{"gene":"SSTR2","run_date":"2026-06-10T07:46:41","timeline":{"discoveries":[{"year":1993,"finding":"SSTR2 selectively associates with Gi alpha 3 and G(o) alpha 2 pertussis toxin-sensitive G proteins, as demonstrated by immunoprecipitation with peptide-directed antisera in CHO cells expressing the cloned receptor; Gi alpha 1 and Gi alpha 2 antisera did not uncouple SSTR2/G protein complexes.","method":"Immunoprecipitation with subtype-specific G protein antisera in CHO and HEK293 cells stably expressing SSTR2","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal immunoprecipitation approach, replicated across two cell lines (CHO and HEK293) with multiple G protein antisera providing subtype specificity","pmids":["8098703"],"is_preprint":false},{"year":1993,"finding":"Rat SSTR2 expressed in CHO cells is coupled to inhibition of adenylyl cyclase: somatostatin-14 inhibited forskolin-stimulated cAMP accumulation by ~75% with EC50 ~350 pM.","method":"cAMP accumulation assay in CHO cells stably transfected with rat SSTR2 cDNA","journal":"Biochemical and biophysical research communications","confidence":"High","confidence_rationale":"Tier 1 / Strong — direct in vitro enzymatic assay (adenylyl cyclase inhibition), replicated across multiple papers (PMID 8096694, 7907016, 8144617)","pmids":["8096694","7907016","8144617"],"is_preprint":false},{"year":1994,"finding":"SSTR2 activation stimulates tyrosine phosphatase activity and inhibits serum-stimulated cell proliferation (EC50 in low pM range for RC-160 and SMS 201-995), implicating tyrosine phosphatase as a transducer of the SSTR2 growth-inhibition signal.","method":"Tyrosine phosphatase activity assay and cell proliferation assay in COS-7 and NIH 3T3 cells expressing human SSTR2; pharmacological dose-response with selective analogues","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Strong — dose-response correlation between receptor binding affinity, phosphatase stimulation, and growth inhibition; replicated in CHO cells in PMID 7878022","pmids":["7907795","7878022"],"is_preprint":false},{"year":1994,"finding":"SSTR2 couples to phospholipase C and Ca2+ mobilization in addition to inhibiting adenylyl cyclase; the PLC/Ca2+ response is only partially sensitive to pertussis toxin, indicating involvement of both PTX-sensitive and PTX-insensitive G proteins.","method":"Transfection of human SSTR2 cDNA into COS-7 cells; measurement of cAMP, inositol phosphates, and intracellular Ca2+ with pertussis toxin treatment","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple signaling readouts in one study, single lab; replicated partially in rat pituitary cells (PMID 9228036)","pmids":["7910018","9228036"],"is_preprint":false},{"year":1994,"finding":"SSTR2 coupling to adenylyl cyclase inhibition requires the presence of Gi alpha 1 protein: human SSTR2 in CHO cells (which lack Gi alpha 1) does not inhibit cAMP unless Gi alpha 1 is co-expressed; the effect is pertussis toxin-sensitive.","method":"Co-expression of human SSTR2 with individual Gi alpha subunits in CHO cells; cAMP assay with pertussis toxin","journal":"Biochemical and biophysical research communications","confidence":"High","confidence_rationale":"Tier 1 / Moderate — reconstitution approach (co-expression of specific G protein subunit rescues signaling), with pertussis toxin control; single lab","pmids":["7914078"],"is_preprint":false},{"year":1994,"finding":"SSTR2 inhibits high-voltage-activated (HVA) Ca2+ currents in RINm5F insulinoma cells; SSTR1 expressed in the same cells does not inhibit these currents, demonstrating subtype specificity.","method":"Patch-clamp electrophysiology in RINm5F cells stably expressing human SSTR2 or SSTR1","journal":"FEBS letters","confidence":"High","confidence_rationale":"Tier 1 / Moderate — direct electrophysiological measurement with isogenic cell lines differing only in receptor subtype; within-study control","pmids":["7982482"],"is_preprint":false},{"year":1994,"finding":"SSTR2 couples exclusively to pertussis toxin-sensitive G proteins (evidenced by GTPγS and PTX effects on ligand binding), whereas SSTR1 couples to both PTX-sensitive and -insensitive G proteins; only SSTR1, not SSTR2, mediates somatostatin inhibition of Na+-H+ exchange activity via a PTX-insensitive mechanism.","method":"Stable/transient expression of SSTR1, SSTR2, and chimeric receptors in Ltk- and HEK293 cells; Na+-H+ exchange assay, cAMP assay, pertussis toxin treatment, chimeric receptor mapping","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — chimeric receptor structure-function mapping plus multiple functional readouts; identifies molecular determinants of subtype-specific signaling","pmids":["8144617"],"is_preprint":false},{"year":1995,"finding":"Two amino acids in transmembrane domains VI (Gln291→Asn) and VII (Ser305→Phe) of SSTR2 largely determine the high-affinity selectivity of the peptide agonist SMS 201-995; single Ser305→Phe mutation in SSTR1 increases SMS 201-995 affinity ~100-fold, and combining with Gln291→Asn yields near-full SMS 201-995 susceptibility.","method":"Site-directed mutagenesis of SSTR1 with sequential introduction of SSTR2 residues; radioligand binding assays","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1 / Strong — systematic site-directed mutagenesis with quantitative binding, multiple mutant constructs tested; identifies two specific residues","pmids":["7882976"],"is_preprint":false},{"year":1995,"finding":"Asp122 in transmembrane domain III of SSTR2 is a critical contact residue for somatostatin-14 binding: charge-switch mutations (D122K receptor + asp9-S-14 ligand) restore binding, implicating an ionic interaction between Lys9 of S-14 and Asp122 of SSTR2.","method":"Site-directed mutagenesis of rat SSTR2 (D89A, D89E, D122K); radioligand binding with wild-type and charge-substituted somatostatin analogues","journal":"Biochemical and biophysical research communications","confidence":"High","confidence_rationale":"Tier 1 / Moderate — charge-swap mutagenesis with restored binding demonstrates specific ionic contact; rigorous approach","pmids":["7488212"],"is_preprint":false},{"year":1995,"finding":"SSTR2-mediated inhibition of cell proliferation acts through tyrosine phosphatase activation (suppressed by orthovanadate), whereas SSTR5-mediated growth inhibition operates through inhibition of intracellular Ca2+ mobilization (not through the phosphatase pathway); distinct mechanisms for each subtype.","method":"CHO cells stably expressing individual SSTR subtypes 1–5; proliferation assays with orthovanadate and phosphatase inhibitors; intracellular calcium measurements","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Strong — isogenic CHO lines expressing each of 5 SSTR subtypes; pharmacological inhibitors of phosphatase pathway selectively block SSTR2-mediated but not SSTR5-mediated growth inhibition","pmids":["7878022"],"is_preprint":false},{"year":1996,"finding":"SSTR2 couples to inhibition of L-type Ca2+ channels in AtT-20 pituitary cells via pertussis toxin-sensitive G proteins; this coupling is not desensitized by SSTR2-selective agonist pretreatment (unlike SSTR5, which undergoes desensitization).","method":"Whole-cell patch-clamp in AtT-20 cells; SSTR2-selective agonists (MK 678, BIM 23027, NC8-12); pertussis toxin pretreatment","journal":"Neuroscience","confidence":"High","confidence_rationale":"Tier 1 / Moderate — direct electrophysiology with subtype-selective agonists and PTX, functional comparison between SSTR2 and SSTR5 coupling and desensitization","pmids":["8684611"],"is_preprint":false},{"year":1994,"finding":"SSTR2 protein migrates at 93 kDa in CHO cells expressing the cloned receptor and at 148 kDa in rat brain regions with high SSTR2 mRNA, indicating differential post-translational modification (likely glycosylation) in native tissue versus transfected cells.","method":"Peptide-directed antibody immunoblotting and immunoprecipitation of SSTR2 from transfected CHO cells and rat brain","journal":"Journal of neurochemistry","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — immunoblotting and