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Cyclin E-CDK2 is a regulator of p27Kip1
R J Sheaff1, M Groudine, M Gordon
1Division of Basic Sciences, Fred Hutchinson Cancer Research Center (FHCRC), Seattle, Washington 98104, USA.
Genes & Development
|June 1, 1997
Summary
Cyclin-CDK complexes promote cell cycle progression by phosphorylating and degrading CDK inhibitors like p27Kip1. This phosphorylation event, dependent on ATP levels, allows cells to move from G1 to S phase.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- Cyclin-dependent kinase (CDK) inhibitors are known to halt cell proliferation.
- The role of cyclin-CDK complexes in regulating CDK inhibitors remains less understood.
Purpose of the Study:
- To investigate the potential for cyclin-CDK complexes to promote cell cycle progression by down-regulating CDK inhibitors.
- To elucidate the mechanism by which cyclin E-CDK2 regulates the CDK inhibitor p27Kip1.
Main Methods:
- Phosphorylation assays using murine fibroblasts and in vitro kinase reactions.
- Site-directed mutagenesis of p27Kip1.
- Kinetic analysis of p27Kip1 and cyclin E-CDK2 interactions.
- ATP concentration dependency studies.
Main Results:
- Cyclin E-CDK2 directly phosphorylates p27Kip1 at threonine 187 (T187).
- Phosphorylation of p27Kip1 by cyclin E-CDK2 leads to its degradation and cell cycle progression from G1 to S phase.
- Mutation of T187 renders p27Kip1 resistant to cyclin E-mediated regulation and causes a G1 block.
- Kinetic analysis reveals two distinct interaction modes between p27Kip1 and cyclin E-CDK2, dependent on ATP concentration.
Conclusions:
- p27Kip1 is a direct substrate of cyclin E-CDK2, and its phosphorylation has significant physiological consequences for cell cycle control.
- ATP concentration dictates whether p27Kip1 acts as an inhibitor or a substrate of cyclin E-CDK2.
- This study provides a kinetic model explaining how p27Kip1 can function as both an inhibitor and a substrate for the same kinase complex.