IκB-α, the NF-κB Inhibitory Subunit, Interacts with ANT, the Mitochondrial ATP/ADP Translocator

The transcription factor NF-κB regulates a wide set of genes involved in the establishment of many cellular processes that control cell activation, proliferation, and apoptosis. IκB inhibitory subunits integrate NF-κB activation signals through phosphorylation and ubiquitination of its N-terminal domain. Using the two-hybrid system in yeast, we searched for IκB-α N-terminal domain interactors and therefore potential NF-κ-B regulators. An interaction of IκB-α with the mitochondrial ATP/ADP translocator ANT was detected in yeast and confirmed in glutathione S-transferase pull-down assays and co-precipitation experiments in transfected cells. Subcellular cell fractionation, resistance to proteinase K treatment, and electron microscopy experiments demonstrated the presence of IκB-α and associated p65 NF-κB in the mitochondrial intermembrane space. IκB-α·NF-κB appeared to be released from mitochondria upon the induction of apoptosis by engagement of the Fas receptor. These data suggest that the mitochondrial IκB-α ·NF-κB pool participates in the regulation of apoptosis.