immunoprecipitation with two independent antibodies; single lab but two orthogonal antibodies and two cell sources","pmids":["7518495"],"is_preprint":false},{"year":1995,"finding":"SSTR2 activation in AR42J pancreatic cells opens cell-surface calcium channels in a phospholipase C-independent manner: SSTR2-selective agonists increase intracellular Ca2+ that is abolished in Ca2+-free medium but do not stimulate inositol phosphate turnover.","method":"Intracellular Ca2+ measurement and inositol phosphate assay in AR42J cells using SSTR subtype-selective agonists","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — two complementary assays (Ca2+ imaging and IP turnover) with pharmacological selectivity; single lab","pmids":["7669056"],"is_preprint":false},{"year":1997,"finding":"SSTR2 activation in pituitary F4C1 cells stimulates phospholipase C and raises intracellular Ca2+ from intracellular stores (partially PTX-resistant); sequences beyond the intracellular loops—not only the third intracellular loop—are required for SSTR2 coupling to PLC, as chimeras containing only SSTR2 intracellular loops in SSTR1 background did not reconstitute PLC stimulation.","method":"Expression of SSTR1, SSTR2, and chimeric receptors in pituitary GH12C1 and F4C1 cells; adenylyl cyclase inhibition, PLC activity, and [Ca2+]i measurements with pertussis toxin","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — chimeric receptor mapping combined with multiple functional readouts in cells lacking endogenous SSTRs; identifies structural requirements beyond intracellular loops","pmids":["9228036"],"is_preprint":false},{"year":1997,"finding":"In human fetal pituitary cells, prolactin suppression is mediated predominantly by SSTR2, whereas GH and TSH suppression are mediated by both SSTR2 and SSTR5, as shown by subtype-selective somatostatin analogues with defined binding affinities.","method":"Primary human fetal pituitary cultures treated with SSTR2- or SSTR5-selective analogues; hormone secretion assays correlated with receptor binding affinities in stably transfected cell lines","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 2 / Strong — primary human tissue with pharmacologically characterized subtype-selective ligands; functional hormone secretion endpoints","pmids":["9045884"],"is_preprint":false},{"year":2002,"finding":"In the gastrointestinal tract, SSTR2 is expressed on parietal cells and enterochromaffin-like (ECL) cells in the stomach, and on NOS-positive neurons in the myenteric and submucosal plexuses of the intestine, as identified using Sstr2 knockout/lacZ knockin mice.","method":"LacZ knockin reporter mice; beta-galactosidase staining combined with immunostaining for H+K+ATPase (parietal cells), histidine decarboxylase (ECL cells), and NOS","journal":"The Journal of comparative neurology","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic reporter knockin provides unambiguous cell-type identification; multiple co-labeling markers across multiple GI segments","pmids":["12442323"],"is_preprint":false},{"year":2003,"finding":"SSTR2 on cholangiocytes mediates somatostatin-induced stimulation of ductal bile absorption and inhibition of secretin-stimulated ductal bile secretion; these effects involve increases in intracellular cGMP and inhibition of secretin-stimulated cAMP, and are absent in SSTR2 knockout mice.","method":"Isolated intrahepatic bile duct units from wild-type and SSTR2 knockout mice; luminal area measurement, cAMP and cGMP assays, SSTR2-selective agonist L-779976","journal":"American journal of physiology. Cell physiology","confidence":"High","confidence_rationale":"Tier 2 / Strong — knockout vs. wild-type comparison with selective agonist and second messenger readouts; multiple orthogonal methods","pmids":["12676656"],"is_preprint":false},{"year":2012,"finding":"In human pancreatic β- and α-cells, SSTR2 is the dominant somatostatin receptor mediating SST-induced inhibition of secretion through: (1) activation of GIRK channels causing membrane hyperpolarization, (2) reduction of P/Q-type Ca2+ currents, and (3) direct inhibition of exocytosis; SSTR5 is only marginally effective.","method":"Human islets: quantitative PCR, immunohistochemistry, whole-cell patch-clamp (GIRK channel blocker tertiapin-Q, tolbutamide), Ca2+ current recordings, exocytosis measurements with SSTR subtype-selective agonists","journal":"American journal of physiology. Endocrinology and metabolism","confidence":"High","confidence_rationale":"Tier 1 / Strong — primary human tissue with multiple orthogonal electrophysiological and secretion assays; multiple pharmacological tools; mechanistic dissection of three parallel inhibitory mechanisms","pmids":["22932785"],"is_preprint":false},{"year":2018,"finding":"SSTR2 undergoes transient interactions with the cytoskeletal protein filamin A (FLNA) preferentially along actin fibers; agonist stimulation increases SSTR2 localization along actin fibers, clustering, and recruitment to clathrin-coated pits (CCPs). Blocking SSTR2-FLNA binding with a dominant-negative FLNA fragment increases SSTR2 mobility, disrupts clustering along actin, and impairs both recruitment to CCPs and receptor internalization.","method":"Fast multicolor single-molecule microscopy in living cells; dominant-negative FLNA fragment; tracking of individual SSTR2 and FLNA molecules at the plasma membrane","journal":"Endocrinology","confidence":"High","confidence_rationale":"Tier 1 / Strong — single-molecule live-cell imaging with loss-of-function dominant-negative approach; mechanistically links FLNA interaction to SSTR2 nanoscale organization, clustering, and internalization","pmids":["29931263"],"is_preprint":false},{"year":2002,"finding":"In HIT-T15 clonal beta-cells, SSTR2 (not SSTR1, 3, 4, or 5) specifically mediates somatostatin-induced increase in intracellular Ca2+ and insulin secretion in the presence of arginine vasopressin; this effect is blocked by the SSTR2-specific antagonist PRL-2903.","method":"Subtype-selective SSTR agonists and SSTR2 antagonist PRL-2903; intracellular Ca2+ measurement and insulin secretion assay in HIT-T15 cells","journal":"Life sciences","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — pharmacological selectivity with five subtype-specific agonists plus an SSTR2 antagonist; single lab","pmids":["12084389"],"is_preprint":false},{"year":2024,"finding":"Cortistatin binds specifically to SSTR2 and activates AMPK, which inhibits Drp1-mediated mitochondrial fission, reduces ROS, and thereby suppresses NLRP3 inflammasome activation and cardiomyocyte pyroptosis in septic cardiomyopathy; pharmacological inhibition and genetic ablation of SSTR2 abolish these protective effects.","method":"Sepsis mouse model; SSTR2 pharmacological inhibition and genetic ablation; AMPK phosphorylation, Drp1 activity, caspase-1 cleavage, IL-1β, gasdermin D, and cardiac function measurements","journal":"International immunopharmacology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic and pharmacological loss-of-function approaches with multiple downstream pathway readouts; single lab","pmids":["38733824"],"is_preprint":false},{"year":2006,"finding":"SSTR2 overexpression in SSTR2-negative pancreatic carcinoma cells (BXPC-3) reduces cell migration and invasion through Matrigel, accompanied by reduced MMP-2 mRNA and increased TIMP-2 mRNA expression.","method":"Adenovirus-mediated SSTR2 transfection in BXPC-3 cells; Matrigel-coated Transwell migration/invasion assay; RT-PCR for MMP-2 and TIMP-2","journal":"Journal of Huazhong University of Science and Technology. Medical sciences","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, single set of assays, no rescue or mechanistic dissection beyond mRNA correlation","pmids":["16711011"],"is_preprint":false},{"year":2025,"finding":"miR-375 epigenetically downregulates SSTR2 expression in corticotroph pituitary cells: glucocorticoid (dexamethasone) treatment increases miR-375, which targets Sstr2 mRNA; miR-375 inhibition increases SSTR2 membranous protein expression, enhances receptor internalization upon octreotide treatment, and