Profilin is required for viral morphogenesis, syncytium formation, and cell-specific stress fiber induction by respiratory syncytial virus.
BACKGROUND
Actin is required for the gene expression and morphogenesis of respiratory syncytial virus (RSV), a clinically important Pneumovirus of the Paramyxoviridae family. In HEp-2 cells, RSV infection also induces actin stress fibers, which may be important in the immunopathology of the RSV disease. Profilin, a major regulator of actin polymerization, stimulates viral transcription in vitro. Thus, we tested the role of profilin in RSV growth and RSV-actin interactions in cultured cells (ex vivo).


RESULTS
We tested three cell lines: HEp-2 (human), A549 (human), and L2 (rat). In all three, RSV grew well and produced fused cells (syncytium), and two RSV proteins, namely, the phosphoprotein P and the nucleocapsid protein N, associated with profilin. In contrast, induction of actin stress fibers by RSV occurred in HEp-2 and L2 cells, but not in A549. Knockdown of profilin by RNA interference had a small effect on viral macromolecule synthesis but strongly inhibited maturation of progeny virions, cell fusion, and induction of stress fibers.


CONCLUSIONS
Profilin plays a cardinal role in RSV-mediated cell fusion and viral maturation. In contrast, interaction of profilin with the viral transcriptional proteins P and N may only nominally activate viral RNA-dependent RNA polymerase. Stress fiber formation is a cell-specific response to infection, requiring profilin and perhaps other signaling molecules that are absent in certain cell lines. Stress fibers per se play no role in RSV replication in cell culture. Clearly, the cellular architecture controls multiple steps of host-RSV interaction, some of which are regulated by profilin.
Department of Biochemistry and Molecular Biology, University of South Alabama, College of Medicine, 307 University Blvd, Mobile 36688-0002, USA. virabitko@hotmail.com
Vira
V
Bitko
Anja
A
Oldenburg
Nicolle E
NE
Garmon
Sailen
S
Barik
D000818:Animals; D002460:Cell Line; D003285:Contractile Proteins; D015967:Gene Expression Regulation, Viral; D015726:Giant Cells / Q000166:cytology / Q000821:virology*; D006801:Humans; D008840:Microfilament Proteins / Q000502:physiology*; D009024:Morphogenesis; D051304:Profilins; D051381:Rats; D012136:Respiratory Syncytial Viruses / Q000235:genetics / Q000254:growth & development* / Q000472:pathogenicity*; D022502:Stress Fibers / Q000648:ultrastructure*; D014764:Viral Proteins / Q000378:metabolism; D014771:Virion / Q000254:growth & development
D003285:Contractile Proteins; D008840:Microfilament Proteins; C495738:PFN1 protein, human; C495740:Pfn1 protein, rat; D051304:Profilins; D014764:Viral Proteins