Autocrine-paracrine role of endothelin-1 in the regulation of aldosterone synthase expression and intracellular Ca2+ in human adrenocortical carcinoma NCI-H295 cells

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 adrenocortical carcinoma cells has been investigated. Reverse transcription-PCR with primers specific for prepro-ET-1, human ET-1 converting enzyme-1, ETA, and ETB complementary DNAs consistently demonstrated the expression of all genes in NCI-H295 cells. The presence of mature ET-1 and both its receptor subtypes was confirmed by immunocytochemistry and autoradiography, respectively. Aldosterone synthase (AS) messenger RNA was also detected in NCI-H295 cells, and AS gene expression was enhanced 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 antagonist BQ-788. A clear-cut increase in the intracellular Ca2+ concentration in NCI-H295 cells in response to ETB, but not ETA, activation was observed. In light of these findings, the following conclusions can be drawn: 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 autocrine/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 exclusively mediated by the ETB receptor.