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Identification of Cyclin-dependent Kinase 1 Specific Phosphorylation Sites by an In Vitro Kinase Assay
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Akt-dependent phosphorylation of p27Kip1 promotes binding to 14-3-3 and cytoplasmic localization

Naoya Fujita1, Saori Sato, Kazuhiro Katayama

  • 1Institute of Molecular and Cellular Biosciences, University of Tokyo, Tokyo 113-0032, Japan.

The Journal of Biological Chemistry
|June 4, 2002
PubMed

Insights

The Akt kinase phosphorylates p27(Kip1) at Thr198, promoting its binding to 14-3-3 proteins. This interaction leads to p27(Kip1) cytoplasmic localization, driving cell-cycle progression in human cancers.

Area of Science:

  • Molecular Biology
  • Cell Biology
  • Cancer Research

Background:

  • Low p27(Kip1) expression in human cancers correlates with poor survival.
  • Akt signaling inhibition can induce cell-cycle arrest via p27(Kip1) upregulation.
  • The precise role of Akt-dependent phosphorylation in p27(Kip1) regulation remains unclear.

Purpose of the Study:

  • To elucidate the role of Akt-dependent phosphorylation in p27(Kip1) regulation.
  • To identify specific phosphorylation sites on p27(Kip1) targeted by Akt.
  • To investigate the functional consequences of Akt-mediated p27(Kip1) phosphorylation.

Main Methods:

  • Direct binding assays between Akt and p27(Kip1).
  • Phosphorylation site mapping of p27(Kip1) by Akt.
  • Analysis of 14-3-3 protein binding to phosphorylated p27(Kip1).
  • Cellular localization studies of p27(Kip1).

Main Results:

  • Akt directly binds and phosphorylates p27(Kip1).
  • Thr198 is identified as a novel Akt phosphorylation site on p27(Kip1).
  • Akt-mediated phosphorylation of Thr198 facilitates 14-3-3 protein binding.
  • Phosphorylated p27(Kip1) at Thr198 is localized to the cytoplasm, unlike other sites.
  • Akt promotes cell-cycle progression through p27(Kip1) phosphorylation and cytoplasmic retention.

Conclusions:

  • Akt-dependent phosphorylation of p27(Kip1) at Thr198 is a key regulatory mechanism.
  • This phosphorylation event drives 14-3-3 binding and cytoplasmic localization of p27(Kip1).
  • These findings reveal a novel pathway by which Akt promotes cancer cell proliferation.

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