{"gene":"SSTR5","run_date":"2026-04-28T20:42:08","timeline":{"discoveries":[{"year":1993,"finding":"SSTR5 was cloned and pharmacologically characterized: it binds somatostatin analogues with distinct selectivity profiles compared to other SSTR subtypes, and mediates inhibition of forskolin-stimulated cAMP accumulation in CHO/COS cells, consistent with Gi coupling.","method":"Radioligand binding competition assay, cAMP accumulation assay in transfected CHO-K1/COS-1 cells","journal":"Molecular pharmacology","confidence":"High","confidence_rationale":"Tier 1 — in vitro functional assay with expressed receptor, multiple pharmacological methods, foundational characterization paper","pmids":["8102785"],"is_preprint":false},{"year":1994,"finding":"Human SSTR5 was cloned and expressed; it mediates inhibition of forskolin-stimulated cAMP accumulation via Gi, but unlike rat SSTR5, the clinically used analogue SMS 201-995 does not inhibit cAMP in human SSTR5-expressing cells, demonstrating species-dependent pharmacology. Human SSTR5 mRNA is selectively expressed in small intestine, heart, adrenal, cerebellum, pituitary, placenta, and skeletal muscle.","method":"Stable expression in CHO-K1 cells, radioligand binding, cAMP accumulation assay, RT-PCR for tissue distribution","journal":"Molecular pharmacology","confidence":"High","confidence_rationale":"Tier 1 — in vitro functional reconstitution with cloned human receptor, multiple orthogonal methods","pmids":["8078491"],"is_preprint":false},{"year":1995,"finding":"SSTR5 mediates antiproliferative effects of the somatostatin analogue RC-160 through inhibition of intracellular calcium mobilization (inositol phospholipid/Ca2+ pathway), a mechanism distinct from SSTR2 (which acts via tyrosine phosphatase). SSTR5-expressing CHO cells showed RC-160 inhibition of CCK-stimulated Ca2+ and CCK-induced proliferation, and this effect was not blocked by phosphatase inhibitors.","method":"Cell proliferation assay, intracellular calcium measurement, phosphatase activity assay, pharmacological inhibitors in CHO cells stably expressing SSTR5","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 — multiple orthogonal functional assays in defined cell system, mechanistic pathway dissection with inhibitors","pmids":["7878022"],"is_preprint":false},{"year":1996,"finding":"SSTR5 couples to L-type Ca2+ channels in AtT-20 pituitary cells via pertussis toxin-sensitive G proteins (Gi/Go), mediating inhibition of Ca2+ currents. SSTR5-mediated inhibition undergoes pronounced desensitization upon agonist pretreatment, in contrast to SSTR2. The compound L362,855 acts as an antagonist/partial agonist at SSTR5.","method":"Whole-cell patch clamp electrophysiology, pertussis toxin pretreatment, selective agonist/antagonist pharmacology in AtT-20 cells","journal":"Neuroscience","confidence":"High","confidence_rationale":"Tier 1 — direct electrophysiological recording with pharmacological dissection, pertussis toxin mechanistic validation","pmids":["8684611"],"is_preprint":false},{"year":1997,"finding":"SSTR5 mediates somatostatin-induced suppression of GH and TSH secretion in primary human fetal pituitary cultures; SSTR5-selective analogue exclusively inhibited GH in acromegalic tumor cells, demonstrating SSTR5 is sufficient for GH and TSH regulation but not prolactin suppression (which requires SSTR2).","method":"Primary human fetal pituitary cell culture, SSTR subtype-selective analogue treatment, hormone secretion assays (RIA/ELISA), radioligand binding","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 2 — selective pharmacological dissection in primary human cells with multiple hormones measured, replicated in acromegalic tumor cells","pmids":["9045884"],"is_preprint":false},{"year":2003,"finding":"Pancreatic somatostatin inhibits insulin secretion through SSTR5 in mouse pancreas: SSTR5-knockout mice showed enhanced glucose-stimulated insulin secretion at 12 months; octreotide suppressed insulin secretion in wild-type but not SSTR5-/- mice; immunoneutralization of somatostatin increased insulin in WT but decreased it in knockouts.","method":"Isolated perfused mouse pancreas model, SSTR5 global gene knockout, somatostatin immunoneutralization, octreotide pharmacological challenge","journal":"Pancreas","confidence":"High","confidence_rationale":"Tier 2 — genetic knockout with specific functional readout, multiple experimental approaches including pharmacological rescue","pmids":["12657967"],"is_preprint":false},{"year":2004,"finding":"Double-gene ablation of SSTR1 and SSTR5 results in islet hyperplasia, hyperinsulinemia, and improved glucose tolerance in mice; isolated SSTR1/5-/- islets showed no response to somatostatin peptides, confirming both receptors coordinately regulate insulin secretion and glucose homeostasis.","method":"Double-gene knockout mouse model, intraperitoneal glucose tolerance test, isolated perfused pancreas, islet culture, immunohistochemistry","journal":"Surgery","confidence":"High","confidence_rationale":"Tier 2 — genetic epistasis with double knockout, multiple orthogonal phenotypic readouts","pmids":["15349106"],"is_preprint":false},{"year":2005,"finding":"Beta-cell-specific conditional knockdown of SSTR5 (using Cre-lox) causes glucose intolerance with absent insulin response and reduced serum insulin at 3 months, and persistently elevated insulin at 12 months; SSTR5-deficient islets do not respond to SST-28 stimulation, confirming SSTR5's direct role in beta-cell insulin secretion.","method":"Conditional Cre-lox knockout in pancreatic beta cells, glucose tolerance test, insulin tolerance test, in vitro islet stimulation with SST-28, immunohistochemistry","journal":"FEBS letters","confidence":"High","confidence_rationale":"Tier 2 — cell-type-specific genetic ablation with multiple functional and in vitro readouts","pmids":["15919085"],"is_preprint":false},{"year":2005,"finding":"Global SSTR5 knockout mice show age-dependent glucose regulation changes: glucose intolerance at 3 months (despite normal insulin secretion) and basal hypoglycemia with hyperinsulinemia at 12 months; SSTR1 expression increases compensatorily in islets at 3 months but becomes absent at 12 months, suggesting coordinate regulation between SSTR1 and SSTR5.","method":"Global SSTR5-/- mouse model, glucose tolerance test, in vitro pancreas perfusion, immunohistochemistry for SSTR1/SST/insulin","journal":"The Journal of surgical research","confidence":"High","confidence_rationale":"Tier 2 — genetic knockout, multiple ages studied, compensatory receptor expression quantified","pmids":["16026801"],"is_preprint":false},{"year":2011,"finding":"The P335L single nucleotide polymorphism of SSTR5 produces a hypofunctional receptor: overexpression of SSTR5-L335 (vs. P335) in pancreatic cancer cells enhanced proliferation, blocked the inhibitory effect of SSTR5-selective agonist RPL-1980 on proliferation and glucose-stimulated insulin secretion, and increased PDX-1 expression.","method":"Site-directed mutagenesis, transient transfection in HEK293/Mia PaCa-2/β-TC-6 cells, MTS proliferation assay, insulin ELISA, SNP genotyping","journal":"World journal of surgery","confidence":"High","confidence_rationale":"Tier 1 — mutagenesis combined with functional assays in multiple cell lines, mechanistic comparison of variants","pmids":["21249361"],"is_preprint":false},{"year":2019,"finding":"SST/SSTR5 signaling upregulates colonic MUC2 expression and mucus secretion through suppression of the Notch-Hes1 pathway; SSTR5-specific siRNA knockdown abolished SST-induced MUC2 upregulation, and SSTR5 agonist L817,818 replicated the effect.","method":"siRNA knockdown of SSTR5 in LS174T cells, SSTR5 agonist