NEDD4–1‐mediated ubiquitination regulates pAKT nuclear trafficking in IGF‐1 response

Abstract

AKT is a downstream effector kinase of the PI3K pathway involved in regulation of cell growth, death, differentiation and migration. Regulation of the activated phospho‐AKT (pAKT) translocation to its action sites remains unclear. The objective of this study was to investigate whether AKT is directly regulated by NEDD4–1 E3 ligase through ubiquitination in IGF‐1 response. We found that NEDD4–1 promotes HECT domain‐dependent ubiquitination of exogenous and endogenous AKT in in vivo ubiquitination assays. Co‐imunocpreciptation results indicated that NEDD4–1 physically interacts with AKT. Plasma membrane binding is the key step for AKT ubiquitination by NEDD4–1 in vivo. Ubiquitinated pAKT translocates to perinuclear regions, where it is either released into the cytoplasm, imported into the nucleus or coupled with proteasomal degradation. IGF‐1 signaling stimulates NEDD4–1‐mediated ubiquitination of pAKT but not total AKT. NEDD4–1 catalyzes K63‐type polyubiquitin chain formation on AKT in an in vitro ubiquitination assay. A cancer‐derived plasma membrane‐philic mutant AKT(E17K) is more effectively ubiquitinated by NEDD4–1 and more efficiently trafficked into the nucleus compared with AKT. This study established that AKT is a substrate of NEDD4–1 and NEDD4–1‐mediated ubiquitination plays a role in nuclear trafficking of pAKT that contributes to AKT activation process in IGF‐1 response.