The microRNA miR-485 targets host and influenza virus transcripts to regulate antiviral immunity and restrict viral replication.

MicroRNAs (miRNAs) are small noncoding RNAs that are responsible for dynamic changes in gene expression, and some regulate innate antiviral responses. Retinoic acid-inducible gene I (RIG-I) is a cytosolic sensor of viral RNA; RIG-I activation induces an antiviral immune response. We found that miR-485 of the host was produced in response to viral infection and targeted RIG-I mRNA for degradation, which led to suppression of the antiviral response and enhanced viral replication. Thus, inhibition of the expression of mir-485 markedly reduced the replication of Newcastle disease virus (NDV) and the H5N1 strain of influenza virus in mammalian cells. Unexpectedly, miR-485 also bound to the H5N1 gene PB1 (which encodes an RNA polymerase required for viral replication) in a sequence-specific manner, thereby inhibiting replication of the H5N1 virus. Furthermore, miR-485 exhibited bispecificity, targeting RIG-I in cells with a low abundance of H5N1 virus and targeting PB1 in cells with increased amounts of the H5N1 virus. These findings highlight the dual role of miR-485 in preventing spurious activation of antiviral signaling and restricting influenza virus infection.