Affinage

SSTR3

Somatostatin receptor type 3 · UniProt P32745

Length
418 aa
Mass
45.8 kDa
Annotated
2026-06-10
28 papers in source corpus 14 papers cited in narrative 14 extracted findings
Cross-family judge vs UniProt: Affinage preferred faithfulness: 5/5 claims corpus-supported (100%)

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

SSTR3 is a Gi-coupled G protein-coupled receptor that binds somatostatin-14 and somatostatin-28 with high affinity and transduces somatostatin signaling by inhibiting adenylyl cyclase through pertussis toxin-sensitive G proteins to lower cAMP (PMID:1328199, PMID:1337145, PMID:8097479). Cryo-EM structures of Gi-coupled SSTR3 bound to the panagonist pasireotide and a selective small-molecule agonist have defined the orthosteric binding pocket and the molecular determinants of ligand selectivity and receptor activation (PMID:39361640). Beyond canonical cAMP suppression, agonist-engaged SSTR3 modulates ERK1/2 and p38 signaling and drives antiproliferative and proapoptotic outcomes, including in heterodimers with SSTR2 (PMID:22651821). SSTR3 localizes to primary cilia via two redundant ciliary targeting sequences in its third intracellular loop and C-terminal tail that engage the trafficking adaptors TULP3 and RABL2 (PMID:33372037), and ciliary SSTR3 on pancreatic beta cells mediates somatostatin-dependent changes in calcium flux that suppress insulin secretion (PMID:37660302). Across diverse cell types SSTR3 signaling restrains proliferation and reshapes cell fate—promoting apoptosis in tumor and neuronal contexts (PMID:28176050, PMID:15197339) and suppressing T-cell proliferation and mitochondrial respiration through GSK3 (PMID:38426092).

Mechanistic history

Synthesis pass · year-by-year structured walk · 13 steps
  1. 1992 High

    Established that SSTR3 is a functional somatostatin receptor coupled to inhibition of adenylyl cyclase, defining its core signaling output.

    Evidence Radioligand binding, pertussis toxin treatment, and cAMP assays on mouse and human SSTR3 in transfected cells

    PMID:1328199 PMID:1337145

    Open questions at the time
    • Did not resolve which Gi/Go subtype mediates coupling
    • Downstream effectors beyond cAMP not addressed
  2. 1993 High

    Defined the SSTR3 gene structure, chromosomal location, and ligand affinity rank order, distinguishing its pharmacology among somatostatin receptors.

    Evidence Genomic cloning, COS-7 expression, radioligand binding, and chromosomal mapping

    PMID:8097479

    Open questions at the time
    • No functional signaling readout in this study
    • Tissue expression pattern not established
  3. 2004 Medium

    Showed SSTR3 is required for somatostatin-analog (octreotide)-induced growth inhibition and apoptosis in gastric cancer cells, linking the receptor to antitumor effects.

    Evidence Immunofluorescence, Western blot, MTT and apoptosis assays, and antibody-mediated receptor blockade in cancer cell lines

    PMID:15197339

    Open questions at the time
    • Downstream apoptotic pathway not delineated
    • Single lab, antibody blockade not genetic
  4. 2012 Medium

    Demonstrated SSTR2–SSTR3 heterodimerization and linked agonist activation to MAPK modulation and Gi-dependent antiproliferative/proapoptotic signaling.

    Evidence Co-immunoprecipitation, confocal colocalization, cAMP and kinase phosphorylation assays, TUNEL and proliferation assays in HEK-293 cells

    PMID:22651821

    Open questions at the time
    • Heterodimer demonstrated in overexpression system, not endogenous
    • Causal link between dimerization and signaling outcomes not isolated
  5. 2017 Medium

    Implicated SSTR3 as a driver of neuronal apoptosis after intracerebral hemorrhage, extending its proapoptotic role to neural injury.

    Evidence Western blot, immunohistochemistry, immunofluorescence in rat ICH model, and siRNA knockdown in PC12 cells

    PMID:28176050

    Open questions at the time
    • Direct signaling pathway from SSTR3 to p53/Bax/caspase-3 not established
    • Endogenous ligand driving upregulation unknown
  6. 2020 High

    Resolved how SSTR3 reaches primary cilia, identifying two redundant ciliary targeting sequences and the adaptors TULP3 and RABL2 that mediate trafficking.