potentiates octreotide-induced antiproliferative and apoptotic effects (PARP cleavage, caspase-3, ERK1/2 phosphorylation).","method":"RT-qPCR, Western blot, immunofluorescence, miR-375 inhibitor, proliferation assay, flow cytometry in AtT20/D16 cells and primary human corticotroph cultures","journal":"Endocrinology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — miRNA loss-of-function with multiple downstream readouts in both cell line and primary cultures; single lab","pmids":["40488558"],"is_preprint":false}],"current_model":"SSTR2 is a G protein-coupled receptor that selectively couples to Gi alpha 3 and Go alpha to inhibit adenylyl cyclase, activate tyrosine phosphatase (mediating growth inhibition), stimulate phospholipase C/Ca2+ mobilization via partially PTX-insensitive pathways, and inhibit voltage-gated Ca2+ channels and GIRK-mediated membrane currents; ligand selectivity is conferred by Asp122 (TM III, ionic contact with somatostatin Lys9), Gln291 (TM VI), and Ser305 (TM VII); at the plasma membrane, dynamic interactions with filamin A along actin fibers control SSTR2 nanoscale clustering and clathrin-mediated internalization; in specific tissues SSTR2 mediates somatostatin inhibition of insulin/glucagon secretion (via GIRK, P/Q-type Ca2+ channels, and direct exocytosis inhibition), ductal bile homeostasis (via cAMP/cGMP), and gastric acid secretion (on parietal and ECL cells); SSTR2 expression is epigenetically regulated by promoter methylation and by glucocorticoid-induced miR-375."},"narrative":{"mechanistic_narrative":"SSTR2 is a Gi/Go-coupled somatostatin receptor that transduces somatostatin signals into inhibition of secretion, growth, and metabolic output across endocrine, gastrointestinal, and pituitary tissues [PMID:8098703, PMID:8096694, PMID:7907016, PMID:8144617, PMID:22932785]. It selectively associates with pertussis toxin-sensitive Gi alpha 3 and Go alpha subunits and inhibits adenylyl cyclase, an effect that depends on the available Gi pool [PMID:8098703, PMID:8096694, PMID:7907016, PMID:8144617, PMID:7914078]. Beyond cAMP suppression, SSTR2 activates a tyrosine phosphatase that mediates its antiproliferative signal—mechanistically distinct from the Ca2+-based growth inhibition of SSTR5—and engages phospholipase C/Ca2+ mobilization through partially PTX-insensitive pathways that require receptor regions beyond the intracellular loops [PMID:7907795, PMID:7878022, PMID:9228036]. SSTR2 also couples to inhibition of high-voltage-activated and L-type Ca2+ channels and, in human islet cells, suppresses insulin/glucagon secretion through GIRK channel activation, reduction of P/Q-type Ca2+ currents, and direct inhibition of exocytosis [PMID:7982482, PMID:8684611, PMID:22932785]. Ligand selectivity is encoded by specific transmembrane residues: Asp122 (TM III) forms an ionic contact with somatostatin Lys9, while Gln291 (TM VI) and Ser305 (TM VII) determine high-affinity peptide agonist recognition [PMID:7882976, PMID:7488212]. At the plasma membrane, transient interactions with filamin A along actin fibers control SSTR2 nanoscale clustering and clathrin-mediated internalization [PMID:29931263]. Tissue-level roles include suppression of pituitary hormone release, regulation of ductal bile homeostasis via cGMP and cAMP, and control of gastric acid secretion through expression on parietal and ECL cells [PMID:9045884, PMID:12442323, PMID:12676656]. SSTR2 abundance is regulated post-transcriptionally by glucocorticoid-induced miR-375, which limits receptor expression and dampens octreotide responsiveness [PMID:40488558].","teleology":[{"year":1993,"claim":"Established the G protein coupling specificity of SSTR2, defining which transducers carry its signal and distinguishing it from related receptors.","evidence":"Subtype-specific G protein antisera immunoprecipitation in CHO and HEK293 cells, plus cAMP accumulation assays in transfected CHO cells","pmids":["8098703","8096694","7907016","8144617"],"confidence":"High","gaps":["Stoichiometry and dynamics of Gi alpha 3/Go alpha selection not resolved","Did not address PTX-insensitive coupling later observed for PLC"]},{"year":1994,"claim":"Resolved that adenylyl cyclase inhibition by SSTR2 depends on the available Gi alpha subunit pool, explaining cell-context dependence of cAMP responses.","evidence":"Co-expression of SSTR2 with individual Gi alpha subunits in Gi alpha 1-deficient CHO cells with PTX controls","pmids":["7914078"],"confidence":"High","gaps":["Reconciliation with the earlier Gi alpha 3/Go alpha association data not addressed","Single lab, single cell background"]},{"year":1994,"claim":"Identified tyrosine phosphatase activation as the transducer of SSTR2 growth inhibition, separating its antiproliferative mechanism from second-messenger pathways.","evidence":"Tyrosine phosphatase and proliferation assays with selective analogues in COS-7, NIH 3T3 and CHO cells; orthovanadate suppression","pmids":["7907795","7878022","7878022"],"confidence":"High","gaps":["Identity of the specific phosphatase not established","Downstream substrates of the phosphatase unknown"]},{"year":1994,"claim":"Demonstrated SSTR2 couples to PLC/Ca2+ and to Ca2+ channel inhibition, broadening its effector repertoire beyond cAMP and showing subtype-specific channel control.","evidence":"Inositol phosphate/Ca2+ measurements with PTX in COS-7 cells; patch-clamp of HVA Ca2+ currents in RINm5F cells expressing SSTR2 versus SSTR1","pmids":["7910018","7982482","9228036"],"confidence":"Medium","gaps":["Identity of the PTX-insensitive G protein driving PLC not defined","Link between PLC and channel effects not integrated"]},{"year":1995,"claim":"Mapped the molecular determinants of somatostatin ligand recognition, defining how SSTR2 achieves selective high-affinity binding.","evidence":"Site-directed and charge-swap mutagenesis of SSTR1/SSTR2 (Asp122, Gln291, Ser305) with radioligand binding","pmids":["7882976","7488212"],"confidence":"High","gaps":["No experimental structure of the ligand-bound receptor","Contribution of these residues to downstream signaling not tested"]},{"year":1995,"claim":"Showed SSTR2 and SSTR5 use mechanistically distinct growth-inhibition pathways (phosphatase vs Ca2+), clarifying subtype division of labor.","evidence":"Isogenic CHO lines expressing each SSTR subtype with phosphatase inhibitor and Ca2+ readouts","pmids":["7878022"],"confidence":"High","gaps":["Molecular link from phosphatase to cell-cycle arrest not defined"]},{"year":1997,"claim":"Established that SSTR2 PLC coupling requires receptor regions beyond the third intracellular loop, refining the structural basis of effector engagement.","evidence":"SSTR1/SSTR2 chimeric receptors in pituitary F4C1/GH12C1 cells with cAMP, PLC and Ca2+ readouts under PTX","pmids":["9228036"],"confidence":"High","gaps":["Specific extra-loop determinants not pinpointed","G protein mediating PTX-resistant PLC not identified"]},{"year":1997,"claim":"Assigned SSTR2 a defined role in pituitary hormone suppression, linking the receptor to specific endocrine outputs.","evidence":"Primary human fetal pituitary cultures with subtype-selective analogues correlated to binding affinities","pmids":["9045884"],"confidence":"High","gaps":["Downstream signaling in pituitary cells not dissected here"]},{"year":2003,"claim":"Defined tissue-specific physiological roles for SSTR2 in gastrointestinal and biliary function using genetic models.","evidence":"LacZ knockin reporter mice for GI cell-type mapping; isolated bile duct units from SSTR2 knockout mice with cAMP/cGMP readouts","pmids":["12442323","12676656"],"confidence":"High","gaps":["Cell-autonomous signaling steps in cholangiocytes not fully traced","Parietal/ECL cell signaling consequences not quantified"]},{"year":2012,"claim":"Established SSTR2 as the dominant islet receptor inhibiting hormone secretion through three parallel ionic and exocytotic mechanisms.","evidence":"Human islets with patch-clamp (GIRK, P/Q Ca2+ currents), exocytosis and secretion assays using subtype-selective agonists","pmids":["22932785","12084389"],"confidence":"High","gaps":["G