An NF-κB p65-cIAP2 link is necessary for mediating resistance to TNF-α induced cell death in gliomas

Malignant gliomas are diffusively infiltrative and remain among the deadliest of all cancers. NF-kappa B is a transcription factor that mediates cell growth, migration and invasion, angiogenesis and resistance to apoptosis. Normally, the activity of NF-kappa B is tightly regulated by numerous mechanisms. However, in many cancers, NF-kappa B is constitutively activated and may function as a tumor promoter. Herein, we show that in gliomas, NF-kappa B is constitutively activated and the levels of cIAP2, Bcl-2, Bcl-xL and Survivin are elevated. These genes are regulated by NF-kappa B and can inhibit apoptosis. To understand the potential role of NF-kappa B p65 in suppressing apoptosis, we generated human glioma cell lines that inducibly express shRNA molecules specific for p65. We demonstrate that in the absence of p65, TNF-alpha induced cIAP2 expression is significantly reduced while the levels of Bcl-2, Bcl-xL and Survivin are not affected. These data suggest that of these genes, only cIAP2 is a direct target of p65, which was confirmed using RT-PCR and chromatin immunoprecipitation (ChIP) assays. By reducing the levels of p65 and/or cIAP2 levels, we demonstrate that the levels of RIP poly-ubiquitination are reduced, and that p65-deficient glioma cells are more sensitive to the cytotoxic effects of TNF-alpha. Specifically, in the presence of TNF-alpha glioma cells lacking p65 and/or cIAP2 showed cellular proliferation defects and underwent cell death. These data suggest that NF-kappa B and/or cIAP2 may be therapeutically relevant targets for the treatment of malignant gliomas.