Genomic structure and transcriptional regulation of the human somatostatin receptor type 2.

Somatostatin exerts inhibitory effects on virtually all endocrine and exocrine secretions. The somatostatin receptor subtype 2 (sst2) acts as a critical molecule for growth hormone regulation and cell proliferation. We investigated the structure and regulation of the human sst2 gene. A genomic clone including the sst2 gene was isolated, 1.5 kb of the promoter was sequenced and putative transcription factor binding sites were identified. The transcription start site was located 93 nucleotides upstream of the translation start site. The nucleotide sequences of the complete gene and 0.5 kb of 3' region were determined. A possible polyadenylation signal was identified. Transcriptional regulation was investigated by transient transfections using various promoter fragments. A -1100 sst2 promoter directed significant levels of luciferase expression in GH4 rat pituitary cells and Skut1-B endometrium cells whereas only low activity was detected in JEG3 chorion carcinoma cells or COS-7 monkey kidney cells. A minimal -252 promoter allowed cell specific expression. We did not find any regulation of the sst2 promoter by somatostatin, forskolin, TRH, TPA, T3, and 17beta-estradiol. Glucocorticoids lead to a significant inhibition of sst2 promoter activity. Further mapping suggest a glucocorticoid-responsive element between -905 and -707 and between -252 and -163. These studies demonstrate the nature of the human sst2 gene and identify its 5' and 3' flanking regions. Furthermore, specific activity of the promoter and regulation by various hormones is demonstrated.