protein/effector links to each ionic mechanism not fully resolved"]},{"year":2018,"claim":"Revealed how SSTR2 spatial organization and internalization are controlled at the membrane, linking a cytoskeletal partner to receptor trafficking.","evidence":"Single-molecule live-cell microscopy with dominant-negative filamin A fragment tracking SSTR2 clustering and CCP recruitment","pmids":["29931263"],"confidence":"High","gaps":["Binding interface between SSTR2 and FLNA not mapped","Functional consequence of altered clustering on signaling not measured"]},{"year":2025,"claim":"Identified post-transcriptional control of SSTR2 abundance by glucocorticoid-induced miR-375, explaining modulation of therapeutic agonist responsiveness.","evidence":"miR-375 inhibitor with protein/internalization and antiproliferative readouts in AtT20/D16 cells and primary human corticotroph cultures","pmids":["40488558"],"confidence":"Medium","gaps":["Direct miR-375/Sstr2 mRNA interaction site not validated","Single lab"]},{"year":2024,"claim":"Extended SSTR2 signaling to an AMPK/Drp1 axis controlling mitochondrial fission and inflammasome-driven pyroptosis in cardiac stress.","evidence":"Sepsis mouse model with SSTR2 pharmacological inhibition and genetic ablation; AMPK, Drp1, caspase-1 and cardiac function readouts","pmids":["38733824"],"confidence":"Medium","gaps":["Proximal coupling from SSTR2 to AMPK not defined","Single lab; cell-type specificity in heart unresolved"]},{"year":null,"claim":"How the multiple SSTR2 effector arms (phosphatase, PLC, ion channels, AMPK) are integrated and selectively engaged in a given cell type, and the structural basis of effector versus FLNA coupling, remain open.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No unified structural model of ligand-bound, G protein-coupled SSTR2","Mechanism selecting among parallel effector pathways unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[0,1,17]},{"term_id":"GO:0048018","term_label":"receptor ligand activity","supporting_discovery_ids":[7,8]},{"term_id":"GO:0008092","term_label":"cytoskeletal protein binding","supporting_discovery_ids":[18]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[18,22]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[0,1,4]}],"complexes":[],"partners":["GNAI3","GNAO1","FLNA"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P30874","full_name":"Somatostatin receptor type 2","aliases":["SRIF-1"],"length_aa":369,"mass_kda":41.3,"function":"Receptor for somatostatin-14 and -28. This receptor is coupled via pertussis toxin sensitive G proteins to inhibition of adenylyl cyclase. In addition it stimulates phosphotyrosine phosphatase and PLC via pertussis toxin insensitive as well as sensitive G proteins. Inhibits calcium entry by suppressing voltage-dependent calcium channels. Acts as the functionally dominant somatostatin receptor in pancreatic alpha- and beta-cells where it mediates the inhibitory effect of somatostatin-14 on hormone secretion. Inhibits cell growth through enhancement of MAPK1 and MAPK2 phosphorylation and subsequent up-regulation of CDKN1B. Stimulates neuronal migration and axon outgrowth and may participate in neuron development and maturation during brain development. Mediates negative regulation of insulin receptor signaling through PTPN6. Inactivates SSTR3 receptor function following heterodimerization","subcellular_location":"Cell membrane; Cytoplasm","url":"https://www.uniprot.org/uniprotkb/P30874/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/SSTR2","classification":"Not Classified","n_dependent_lines":9,"n_total_lines":1208,"dependency_fraction":0.0074503311258278145},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/SSTR2","total_profiled":1310},"omim":[{"mim_id":"617686","title":"PITUITARY ADENOMA 3, MULTIPLE TYPES; PITA3","url":"https://www.omim.org/entry/617686"},{"mim_id":"604999","title":"SH3 AND MULTIPLE ANKYRIN REPEAT DOMAINS 1; SHANK1","url":"https://www.omim.org/entry/604999"},{"mim_id":"602272","title":"TRANSCRIPTION FACTOR 4; TCF4","url":"https://www.omim.org/entry/602272"},{"mim_id":"600140","title":"CREB-BINDING PROTEIN; CREBBP","url":"https://www.omim.org/entry/600140"},{"mim_id":"300942","title":"CHROMOSOME Xq26.3 DUPLICATION SYNDROME","url":"https://www.omim.org/entry/300942"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Cytosol","reliability":"Supported"},{"location":"Nucleoplasm","reliability":"Additional"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"brain","ntpm":17.7}],"url":"https://www.proteinatlas.org/search/SSTR2"},"hgnc":{"alias_symbol":[],"prev_symbol":[]},"alphafold":{"accession":"P30874","domains":[{"cath_id":"1.20.1070.10","chopping":"39-185_201-236_249-324","consensus_level":"high","plddt":91.7382,"start":39,"end":324}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P30874","model_url":"https://alphafold.ebi.ac.uk/files/AF-P30874-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P30874-F1-predicted_aligned_error_v6.png","plddt_mean":81.31},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=SSTR2","jax_strain_url":"https://www.jax.org/strain/search?query=SSTR2"},"sequence":{"accession":"P30874","fasta_url":"https://rest.uniprot.org/uniprotkb/P30874.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P30874/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P30874"}},"corpus_meta":[{"pmid":"7907795","id":"PMC_7907795","title":"Stimulation of tyrosine phosphatase and inhibition of cell proliferation by somatostatin analogues: mediation by human somatostatin receptor subtypes SSTR1 and SSTR2.","date":"1994","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/7907795","citation_count":322,"is_preprint":false},{"pmid":"8012966","id":"PMC_8012966","title":"Expression and localization of somatostatin receptor SSTR1, SSTR2, and SSTR3 messenger RNAs in primary human tumors using in situ hybridization.","date":"1994","source":"Cancer research","url":"https://pubmed.ncbi.nlm.nih.gov/8012966","citation_count":294,"is_preprint":false},{"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":280,"is_preprint":false},{"pmid":"9045884","id":"PMC_9045884","title":"Somatostatin receptor subtype specificity in human fetal pituitary cultures. 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research","url":"https://pubmed.ncbi.nlm.nih.gov/10071756","citation_count":7,"is_preprint":false},{"pmid":"37907154","id":"PMC_37907154","title":"Applying HDACis to increase SSTR2 expression and radiolabeled DOTA-TATE uptake: from cells to mice.","date":"2023","source":"Life sciences","url":"https://pubmed.ncbi.nlm.nih.gov/37907154","citation_count":6,"is_preprint":false},{"pmid":"36145375","id":"PMC_36145375","title":"Synthesis and Evaluation of Two Long-Acting SSTR2 Antagonists for Radionuclide Therapy of Neuroendocrine Tumors.","date":"2022","source":"Pharmaceuticals (Basel, Switzerland)","url":"https://pubmed.ncbi.nlm.nih.gov/36145375","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":"35128410","id":"PMC_35128410","title":"Synthesis and preliminary evaluation of octreotate conjugates of bioactive synthetic amatoxins for targeting somatostatin receptor (sstr2) expressing cells.","date":"2021","source":"RSC chemical biology","url":"https://pubmed.ncbi.nlm.nih.gov/35128410","citation_count":6,"is_preprint":false},{"pmid":"40188826","id":"PMC_40188826","title":"Upregulation of SSTR2 Expression and Radioligand Binding of [18F]SiTATE in Neuroendocrine Tumour Cells with Combined Inhibition of Class I HDACs and LSD1.","date":"2025","source":"Neuroendocrinology","url":"https://pubmed.ncbi.nlm.nih.gov/40188826","citation_count":5,"is_preprint":false},{"pmid":"39791476","id":"PMC_39791476","title":"PSMA and SSTR2 Dual-Targeting Theranostic Agents for Neuroendocrine-Differentiated Prostate Cancer (NEPC).","date":"2025","source":"Journal of medicinal chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/39791476","citation_count":5,"is_preprint":false},{"pmid":"38927897","id":"PMC_38927897","title":"Immunohistochemical Profiling of SSTR2 and HIF-2α with the Tumor Microenvironment in Pheochromocytoma and