AUTOCRINE-PARACRINE ROLE OF ENDOTHELIN-1 IN THE REGULATION OF ALDOSTERONE SYNTHASE EXPRESSION AND INTRACELLULAR CA2-H295 CELLS( IN HUMAN ADRENOCORTICAL CARCINOMA NCI)

The role played by endothelin (ET-1) and its receptor subtypes A and B (ETA and ETB) in the functional regulation of human NCI-H295 adrenoco rtical carcinoma cells has been investigated. Reverse transcription-PC R with primers specific for prepro-ET-1, human ET-1 converting enzyme- 1, ETA, and ETB complementary DNAs consistently demonstrated the expre ssion of all genes in NCI-H295 cells. The presence of mature ET-1 and both its receptor subtypes was confirmed by immunocytochemistry and au toradiography, respectively. Aldosterone synthase (AS) messenger RNA w as also detected in NCI-H295 cells, and AS gene expression was enhance d by both ET-1 and the specific ETB agonist IRL-1620; this effect was not inhibited by either the ETA antagonist BQ-123 or the ETB antagonis t BQ-788. A clear-cut increase in the intracellular Ca2+ concentration in NCI-H295 cells in response to ETB, but not ETA, activation was obs erved. In light of these findings, the following conclusions can be dr awn: 1) NCI-H295 cells possess an active ET-1 biosynthetic pathway and are provided with ETA and ETB receptors; 2) ET-1 regulates in an auto crine/paracrine fashion the secretion of aldosterone by NCI-H295 cells by enhancing both AS transcription and raising the intracellular Ca2 concentration; and 3) the former effect of ET-1 probably involves the activation of both receptor subtypes, whereas calcium response is exc lusively mediated by the ETB receptor.