ILF3 represses repeat-derived microRNAs targeting RIG-I mediated type I interferon response.

MicroRNAs (miRNAs) play important roles in regulated gene expression and miRNA biogenesis is also subject to regulation, together constituting critical regulatory circuitries in numerous physiological and pathological processes. As a dsRNA binding protein, interleukin enhancer binding factor 3 (ILF3) has been implicated as a negative regulator in miRNA biogenesis, but the mechanism and specificity have remained undefined. Here, combining small-RNA-seq and CLIP-seq, we showed that ILF3 directly represses many miRNAs or perhaps other types of small RNAs annotated in both miRBase and MirGeneDB. We demonstrated that ILF3 preferentially binds to A/U-enriched motifs, which tend to lengthen and/or stabilize the stem-loop in pri-miRNAs, thereby effectively competing with the Microprocessor to block miRNA biogenesis. Focusing on the biological function of ILF3-suppressed miR-582-3p, we discovered that this LINE-derived miRNA targets a critical interferon-inducible gene RIG-I for repression, thus establishing a novel ILF3/miR-582/RIG-I axis in the antiviral response.