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Intracellular processing of epidermal growth factor. II. Intracellular cleavage of the COOH-terminal region of 125I-epidermal growth factor.

1984; Elsevier BV; Volume: 259; Issue: 5 Linguagem: Inglês

10.1016/s0021-9258(17)43258-3

1083-351X

Stephen R. Planck, Joanne S. Finch, Bruce E. Magun,

HER2/EGFR in Cancer Research

Epidermal growth factor (EGF) undergoes a speci€ic series of alterations during the course of its binding and internalization into cultured fibroblasts.The modified EGF species can be distinguished from each other and from native EGF by their isoelectric points.We employed peptide mapping techniques to determine the nature of these alterations.We found that'261-EGF with a pJ of 4.55 was converted to a pI4.2 species by removal of 1 or 2 amino acid moieties from the COOHterminal end of the protein.A p1 4.35 species was generated by a trypsin-like cut between amino acid residues 48 and 49, for a total of 5 amino acid moieties removed from the native EGF.The PI 4.0 species was formed by removal of at least the COOH-terminal arginine from the PI 4.35 species.Thus, upon binding and internalization, EGF was sequentially cleaved in the COOH-terminal region.Removal of the COOHterminal polypeptide has been shown to dramatically reduce the affinity of EGF for its receptor, raising the possibility that intracellular dissociation of EGF from its receptor may be a direct result of the intracellular processing of EGF.Epidermal growth factor elicits its biological activity through a mechanism involving the binding of EGF' to specific receptors on the surface of target cells.The receptor-EGF complexes form clusters on the plasma membrane and are endocytosed within clathrin-coated vesicles (1).During these early steps most bound '251-labeled EGF is converted from PI 4.55 to a PI 4.2 form (2, 3).The vesicles containing receptor-EGF complexes cofractionate on Percoll density gradients with markers for coated vesicles, Golgi, and endoplasmic reticulum.As shown in the accompanying paper (31, '"I-EGF is converted in these vesicles to a pI 4.35 species.Eventually, the '251-EGF is modified to PI 4.0 and is found in dense, lysosomal-like organelles.The relationship of each of the preceding steps to the triggering of the biological response of cells to EGF remains unknown.The modified lZ51-EGF species can be distinguished from the original '251-EGF by their isoelectric points and their affinities for EGF receptors but not by size as measured by chromatography on Sephadex G-75 columns (2).Thus, the altered EGF species may result from small additions or dele-