Casein Kinase II Phosphorylation Regulates αNAC Subcellular Localization and Transcriptional Coactivating Activity

摘要

The subcellular localization of the αNAC coactivator is regulated, but the signaling pathways controlling its nucleocytoplasmic shuttling and coactivation function are not completely characterized. We report here that casein kinase II (CK2) phosphorylated αNAC on several phosphoacceptor sites, especially in an amino-terminal cluster. Deletion or mutation of the clustered CK2 sites induced nuclear accumulation of αNAC in cells. αNAC also localized to the nucleus when endogenous CK2 activity was inhibited by quercetin or 5,6-dichloro-1-β-d-ribofuranosylbenzimidazole (DRB). These observations suggested that phosphorylation by CK2 might play a signaling role in the nuclear export of αNAC. Interestingly, inhibition of the chromosome region maintenance 1 (CRM1) exportin by leptomycin B (LMB) led to accumulation of αNAC in the nucleus. We conclude that CK2 phosphorylation of the N-terminal cluster corresponds to the signal for αNAC’s nuclear export via a CRM1-dependent pathway. Finally, the nuclear accumulation of the protein resulting from the lack of CK2 phosphorylation mediated a slight but significant increase of the αNAC coactivating function on AP-1 transcriptional activity. Thus, αNAC’s exit from the nucleus and capacity to potentiate transcription appear dependent on its phosphorylation status.