CircCBP Inhibits Influenza A Virus Replication by Interfering the vRNP Activity and Enhancing Antiviral Immune Response.

Influenza A virus (IAV) is an essential pathogen which can cause pandemic and seasonal flu. Host factors, including noncoding RNAs have been found to be participated in the replication of IAV. However, the mechanism by which circular RNAs (circRNAs) regulating IAV replication remains unclear. By taking the approach of RNA deep sequencing to analyze the circRNA profiles of A549 cells upon IAV infection, we identified that circular CREB binding protein (circCBP) is significantly upregulated after IAV infection or interferon (IFN) treatment. Overexpression of circCBP inhibited IAV replication, while knockdown of circCBP promoted viral replication, indicating that circCBP inhibits IAV replication. We found that circCBP interacts with the viral nucleoprotein (NP) and reduces its interaction with viral polymerase subunits PB1 and PB2, and consequently blocks the vRNP activity. CircCBP can also bind with nonstructural protein 1 (NS1) and alleviate the inhibitory effect of NS1 on antiviral immune response. In addition, circCBP binds with the major stress granule proteins such as G3BP1. Further study revealed that circCBP enhances the oligomerization of G3BP1, which in turn promotes the formation of stress granules and the transcription of IFN-β. Our study reveals the novel functions of circCBP in regulating virus replication and stress granule-related antiviral immune response, providing a new clue to develop circRNA-based antiviral inhibitors.