Estrogen-triggered activation of GTP cyclohydrolase 1 gene expression: Role of estrogen receptor subtypes and interaction with cyclic AMP

Guanosinetriphosphate cyclohydrolase I (GTPCH) catalyzes the initial step in the de novo biosynthesis of (6R)5,6,7,8-tetrahydrobiopterin, an important determinant of the rate of catecholamine and nitric oxide biosynthesis. Administration of estrogen in vivo was found to elevate GTPCH mRNA levels in several catecholaminergic locations. To examine the mechanism, PC12 cells were co-transfected with a reporter construct containing 2988 bp of rat GTPCH promoter fused to luciferase gene, and expression vectors for estrogen receptors. Addition of 2.5-20 nM of 17 beta-estradiol increased GTPCH promoter-driven luciferase activity in the presence of either estrogen receptor a or estrogen receptor beta indicating, for the first time, that 17 beta-estradiol can regulate GTPCH gene expression via transcriptional mechanisms. However, there were differences in dose dependence and time course with estrogen receptor a or estrogen receptor beta. With estrogen receptor a, the effect was greater with lower doses of 17 beta-estradiol. At the same dose, the response with estrogen receptor 13 was observed somewhat earlier than with estrogen receptor a and with 20 nM 17 beta-estradiol was effective even after 6 h. These responses to 17 beta-estradiol required estrogen receptors and specific agonists for estrogen receptor a and estrogen receptor beta, 4,4,4,-(4-propil-[1H-pyrazole-1,3,5triyl)tris-phenol and 2,3-bis[4-hydroxyphenyl]proplonitrile respectively, triggered increased GTPCH promoter activity. In addition, neither estradiol, nor the selective agonists activated GTPCH promoter without transfection of appropriate estrogen receptor expression vectors. Addition of 17 beta-estradiol, or the selective agonists, also elevated endogenous GTPCH mRNA levels. The results demonstrate that estrogen can have a direct effect on GTPCH gene expression. Although estradiol increased GTPCH promoter activity in the presence of estrogen receptors, it attenuated the response of the promoter and endogenous gene to cyclic AMP, suggesting the crosstalk between estrogen and cyclic AMP pathways in the regulation of GTPCH gene expression. These findings reveal the significance of estrogen in modulating regulation of rate limiting enzyme in the (6R)-5,6,7,8-tetrahydroblopterin biosynthesis, which may have implications for sex-related differences in vulnerability in related disorders. (c) 2006 IBRO. Published by Elsevier Ltd. All rights reserved.