Identification of Protein Phosphatase 4 Inhibitory Protein That Plays an Indispensable Role in DNA Damage Response
Jaehong Park1, Jihye Lee1, and Dong-Hyun Lee1,2,*
1Department of Biological Sciences, College of Natural Sciences and 2Research Center of Ecomimetics, Chonnam National University, Gwangju 61186, Korea
Received January 27, 2019; Revised June 11, 2019; Accepted June 19, 2019.; Published online July 5, 2019.
© Korean Society for Molecular and Cellular Biology. All rights reserved.

Protein phosphatase 4 (PP4) is a crucial protein complex that plays an important role in DNA damage response (DDR), including DNA repair, cell cycle arrest and apoptosis. Despite the significance of PP4, the mechanism by which PP4 is regulated remains to be elucidated. Here, we identified a novel PP4 inhibitor, protein phosphatase 4 inhibitory protein (PP4IP) and elucidated its cellular functions. PP4IP-knockout cells were generated using the CRISPR/Cas9 system, and the phosphorylation status of PP4 substrates (H2AX, KAP1, and RPA2) was analyzed. Then we investigated that how PP4IP affects the cellular functions of PP4 by immunoprecipitation, immunofluorescence, and DNA double-strand break (DSB) repair assays. PP4IP interacts with PP4 complex, which is affected by DNA damage and cell cycle progression and decreases the dephosphorylational activity of PP4. Both overexpression and depletion of PP4IP impairs DSB repairs and sensitizes cells to genotoxic stress, suggesting timely inhibition of PP4 to be indispensable for cells in responding to DNA damage. Our results identify a novel inhibitor of PP4 that inhibits PP4-mediated cellular functions and establish the physiological importance of this regulation. In addition, PP4IP might be developed as potential therapeutic reagents for targeting tumors particularly with high level of PP4C expression.
Keywords: dephosphorylation, DNA damage response, DNA double-strand break repair, protein phosphatase 4, protein phosphatase 4 inhibitory protein

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30 June 2019 Volume 42,
Number 6, pp. 441~501

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