treatment, Western blot for NICD and Hes1, MUC2 expression assay, in vivo octreotide administration in mice","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 — siRNA knockdown and agonist rescue with pathway marker readout, supported by in vivo correlate","pmids":["31733832"],"is_preprint":false},{"year":2019,"finding":"UTS2B (urotensin 2B), produced by a novel enteroendocrine cell type, inhibits GLP-1 secretion through SSTR5 (not its cognate receptor UTS2R) acting in a paracrine manner in mouse intestinal crypts; SSTR5-mediated inhibition of GLP-1 was confirmed using intestinal organoids.","method":"Mouse intestinal crypt and organoid culture, receptor identification by pharmacological antagonism, in vivo peptide administration with plasma GLP-1/insulin measurement","journal":"Endocrinology","confidence":"Medium","confidence_rationale":"Tier 2 — receptor identification by specific antagonists in ex vivo system, in vivo validation","pmids":["31556942"],"is_preprint":false},{"year":2023,"finding":"ZDHHC5 catalyzes palmitoylation of SSTR5; pharmacological blockade of ZDHHC5 with lomitapide inhibits SSTR5 palmitoylation and attenuates pancreatic cancer cell growth in vitro and in vivo.","method":"Single-cell transcriptomics comparison, ZDHHC5 inhibition with lomitapide, cell proliferation assay, in vivo xenograft model","journal":"Cell death discovery","confidence":"Medium","confidence_rationale":"Tier 3 — pharmacological ZDHHC5 inhibition identifies palmitoylation dependency of SSTR5, but direct biochemical confirmation of palmitoylation site on SSTR5 not detailed in abstract","pmids":["36774350"],"is_preprint":false},{"year":2024,"finding":"SSTR5 (and SSTR3) localizes to primary cilia of pancreatic β-cells; activation of ciliary SSTR5 lowers ciliary cAMP concentration via Gαi. δ-cells are positioned near primary cilia of other islet cells and direct somatostatin secretion toward cilia. Sustained somatostatin exposure promotes nuclear entry of the transcription factor GLI2 via a ciliary Ca2+ signaling mechanism, extending SSTR5 function beyond acute hormone suppression.","method":"Live-cell fluorescence imaging (ciliary cAMP biosensor), subcellular fractionation/localization, islet morphology by confocal microscopy, GLI2 nuclear translocation assay, cilia length measurement in human T2D donor islets","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 — direct live imaging of ciliary cAMP with biosensor, mechanistic dissection of ciliary vs. cytosolic signaling; preprint not yet peer-reviewed","pmids":["bio_10.1101_2024.06.05.597562"],"is_preprint":true},{"year":2024,"finding":"TRPV1+ sensory nerves release somatostatin that binds SSTR5 on mast cells and conjunctival fibroblasts to suppress TNF-α production in mast cells and CCL11 (eotaxin-1) expression in fibroblasts, thereby reducing eosinophil infiltration in allergic conjunctivitis.","method":"TRPV1+ nerve ablation (resiniferatoxin), TRPV1 blockade, SST-SSTR5 agonist treatment, in vivo murine allergic conjunctivitis model, gene expression and cell infiltration analysis","journal":"Mucosal immunology","confidence":"Medium","confidence_rationale":"Tier 2 — nerve ablation and pharmacological dissection in vivo with specific cellular readouts on mast cells and fibroblasts","pmids":["38331094"],"is_preprint":false},{"year":2024,"finding":"Activation of SSTR5 with the agonist L-817,818 reduces inflammatory response after corneal epithelial injury and promotes re-epithelialization and nerve regeneration in diabetic mice, acting by inhibiting neutrophil infiltration and shifting macrophage polarization from M1 to M2.","method":"Topical SST/SSTR5 agonist (L-817,818) administration, streptozotocin diabetic mouse corneal wound model, gene expression, immunofluorescence for macrophage polarization, neutrophil quantification","journal":"Mucosal immunology","confidence":"Medium","confidence_rationale":"Tier 2 — specific SSTR5 agonist with defined cellular and molecular phenotypes in vivo","pmids":["38866206"],"is_preprint":false},{"year":2024,"finding":"SSTR5 antagonism (with oral SCO-240) stimulates robust growth hormone (GH) secretion in healthy humans without affecting other pituitary hormones, demonstrating that endogenous SSTR5 tonically suppresses GH release in vivo.","method":"Phase I randomized double-blind placebo-controlled human clinical trial with pharmacokinetic and pharmacodynamic readouts (serum GH, insulin, GLP-1, gallbladder contractions)","journal":"Clinical pharmacology and therapeutics","confidence":"High","confidence_rationale":"Tier 2 — controlled human trial with specific SSTR5 antagonist, robust GH secretion phenotype, multiple hormone readouts","pmids":["38549435"],"is_preprint":false},{"year":2020,"finding":"Cortistatin suppresses angiotensin II-induced vascular smooth muscle cell proliferation and autophagy partially through SSTR3 and SSTR5; blocking SSTR3 and SSTR5 with antagonists partially abrogated cortistatin's anti-proliferative and anti-autophagic effects.","method":"Rat VSMC culture, CCK-8 proliferation assay, Western blot, immunofluorescence, transmission electron microscopy, SSTR3/5 antagonist pharmacology","journal":"Life sciences","confidence":"Medium","confidence_rationale":"Tier 3 — pharmacological receptor antagonism identifies SSTR5 involvement, but effect is partial and shared with SSTR3","pmids":["32348837"],"is_preprint":false}],"current_model":"SSTR5 is a Gi-coupled G protein-coupled receptor that suppresses hormone secretion (GH, TSH, insulin, GLP-1) and cell proliferation through inhibition of adenylyl cyclase (lowering cAMP), inhibition of L-type Ca2+ channels via pertussis toxin-sensitive Gi/Go proteins, and suppression of intracellular calcium mobilization via the phospholipid/Ca2+ pathway; it localizes to primary cilia of pancreatic β-cells where it modulates ciliary cAMP and triggers GLI2-dependent transcriptional responses, is palmitoylated by ZDHHC5, and a hypofunctional P335L SNP impairs its anti-proliferative and insulin-inhibitory signaling."},"narrative":{"teleology":[{"year":1993,"claim":"Cloning and functional expression of SSTR5 established it as a Gi-coupled receptor with a pharmacological profile distinct from other SSTR subtypes, resolving the question of whether a fifth somatostatin receptor subtype existed with unique ligand selectivity.","evidence":"Radioligand binding and cAMP accumulation assays in transfected CHO-K1/COS-1 cells","pmids":["8102785"],"confidence":"High","gaps":["Downstream effectors beyond cAMP not yet identified","In vivo physiological role unknown"]},{"year":1994,"claim":"Cloning of human SSTR5 revealed species-dependent pharmacology — the clinically used analogue octreotide (SMS 201-995) did not inhibit cAMP at human SSTR5 — establishing that rodent pharmacology could not be directly extrapolated to human drug design.","evidence":"Stable expression in CHO-K1 cells, radioligand binding, cAMP assay, RT-PCR tissue distribution","pmids":["8078491"],"confidence":"High","gaps":["Structural basis for species selectivity difference unknown","Native tissue function not yet demonstrated"]},{"year":1995,"claim":"SSTR5's antiproliferative mechanism was shown to operate through inhibition of the phospholipid/Ca²⁺ pathway rather than tyrosine phosphatase activation, distinguishing it mechanistically from SSTR2 and identifying a second effector arm.","evidence":"Cell proliferation assay, intracellular calcium measurement, phosphatase activity assay with pharmacological inhibitors in CHO-SSTR5 cells","pmids":["7878022"],"confidence":"High","gaps":["Identity of the phospholipase/Ca²⁺ intermediary not defined","Relevance to native tissues expressing SSTR5 not