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Somatostatin Receptor

Somatostatin is a naturally occurring inhibitory polypeptide hormone first isolated from the sheep hypothalamus, two biological forms of somatostatin exist: somatostatin-14 and -28, which are derived from a 92-amino acid pro-somatostatin precursor. Somatostatin and its analogs bind to receptors belonging to the seven transmembrane G protein coupled receptor superfamily. Native somatostatin-14 binds to somatostatin receptor (SSTR) 1–4 with higher affinity, while somatostatin-28 is more SSTR5 selective. Octreotide and lanreotide, on the other hand, bind preferentially to SSTR2, with moderate affinity for SSTR5 and SSTR3.  All SSTRs associate with the pertussis toxin-sensitive Gi protein and are coupled to adenylate cyclase. Ligand binding triggers the recruitment of membrane adaptors/enzymes and the activation/inhibition of cytoplasmic targets, leading to multiple intracellular signaling pathways, some but not all of which are pertussis toxin sensitive (Gi dependent). While SSTR signal transduction pathways share certain similarities, differences between the SSTRs ensure that each receptor is responsible for a range of different actions.  SSTR1, 2, and 3 transduce their antiproliferative action by stimulating one or more PTPs, which in turn affects the mitogenic MAPK and the survival PI3K pathways. In contrast, SSTR5 mediates its antiproliferative action through PTP-independent pathways.  Increased understanding of SSTR signaling and function has highlighted the antiproliferative role of somatostatin and provided the rationale for the design of novel somatostatin analogs and therapeutics.

References

1.Theodoropoulou M, et al. Front Neuroendocrinol. 2013;34(3):228–252.