Sensing Self and Foreign Circular RNAs by Intron Identity

5 years ago

Sensing Self and Foreign Circular RNAs by Intron Identity

Circular RNAs (circRNAs) are single-stranded RNAs that are joined head to tail with largely unknown functions. Here we show that transfection of purified in vitro generated circRNA into mammalian cells led to potent induction of innate immunity genes and confers protection against viral infection. The nucleic acid sensor RIG-I is necessary to sense foreign circRNA, and RIG-I and foreign circRNA co-aggregate in cytoplasmic foci. CircRNA activation of innate immunity is independent of a 5′ triphosphate, double-stranded RNA structure, or the primary sequence of the foreign circRNA. Instead, self-nonself discrimination depends on the intron that programs the circRNA. Use of a human intron to express a foreign circRNA sequence abrogates immune activation, and mature human circRNA is associated with diverse RNA binding proteins reflecting its endogenous splicing and biogenesis. These results reveal innate immune sensing of circRNA and highlight introns—the predominant output of mammalian transcription—as arbiters of self-nonself identity.

Graphical abstract

Teaser

Chen et al. show that exogenous circRNAs trigger an immune response that can protect against viral infection. They find that cells distinguish self from nonself circRNAs based on their biogenesis. CircRNAs spliced by endogenous human spliceosomes associate with many RNA-binding proteins that mark their origin as self molecules.

Publisher URL: www.sciencedirect.com/science

DOI: S1097276517303623