Mihrshahi Robin, Lewis John G, Ali Sinan O
Department of Biological Sciences, Macquarie University, Sydney, NSW 2109, Australia.
J Steroid Biochem Mol Biol. 2006 Nov;101(4-5):275-85. doi: 10.1016/j.jsbmb.2006.06.031. Epub 2006 Oct 9.
Corticosteroid-binding globulin (CBG) is a plasma glycoprotein that is primarily synthesized in the liver and binds cortisol and progesterone with high affinity. In this study, a CBG secreting hepatocellular carcinoma derived cell line (HepG2) was used to investigate the hormonal regulation of hepatic CBG synthesis. HepG2 cells were grown for 72 h in 30, 300 and 3000 nM concentrations of estradiol (E2), testosterone (T), insulin, thyroxin (T4) and dexamethasone (DMZ) and the secreted CBG quantified by a novel enzyme-linked immunosorbent assay (ELISA). Two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) was carried out to determine the effects of these hormones on the relative distribution of CBG glycoforms. Insulin, T4 and high concentrations of E2 decreased the secretion of CBG by HepG2 cells (p<0.05). Ethanol, the solvent used for E2, T and DMZ, also significantly attenuated CBG secretion. 2D-PAGE resolved 13-14 glycoforms of CBG produced by HepG2 cells. Insulin caused a reduction in the synthesis of more acidic, while T4 and DMZ decreased the production of more basic CBG glycoforms. Stimulation with E2 resulted in the synthesis of additional isoforms of increased acidity, which may represent a type of CBG only seen during pregnancy in vivo. Possible physiological implications of these findings are discussed.
皮质类固醇结合球蛋白（CBG）是一种血浆糖蛋白，主要在肝脏中合成，能以高亲和力结合皮质醇和孕酮。在本研究中，使用一种分泌CBG的肝癌衍生细胞系（HepG2）来研究肝脏CBG合成的激素调节。将HepG2细胞分别在浓度为30、300和3000 nM的雌二醇（E2）、睾酮（T）、胰岛素、甲状腺素（T4）和地塞米松（DMZ）中培养72小时，并用一种新型酶联免疫吸附测定法（ELISA）对分泌的CBG进行定量。进行二维聚丙烯酰胺凝胶电泳（2D-PAGE）以确定这些激素对CBG糖型相对分布的影响。胰岛素、T4和高浓度的E2降低了HepG2细胞分泌CBG的量（p<0.05）。用于溶解E2、T和DMZ的溶剂乙醇也显著减弱了CBG的分泌。2D-PAGE分离出了HepG2细胞产生的13 - 14种CBG糖型。胰岛素导致更多酸性CBG糖型的合成减少，而T4和DMZ则降低了更多碱性CBG糖型的产生。用E2刺激导致合成了更多酸性增加的异构体，这可能代表了一种仅在体内妊娠期间才出现的CBG类型。讨论了这些发现可能的生理学意义。
