RNA 5-methylcytosine marks mitochondrial double-stranded RNAs for degradation and cytosolic release

Area of Science:

• Immunology
• Molecular Biology
• RNA Biology

Background:

• Mitochondria play a crucial role in innate immunity.
• Mitochondrial double-stranded RNAs (mt-dsRNAs) can trigger immune responses when released into the cytosol.
• Regulation of mt-dsRNA release and immune activation is poorly understood.

Purpose of the Study:

• To identify key regulators of mt-dsRNA expression and degradation.
• To elucidate the mechanism controlling mtRNA turnover and cytosolic release.
• To understand how mitochondrial self-immunogenic RNAs are regulated.

Main Methods:

• CRISPR screening of mitochondrial RNA (mtRNA)-binding proteins.
• Analysis of 5-methylcytosine (m⁵C) modification on mtRNAs.
• Investigating the roles of NSUN4 and C1QBP in mtRNA regulation and immune response.
• Assessing mt-dsRNA levels in cytosolic and mitochondrial compartments.

Main Results:

• NSUN4 was identified as a key regulator of mt-dsRNA expression.
• NSUN4 mediates m⁵C modification on mtRNAs, particularly light-strand long noncoding RNAs.
• m⁵C-modified mtRNAs are recognized by C1QBP, promoting RNA turnover.
• Suppression of NSUN4 or C1QBP leads to increased mt-dsRNA levels and immune activation.

Conclusions:

• A novel mechanism for selective degradation of light-strand mtRNAs is revealed.
• m⁵C modification on mtRNAs serves as a molecular mark for decay and controls cytosolic release.
• This pathway is critical for preventing aberrant immune activation by mitochondrial components.