Time-dependent onset of Interferon-α2b-induced apoptosis in isolated hepatocytes from preneoplastic rat livers

We have already demonstrated that interferon alfa-2b (IFN-α2b) induces apoptosis in isolated hepatocytes from preneoplastic rat livers via the secretion of transforming growth factor β1 (TGF-β1), and this process is accompanied by caspase-3 activation. The aim of this study was to further investigate the mechanism of this activation. Isolated hepatocytes from preneoplastic livers induced DNA fragmentation in response to IFN-α2b, which was completely blocked when anti-TGF-β1 was added to the culture media. IFN-α2b mediated radical oxygen species (ROS) production that preceded the loss of mitochondrial transmembrane potential (ΔΨ), release of cytochrome c, and activation of caspase-3. Bax levels increased in a time-dependent fashion, and Bcl-xL was down-regulated in the early hours of IFN-α2b treatment. The delayed translocation of Bid into the mitochondria was in concordance with late caspase-8 activation. In conclusion, endogenous TGF-β1 secreted under IFN-α2b stimulus seems to induce cytochrome c release through a mechanism related to Bcl-2 family members and loss of mitochondrial ΔΨ. Bax protein could be responsible of the release of cytochrome c during the initial hours of IFN-α2b-induced apoptosis via TGF-β1. Activated Bid by caspases could amplificate the mitochondrial events, enhancing the release of cytochrome c.