NF-κB inhibits T-cell activation-induced, p73-dependent cell death by induction of MDM2

NF-kappa B is a key transcription factor involved in the regulation of T-cell activation and proliferation upon engagement of the T-cell receptor (TCR). T cells that lack the I kappa B kinase (IKK beta) are unable to activate NF-kappa B, and rapidly undergo apoptosis upon activation. NF-kappa B activation following T-cell receptor engagement induces the expression of Mdm2 through interaction with NF-kappa B sites in its P1 promoter, and enforced expression of Mdm2 protected T cells deficient for NF-kappa B activation from activation-induced cell death. In T cells with intact NF-kappa B signaling, ablation or pharmacologic inhibition of Mdm2 resulted in activation-induced apoptosis. Mdm2 coprecipitates with p73 in activated T cells, and apoptosis induced by inhibition of Mdm2 was p73-dependent. Further, Bim was identified as a p73 target gene required for cell death induced by Mdm2 inhibition, and a p73-responsive element in intron 1 of Bim was characterized. Our results demonstrate a pathway for survival of activated T cells through NF-kappa B-induced Mdm2, which blocks Bim-dependent apoptosis through binding and inhibition of p73.