Polarized cells, such as neurons and epithelial cells, maintain separate plasma membrane domains, each with a distinct protein and lipid composition, created through intracellular sorting mechanisms that recognize classes of proteins, and deliver them into separate vesicles for transport to the cognate surface. The recognition events responsible for specifying transport to the basolateral surface of epithelial cells, or to cell bodies of neurons, have been found to mostly localize in the cytoplasmic domains of transmembrane glycoproteins. In addition to basolateral signals, many distinct types of signals for sorting proteins to the apical surface of epithelial cells or to axon of neurons, have been characterized. Oligosaccharides on some secreted proteins specify apical transport although this mechanism does not apply to all secreted proteins. Thus, it appears that apical sorting involves multiple signals that are more variable than those involved in basolateral targeting.
Viruses follow specific sorting mechanisms in epithelial cells.
Several studies have considered that the site of virus release is coupled to the sorting pattern of the envelope proteins. We are interested to identify determinants that control polarized release of MV, and the implication of MV-proteins sorting in virus transmission and disease progression. Other cellular membrane glycoproteins are being used as internal markers to elucidate such a mechanism. For MV, we have evidence that viral proteins other than envelope glycoproteins determine the site of virus release. There are other cellular candidates that are involved in such a mechanism, which are currently under investigation.