Molecular cloning and expression of a pituitary somatostatin receptor with preferential affinity for somatostatin-28.

SSTR5 (originally called SSTR4) was cloned from rat pituitary and shown to bind somatostatin-28 with ~30-fold higher affinity than somatostatin-14, and to couple to inhibitory G proteins to inhibit adenylyl cyclase.

"SRIF-28 was the most potent competitor of 125I-Tyr11-SRIF binding, with a approximately 30-fold greater affinity for the receptor than that of SRIF...binding of 125I-Tyr11-SRIF was markedly reduced in the presence of Na+ ions and GTP, indicating coupling of rAP6-26 receptors to inhibitory G proteins...forskolin-induced cAMP accumulation was inhibited by SRIF and SRIF-28"
SSTR5 mRNA is expressed in pituitary but not brain, liver, kidney, pancreas, cerebellum, or cortex by Northern blot.

"a approximately 2.6 kilobase mRNA encoding the receptor was present in the pituitary but not in the liver, small intestine, kidney, pancreas, cerebellum, or cortex"

Molecular cloning, functional characterization, and chromosomal localization of a human somatostatin receptor (somatostatin receptor type 5) with preferential affinity for somatostatin-28.

Human SSTR5 confirmed as SST-28-selective receptor coupled to pertussis toxin-sensitive G proteins, with SSTR5 mRNA selectively localized in rat anterior pituitary.

"hSSTR5 bound SST-28 with a 12.6-fold greater affinity (Ki = 0.19 nM), compared with SST-14 (Ki = 2.24 nM)...hSSTR5 is coupled to pertussis toxin-sensitive G proteins ...In situ hybridization of the rat pituitary showed that SSTR5 mRNA is selectively localized in the anterior lobe"

PMID:14512709

Role of glucocorticoids in the regulation of pituitary somatostatin receptor subtype (sst1-sst5) mRNA levels: evidence for direct and somatostatin-mediated effects.

Dexamethasone increases sst5 mRNA levels in rat pituitary while decreasing sst1-sst4, both in vivo and in vitro.

"High-dose DEX resulted in a decrease in sst1-sst4 mRNA and an increase in sst5 mRNA, independent of adrenal status...DEX also decreased sst2, sst3 and sst4 mRNA levels and increased sst5 mRNA levels by short-term in vitro application (10 nM, 4 h) in primary rat pituitary cell cultures"

PMID:21820437

Somatostatin receptor 5 is palmitoylated by the interacting ZDHHC5 palmitoyltransferase.

SSTR5 is palmitoylated by the palmitoyltransferase ZDHHC5, the first palmitoyltransferase identified for any GPCR.

"Coexpression of ZDHHC5 in HEK293 cells increased palmitoylation of SSTR5 whereas knock-down of endogenous ZDHHC5 by siRNAs decreased it"

PMID:12511609

Somatostatin receptor subtype 5 regulates insulin secretion and glucose homeostasis.

SSTR5 knockout mice show decreased blood glucose, altered insulin secretion, and resistance to diet-induced insulin resistance, demonstrating SSTR5 mediates somatostatin inhibition of insulin secretion.

"sst(5) KO mice exhibited decreased blood glucose and plasma insulin levels and increased leptin and glucagon concentrations...sst(5) KO mice displayed decreased susceptibility to high fat diet-induced insulin resistance"

PMID:18653781

Cell growth inhibition and functioning of human somatostatin receptor type 2 are modulated by receptor heterodimerization.

SSTR2 and SSTR5 heterodimerize, and SSTR5 enhances SSTR2-mediated adenylyl cyclase inhibition, ERK1/2 activation, p27 induction, and growth inhibition.

