ADAR1 links R-loop homeostasis to ATR activation in replication stress response

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• Unscheduled RNA-DNA hybrids (R-loops) cause replication stress and DNA damage.
• ATR kinase is known to suppress R-loop-induced replication defects.
• The role of R-loops in activating ATR kinase remains unclear.

Purpose of the Study:

• To investigate if R-loops actively participate in ATR kinase activation.
• To elucidate the mechanism by which R-loops might influence ATR activation.
• To understand the function of ADAR1 in R-loop resolution and genome stability.

Main Methods:

• Investigated the interaction between ADAR1, TOPBP1, and the 9-1-1 complex.
• Utilized techniques to observe protein translocation and complex assembly at replication forks.
• Assessed the role of ADAR1's double-stranded RNA-binding domains in ATR activation and R-loop resolution.
• Examined the recruitment of RNA helicases DHX9 and DDX21 by ADAR1.

Main Results:

• Nuclear ADAR1 promotes ATR activation and resolves genome-wide R-loops.
• ADAR1 facilitates TOPBP1 loading onto replication forks by enhancing TOPBP1-RAD9 association.
• DNA-RNA hybrids induce ADAR1 translocation to R-loop regions, where it recruits DHX9 and DDX21 to unwind R-loops.
• This unwinding allows TOPBP1 to efficiently stimulate ATR kinase.

Conclusions:

• ADAR1 acts as a crucial link between R-loop clearance and ATR activation.
• The assembly of ADAR1-nucleated complexes is regulated in time and space to maintain genome integrity.
• R-loops crosstalk with blocked replication forks, modulating ADAR1 activity to fine-tune ATR signaling and safeguard the genome.