Type I interferon and TNFα cooperate with type II interferon for TRAIL induction and triggering of apoptosis in SK-N-MC EWING tumor cells

Ewing's sarcoma is the second most common human bone tumor in childhood. Here, we investigated the sensitivity of the Ewing tumor cell line, SK-N-MC, to the apoptotic effect of type I (IFNalpha) and type II (IFNgamma) interferons and TNFalpha. We demonstrate that although IFNalpha and TNFalpha alone are unable to induce cell death, they act in synergy with IFNgamma to induce SK-N-MC cell apoptosis. The synergistic induction of apoptosis correlated with the synergistic induction of TNFalpha-related apoptosis-inducing ligand ( TRAIL) mRNA and TRAIL protein synthesis as well as of TRAIL secretion. Preparations of inducer-free supernatants from SK-N-MC cells stimulated with combinations of cytokines were shown to be cytotoxic for untreated SK-N-MC cells. This cytotoxicity was partially inhibited by addition of TRAILR2/Fc fusion protein, indicating that the secreted TRAIL mediates, at least in part, the apoptotic effect displayed by the supernatants of stimulated SK-N-MC cells. We have shown that the presence of IFNgamma is required to allow the sustained expression of IRF1 in SK-N-MC cells stimulated by addition of IFNalpha or TNFalpha suggesting that IRF1 plays a role in the synergistic induction of apoptosis by combinations of cytokines. Furthermore, we have shown that inhibition of NF-kappaB activation contributes to the IFNgamma-mediated sensitization to the apoptotic effect of TNFalpha. To our knowledge, this is the first report showing that interferon/cytokine combinations are able to induce TRAIL gene expression and TRAIL protein synthesis and secretion in Ewing sarcoma-derived cells. We believe that the observations reported here might contribute to the development of alternative new approaches to the treatment of Ewing tumors resistant to conventional therapy.