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Cdc2-cyclin E complexes regulate the G1/S phase transition

Eiman Aleem1, Hiroaki Kiyokawa, Philipp Kaldis

  • 1Mouse Cancer Genetics Program, National Cancer Institute, NCI-Frederick, Bldg 560/22-56, 1050 Boyles Street, Frederick, MD 21702-1201, USA.

Nature Cell Biology
|July 12, 2005
PubMed

Insights

The cyclin-dependent kinase inhibitor p27 (Kip1) normally suppresses tumors. However, in mice lacking both p27 and Cdk2, Cdc2 activity compensates, indicating parallel pathways in cell cycle regulation.

Area of Science:

  • Molecular Biology
  • Cell Biology
  • Cancer Research

Background:

  • The cyclin-dependent kinase inhibitor p27 (Kip1) is a known tumor suppressor and negative regulator of cell-cycle progression.
  • Cyclin-dependent kinase 2 (Cdk2) is a primary target of p27.
  • The genetic deletion of p27 in mice leads to specific phenotypes, and its interaction with Cdk2 is crucial for understanding cell cycle control.

Purpose of the Study:

  • To investigate the phenotypic consequences of combined p27 and Cdk2 deficiency in mice.
  • To determine if the loss of Cdk2 activity modifies the p27 knockout mouse phenotype.
  • To explore potential compensatory mechanisms in cell cycle regulation when Cdk2 function is lost.

Main Methods:

  • Generation and analysis of p27(-/-) Cdk2(-/-) double-knockout mice.
  • Tumorigenesis assessment in ovaries and pituitary glands.
  • Analysis of S phase and mitosis levels in mouse tissues.
  • Biochemical assays to measure Cdc2 activity and protein complex formation.

Main Results:

  • p27(-/-) Cdk2(-/-) mice developed ovary and pituitary tumors, but no functional complementation was observed, suggesting parallel pathways.
  • Elevated S phase and mitosis were detected in tissues of double-knockout mice.
  • Cdc2 activity was elevated in double-knockout mouse extracts, and p27 was found to bind to Cdc2 and cyclin complexes.
  • Cyclin E was observed to bind and activate Cdc2, suggesting a compensatory role.

Conclusions:

  • The loss of Cdk2 function is not fully compensated by p27 deficiency alone, indicating parallel regulatory pathways.
  • Cdc2 activity can compensate for the loss of Cdk2 function in vivo.
  • These findings highlight the complex interplay of cell cycle regulators and suggest Cdc2 as a potential therapeutic target in cancers associated with p27 dysfunction.

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