TARGETING OF CFTR PROTEIN IS LINKED TO THE POLARIZATION OF HUMAN PANCREATIC DUCT CELLS IN CULTURE

A relationship between targeting of the protein CFTR (Cystic Fibrosis Transmembrane conductance Regulator) and cellular polarization has bee n observed in various types of epithelial cells. However, there are no reports on this in human exocrine pancreatic cells, which are functio nally altered in patients with cystic fibrosis. The expression of CFTR and its targeting to apical plasma membranes was investigated during growth and polarization of human ductal pancreatic cancerous Capan-1 c ells. Despite their neoplastic origin, the cancerous pancreatic duct c ells of the Capan-1 line secrete Cl- and HCO3- ions. We showed by elec tron microscopy, impregnation of cells with tannin and freeze-fracture that these cells become polarized during growth in culture, and are j oined by tight junctions. The expression of CFTR and the various stage s in its anchorage to membranes was followed using a specific polyclon al antibody, ECL-885, directed against a synthetic peptide mimicking o ne of the extracellular loops of CFTR. Qualitative and quantitative co nfocal microscopic studies showed that: (i) the expression of CFTR was constant during growth, irrespective of cellular conformation, (ii) t he number of cells presenting CFTR anchored to membranes increased wit h time in culture, (iii) the rise in membrane-bound CFTR-immunoreactiv ity accompanied the polarization of the cells, (iv) CFTR anchored to p lasma membranes was distributed regularly over the surface of non-pola rized cells, but was localized only at the apical membranes of the pol arized cells. Moreover, patch-clamp studies indicated the presence of few Cl- cAMP-dependent conductance CFTR channels on unpolarized cells, and a larger number of CFTR channels on the apical plasma membranes o f polarized cells. These results indicated that the anchorage of a fun ctional CFTR to the plasma membrane is progressive and occurs in step with polarization of these human pancreatic duct cells in culture. We suggest that the targeting of CFTR to the apical membranes is directly Linked to the process of cellular polarization.