R-loop-derived cytoplasmic RNA-DNA hybrids activate an immune response

Area of Science:

• Molecular Biology
• Genetics
• Immunology

Background:

• R-loops are crucial nucleic acid structures involved in cellular processes.
• Dysregulation of R-loop dynamics is linked to DNA damage and genome instability.
• The role of endonucleases like XPG in R-loop processing and its consequences were unclear.

Purpose of the Study:

• To identify and characterize a novel population of cytoplasmic RNA-DNA hybrids.
• To elucidate the mechanisms of R-loop processing and the formation of cytoplasmic hybrids.
• To investigate the cellular consequences of aberrant R-loop processing, including immune activation and cell death.

Main Methods:

• Perturbation of nuclear R-loops by depleting senataxin (SETX) or BRCA1.
• Identification of cytoplasmic RNA-DNA hybrids.
• Assessing the binding of hybrids to pattern recognition receptors (cGAS, TLR3).
• Monitoring IRF3 activation and apoptosis induction.
• Analysis of patient-derived cells with SETX or BRCA1 mutations.

Main Results:

• A new population of cytoplasmic RNA-DNA hybrids was identified as R-loop processing products.
• Cytoplasmic hybrid formation was dependent on XPG and XPF.
• These hybrids originate from specific nuclear R-loops.
• Cytoplasmic hybrids activate the innate immune response via cGAS and TLR3, leading to IRF3 activation and apoptosis.
• R-loop processing and immune activation were observed in cells from patients with ataxia and in BRCA1-mutated cancer cells.

Conclusions:

• RNA-DNA hybrids can be immunogenic when aberrantly processed and accumulated in the cytoplasm.
• R-loop processing contributes to cell death through innate immune activation.
• Aberrant R-loop processing and immune activation may play a role in neurodegeneration and cancer.