The polymeric immunoglobulin receptor

As a model system to study protein traffic in epithelial cells 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 endosomes. The receptor is sorted into transcytotic vesicles which are exocytosed at the apical surface. The 103 amino acid cytoplasmic domain of the receptor contains several sorting signals. The 17 residues closest to the membrane are an autonomous signal for basolateral sorting. For endocytosis there are two signals, both of which contain tyrosines. Finally, transcytosis is signaled by serine phosphorylation.