DHX9 SUMOylation is required for the suppression of R-loop-associated genome instability.

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• RNA helicase DHX9 is crucial for maintaining genome stability through R-loop resolution.
• The precise regulatory mechanisms governing DHX9 function are not fully understood.

Purpose of the Study:

• To investigate the role of SUMOylation in DHX9 function and its impact on genome stability.
• To elucidate how DHX9 interacts with other proteins involved in R-loop regulation.

Main Methods:

• Site-directed mutagenesis to create a non-SUMOylatable DHX9 K120R mutant.
• Assessing R-loop levels, DNA damage, and cell viability in cells expressing wild-type and mutant DHX9.
• Investigating protein-protein interactions using techniques like co-immunoprecipitation.
• Overexpression of RNase H and SUMO2 fusion constructs.

Main Results:

• SUMOylation at lysine 120 (K120) is essential for DHX9's ability to resolve R-loops.
• The DHX9 K120R mutant exhibits R-loop dysregulation, increased DNA damage, and sensitivity to genotoxic agents.
• SUMOylation facilitates DHX9's interaction with R-loop-associated proteins like PARP1 and DDX21 via SUMO-interacting motifs.
• Fusion of SUMO2 to the K120R mutant restored protein interactions, reduced R-loops, and improved cell survival.

Conclusions:

• DHX9 SUMOylation at K120 is a critical regulatory mechanism for maintaining genome stability.
• This SUMOylation event is essential for proper R-loop balance by mediating interactions with key proteins.
• Targeting DHX9 SUMOylation could offer therapeutic strategies for genome instability-related diseases.