Evidence of autophagic and Wnt/β-catenin signaling occurrence during Schmallenberg virus (SBV) infection on BHK-21 cells

Schmallenberg virus (SBV) is a ruminant pathogen that is widely distributed around the world, but little is known about its interactions with permissive cells or about its pathogenetic mechanisms. This study highlighted, through a phenotypic approach, the changes in the expression of some autophagy and Wnt/β-catenin pathway markers that SBV causes on baby hamster kidney (BHK-21) cells. Western blot analysis revealed that SBV caused autophagy induction at 48 h post infection. Several markers, such as PI3K, Akt, and Wnt/β-catenin, were downregulated at the same time point. Furthermore, downregulation in the expression of PI3K, p-mTOR and Beclin-1 showed differences between multiplicity of infection (MOI) 0.05 and 0.5, but not between MOI 0.5 and 1.5. Exceptions for this trend were Akt and LC3-II, which progressively decreased depending on time, and β-catenin, whose expression almost disappeared regardless of MOI. The use of several chemical inducers and inhibitors has demonstrated the efficacy of late autophagy inhibitors (bafilomycin and chloroquine) in significantly lowering SBV infection and also preventing the changes caused by viral replication. Early autophagy inhibitors and inducers showed no effect on cellular viability or viral titers. Silencing the expression of Akt and β-catenin revealed a slight increase in the expression of viral glycoprotein Gc. These findings revealed the relationship that SBV has in important cellular regulatory pathways, expanding the knowledge about the cellular interactions of this virus and suggesting a central role for late stages of autophagy in the replication of this bunyavirus.