confirmed"]},{"year":1996,"claim":"SSTR5 was shown to inhibit L-type Ca²⁺ channels through pertussis toxin-sensitive Gi/Go proteins and to undergo pronounced desensitization, providing the first direct electrophysiological characterization of SSTR5 effector coupling.","evidence":"Whole-cell patch clamp in AtT-20 pituitary cells with pertussis toxin and selective agonist/antagonist pharmacology","pmids":["8684611"],"confidence":"High","gaps":["Specific Gα subunit identity not resolved","Desensitization mechanism (GRK/β-arrestin involvement) not defined"]},{"year":1997,"claim":"SSTR5-selective pharmacology in primary human pituitary cells demonstrated that SSTR5 is sufficient to suppress GH and TSH secretion but not prolactin, assigning specific endocrine functions to this subtype in humans.","evidence":"Primary human fetal pituitary cultures and acromegalic tumor cells treated with SSTR5-selective analogues, hormone RIA/ELISA","pmids":["9045884"],"confidence":"High","gaps":["Relative contribution of SSTR5 vs. SSTR2 in combined pituitary signaling not quantified","Downstream intracellular pathway in pituitary GH suppression not mapped"]},{"year":2003,"claim":"Genetic ablation of SSTR5 in mice proved that SSTR5 is the receptor mediating somatostatin's tonic inhibition of insulin secretion in pancreatic islets, resolving which SSTR subtype controls β-cell insulin release.","evidence":"SSTR5 global knockout mice, isolated perfused pancreas, octreotide challenge, somatostatin immunoneutralization","pmids":["12657967"],"confidence":"High","gaps":["Cell-autonomous vs. paracrine contribution not yet separated","Compensatory SSTR expression changes not fully characterized"]},{"year":2004,"claim":"Double knockout of SSTR1 and SSTR5 produced islet hyperplasia and hyperinsulinemia exceeding single knockouts, establishing that SSTR1 and SSTR5 coordinate to restrain insulin secretion and β-cell mass.","evidence":"SSTR1/SSTR5 double-knockout mice, glucose tolerance tests, perfused pancreas, islet culture","pmids":["15349106"],"confidence":"High","gaps":["Whether SSTR1 and SSTR5 signal through the same or distinct intracellular pathways in islets unclear"]},{"year":2005,"claim":"β-cell-specific conditional knockout confirmed cell-autonomous SSTR5 function and revealed age-dependent insulin secretory phenotypes, while global knockouts showed compensatory upregulation of SSTR1 at early ages followed by loss at later ages.","evidence":"Cre-lox β-cell-specific and global SSTR5 knockout mice, glucose/insulin tolerance tests, in vitro islet SST-28 stimulation, immunohistochemistry","pmids":["15919085","16026801"],"confidence":"High","gaps":["Molecular mechanism of SSTR1 compensatory regulation unknown","Whether age-dependent phenotype applies to humans undetermined"]},{"year":2011,"claim":"The P335L SNP was identified as a hypofunctional SSTR5 variant that impairs antiproliferative signaling and insulin suppression, linking receptor coding variation to functional output and potential disease susceptibility.","evidence":"Site-directed mutagenesis, transfection in HEK293/MiaPaCa-2/βTC-6 cells, proliferation and insulin secretion assays","pmids":["21249361"],"confidence":"High","gaps":["Structural basis for P335L hypofunction unknown","Population frequency and clinical significance not established in patient cohorts"]},{"year":2019,"claim":"SSTR5 was shown to regulate intestinal physiology through two distinct mechanisms: suppression of the Notch-Hes1 pathway to upregulate colonic MUC2/mucus secretion, and paracrine inhibition of GLP-1 secretion in intestinal crypts by the non-canonical ligand UTS2B.","evidence":"siRNA knockdown and SSTR5 agonist in LS174T cells with Western blot; mouse intestinal crypt/organoid culture with receptor pharmacological antagonism and in vivo peptide administration","pmids":["31733832","31556942"],"confidence":"Medium","gaps":["Direct binding of UTS2B to SSTR5 not demonstrated biochemically","In vivo relevance of MUC2 regulation in SSTR5 knockout not tested"]},{"year":2020,"claim":"Cortistatin's suppression of vascular smooth muscle proliferation and autophagy was partially attributed to SSTR5 (shared with SSTR3), extending SSTR5's antiproliferative role to the vasculature.","evidence":"Rat VSMC culture, SSTR3/5 antagonist pharmacology, proliferation and autophagy assays","pmids":["32348837"],"confidence":"Medium","gaps":["Effect is partial and shared with SSTR3, making specific SSTR5 contribution uncertain","No genetic confirmation of SSTR5 involvement"]},{"year":2023,"claim":"ZDHHC5 was identified as the palmitoyl acyltransferase for SSTR5, and pharmacological inhibition of ZDHHC5 attenuated pancreatic cancer growth dependent on SSTR5 palmitoylation.","evidence":"Single-cell transcriptomics, lomitapide-mediated ZDHHC5 inhibition, cell proliferation assay, in vivo xenograft","pmids":["36774350"],"confidence":"Medium","gaps":["Direct biochemical identification of palmitoylation sites on SSTR5 not reported","Whether palmitoylation affects SSTR5 trafficking, stability, or signaling not distinguished"]},{"year":2024,"claim":"Multiple 2024 studies expanded SSTR5's functional scope: ciliary localization in β-cells with local cAMP reduction and GLI2 nuclear translocation; anti-inflammatory roles via TNF-α suppression on mast cells and M1-to-M2 macrophage polarization; and human clinical proof that SSTR5 tonically suppresses GH secretion in healthy adults.","evidence":"Live-cell ciliary cAMP biosensor imaging (preprint); TRPV1+ nerve ablation and SSTR5 agonist in murine allergic conjunctivitis; SSTR5 agonist in diabetic corneal wound model; phase I RCT with oral SSTR5 antagonist in humans","pmids":["bio_10.1101_2024.06.05.597562","38331094","38866206","38549435"],"confidence":"Medium","gaps":["Ciliary cAMP/GLI2 findings from preprint await peer review","How ciliary vs. plasma membrane SSTR5 signaling pools are differentially regulated is undefined","Anti-inflammatory mechanisms need genetic confirmation in SSTR5 knockout models"]},{"year":null,"claim":"Key open questions include: the structural basis for SSTR5's distinct effector coupling and desensitization properties; how SSTR5 palmitoylation by ZDHHC5 modulates trafficking and signaling; the physiological significance of ciliary vs. non-ciliary SSTR5 signaling; and whether SSTR5 coding variants (e.g. P335L) predispose to metabolic or neoplastic disease in human populations.","evidence":"","pmids":[],"confidence":"Low","gaps":["No high-resolution structure of SSTR5 in active or inactive state","No systematic human genetic association studies for SSTR5 variants","Ciliary signaling findings not yet peer-reviewed or replicated"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[0,1,3,4,5,16]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[2,3,10,14,15]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[0,1,2,3]},{"term_id":"GO:0005929","term_label":"cilium","supporting_discovery_ids":[13]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[0,1,2,3,10,13]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[14,15]},{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[12]}],"complexes":[],"partners":["SSTR1","SSTR3","ZDHHC5","GLI2"],"other_free_text":[]},"mechanistic_narrative":"SSTR5 is a Gi/Go-coupled somatostatin receptor that tonically suppresses hormone secretion and cell proliferation across endocrine, gastrointestinal, and immune cell types. It inhibits adenylyl cyclase to lower cAMP and suppresses L-type Ca²⁺ channel currents via pertussis toxin-sensitive G proteins, while independently inhibiting intracellular calcium mobilization through the phospholipid/Ca²⁺ pathway to exert antiproliferative effects distinct from SSTR2's phosphatase-dependent mechanism [PMID:8102785, PMID:8684611, PMID:7878022]. In pancreatic β-cells, SSTR5 is the principal receptor mediating somatostatin-dependent inhibition of insulin secretion, as demonstrated by global and β-cell-specific knockouts that produce hyperinsulinemia and altered glucose homeostasis, and it localizes to primary cilia where it lowers ciliary cAMP and promotes GLI2 nuclear translocation [PMID:12657967, PMID:15919085, PMID:38549435]. SSTR5 also suppresses GH and TSH release from pituitary cells, inhibits GLP-1 secretion in intestinal crypts, upregulates colonic MUC2 via Notch-Hes1 pathway suppression, and exerts anti-inflammatory effects by reducing TNF-α production and promoting M2 macrophage polarization [PMID:9045884, PMID:31556942, PMID:31733832, PMID:38331094]."