WIP1 Promotes Homologous Recombination and Modulates Sensitivity to PARP Inhibitors.

Kamila Burdova,Libor Macurek,Radka Storchova,Matous Palek

doi:10.3390/cells8101258

Abstract

Genotoxic stress triggers a combined action of DNA repair and cell cycle checkpoint pathways. Protein phosphatase 2C delta (referred to as WIP1) is involved in timely inactivation of DNA damage response by suppressing function of p53 and other targets at chromatin. Here we show that WIP1 promotes DNA repair through homologous recombination. Loss or inhibition of WIP1 delayed disappearance of the ionizing radiation-induced 53BP1 foci in S/G2 cells and promoted cell death. We identify breast cancer associated protein 1 (BRCA1) as interactor and substrate of WIP1 and demonstrate that WIP1 activity is needed for correct dynamics of BRCA1 recruitment to chromatin flanking the DNA lesion. In addition, WIP1 dephosphorylates 53BP1 at Threonine 543 that was previously implicated in mediating interaction with RIF1. Finally, we report that inhibition of WIP1 allowed accumulation of DNA damage in S/G2 cells and increased sensitivity of cancer cells to a poly-(ADP-ribose) polymerase inhibitor olaparib. We propose that inhibition of WIP1 may increase sensitivity of BRCA1-proficient cancer cells to olaparib.

Highlights

Cells are constantly challenged with DNA damage that comes both from endogenous and exogenous sources
double strand breaks (DSBs) are recognized by either DNA-PK to allow non-homologous end joining (NHEJ) or MRE11-RAD50-NBS1 (MRN) complex that starts the process of DNA end resection to allow HR
As WIP1 interacts with and dephosphorylates breast cancer associated protein 1 (BRCA1) and 53BP1, we aimed to evaluate its role in DNA resection that is controlled by the balance between BRCA1 and 53BP1 at DSBs

Summary

Introduction

Cells are constantly challenged with DNA damage that comes both from endogenous and exogenous sources. NHEJ operates throughout the cell cycle and results in ligation of two ends of DNA that are not extensively processed [1]. HR is restricted to S and G2 phases of the cell cycle as the homologous sequence required as template for repair usually comes from the sister chromatid and the whole process depends on activity of cyclin-dependent kinases [1,2]. DSBs are recognized by either DNA-PK to allow NHEJ or MRE11-RAD50-NBS1 (MRN) complex that starts the process of DNA end resection to allow HR. Exonuclease activity of MRE11 removes the DNA towards DSB ends that is followed by long-range resection mediated by Exo and DNA2 [2,5]. SsDNA-RPA facilitates activation of ATR kinase that further supports repair by HR [7]. RAD51 nucleofilament is stabilized by BRCA1-BARD1 complex and invades the sister chromatid to search for homology that is facilitated

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