Centrosomal P4.1-associated Protein Is a New Member of Transcriptional Coactivators for Nuclear Factor-κB

Abstract Nuclear factor-κB (NF-κB) is a transcription factor important for various cellular events such as inflammation, immune response, proliferation, and apoptosis. In this study, we performed a yeast two-hybrid screening using the N-terminal domain of the p65 subunit (RelA) of NF-κB as bait and isolated centrosomal P4.1-associated protein (CPAP) as a candidate for a RelA-associating partner. Glutathione S-transferase pull-down assays and co-immunoprecipitation experiments followed by Western blotting also showed association of CPAP with RelA. When overexpressed, CPAP enhanced NF-κB-dependent transcription induced by tumor necrosis factor-α (TNFα). Reduction of the protein level of endogenous CPAP by RNA interference resulted in decreased activation of NF-κB by TNFα. After treatment with TNFα, a portion of CPAP was observed to accumulate in the nucleus, although CPAP was found primarily in the cytoplasm without any stimulation. Moreover, CPAP was observed in a complex recruited to the transcriptional promoter region containing the NF-κB-binding motif. One hybrid assay showed that CPAP has the potential to activate gene expression when tethered to the transcriptional promoter. These data suggest that CPAP functions as a coactivator of NF-κB-mediated transcription. Since a physiological interaction between CPAP and the coactivator p300/CREB-binding protein was also observed and synergistic activation of NF-κB-mediated transcription was achieved by these proteins, CPAP-dependent transcriptional activation is likely to include p300/CREB-binding protein.