Human ADAR1 Prevents Endogenous RNA from Triggering Translational Shutdown

Area of Science:

• Immunology
• Molecular Biology
• Genetics

Background:

• Type I interferon (IFN) production is triggered by host sensors detecting foreign nucleic acids.
• The mechanism by which these sensors differentiate self from non-self double-stranded RNA (dsRNA) remains unclear.
• Mutations in ADAR1, an enzyme that edits dsRNA, are linked to Aicardi-Goutières syndrome, characterized by autoinflammation and neurological issues.

Purpose of the Study:

• To investigate the substrates and function of ADAR1 in human cells.
• To understand how ADAR1 distinguishes self from non-self nucleic acids.
• To elucidate ADAR1's role in regulating the interferon response and preventing autoinflammation.

Main Methods:

• Generated ADAR1 knockout human cells for functional studies.
• Analyzed ADAR1 editing activity on RNA polymerase II (pol II) and pol III transcripts.
• Assessed the impact of ADAR1 on PKR activation and translational shutdown during IFN response.
• Investigated ADAR1's role in MDA5-dependent interferon production in neuronal progenitor cells.

Main Results:

• ADAR1 primarily edited Alu elements in pol II-transcribed mRNAs, not pol III-transcribed Alus.
• ADAR1 inhibited hyperactivation of the dsRNA sensor PKR, preventing translational shutdown during IFN response.
• Both dsRNA binding and catalytic activities of ADAR1 were essential to prevent endogenous RNA from activating PKR.
• ADAR1 knockout neuronal progenitor cells displayed spontaneous, MDA5-dependent interferon production, PKR activation, and cell death.

Conclusions:

• Human ADAR1 plays a critical role in regulating the sensing of self versus non-self RNA.
• ADAR1 allows for pathogen detection while preventing detrimental autoinflammatory responses.
• Dysregulation of ADAR1 contributes to autoinflammatory conditions by impairing self-RNA tolerance.