Interactions of Vaccinia virus with the host cell
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Vaccinia virus (VACV) is a double-strand DNA virus belonging to Orthopoxvirus genus of the family Poxviridae. After entry VACV replicates entirely in cytoplasm of the host cell, using virally-encoded DNA replication and transcription machinery. Nevertheless, a recent siRNA screen revealed that the nuclear export protein nucleoporin 62 (NUP62) plays a role in VACV morphogenesis, suggesting VACV requires the host cell nucleus for virus replication. In order to investigate this further we analysed the effect of two chemical inhibitors of nuclear-cytoplasmic transport, leptomycin B and 335, on the replication of VACV in HeLa and A549 cells. No significant difference was detected in viral titre when nuclear export was inhibited with drug treatment, as this resulted in only a three-fold reduction in virus titre. In contrast, both drugs reduced the yield of influenza virus (which is known to be dependent on nuclear-cytoplasmic transport) by 200 fold. These results indicate that VACV is able to replicate to near normal titres in cells with reduced nuclear export. A siRNA interference study also uncovered MAST3 (microtubule-associated serine/threonine kinase 3) as a putative pro-viral cellular protein. MAST3 contains a serine/threonine kinase domain and a PDZ protein interaction domain. The present study demonstrated a statistically significant reduction of VACV replication in HeLa cells in the presence of MAST3-targeted siRNA. This work provides new information on the complex interactions between VACV and the host cell.