ADAR1 (Adenosine Deaminase Acting on RNA 1)

ADAR1 is an enzyme that catalyzes adenosine-to-inosine (A-to-I) RNA editing, converting adenosines within double-stranded RNA regions into inosine, which is read by the cell as guanosine. It is expressed as two isoforms: a constitutively expressed, predominantly nuclear p110 isoform, and an interferon-inducible, predominantly cytoplasmic p150 isoform. By editing self double-stranded RNA, ADAR1 is a central mechanism by which cells prevent their own endogenous RNA from being mistaken for viral RNA and triggering an inappropriate innate immune response; loss of ADAR1 function causes embryonic lethality and autoinflammatory disease in mice and humans, respectively, while ADAR1 upregulation is frequently exploited by cancer cells for immune evasion.