An R-loop-initiated CSB-RAD52-POLD3 pathway suppresses ROS-induced telomeric DNA breaks.

Laiyee Phoon,Meihan Duan,Lee Zou,Xiangyu Wang,Li Lan,Jun Tan,Jia-Min Zhang,Tribhuwan Yadav

doi:10.1093/nar/gkz1114

Laiyee Phoon, Meihan Duan + Show 6 more

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https://doi.org/10.1093/nar/gkz1114

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Abstract

Reactive oxygen species (ROS) inflict multiple types of lesions in DNA, threatening genomic integrity. How cells respond to ROS-induced DNA damage at telomeres is still largely unknown. Here, we show that ROS-induced DNA damage at telomeres triggers R-loop accumulation in a TERRA- and TRF2-dependent manner. Both ROS-induced single- and double-strand DNA breaks (SSBs and DSBs) contribute to R-loop induction, promoting the localization of CSB and RAD52 to damaged telomeres. RAD52 is recruited to telomeric R-loops through its interactions with both CSB and DNA:RNA hybrids. Both CSB and RAD52 are required for the efficient repair of ROS-induced telomeric DSBs. The function of RAD52 in telomere repair is dependent on its ability to bind and recruit POLD3, a protein critical for break-induced DNA replication (BIR). Thus, ROS-induced telomeric R-loops promote repair of telomeric DSBs through CSB–RAD52–POLD3-mediated BIR, a previously unknown pathway protecting telomeres from ROS. ROS-induced telomeric SSBs may not only give rise to DSBs indirectly, but also promote DSB repair by inducing R-loops, revealing an unexpected interplay between distinct ROS-induced DNA lesions.

Highlights

Reactive oxygen species (ROS) induce multiple types of DNA damage, including oxidized bases, single-strand breaks (SSBs) and double-strand breaks (DSBs), throughout the genome [1]
Consistent with the distinct roles of XRCC1 and Cockayne Syndrome protein B (CSB) in the repair of telomeric SSBs and DSBs, knockdown of tankyrase, which is required for the recruitment of XRCC1 to damaged telomeres [28], did not affect the telomere localization of CSB (Figure 2D). These results suggest that the CSB–RAD52 axis is important for the repair of ROSinduced DSBs
We show that the breakinduced DNA replication (BIR) pathway activated by ROS is triggered by telomeric R-loops dependently on TERRA

Summary

Introduction

Reactive oxygen species (ROS) induce multiple types of DNA damage, including oxidized bases, single-strand breaks (SSBs) and double-strand breaks (DSBs), throughout the genome [1]. ROS arises from both endogenous and exogenous sources. Elevation of ROS levels is associated with cancer progression and treatment resistance [2]. How cells respond to ROS-induced DNA damage is still incompletely understood. ROS-induced DNA damage at telomeres is still largely unknown. Cancer cells use either telomerase or the Alternative Lengthening of Telomeres (ALT) pathway to extend telomeres [3]. It is unknown how ROS-induced DNA damage is repaired in telomerase- and ALT-positive cancer cells

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