Summary auto-generated
This study investigates how mouse hepatitis virus strain A59 (MHV-A59) exits polarized epithelial cells, finding that release direction varies by cell type. Researchers infected three epithelial cell lines—murine kidney cells, human colon carcinoma (Caco-2) cells, and canine kidney (MDCK) cells—all engineered to express the MHV receptor. MHV-A59 was released from the basolateral membrane of Caco-2 cells, consistent with previous observations in murine cells. Surprisingly, the same virus was released almost exclusively from the apical membrane of MDCK cells. Virus entry, however, was consistently apical-preferential across all cell types once monolayers matured. The MHV receptor glycoprotein localized to both apical and basolateral surfaces in young MDCK cells but became increasingly restricted to the apical surface as cells aged. These findings demonstrate that coronavirus targeting to specific plasma membrane domains during exocytosis is cell-type dependent, suggesting different epithelial cells employ distinct sorting mechanisms for virus transport, despite the virus using the same general secretory pathway.
Key findings
- MHV-A59 is released from the basolateral surface of human colon carcinoma (Caco-2) cells but from the apical surface of canine kidney (MDCK) cells, indicating cell-type-dependent release polarity
- Virus entry preferentially occurs through the apical membrane across all epithelial cell types once cells become fully polarized
- The MHV receptor glycoprotein becomes progressively restricted to the apical membrane of MDCK cells with time, correlating with the loss of basolateral infectivity
- Different epithelial cell types employ distinct sorting machinery or mechanisms that direct the same coronavirus to opposite plasma membrane domains during exocytosis
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Abstract
Coronaviruses infect humans and animals through epithelial cells of the gastrointestinal and respiratory tracts that serve as their primary target. When studying infections in cultured polarized epithelial cells, we found previously that coronaviruses are released from specific plasma-membrane domains; thus, mouse hepatitis virus (strain A59; MHV-A59) leaves murine epithelial kidney cells from the basolateral surface, whereas release of transmissible gastroenteritis virus from porcine epithelial kidney cells is confined to the apical membrane. This observation begged the question whether a particular coronavirus is consistently shed through the same membrane, irrespective of the nature of the epithelial cell. We therefore extended our studies with MHV-A59 to Madin-Darby canine kidney (MDCK) strain I and human colon carcinoma (Caco-2) cells, both of which are naturally refractory to MHV-A59 but were made susceptible to infection by transfection with recombinant MHV receptor cDNA. The release of MHV- A59 from Caco(MHVR) cells occurred preferentially from the basolateral side, consistent with our previous observations. In contrast, release from MDCK(MHVR) cells occurred almost exclusively from the apical surface. Because of this difference, we studied MHV-A59 infection of MDCK(MHVR) cells in more detail. The virus entered the cells preferentially from the apical side, a situation similar to that in murine epithelial cells, where the highest density of MHV receptor glycoprotein was found. The results from this and previous studies show that targeting of vesicles containing MHV-A59 to a specific side of epithelial cells may vary in different epithelial cell types.