Resolution of ROS‐induced G‐quadruplexes and R‐loops at transcriptionally active sites is dependent on BLM helicase

Abstract

R‐loops and G‐quadruplexes (G4s) are noncanonical secondary DNA structures. Here, we show that reactive oxygen species (ROS) induce G4 formation as well as R‐loops at transcriptionally active sites. Importantly, the G4 structure is subsequently triggered by R‐loop formation after damage. Once G4 is formed within an R‐loop, it reversely stabilizes the R‐loop. Notably, the helicase activity of Bloom syndrome protein is essential for the resolution of both R‐loops and G4s. Unresolved G4s and R‐loops delay the repair of ROS‐induced damage at actively transcribed sites. Together, our results demonstrate that interregulation between R‐loops and G4s induced by ROS is essential for repair at transcriptionally active sites.

DNA folds threaten genetic stability and can be leveraged for chemotherapy

“…Similarly, BLM was overexpressed to reverse reactive oxygen species (ROS)-induced G4 (and R-loop) formation at transcriptionally active sites, thus restoring the repair process. 250 3c. G4 stabilising ligands and chemical biology.…”

Epigenetic Regulation of Genomic Stability by Vitamin C

“…Furthermore, 8-oxo-dG DNA glycosylase (OGG1) recruited to these lesions interacts with TET1 that can trigger active DNA demethylation by BER ( Zhou et al, 2016 ). ROS can also induce G quadruplex formation as well as R-loops (DNA-RNA hybrids that are enriched at CpG islands), which can cause genomic instability at active transcriptional sites and delay the removal and repair of these ROS-induced damaged bases ( Tan et al, 2020 ). Further direct evidence of the involvement of TET enzymes in DNA repair come from studies in ESCs, where genotoxic insults such as aphidicolin treatment to induce double strand breaks (DSBs) were shown to induce 5hmC, but not 5mC, foci that co-localized with γH2AX marks, and the repair proteins 53BP1 and RAD51 ( Kafer et al, 2016 ).…”

DDX5 resolves R-loops at DNA double-strand breaks to promote DNA repair and avoid chromosomal deletions

“…Topoisomerases TOP1 and TOP3B play a key role in maintaining the DNA tension in chromatin during transcription and their deficiency accumulates R-loops ( 8 , 9 ). Many RNA and DNA helicases have been identified to resolve persistent R-loops, including senataxin (SETX) ( 10 , 11 ), aquarius (AQR) ( 12 ), BLM ( 13 , 14 ), DDX1 ( 15 , 16 ), DDX5 ( 17 ), DDX21 ( 18 ), DDX23 ( 19 ), DHX9 ( 20 ) and PIF1 ( 21 ). Another class of enzyme that suppresses R-loops is the RNAse H1 and RNase H2 able to degrade the RNA component in the R-loop ( 22 ).…”