title: Ligand-induced association of epidermal growth factor receptor to the cytoskeleton of A431 cells.
abstract: Recently, we have obtained evidence in favor of a structural interaction between the epidermal growth factor (EGF) receptor and the Triton X-100-insoluble cytoskeleton of epidermoid carcinoma A431 cells. Here we present a further analysis of the properties of EGF receptors attached to the cytoskeleton. Steady-state EGF binding studies, analyzed according to the Scatchard method, showed that A431 cells contain two classes of EGF-binding sites: a high-affinity site with an apparent dissociation constant (KD) of 0.7 nM (7.5 x 10(4) sites per cell) and a low-affinity site with a KD of 8.5 nM (1.9 x 10(6) sites per cell). Non-equilibrium binding studies revealed the existence of two kinetically distinguishable sites: a fast-dissociating site, with a dissociation rate constant (k-1) of 1.1 x 10(-3) s-1 (1.0-1.3 x 10(6) sites per cell) and a slow-dissociating site, with a k-1 of 3.5 x 10(-5) s-1 (0.6-0.7 x 10(6) sites per cell). The cytoskeleton of A431 cells was isolated by Triton X-100 extraction. Scatchard analysis revealed that approximately 5% of the original number of receptors were associated with the cytoskeleton predominantly via high-affinity sites (KD = 1.5 nM). This class of receptors is further characterized by the presence of a fast-dissociating component (k-1 = 2.0 x 10(-3) s-1) and a slow-dissociating component (k-1 = 9.1 x 10(-5) s-1). The distribution between fast and slow sites of the cytoskeleton was similar to that of intact cells (65% fast and 35% slow sites). Incubation of A431 cells for 2 h at 4 degrees C in the presence of EGF resulted in a dramatic increase in the number of EGF receptors associated to the cytoskeleton. These newly cytoskeleton-associated receptors appeared to represent low-affinity binding sites (KD = 7 nM). Dissociation kinetics also revealed an increase of fast-dissociating sites. These results indicate that at 4 degrees C EGF induces the binding of low-affinity, fast-dissociating sites to the cytoskeleton of A431 cells.
authors.affiliation: Department of Molecular Cell Biology, University of Utrecht, Netherlands.
authors.forename: P M
authors.initials: PM
authors.lastname: van Bergen en Henegouwen
authors.forename: L H
authors.initials: LH
authors.lastname: Defize
authors.forename: J
authors.initials: J
authors.lastname: de Kroon
authors.forename: H
authors.initials: H
authors.lastname: van Damme
authors.forename: A J
authors.initials: AJ
authors.lastname: Verkleij
authors.forename: J
authors.initials: J
authors.lastname: Boonstra
mesh_terms: D002294:Carcinoma, Squamous Cell / Q000378:metabolism; D003599:Cytoskeleton / Q000378:metabolism*; D066246:ErbB Receptors / Q000187:drug effects / Q000378:metabolism*; D006801:Humans; D017830:Octoxynol; D010743:Phospholipids / Q000378:metabolism; D011092:Polyethylene Glycols / Q000494:pharmacology; D011506:Proteins / Q000378:metabolism; D014407:Tumor Cells, Cultured / Q000378:metabolism
chemical_list: D010743:Phospholipids; D011506:Proteins; D011092:Polyethylene Glycols; D017830:Octoxynol; D066246:ErbB Receptors