    Evidence Domain mutagenesis, live-cell ciliary imaging, GPCR chimera transplantation, and interaction studies with TULP3 and RABL2

    PMID:33372037

    Open questions at the time
    • Stoichiometry and direct binding mode of adaptor engagement not fully resolved
    • How ciliary localization shapes signaling output not addressed here
  7. 2020 Medium

    Extended SSTR3 ligand sensing to cortistatin, showing partial mediation of suppression of vascular smooth muscle proliferation and autophagy.

    Evidence Proliferation assays, Western blot, electron microscopy, autophagy inhibitor, and receptor blockade in rat VSMCs

    PMID:32348837

    Open questions at the time
    • SSTR3 contribution cannot be cleanly separated from SSTR5
    • Molecular link to autophagy machinery undefined
  8. 2023 High

    Established ciliary SSTR3 as the beta cell receptor mediating somatostatin suppression of insulin secretion via calcium flux, requiring intact primary cilia.

    Evidence GCaMP6f calcium imaging in reporter mice, isoform-specific antagonists, SSTR3 knockout, and cilia disruption

    PMID:37660302

    Open questions at the time
    • Coupling between ciliary localization and calcium effect not mechanistically dissected
    • Relative contribution versus other islet receptors not quantified
  9. 2023 Medium

    Characterized a high-affinity full SSTR3 agonist (ITF2984), linking receptor internalization, phosphorylation, and G-protein signaling to SSTR3-dependent antitumor activity.

    Evidence Radioligand binding, internalization/phosphorylation assays, NMR, molecular modeling, and in vivo MENX rat NFPA model

    PMID:37444563

    Open questions at the time
    • Antitumor mechanism downstream of receptor activation not fully mapped
    • Single lab, one tumor model
  10. 2024 Medium

    Identified an SSTR3-GSK3 axis that suppresses T-cell proliferation and mitochondrial respiration, extending SSTR3 to immunometabolic control.

    Evidence Proliferation and cytokine assays, OXPHOS/glycolysis metabolic profiling, inhibitors, and genetic manipulation in human T cells

    PMID:38426092

    Open questions at the time
    • Direct link from SSTR3 to GSK3 not biochemically defined
    • Mechanism of selective OXPHOS suppression unclear
  11. 2024 Medium

    Revealed post-transcriptional control of SSTR3 by CPEB2, which represses SSTR3 translation via poly(A) shortening to regulate trophoblast behavior.

    Evidence RIP, dual-luciferase reporter, poly(A) tail assay, Western blot, proliferation/invasion assays in trophoblast cells and rat preeclampsia model

    PMID:38648900

    Open questions at the time
    • Signaling consequences of altered SSTR3 levels in trophoblasts not mechanistically traced
    • Single lab
  12. 2024 High

    Provided atomic-resolution insight into SSTR3 activation, defining the Gi-coupled receptor's orthosteric pocket and determinants of agonist selectivity.

    Evidence Cryo-EM of SSTR3-Gi complexes with pasireotide and L-796778, with mutagenesis and binding assays

    PMID:39361640

    Open questions at the time
    • Structures of antagonist-bound or inactive states not resolved
    • Structural basis of ciliary trafficking and heterodimerization not addressed
  13. 2025 Medium

    Quantified the relative potency of SSTR3 signaling in islets, showing SSTR3 strongly inhibits beta cell cAMP but only weakly inhibits beta cell calcium, placing direct beta cell inhibition as secondary to indirect alpha cell control.

    Evidence Genetically encoded cAMP and Ca2+ sensors with cell-specific antagonists in intact mouse islets (preprint)

    PMID:bio_10.1101_2025.11.13.688371

    Open questions at the time
    • Preprint not yet peer-reviewed
    • Human islet relevance not established
    • Reconciliation with earlier calcium-suppression model incomplete

Open questions

Synthesis pass · forward-looking unresolved questions
  • How ciliary localization, heterodimerization, and tissue-specific G-protein coupling combine to set SSTR3's distinct signaling outputs across beta cells, immune cells, and tumors remains unresolved.
  • No structure linking ciliary trafficking to active signaling state
  • Endogenous heterodimer composition in native tissues unknown
  • Determinants of cell-type-specific cAMP versus calcium outputs undefined

