Kraus J, Wöltje M, Schönwetter N, Höllt V
Institut für Pharmakologie und Toxikologie, Universität Magdeburg, Germany.
J Physiol Paris. 2000 May-Aug;94(3-4):199-204. doi: 10.1016/s0928-4257(00)00205-9.
The diverse biological effects of the hormone somatostatin are mediated by five genetic different receptor subtypes (sst1-sst5), which belong to the superfamily of G-protein coupled receptors with seven transmembrane domains. The sst2 subtype is unique among the somatostatin receptors in its structure, since it is expressed in two protein variants which differ within their carboxy-terminal ends, generated by alternative splicing. Within the 5' untranslated region of the gene two introns separate three transcriptional units with distinct promoters. Due to the latter feature, the sst2 gene is also unique among all somatostatin receptor genes regarding its transcriptional regulation. The three alternative promoters are tissue specifically active and show alternative responsiveness to extracellular signals. The second sst2 promoter is important for expression of the gene in tissues where somatostatin has essential physiological functions, such as brain, pituitary and gastrointestinal tissues. Furthermore, it contains cis-acting regulatory elements involved in the transcriptional response to elevated cyclic AMP levels and glucocorticoids.
生长抑素这种激素的多种生物学效应是由五种基因不同的受体亚型（sst1 - sst5）介导的，这些亚型属于具有七个跨膜结构域的G蛋白偶联受体超家族。sst2亚型在生长抑素受体中结构独特，因为它以两种蛋白质变体形式表达，这两种变体在其羧基末端存在差异，是由可变剪接产生的。在该基因的5'非翻译区，两个内含子将具有不同启动子的三个转录单元分隔开。由于这一特征，就转录调控而言，sst2基因在所有生长抑素受体基因中也很独特。这三个可变启动子具有组织特异性活性，并对细胞外信号表现出不同的反应性。第二个sst2启动子对于该基因在生长抑素具有重要生理功能的组织（如脑、垂体和胃肠道组织）中的表达至关重要。此外，它还包含参与对升高的环磷酸腺苷水平和糖皮质激素的转录反应的顺式作用调控元件。
