STIMULATION OF TRANSCYTOSIS OF THE POLYMERIC IMMUNOGLOBULIN RECEPTOR BY DIMERIC IGA

The polymeric immunoglobulin receptor (pIgR) is transcytosed from the basolateral to the apical surface of polarized epithelial cells. We ha ve previously shown that phosphorylation of Ser-664 in the cytoplasmic domain of the pIgR is a signal for its transcytosis. We now report th at binding of a physiological ligand, dimeric IgA, to pIgR stimulates pIgR transcytosis. This stimulation occurs in both the presence or abs ence of Ser-664 phosphorylation. We have used three methods to measure transcytosis of the pIgR. (i) The pIgR was biosynthetically labeled a nd its cleavage to secretory component after transcytosis was measured . (ii) The pIgR was labeled with biotin at the basolateral surface. Af ter transcytosis, release of the biotin-labeled secretory component in to the apical medium was measured. (iii) Transcytosis of a ligand boun d to the pIgR was measured. All three methods indicated that dimeric I gA stimulates transcytosis of the pIgR.