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0060089 molecular transducer activity 3 GO:0048018 receptor ligand activity 2
Localization
GO:0005886 plasma membrane 2 GO:0005929 cilium 2
Pathway
R-HSA-162582 Signal Transduction 3 R-HSA-5357801 Programmed Cell Death 2
Partners
RABL2SSTR2TULP3

Evidence

Reading pass · 14 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
1992 Mouse SSTR3 binds somatostatin-14 and somatostatin-28 with high affinity, is coupled to pertussis toxin-sensitive G proteins, and mediates somatostatin inhibition of forskolin-stimulated and dopamine D1 receptor-stimulated cAMP formation, establishing coupling to adenylyl cyclase. Radioligand binding assays, pertussis toxin treatment, cAMP assay in transfected cells The Journal of biological chemistry High 1328199
1992 Human SSTR3 (418 amino acids) expressed in COS-1 cells binds somatostatin agonists with high affinity (rank order: somatostatin-28 = CGP 23996 > somatostatin-14 > SMS-201-995) and inhibits dopamine D1 receptor-stimulated cAMP formation, confirming functional coupling to adenylyl cyclase. Transient transfection of COS-1 cells, radioligand binding, cAMP assay with co-expressed D1 receptor Molecular endocrinology High 1337145
1993 Human SSTR3 gene is intronless, encodes a 418 amino acid GPCR, maps to human chromosome 22, and displays preferential affinity for somatostatin-14-like peptides with rank order D-Trp8 SST-14 > SST-14 > SMS-201-995 > SST-28 in COS-7 cell membranes. Genomic cloning, COS-7 cell expression, radioligand binding assay, chromosomal mapping FEBS letters High 8097479
2012 SSTR2 and SSTR3 form heterodimers at the plasma membrane in HEK-293 cells; agonist activation causes internalization and intracellular co-localization, reduces cAMP, modulates ERK1/2 and p38 phosphorylation in a time- and concentration-dependent manner, and inhibits cell proliferation via Gi-dependent mechanisms accompanied by increased PARP-1 expression, TUNEL staining, and upregulation of p21 and p27Kip1. Co-immunoprecipitation, confocal colocalization, cAMP assay, Western blot for pERK1/2 and p38, TUNEL staining, cell proliferation assay in transfected HEK-293 cells Journal of molecular signaling Medium 22651821
2020 SSTR3 ciliary targeting requires two redundant ciliary targeting sequences (CTS): one in the third intracellular loop (IC3-CTS1) and one in the C-terminal tail (CT-CTS2); in SSTR3, APASCQ/APAACQ motifs in IC3 and juxtamembrane residues in the CT are critical for ciliary localization; these CTSs promote ciliary targeting by modulating binding to ciliary trafficking adaptors TULP3 and RABL2. Mutagenesis of SSTR3 IC3 and CT domains, live-cell imaging of ciliary localization, GPCR chimera transplantation assays, interaction studies with TULP3 and RABL2 Life science alliance High 33372037
2023 Ciliary SSTR3 mediates somatostatin suppression of insulin secretion in mouse beta cells; somatostatin alters beta cell calcium flux after glucose stimulation in a manner dependent on endogenous SSTR3 expression and intact primary cilia on beta cells. GCaMP6f calcium imaging in beta cell-specific reporter mice, SSTR isoform antagonists, genetic SSTR3 knockout, primary cilia disruption Islets High 37660302
2024 Somatostatin inhibits human T-cell proliferation and IL-2 production by acting through SSTR3; SSTR3-mediated signaling suppresses T-cell mitochondrial respiration (OXPHOS) via the metabolic checkpoint kinase GSK3, without affecting TCR-induced glycolysis. Cell culture proliferation assays, cytokine measurement, metabolic profiling (OXPHOS/glycolysis), pharmacological inhibitors, genetic manipulation of SSTR3 in human T cells Frontiers in immunology Medium 38426092
