The activation of plasminogen activator inhibitor-1 expression by IL-1β is attenuated by estrogen in hepatoblastoma HepG2 cells expressing estrogen receptor α

A low estrogen status in postmenopausal women is associated with elevated plasma levels of plasminogen activator inhibitor-1 (PAI-1). In this study, the ability of estrogen compounds to regulate PAI-1 expression was determined in a hepatocyte HepG2 cell line made to stably express estrogen receptor a (ERa). In both the wild type and ER expressing HepG2 cells, estrogen had no effect on basal PAI-1 expression. However, in the ER expressing cells the ability of IL-1b to increase PAI-1 mRNA and protein levels was attenuated by 17b-estradiol, tamoxifen and twelve estrogen components of Premarin. In contrast, the mixed agonist/antagonist raloxifene had weak agonist activity and like the pure antagonist ICI 182780, it dose dependently blocked the effect of 17b-estradiol on IL-1b stimulated PAI-1 levels. These results suggest that estrogen agonists may lower PAI-1 levels in vivo by inhibiting cytokine activated PAI-1 expression by an ER dependent mechanism.