Transit of epidermal growth factor through coated pits of the Golgi system.

Abstract

Using a direct conjugate of epidermal growth factor (EGF) and horseradish peroxidase, the entry of EGF into KB (human carcinoma) cells was followed. EGF initially was found bound diffusely to the entire cell surface at 4.degree. C; on warming to 37.degree. C, EGF was found clustered in clathrin-coated pits on the plasa membrane in .ltoreq. 1 min. Within 1-2 min at 37.degree. C, EGF began to accumulate in receptosomes within the cell and remained there for up to 10 min. At 10-13 min after warming to 37.degree. C, EGF was found in thin reticular membranous elements of the Golgi system, as well as concentrated in the clathrin-coated pits present on these membranes. by 15 min after warming, EGF began to be delivered to lysosomes located near the Golgi system. Apparently, clathrin-coated pits in the Golgi reticular system accumulate EGF before delivery to lysosomes.