Lipid raft protein Flotillin 2 facilitates alphavirus infection through promoting viral release

Alphaviruses are transmitted to vertebrate hosts via hematophagous arthropod vectors, posing major public health challenges, yet the mechanisms by which they infect vector mosquitoes remain unclear. In this study, we utilized the Sindbis virus (SINV), a model alphavirus, to investigate the infection processes in mosquito and mammalian cells. One member of the Flotillin family of lipid-raft protein from Culex quinquefasciatus, CqFlotillin 2, was found to bind SINV glycoprotein E2 and to facilitate SINV infection in C. quinquefasciatus cell line and live mosquitoes, as well as facilitating viral transmission to mice via mosquito vectors. Notably, instead of affecting viral attachment to cell surface, entry into cells, or replication, CqFlotillin 2 facilitates viral release from cells and intercellular spread, which positively correlates to the formation of filopodial extension. This function is conserved among Flotillin 2 homologs in promoting SINV infection in various mosquito and mammal host cells. Furthermore, Flotillin 2 promotes the infection of another alphavirus, Semliki Forest virus (SFV), in mosquito and mammalian cells by facilitating viral release from cells. This work suggests Flotillin 2 as a potential cellular co-factor implicated in alphavirus release and highlights Flotillin 2 as a promising target for controlling alphavirus infection and transmission.