},"prefetch_data":{"uniprot":{"accession":"P35346","full_name":"Somatostatin receptor type 5","aliases":[],"length_aa":364,"mass_kda":39.2,"function":"Receptor for somatostatin 28 and to a lesser extent for somatostatin-14. The activity of this receptor is mediated by G proteins which inhibit adenylyl cyclase. Increases cell growth inhibition activity of SSTR2 following heterodimerization","subcellular_location":"Cell membrane","url":"https://www.uniprot.org/uniprotkb/P35346/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/SSTR5","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/SSTR5","total_profiled":1310},"omim":[{"mim_id":"617686","title":"PITUITARY ADENOMA 3, MULTIPLE TYPES; PITA3","url":"https://www.omim.org/entry/617686"},{"mim_id":"614586","title":"ZDHHC PALMITOYLTRANSFERASE 5; ZDHHC5","url":"https://www.omim.org/entry/614586"},{"mim_id":"609445","title":"RELAXIN/INSULIN-LIKE FAMILY PEPTIDE RECEPTOR 3; RXFP3","url":"https://www.omim.org/entry/609445"},{"mim_id":"601313","title":"POLYCYSTIN 1; PKD1","url":"https://www.omim.org/entry/601313"},{"mim_id":"600140","title":"CREB-BINDING PROTEIN; CREBBP","url":"https://www.omim.org/entry/600140"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Plasma membrane","reliability":"Supported"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in some","driving_tissues":[{"tissue":"adrenal gland","ntpm":2.1},{"tissue":"blood vessel","ntpm":2.6},{"tissue":"heart muscle","ntpm":2.4},{"tissue":"kidney","ntpm":3.9},{"tissue":"pituitary gland","ntpm":2.1}],"url":"https://www.proteinatlas.org/search/SSTR5"},"hgnc":{"alias_symbol":[],"prev_symbol":[]},"alphafold":{"accession":"P35346","domains":[{"cath_id":"1.20.1070.10","chopping":"37-232_239-320","consensus_level":"high","plddt":92.3669,"start":37,"end":320}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P35346","model_url":"https://alphafold.ebi.ac.uk/files/AF-P35346-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P35346-F1-predicted_aligned_error_v6.png","plddt_mean":81.25},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=SSTR5","jax_strain_url":"https://www.jax.org/strain/search?query=SSTR5"},"sequence":{"accession":"P35346","fasta_url":"https://rest.uniprot.org/uniprotkb/P35346.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P35346/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P35346"}},"corpus_meta":[{"pmid":"7878022","id":"PMC_7878022","title":"Inhibition of cell proliferation by the somatostatin analogue RC-160 is mediated by somatostatin receptor subtypes SSTR2 and SSTR5 through different mechanisms.","date":"1995","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/7878022","citation_count":279,"is_preprint":false},{"pmid":"9045884","id":"PMC_9045884","title":"Somatostatin receptor subtype specificity in human fetal pituitary cultures. Differential role of SSTR2 and SSTR5 for growth hormone, thyroid-stimulating hormone, and prolactin regulation.","date":"1997","source":"The Journal of clinical investigation","url":"https://pubmed.ncbi.nlm.nih.gov/9045884","citation_count":266,"is_preprint":false},{"pmid":"7521350","id":"PMC_7521350","title":"Expression of three somatostatin receptor subtypes in pituitary adenomas: evidence for preferential SSTR5 expression in the mammosomatotroph lineage.","date":"1994","source":"The Journal of clinical endocrinology and metabolism","url":"https://pubmed.ncbi.nlm.nih.gov/7521350","citation_count":169,"is_preprint":false},{"pmid":"8102785","id":"PMC_8102785","title":"Characterization of cloned somatostatin receptors SSTR4 and SSTR5.","date":"1993","source":"Molecular pharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/8102785","citation_count":127,"is_preprint":false},{"pmid":"8078491","id":"PMC_8078491","title":"Characterization of cloned human somatostatin receptor SSTR5.","date":"1994","source":"Molecular pharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/8078491","citation_count":112,"is_preprint":false},{"pmid":"24182563","id":"PMC_24182563","title":"Expression of somatostatin receptors, SSTR2A and SSTR5, in 108 endocrine pituitary tumors using immunohistochemical detection with new specific monoclonal antibodies.","date":"2013","source":"Human pathology","url":"https://pubmed.ncbi.nlm.nih.gov/24182563","citation_count":85,"is_preprint":false},{"pmid":"8684611","id":"PMC_8684611","title":"Somatostatin receptor subtypes SSTR2 and SSTR5 couple negatively to an L-type Ca2+ current in the pituitary cell line AtT-20.","date":"1996","source":"Neuroscience","url":"https://pubmed.ncbi.nlm.nih.gov/8684611","citation_count":73,"is_preprint":false},{"pmid":"26722517","id":"PMC_26722517","title":"Expression of somatostatin receptors (SSTR1-SSTR5) in meningiomas and its clinicopathological significance.","date":"2015","source":"International journal of clinical and experimental pathology","url":"https://pubmed.ncbi.nlm.nih.gov/26722517","citation_count":72,"is_preprint":false},{"pmid":"31196171","id":"PMC_31196171","title":"Aberrant methylation-mediated downregulation of lncRNA SSTR5-AS1 promotes progression and metastasis of laryngeal squamous cell carcinoma.","date":"2019","source":"Epigenetics & chromatin","url":"https://pubmed.ncbi.nlm.nih.gov/31196171","citation_count":41,"is_preprint":false},{"pmid":"12657967","id":"PMC_12657967","title":"Pancreatic somatostatin inhibits insulin secretion via SSTR-5 in the isolated perfused mouse pancreas model.","date":"2003","source":"Pancreas","url":"https://pubmed.ncbi.nlm.nih.gov/12657967","citation_count":38,"is_preprint":false},{"pmid":"8954784","id":"PMC_8954784","title":"The tuberin (TSC2), autosomal dominant polycystic kidney disease (PKD1), and somatostatin type V receptor (SSTR5) genes form a synteny group in the Fugu genome.","date":"1996","source":"Genomics","url":"https://pubmed.ncbi.nlm.nih.gov/8954784","citation_count":30,"is_preprint":false},{"pmid":"16601280","id":"PMC_16601280","title":"Somatostatin receptor subtype 5 (SSTR5) mRNA expression is related to histopathological features of cell proliferation in insulinomas.","date":"2006","source":"Endocrine-related cancer","url":"https://pubmed.ncbi.nlm.nih.gov/16601280","citation_count":30,"is_preprint":false},{"pmid":"15919085","id":"PMC_15919085","title":"SSTR5 ablation in islet results in alterations in glucose homeostasis in mice.","date":"2005","source":"FEBS letters","url":"https://pubmed.ncbi.nlm.nih.gov/15919085","citation_count":30,"is_preprint":false},{"pmid":"16026801","id":"PMC_16026801","title":"The effect of global SSTR5 gene ablation on the endocrine pancreas and glucose regulation in aging mice.","date":"2005","source":"The Journal of surgical 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autism.","date":"2003","source":"American journal of medical genetics. Part B, Neuropsychiatric genetics : the official publication of the International Society of Psychiatric