[Molecular signals in protein sorting in epithelial cells: implication of the transmembrane domain and the post-translational process]

Protein sorting in epithelial cells is the major event that drive the onset and the maintenance of the functional cell polarity. A lot of interdependent steps are involved in protein sorting and targeting. Recent data describing the last results obtained in this field will be reviewed in the first part of this article. Molecular signals harbored by proteins to specify their destination are thought to be the driven force to sort given protein in a given pathway. The basolateral targeting signals so far identified are known for several years and are of the same nature, whereas apical targeting signals are still discussed and are of diverse molecular nature. Dipeptidyl peptidase IV (DPP IV/CD26) targeting signals have not been described so far and it will be interesting to study these signals, since the protein reach the apical membrane of epithelial cells through different pathways that strongly depend on the cell type considered. These different pathways result in DPP IV membrane localizations that may explain the multifunctional properties of DPP IV such as enzymatic digestion, interaction with extracellular matrix proteins, capture and transport of circulating proteins. We have undertaken the study of DPP IV molecular targeting signals and we will described here how the transmembrane domain and the glycosylation of the ectodomain may be involved in DPP IV apical targeting, with a special reference to the cell type specificity.