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Mitotic regulation of CDK4 by the serine/threonine phosphatase, calcineurin

Renfred Chow1, Jamie Olesen, Christina Onyskiw

  • 1Department of Pediatrics, University of Alberta, Room B066, Dentistry/Pharmacy Centre, Edmonton, Alta, Canada T6G 2N8.

Biochemical and Biophysical Research Communications
|September 26, 2007
PubMed

Insights

Calcineurin dephosphorylates CDK4 at T-172, reducing its activity during mitosis. This interaction, localized to CDK4

Area of Science:

  • Cell Biology
  • Molecular Biology
  • Biochemistry

Background:

  • Cyclin-dependent kinase 4 (CDK4) is a crucial regulator of the cell cycle.
  • CDK4 activity is tightly controlled by post-translational modifications, including phosphorylation.
  • Calcineurin, a calcium-dependent phosphatase, has been implicated in regulating protein phosphorylation.

Purpose of the Study:

  • To investigate the role of calcineurin in regulating CDK4 phosphorylation at threonine 172 (T-172).
  • To elucidate the mechanism by which calcineurin modulates CDK4 activity.
  • To determine the cell cycle-dependent regulation of CDK4 by calcineurin.

Main Methods:

  • Co-immunoprecipitation assays to assess calcineurin-CDK4 association.
  • Inhibition of calcineurin phosphatase activity.
  • Analysis of CDK4 phosphorylation and activity levels during the cell cycle.
  • Site-directed mutagenesis to map the calcineurin interaction site on CDK4.

Main Results:

  • Calcineurin associates with the cytoplasmic form of CDK4 in the absence of cyclin D.
  • Inhibition of calcineurin increases CDK4 phosphorylation and activity in mitotic cells.
  • Calcineurin-CDK4 interaction peaks during mitosis, correlating with reduced CDK4 phosphorylation.
  • The calcineurin binding site on CDK4 is within the N-terminal residues crucial for cyclin D and p16INK4a binding.

Conclusions:

  • Calcineurin negatively regulates CDK4 kinase activity in a cell cycle-dependent manner.
  • Calcineurin's interaction with CDK4 during mitosis suggests a role in cell cycle control.
  • Calcineurin may be a key component in the negative feedback loop regulating CDK4 activity.

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