Effect of Phthalate Esters on the Expression of Aromatase and Its Action Mechanism

邻苯二甲酸酯被广泛用作聚氯乙烯的增塑剂，并被怀疑具有内分泌干扰物的功能。邻苯二甲酸二（2-乙基己基）酯（DEHP）是商业用途中最重要的邻苯二甲酸酯，据报道可作为啮齿动物生殖毒物。在本研究中，我们研究了邻苯二甲酸酯对人肾上腺皮质癌细胞系NCI-H295 R中芳香化酶（CYP 19）活性及其基因表达的影响。邻苯二甲酸单（2-乙基己基）酯（MEHP）是DEHP的主要代谢产物，其剂量依赖性抑制芳香酶活性及其转录水平。此外，MEHP快速和瞬时诱导编码核受体4A亚家族成员（Nur 77，Nurr 1和NOR-1）的基因转录，并上调Nur 77启动子激活和Nur 77蛋白表达。MEHP诱导的Nur 77转录被双吲哚马来酰亚胺I（蛋白激酶C抑制剂）和渥曼青霉素（磷酸肌醇3-激酶抑制剂）抑制。最后，异位表达的Nur 77显着抑制毛喉素诱导的转录激活的启动子I.3和启动子II的CYP 19基因。这些结果表明，芳香化酶活性和转录水平的抑制MEHP暴露于NCI-H295 R细胞通过调节Nur 77基因的快速和瞬时表达。

Phthalate esters are widely used as plasticizers for polyvinylchloride and are suspected of functioning as endocrine disrupters. Di-(2-ethylhexyl) phthalate (DEHP), the most important phthalate ester in commercial use, has been reported to act as a rodent reproductive toxicant. In the present study, we investigated the effects of phthalate esters on aromatase(CYP19) activity and on its gene expression in a human adrenocortical carcinoma cell line, NCI-H295R. Mono-(2-ethylhexyl) phthalate(MEHP), a principle metabolite of DEHP, dose-dependently suppressed aromatase activity and its transcription level. Furthermore, MEHP rapidly and transiently induced transcription of the genes which encode nuclear receptor 4A subfamily members(Nur77, Nurr1, and NOR-1), and up-regulated Nur77promoter activation and Nur77 protein expression in the cells. MEHP-induced Nur77 transcription was inhibited by bisindolylmaleimide I(protein kinase C inhibitor) and wortmannin(phosphoinositide 3-kinase inhibitor). Finally, ectopic expression of Nur77 markedly suppressed forskolin-induced transcriptional activation of promoter I.3 and promoter II of the CYP19 gene. These results suggest that the suppression of aromatase activity and its transcription level by MEHP exposure to NCI-H295R cells was regulated through the rapid and transient expression of Nur77 gene.