IFNα sensitizes ME-180 human cervical cancer cells to TNFα-induced apoptosis by inhibiting cytoprotective NF-κ-B activation

Tumor necrosis factor alpha (TNF alpha) induces apoptosis of a variety of tumor cell types, The anti-tumor effect of TNF alpha is often augmented by interferon (IFN) gamma, We hypothesized that IFN alpha, which shares many biological activities with IFN gamma, might also synergize with TNF alpha for the induction of tumor cell death. We tested our hypothesis using ME-180 human cervical cancer cells exposed to either IFN alpha or TNF alpha alone or both. We analyzed the death of ME-180 cells by biochemical and cytological means, and investigated the molecular mechanism underlying cytotoxic synergism between the two cytokines, We found that (i) IFN alpha /TNF alpha synergistically induced apoptosis of ME-180 cells, which was accompanied by activation of caspases-3 and -8; (ii) IFN alpha induced signal transducer and activator of transcription (STAT) 1 phosphorylation, and transfection of phosphorylation-defective STAT1 dominant-negative mutant inhibited IFN alpha /TNF alpha -induced apoptosis; (iii) inhibition of nuclear factor kappaB (NF-kappaB) by proteasome inhibitor MG-132 sensitized ME-180 cells to TNF alpha alone; (i,) IFN alpha treatment attenuated TNF alpha -induced NF-kappaB reporter activity, while it did not inhibit DNA binding of NF-kappaB, Taken collectively, our results indicate that IFN alpha sensitizes ME-180 cells to TNF alpha -induced apoptosis by inhibiting TNF alpha -mediated cytoprotective NF-kappaB activation, and this sensitizing effect of IFN alpha is mediated through a STAT1-dependent pathway. (C) 2001 Published by Elsevier Science B,V, on behalf of the Federation of European Biochemical Societies.