N6-Methyladenosine Modification Controls Circular RNA Immunity

• Published in: Molecular cell 2019-10, Vol.76 (1), p.96-109.e9
• Main Authors: Chen, Y. Grace, Chen, Robert, Ahmad, Sadeem, Verma, Rohit, Kasturi, Sudhir Pai, Amaya, Laura, Broughton, James P., Kim, Jeewon, Cadena, Cristhian, Pulendran, Bali, Hur, Sun, Chang, Howard Y.
• Format: Article
• Language: English
• Subjects: Adaptor Proteins, Signal Transducing - immunology; Adaptor Proteins, Signal Transducing - metabolism; Adenosine - administration & dosage; Adenosine - analogs & derivatives; Adenosine - immunology; Adenosine - metabolism; Adjuvants, Immunologic - administration & dosage; Animals; cancer immunotherapy; CD8-Positive T-Lymphocytes - immunology; CD8-Positive T-Lymphocytes - metabolism; circular RNA; DEAD Box Protein 58 - immunology; DEAD Box Protein 58 - metabolism; Female; HEK293 Cells; HeLa Cells; Humans; Immunity, Innate; Immunization; Interferon Regulatory Factor-3 - immunology; Interferon Regulatory Factor-3 - metabolism; Interferons - immunology; Interferons - metabolism; Lymphocytes, Tumor-Infiltrating - immunology; Lymphocytes, Tumor-Infiltrating - metabolism; Melanoma, Experimental - immunology; Melanoma, Experimental - metabolism; Melanoma, Experimental - pathology; Melanoma, Experimental - therapy; Mice, Inbred C57BL; N6-methyladenosine; Polyubiquitin - immunology; Polyubiquitin - metabolism; Protein Multimerization; Receptors, Immunologic; RIG-I; RNA, Circular - administration & dosage; RNA, Circular - immunology; RNA, Circular - metabolism; RNA-Binding Proteins - immunology; RNA-Binding Proteins - metabolism; self/non-self; Ubiquitination; vaccine; YTHDF
• ISSN: 1097-2765; 1097-4164
• DOI: 10.1016/j.molcel.2019.07.016

Circular RNAs (circRNAs) are prevalent in eukaryotic cells and viral genomes. Mammalian cells possess innate immunity to detect foreign circRNAs, but the molecular basis of self versus foreign identity in circRNA immunity is unknown. Here, we show that N6-methyladenosine (m6A) RNA modification on human circRNAs inhibits innate immunity. Foreign circRNAs are potent adjuvants to induce antigen-specific T cell activation, antibody production, and anti-tumor immunity in vivo, and m6A modification abrogates immune gene activation and adjuvant activity. m6A reader YTHDF2 sequesters m6A-circRNA and is essential for suppression of innate immunity. Unmodified circRNA, but not m6A-modified circRNA, directly activates RNA pattern recognition receptor RIG-I in the presence of lysine-63-linked polyubiquitin chain to cause filamentation of the adaptor protein MAVS and activation of the downstream transcription factor IRF3. CircRNA immunity has considerable parallel to prokaryotic DNA restriction modification system that transforms nucleic acid chemical modification into organismal innate immunity. [Display omitted] •Unmodified circRNA adjuvant induces antigen-specific T and B cell responses•m6A RNA modification marks self circRNAs and abrogates circRNA immunity•Unmodified circRNA and K63-polyubiquitin activate RIG-I and innate immune signaling•YTHDF2 binding of m6A-circRNA additionally suppresses circRNA immunity Mammalian cells distinguish between foreign and endogenous circular RNAs (circRNAs), but the molecular basis is unknown. Chen et al. identify N6-methyladenosine (m6A) RNA modification as a marker for “self.” Unmodified circRNA, but not m6A-modified circRNA, activates RIG-I in the presence of K63-polyubiquitin to cause MAVS filamentation, IRF3 dimerization, and interferon production.