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Molecular Endocrinology (Baltimore, Md.) Feb 2010Pasireotide (SOM230) is currently under clinical evaluation as a successor compound to octreotide for the treatment of acromegaly, Cushing's disease, and carcinoid...
Pasireotide (SOM230) is currently under clinical evaluation as a successor compound to octreotide for the treatment of acromegaly, Cushing's disease, and carcinoid tumors. Whereas octreotide acts primarily via the sst(2A) somatostatin receptor, pasireotide was designed to exhibit octreotide-like sst(2A) activity combined with enhanced binding to other somatostatin receptor subtypes. In the present study, we used phophosite-specific antibodies to examine agonist-induced phosphorylation of the rat sst(2A) receptor. We show that somatostatin and octreotide stimulate the complete phosphorylation of a cluster of four threonine residues within the cytoplasmic (353)TTETQRT(359) motif in a variety of cultured cell lines in vitro as well as in intact animals in vivo. This phosphorylation was mediated by G protein-coupled receptor kinases (GRK) 2 and 3 and followed by rapid cointernalization of the receptor and ss-arrestin into the same endocytic vesicles. In contrast, pasireotide failed to promote substantial phosphorylation and internalization of the rat sst(2A) receptor. In the presence of octreotide or SS-14, SOM230 showed partial agonist behavior, inhibiting phosphorylation, and internalization of sst(2A). Upon overexpression of GRK2 or GRK3, pasireotide stimulated selective phosphorylation of Thr356 and Thr359 but not of Thr353 or Thr354 within the (353)TTETQRT(359) motif. Pasireotide-mediated phosphorylation led to the formation of relatively unstable beta-arrestin-sst(2A) complexes that dissociated at or near the plasma membrane. Thus, octreotide and pasireotide are equally active in inducing classical G protein-dependent signaling via the sst(2A) somatostatin receptor. Yet, we find that they promote strikingly different patterns of sst(2A) receptor phosphorylation and, hence, stimulate functionally distinct pools of beta-arrestin.
Topics: Animals; Antibodies, Phospho-Specific; Arrestins; Cell Line; Cell Line, Tumor; Cell Membrane; Endocytosis; Humans; Ligands; Male; Octreotide; Pancreas; Phosphorylation; Pituitary Gland; Protein Isoforms; Protein Processing, Post-Translational; Rats; Rats, Wistar; Receptors, Somatostatin; Somatostatin; Threonine; beta-Adrenergic Receptor Kinases; beta-Arrestins
PubMed: 20051480
DOI: 10.1210/me.2009-0315 -
Bailliere's Clinical Endocrinology and... Jan 1996A variety of human neuroendocrine tumours express SSTR. The five recently cloned human SSTR subtypes have a distinct chromosomal localization and pharmacological... (Review)
Review
A variety of human neuroendocrine tumours express SSTR. The five recently cloned human SSTR subtypes have a distinct chromosomal localization and pharmacological profile, and a tissue-specific expression pattern which suggests a differential function of SSTR subtypes in different organ systems. Most tumours carrying SSTR may express multiple SSTR subtypes, while the SSTR2 subtype is most predominantly expressed. The somatostatin analogue, octreotide, binds with high affinity to the SSTR2 and SSTR5 subtype and with a low affinity to the SSTR3 subtype. This analogue does not bind to the SSTR1 and SSTR4 subtypes. No major differences in the binding characteristics have been found between octreotide and two other clinically used octapeptide SST-analogues, BIM-23014 and RC-160. Our preliminary data indicate that an absent hormonal response to octreotide in vitro also implies an absent response to BIM-23014 and RC-160. The expression of the SSTR2 subtype in human tumours is proposed to be related to a clinical beneficial effect of octreotide treatment, while the functional significance of the other SSTR subtypes is not clear at present. In addition it is unclear which subtype(s) is involved in the antimitotic actions of SST(-analogues). Further developments with regard to the oncological application of SST analogues await the identification of the SSTR subtype(s) mediating anti-proliferative effects, as well as the development of analogues which selectively activate this subtype(s). A good correlation has been found between the presence of SSTR2 subtype mRNA and binding of [125I-Tyr3]octreotide in human primary tumours. Therefore, SSTR scintigraphy of human primary tumours and their metastases presumably visualizes SSTR2-expressing tumours, although it is reasonable to assume that SSTR5, and to a lesser extent SSTR3, when expressed simultaneously with SSTR2, also contribute to the visualization of tumours.
