Surface expression of viral glycoproteins is polarized in epithelial cells infected with recombinant vaccinia viral vectors

In polarized epithelial cells, maturation sites of enveloped viruses that form by budding at cell surfaces are restricted to particular membrane domains. Recombinant vaccinia viruses were used to investigate the sites of surface expression in the Madin-Darby canine kidney (MDCK) cell line of the hemagglutinin (HA) of influenza virus, the G glycoprotein of vesicular stomatitis virus (VSV), and gp70/p15E of Friend murine leukemia virus (MuLV). These glycoproteins could be demonstrated by immunofluorescence on the surfaces of MDCK cells as early as 4 h post-infection. In intact MDCK monolayers, vaccinia recombinants expressing HA produced a pattern of surface fluorescence typical of an apically expressed glycoprotein. In contrast, cells infected with vaccinia recombinants expressing VSV-G or MuLV gp70/p15E exhibited surface fluorescence only when monolayers were treated with EGTA to disrupt tight junctions, as expected of glycoproteins expressed on basolateral surfaces. Immunoferritin labeling in conjunction with electron microscopy confirmed that MDCK cells infected with the HA recombinant exhibited specific labeling of the apical surfaces whereas the VSV-G and MuLV recombinants exhibited the respective antigens predominantly on the basolateral membranes. Quantitation of surface expression by [125I]protein A binding assays on intact and EGTA-treated monolayers confirmed the apical localization of the vaccinia-expressed HA and demonstrated that 95% of the VSV-G and 97% of the MuLV gp70/p15E glycoproteins were localized on the basolateral surfaces. These results demonstrate that glycoproteins of viruses that normally mature at basolateral surfaces of polarized epithelial cells contain all of the structural information required for their directional transport to basolateral plasma membranes.