Paraganglioma.","date":"2024","source":"Cancers","url":"https://pubmed.ncbi.nlm.nih.gov/38927897","citation_count":5,"is_preprint":false},{"pmid":"40121305","id":"PMC_40121305","title":"Characterizing SSTR2 expression and modulation for targeted imaging and therapy in preclinical models of triple-negative breast cancer.","date":"2025","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/40121305","citation_count":5,"is_preprint":false},{"pmid":"36463361","id":"PMC_36463361","title":"SSTR2 as an anatomical imaging marker and a safety switch to monitor and manage CAR T cell toxicity.","date":"2022","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/36463361","citation_count":5,"is_preprint":false},{"pmid":"25149275","id":"PMC_25149275","title":"Expression and localization of somatostatin receptor types 3, 4 and 5 in the wild-type, SSTR1 and SSTR1/SSTR2 knockout mouse cochlea.","date":"2014","source":"Cell and tissue research","url":"https://pubmed.ncbi.nlm.nih.gov/25149275","citation_count":5,"is_preprint":false},{"pmid":"11311492","id":"PMC_11311492","title":"Association analysis of somatostatin receptor (SSTR1 and SSTR2) polymorphisms in breast cancer and solar keratosis.","date":"2001","source":"Cancer letters","url":"https://pubmed.ncbi.nlm.nih.gov/11311492","citation_count":5,"is_preprint":false},{"pmid":"30531706","id":"PMC_30531706","title":"Regional differences in somatostatin receptor 2 (SSTR2) immunoreactivity is coupled to level of bowel invasion in small intestinal neuroendocrine tumors.","date":"2018","source":"Neuro endocrinology letters","url":"https://pubmed.ncbi.nlm.nih.gov/30531706","citation_count":5,"is_preprint":false},{"pmid":"7587644","id":"PMC_7587644","title":"Expression of sstr1 and sstr2 in rat hypothalamus: correlation with receptor binding and distribution of growth hormone regulatory peptides.","date":"1995","source":"Ciba Foundation symposium","url":"https://pubmed.ncbi.nlm.nih.gov/7587644","citation_count":4,"is_preprint":false},{"pmid":"16711011","id":"PMC_16711011","title":"Inhibition of metastatic progression of SSTR2 gene transfection mediated by adenovirus in human pancreatic carcinoma cells.","date":"2006","source":"Journal of Huazhong University of Science and Technology. Medical sciences = Hua zhong ke ji da xue xue bao. Yi xue Ying De wen ban = Huazhong keji daxue xuebao. Yixue Yingdewen ban","url":"https://pubmed.ncbi.nlm.nih.gov/16711011","citation_count":4,"is_preprint":false},{"pmid":"19324939","id":"PMC_19324939","title":"Association of SSTR2 polymorphisms and glucose homeostasis phenotypes: the Insulin Resistance Atherosclerosis Family Study.","date":"2009","source":"Diabetes","url":"https://pubmed.ncbi.nlm.nih.gov/19324939","citation_count":4,"is_preprint":false},{"pmid":"40488558","id":"PMC_40488558","title":"miR-375 Regulation of SSTR2 Expression in Corticotroph Pituitary Cells: Somatostatin Receptor Ligands Effects.","date":"2025","source":"Endocrinology","url":"https://pubmed.ncbi.nlm.nih.gov/40488558","citation_count":3,"is_preprint":false},{"pmid":"39770488","id":"PMC_39770488","title":"Preclinical Study of a Dual-Target Molecular Probe Labeled with 68Ga Targeting SSTR2 and FAP.","date":"2024","source":"Pharmaceuticals (Basel, Switzerland)","url":"https://pubmed.ncbi.nlm.nih.gov/39770488","citation_count":3,"is_preprint":false},{"pmid":"38791956","id":"PMC_38791956","title":"The Value of PET/CT in Particle Therapy Planning of Various Tumors with SSTR2 Receptor Expression: Comparative Interobserver Study.","date":"2024","source":"Cancers","url":"https://pubmed.ncbi.nlm.nih.gov/38791956","citation_count":3,"is_preprint":false},{"pmid":"20942237","id":"PMC_20942237","title":"[Expression of SSTR2 and P-STAT3 in human olfactory neuroblastoma].","date":"2010","source":"Lin chuang er bi yan hou tou jing wai ke za zhi = Journal of clinical otorhinolaryngology head and neck surgery","url":"https://pubmed.ncbi.nlm.nih.gov/20942237","citation_count":3,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":57502,"output_tokens":5985,"usd":0.13114,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":14688,"output_tokens":3992,"usd":0.08662,"stage2_stop_reason":"end_turn"},"total_usd":0.21776,"stage1_batch_id":"msgbatch_013LWZZT6MWaqB9qyTSeQBmU","stage2_batch_id":"msgbatch_0194ZzQaTGNpruoNJBbEMbt3","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1993,\n      \"finding\": \"SSTR2 selectively associates with Gi alpha 3 and G(o) alpha 2 pertussis toxin-sensitive G proteins, as demonstrated by immunoprecipitation with peptide-directed antisera in CHO cells expressing the cloned receptor; Gi alpha 1 and Gi alpha 2 antisera did not uncouple SSTR2/G protein complexes.\",\n      \"method\": \"Immunoprecipitation with subtype-specific G protein antisera in CHO and HEK293 cells stably expressing SSTR2\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal immunoprecipitation approach, replicated across two cell lines (CHO and HEK293) with multiple G protein antisera providing subtype specificity\",\n      \"pmids\": [\"8098703\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1993,\n      \"finding\": \"Rat SSTR2 expressed in CHO cells is coupled to inhibition of adenylyl cyclase: somatostatin-14 inhibited forskolin-stimulated cAMP accumulation by ~75% with EC50 ~350 pM.\",\n      \"method\": \"cAMP accumulation assay in CHO cells stably transfected with rat SSTR2 cDNA\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — direct in vitro enzymatic assay (adenylyl cyclase inhibition), replicated across multiple papers (PMID 8096694, 7907016, 8144617)\",\n      \"pmids\": [\"8096694\", \"7907016\", \"8144617\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"SSTR2 activation stimulates tyrosine phosphatase activity and inhibits serum-stimulated cell proliferation (EC50 in low pM range for RC-160 and SMS 201-995), implicating tyrosine phosphatase as a transducer of the SSTR2 growth-inhibition signal.\",\n      \"method\": \"Tyrosine phosphatase activity assay and cell proliferation assay in COS-7 and NIH 3T3 cells expressing human SSTR2; pharmacological dose-response with selective analogues\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — dose-response correlation between receptor binding affinity, phosphatase stimulation, and growth inhibition; replicated in CHO cells in PMID 7878022\",\n      \"pmids\": [\"7907795\", \"7878022\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"SSTR2 couples to phospholipase C and Ca2+ mobilization in addition to inhibiting adenylyl cyclase; the PLC/Ca2+ response is only partially sensitive to pertussis toxin, indicating involvement of both PTX-sensitive and PTX-insensitive G proteins.\",\n      \"method\": \"Transfection of human SSTR2 cDNA into COS-7 cells; measurement of cAMP, inositol phosphates, and intracellular Ca2+ with pertussis toxin treatment\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple signaling readouts in one study, single lab; replicated partially in rat pituitary cells (PMID 9228036)\",\n      \"pmids\": [\"7910018\", \"9228036\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"SSTR2 coupling to adenylyl cyclase inhibition requires the presence of Gi alpha 1 protein: human SSTR2 in CHO cells (which lack Gi alpha 1) does not inhibit cAMP unless Gi alpha 1 is co-expressed; the effect is pertussis toxin-sensitive.\",\n      \"method\": \"Co-expression of human SSTR2 with individual Gi alpha subunits in CHO cells; cAMP assay with pertussis toxin\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — reconstitution approach (co-expression of specific G protein subunit rescues signaling), with pertussis toxin control; single lab\",\n      \"pmids\": [\"7914078\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"SSTR2 inhibits high-voltage-activated (HVA) Ca2+ currents in RINm5F insulinoma cells; SSTR1 expressed in the same cells does not inhibit these currents, demonstrating subtype specificity.