Exon junction complex mediates the cap-independent translation of circular RNA.

Evidence that circular RNAs (circRNAs) serve as protein template is accumulating. However, how the cap-independent translation is controlled remains largely uncharacterized. Here we show that the presence of intron and thus splicing promote cap-independent translation. By acquiring the exon junction complex (EJC) after splicing, the interaction between circRNA and ribosomes was promoted, thereby facilitating translation. Prevention of splicing by treatment with spliceosome inhibitor or mutating splicing signal hindered cap-independent translation of circRNA. Moreover, EJC-tethering using Cas13 technology reconstituted EJC-dependent circRNA translation. Finally, the level of a coding circRNA from succinate dehydrogenase assembly factor 2 (circSDHAF2) was found to be elevated in the tumorous tissues from patients with colorectal cancer (CRC) and shown to be critical in tumorigenesis of CRC in both cell and murine models. These findings reveal that EJC-dependent control of circSDHAF2 translation is involved in the regulation of oncogenic pathways. Implications: EJC-mediated cap-independent translation of circRNA is implicated in the tumorigenesis of colorectal cancer.