Role of cellular actin in the gene expression and morphogenesis of human respiratory syncytial virus

Cytoskeletal protein actin and nonactin cellular proteins were essential fo r human respiratory syncytial virus (RSV) gene expression. in vitro, specif ic antibodies against actin inhibited RSV transcription, whereas antibodies against other cytoskeletal proteins had little or no effect. Affinity puri fied cellular actin or bacterially expressed recombinant actin activated RS V transcription. However, optimal transcription required additional cellula r protein(s) that appeared to function as accessory factor(s) for actin. in the absence of actin, these proteins did not activate viral transcription. Purified Viral nucleocapsids contained actin, but no cytokeratin, tubulin, or vimentin. Cytochalasin D or DNasei - agents that destabilize actin poly mers-had little effect on RSV transcription. RSV infection itself seemed to alter the structure of the cellular actin filaments. Treatment of infected cells with cytochalasin D produced a more severe disruption of the filamen ts and drastically reduced the production of infectious virus particles but still had little effect on intracellular synthesis of viral macromolecules . Thus actin seems to serve a dual role in RSV life cycle: its monomeric fo rm as well as polymeric form activate viral transcription, while only the m icrofilament form may take part in viral morphogenesis and/or budding. (C) 1998 Academic Press.