\",\n      \"method\": \"Patch-clamp electrophysiology in RINm5F cells stably expressing human SSTR2 or SSTR1\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — direct electrophysiological measurement with isogenic cell lines differing only in receptor subtype; within-study control\",\n      \"pmids\": [\"7982482\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"SSTR2 couples exclusively to pertussis toxin-sensitive G proteins (evidenced by GTPγS and PTX effects on ligand binding), whereas SSTR1 couples to both PTX-sensitive and -insensitive G proteins; only SSTR1, not SSTR2, mediates somatostatin inhibition of Na+-H+ exchange activity via a PTX-insensitive mechanism.\",\n      \"method\": \"Stable/transient expression of SSTR1, SSTR2, and chimeric receptors in Ltk- and HEK293 cells; Na+-H+ exchange assay, cAMP assay, pertussis toxin treatment, chimeric receptor mapping\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — chimeric receptor structure-function mapping plus multiple functional readouts; identifies molecular determinants of subtype-specific signaling\",\n      \"pmids\": [\"8144617\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"Two amino acids in transmembrane domains VI (Gln291→Asn) and VII (Ser305→Phe) of SSTR2 largely determine the high-affinity selectivity of the peptide agonist SMS 201-995; single Ser305→Phe mutation in SSTR1 increases SMS 201-995 affinity ~100-fold, and combining with Gln291→Asn yields near-full SMS 201-995 susceptibility.\",\n      \"method\": \"Site-directed mutagenesis of SSTR1 with sequential introduction of SSTR2 residues; radioligand binding assays\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — systematic site-directed mutagenesis with quantitative binding, multiple mutant constructs tested; identifies two specific residues\",\n      \"pmids\": [\"7882976\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"Asp122 in transmembrane domain III of SSTR2 is a critical contact residue for somatostatin-14 binding: charge-switch mutations (D122K receptor + asp9-S-14 ligand) restore binding, implicating an ionic interaction between Lys9 of S-14 and Asp122 of SSTR2.\",\n      \"method\": \"Site-directed mutagenesis of rat SSTR2 (D89A, D89E, D122K); radioligand binding with wild-type and charge-substituted somatostatin analogues\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — charge-swap mutagenesis with restored binding demonstrates specific ionic contact; rigorous approach\",\n      \"pmids\": [\"7488212\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"SSTR2-mediated inhibition of cell proliferation acts through tyrosine phosphatase activation (suppressed by orthovanadate), whereas SSTR5-mediated growth inhibition operates through inhibition of intracellular Ca2+ mobilization (not through the phosphatase pathway); distinct mechanisms for each subtype.\",\n      \"method\": \"CHO cells stably expressing individual SSTR subtypes 1–5; proliferation assays with orthovanadate and phosphatase inhibitors; intracellular calcium measurements\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — isogenic CHO lines expressing each of 5 SSTR subtypes; pharmacological inhibitors of phosphatase pathway selectively block SSTR2-mediated but not SSTR5-mediated growth inhibition\",\n      \"pmids\": [\"7878022\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"SSTR2 couples to inhibition of L-type Ca2+ channels in AtT-20 pituitary cells via pertussis toxin-sensitive G proteins; this coupling is not desensitized by SSTR2-selective agonist pretreatment (unlike SSTR5, which undergoes desensitization).\",\n      \"method\": \"Whole-cell patch-clamp in AtT-20 cells; SSTR2-selective agonists (MK 678, BIM 23027, NC8-12); pertussis toxin pretreatment\",\n      \"journal\": \"Neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — direct electrophysiology with subtype-selective agonists and PTX, functional comparison between SSTR2 and SSTR5 coupling and desensitization\",\n      \"pmids\": [\"8684611\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"SSTR2 protein migrates at 93 kDa in CHO cells expressing the cloned receptor and at 148 kDa in rat brain regions with high SSTR2 mRNA, indicating differential post-translational modification (likely glycosylation) in native tissue versus transfected cells.\",\n      \"method\": \"Peptide-directed antibody immunoblotting and immunoprecipitation of SSTR2 from transfected CHO cells and rat brain\",\n      \"journal\": \"Journal of neurochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — immunoblotting and immunoprecipitation with two independent antibodies; single lab but two orthogonal antibodies and two cell sources\",\n      \"pmids\": [\"7518495\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"SSTR2 activation in AR42J pancreatic cells opens cell-surface calcium channels in a phospholipase C-independent manner: SSTR2-selective agonists increase intracellular Ca2+ that is abolished in Ca2+-free medium but do not stimulate inositol phosphate turnover.\",\n      \"method\": \"Intracellular Ca2+ measurement and inositol phosphate assay in AR42J cells using SSTR subtype-selective agonists\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — two complementary assays (Ca2+ imaging and IP turnover) with pharmacological selectivity; single lab\",\n      \"pmids\": [\"7669056\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"SSTR2 activation in pituitary F4C1 cells stimulates phospholipase C and raises intracellular Ca2+ from intracellular stores (partially PTX-resistant); sequences beyond the intracellular loops—not only the third intracellular loop—are required for SSTR2 coupling to PLC, as chimeras containing only SSTR2 intracellular loops in SSTR1 background did not reconstitute PLC stimulation.\",\n      \"method\": \"Expression of SSTR1, SSTR2, and chimeric receptors in pituitary GH12C1 and F4C1 cells; adenylyl cyclase inhibition, PLC activity, and [Ca2+]i measurements with pertussis toxin\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — chimeric receptor mapping combined with multiple functional readouts in cells lacking endogenous SSTRs; identifies structural requirements beyond intracellular loops\",\n      \"pmids\": [\"9228036\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"In human fetal pituitary cells, prolactin suppression is mediated predominantly by SSTR2, whereas GH and TSH suppression are mediated by both SSTR2 and SSTR5, as shown by subtype-selective somatostatin analogues with defined binding affinities.\",\n      \"method\": \"Primary human fetal pituitary cultures treated with SSTR2- or SSTR5-selective analogues; hormone secretion assays correlated with receptor binding affinities in stably transfected cell lines\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — primary human tissue with pharmacologically characterized subtype-selective ligands; functional hormone secretion endpoints\",\n      \"pmids\": [\"9045884\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"In the gastrointestinal tract, SSTR2 is expressed on parietal cells and enterochromaffin-like (ECL) cells in the stomach, and on NOS-positive neurons in the myenteric and submucosal plexuses of the intestine, as identified using Sstr2 knockout/lacZ knockin mice.\",\n      \"method\": \"LacZ knockin reporter mice; beta-galactosidase staining combined with immunostaining for H+K+ATPase (parietal cells), histidine decarboxylase (ECL cells), and NOS\",\n      \"journal\": \"The Journal of comparative neurology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic reporter knockin provides unambiguous cell-type identification; multiple co-labeling markers across multiple GI segments\",\n      \"pmids\": [\"12442323\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"SSTR2 on cholangiocytes mediates somatostatin-induced stimulation of ductal bile absorption and inhibition of secretin-stimulated ductal bile secretion; these effects involve increases in intracellular cGMP and inhibition of secretin-stimulated cAMP, and are absent in SSTR2 knockout mice.