title: Binding and internalization of epidermal growth factor by rat pituitary tumor cells.
abstract: Epidermal growth factor (EGF) regulates hormone synthesis and decreases the growth rate of clonal lines of rat pituitary tumor cells. [125I]iodo-EGF bound to specific receptors on GH4C1 rat pituitary cells with an apparent Kd of 0.34 nM. At 0 degrees C, 84% of specifically bound [125I]iodo-EGF appeared to be on the cell surface, while at 37 degrees C, 84% of bound [125I]iodo-EGF appeared to be internalized and could not be removed by treatment with an acidic high-salt buffer. Internalization of surface-bound [125I]iodo-EGF required 10 min to reach completion and was markedly temperature-dependent. Monodansylcadaverine, bacitracin, ammonium chloride, chloroquine, quinacrine and vinblastin did not inhibit internalization of [125I]iodo-EGF, suggesting that transglutaminase is not involved; but these drugs did cause an increased accumulation of radioactivity, probably by inhibiting degradation. In 2 h at 37 degrees C, approx. 35% of cell-associated [125I]iodo-EGF was degraded as analyzed by gel filtration, and 72% of the material that dissociated from the cells migrated as low molecular weight material or iodo-Tyr. Incubation of GH4C1 cells with unlabeled EGF caused a prolonged and dose-related decrease in the ability of the cells to bind [125I]iodo-EGF in a subsequent incubation, i.e. down-regulation. The pathway for internalization and degradation of the EGF-receptor complex in GH4C1 cells resembles that described for fibroblasts, in which the cellular response is different, but differs from the behavior of other hormone-receptor complexes in GH4C1 pituitary cells.
mesh_terms: D000818:Animals; D002103:Cadaverine / Q000031:analogs & derivatives / Q000494:pharmacology; D002460:Cell Line; D004815:Epidermal Growth Factor / Q000378:metabolism*; D066246:ErbB Receptors; D010911:Pituitary Neoplasms / Q000378:metabolism*; D051381:Rats; D011956:Receptors, Cell Surface / Q000378:metabolism; D013696:Temperature; D013997:Time Factors
chemical_list: D011956:Receptors, Cell Surface; D004815:Epidermal Growth Factor; D066246:ErbB Receptors; C008542:monodansylcadaverine; D002103:Cadaverine