Serova L I, Filipenko M, Schilt N, Veerasirikul M, Sabban E L
Department of Biochemistry and Molecular Biology, New York Medical College, Valhalla, NY 10595, USA.
Neuroscience. 2006 Jul 21;140(4):1253-63. doi: 10.1016/j.neuroscience.2006.03.017. Epub 2006 May 2.
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 alpha 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 alpha or estrogen receptor beta. With estrogen receptor alpha, the effect was greater with lower doses of 17 beta-estradiol. At the same dose, the response with estrogen receptor beta was observed somewhat earlier than with estrogen receptor alpha 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 alpha and estrogen receptor beta, 4,4,4,-(4-propil-[1H-pyrazole-1,3,5-triyl)tris-phenol and 2,3-bis[4-hydroxyphenyl]propionitrile 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-tetrahydrobiopterin biosynthesis, which may have implications for sex-related differences in vulnerability in related disorders.
鸟苷三磷酸环化水解酶I（GTPCH）催化（6R）-5,6,7,8-四氢生物蝶呤从头生物合成的第一步，（6R）-5,6,7,8-四氢生物蝶呤是儿茶酚胺和一氧化氮生物合成速率的重要决定因素。研究发现，体内给予雌激素可提高多个儿茶酚胺能部位的GTPCH mRNA水平。为了探究其机制，将含有与荧光素酶基因融合的2988 bp大鼠GTPCH启动子的报告基因构建体与雌激素受体表达载体共转染至PC12细胞。添加2.5 - 20 nM的17β-雌二醇可增加GTPCH启动子驱动的荧光素酶活性，无论存在雌激素受体α还是雌激素受体β，这首次表明17β-雌二醇可通过转录机制调节GTPCH基因表达。然而，雌激素受体α和雌激素受体β在剂量依赖性和时间进程上存在差异。对于雌激素受体α，较低剂量的17β-雌二醇效果更佳。在相同剂量下，雌激素受体β的反应比雌激素受体α稍早出现，并且20 nM的17β-雌二醇即使在6小时后仍有效。这些对17β-雌二醇的反应需要雌激素受体以及雌激素受体α和雌激素受体β的特异性激动剂，分别为4,4,4,-(4-丙基-[1H-吡唑-1,3,5-三基]三苯酚和2,3-双[4-羟基苯基]丙腈，可触发GTPCH启动子活性增加。此外，在未转染适当雌激素受体表达载体的情况下，雌二醇和选择性激动剂均未激活GTPCH启动子。添加17β-雌二醇或选择性激动剂也可提高内源性GTPCH mRNA水平。结果表明雌激素可对GTPCH基因表达产生直接影响。虽然在存在雌激素受体的情况下雌二醇增加了GTPCH启动子活性，但它减弱了启动子和内源性基因对环磷酸腺苷的反应，提示在GTPCH基因表达调控中雌激素和环磷酸腺苷途径之间存在相互作用。这些发现揭示了雌激素在调节（6R）-5,6,7,8-四氢生物蝶呤生物合成限速酶中的重要性，这可能对相关疾病易感性的性别差异具有影响。
