Previously we have shown that interferon (IFN)-α induced apoptosis is predominantly mediated by the upregulation of tumor necrosis factor related apoptosis-inducing ligand (TRAIL) via the caspase-8 pathway. It was also shown that recruitment of mitochondria in IFN-α induced apoptosis involves the cleavage of BH3 interacting domain death agonist (Bid) to truncated Bid (tBid). In the present study, we demonstrate that tBid induced by IFN-α2a activates mitochondrial Bak to trigger the loss of mitochondrial membrane integrity, consequently causing release of apoptosis-inducing factor (AIF) in ovarian cancer cells, OVCAR3. AIF translocates from the mitochondria to the nucleus and induces nuclear fragmentation and cell death. Both a small molecule Bid inhibitor (BI-6C9) or Bid-RNA interference (RNAi) preserved mitochondrial membrane potential, prevented nuclear translocation of AIF, and abrogated IFN-α2a-induced cell death. Cell death induced by tBid was inhibited by AIF-RNAi, indicating that caspase-independent AIF signaling is the main pathway through which Bid mediates cell death. This was further supported by experiments showing that BI-6C9 did not prevent the release of cytochrome c from mitochondria to cytosol, while the release of AIF was prevented. In conclusion, IFN-α2a-induced apoptosis is mediated via the mitochondria-associated pathway involving the cleavage of Bid followed by AIF release that involves Bak activation and translocation of AIF from the mitochondria to the nucleus in OVCAR3 cells.
Published by Elsevier B.V.