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Mol Cell. 2017 Jul 20;67(2):228-238.e5. doi: 10.1016/j.molcel.2017.05.022. Epub 2017 Jun 15.

Sensing Self and Foreign Circular RNAs by Intron Identity.

Author information

1
Center for Personal Dynamic Regulomes and Program in Epithelial Biology, Stanford University School of Medicine, Stanford, CA 94305, USA.
2
Department of Immunobiology, Howard Hughes Medical Institute, Yale School of Medicine, New Haven, CT 06519, USA.
3
Department of Biochemistry and Biophysics, University of Pennsylvania, Perelman School of Medicine, Philadelphia, PA 19104, USA.
4
Center for Personal Dynamic Regulomes and Program in Epithelial Biology, Stanford University School of Medicine, Stanford, CA 94305, USA. Electronic address: howchang@stanford.edu.

Abstract

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.

KEYWORDS:

Circular RNA; circRNA; innate immunity; introns; self-nonself

PMID:
28625551
PMCID:
PMC5610545
DOI:
10.1016/j.molcel.2017.05.022
[Indexed for MEDLINE]
Free PMC Article

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