2024 Cryo-EM structures of Gi-coupled SSTR3 activated by pasireotide (panagonist) and selective small molecule agonist L-796778 reveal a conserved extended binding pocket for pasireotide distinct from SST14/octreotide/lanreotide; mutagenesis identifies key determinants of ligand selectivity across the orthosteric pocket and reveals the molecular mechanism of receptor activation. Cryo-electron microscopy structure determination, mutagenesis analyses, ligand binding assays Proceedings of the National Academy of Sciences of the United States of America High 39361640
2017 SSTR3 expression is upregulated in neurons surrounding hematoma after intracerebral hemorrhage (ICH) in rats; SSTR3 upregulation correlates with increased p53, Bax, and active caspase-3; SSTR3 knockdown in PC12 cells reduces neuronal apoptosis, indicating SSTR3 promotes neuronal apoptosis. Western blot, immunohistochemistry, double immunofluorescence in rat ICH model, siRNA knockdown in PC12 cells, caspase-3 co-localization Cellular and molecular neurobiology Medium 28176050
2004 SSTR3 expressed on the membrane of gastric cancer cells mediates octreotide-induced growth inhibition and apoptosis; co-administration of SSTR3 antibody dramatically reduces octreotide's effect, and cells lacking SSTR3 expression are unaffected by octreotide. Immunofluorescence, Western blot, MTT cell growth assay, flow cytometry apoptosis assay, competitive protein binding with SSTR3 antibody Cancer biology & therapy Medium 15197339
2020 Cortistatin inhibits Ang II-induced vascular smooth muscle cell proliferation and autophagy partially through SSTR3 (and SSTR5); blocking SSTR3 and SSTR5 partially abrogates cortistatin's suppressive effects on VSMC proliferation and autophagy. CCK8 cell proliferation assay, Western blot, immunofluorescence, transmission electron microscopy, autophagy inhibitor (3-MA), receptor blockade in cultured rat VSMCs Life sciences Medium 32348837
2024 CPEB2 binds to the CPE site in the 3'-UTR of SSTR3 mRNA and suppresses SSTR3 translation by reducing poly(A) tail length; reduced SSTR3 protein promotes trophoblast cell proliferation, migration, invasion, and EMT, while SSTR3 overexpression suppresses these functions. RIP assay, dual-luciferase reporter assay, PCR poly(A) tail assay, Western blot, CCK-8, EdU assay, flow cytometry, transwell assay in trophoblast cells and rat PE model Biochimica et biophysica acta. Molecular basis of disease Medium 38648900
2025 In mouse pancreatic islets, SSTR3 is the only somatostatin receptor expressed by beta cells (SSTR2 is absent from beta cells); SSTR3 activation robustly inhibits beta cell cAMP but inhibits beta cell Ca2+ with significantly lower potency than SSTR2 inhibits alpha cell Ca2+; this differential signaling means somatostatin primarily gates insulin secretion indirectly by suppressing alpha cell glucagon release via SSTR2, with direct SSTR3-mediated beta cell inhibition playing a secondary role under strong nutrient stimulation. Genetically encoded cAMP and Ca2+ sensors in alpha and beta cells of intact mouse islets, cell-specific SSTR antagonists, live islet imaging bioRxivpreprint Medium bio_10.1101_2025.11.13.688371
2023 ITF2984, a full SSTR3 agonist with 10-fold improved affinity for SSTR3 vs. octreotide/pasireotide, induces SSTR3 receptor internalization and phosphorylation, triggers G-protein signaling at pharmacologically relevant concentrations, and displays antitumor activity dependent on SSTR3 expression levels in the MENX rat NFPA model; NMR and molecular modeling indicate higher SSTR3 affinity correlates with greater stability of a distorted β-I turn in the cyclic peptide backbone. Radioligand binding, receptor internalization/phosphorylation assay, G-protein signaling assay, NMR, molecular modeling, in vivo MENX rat model Cancers Medium 37444563

