Interferon-a sensitizes human hepatoma cells to TRAIL-iduced apoptosis through DRS upregulation and NF-κB inactivation

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Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL), a member of the TNF superfamily, induces apoptosis in a variety of cancer cells with little or no effect on normal cells. Human hepatoma cells, however, are resistant to TRAIL-induced apoptosis. Since interferon-a (IFN-α) is capable of enhancing TNF-a-induced apoptosis in certain cancer cells, we evaluated the effect of IFN-α on TRAIL-induced apoptosis of human hepatoma cells. IFN-α pretreatment enhanced TRAIL-induced apoptosis of HuH-7 and Hep3B cells, in which IFN-α upregulated the expression of DRS, a death receptor of TRAIL, and downregulated the expression of survivin, which has an anti-apoptotic function. In contrast, IFN-α did not enhance TRAIL-induced apoptosis of HepG2 cells, in which expression of DRS and survivin was not affected by IFN-α. On the other hand, TRAIL activated NF-κB composed of Re1A-p50 heterodimer, a key transcription factor regulating cell survival, in HuH-7 and HepG2 cells : However, IFN-α pretreatment repressed the TRAIL-mediated activation of NF-κB and decreased its transcriptional activity in HuH-7 but not in HepG2 cells. Moreover, IFN-α pretreatment clearly augmented TRAIL-mediated caspase-8 activation in HuH-7 cells. Our results suggest that IFN-α could sensitize eertain human hepatoma cells to TRAIL-induced apoptosis by stimulating its death signaling and by repressing the survival function in these cells.