Exosome-delivered and Y RNA-derived small RNA suppresses influenza virus replication.

Multiple interplays between viral and host factors are involved in influenza virus replication and pathogenesis. Several small RNAs have recently emerged as important regulators of host response to viral infections. The aim of this study was to characterize the functional role of hsa-miR-1975, a Y5 RNA-derived small RNA, in defending influenza virus and delineate the mechanisms. We performed high throughput sequencing of small RNAs in influenza virus-infected cells to identify up- or down- regulated small RNA species. The expression of the most abundant RNA species (hsa-miR-1975) was validated by stem-loop reverse transcription-polymerase chain reaction (RT-PCR). Antiviral effects of hsa-miR-1975 were confirmed by Western Blot, RT-PCR and plaque assay. In vitro perturbation of hsa-miR-1975 combined with exosomes isolation was used to elucidate the role and mechanism of hsa-miR-1975 in the context of antiviral immunity. Small RNA sequencing revealed that hsa-miR-1975 was the most up-regulated small RNA in influenza virus-infected cells. The amount of intracellular hsa-miR-1975 increased in the late stage of the influenza virus replication cycle. The increased hsa-miR-1975 was at least partially derived from degradation of Y5RNA as a result of cellular apoptosis. Unexpectedly, hsa-miR-1975 mimics inhibited influenza virus replication while hsa-miR-1975 sponges enhanced the virus replication. Moreover, hsa-miR-1975 was secreted in exosomes and taken up by the neighboring cells to induce interferon expression. Our findings unravel a critical role of Y-class small RNA in host's defense against influenza virus infection and reveal its antiviral mechanism through exosome delivery. This may provide a new candidate for targeting influenza virus.