Cytokine regulation of pro- and anti-apoptotic genes in rat hepatocytes: NF-κB-regulated inhibitor of apoptosis protein 2 (cIAP2) prevents apoptosis

Background/Aims: In acute liver failure, hepatocytes are exposed to various cytokines that activate both cell survival and apoptotic pathways. NF-κB is a central transcription factor in these responses. Recent studies indicate that blocking NF-κB causes apoptosis, indicating the existence of NF-κB-regulated anti-apoptotic genes. In the present study the relationship between NF-κB activation and apoptosis has been investigated in hepatocytes. Methods: Primary rat hepatocytes were exposed to a cytokine mixture of tumor necrosis factor α, interleukin-1β, interferon-γ and lipopolysaccharide. Modulation of signalling pathways was performed by using dominant negative adenoviral constructs. Apoptosis and NF-κB activation were determined by caspase-3 activity, Hoechst staining and electrophoretic mobility shift assay, respectively. Furthermore, expression and regulation of apoptosis-related genes were investigated. Results: (1) Inhibition of NF-κB activation results in apoptosis. (2) Inhibitor of apoptosis protein (IAP) family members, inhibitor of apoptosis protein1 (cIAP1), and X-chromosome-linked IAP, are expressed in rat hepatocytes. cIAP2 is induced by cytokines in an NF-κB-dependent manner and overexpression of cIAP2 inhibits apoptosis. (3) The anti-apoptotic Bcl-2 family member A1/Bfl-1 and the pro-apoptotic members Bak and Bid are induced by cytokines and NF-κB-dependent. (4) Nitric oxide inhibits caspase-3 activity in hepatocytes. Conclusions: In inflammatory conditions, hepatocyte survival is dependent on NF-κB activation and cIAP2 contributes significantly to this protection.