Activation of cyclin D1-kinase in murine fibroblasts lacking both p21(Cip1) and p27(Kip1)

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Analysis of Cell Cycle Position in Mammalian Cells
12:19

Analysis of Cell Cycle Position in Mammalian Cells

Published on: January 21, 2012

Masataka Sugimoto1, Nicholas Martin, Deepti P Wilks

  • 1Cancer Research UK, Paterson Institute for Cancer Research, Christie Hospital NHS Trust, Manchester M20 4BX, UK.

Oncogene
|November 22, 2002
PubMed

Insights

p21(Cip1) and p27(Kip1) are not essential activators for cyclin D-CDK4/6 kinase assembly. Instead, multiple mechanisms regulate this process, particularly during cell cycle re-entry from quiescence.

Area of Science:

  • Molecular Biology
  • Cell Biology
  • Biochemistry

Background:

  • Cyclin-dependent kinases (CDKs) like CDK4 and CDK6 are crucial for cell cycle control and are frequently deregulated in cancers.
  • Activation of CDK4/6 requires assembly with D-type cyclins.
  • CDK inhibitors p21(Cip1) and p27(Kip1) were previously thought to be essential for cyclin D-CDK4/6 activation.

Purpose of the Study:

  • To investigate the role of p21(Cip1) and p27(Kip1) in the assembly and activation of the cyclin D1-CDK4 complex.
  • To identify alternative mechanisms regulating cyclin D1-CDK4 kinase activity.
  • To understand the regulation of cell cycle re-entry in the absence of p21(Cip1) and p27(Kip1).

Main Methods:

  • Utilized mouse embryo fibroblasts (MEFs) lacking both p21(Cip1) and p27(Kip1) (p21/p27-null MEFs).
  • Stimulated quiescent p21/p27-null MEFs to re-enter the cell cycle.
  • Assessed cyclin D1-CDK4 complex assembly and kinase activity.
  • Investigated the effects of p16(INK4a) overexpression and p34(SEI-1) ectopic expression.

Main Results:

  • Cyclin D1-CDK4 complex assembly and activation occur in quiescent p21/p27-null MEFs upon mitogen stimulation.
  • Mitogen-induced kinase activity is inhibited by p16(INK4a) overexpression, blocking S phase entry.
  • Ectopic expression of p34(SEI-1) enhances active cyclin D1-CDK4 complex levels in asynchronously proliferating cells.

Conclusions:

  • p21(Cip1) and p27(Kip1) are not essential activators for cyclin D1-CDK4 kinase assembly.
  • Multiple independent mechanisms can stimulate cyclin D1-CDK4 kinase assembly.
  • Additional regulatory mechanisms beyond p21/p27 function are critical for G0 to S phase transition.

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