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

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Abstract

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 (IFNα) and type II (IFNγ) interferons and TNFα. We demonstrate that although IFNα and TNFα alone are unable to induce cell death, they act in synergy with IFNγ to induce SK-N-MC cell apoptosis. The synergistic induction of apoptosis correlated with the synergistic induction of TNFα-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 IFNγ is required to allow the sustained expression of IRF1 in SK-N-MC cells stimulated by addition of IFNα or TNFα suggesting that IRF1 plays a role in the synergistic induction of apoptosis by combinations of cytokines. Furthermore, we have shown that inhibition of NF-κB activation contributes to the IFNγ-mediated sensitization to the apoptotic effect of TNFα. 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.

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