Survivin signaling is regulated through nuclear factor-kappa B pathway during glycochenodeoxycholate-induced hepatocyte apoptosis

Hepatocytes in primary culture undergo apoptosis upon exposure to glycochenodeoxycholate (GCDC). The signaling mechanisms of GCDC-induced apoptosis remain unclear. To investigate the role of antiapoptotic genes, we compared apoptotic response in primary hepatocytes following GCDC treatment. The hepatocytes from adult Sprague–Dawley rats were cultured in collagen-coated dishes and treated with GCDC in varying concentrations, or the same concentration at different time intervals. Apoptosis was detected by the terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) assay, DNA fragmentation assay, and caspase assays. Expression of apoptosis-related genes and proteins was evaluated by RT-PCR, quantitative real-time PCR (qRT-PCR), and Western blotting, respectively. The DNA-binding property of a nuclear protein was assessed by electrophoretic mobility shift assay (EMSA) and chromatin immunoprecipitation (ChIP) assay. An interesting result was that GCDC caused hepatocyte apoptosis to display a biphasic phenomenon at a dosage of 50 μM, whereas it was not found at higher dosages such as 200 μM. GCDC stimulated the expression of antiapoptotic Survivin, which also presented a biphasic response. The activation of nuclear factor-kappaB (NF-κB) corresponded with the up-regulation of Survivin. The inhibitor of NF-κB, BAY 11-7082, suppressed the expression of Survivin and simultaneously eliminated the biphasic response. The expression of Survivin was transcriptionally mediated by the activation of NF-κB, as shown by EMSA and ChIP assay. Conclusions: These results demonstrated that a low dosage of GCDC induced the hepatocyte apoptosis to exhibit the biphasic response, which was regulated by the expression of Survivin through NF-κB signaling pathway.

Research Highlights►GCDC induces the hepatocyte apoptosis to exhibit the biphasic response. The biphasic response depends on GCDC dosage. The activation of Survivin regulates the biphasic response. NF-κB modulates Survivin signaling.