Somatostatin Receptor

Somatostatin receptors (SSTR1, 2A and B, 3, 4 and 5) belong to the G protein coupled receptor family. Somatostatin receptors are expressed in a variety of human tumors, including most tumors of neuroendocrine origin, breast tumors, certain brain tumors, renal cell tumors, lymphomas, and prostate cancer. Somatostatin triggers cytostatic and cytotoxic effects and has a general inhibitory effect on secretion mediated through its interaction with somatostatin receptors.

The SSTRs 1-4 display weak selectivity for somatostatin-14 binding, whereas SSTR5 is somatostatin-28-selective. Based on structural similarity and reactivity for octapeptide and hexapeptide somatostatin receptor analogs, SSTRs 2, 3 and SSTR5 belong to a similar somatostatin receptor subclass; SSTRs 1-4 react poorly with these analogs and belong to a separate subclass. All five somatostatin receptors are functionally coupled to inhibition of adenylyl cyclase via pertussis toxin-sensitive guanosine triphosphate (GTP)-binding proteins. mRNA for SSTRs 1-5 is widely expressed in brain and peripheral organs and displays an overlapping but characteristic pattern that is subtype-selective and tissue- and species-specific. All pituitary cell subsets express SSTR2 and SSTR5, with SSTR5 being more abundant. Individual pituitary cells coexpress multiple somatostatin receptor subtypes.