Adaptor protein complex 1 gamma 1 subunit is an important host factor involved in both Zika virus and dengue virus infections.

Mosquito-borne flaviviruses, such as Zika virus (ZIKV) and dengue virus (DENV), cause diverse severe clinical manifestations including fever, rash, hepatitis, arthralgia, and congenital anomalies. Here, we identified a host factor, the adaptor protein complex 1 gamma 1 subunit (AP1G1), which plays an important role in both ZIKV and dengue virus 2 (DENV2) infections. We explored the role of AP1G1 in ZIKV and DENV2 infections using CRISPR/Cas9 gene editing technology and RNA interference (RNAi) techniques. Knockout or silencing of AP1G1 decreases the replication of ZIKV and DENV2 in multiple human cell lines. Intriguingly, depletion of AP1G1 results in a significant reduction in ZIKV at an early stage, but decreases DENV2 replication levels during the late stage, suggesting that AP1G1 plays distinct roles in the infection by ZIKV and DENV2. Furthermore, we determined that AP1G1 mediates ZIKV-endosomal membrane fusion through inhibitor experiments and fluorescence labeling assays. Mechanistically, we found that AP1G1 exerts its pro-viral effect through binding to the ZIKV envelope glycoprotein (E protein). This interaction promotes the fusion of viral and endosomal membranes, during which the ZIKV genomic RNAs are released from the endosome into the cytoplasm, a process that facilitates viral replication. However, for DENV2 infection, AP1G1 primarily affects its viral RNA replication stage, rather than the fusion of virus-endosomal membrane. Taken together, our work demonstrates that AP1G1 plays a pro-viral role in both ZIKV and DENV2 infections via distinct mechanisms, highlighting its potential as a therapeutic target for antiviral strategies.