CFTR IS INVOLVED IN MEMBRANE ENDOCYTOSIS BUT NOT IN FLUID-PHASE AND RECEPTOR-MEDIATED ENDOCYTOSIS IN HUMAN RESPIRATORY EPITHELIAL-CELLS

Cystic fibrosis transmembrane conductance regulator (CFTR) protein has been reported to be a cAMP-regulator of plasma membrane recycling in epithelial cells overexpressing CFTR. To assess its role in the differ ent endocytic processes in human respiratory epithelial cells, the rat es of internalization of membrane, fluid-phase and receptor-mediator t racers were compared, under control conditions and after treatment wit h the cAMP agonist forskolin in normal and cystic fibrosis (CF) cells. In both control and treated-cells, CFTR was only present in the plasm a membrane of normal hut not in CF cells. Similarly, activation of Cl- efflux only occurred in normal and not in CF-treated cells. The rate of membrane endocytosis was significantly decreased by 35% in normal t reated-cells, whereas it was not significantly decreased (12%) in CF-t reated cells. Upon forskolin treatment, the decrease of the rate of bo th fluid-phase and receptor-mediated endocytosis was not significantly different between normal and CF cells. These results demonstrate that CFTR is involved in membrane endocyrosis but not in fluid-phase and r eceptor-mediated endocytosis in human respiratory epithelial cells. (C ) 1996 Academic Press, Inc.