Hormonal effects on the secretion and glycoform profile of corticosteroid-binding globulin

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 (E ₂), testosterone (T), insulin, thyroxin (T ₄) 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, T ₄ and high concentrations of E ₂ decreased the secretion of CBG by HepG2 cells (p < 0.05). Ethanol, the solvent used for E ₂, 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 T ₄ and DMZ decreased the production of more basic CBG glycoforms. Stimulation with E ₂ 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.