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TTK/Mps1 controls nuclear targeting of c-Abl by 14-3-3-coupled phosphorylation in response to oxidative stress

K Nihira1, N Taira, Y Miki

  • 1Department of Molecular Genetics, Medical Research Institute, Tokyo Medical and Dental University, Tokyo, Japan.

Oncogene
|September 17, 2008
PubMed

Insights

The TTK kinase phosphorylates c-Abl at Thr735, regulating its nuclear import. This phosphorylation is crucial for preventing c-Abl nuclear accumulation under oxidative stress and mitigating apoptosis.

Area of Science:

  • Cellular signaling
  • Molecular biology
  • Cancer research

Background:

  • Genotoxic stress triggers c-Abl tyrosine kinase nuclear translocation.
  • Phosphorylation of c-Abl at Thr735 is essential for its cytoplasmic sequestration by 14-3-3 proteins.
  • The kinases responsible for c-Abl Thr735 phosphorylation were previously unidentified.

Purpose of the Study:

  • To identify kinases that phosphorylate c-Abl at Thr735.
  • To elucidate the role of Thr735 phosphorylation in c-Abl regulation and cellular response to stress.
  • To investigate the physiological kinase responsible for c-Abl Thr735 phosphorylation.

Main Methods:

  • Expression cloning using a phosphospecific antibody to identify novel kinases.
  • In vitro kinase assays and cell-based expression studies.
  • RNA interference (siRNA) to knockdown candidate kinases and assess phosphorylation and localization of c-Abl.

Main Results:

  • CLK1, CLK4, MST1, MST2, and TTK were identified as in vitro Thr735 kinases for c-Abl.
  • Oxidative stress transiently upregulates Thr735 phosphorylation.
  • Knockdown of TTK, but not CLK1, CLK4, MST1, or MST2, attenuated Thr735 phosphorylation, identifying TTK as the physiological kinase.
  • TTK knockdown led to nuclear accumulation of c-Abl even under unstressed conditions and enhanced oxidative stress-induced apoptosis.

Conclusions:

  • TTK directly phosphorylates c-Abl at Thr735.
  • This TTK-mediated phosphorylation is critical for maintaining c-Abl in the cytoplasm.
  • Dysregulation of TTK-dependent c-Abl phosphorylation contributes to nuclear entrapment and increased apoptosis under stress.

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