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An overlapping kinase and phosphatase docking site regulates activity of the retinoblastoma protein

Alexander Hirschi1, Matthew Cecchini, Rachel C Steinhardt

  • 1Department of Molecular, Cell, and Developmental Biology, University of California, Santa Cruz, California, USA.

Nature Structural & Molecular Biology
|August 10, 2010
PubMed

Insights

Protein phosphatase 1 (PP1) binds the retinoblastoma tumor suppressor protein (Rb) at a site that also binds cyclin-dependent kinase (Cdk). PP1 binding to Rb regulates Rb activity and cell cycle progression.

Area of Science:

  • Molecular biology
  • Cell biology
  • Biochemistry

Background:

  • The retinoblastoma tumor suppressor protein (Rb) controls cell cycle progression.
  • Rb activity is regulated by phosphorylation, which is modulated by kinases and phosphatases.

Purpose of the Study:

  • To characterize the molecular interaction between Rb and protein phosphatase 1 catalytic subunit (PP1c).
  • To elucidate the mechanism by which PP1c regulates Rb activity.

Main Methods:

  • X-ray crystallography to determine the structure of Rb bound to PP1c.
  • Biochemical assays to assess PP1c activity on Rb.
  • Cell-based assays to evaluate the effect of PP1c binding on Rb activity and cell cycle progression.

Main Results:

  • A crystal structure revealed an enzyme docking site in the Rb C-terminal domain essential for PP1c activity.
  • This PP1c docking site overlaps with the cyclin-dependent kinase (Cdk) docking site.
  • Competition between PP1 and Cdk-cyclins for Rb binding maintains Rb activity and inhibits cell-cycle advancement.

Conclusions:

  • Detailed molecular insights into Rb activation by PP1c.
  • A novel regulatory mechanism for Rb involving competition between kinase and phosphatase docking sites.
  • Establishes a new paradigm for understanding cell cycle control by Rb.

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