Topics: Gene Expression; Humans; Neoplasms; Octreotide; Radionuclide Imaging; Receptors, Somatostatin
PubMed: 8734455
DOI: 10.1016/s0950-351x(96)80362-4 -
Molecular and Cellular Endocrinology May 2008The neuropeptide somatostatin (SST) is highly expressed in brain regions associated with seizures. In hippocampus, SST expression and release is regulated by seizures,... (Review)
Review
The neuropeptide somatostatin (SST) is highly expressed in brain regions associated with seizures. In hippocampus, SST expression and release is regulated by seizures, and SST-containing neurons within the hilus of the dentate gyrus are sensitive to seizure-induced death. In vivo and in vitro studies suggest that the loss of SST function in the dentate could contribute to epileptogenesis and seizure susceptibility. SST also has inhibitory actions in the CA1 and CA3 hippocampus indicating this peptide is an important homeostatic regulator throughout the hippocampus. In vivo studies show SST has robust antiepileptic properties with the major site of action being hippocampus. In rodents, somatostatin receptor subtype 2 (SST(2)) and SST(4) appear to mediate the majority of the antiepileptic actions of SST, with SST(2) predominate in rat and SST(4) in mouse. Thus SST receptors may be appropriate targets for new antiepileptic drugs (AEDs), although validation in human tissue is lacking.
Topics: Animals; Anticonvulsants; Dentate Gyrus; Epilepsy; Hippocampus; Humans; Neurons; Receptors, Somatostatin; Seizures; Somatostatin
PubMed: 18221832
DOI: 10.1016/j.mce.2007.12.004 -
Journal of Neurochemistry Jun 2004This review summarizes the latest advances that have been made to elucidate the somatostatinergic system in respect to somatostatin receptor evolution, the development... (Review)
Review
This review summarizes the latest advances that have been made to elucidate the somatostatinergic system in respect to somatostatin receptor evolution, the development of receptor agonists/antagonists, receptor regulation, signal transduction, effects on cell proliferation, receptor-receptor or receptor-protein interactions and receptor function.
Topics: Animals; Cell Division; Central Nervous System; Gastrointestinal Tract; Humans; Ligands; Receptors, Somatostatin; Signal Transduction; Somatostatin
PubMed: 15147500
DOI: 10.1111/j.1471-4159.2004.02402.x -
Molecules (Basel, Switzerland) Dec 2020Hematological and oncological disorders represent leading causes of childhood mortality. Neuropeptide somatostatin (SST) has been previously demonstrated in various...
Hematological and oncological disorders represent leading causes of childhood mortality. Neuropeptide somatostatin (SST) has been previously demonstrated in various pediatric tumors, but limited information exists on the expression and characteristics of SST receptors (SSTR) in hematological and oncological disorders of children. We aimed to investigate the expression of mRNA for SSTR subtypes (SSTR-1-5) in 15 pediatric hematological/oncological specimens by RT-PCR. The presence and binding characteristics of SSTRs were further studies by ligand competition assay. Our results show that the pediatric tumor samples highly expressed mRNA for the five SSTR subtypes with various patterns. The mRNA for SSTR-2 was detected in all specimens independently of their histological type. A Hodgkin lymphoma sample co-expressed mRNA for all five SSTR subtypes. SSTR-3 and SSTR-5 were detected only in malignant specimens, such as rhabdomyosarcoma, Hodgkin lymphoma, acute lymphoblastic leukemia, and a single nonmalignant condition, hereditary spherocytosis. The incidence of SSTR-1 and SSTR-4 was similar (60%) in the 15 specimens investigated. Radioligand binding studies demonstrated the presence of specific SSTRs and high affinity binding of SST analogs in pediatric solid tumors investigated. The high incidence of SSTRs in hematological and oncological disorders in children supports the merit of further investigation of SSTRs as molecular targets for diagnosis and therapy.
Topics: Adolescent; Age Factors; Child; Child, Preschool; Female; Follow-Up Studies; Gene Expression Regulation, Neoplastic; Hematologic Neoplasms; Humans; Infant; Male; Models, Biological; Neoplasms; Protein Binding; Receptors, Somatostatin
PubMed: 33297556
DOI: 10.3390/molecules25235775 -
Nuclear Medicine Review. Central &... 2018Spleen shows a high physiological uptake on radionuclide somatostatin receptor (SSTR) imaging studies. Autoradiography and immunohistochemistry studies showed that SSTRs... (Review)
Review
Spleen shows a high physiological uptake on radionuclide somatostatin receptor (SSTR) imaging studies. Autoradiography and immunohistochemistry studies showed that SSTRs are mainly located in the red pulp of the spleen. In this review article we will summarize the significance of splenic uptake in SSTR imaging studies and will also present high resolution splenic images of Ga-68 DOTANOC PET in which splenic distribution of the radiotracer appears to be correlating with the distribution of red pulp.