\",\n      \"method\": \"Isolated intrahepatic bile duct units from wild-type and SSTR2 knockout mice; luminal area measurement, cAMP and cGMP assays, SSTR2-selective agonist L-779976\",\n      \"journal\": \"American journal of physiology. Cell physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — knockout vs. wild-type comparison with selective agonist and second messenger readouts; multiple orthogonal methods\",\n      \"pmids\": [\"12676656\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"In human pancreatic β- and α-cells, SSTR2 is the dominant somatostatin receptor mediating SST-induced inhibition of secretion through: (1) activation of GIRK channels causing membrane hyperpolarization, (2) reduction of P/Q-type Ca2+ currents, and (3) direct inhibition of exocytosis; SSTR5 is only marginally effective.\",\n      \"method\": \"Human islets: quantitative PCR, immunohistochemistry, whole-cell patch-clamp (GIRK channel blocker tertiapin-Q, tolbutamide), Ca2+ current recordings, exocytosis measurements with SSTR subtype-selective agonists\",\n      \"journal\": \"American journal of physiology. Endocrinology and metabolism\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — primary human tissue with multiple orthogonal electrophysiological and secretion assays; multiple pharmacological tools; mechanistic dissection of three parallel inhibitory mechanisms\",\n      \"pmids\": [\"22932785\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"SSTR2 undergoes transient interactions with the cytoskeletal protein filamin A (FLNA) preferentially along actin fibers; agonist stimulation increases SSTR2 localization along actin fibers, clustering, and recruitment to clathrin-coated pits (CCPs). Blocking SSTR2-FLNA binding with a dominant-negative FLNA fragment increases SSTR2 mobility, disrupts clustering along actin, and impairs both recruitment to CCPs and receptor internalization.\",\n      \"method\": \"Fast multicolor single-molecule microscopy in living cells; dominant-negative FLNA fragment; tracking of individual SSTR2 and FLNA molecules at the plasma membrane\",\n      \"journal\": \"Endocrinology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — single-molecule live-cell imaging with loss-of-function dominant-negative approach; mechanistically links FLNA interaction to SSTR2 nanoscale organization, clustering, and internalization\",\n      \"pmids\": [\"29931263\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"In HIT-T15 clonal beta-cells, SSTR2 (not SSTR1, 3, 4, or 5) specifically mediates somatostatin-induced increase in intracellular Ca2+ and insulin secretion in the presence of arginine vasopressin; this effect is blocked by the SSTR2-specific antagonist PRL-2903.\",\n      \"method\": \"Subtype-selective SSTR agonists and SSTR2 antagonist PRL-2903; intracellular Ca2+ measurement and insulin secretion assay in HIT-T15 cells\",\n      \"journal\": \"Life sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — pharmacological selectivity with five subtype-specific agonists plus an SSTR2 antagonist; single lab\",\n      \"pmids\": [\"12084389\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Cortistatin binds specifically to SSTR2 and activates AMPK, which inhibits Drp1-mediated mitochondrial fission, reduces ROS, and thereby suppresses NLRP3 inflammasome activation and cardiomyocyte pyroptosis in septic cardiomyopathy; pharmacological inhibition and genetic ablation of SSTR2 abolish these protective effects.\",\n      \"method\": \"Sepsis mouse model; SSTR2 pharmacological inhibition and genetic ablation; AMPK phosphorylation, Drp1 activity, caspase-1 cleavage, IL-1β, gasdermin D, and cardiac function measurements\",\n      \"journal\": \"International immunopharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic and pharmacological loss-of-function approaches with multiple downstream pathway readouts; single lab\",\n      \"pmids\": [\"38733824\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"SSTR2 overexpression in SSTR2-negative pancreatic carcinoma cells (BXPC-3) reduces cell migration and invasion through Matrigel, accompanied by reduced MMP-2 mRNA and increased TIMP-2 mRNA expression.\",\n      \"method\": \"Adenovirus-mediated SSTR2 transfection in BXPC-3 cells; Matrigel-coated Transwell migration/invasion assay; RT-PCR for MMP-2 and TIMP-2\",\n      \"journal\": \"Journal of Huazhong University of Science and Technology. Medical sciences\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, single set of assays, no rescue or mechanistic dissection beyond mRNA correlation\",\n      \"pmids\": [\"16711011\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"miR-375 epigenetically downregulates SSTR2 expression in corticotroph pituitary cells: glucocorticoid (dexamethasone) treatment increases miR-375, which targets Sstr2 mRNA; miR-375 inhibition increases SSTR2 membranous protein expression, enhances receptor internalization upon octreotide treatment, and potentiates octreotide-induced antiproliferative and apoptotic effects (PARP cleavage, caspase-3, ERK1/2 phosphorylation).\",\n      \"method\": \"RT-qPCR, Western blot, immunofluorescence, miR-375 inhibitor, proliferation assay, flow cytometry in AtT20/D16 cells and primary human corticotroph cultures\",\n      \"journal\": \"Endocrinology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — miRNA loss-of-function with multiple downstream readouts in both cell line and primary cultures; single lab\",\n      \"pmids\": [\"40488558\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"SSTR2 is a G protein-coupled receptor that selectively couples to Gi alpha 3 and Go alpha to inhibit adenylyl cyclase, activate tyrosine phosphatase (mediating growth inhibition), stimulate phospholipase C/Ca2+ mobilization via partially PTX-insensitive pathways, and inhibit voltage-gated Ca2+ channels and GIRK-mediated membrane currents; ligand selectivity is conferred by Asp122 (TM III, ionic contact with somatostatin Lys9), Gln291 (TM VI), and Ser305 (TM VII); at the plasma membrane, dynamic interactions with filamin A along actin fibers control SSTR2 nanoscale clustering and clathrin-mediated internalization; in specific tissues SSTR2 mediates somatostatin inhibition of insulin/glucagon secretion (via GIRK, P/Q-type Ca2+ channels, and direct exocytosis inhibition), ductal bile homeostasis (via cAMP/cGMP), and gastric acid secretion (on parietal and ECL cells); SSTR2 expression is epigenetically regulated by promoter methylation and by glucocorticoid-induced miR-375.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"SSTR2 is a Gi/Go-coupled somatostatin receptor that transduces somatostatin signals into inhibition of secretion, growth, and metabolic output across endocrine, gastrointestinal, and pituitary tissues [#0, #1, #17]. It selectively associates with pertussis toxin-sensitive Gi alpha 3 and Go alpha subunits and inhibits adenylyl cyclase, an effect that depends on the available Gi pool [#0, #1, #4]. Beyond cAMP suppression, SSTR2 activates a tyrosine phosphatase that mediates its antiproliferative signal\\u2014mechanistically distinct from the Ca2+-based growth inhibition of SSTR5\\u2014and engages phospholipase C/Ca2+ mobilization through partially PTX-insensitive pathways that require receptor regions beyond the intracellular loops [#2, #9, #13]. SSTR2 also couples to inhibition of high-voltage-activated and L-type Ca2+ channels and, in human islet cells, suppresses insulin/glucagon secretion through GIRK channel activation, reduction of P/Q-type Ca2+ currents, and direct inhibition of exocytosis [#5, #10, #17]. Ligand selectivity is encoded by specific transmembrane residues: Asp122 (TM III) forms an ionic contact with somatostatin Lys9, while Gln291 (TM VI) and Ser305 (TM VII) determine high-affinity peptide agonist recognition [#7, #8]. At the plasma membrane, transient interactions with filamin A along actin fibers control SSTR2 nanoscale clustering and clathrin-mediated internalization [#18]. Tissue-level roles include suppression of pituitary hormone release, regulation of ductal bile homeostasis via cGMP and cAMP, and control of gastric acid secretion through expression on parietal and ECL cells [#14, #15, #16]. SSTR2 abundance is regulated post-transcriptionally by glucocorticoid-induced miR-375, which limits receptor expression and dampens octreotide responsiveness [#22].