Somatostatin receptor type 2 is a protein that in humans is encoded by the SSTR2 gene. The SSTR2 gene is located on chromosome 17 on the long arm in position 25.1 in humans. It is also found in most other vertebrates. The somatostatin receptor 2 (SSTR2), which belongs to the G-protein coupled receptor family, is a protein which is most highly expressed in the pancreas (both alpha- and beta-cells), but also in other tissues such as the cerebrum and kidney and in lower amount in the jejunum, colon and liver. In the pancreas, after binding to somatostatin, it inhibits the secretion of peptide hormones from pancreatic islets. During development, it stimulates neuronal migration and axon outgrowth. The somatostatin receptor 2 is expressed in most tumors. Patients with neuroendocrine tumors that over-express the somatostatin receptor 2 have an improved prognosis. The over expression of SSTR2 in tumors can be exploited to selectively deliver radio-peptides to tumors to either detect or destroy them. Somatostatin receptor 2 also has the ability to stimulate apoptosis in many cells including cancer cells. The somatostatin receptor 2 is also being looked at as a possible target in cancer treatment for its ability to inhibit tumor growth.
Function The gene for somatostatin receptor 2, SSTR2 for short, is responsible for making a receptor for the signalling peptide, somatostatin (SST). Production occurs in the central nervous system, especially the hypothalamus, as well as the digestive system, and pancreas. SSTR2 is a receptor for somatostatin-14 and -28 respectively. The numbers 14 and 28 represent the amount of amino acids in each protein sequence. All somatostatin receptors including SSTR2 may have different specific functions, but all fall under the same receptor super family, the G-protein binding family and all of which are a major inhibitor for other hormones. For all somatostatin inhibitors, somatostatin-14 and -28 work by binding to the receptor with the help of a G-protein. This inhibits adenylyl cyclase and calcium channels. These proteins are released in various parts of the human body and vary in the amount emitted from each organ system. In secretory cells this protein is in a greater volume compared to amount released from activated immune and inflammatory cells. These proteins have a tendency of being emitted in response to items such as: ions, nutrients, neuropeptides, neurotransmitters, hormones, growth factors, and cytokines. In general, somatostatin can put a cell in cycle arrest using the phosphotyrosine phosphatase dependent regulation of nitrogen-activated protein kinase, this process can lead to a halt in the cell cycle or apoptosis of the cell and is used as a tumor suppressor in the genome. This hormone is also known to perform agonist-dependent endocytosis, which allows a cell to take in receptors, ions, and other molecules. Because this protein is found in multiple organs, it has a different specific role in each organ or organ system. A major function of the protein made by the gene SSTR2 is pancreatic interaction with the alpha and beta cells. In the delta cells of the pancreas, this hormone inhibits the secretion of both glucagon and insulin in the alpha and beta cells when stimulated by basic nutrients like sugars, proteins, and fats. In fact, this protein, is the dominant one out of all of the somatostatins in the pancreas. In the stomach, it reduces activity of the digestive tract by inhibiting secretion of gastric acid, pepsin, bile, and colonic acid when in the presence of luminal nutrients; all of these secretions are needed for proper digestion. It also represses motor activity in the gut by blocking segmentation of the intestines, gallbladder contraction, and emptying of the bowels. This inhibition by somatostatin allows the body to uptake the maximum amount of nutrients in the digestive system. Along with the gut and pancreas, SSTR2 also inhibits secretion of neurotransmitters in the central and peripheral nervous system. These hormones include dopamine, norepinephrine, thyrotropin-releasing hormone, and corticotropin-releasing hormone. Many of these hormones help the body maintain homeostasis or react properly to a stimulus such as something pleasurable or a stress in the environment. Because of which, the receptors for somatostatin type 2 impact the body's locomotor, sensory, autonomic, and cognitive functions.
Interactions Somatostatin receptor 2 has been shown to interact with SHANK2.
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