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Identification of Cyclin-dependent Kinase 1 Specific Phosphorylation Sites by an In Vitro Kinase Assay
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Differential association of p21Cip1 and p27Kip1 with cyclin E-CDK2 during rat liver regeneration

M J Pujol1, M Jaime, J Serratosa

  • 1Department of Cell Biology, Faculty of Medicine, Institut d'Investigacions Biomèdiques August Pi Sunyer (IDIBAPS), University of Barcelona, Spain.

Journal of Hepatology
|August 22, 2000
PubMed
Abstract

Insights

p27Kip1 inhibits CDK2 activity early in liver regeneration, while both p21Cip1 and p27Kip1 later down-regulate cyclin A-CDK2 activity. This study clarifies the roles of these cell cycle inhibitors in regulating CDK2 during liver regeneration.

Area of Science:

  • Cell Biology
  • Molecular Biology
  • Hepatology

Background:

  • Cell cycle inhibitors p21Cip1 and p27Kip1 are known regulators of cyclin-dependent kinases (CDKs).
  • Their specific roles in modulating CDK2 activity during liver regeneration are not fully understood.

Purpose of the Study:

  • To investigate the association of p21Cip1 and p27Kip1 with cyclin E-CDK2 and cyclin A-CDK2 complexes.
  • To correlate inhibitor binding with CDK2 activity during rat liver regeneration.

Main Methods:

  • Immunoprecipitation of rat liver homogenates post-partial hepatectomy (PH).
  • Analysis of p21Cip1 and p27Kip1 association with cyclin E/A-CDK2 complexes.
  • Western blotting and kinase assays to determine complex activity.

Main Results:

  • High p27Kip1 bound to cyclin E-CDK2 early (0-13h) correlating with low CDK2 activity.
  • Maximal CDK2 activity at 24h showed decreased p27Kip1 binding and increased p21Cip1 binding.
  • Cyclin A-CDK2 complexes appeared at 24h with low inhibitor levels, increasing by 28h.

Conclusions:

  • p27Kip1 functions as an early inhibitor of cyclin E-CDK2 activity post-PH.
  • Both p21Cip1 and p27Kip1 down-regulate cyclin A-CDK2 activity after its peak activation at 28h post-PH.

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