Genetics","url":"https://pubmed.ncbi.nlm.nih.gov/12898583","citation_count":7,"is_preprint":false},{"pmid":"38331094","id":"PMC_38331094","title":"TRPV1+ sensory nerves suppress conjunctival inflammation via SST-SSTR5 signaling in murine allergic conjunctivitis.","date":"2024","source":"Mucosal immunology","url":"https://pubmed.ncbi.nlm.nih.gov/38331094","citation_count":6,"is_preprint":false},{"pmid":"20464704","id":"PMC_20464704","title":"Does the response of GH-secreting pituitary adenomas to octreotide depend on the cellular localization of the somatostatin receptor subtypes SSTR2 and SSTR5?","date":"2010","source":"Endokrynologia Polska","url":"https://pubmed.ncbi.nlm.nih.gov/20464704","citation_count":6,"is_preprint":false},{"pmid":"35559027","id":"PMC_35559027","title":"Identification of SSTR5 Gene Polymorphisms and Their Association With Growth Traits in Hulun Buir Sheep.","date":"2022","source":"Frontiers in genetics","url":"https://pubmed.ncbi.nlm.nih.gov/35559027","citation_count":5,"is_preprint":false},{"pmid":"38866206","id":"PMC_38866206","title":"Activation of the SST-SSTR5 signaling pathway enhances corneal wound healing in diabetic mice.","date":"2024","source":"Mucosal immunology","url":"https://pubmed.ncbi.nlm.nih.gov/38866206","citation_count":5,"is_preprint":false},{"pmid":"31556942","id":"PMC_31556942","title":"UTS2B Defines a Novel Enteroendocrine Cell Population and Regulates GLP-1 Secretion Through SSTR5 in Male Mice.","date":"2019","source":"Endocrinology","url":"https://pubmed.ncbi.nlm.nih.gov/31556942","citation_count":4,"is_preprint":false},{"pmid":"19140390","id":"PMC_19140390","title":"[Somatostatin receptors expression (SSTR1-SSTR5) in pheochromocytomas].","date":"2008","source":"Przeglad lekarski","url":"https://pubmed.ncbi.nlm.nih.gov/19140390","citation_count":4,"is_preprint":false},{"pmid":"22136833","id":"PMC_22136833","title":"SSTR5 P335L monoclonal antibody differentiates pancreatic neuroendocrine neuroplasms with different SSTR5 genotypes.","date":"2011","source":"Surgery","url":"https://pubmed.ncbi.nlm.nih.gov/22136833","citation_count":3,"is_preprint":false},{"pmid":"38070432","id":"PMC_38070432","title":"Discovery and exploration of novel somatostatin receptor subtype 5 (SSTR5) antagonists for the treatment of cholesterol gallstones.","date":"2023","source":"European journal of medicinal chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/38070432","citation_count":2,"is_preprint":false},{"pmid":"39202532","id":"PMC_39202532","title":"Pituitary Adenoma: SSTR2 rs2236750, SSTR5 rs34037914, and AIP rs267606574 Genetic Variants, Serum Levels, and Ki-67 Labeling Index Associations.","date":"2024","source":"Medicina (Kaunas, Lithuania)","url":"https://pubmed.ncbi.nlm.nih.gov/39202532","citation_count":1,"is_preprint":false},{"pmid":"40716132","id":"PMC_40716132","title":"The mechanism of lncRNA SSTR5-AS1 promoting ferroptosis resistance and immune escape in ovarian cancer cells by recruiting STAT3 to regulate SLC7A11 expression.","date":"2025","source":"Cancer genetics","url":"https://pubmed.ncbi.nlm.nih.gov/40716132","citation_count":1,"is_preprint":false},{"pmid":"39234955","id":"PMC_39234955","title":"LncRNA SSTR5-AS1 promotes esophageal carcinoma through regulating ITGB6/JAK1/STAT3 signaling.","date":"2024","source":"Epigenomics","url":"https://pubmed.ncbi.nlm.nih.gov/39234955","citation_count":1,"is_preprint":false},{"pmid":"21110926","id":"PMC_21110926","title":"[Expression and their clinical significance of SSTR2A, SSTR5 and EGFR in non-small cell lung cancer].","date":"2007","source":"Zhongguo fei ai za zhi = Chinese journal of lung cancer","url":"https://pubmed.ncbi.nlm.nih.gov/21110926","citation_count":1,"is_preprint":false},{"pmid":"41444600","id":"PMC_41444600","title":"Upregulation of lncRNA SSTR5-AS1 promotes osteoblast differentiation and reduces apoptosis.","date":"2025","source":"Journal of orthopaedic surgery and research","url":"https://pubmed.ncbi.nlm.nih.gov/41444600","citation_count":0,"is_preprint":false},{"pmid":"16335667","id":"PMC_16335667","title":"[Production and preliminary characteristics of polyclonal antibodies specific to SSTR2A and SSTR5 receptors in the pituitary gland].","date":"2005","source":"Endokrynologia Polska","url":"https://pubmed.ncbi.nlm.nih.gov/16335667","citation_count":0,"is_preprint":false},{"pmid":"38549435","id":"PMC_38549435","title":"Oral SSTR5 Antagonist SCO-240 for Growth Hormone Stimulation: A Phase I Single-Dose Study in Healthy Individuals.","date":"2024","source":"Clinical pharmacology and 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primary cilia to modulate pancreatic β-cell function","date":"2024-06-06","source":"bioRxiv","url":"https://doi.org/10.1101/2024.06.05.597562","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":30810,"output_tokens":4473,"usd":0.079763},"stage2":{"model":"claude-opus-4-6","input_tokens":7947,"output_tokens":3423,"usd":0.187965},"total_usd":0.267728,"stage1_batch_id":"msgbatch_011rkcQdVV1RaFq9XhcG6df6","stage2_batch_id":"msgbatch_01RzgrJafdF4EWHhj5mNi6dh","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1993,\n      \"finding\": \"SSTR5 was cloned and pharmacologically characterized: it binds somatostatin analogues with distinct selectivity profiles compared to other SSTR subtypes, and mediates inhibition of forskolin-stimulated cAMP accumulation in CHO/COS cells, consistent with Gi coupling.\",\n      \"method\": \"Radioligand binding competition assay, cAMP accumulation assay in transfected CHO-K1/COS-1 cells\",\n      \"journal\": \"Molecular pharmacology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro functional assay with expressed receptor, multiple pharmacological methods, foundational characterization paper\",\n      \"pmids\": [\"8102785\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"Human SSTR5 was cloned and expressed; it mediates inhibition of forskolin-stimulated cAMP accumulation via Gi, but unlike rat SSTR5, the clinically used analogue SMS 201-995 does not inhibit cAMP in human SSTR5-expressing cells, demonstrating species-dependent pharmacology. Human SSTR5 mRNA is selectively expressed in small intestine, heart, adrenal, cerebellum, pituitary, placenta, and skeletal muscle.\",\n      \"method\": \"Stable expression in CHO-K1 cells, radioligand binding, cAMP accumulation assay, RT-PCR for tissue distribution\",\n      \"journal\": \"Molecular pharmacology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro functional reconstitution with cloned human receptor, multiple orthogonal methods\",\n      \"pmids\": [\"8078491\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"SSTR5 mediates antiproliferative effects of the somatostatin analogue RC-160 through inhibition of intracellular calcium mobilization (inositol phospholipid/Ca2+ pathway), a mechanism distinct from SSTR2 (which acts via tyrosine phosphatase). SSTR5-expressing CHO cells showed RC-160 inhibition of CCK-stimulated Ca2+ and CCK-induced proliferation, and this effect was not blocked by phosphatase inhibitors.\",\n      \"method\": \"Cell proliferation assay, intracellular calcium measurement, phosphatase activity assay, pharmacological inhibitors in CHO cells stably expressing SSTR5\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — multiple orthogonal functional assays in defined cell system, mechanistic pathway dissection with inhibitors\",\n      \"pmids\": [\"7878022\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"SSTR5 couples to L-type Ca2+ channels in AtT-20 pituitary cells via pertussis toxin-sensitive G proteins (Gi/Go), mediating inhibition of Ca2+ currents. SSTR5-mediated inhibition undergoes pronounced desensitization upon agonist pretreatment, in contrast to SSTR2. The compound L362,855 acts as an antagonist/partial agonist at SSTR5.