Source papers

Stage 0 corpus · 28 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
1992 Cloning of a novel somatostatin receptor, SSTR3, coupled to adenylylcyclase. The Journal of biological chemistry 320 1328199
1992 Somatostatin receptors, an expanding gene family: cloning and functional characterization of human SSTR3, a protein coupled to adenylyl cyclase. Molecular endocrinology (Baltimore, Md.) 295 1337145
1994 Expression and localization of somatostatin receptor SSTR1, SSTR2, and SSTR3 messenger RNAs in primary human tumors using in situ hybridization. Cancer research 294 8012966
1994 Localization of somatostatin (SRIF) SSTR-1, SSTR-2 and SSTR-3 receptor mRNA in rat brain by in situ hybridization. Naunyn-Schmiedeberg's archives of pharmacology 109 8170498
1994 Differential expression of messenger RNAs for somatostatin receptor subtypes SSTR1, SSTR2 and SSTR3 in adult rat brain: analysis by RNA blotting and in situ hybridization histochemistry. Neuroscience 103 8190266
1993 A human somatostatin receptor (SSTR3), located on chromosome 22, displays preferential affinity for somatostatin-14 like peptides. FEBS letters 69 8097479
2014 SSTR3 is a putative target for the medical treatment of gonadotroph adenomas of the pituitary. Endocrine-related cancer 62 25515731
2014 Increased SSTR2A and SSTR3 expression in succinate dehydrogenase-deficient pheochromocytomas and paragangliomas. Human pathology 61 25554089
1995 Co-expression of somatostatin SSTR-3 and SSTR-4 receptor messenger RNAs in the rat brain. Neuroscience 50 7708209
2004 The effect of somatostatin and SSTR3 on proliferation and apoptosis of gastric cancer cells. Cancer biology & therapy 34 15197339
2020 HTR6 and SSTR3 ciliary targeting relies on both IC3 loops and C-terminal tails. Life science alliance 28 33372037
2012 Coexpression of human somatostatin receptor-2 (SSTR2) and SSTR3 modulates antiproliferative signaling and apoptosis. Journal of molecular signaling 22 22651821
2021 HTR6 and SSTR3 targeting to primary cilia. Biochemical Society transactions 17 33599752
2015 mRNA expression of somatostatin receptor subtypes SSTR-2, SSTR-3, and SSTR-5 and its significance in pancreatic cancer. World journal of surgical oncology 13 25890201
2023 Beta cell primary cilia mediate somatostatin responsiveness via SSTR3. Islets 12 37660302
2024 Somatostatin-SSTR3-GSK3 modulates human T-cell responses by inhibiting OXPHOS. Frontiers in immunology 11 38426092
2020 Cortistatin ameliorates Ang II-induced proliferation of vascular smooth muscle cells by inhibiting autophagy through SSTR3 and SSTR5. Life sciences 11 32348837
2014 Investigation of Cardiovascular Effects of Tetrahydro-β-carboline sstr3 antagonists. ACS medicinal chemistry letters 9 25050159
2017 Upregulated Expression of SSTR3 is Involved in Neuronal Apoptosis After Intracerebral Hemorrhage in Adult Rats. Cellular and molecular neurobiology 8 28176050
2024 The Novel SSTR3 Agonist ITF2984 Exerts Antimitotic and Proapoptotic Effects in Human Non-Functioning Pituitary Neuroendocrine Tumor (NF-PitNET) Cells. International journal of molecular sciences 6 38612419
2023 Identification of a Novel SSTR3 Full Agonist for the Treatment of Nonfunctioning Pituitary Adenomas. Cancers 6 37444563
2016 SAR exploration at the C-3 position of tetrahydro-β-carboline sstr3 antagonists. Bioorganic & medicinal chemistry letters 6 26898814
2024 Selective ligand recognition and activation of somatostatin receptors SSTR1 and SSTR3. Proceedings of the National Academy of Sciences of the United States of America 4 39361640
2010 Influence of cigarette smoking on the level of mRNA of somatostatin receptor 3 (SSTR3) in the gastric mucosa of patients with functional dyspepsia. Advances in medical sciences 4 20570798
2024 The Novel SSTR3 Full Agonist ITF2984 Shows Antitumor Properties against Pancreatic Neuroendocrine Tumors. Neuroendocrinology 2 39733775
2024 CPEB2 inhibits preeclampsia progression by regulating SSTR3 translation through polyadenylation. Biochimica et biophysica acta. Molecular basis of disease 1 38648900
2025 Identification of the LncRNA PRNCR1/miR-642a-5p/SSTR3 CeRNA network and its diagnostic value in type 2 diabetes mellitus. Diabetology & metabolic syndrome 0 41456020
2007 [Somatostatin receptor subtype 3 (SSTR3) mRNA level in gastric mucosa of patients with dyspepsia]. Polski merkuriusz lekarski : organ Polskiego Towarzystwa Lekarskiego 0 17679363

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