Non-canonical TGF-β/Smad signalling enhances cell-to-cell spread during vaccinia virus infection

Gowripalan A, McKenzie CD and Newsome TP

School of Life and Environmental Sciences, University of Sydney, NSW, Australia, 2006.

The ability of viruses to manipulate the hostile cell microenvironment is often crucial to ensuring their prolonged survival within the host. The pathways they influence range from those which mediate apoptosis and cell proliferation, to others that control migration and cytoskeletal structure. One commonly manipulated host system is the TGF-β signalling cascade. Observations in our lab suggest vaccinia virus (VACV) can exploit elements of this pathway during infection. Specifically, we found, via luciferase assay and western blots, that VACV can potently activate the TGF-β-associated, R-Smad transcription factors, Smad2 and Smad3, as well as the common Smad, Smad4. Using CRISPR-Cas9 and siRNA technologies, we have also demonstrated a role for Smad4 in a number of aspects of viral infection, including viral replication, cell-to-cell spread and cell migration. Global transcriptomic analysis uncovered a number of Smad4-dependent transcriptional targets which may play a role in enhancing VACV spread. Interestingly, it appears that activation of these Smad proteins occurs entirely independently of TGF-β receptor phosphorylation in the VACV context. To our knowledge, no other microbe is able to stimulate this pathway in the same manner. VACV seems to be unique in this ability, as closely related virus, Ectromelia virus is unable to activate this pathway. Understanding how VACV is able to induce this signalling cascade independently of the TGF-β receptor, could be critical in understanding regulation of non-canonical Smad signalling and also provide new insights into oncolytic virus research and tumour cell dynamics.