PROTEIN TRAFFIC IN POLARIZED EPITHELIAL-CELLS - THE POLYMERIC IMMUNOGLOBULIN RECEPTOR AS A MODEL SYSTEM

As a model system to study protein traffic in polarized epithelial cel ls, we have used the polymeric immunoglobulin receptor. This receptor travels first to the basolateral surface, where it can bind polymeric IgA or IgM. The receptor is then endocytosed and delivered to endosome s. The receptor is sorted into transcytotic vesicles, which are exocyt osed at the apical surface. The 103-amino acid cytoplasmic domain of t he receptor contains several sorting signals. The 17 residues closest to the membrane are an autonomous signal that is necessary and suffici ent for basolateral sorting. For rapid endocytosis there are two indep endent signals, both of which contain critical tyrosine residues. Fina lly, transcytosis is signaled by phosphorylation of a particular serin e.