A PP4-Phosphatase Complex Dephosphorylates γ-H2AX Generated during DNA Replication

Dipanjan Chowdhury, Xingzhi Xu, Xueyan Zhong, Fariyal Ahmed, Jianing Zhong, Ji Liao, Derek M. Dykxhoorn, David M. Weinstock, Gerd P. Pfeifer, Judy Lieberman

Research output: Contribution to journalArticlepeer-review

169 Scopus citations


The histone H2A variant H2AX is rapidly phosphorylated in response to DNA double-stranded breaks to produce γ-H2AX. γ-H2AX stabilizes cell-cycle checkpoint proteins and DNA repair factors at the break site. We previously found that the protein phosphatase PP2A is required to resolve γ-H2AX foci and complete DNA repair after exogenous DNA damage. Here we describe a three-protein PP4 phosphatase complex in mammalian cells, containing PP4C, PP4R2, and PP4R3β, that specifically dephosphorylates ATR-mediated γ-H2AX generated during DNA replication. PP4 efficiently dephosphorylates γ-H2AX within mononucleosomes in vitro and does not directly alter ATR or checkpoint kinase activity, suggesting that PP4 acts directly on γ-H2AX in cells. When the PP4 complex is silenced, repair of DNA replication-mediated breaks is inefficient, and cells are hypersensitive to DNA replication inhibitors, but not radiomimetic drugs. Therefore, γ-H2AX elimination at DNA damage foci is required for DNA damage repair, but accomplishing this task involves distinct phosphatases with potentially overlapping roles.

Original languageEnglish (US)
Pages (from-to)33-46
Number of pages14
JournalMolecular Cell
Issue number1
StatePublished - Jul 11 2008
Externally publishedYes


  • DNA

ASJC Scopus subject areas

  • Molecular Biology


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