\",\n      \"method\": \"Whole-cell patch clamp electrophysiology, pertussis toxin pretreatment, selective agonist/antagonist pharmacology in AtT-20 cells\",\n      \"journal\": \"Neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct electrophysiological recording with pharmacological dissection, pertussis toxin mechanistic validation\",\n      \"pmids\": [\"8684611\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"SSTR5 mediates somatostatin-induced suppression of GH and TSH secretion in primary human fetal pituitary cultures; SSTR5-selective analogue exclusively inhibited GH in acromegalic tumor cells, demonstrating SSTR5 is sufficient for GH and TSH regulation but not prolactin suppression (which requires SSTR2).\",\n      \"method\": \"Primary human fetal pituitary cell culture, SSTR subtype-selective analogue treatment, hormone secretion assays (RIA/ELISA), radioligand binding\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — selective pharmacological dissection in primary human cells with multiple hormones measured, replicated in acromegalic tumor cells\",\n      \"pmids\": [\"9045884\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Pancreatic somatostatin inhibits insulin secretion through SSTR5 in mouse pancreas: SSTR5-knockout mice showed enhanced glucose-stimulated insulin secretion at 12 months; octreotide suppressed insulin secretion in wild-type but not SSTR5-/- mice; immunoneutralization of somatostatin increased insulin in WT but decreased it in knockouts.\",\n      \"method\": \"Isolated perfused mouse pancreas model, SSTR5 global gene knockout, somatostatin immunoneutralization, octreotide pharmacological challenge\",\n      \"journal\": \"Pancreas\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic knockout with specific functional readout, multiple experimental approaches including pharmacological rescue\",\n      \"pmids\": [\"12657967\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Double-gene ablation of SSTR1 and SSTR5 results in islet hyperplasia, hyperinsulinemia, and improved glucose tolerance in mice; isolated SSTR1/5-/- islets showed no response to somatostatin peptides, confirming both receptors coordinately regulate insulin secretion and glucose homeostasis.\",\n      \"method\": \"Double-gene knockout mouse model, intraperitoneal glucose tolerance test, isolated perfused pancreas, islet culture, immunohistochemistry\",\n      \"journal\": \"Surgery\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis with double knockout, multiple orthogonal phenotypic readouts\",\n      \"pmids\": [\"15349106\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Beta-cell-specific conditional knockdown of SSTR5 (using Cre-lox) causes glucose intolerance with absent insulin response and reduced serum insulin at 3 months, and persistently elevated insulin at 12 months; SSTR5-deficient islets do not respond to SST-28 stimulation, confirming SSTR5's direct role in beta-cell insulin secretion.\",\n      \"method\": \"Conditional Cre-lox knockout in pancreatic beta cells, glucose tolerance test, insulin tolerance test, in vitro islet stimulation with SST-28, immunohistochemistry\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — cell-type-specific genetic ablation with multiple functional and in vitro readouts\",\n      \"pmids\": [\"15919085\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Global SSTR5 knockout mice show age-dependent glucose regulation changes: glucose intolerance at 3 months (despite normal insulin secretion) and basal hypoglycemia with hyperinsulinemia at 12 months; SSTR1 expression increases compensatorily in islets at 3 months but becomes absent at 12 months, suggesting coordinate regulation between SSTR1 and SSTR5.\",\n      \"method\": \"Global SSTR5-/- mouse model, glucose tolerance test, in vitro pancreas perfusion, immunohistochemistry for SSTR1/SST/insulin\",\n      \"journal\": \"The Journal of surgical research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic knockout, multiple ages studied, compensatory receptor expression quantified\",\n      \"pmids\": [\"16026801\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"The P335L single nucleotide polymorphism of SSTR5 produces a hypofunctional receptor: overexpression of SSTR5-L335 (vs. P335) in pancreatic cancer cells enhanced proliferation, blocked the inhibitory effect of SSTR5-selective agonist RPL-1980 on proliferation and glucose-stimulated insulin secretion, and increased PDX-1 expression.\",\n      \"method\": \"Site-directed mutagenesis, transient transfection in HEK293/Mia PaCa-2/β-TC-6 cells, MTS proliferation assay, insulin ELISA, SNP genotyping\",\n      \"journal\": \"World journal of surgery\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — mutagenesis combined with functional assays in multiple cell lines, mechanistic comparison of variants\",\n      \"pmids\": [\"21249361\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"SST/SSTR5 signaling upregulates colonic MUC2 expression and mucus secretion through suppression of the Notch-Hes1 pathway; SSTR5-specific siRNA knockdown abolished SST-induced MUC2 upregulation, and SSTR5 agonist L817,818 replicated the effect.\",\n      \"method\": \"siRNA knockdown of SSTR5 in LS174T cells, SSTR5 agonist treatment, Western blot for NICD and Hes1, MUC2 expression assay, in vivo octreotide administration in mice\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — siRNA knockdown and agonist rescue with pathway marker readout, supported by in vivo correlate\",\n      \"pmids\": [\"31733832\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"UTS2B (urotensin 2B), produced by a novel enteroendocrine cell type, inhibits GLP-1 secretion through SSTR5 (not its cognate receptor UTS2R) acting in a paracrine manner in mouse intestinal crypts; SSTR5-mediated inhibition of GLP-1 was confirmed using intestinal organoids.\",\n      \"method\": \"Mouse intestinal crypt and organoid culture, receptor identification by pharmacological antagonism, in vivo peptide administration with plasma GLP-1/insulin measurement\",\n      \"journal\": \"Endocrinology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — receptor identification by specific antagonists in ex vivo system, in vivo validation\",\n      \"pmids\": [\"31556942\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"ZDHHC5 catalyzes palmitoylation of SSTR5; pharmacological blockade of ZDHHC5 with lomitapide inhibits SSTR5 palmitoylation and attenuates pancreatic cancer cell growth in vitro and in vivo.\",\n      \"method\": \"Single-cell transcriptomics comparison, ZDHHC5 inhibition with lomitapide, cell proliferation assay, in vivo xenograft model\",\n      \"journal\": \"Cell death discovery\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — pharmacological ZDHHC5 inhibition identifies palmitoylation dependency of SSTR5, but direct biochemical confirmation of palmitoylation site on SSTR5 not detailed in abstract\",\n      \"pmids\": [\"36774350\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"SSTR5 (and SSTR3) localizes to primary cilia of pancreatic β-cells; activation of ciliary SSTR5 lowers ciliary cAMP concentration via Gαi. δ-cells are positioned near primary cilia of other islet cells and direct somatostatin secretion toward cilia. Sustained somatostatin exposure promotes nuclear entry of the transcription factor GLI2 via a ciliary Ca2+ signaling mechanism, extending SSTR5 function beyond acute hormone suppression.