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 different endocytic processes in human respiratory epithelial cells, the rates of internalization of membrane, fluid-phase and receptor-mediator tracers were compared, under control conditions and after treatment with the cAMP agonist forskolin in normal and cystic fibrosis (CF) cells. In both control and treated-cells, CFTR was only present in the plasma 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 treated-cells, whereas it was not significantly decreased (12%) in CF-treated cells. Upon forskolin treatment, the decrease of the rate of both 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 receptor-mediated endocytosis in human respiratory epithelial cells. (C) 1996 Academic Press, Inc.