Traffic through and around the Golgi apparatus in epithelia -determine the apical and basolateral surface glycoproteomes

The cell surface is decorated with glycans attached to lipids and proteins. Different plasma membrane regions display a specific composition of glycanated proteins and contribute to the definition of interactions at the cell boundary. For epithelial cells , glycans (particularly glycosaminoglycans on proteoglycans) at the basolateral blood-side are involved in receptor-growth factor interactions and signaling, but also other classes of glycans play a role in regulating receptor activity and lifetime. Glyca ns at the apical membrane face the "external environment" of body cavities and are frequently the target of viruses (i.e. influenza), bacteria, and other microorganisms. Thus the apical and basolateral glycoproteomes of epithelial cells are highly importa nt in health and disease. Typically, proteins acquire their glycans after translocation through the endoplasmic reticulum (ER) membrane and subsequently, when passing through the Golgi apparatus. In recent years, however, it has become clear that many pro teins arrive at the cell surface without typical Golgi modifications, only possessing those acquired in the ER. At the same time we have suggested that the classical apical and basolateral secretory pathways actually are segregated. Thus, our research now focuses on the pre-Golgi intermediate compartment (IC) as a sorting station of particular interest in epithelial cells, but also in mammalian cells in general. We aim at determining morphological changes to this compartment during development of polarize d epithela, by following the proteins rab1 and p58. By enrichment of IC using subcellular fractionation, we aim at identifying endogenous cargo molecules that may be followed during and after the polarization process, with respect to glycan modification a nd surface transport. At present our studies have been confined to recombinant proteins expressed by transfection. The ultimate goal is to shed light on the physiological importance of the Golgi bypass route.