\",\n      \"method\": \"Live-cell fluorescence imaging (ciliary cAMP biosensor), subcellular fractionation/localization, islet morphology by confocal microscopy, GLI2 nuclear translocation assay, cilia length measurement in human T2D donor islets\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct live imaging of ciliary cAMP with biosensor, mechanistic dissection of ciliary vs. cytosolic signaling; preprint not yet peer-reviewed\",\n      \"pmids\": [\"bio_10.1101_2024.06.05.597562\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"TRPV1+ sensory nerves release somatostatin that binds SSTR5 on mast cells and conjunctival fibroblasts to suppress TNF-α production in mast cells and CCL11 (eotaxin-1) expression in fibroblasts, thereby reducing eosinophil infiltration in allergic conjunctivitis.\",\n      \"method\": \"TRPV1+ nerve ablation (resiniferatoxin), TRPV1 blockade, SST-SSTR5 agonist treatment, in vivo murine allergic conjunctivitis model, gene expression and cell infiltration analysis\",\n      \"journal\": \"Mucosal immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — nerve ablation and pharmacological dissection in vivo with specific cellular readouts on mast cells and fibroblasts\",\n      \"pmids\": [\"38331094\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Activation of SSTR5 with the agonist L-817,818 reduces inflammatory response after corneal epithelial injury and promotes re-epithelialization and nerve regeneration in diabetic mice, acting by inhibiting neutrophil infiltration and shifting macrophage polarization from M1 to M2.\",\n      \"method\": \"Topical SST/SSTR5 agonist (L-817,818) administration, streptozotocin diabetic mouse corneal wound model, gene expression, immunofluorescence for macrophage polarization, neutrophil quantification\",\n      \"journal\": \"Mucosal immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — specific SSTR5 agonist with defined cellular and molecular phenotypes in vivo\",\n      \"pmids\": [\"38866206\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"SSTR5 antagonism (with oral SCO-240) stimulates robust growth hormone (GH) secretion in healthy humans without affecting other pituitary hormones, demonstrating that endogenous SSTR5 tonically suppresses GH release in vivo.\",\n      \"method\": \"Phase I randomized double-blind placebo-controlled human clinical trial with pharmacokinetic and pharmacodynamic readouts (serum GH, insulin, GLP-1, gallbladder contractions)\",\n      \"journal\": \"Clinical pharmacology and therapeutics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — controlled human trial with specific SSTR5 antagonist, robust GH secretion phenotype, multiple hormone readouts\",\n      \"pmids\": [\"38549435\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Cortistatin suppresses angiotensin II-induced vascular smooth muscle cell proliferation and autophagy partially through SSTR3 and SSTR5; blocking SSTR3 and SSTR5 with antagonists partially abrogated cortistatin's anti-proliferative and anti-autophagic effects.\",\n      \"method\": \"Rat VSMC culture, CCK-8 proliferation assay, Western blot, immunofluorescence, transmission electron microscopy, SSTR3/5 antagonist pharmacology\",\n      \"journal\": \"Life sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — pharmacological receptor antagonism identifies SSTR5 involvement, but effect is partial and shared with SSTR3\",\n      \"pmids\": [\"32348837\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"SSTR5 is a Gi-coupled G protein-coupled receptor that suppresses hormone secretion (GH, TSH, insulin, GLP-1) and cell proliferation through inhibition of adenylyl cyclase (lowering cAMP), inhibition of L-type Ca2+ channels via pertussis toxin-sensitive Gi/Go proteins, and suppression of intracellular calcium mobilization via the phospholipid/Ca2+ pathway; it localizes to primary cilia of pancreatic β-cells where it modulates ciliary cAMP and triggers GLI2-dependent transcriptional responses, is palmitoylated by ZDHHC5, and a hypofunctional P335L SNP impairs its anti-proliferative and insulin-inhibitory signaling.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"SSTR5 is a Gi/Go-coupled somatostatin receptor that tonically suppresses hormone secretion and cell proliferation across endocrine, gastrointestinal, and immune cell types. It inhibits adenylyl cyclase to lower cAMP and suppresses L-type Ca²⁺ channel currents via pertussis toxin-sensitive G proteins, while independently inhibiting intracellular calcium mobilization through the phospholipid/Ca²⁺ pathway to exert antiproliferative effects distinct from SSTR2's phosphatase-dependent mechanism [PMID:8102785, PMID:8684611, PMID:7878022]. In pancreatic β-cells, SSTR5 is the principal receptor mediating somatostatin-dependent inhibition of insulin secretion, as demonstrated by global and β-cell-specific knockouts that produce hyperinsulinemia and altered glucose homeostasis, and it localizes to primary cilia where it lowers ciliary cAMP and promotes GLI2 nuclear translocation [PMID:12657967, PMID:15919085, PMID:38549435]. SSTR5 also suppresses GH and TSH release from pituitary cells, inhibits GLP-1 secretion in intestinal crypts, upregulates colonic MUC2 via Notch-Hes1 pathway suppression, and exerts anti-inflammatory effects by reducing TNF-α production and promoting M2 macrophage polarization [PMID:9045884, PMID:31556942, PMID:31733832, PMID:38331094].\",\n  \"teleology\": [\n    {\n      \"year\": 1993,\n      \"claim\": \"Cloning and functional expression of SSTR5 established it as a Gi-coupled receptor with a pharmacological profile distinct from other SSTR subtypes, resolving the question of whether a fifth somatostatin receptor subtype existed with unique ligand selectivity.\",\n      \"evidence\": \"Radioligand binding and cAMP accumulation assays in transfected CHO-K1/COS-1 cells\",\n      \"pmids\": [\"8102785\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Downstream effectors beyond cAMP not yet identified\", \"In vivo physiological role unknown\"]\n    },\n    {\n      \"year\": 1994,\n      \"claim\": \"Cloning of human SSTR5 revealed species-dependent pharmacology — the clinically used analogue octreotide (SMS 201-995) did not inhibit cAMP at human SSTR5 — establishing that rodent pharmacology could not be directly extrapolated to human drug design.\",\n      \"evidence\": \"Stable expression in CHO-K1 cells, radioligand binding, cAMP assay, RT-PCR tissue distribution\",\n      \"pmids\": [\"8078491\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis for species selectivity difference unknown\", \"Native tissue function not yet demonstrated\"]\n    },\n    {\n      \"year\": 1995,\n      \"claim\": \"SSTR5's antiproliferative mechanism was shown to operate through inhibition of the phospholipid/Ca²⁺ pathway rather than tyrosine phosphatase activation, distinguishing it mechanistically from SSTR2 and identifying a second effector arm.\",\n      \"evidence\": \"Cell proliferation assay, intracellular calcium measurement, phosphatase activity assay with pharmacological inhibitors in CHO-SSTR5 cells\",\n      \"pmids\": [\"7878022\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of the phospholipase/Ca²⁺ intermediary not defined\", \"Relevance to native tissues expressing SSTR5 not confirmed\"]\n    },\n    {\n      \"year\": 1996,\n      \"claim\": \"SSTR5 was shown to inhibit L-type Ca²⁺ channels through pertussis toxin-sensitive Gi/Go proteins and to undergo pronounced desensitization, providing the first direct electrophysiological characterization of SSTR5 effector coupling.