Astrovirus-induced epithelial-mesenchymal transition via activated TGF-β increases viral replication.

Human astroviruses (HAstV), positive sense single-stranded RNA viruses, are one of the leading causes of diarrhea worldwide. Despite their high prevalence, the cellular mechanisms of astrovirus pathogenesis remain ill-defined. Previous studies showed HAstV increased epithelial barrier permeability by causing a re-localization of the tight junction protein, occludin. In these studies, we demonstrate that HAstV replication induces epithelial-mesenchymal transition (EMT), by upregulating the transcription of EMT-related genes within 8 hours post-infection (hpi), followed by the loss of cell-cell contacts and disruption of polarity by 24 hpi. While multiple classical HAstV serotypes, including clinical isolates, induce EMT, the non-classical genotype HAstV-VA1 and two strains of reovirus are incapable of inducing EMT. Unlike the re-localization of tight junction proteins, HAstV-induced EMT requires productive replication and is dependent transforming growth factor-β (TGF-β) activity. Finally, inhibiting TGF-β signaling and EMT reduces viral replication, highlighting its importance in the viral life cycle. This finding puts classical strains of HAstV-1 in an exclusive group of non-oncogenic viruses triggering EMT.