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The cell-cycle regulatory protein Cks1 is required for SCF(Skp2)-mediated ubiquitinylation of p27

D Ganoth1, G Bornstein, T K Ko

  • 1Unit of Biochemistry, B. Rappaport Faculty of Medicine, Technion-Israel Institute of Technology, Haifa, 31096, Israel.

Nature Cell Biology
|March 7, 2001
PubMed

Insights

The cyclin-dependent kinase (CDK) inhibitor p27 requires CDK subunit 1 (Cks1) for ubiquitination and degradation, a crucial step for cell cycle progression. Cks1 acts as a missing factor, enabling the SCFSkp2 complex to bind and ubiquitinate phosphorylated p27.

Area of Science:

  • Cell Biology
  • Molecular Biology
  • Biochemistry

Background:

  • The cyclin-dependent kinase (CDK) inhibitor p27 regulates cell cycle progression from G1 to S phase.
  • p27 degradation via the ubiquitin pathway is essential for driving cells into S phase.
  • Ubiquitinylation of p27 requires phosphorylation at Thr 187 and recognition by S-phase kinase associated protein 2 (Skp2).

Purpose of the Study:

  • To identify the missing factor required for the in vitro ubiquitination of p27 by the SCFSkp2 complex.
  • To elucidate the role of CDK subunit 1 (Cks1) in the SCFSkp2-mediated degradation of p27.

Main Methods:

  • Purified protein system reconstitution assays.
  • In vitro ubiquitination assays.
  • Protein binding assays.

Main Results:

  • CDK subunit 1 (Cks1) was identified as the missing component necessary for p27 ubiquitination.
  • Human Cks1 reconstituted the ubiquitination of p27 in a purified system.
  • Cks1 binds to Skp2 and enhances the binding of phosphorylated p27 to Skp2.

Conclusions:

  • Cks1 is essential for the activity of the SCFSkp2 ubiquitin ligase complex.
  • This study provides the first evidence of an accessory protein requirement for SCF complex activity and substrate binding.
  • Cks1 plays a critical role in regulating p27 degradation and cell cycle progression.

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