Identification of nuclear localization signal in IRF2BP2

Interferon regulatory factor 2 binding protein 2 (IRF2BP2) is an ischemia‐inducible and muscle‐enriched transcription factor required to activate vascular endothelial growth factor‐A (VEGF‐A) expression in muscles. Endogenous IRF2BP2 is found in the nuclei of cardiac and skeletal muscle cells under normoxic condition, but is largely cytoplasmic in ischemic tissues. The mechanism that controls nucleocytoplasmic localization of IRF2BP2 is not yet known. Here, we mapped the nuclear localization signal (NLS) to an evolutionarily conserved 354ARKRKSP361 sequence in IRF2BP2. Whereas the arginine and lysine were necessary for nuclear localization, they were not sufficient. Nuclear targeting required the phosphorylation of serine 360 (S360). Alanine substitution at this site abolished IRF2BP2 nuclear entry. Thus, loss of protein kinase activity in ischemic tissues likely accounts for cytoplasmic accumulation of IRF2BP2 and impaired revascularization.