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Functional interaction between a novel protein phosphatase 2A regulatory subunit, PR59, and the
P M Voorhoeve1, E M Hijmans, R Bernards
1Division of Molecular Carcinogenesis, The Netherlands Cancer Institute, Amsterdam.
Abstract:
The proteins of the retinoblastoma family are potent inhibitors of cell cycle progression. It is well documented that their growth-inhibitory activity can be abolished by phosphorylation on serine and threonine residues by cyclin dependent kinases. In contrast, very little is known about the dephosphorylation of retinoblastoma-family proteins. We report here the isolation, by virtue of its ability to associate with p107, of a novel Protein Phosphatase 2A (PP2A) regulatory subunit, named PR59. PR59 shares sequence homology with a known regulatory subunit of PP2A, PR72, but differs from PR72 in its expression pattern and its functional properties. We show that PR59 co-immunoprecipitates with the PP2A catalytic subunit, indicating that PR59 is a genuine component of PP2A holo-enzymes. In vivo, PR59 associates specifically with p107, but not with pRb. Elevated expression of PR59 results in dephosphorylation of p107, but not of pRb, and inhibits cell proliferation by causing cells to accumulate in G1. These data support a model in which the distinct PP2A regulatory subunits act to target the PP2A catalytic subunit to specific substrates and suggest a role for PP2A in regulation of p107.
Insights
Researchers discovered a new Protein Phosphatase 2A (PP2A) subunit, PR59, which dephosphorylates p107. This dephosphorylation inhibits cell proliferation, highlighting PP2A
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- Retinoblastoma family proteins are key cell cycle inhibitors.
- Phosphorylation by cyclin-dependent kinases inactivates these proteins.
- Mechanisms of retinoblastoma protein dephosphorylation remain largely unknown.
Purpose of the Study:
- To investigate the dephosphorylation of retinoblastoma-family proteins.
- To identify novel regulatory subunits of Protein Phosphatase 2A (PP2A) involved in this process.
Main Methods:
- Isolation of a novel PP2A regulatory subunit (PR59) by its association with p107.
- Co-immunoprecipitation assays to confirm PR59's association with the PP2A catalytic subunit.
- In vivo studies to assess PR59's interaction with p107 and pRb.
- Analysis of p107 and pRb phosphorylation status upon PR59 expression.
- Cell proliferation assays to evaluate the impact of PR59 on cell cycle progression.
Main Results:
- A novel PP2A regulatory subunit, PR59, was identified.
- PR59 specifically associates with p107 and dephosphorylates it.
- PR59 expression leads to G1 cell cycle arrest, inhibiting proliferation.
- PR59 differs functionally and in expression from the known PP2A subunit PR72.
Conclusions:
- PR59 is a functional component of PP2A holo-enzymes.
- Distinct PP2A regulatory subunits, like PR59, target the catalytic subunit to specific substrates.
- PP2A, through PR59, plays a significant role in regulating p107 activity and cell proliferation.