A functional link between the actin cytoskeleton and lipid rafts during budding of filamentous influenza virions

Abstract

Morphogenesis of influenza virus is a poorly understood process that produces two types of enveloped virion: ∼100-nm spheres and similar diameter filaments that reach 20 μm in length. Spherical particles assemble at plasma membrane lipid rafts in a process independent of microfilaments. The budding site of filamentous virions is hitherto uncharacterised but their formation involves the actin cytoskeleton. We confirm microfilament involvement in filamentous budding and show that after disruption of cortical actin by jasplakinolide, HA, NP, and M1 redistributed around β-actin clusters to form novel annular membrane structures. HA in filamentous virions and jasplakinolide-induced annuli was detergent insoluble at 4°C. Furthermore, in both cases HA partitioned into low buoyant density detergent-insoluble glycolipid domains, indicating that filamentous virions and annuli contain reorganised lipid rafts. We propose that the actin cytoskeleton is required to maintain the correct organisation of lipid rafts for incorporation into budding viral filaments. © 2002 Elsevier Science (USA).