Actin filaments participate in West Nile (Sarafend) virus maturation process

West Nile (Sarafend) virus has previously been shown to egress by budding at the plasma membrane of infected cells, but relatively little is known about the mechanism involved in this mode of release. During the course of this study, it was discovered that actin filaments take part in the virus maturation process. Using dual-labeled immunofluorescence and immunoelectron microscopy at late infection (10 hr p.i.), co-localization of viral structural (envelope and capsid) proteins with actin filaments was confirmed. The virus structural proteins were also immuno-precipitated with anti-actin antibody, further demonstrating the strong association between the two components. Perturbation of actin filaments by cytochalasin B strongly inhibited the release of West Nile virus (similar to10,000-fold inhibition) when compared with the untreated cells. Infectious virus particles were recovered after the removal of cytochalasin B. Further confirmation was obtained when nucleocapsid particles were found associated with disrupted actin filaments at the periphery of cytochalasin B-treated cells. Together, these results showed that actin filaments do indeed have a key role in the release of West Nile (Sarafend) virions.