HSSB1 (NABP2/ OBFC2B) is required for the repair of 8-oxo-guanine by the hOGG1-mediated base excision repair pathway.

Nicolas Paquet,Nicholas W Ashton,Liza Cubeddu,Sam Beard,Ken J O'Byrne,Mark N Adams,Roland Gamsjaeger,Joshua T Burgess,Emma Bolderson,Derek J Richard,Vincent Leong,Christine Touma

doi:10.1093/nar/gkv790

Abstract

The maintenance of genome stability is essential to prevent loss of genetic information and the development of diseases such as cancer. One of the most common forms of damage to the genetic code is the oxidation of DNA by reactive oxygen species (ROS), of which 8-oxo-7,8-dihydro-guanine (8-oxoG) is the most frequent modification. Previous studies have established that human single-stranded DNA-binding protein 1 (hSSB1) is essential for the repair of double-stranded DNA breaks by the process of homologous recombination. Here we show that hSSB1 is also required following oxidative damage. Cells lacking hSSB1 are sensitive to oxidizing agents, have deficient ATM and p53 activation and cannot effectively repair 8-oxoGs. Furthermore, we demonstrate that hSSB1 forms a complex with the human oxo-guanine glycosylase 1 (hOGG1) and is important for hOGG1 localization to the damaged chromatin. In vitro, hSSB1 binds directly to DNA containing 8-oxoguanines and enhances hOGG1 activity. These results underpin the crucial role hSSB1 plays as a guardian of the genome.

Highlights

Eukaryotic cells are subject to constant DNA damage, with the oxidation of nucleotides being the most common form of damage in unperturbed cells [1]
To explore the possibility that human single-stranded DNAbinding protein 1 (hSSB1) may function in the repair of oxidative DNA damage, we investigated whether hSSB1 is recruited to chromatin after oxidative stress
Immunoblots were performed on whole cell lysates and chromatin fractions prepared from U2OS cells following the same treatment

Summary

INTRODUCTION

Eukaryotic cells are subject to constant DNA damage, with the oxidation of nucleotides being the most common form of damage in unperturbed cells [1]. As 8-oxoG may pair with either cytosine or adenine nucleotides, the untimely repair of these lesions may result in G:C to A:T transversion during replication, a mutagenic feature common in many cancers [3,4]. While rapid removal of oxidized nucleotides is normally achieved by the base excision repair (BER) pathway [5], accumulation of oxidative DNA lesions is a feature of many conditions including cancer, Alzheimer’s disease and Type II diabetes mellitus [6]. HSSB1 functions to recruit the Mre11-Rad50Nbs (MRN) complex, allowing activation of the ATM kinase and cell cycle checkpoints [20,21,24]. We establish a novel role for hSSB1 in the base excision repair pathway where it is required for cell survival following a oxidative stress. In the absence of hSSB1, human 8-oxoguanine glycosylase 1 does not localize to chromatin, resulting in the accumulation of 8-oxoguanine in the genome

EXPERIMENTAL PROCEDURES

RESULTS

DISCUSSION