Distinct endocytotic pathways in epidermal growth factor-stimulated human carcinoma A431 cells.
Addition of EGF to human epidermoid carcinoma A431 cells increases the rate of fluid-phase pinocytosis 6-10-fold as measured by horseradish peroxidase uptake (Haigler, H.T., J. A. McKanna, and S. Cohen. 1979. J. Cell Biol. 83:82-90). We show here that in the absence of extracellular Na+ or in the presence of amiloride the stimulation of pinocytosis by EGF is substantially reduced. Amiloride had no effect on the endocytosis of EGF itself or of transferrin, demonstrating that the receptor-mediated endocytotic pathway operated normally under conditions that blocked stimulated pinocytosis. Amiloride blocked EGF-stimulated pinocytosis in both HCO3(-)-containing and HCO3(-)-free media. The EGF-stimulated pinocytotic activity can frequently be localized to areas of the cell where membrane spreading and ruffling are taking place. These results demonstrate that (a) EGF induces a distinct amiloride-sensitive endocytotic pathway on A431 cells; (b) occupied EGF receptors do not utilize this pathway for their own entry; (c) endocytosis of occupied EGF receptors is not in itself sufficient to stimulate pinocytosis.
West
M A
MA
Department of Biochemistry, University of Dundee, UK.
Bretscher
M S
MS
Watts
C
C
D000584:Amiloride / Q000494:pharmacology; D001639:Bicarbonates / Q000494:pharmacology; D002352:Carrier Proteins / Q000378:metabolism; D002460:Cell Line; D004705:Endocytosis / Q000187:drug effects*; D004815:Epidermal Growth Factor / Q000494:pharmacology*; D006801:Humans; D007700:Kinetics; D010873:Pinocytosis / Q000187:drug effects; D017923:Sodium-Hydrogen Exchangers; D014407:Tumor Cells, Cultured / Q000187:drug effects / Q000378:metabolism*
D001639:Bicarbonates; D002352:Carrier Proteins; D017923:Sodium-Hydrogen Exchangers; D004815:Epidermal Growth Factor; D000584:Amiloride