Down-regulation of the epidermal growth factor receptor in KB cells is due to receptor internalization and subsequent degradation in lysosomes.

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Abstract
Using a monoclonal antibody to the human epidermal growth factor (EGF) receptor (EGF-RI), the metabolism of the receptor and the pathway of its internalization was followed in KB cells after the addition of EGF. Measurement of surface binding of 125I-labeled EGF showed that .apprx. 80% of EGF binding activity disappeared from the plasma membrane after a 10 min exposure to EGF at 37.degree. C. Immunoprecipitation of the receptor from [35S]Met-labeled cell extracts with EGF-RI showed that EGF caused the receptor to be degraded with a half-life of 40 min. Immunofluorescence using EGF-R1 showed an EGF-dependent redistribution of the EGF receptor. In cells not exposed to EGF, almost all of the receptor was diffusely distributed on the cell surface. After EGF addition, the receptor was rapidly internalized, first appearing in small punctate organelles characteristic of receptosomes and then in larger perinuclear lysosome-like structures. By 120 min almost all of the immunoreactive EGF receptor had disappeared from the cells. Immunocytochemistry at the EM level confirmed these light microscopic findings. The diffusely distributed receptor on the cell surface first clustered into clathrin-coated pits in the presence of EGF, next was internalized into receptosomes, appeared transiently in transreticular Golgi elements and finally was seen in lysosomes. This EGF-dependent down-regulation and degradation of the EGF receptor in KB cells provides a striking example of ligand-dependent clustering and internalization of a receptor, followed by degradation in lysosomes of both ligand and receptor.

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