RNA exonuclease REXO4 resolves m⁶A-marked R-loops and suppresses anti-tumor immunity

Area of Science:

• Molecular Biology
• Cancer Biology
• Immunology

Background:

• Aberrant R-loop formation in tumor cells drives genome instability.
• Regulation of R-loop homeostasis and its role in tumorigenesis require investigation.

Purpose of the Study:

• Investigate the role of RNA exonuclease REXO4 in resolving R-loops.
• Elucidate the mechanism of R-loop resolution and its impact on cancer progression and immune response.

Main Methods:

• Studied REXO4's 3'-5' exonucleolytic activity on RNA within RNA-DNA hybrids.
• Investigated the role of N⁶-methyladenosine (m⁶A) modification in REXO4 localization and R-loop removal.
• Assessed the effects of REXO4 ablation on DNA damage, interferon response, and tumor immune infiltration in mouse squamous cell carcinoma (SCC).
• Evaluated the impact of REXO4 inhibition on PD-1 blockade efficacy in SCC.

Main Results:

• REXO4 resolves R-loops by cleaving the RNA strand in RNA-DNA hybrids.
• m⁶A modification promotes REXO4 localization and R-loop clearance.
• REXO4 ablation triggers DNA damage, stimulates interferon response, and enhances anti-tumor immunity by recruiting CD8⁺ T cells, suppressing SCC progression.
• REXO4 inhibition potentiates anti-tumor effects of PD-1 blockade in SCC.

Conclusions:

• m⁶A and REXO4 form a machinery for R-loop clearance and genome maintenance.
• This epitranscriptional machinery restrains innate immune response and facilitates SCC immune evasion.
• Targeting REXO4 presents a potential therapeutic strategy to enhance anti-cancer immunity.