Function of rafts and caveolae as virus infection

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CD13, a receptor for human coronavirus (HCoV)-229E, was identified as a major component of the Triton X-100-resistant membrane microdomain in human fibroblasts. Incubation of living fibroblasts with an anti-CD13 antibody on ice gave punctate labeling that was evenly distributed on the cell surface, but raising the temperature to 37℃ before fixation caused aggregation of the labeling. The aggregated labeling of CD13 colocalized with caveolin-1 in most cells. The HCoV-229E virus particle showed a binding and redistribution pattern similar to the anti-CD13 antibody : the virus bound to the cell evenly when incubated on ice, but became colocalized with caveolin-1 at 37℃ ; importantly, the virus also caused sequestration of CD13 to the caveolin-1-positive area. Electron microscopy confirmed that HCoV-229E was localized near or at the orifice of caveolae after the incubation at 37℃. Depletion of plasmalemmal cholesterol with methyl □-cyclodextrin significantly reduced the HCoV-229E redistribution and the subsequent infection. Caveolin-1 knockdown by RNA interference also reduced the HCoV-229E infection considerably. The result indicates that HCoV-229E first binds to CD13 in the Triton X-100-resistant microdomain, clusters CD13 by cross-linking, and thereby reaches the caveolar region before entering cells.