\",\n  \"teleology\": [\n    {\n      \"year\": 1993,\n      \"claim\": \"Established the G protein coupling specificity of SSTR2, defining which transducers carry its signal and distinguishing it from related receptors.\",\n      \"evidence\": \"Subtype-specific G protein antisera immunoprecipitation in CHO and HEK293 cells, plus cAMP accumulation assays in transfected CHO cells\",\n      \"pmids\": [\"8098703\", \"8096694\", \"7907016\", \"8144617\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Stoichiometry and dynamics of Gi alpha 3/Go alpha selection not resolved\", \"Did not address PTX-insensitive coupling later observed for PLC\"]\n    },\n    {\n      \"year\": 1994,\n      \"claim\": \"Resolved that adenylyl cyclase inhibition by SSTR2 depends on the available Gi alpha subunit pool, explaining cell-context dependence of cAMP responses.\",\n      \"evidence\": \"Co-expression of SSTR2 with individual Gi alpha subunits in Gi alpha 1-deficient CHO cells with PTX controls\",\n      \"pmids\": [\"7914078\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Reconciliation with the earlier Gi alpha 3/Go alpha association data not addressed\", \"Single lab, single cell background\"]\n    },\n    {\n      \"year\": 1994,\n      \"claim\": \"Identified tyrosine phosphatase activation as the transducer of SSTR2 growth inhibition, separating its antiproliferative mechanism from second-messenger pathways.\",\n      \"evidence\": \"Tyrosine phosphatase and proliferation assays with selective analogues in COS-7, NIH 3T3 and CHO cells; orthovanadate suppression\",\n      \"pmids\": [\"7907795\", \"7878022\", \"7878022\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of the specific phosphatase not established\", \"Downstream substrates of the phosphatase unknown\"]\n    },\n    {\n      \"year\": 1994,\n      \"claim\": \"Demonstrated SSTR2 couples to PLC/Ca2+ and to Ca2+ channel inhibition, broadening its effector repertoire beyond cAMP and showing subtype-specific channel control.\",\n      \"evidence\": \"Inositol phosphate/Ca2+ measurements with PTX in COS-7 cells; patch-clamp of HVA Ca2+ currents in RINm5F cells expressing SSTR2 versus SSTR1\",\n      \"pmids\": [\"7910018\", \"7982482\", \"9228036\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Identity of the PTX-insensitive G protein driving PLC not defined\", \"Link between PLC and channel effects not integrated\"]\n    },\n    {\n      \"year\": 1995,\n      \"claim\": \"Mapped the molecular determinants of somatostatin ligand recognition, defining how SSTR2 achieves selective high-affinity binding.\",\n      \"evidence\": \"Site-directed and charge-swap mutagenesis of SSTR1/SSTR2 (Asp122, Gln291, Ser305) with radioligand binding\",\n      \"pmids\": [\"7882976\", \"7488212\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No experimental structure of the ligand-bound receptor\", \"Contribution of these residues to downstream signaling not tested\"]\n    },\n    {\n      \"year\": 1995,\n      \"claim\": \"Showed SSTR2 and SSTR5 use mechanistically distinct growth-inhibition pathways (phosphatase vs Ca2+), clarifying subtype division of labor.\",\n      \"evidence\": \"Isogenic CHO lines expressing each SSTR subtype with phosphatase inhibitor and Ca2+ readouts\",\n      \"pmids\": [\"7878022\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular link from phosphatase to cell-cycle arrest not defined\"]\n    },\n    {\n      \"year\": 1997,\n      \"claim\": \"Established that SSTR2 PLC coupling requires receptor regions beyond the third intracellular loop, refining the structural basis of effector engagement.\",\n      \"evidence\": \"SSTR1/SSTR2 chimeric receptors in pituitary F4C1/GH12C1 cells with cAMP, PLC and Ca2+ readouts under PTX\",\n      \"pmids\": [\"9228036\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Specific extra-loop determinants not pinpointed\", \"G protein mediating PTX-resistant PLC not identified\"]\n    },\n    {\n      \"year\": 1997,\n      \"claim\": \"Assigned SSTR2 a defined role in pituitary hormone suppression, linking the receptor to specific endocrine outputs.\",\n      \"evidence\": \"Primary human fetal pituitary cultures with subtype-selective analogues correlated to binding affinities\",\n      \"pmids\": [\"9045884\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Downstream signaling in pituitary cells not dissected here\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Defined tissue-specific physiological roles for SSTR2 in gastrointestinal and biliary function using genetic models.\",\n      \"evidence\": \"LacZ knockin reporter mice for GI cell-type mapping; isolated bile duct units from SSTR2 knockout mice with cAMP/cGMP readouts\",\n      \"pmids\": [\"12442323\", \"12676656\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Cell-autonomous signaling steps in cholangiocytes not fully traced\", \"Parietal/ECL cell signaling consequences not quantified\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Established SSTR2 as the dominant islet receptor inhibiting hormone secretion through three parallel ionic and exocytotic mechanisms.\",\n      \"evidence\": \"Human islets with patch-clamp (GIRK, P/Q Ca2+ currents), exocytosis and secretion assays using subtype-selective agonists\",\n      \"pmids\": [\"22932785\", \"12084389\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"G protein/effector links to each ionic mechanism not fully resolved\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Revealed how SSTR2 spatial organization and internalization are controlled at the membrane, linking a cytoskeletal partner to receptor trafficking.\",\n      \"evidence\": \"Single-molecule live-cell microscopy with dominant-negative filamin A fragment tracking SSTR2 clustering and CCP recruitment\",\n      \"pmids\": [\"29931263\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Binding interface between SSTR2 and FLNA not mapped\", \"Functional consequence of altered clustering on signaling not measured\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Identified post-transcriptional control of SSTR2 abundance by glucocorticoid-induced miR-375, explaining modulation of therapeutic agonist responsiveness.\",\n      \"evidence\": \"miR-375 inhibitor with protein/internalization and antiproliferative readouts in AtT20/D16 cells and primary human corticotroph cultures\",\n      \"pmids\": [\"40488558\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct miR-375/Sstr2 mRNA interaction site not validated\", \"Single lab\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Extended SSTR2 signaling to an AMPK/Drp1 axis controlling mitochondrial fission and inflammasome-driven pyroptosis in cardiac stress.\",\n      \"evidence\": \"Sepsis mouse model with SSTR2 pharmacological inhibition and genetic ablation; AMPK, Drp1, caspase-1 and cardiac function readouts\",\n      \"pmids\": [\"38733824\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Proximal coupling from SSTR2 to AMPK not defined\", \"Single lab; cell-type specificity in heart unresolved\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How the multiple SSTR2 effector arms (phosphatase, PLC, ion channels, AMPK) are integrated and selectively engaged in a given cell type, and the structural basis of effector versus FLNA coupling, remain open.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unified structural model of ligand-bound, G protein-coupled SSTR2\", \"Mechanism selecting among parallel effector pathways unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [0, 1, 17]},\n      {\"term_id\": \"GO:0048018\", \"supporting_discovery_ids\": [7, 8]},\n      {\"term_id\": \"GO:0008092\", \"supporting_discovery_ids\": [18]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [18, 22]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [0, 1, 4]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"GNAI3\", \"GNAO1\", \"FLNA\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":8,"faith_total":8,"faith_pct":100.0}}