Host S100A6 inhibits ZIKV replication by degrading NS3 through lysosomal pathway

Zika virus (ZIKV) is a mosquito-borne arbovirus. Maternal infection may cause severe complications such as neonatal microcephaly and neurological defects. To date, there is no clinically approved vaccine or specific drug against ZIKV infection. The host calcium-binding protein, S100A6, is a member of S100 protein family, regulates various cellular processes, and has been recognized as a host-dependent factor for Flavivirus infection.

S100A6 expression in host cells after ZIKV infection was detected by western blotting (WB). The effects of host S100A6 on ZIKV replication as indicated by the RNA and protein levels of nonstructural protein 3 (NS3) were detected by qRT-PCR, plaque assay, immunofluorescence assay (IFA), and WB respectively. The interaction and co-localization of S100A6 with NS3 were examined through co-immunoprecipitation (Co-IP) and IFA. Proteasome inhibitor and lysosomal acidification inhibitor were used to explore the degradation pathway of NS3 mediated by S100A6.

ZIKV infection induced a dose- and time-dependent increase in host S100A6 expression. Overexpression of S100A6 in HeLa cells did not affect ZIKV binding or entry into host cells but significantly inhibited viral replication. Conversely, S100A6 knockdown led to a significant increase in ZIKV replication. Moreover, S100A6 was found binding to ZIKV-NS3, leading to NS3 degradation without affecting genome copies. The use of lysosomal acidification inhibitor NH₄Cl significantly reversed S100A6-mediated downregulation of NS3 protein levels, suggesting that S100A6 degrades NS3 via the lysosomal pathway.

ZIKV infection upregulated host S100A6, which acted as an anti-infection factor by specifically targeting ZIKV-NS3 for degradation, thereby inhibiting viral replication. These findings provide insights into a potential mechanism of host resistance to ZIKV infection and enhance our understanding of the ZIKV-host interaction.