Regulation of FOXO1 by TAK1-Nemo-like Kinase Pathway

Abstract

The FOXO family of forkhead transcription factors has a variety of important functions in stress response, metabolism, cell cycle, apoptosis, longevity, etc. The transcriptional activity and subcellular localization of FOXO are tightly regulated by post-translational modifications, including phosphorylation by various kinases. Here, we report that the transforming growth factor-beta-activated kinase (TAK1)-Nemo-like kinase (NLK) pathway negatively regulates FOXO1. We show that NLK binds and phosphorylates FOXO1 at Pro-directed Ser/Thr residues in the transactivation domain. The phosphorylation by TAK1-NLK pathway inhibits the transcriptional activity of FOXO1 and excludes FOXO1 from the nucleus, which is independent of phosphatidylinositol 3-kinase/Akt pathway. Consistently, knockdown of TAK1-NLK pathway dephosphorylates FOXO1 and decreases phospho-Ser-329 FOXO1 level. It also induces translocation of FOXO1 into the nucleus and leads to an increase in mRNA levels of FOXO target genes and poly(ADPribose) polymerase cleavage. In addition, we show the interaction between NLK and FOXO1 is evolutionarily conserved in Drosophila. Collectively, these findings provide the first evidence that TAK1-NLK pathway is a novel regulator of FOXO1.