"SSTR2 and SSTR5 heterodimerize...The SSTR2-selective agonist L-779,976 is more efficacious at inhibiting adenylate cyclase, activating ERK1/2, and inducing the cyclin-dependent kinase inhibitor p27(Kip1) in cells expressing both SSTR2 and SSTR5 compared with SSTR2 alone"

GO_REF:0000002

Gene Ontology annotation through association of InterPro records with GO terms

GO_REF:0000033

Annotation inferences using phylogenetic trees

GO_REF:0000044

Gene Ontology annotation based on UniProtKB/Swiss-Prot Subcellular Location vocabulary mapping, accompanied by conservative changes to GO terms applied by UniProt

GO_REF:0000108

Automatic assignment of GO terms using logical inference, based on inter-ontology links

GO_REF:0000117

Electronic Gene Ontology annotations created by ARBA machine learning models

GO_REF:0000121

RGD ISO annotations to rat from other mammalian species

file:rat/Sstr5/Sstr5-deep-research-bioreason-sft.md

BioReason-Pro SFT reasoning trace for Sstr5

BioReason correctly identifies the core GPCR/Gi-coupled signaling and adenylyl cyclase inhibition but incorrectly states preference for somatostatin-14 over somatostatin-28.

file:rat/Sstr5/Sstr5-deep-research-falcon.md

Falcon (Edison Scientific) deep research report on rat Sstr5 (UniProt P30938)

Falcon confirms rat Sstr5 (P30938) is a class A/rhodopsin-like 7TM GPCR of the somatostatin receptor family that mediates the inhibitory actions of the somatostatin neuropeptide.

"Somatostatin receptors (SSTR1–5) are **class A/rhodopsin-like GPCRs** with a **canonical 7TM topology**. They mediate the inhibitory endocrine and neuromodulatory actions of the peptide hormone **somatostatin** (SST)."
SSTR5 binds both somatostatin peptides with ~10-fold higher affinity for SST-28 than SST-14, corroborating the SST-28 preference established in the original cloning papers.

"SSTR5 has been reported to bind both SST forms, with **~10-fold higher affinity for SST-28 than SST-14**, a property often invoked to explain subtype-selective physiological regulation."
SSTR activation is canonically Gi/Go-coupled and pertussis-toxin-sensitive, inhibiting adenylyl cyclase and decreasing intracellular cAMP, supporting the core adenylate cyclase-inhibiting GPCR signaling annotation.

"Across subtypes, SSTR activation is canonically **Gi/Go-coupled** (pertussis-toxin-sensitive), producing **inhibition of adenylyl cyclase** and decreased intracellular **cAMP**, often accompanied by reduced Ca2+ signaling and suppression of secretion."
Sstr5 functions as an inhibitory GPCR node that restrains secretion in pancreatic islet and pituitary endocrine circuits, supporting roles in insulin secretion regulation.

"Sstr5 acts as an inhibitory GPCR node in paracrine/endocrine circuits where SST restrains secretion (e.g., pancreatic islet hormone release, pituitary hormone output) and can modulate growth-related signaling via phosphatases and MAPK branches."
SSTR5 localizes to the plasma membrane as a classical GPCR; rat-specific subcellular microdomain localization was not directly documented in the retrieved evidence.

"The provided evidence base primarily supports **plasma membrane localization** as a classical GPCR and notes family-wide processes such as phosphorylation-dependent desensitization and internalization (general SSTR biology)."
Genetic SSTR5 deletion (and selective antagonism) lowers glycemic markers and improves insulin sensitivity, supporting SSTR5's role in glucose homeostasis and insulin secretion regulation.

"genetic SSTR5 deletion and an orally delivered selective antagonist (compound-1) lowered glycemic markers and improved insulin sensitivity indices."
A 2024 cryo-EM structure of agonist-bound SSTR5–Gi complexes confirms direct Gi coupling and provides residue-level evidence for the receptor's activation mechanism.

"A major 2024 advance is the **cryo-EM solution of SSTR5–Gi complexes** bound to cyclic peptide agonists **cortistatin-17** and **octreotide** at **2.7–2.9 Å resolution**, enabling residue-level mapping of agonist recognition and activation."