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

Abstract

Tumor necrosis factor α (TNFα) induces apoptosis of a variety of tumor cell types. The anti-tumor effect of TNFα is often augmented by interferon (IFN) γ. We hypothesized that IFNα, which shares many biological activities with IFNγ, might also synergize with TNFα for the induction of tumor cell death. We tested our hypothesis using ME-180 human cervical cancer cells exposed to either IFNα or TNFα 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) IFNα/TNFα synergistically induced apoptosis of ME-180 cells, which was accompanied by activation of caspases-3 and -8; (ii) IFNα induced signal transducer and activator of transcription (STAT) 1 phosphorylation, and transfection of phosphorylation-defective STAT1 dominant-negative mutant inhibited IFNα/TNFα-induced apoptosis; (iii) inhibition of nuclear factor κB (NF-κB) by proteasome inhibitor MG-132 sensitized ME-180 cells to TNFα alone; (iv) IFNα treatment attenuated TNFα-induced NF-κB reporter activity, while it did not inhibit DNA binding of NF-κB. Taken collectively, our results indicate that IFNα sensitizes ME-180 cells to TNFα-induced apoptosis by inhibiting TNFα-mediated cytoprotective NF-κB activation, and this sensitizing effect of IFNα is mediated through a STAT1-dependent pathway.