Topics: Biological Transport; Humans; Molecular Imaging; Radiopharmaceuticals; Receptors, Somatostatin; Spleen
PubMed: 29319140
DOI: 10.5603/NMR.a2018.0012 -
International Journal of Molecular... Nov 2021Among the five somatostatin receptors (SST1-SST5), SST4 is the least characterized, which is in part due to the lack of specific monoclonal antibodies. We generated a...
Among the five somatostatin receptors (SST1-SST5), SST4 is the least characterized, which is in part due to the lack of specific monoclonal antibodies. We generated a knockin mouse model that expresses a carboxyl-terminal SST4-eGFP fusion protein. In addition, we extensively characterized the novel rabbit monoclonal anti-human SST4 antibody 7H49L61 using transfected cells and receptor-expressing tissues. 7H49L61 was then subjected to immunohistochemical staining of a series of formalin-fixed, paraffin-embedded normal and neoplastic human tissues. Characterization of SST4-eGFP mice revealed prominent SST4 expression in cortical pyramidal cells and trigeminal ganglion cells. In the human cortex, 7H49L61 disclosed a virtually identical staining pattern. Specificity of 7H49L61 was demonstrated by detection of a broad band migrating at 50-60 kDa in immunoblots. Tissue immunostaining was abolished by preadsorption of 7H49L61 with its immunizing peptide. In the subsequent immunohistochemical study, 7H49L61 yielded a predominant plasma membrane staining in adrenal cortex, exocrine pancreas, and placenta. SST4 was also found in glioblastomas, parathyroid adenomas, gastric and pancreatic adenocarcinomas, pheochromocytomas, and lymphomas. Altogether, we provide the first unequivocal localization of SST4 in normal and neoplastic human tissues. The monoclonal antibody 7H49L61 may also prove of great value for identifying SST4-expressing tumors during routine histopathological examinations.
Topics: Animals; Antibodies, Monoclonal; Cell Line; Gene Knock-In Techniques; Green Fluorescent Proteins; HEK293 Cells; Humans; Immunohistochemistry; Mice; Mice, Inbred C57BL; Models, Animal; Neoplasms; Receptors, Somatostatin; Recombinant Fusion Proteins; Staining and Labeling
PubMed: 34884783
DOI: 10.3390/ijms222312981 -
Diabetologia Nov 2012Glucose-dependent insulinotropic polypeptide (GIP) is an enteroendocrine hormone that promotes storage of glucose and fat. Its secretion from intestinal K cells is...
AIMS/HYPOTHESIS
Glucose-dependent insulinotropic polypeptide (GIP) is an enteroendocrine hormone that promotes storage of glucose and fat. Its secretion from intestinal K cells is triggered by nutrient ingestion and is modulated by intracellular cAMP. In view of the proadipogenic actions of GIP, this study aimed to identify pathways in K cells that lower cAMP levels and GIP secretion.
METHODS
Murine K cells purified by flow cytometry were analysed for expression of G(αi)-coupled receptors by transcriptomic microarrays. Somatostatin and cannabinoid receptor expression was confirmed by quantitative RT-PCR. Hormone secretion in vitro was measured in GLUTag and primary murine intestinal cultures. cAMP was monitored in GLUTag cells using the genetically encoded sensor Epac2-camps. In vivo tolerance tests were performed in cannulated rats.
RESULTS
Purified murine K cells expressed high mRNA levels for somatostatin receptors (Sstrs) Sstr2, Sstr3 and Sstr5, and cannabinoid receptor type 1 (Cnr1, CB1). Somatostatin inhibited GIP and glucagon-like peptide-1 (GLP-1) secretion from primary small intestinal cultures, in part through SSTR5, and reduced cAMP generation in GLUTag cells. Although the CB1 agonist methanandamide (mAEA) inhibited GIP secretion, no significant effect was observed on GLP-1 secretion from primary cultures. In cannulated rats, treatment with mAEA prior to an oral glucose tolerance test suppressed plasma GIP but not GLP-1 levels, whereas the CB1 antagonist AM251 elevated basal GIP concentrations.
CONCLUSIONS/INTERPRETATION
GIP release is inhibited by somatostatin and CB1 agonists. The differential effects of CB1 ligands on GIP and GLP-1 release may provide a new tool to dissociate secretion of these incretin hormones and lower GIP but not GLP-1 levels in vivo.
