IκB-α, the NF-κB inhibitors subunit, interacts with ANT, the mitochondrial ATP/ADP translocator

The transcription factor NF-kappaB regulates a wide set of genes involved in the establishment of many cellular processes that control cell activation, proliferation, and apoptosis. I kappaB inhibitory subunits integrate NF-kappaB activation signals through phosphorylation and ubiquitination of its N-terminal domain. Using the two-hybrid system in yeast, we searched for I kappaB-alpha N-terminal domain interactors and therefore potential NF-kappaB regulators. An interaction of I kappaB-alpha 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 I kappaB-alpha and associated p65 NF-kappaB in the mitochondrial intermembrane space. I kappaB-. alpha .NF-kappaB appeared to be released from mitochondria upon the induction of apoptosis by engagement of the Fas receptor. These data suggest that the mitochondrial I kappaB-alpha .NF-kappaB pool participates in the regulation of apoptosis.