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Regulation of FOXO1 by TAK1-Nemo-like kinase pathway

Sunhong Kim1, Yongsung Kim, Jiwoon Lee

  • 1Center for Molecular Cancer Research, Korea Research Institute of Bioscience and Biotechnology, Chungbuk 363-883, Korea.

The Journal of Biological Chemistry
|January 12, 2010
PubMed

Insights

The TAK1-NLK pathway negatively regulates FOXO1 by phosphorylating it, inhibiting its transcriptional activity and nuclear localization. This discovery reveals a novel regulatory mechanism for FOXO1 function.

Area of Science:

  • Molecular Biology
  • Cell Signaling
  • Genetics

Background:

  • FOXO transcription factors regulate critical cellular processes like stress response, metabolism, and apoptosis.
  • Post-translational modifications, particularly phosphorylation, are key regulators of FOXO activity and localization.
  • The phosphatidylinositol 3-kinase/Akt pathway is a known regulator of FOXO, but other pathways remain less understood.

Purpose of the Study:

  • To investigate the role of the transforming growth factor-beta-activated kinase (TAK1)-Nemo-like kinase (NLK) pathway in regulating FOXO1.
  • To elucidate the mechanism by which TAK1-NLK influences FOXO1 transcriptional activity and subcellular localization.

Main Methods:

  • Co-immunoprecipitation to assess protein-protein interactions between NLK and FOXO1.
  • In vitro kinase assays and site-directed mutagenesis to identify phosphorylation sites on FOXO1.
  • Western blotting to detect phosphorylation levels and subcellular localization of FOXO1.
  • Quantitative PCR to measure mRNA levels of FOXO1 target genes.
  • RNA interference (siRNA) to knockdown TAK1 and NLK expression.
  • Orthologous interaction studies in Drosophila.

Main Results:

  • The TAK1-NLK pathway directly binds and phosphorylates FOXO1 at specific Pro-directed Ser/Thr residues within the transactivation domain.
  • Phosphorylation by TAK1-NLK inhibits FOXO1 transcriptional activity and promotes its exclusion from the nucleus, independently of the PI3K/Akt pathway.
  • Knockdown of TAK1-NLK leads to FOXO1 dephosphorylation, increased nuclear localization, enhanced expression of FOXO1 target genes, and increased poly(ADP-ribose) polymerase cleavage.
  • The interaction between NLK and FOXO1 is evolutionarily conserved, as demonstrated in Drosophila.

Conclusions:

  • The TAK1-NLK pathway represents a novel negative regulator of FOXO1.
  • This pathway modulates FOXO1 activity through direct phosphorylation, impacting its transcriptional function and subcellular distribution.
  • These findings expand our understanding of FOXO1 regulation beyond the canonical PI3K/Akt pathway and have implications for cellular stress response and other FOXO-mediated processes.

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