SSTR5. GLP-1-stimulated S-28 secretion is also autoregulated by SSTR5 activation, suggesting a feedback loop between GLP-1 and S-28 modulated by SSTR5." [Abstract]

Zatelli MC, Tagliati F, Taylor JE, Piccin D, Culler MD, Degli Uberti EC.
Somatostatin, but not Somatostatin Receptor Subtypes 2 and 5 Selective Agonists, Inhibits Calcitonin Secretion and Gene Expression in the Human Medullary Thyroid Carcinoma Cell Line, TT.
Horm Metab Res 2002 May;34(5):229-33
"Somatostatin (SRIH) analogs are commonly used to treat symptoms in medullary thyroid carcinoma (MTC), that expresses SRIH receptors (SSTR1 to SSTR5), as does the human MTC cell line TT. The aim of this work was to evaluate whether SRIH, SSTR2 and SSTR5-selective agonists influence calcitonin (CT) secretion and gene expression in the TT cell line. CT secretion was evaluated by chemiluminescence, and gene expression was analyzed by Northern blot. TT cell line proliferation was also assessed by [ (3)H] thymidine ([ (3)H]thy) incorporation and viable cell number count. SRIH significantly (p < 0.05) reduced [ (3)H]thy incorporation (approx. 50 %), viable cell number (approx. 20 %), CT secretion (- 30 %) and CT gene expression (approx. 2-fold). Exposure to the SSTR2-selective agonist, BIM-23 120, and to the SSTR5-selective agonist, BIM-23 206, did not modify CT secretion and mRNA levels in TT cells. Thus, SRIH inhibits DNA synthesis, cell proliferation, CT secretion and CT gene expression in the TT cell line, while SSTR2 and 5 selective agonists, although influencing DNA synthesis and cell proliferation, do not modify CT gene expression, suggesting that SRIH may influence gene expression acting through SSTRs other than subtypes 2 and 5. Furthermore, these findings may explain the erratic response of MTC patients in terms of CT plasma levels to treatment with SRIH analogs, like octreotide and lanreotide, which interact mainly with SSTR2 and 5." [Abstract]