17 Expression of Viral Receptors and the Vectorial Release of Viruses in Polarized Epithelial Cells

Abstract

The external surfaces of the body are lined with epithelial cells, which act as the primary barrier to virus infection and to dissemination of progeny virus from the infected host. Individual cells in an epithelial layer are joined by junctional complexes that restrict the diffusion of molecules across the cell layer. In addition, the junctional complexes serve to restrict the lateral diffusion of membrane components between the apical and basolateral domains, which, in combination with differential targeting of membrane components, serves to maintain the apical and basolateral surfaces as distinct domains containing different sets of lipids and proteins (Simons and van Meer 1988; Simons and Wandinger-Ness 1990; Compans and Srinivas 1991; Rodriguez-Boulan and Powell 1992). There are several mechanisms employed by viruses to traverse the epithelial barrier (Tucker and Compans 1993), and in many cases the epithelial cells comprising the barrier can serve as sites of virus infection.

In 1978, Rodriguez-Boulan and Sabatini reported the polarized budding of several enveloped viruses from either the apical or the basolateral surfaces of Madin-Darby canine kidney (MDCK) cells. Subsequently, a great deal of interest has developed in studies of virus-infected epithelial cells. Studies of the intracellular transport and surface expression of viral proteins have provided important information about the mechanisms by which membrane proteins are targeted to specific plasma membrane domains of epithelial cells. In addition, the restriction of virus entry or release to specific membrane domains has significant implications for the pathogenesis of viral infections. Many of these studies have involved the...