\",\n      \"evidence\": \"Whole-cell patch clamp in AtT-20 pituitary cells with pertussis toxin and selective agonist/antagonist pharmacology\",\n      \"pmids\": [\"8684611\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Specific Gα subunit identity not resolved\", \"Desensitization mechanism (GRK/β-arrestin involvement) not defined\"]\n    },\n    {\n      \"year\": 1997,\n      \"claim\": \"SSTR5-selective pharmacology in primary human pituitary cells demonstrated that SSTR5 is sufficient to suppress GH and TSH secretion but not prolactin, assigning specific endocrine functions to this subtype in humans.\",\n      \"evidence\": \"Primary human fetal pituitary cultures and acromegalic tumor cells treated with SSTR5-selective analogues, hormone RIA/ELISA\",\n      \"pmids\": [\"9045884\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relative contribution of SSTR5 vs. SSTR2 in combined pituitary signaling not quantified\", \"Downstream intracellular pathway in pituitary GH suppression not mapped\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Genetic ablation of SSTR5 in mice proved that SSTR5 is the receptor mediating somatostatin's tonic inhibition of insulin secretion in pancreatic islets, resolving which SSTR subtype controls β-cell insulin release.\",\n      \"evidence\": \"SSTR5 global knockout mice, isolated perfused pancreas, octreotide challenge, somatostatin immunoneutralization\",\n      \"pmids\": [\"12657967\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Cell-autonomous vs. paracrine contribution not yet separated\", \"Compensatory SSTR expression changes not fully characterized\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Double knockout of SSTR1 and SSTR5 produced islet hyperplasia and hyperinsulinemia exceeding single knockouts, establishing that SSTR1 and SSTR5 coordinate to restrain insulin secretion and β-cell mass.\",\n      \"evidence\": \"SSTR1/SSTR5 double-knockout mice, glucose tolerance tests, perfused pancreas, islet culture\",\n      \"pmids\": [\"15349106\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether SSTR1 and SSTR5 signal through the same or distinct intracellular pathways in islets unclear\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"β-cell-specific conditional knockout confirmed cell-autonomous SSTR5 function and revealed age-dependent insulin secretory phenotypes, while global knockouts showed compensatory upregulation of SSTR1 at early ages followed by loss at later ages.\",\n      \"evidence\": \"Cre-lox β-cell-specific and global SSTR5 knockout mice, glucose/insulin tolerance tests, in vitro islet SST-28 stimulation, immunohistochemistry\",\n      \"pmids\": [\"15919085\", \"16026801\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular mechanism of SSTR1 compensatory regulation unknown\", \"Whether age-dependent phenotype applies to humans undetermined\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"The P335L SNP was identified as a hypofunctional SSTR5 variant that impairs antiproliferative signaling and insulin suppression, linking receptor coding variation to functional output and potential disease susceptibility.\",\n      \"evidence\": \"Site-directed mutagenesis, transfection in HEK293/MiaPaCa-2/βTC-6 cells, proliferation and insulin secretion assays\",\n      \"pmids\": [\"21249361\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis for P335L hypofunction unknown\", \"Population frequency and clinical significance not established in patient cohorts\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"SSTR5 was shown to regulate intestinal physiology through two distinct mechanisms: suppression of the Notch-Hes1 pathway to upregulate colonic MUC2/mucus secretion, and paracrine inhibition of GLP-1 secretion in intestinal crypts by the non-canonical ligand UTS2B.\",\n      \"evidence\": \"siRNA knockdown and SSTR5 agonist in LS174T cells with Western blot; mouse intestinal crypt/organoid culture with receptor pharmacological antagonism and in vivo peptide administration\",\n      \"pmids\": [\"31733832\", \"31556942\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct binding of UTS2B to SSTR5 not demonstrated biochemically\", \"In vivo relevance of MUC2 regulation in SSTR5 knockout not tested\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Cortistatin's suppression of vascular smooth muscle proliferation and autophagy was partially attributed to SSTR5 (shared with SSTR3), extending SSTR5's antiproliferative role to the vasculature.\",\n      \"evidence\": \"Rat VSMC culture, SSTR3/5 antagonist pharmacology, proliferation and autophagy assays\",\n      \"pmids\": [\"32348837\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Effect is partial and shared with SSTR3, making specific SSTR5 contribution uncertain\", \"No genetic confirmation of SSTR5 involvement\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"ZDHHC5 was identified as the palmitoyl acyltransferase for SSTR5, and pharmacological inhibition of ZDHHC5 attenuated pancreatic cancer growth dependent on SSTR5 palmitoylation.\",\n      \"evidence\": \"Single-cell transcriptomics, lomitapide-mediated ZDHHC5 inhibition, cell proliferation assay, in vivo xenograft\",\n      \"pmids\": [\"36774350\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct biochemical identification of palmitoylation sites on SSTR5 not reported\", \"Whether palmitoylation affects SSTR5 trafficking, stability, or signaling not distinguished\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Multiple 2024 studies expanded SSTR5's functional scope: ciliary localization in β-cells with local cAMP reduction and GLI2 nuclear translocation; anti-inflammatory roles via TNF-α suppression on mast cells and M1-to-M2 macrophage polarization; and human clinical proof that SSTR5 tonically suppresses GH secretion in healthy adults.\",\n      \"evidence\": \"Live-cell ciliary cAMP biosensor imaging (preprint); TRPV1+ nerve ablation and SSTR5 agonist in murine allergic conjunctivitis; SSTR5 agonist in diabetic corneal wound model; phase I RCT with oral SSTR5 antagonist in humans\",\n      \"pmids\": [\"bio_10.1101_2024.06.05.597562\", \"38331094\", \"38866206\", \"38549435\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Ciliary cAMP/GLI2 findings from preprint await peer review\", \"How ciliary vs. plasma membrane SSTR5 signaling pools are differentially regulated is undefined\", \"Anti-inflammatory mechanisms need genetic confirmation in SSTR5 knockout models\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key open questions include: the structural basis for SSTR5's distinct effector coupling and desensitization properties; how SSTR5 palmitoylation by ZDHHC5 modulates trafficking and signaling; the physiological significance of ciliary vs. non-ciliary SSTR5 signaling; and whether SSTR5 coding variants (e.g. P335L) predispose to metabolic or neoplastic disease in human populations.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No high-resolution structure of SSTR5 in active or inactive state\", \"No systematic human genetic association studies for SSTR5 variants\", \"Ciliary signaling findings not yet peer-reviewed or replicated\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [0, 1, 3, 4, 5, 16]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [2, 3, 10, 14, 15]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 1, 2, 3]},\n      {\"term_id\": \"GO:0005929\", \"supporting_discovery_ids\": [13]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0162582\", \"supporting_discovery_ids\": [0, 1, 2, 3]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [0, 1, 2, 3, 10, 13]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [14, 15]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [12]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"SSTR1\",\n      \"SSTR3\",\n      \"ZDHHC5\",\n      \"GLI2\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}