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Updated: Aug 15, 2026

Identifying the Effects of BRCA1 Mutations on Homologous Recombination using Cells that Express Endogenous Wild-type BRCA1
08:53

Identifying the Effects of BRCA1 Mutations on Homologous Recombination using Cells that Express Endogenous Wild-type BRCA1

Published on: February 18, 2011

Regulation of BRCA1 phosphorylation by interaction with protein phosphatase 1alpha

Ying Liu1, David M Virshup, Raymond L White

  • 1Department of Oncological Sciences, University of Utah, Salt Lake City, Utah 84112, USA.

Cancer Research
|November 20, 2002
PubMed

Insights

Protein phosphatase 1 alpha (PP1alpha) dephosphorylates the tumor suppressor BRCA1, a key player in DNA damage repair. This interaction suggests BRCA1 regulates PP1alpha activity, impacting cell cycle progression.

Area of Science:

  • Molecular Biology
  • Cell Biology
  • Biochemistry

Background:

  • The tumor suppressor BRCA1 is crucial for DNA damage repair and undergoes phosphorylation during the cell cycle and after DNA damage.
  • While kinases like CDK2, ATM, and ATR are known to phosphorylate BRCA1, the phosphatases responsible for its dephosphorylation remained unidentified.
  • hCds1, downstream of ATM, also phosphorylates a specific BRCA1 fragment (BF4).

Purpose of the Study:

  • To identify protein phosphatases that dephosphorylate BRCA1.
  • To investigate the functional relationship between BRCA1 and its dephosphorylating enzyme.

Main Methods:

  • Used a phosphorylated BRCA1 fragment (GST-BF4-P) as a substrate to screen for phosphatases.
  • Employed recombinant and endogenous protein phosphatase 1 alpha (PP1alpha) and inhibitor 2.
  • Utilized overexpression studies, co-immunoprecipitation, and glutathione S-transferase pull-down assays.

Main Results:

  • Both recombinant and endogenous PP1alpha dephosphorylated the GST-BF4-P substrate, an activity inhibited by Inhibitor 2.
  • PP1alpha overexpression reduced BRCA1 hyperphosphorylation in vivo following ionizing radiation.
  • BRCA1 and PP1alpha were found to co-immunoprecipitate, with PP1alpha directly associating with the BF4 region of BRCA1.
  • BRCA1 was identified as an inhibitor of PP1alpha activity.

Conclusions:

  • Protein phosphatase 1 alpha (PP1alpha) dephosphorylates BRCA1 both in vitro and in vivo.
  • BRCA1 functions as both a substrate and a regulator of PP1alpha.
  • The interaction between BRCA1 and PP1alpha is likely significant for DNA damage repair and cell cycle progression.

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