Characterization and transcriptional regulation of the human somatostatin receptor subtype 1 gene.

Somatostatin (SRIF) exerts inhibitory effects on virtually all endocrine and exocrine secretions. At least five distinct human SRIF receptors have been identified ( SST1-SST5). Analysis of the promoter region may provide tools to understand transcriptional regulation of SSTS in various tissues, indicating specific functions. Transcriptional regulation of the human SST1 was analyzed in the present study. Total RNA from a human somatotropic pituitary tumor was reverse transcribed. 5'cDNA regions of the human SST1 were cloned using an adapted inverse PCR method. Among the 15 PCR clones analyzed, 9 demonstrated an extended 5'-utr of 266 nucleotides, determining a thymidine residue as a major transcription start site. No introns were evident in the 5'-utr region. The promoter region lacked consensus sites for TATA or CAAT boxes, YY1, or an initiator sequence, but contained two CpG islands. Different lengths of 5'-flanking regions cloned by PCR were placed upstream of the luciferase reporter gene and transiently transfected into various cell lines. The 2834 nt of the promoter region directed significant transcriptional activity in a somatotropic pituitary cell line, but neither in COS-7 monkey kidney cells nor in AtT-20 murine corticotrope cells. Transcriptional activity was not affected by incubation with various hormones. Several putative transcription factor binding sites inducing the cell-type specific activity were identified.

Differential expression of the human somatostatin receptor subtypes sst1 to sst5 in various adrenal tumors and normal adrenal gland.

Somatostatin (SRIF) is a widely distributed peptide with growth-inhibiting effects in various tumors. So far, five distinct human SRIF receptor subtypes (sst1-sst5) have been identified. We investigated expression of the five ssts in various adrenal tumors and in normal adrenal gland. Tissue was obtained from ten pheochromocytomas (PHEOs), nine cortisol-secreting adenomas (CPAs), eleven aldosterone secreting adenomas (APAs) and eight non-functional adenomas (NFAs) after retroperitoneoscopic surgery, and used for RNA extraction. Adrenal tissue surrounding the tumor was available for analysis in twenty-seven cases. Receptor expression was studied by RT-PCR using sst-specific primers and subsequently confirmed by Southern blotting. Expression of all five receptor subtypes was observed in RNA obtained from normal adrenal gland. Furthermore, each receptor subtype was expressed in more than 50 % of all tumors analyzed. No sst5 expression was found in PHEOs, while sst1 was present in nearly all of these tumors. Only a few of the CPAs expressed subtypes sst1 and sst4. Expression of all five subtypes was distributed equally in APAs. No sst4 was found in any of the NFAs. Differential expression of ssts in various adrenal tumors may point to new aspects in the pathogenesis of these adenomas. Furthermore, the presence of specific ssts could expand the diagnostic and therapeutic strategies during management. New subtype specific analogues of SRIF may be used in the future depending on the type of adrenal tumor and receptor subtype expressed.