Inhibition of TGF-β-induced apoptosis by ethinyl estradiol in cultured, precision cut rat liver slices and hepatocytes

Ethinyl estradiol (EE) is a strong promoter of hepatocarcinogenesis in the rat. Treatment with EE and other hepatic promoters induces transient growth stimulation followed by growth inhibition (mitosuppression) in hepatocytes. Previously, we identified several genes whose transcript levels were increased during EE-induced mitosuppression, including transforming growth factor beta (TGF-beta), which inhibits growth and induces apoptosis in hepatocytes. Various hepatic promoters, including phenobarbital and several peroxisomal proliferators, have been shown to inhibit TGF-beta-induced apoptosis in rat hepatocytes. The goal of this study was to investigate whether EE is also an inhibitor of TGF-beta-induced apoptosis in rat hepatocytes. Several approaches to detect apoptosis were used, including the TUNEL assay, detection of high molecular weight DNA fragmentation by field inversion gel electrophoresis and determination of cytosolic cytochrome c levels by western analysis. TGF-beta-induced apoptosis in cultured, precision cut liver slices and hepatocytes of female rats. EE (</=3 microM) completely inhibited TGF-beta-induced apoptosis in these systems in the absence of cytotoxicity. These findings add EE to the list of several hepatic promoters that both induce TGF-beta while simultaneously inhibiting its ability to cause apoptosis.