Topics: Animals; Colon; Cyclic AMP; Enteroendocrine Cells; Gastric Inhibitory Polypeptide; Glucagon-Like Peptide 1; Incretins; Intestine, Small; Male; Mice; Mice, Inbred C57BL; Primary Cell Culture; RNA, Messenger; Rats; Rats, Sprague-Dawley; Receptor, Cannabinoid, CB1; Receptors, Somatostatin
PubMed: 22872212
DOI: 10.1007/s00125-012-2663-5 -
Neurochemical Research Mar 2022Somatostatin receptor subtype 4 (SSTR4) is expressed in BV2 microglia, suggesting that SSTR4 agonists may impact microglia function. This study assessed the...
Somatostatin receptor subtype 4 (SSTR4) is expressed in BV2 microglia, suggesting that SSTR4 agonists may impact microglia function. This study assessed the high-affinity SSTR4 agonist SM-I-26 (SMI) (0 nM, 10 nM, 1000 nM) against lipopolysaccharide (LPS)-induced inflammation (0, 10 or 100 ng/ml) over 6 or 24 h in BV2 microglia. Cell viability, nitrite output and mRNA expression changes of genes associated with our target (Sstr4), inflammation (Tnf-α, Il-6, Il-1β, inos), anti-inflammatory and anti-oxidant actions (Il-10, Catalase), and mediators of Aβ binding/phagocytosis (Msr1, Cd33, Trem1, Trem2) were measured. At 6 h SMI showed no effect across all conditions. At 24 h SMI (10 and 1000 nM) upregulated Sstr4 expression under inflammatory and non-inflammatory conditions. At 24 h SMI downregulated expression of the inflammatory cytokines Tnf-α (1000 nM within all LPS concentrations) and Il-6 (10 nM within 0 and 10 ng/ml LPS). At 24 h 10 nM SMI upregulated Il-10, while 1000 nM upregulated Catalase under inflammatory and non-inflammatory conditions. At 24 h Msr1 and Cd33 were upregulated by 1000 nM SMI under non-inflammatory conditions, while Trem1 was downregulated by 10 and 1000 nM SMI under mildly inflammatory and non-inflammatory conditions. These results show that SMI had concentration and time-dependent effects on mRNA expression of genes associated with different states of microglial activation. The SMI reduced Tnf-α and Il-6 inflammatory gene expression, and increased Il-10 anti-inflammatory gene expression, identifies anti-inflammatory actions of SSTR4 agonists extend to microglia.
Topics: Cytokines; Gene Expression; Humans; Inflammation; Lipopolysaccharides; Microglia; Receptors, Somatostatin
PubMed: 34846597
DOI: 10.1007/s11064-021-03482-z -
Prevalence and Clinical Correlations of Somatostatin Receptor-2 (SSTR2) Expression in Neuroblastoma.Journal of Pediatric Hematology/oncology Apr 2019Alternative radiolabeled, targeted agents are being investigated for children with relapsed neuroblastoma (NB) who do not respond to I-metaiodobenzylguanidine (MIBG)...
Alternative radiolabeled, targeted agents are being investigated for children with relapsed neuroblastoma (NB) who do not respond to I-metaiodobenzylguanidine (MIBG) therapy. (DOTA-Tyr)-octreotate targets somatostatin receptors (SSTRs), particularly SSTR2, which are expressed on NB cells. We investigated SSTR2 expression in NB tumors (36 high-risk [HR]; 33 non-HR patients) and correlated SSTR2 levels with clinical features, norepinephrine transporter (NET) expression, and MIBG avidity. SSTR2 and NET immunohistochemistry scores (0 to 3) were calculated on biopsies using digital image analysis based on staining intensity and distribution. Clinical data were correlated with SSTR2 expression. Median SSTR2 score for 69 patients was 1.31 (0.26 to 2.55). Non-HR NB was associated with a higher SSTR2 score (P=0.032). The SSTR2 expression did not correlate with age, International Neuroblastoma Staging System (INSS) stage, MYCN amplification and histology. Higher SSTR2 scores were observed in MIBG-avid versus MIBG-nonavid NB. SSTR2 score was not significantly associated with NET score (r=-0.062, P=0.62). Twenty-six patients who relapsed or progressed had a median SSTR2 score of 1.33 (0.26 to 2.55). Patients with NB including relapsed or progressive disease showed SSTR2 expression at diagnosis, suggesting they could be candidates for radiolabeled-DOTA-conjugated peptide imaging or therapy.
Topics: 3-Iodobenzylguanidine; Disease Progression; Female; Humans; Immunohistochemistry; Male; Molecular Imaging; Molecular Targeted Therapy; Neuroblastoma; Norepinephrine Plasma Membrane Transport Proteins; Prevalence; Radiopharmaceuticals; Receptors, Somatostatin; Recurrence
PubMed: 30334904
DOI: 10.1097/MPH.0000000000001326