title: Role of intracellular degradation of epidermal growth factor in mitogenesis.
abstract: Addition of leupeptin, methylamine and the antitubulin agent nocodazole did not affect the initial rate of association of 125I-labelled epidermal growth factor (125I-EGF) to Swiss mouse 3T3 fibroblast cells in vitro, but continued incubation with these drugs (up to 24 h) led to an increase in cell-associated radioactivity in a time- and dose-dependent fashion. Combinations of these drugs caused additive increments in cell-associated and internalized radioactivity. Throughout the incubation period, 81-89% of the cell-associated 125I-EGF was internalized. Upon incubation of 125I-EGF with 3T3 cells in the presence or absence of the three inhibitors of degradation for periods of up to 24 h, and after removal of the surface-bound material, the internalized 125I-EGF was extracted and 42-53% was found to biochemically intact (by acid precipitation) and 56-65% was antigenically similar to native EGF (using double antibody immunoprecipitation in an EGF radioimmunoassay). The extracted internalized 125I-EGF was capable of binding to fresh 3T3 cells. Despite causing a similar increase in intact internalized 125I-EGF, leupeptin did not interfere with and nocodazole alone or in combination with leupeptin markedly enhanced EGF-stimulated DNA synthesis, whereas methylamine inhibited mitogenesis. These data indicate a dissociation between EGF degradation and DNA synthesis, and are not consistent with the hypothesis that intracellular degradation of EGF is necessary for its mitogenic effects.
mesh_terms: D000818:Animals; D001562:Benzimidazoles / Q000494:pharmacology; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D004247:DNA / Q000096:biosynthesis; D004305:Dose-Response Relationship, Drug; D004815:Epidermal Growth Factor / Q000378:metabolism*; D007976:Leupeptins / Q000494:pharmacology; D008744:Methylamines / Q000494:pharmacology; D051379:Mice; D008938:Mitosis / Q000187:drug effects; D015739:Nocodazole
chemical_list: D001562:Benzimidazoles; D007976:Leupeptins; D008744:Methylamines; D004815:Epidermal Growth Factor; D004247:DNA; D015739:Nocodazole