The secretory fate of flavivirus NS1 in mosquito cells is influenced by the caveolin binding domain

Flaviviruses of major medical importance worldwide such as dengue (DENV), Zika (ZIKV), and yellow fever (YFV) viruses are transmitted by mosquitoes Aedes sp. The non-structural protein 1 (NS1) of these flaviviruses is secreted from the infected cells using different secretion routes depending on the cell and virus nature. The NS1 of DENV and ZIKV contain in the hydrophobic region a conserved caveolin binding domain (CBD) ({Phi}XX{Phi}XXXX{Phi}), which is not conserved in YFV NS1. To ascertain the role of the CBD in the secretory route followed by flavivirus NS1, expression vectors for the NS1 of DENV2, ZIKV and YFV were constructed. Using site-directed mutagenesis, substitutions were made in the aromatic residues within CBD; in addition, the full domain was replaced by those of other flaviviruses, creating chimeras in the CBD of NS1. Substitutions of the aromatic residues to Ala or Thr, or CBD chimeras, results in increased sensitivity of NS1 secretion to brefeldin A treatment, indicating a change to a classical secretion pathway. Likewise, the insertion of the DENV/ZIKV CBD into the recombinant Gaussia-Luciferase results in a loss of sensitivity to BFA treatment, in luciferase secretion. These results suggest that the CBD sequence is a molecular determinant for the unconventional secretory route followed by DENV and ZIKV NS1 in mosquito cells. However, the cellular components that recognize the CBD in the NS1 of DENV and ZIKV and redirect them to an unconventional route and if this secretion route confers unique functions to NS1 within the vector mosquito are aspects currently unknown. ImportanceFlaviviruses are an important cause of mosquito borne diseases to humans. We have previously demonstrated that the non-structural protein 1 from dengue and zika virus are secreted efficiently from mosquito cells using an unconventional route, that depends on caveolin and molecular chaperones. In this work, we show evidence indicating that a caveolin binding domain, well conserved and exposed in dengue and Zika virus NS1, but absent in other flaviviruses such as yellow fever virus or West Nile virus, is important in determining the unconventional secretion pathway followed by dengue and zika virus NS1 in mosquito cells. The unique secretory pathway followed by NS1 in mosquito cells may result in distinctive viral-cellular protein associations required to facilitate viral infection in the mosquito vector. To identify viral and cellular elements that could disturb the traffic of dengue and Zika virus NS1 may be important to design of strategies for vector control.