Annexin A4 interacts with the NF-kB p50 subunit and modulates NF-kB transcriptional activity in a Ca²⁺-dependent manner

Previously, we identified annexin A4 (ANXA4) as a candidate substrate of caspase-3. Proteomic studies were performed to identify interacting proteins with a view to determining the roles of ANXA4. ANXA4 was found to interact with the p105. Subsequent studies revealed that ANXA4 interacts with NF-kB through the Rel homology domain of p50. Furthermore, the interaction is markedly increased by elevated Ca²⁺ levels. NF-kB transcriptional activity assays demonstrated that ANXA4 suppresses NF-kB transcriptional activity in the resting state. Following treatment with TNF-α or PMA, ANXA4 also suppressed NF-kB transcriptional activity, which was upregulated significantly early after etoposide treatment. This difference may be due to the intracellular Ca²⁺ level. Additionally, ANXA4 translocates to the nucleus together with p50, and imparts greater resistance to apoptotic stimulation by etoposide. Our results collectively indicate that ANXA4 differentially modulates the NF-kB signaling pathway, depending on its interactions with p50 and the intracellular Ca²⁺ ion level.