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Cyclin D-CDK subunit arrangement is dependent on the availability of competing INK4 and p21 class inhibitors

D Parry1, D Mahony, K Wills

  • 1DNAX Research Institute of Molecular and Cellular Biology, Palo Alto, California 94304, USA.

Molecular and Cellular Biology
|February 18, 1999
PubMed

Insights

Cyclin D-CDK complexes control cell cycle progression. INK4 proteins inhibit these complexes, but p21 and p27 family members promote their formation by counteracting INK4 effects.

Area of Science:

  • Cell Biology
  • Molecular Biology
  • Biochemistry

Background:

  • D-type cyclins and their partners CDK4/CDK6 regulate cell cycle G0-G1-S transition.
  • This process involves retinoblastoma protein (pRB) phosphorylation and inactivation.
  • INK4 proteins negatively regulate cyclin D-CDK complex assembly.

Purpose of the Study:

  • To investigate the specific interactions between INK4 proteins, p21/p27 family members, and CDK4/CDK6.
  • To elucidate the mechanisms by which INK4 and p21/p27 proteins modulate cyclin D-CDK complex formation and stability.

Main Methods:

  • In vitro association assays to study protein complex formation.
  • Analysis of protein complex stability in proliferating cells.
  • Overexpression studies in 293 cells to assess ternary complex formation.

Main Results:

  • All four INK4 proteins bind CDK4/CDK6 in vitro.
  • Only p16(INK4a) forms stable binary complexes with CDK4/CDK6 in proliferating cells.
  • p21(CIP1) and p27(KIP1) stably associate with CDK4 in cyclin-containing complexes, suggesting an equilibrium.
  • p21(CIP1) overexpression promotes ternary cyclin D-CDK4-p21(CIP1) complex formation.

Conclusions:

  • INK4 proteins differentially associate with CDK4 and CDK6.
  • CDK4 exists in equilibrium between INK4-bound and p21/p27-bound states.
  • p21 family members promote D-type cyclin-CDK associations by counteracting INK4 proteins.

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