Nucleolin is involved in Interferon Regulatory Factor‐2 dependent transcriptional activation

We have previously shown that Interferon regulatory factor‐2 (IRF‐2) is acetylated in a cell growth‐dependent manner, which enables it to contribute to the transcription of cell growth‐regulated promoters. To clarify the function of the acetylation of IRF‐2, we investigated the proteins that associate with acetylated IRF‐2. Transfection of p300/CBP‐associated factor (PCAF) enhanced acetylation of IRF‐2 in 293T cells. In cells transfected with both IRF‐2 and PCAF, IRF‐2 associated with endogenous nucleolin, in contrast, little association was observed when IRF‐2 was transfected with a PCAF HAT deletion mutant. In a pull‐down experiment using stable transfectants, acetylation defective mutant IRF‐2 (IRF‐2K75R) recruited nucleolin to much lower degree than that of wild type IRF‐2, suggesting that nucleolin preferentially associates with acetylated IRF‐2. Confocal analysis indicated that IRF‐2 colocalized with nucleolin in the perinucleolar region. Nucleolin in the presence of PCAF enhanced IRF‐2‐dependent H4 promoter activity in NIH3T3 cells. Affinity DNA binding analysis with H4 promoter DNA indicated that nucleolin associated with IRF‐2 in growing NIH3T3 cells, but not in growth‐arrested counterparts. We conclude that nucleolin is recruited to acetylated IRF‐2, contributing to gene regulation crucial for the control of cell growth.