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Cdk4 activation is dependent on the subunit rearrangement in the complexes

H Takahashi1, M Menjo, Y Kaneko

  • 1Molecular Oncology Group, Nippon Roche Research Center, 200 Kajiwara, Kamakura, Kanagawa, 247, Japan.

Biochemical and Biophysical Research Communications
|January 7, 2000
PubMed

Insights

Cyclin-dependent kinase inhibitor p21 and cyclin D1 cooperate to activate Cdk4. This activation involves releasing INK4 family inhibitors, crucial for cell cycle progression during liver regeneration.

Area of Science:

  • Cell biology
  • Molecular biology
  • Biochemistry

Background:

  • Cdk4 activity regulation is complex, with limited understanding of cyclin-dependent kinase inhibitors (CKIs) roles in mid-G1 phase activation.
  • CKIs, including INK4 and Cip/Kip families, are key regulators of cell cycle progression.

Purpose of the Study:

  • To investigate the role of CKIs in Cdk4 activation during the mid-G1 phase.
  • To elucidate the mechanism by which Cdk4 is activated in response to cellular signals.

Main Methods:

  • Utilized a mouse macrophage cell line (Bac1.2F5) and mouse liver regeneration model.
  • Employed the baculovirus expression system for in vitro reconstitution of Cdk4 activation complexes.

Main Results:

  • In quiescent cells, Cdk4 primarily bound to p15 (an INK4 family CKI).
  • CSF-1 stimulation led to Cdk4 binding with cyclin D1, followed by p21 (a Cip/Kip CKI), and p15 dissociation.
  • Cdk4 activation strongly correlated with p21 binding, forming active cyclin D1/Cdk4/p21 ternary complexes.
  • Active ternary complexes were observed during mouse liver regeneration.

Conclusions:

  • p21 and cyclin D1 act cooperatively to activate Cdk4.
  • This activation mechanism involves the displacement of INK4 family CKIs.
  • The findings provide insights into cell cycle control and Cdk4 regulation.

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