The respiratory syncytial virus (RSV) matrix (M) protein interacts with the actin cytoskeleton in viral assembly and budding. The M-actin interaction may facilitate the transportation of the ribonucleoprotein complexes (RNPs) of RSV to viral assembly and budding sites. Previously, we have shown that RSV M interacts with actin microfilaments in cell culture. In this study we show that the actin-binding protein palladin plays a role in facilitating the M-actin interaction. Here, we also show a role for palladin in RSV budding.
The M-palladin interaction was investigated in cells co-transfected to express M as a green fluorescent-(GFP) tagged protein and palladin as a mCherry fluorescent tagged protein, followed by cytoskeleton enrichment. M and palladin were observed to colocalize towards microfilaments, suggesting that palladin is involved in the M-actin interaction. A co-immunoprecipitation in RSV infected cells further confirmed the association of M with palladin and identified an interaction with two palladin isoforms, 140 kDa and 37 kDa. Moreover, the knockdown of palladin with siRNA led to a reduction in the titre of released RSV and an increase in cell associated titer, suggesting a role for palladin in RSV release.
In conclusion, we show, for the first time, a role for palladin in the infection and replication of a respiratory pathogen and its association with a viral protein. Further investigations are focused on elucidating the M-palladin association further to identify the mechanism whereby the interaction takes place. This will, ultimately, contribute to elucidating how the M-actin interaction facilitates the transport of RNPs to assembly sites and the mechanism through which virions are released.