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Differential modification of p27Kip1 controls its cyclin D-cdk4 inhibitory activity

Melissa K James1, Arpita Ray, Dina Leznova

  • 1Department of Pediatrics, SUNY Downstate Medical Center, 450 Clarkson Ave., Box 49, Brooklyn, NY 11203, USA. stacy.blain@downstate.edu

Molecular and Cellular Biology
|October 3, 2007
PubMed

Insights

The cell cycle regulator p27 can switch between inhibiting and not inhibiting cyclin D-cdk4/6. Growth-state-dependent tyrosine phosphorylation of p27 controls its inhibitory activity.

Area of Science:

  • Cell Biology
  • Molecular Biology
  • Biochemistry

Background:

  • The role of p27 as a cyclin-dependent kinase (CDK) inhibitor is debated.
  • The mechanisms governing p27's switch between inhibitory and non-inhibitory states are unclear.

Purpose of the Study:

  • To investigate the two-state mechanism of p27's inhibition of cyclin D-CDK4/6.
  • To elucidate how p27's inhibitory activity is modulated by growth state.

Main Methods:

  • Analysis of p27 from proliferating and arrested cells.
  • Site-directed mutagenesis of tyrosine residues Y88 and Y89 in p27.
  • In vitro phosphorylation assays using tyrosine kinase Abl.

Main Results:

  • p27 bound to cyclin D-CDK4 exhibits both inhibitory and non-inhibitory functions.
  • Tyrosine phosphorylation of p27 at Y88 and Y89, preferentially in proliferating cells, renders it non-inhibitory.
  • Mutating Y88 and Y89 locks p27 in an inhibitory state.
  • Abl tyrosine kinase directly phosphorylates Y88, converting p27 to a non-inhibitor.

Conclusions:

  • p27's inhibitory activity is dynamically regulated by growth-state-dependent tyrosine phosphorylation.
  • Phosphorylation at Y88 and Y89 is a key mechanism controlling p27's function as a cyclin D-CDK4/6 inhibitor.

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