OPPOSITE SORTING AND TRANSCYTOSIS OF THE POLYMERIC IMMUNOGLOBULIN RECEPTOR IN TRANSFECTED ENDOTHELIAL AND EPITHELIAL-CELLS

We have transfected a polarised endothelial cell line, ECV 304, and an epithelial cell line, MDCK, with a well characterised epithelial prot ein, the rat polymeric immunoglobulin receptor (pIgR), in order to stu dy the protein sorting and transcytosis in endothelial cells, The expr essed protein was normally processed and the steady state distribution between apical and basolateral surfaces was similar in both cell type s. MDCK cells, however, showed a marked polarity in the delivery of ne wly synthesised pIgR to the cell surface, and in the release of secret ory component. 88% of newly synthesised pIgR in MDCK cells was first d elivered to the basolateral surface and 99% of secretory component was released from the apical surface, In contrast the basolateral targeti ng signal of pIgR was only partially recognised in endothelial cells, with 63% of the newly synthesised pIgR being first delivered to the ba solateral surface, At steady state only 43% of the pIgR was found on t he basolateral membrane. The direction of dimeric IgA transcytosis in endothelial cells was from apical to basolateral surfaces, opposite to that in MDCK cells. These data suggest that endothelial cells poorly recognise the targeting signals of proteins from epithelial cells, and that the direction of transcytosis is linked to the biological role o f the cells.