Porcine deltacoronavirus enters cells via two pathways: A protease-mediated one at the cell surface and another facilitated by cathepsins in the endosome [Microbiology] (Journal of Biological Chemistry)

Porcine deltacoronavirus (PDCoV) is a pathogen belonging to the genus Deltacoronavirus that in 2014 caused outbreaks of piglet diarrhea in the United States. To identify suitable therapeutic targets, a more comprehensive understanding of the viral item pathway is required, particularly of the role of proteases. Here, we identified the proteases that activate the viral spike (S) glycoprotein to initiate cell item and also pinpointed the host-cellular pathways that PDCoV uses for item. Our results revealed that cathepsin L (CTSL) and cathepsin B (CTSB) in lysosomes and extracellular trypsin in cell cultures independently activate the S protein for membrane fusion. Pretreating the cells with the lysosomal acidification inhibitor bafilomycin-A1 (Baf-A1) completely inhibited PDCoV item, and siRNA-mediated ablation of CTSL or CTSB expression significantly reduced viral infection, indicating that PDCoV uses an endosomal pathway for item. Of note, trypsin treatment of cell cultures also activated PDCoV item, even when the endosomal pathway was inhibited. This observation indicated that trypsin-induced S protein cleavage and activation in cell cultures enables viral item directly from the cell surface. Our results provide critical insights into the PDCoV infection mechanism, uncovering two distinct viral item pathways: one through cathepsin L and cathepsin B in the endosome and another via a protease at the cell surface. Because PDCoV infection sites represent a proteases-rich environment, these findings suggest that endosome inhibitor treatment alone is insufficient to block PDCoV item into intestinal epithelial cells in vivo. Therefore, approaches that inhibit viral item from the cell membrane should also be considered.