Mutation in DDM1 inhibits the homology directed repair of double strand breaks.

Seung Hee Choi,Sungbeom Lee,Seung Sik Lee,Jeong-Il Kim,Jin-Hong Kim,Tae Ho Ryu,Arthur J Lustig

doi:10.1371/journal.pone.0211878

Abstract

In all organisms, DNA damage must be repaired quickly and properly, as it can be lethal for cells. Because eukaryotic DNA is packaged into nucleosomes, the structural units of chromatin, chromatin modification is necessary during DNA damage repair and is achieved by histone modification and chromatin remodeling. Chromatin remodeling proteins therefore play important roles in the DNA damage response (DDR) by modifying the accessibility of DNA damage sites. Here, we show that mutation in a SWI2/SNF2 chromatin remodeling protein (DDM1) causes hypersensitivity in the DNA damage response via defects in single-strand annealing (SSA) repair of double-strand breaks (DSBs) as well as in the initial steps of homologous recombination (HR) repair. ddm1 mutants such as ddm1-1 and ddm1-2 exhibited increased root cell death and higher DSB frequency compared to the wild type after gamma irradiation. Although the DDM1 mutation did not affect the expression of most DDR genes, it did cause substantial decrease in the frequency of SSA as well as partial inhibition in the γ-H2AX and Rad51 induction, the initial steps of HR. Furthermore, global chromatin structure seemed to be affected by DDM1 mutations. These results suggest that DDM1 is involved in the homology directed repair such as SSA and HR, probably by modifying chromatin structure.

Highlights

DNA damage is caused by cellular metabolic processes such as oxidative respiration, or by toxic chemicals or environmental stresses such as UV/ionizing radiation [1,2,3]
radiation-sensitive 54 (RAD54) is known to be a member of the SWI2/SNF2 family, which is involved in DNA damage repair and development in many organisms [40,41,42]
It has been reported that Arabidopsis SWI2/SNF2 chromatin remodeling genes are involved in the DNA damage response (DDR), including homologous recombination (HR) repair [22]. ddm1 mutants exhibit hypersensitive phenotypes in response to DNA-damaging agents such as gamma radiation, UV, and methyl methane sulfonate (MMS) [30, 31]

Summary

Introduction

DNA damage is caused by cellular metabolic processes such as oxidative respiration, or by toxic chemicals or environmental stresses such as UV/ionizing radiation [1,2,3]. Cells deal with DNA damage through a network of cellular pathways called the DNA damage response (DDR), as unrepaired damage can lead to genome instability and tumorigenesis [4, 5]. It is very important for cells to have efficient, tightly controlled DNA damage response pathways. HDR is mediated via single-strand annealing (SSA) and homologous recombination (HR) The latter HR repair includes double-strand break repair (DSBR), synthesis-dependent strand annealing (SDSA), and break-induced replication (BIR). NHEJ is a more error-prone repair process than HR Both HR and NHEJ mechanisms require DNA processing procedures controlled by post-translational modifications such as phosphorylation and ubiquitination of the chromatin and DNA damage repair proteins. At DSB sites, the histone H2A variant, H2AX, is phosphorylated by phosphatidylinositol 3-kinases ATM and ATR to recruit DNA damage repair proteins [5]

Methods

Results

Conclusion