Time-dependent onset of Interferon-alpha2b-induced apoptosis in isolated hepatocytes from preneoplastic rat livers.
We have already demonstrated that interferon alfa-2b (IFN-alpha2b) induces apoptosis in isolated hepatocytes from preneoplastic rat livers via the secretion of transforming growth factor beta(1) (TGF-beta(1)), 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-alpha2b, which was completely blocked when anti-TGF-beta(1) was added to the culture media. IFN-alpha2b mediated radical oxygen species (ROS) production that preceded the loss of mitochondrial transmembrane potential (DeltaPsi), release of cytochrome c, and activation of caspase-3. Bax levels increased in a time-dependent fashion, and Bcl-x(L) was down-regulated in the early hours of IFN-alpha2b treatment. The delayed translocation of Bid into the mitochondria was in concordance with late caspase-8 activation. In conclusion, endogenous TGF-beta(1) secreted under IFN-alpha2b stimulus seems to induce cytochrome c release through a mechanism related to Bcl-2 family members and loss of mitochondrial DeltaPsi. Bax protein could be responsible of the release of cytochrome c during the initial hours of IFN-alpha2b-induced apoptosis via TGF-beta(1). Activated Bid by caspases could amplificate the mitochondrial events, enhancing the release of cytochrome c.