Bravo! A Mosquito Antiviral Protein that Restricts Arboviruses through an RRM3-Dependent Nuclear Mechanism

Culex quinquefasciatus mosquitoes are vectors for several medically important viruses, yet their antiviral immune responses remain understudied compared to Aedes mosquitoes. The aedine broadly antiviral protein (aBravo) is an RNA-binding protein that was found to inhibit arbovirus replication in Aedes aegypti, but the function of the Cx. quinquefasciatus Bravo ortholog (CqBravo) remains unknown. Here, we examined the role of CqBravo in antiviral immunity in Cx. quinquefasciatus-derived Hsu cells and mosquitoes. We found that CqBravo is also broadly antiviral in Cx. quinquefasciatus, reducing replication of La Crosse virus (LACV) and Usutu virus (USUV) in Hsu cells and Sindbis virus (SINV) in vivo. CqBravo localized to the nucleus, and truncation and mutational analyses identified an RNA recognition motif (RRM3) critical for nuclear localization and antiviral activity. Quantitative proteomic analysis revealed that full-length CqBravo expression was associated with distinct changes in host protein abundance that were lost following removal of RRM3. Proteins altered by CqBravo expression were enriched for pathways involved in genome maintenance, including DNA repair, DNA metabolism, and ATP-dependent DNA processing. Overall, we demonstrate that CqBravo is an important antiviral factor in Cx. quinquefasciatus mosquitoes and may play a broader role in mosquito antiviral immunity across species.