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Human SMAD4 is phosphorylated at Thr9 and Ser138 by interacting with NLK

Yan Shi1, Kan Ye, Huiling Wu

  • 1State Key Laboratory of Genetic Engineering, Institute of Genetics, School of Life Sciences, Fudan University, 220 Handan Rd, 200433, Shanghai, People's Republic of China.

Molecular and Cellular Biochemistry
|August 20, 2009
PubMed

Insights

Nemo-like kinase (NLK) interacts with Smad4, a tumor suppressor. NLK phosphorylates Smad4 at specific sites, suggesting a novel regulatory role in transforming growth factor-beta (TGF-beta) signaling.

Area of Science:

  • Molecular Biology
  • Cell Signaling
  • Oncology

Background:

  • Smads are key intracellular mediators of transforming growth factor-beta (TGF-beta) signaling pathways.
  • Smad4, a tumor suppressor gene, is constitutively phosphorylated, but its kinase remains unidentified.
  • Nuclear translocation of receptor-activated Smads, complexed with Smad4, regulates gene transcription.

Purpose of the Study:

  • To identify the kinase responsible for Smad4 phosphorylation.
  • To investigate the interaction between Smad4 and Nemo-like kinase (NLK).
  • To elucidate the functional consequences of NLK-mediated Smad4 phosphorylation.

Main Methods:

  • Yeast two-hybrid system to identify interacting proteins.
  • In vitro and in vivo confirmation of Smad4-NLK interaction.
  • In vitro kinase assays to determine phosphorylation sites.

Main Results:

  • Smad4 was identified to interact with Nemo-like kinase (NLK).
  • The linker sequence of Smad4 was found sufficient for NLK interaction.
  • NLK phosphorylates Smad4 at Threonine 9 (Thr9) and Serine 138 (Ser138) within the N-terminal MH1 domain.

Conclusions:

  • Nemo-like kinase (NLK) directly interacts with and phosphorylates Smad4.
  • NLK may play a novel role in regulating Smad4 function through phosphorylation.
  • This finding offers new insights into the molecular mechanisms of TGF-beta signaling and cancer.

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