CALCIUM REGULATES HUMAN CYP11B2 TRANSCRIPTION

The CYP11B2 gene encodes aldosterone synthase, a cytochrome P450 (P450 aldo) expressed in high levels in the adrenal zona glomerulosa While t he primary physiologic regulators of aldosterone production are circul ating angiotensin II (Ang II) and potassium (K+) the action of these a gents on CYP11B2 gene transcription have not been examined Because the se factors increase intracellular calcium we have hypothesized that ca lcium signaling pathways are one mechanism controlling CYP11B2 transcr iption. Previously we demonstrated that increases in intracellular cal cium increase P450aldo mRNA. Herein, we analyzed the role of calcium i n the expression of the human CYP11B2 gene using transient transfectio n of a luciferase reporter construct containing 2017 bp of human CYP11 B2 5' flanking DNA in mouse Y-1 and human H295R adrenocortical cell li nes. When transfected into Y-1 cells, reporter gene expression was inc reased following treatment with ACTH or forskolin, but not with Ang II , the L-type calcium channel agonist BAYK8644, or ionomycin In H295R c ells, however, reporter gene expression was increased following treatm ent with Ang II, K+, BAYK8644 ionomycin or dibutyryl cAMP (Bu(2)cAMP). Activation of protein kinase C with TPA did not alter reporter gene e xpression in either cell line. These data demonstrate that both calciu m and cAMP signaling pathways regulate human CYP11B2 gene expression. In addition, the H295R adrenal cell line appears to be an appropriate model to study regulation of CYP11B2 by calcium.