title: Heterodimerization of the epidermal-growth-factor (EGF) receptor and ErbB2 and the affinity of EGF binding are regulated by different mechanisms.
abstract: When clathrin-dependent endocytosis is inhibited in HeLa cells by overexpression of a K44A (Lys(44)-->Ala) mutant of the GTPase dynamin, high-affinity binding of epidermal growth factor (EGF) to the EGF receptor (EGFR) is disrupted [Ringerike, Stang, Johannessen, Sandnes, Levy and Madshus (1998) J. Biol. Chem. 273, 16639-16642]. We now report that the effect of [K44A]dynamin on EGF binding was counteracted by incubation with the non-specific kinase inhibitor staurosporine (SSP), implying that a protein kinase is responsible for disrupted high-affinity binding of EGF upon overexpression of [K44A]dynamin. The effect of [K44A]dynamin on EGF binding was not due to altered phosphorylation of the EGFR, suggesting that the activated kinase is responsible for phosphorylation of a substrate other than EGFR. The number of EGFR molecules was increased in cells overexpressing [K44A]dynamin, while the number of proto-oncoprotein ErbB2 molecules was unaltered. EGF-induced receptor dimerization was not influenced by overexpression of [K44A]dynamin. ErbB2-EGFR heterodimer formation was found to be ligand-independent, and the number of heterodimers was not altered by overexpression of [K44A]dynamin. Neither SSP nor the phorbol ester PMA, which disrupts high-affinity EGF-EGFR interaction, had any effect on the EGFR homo- or hetero-dimerization. Furthermore, the EGF-induced tyrosine phosphorylation of ErbB2 was not affected by overexpression of [K44A]dynamin, implying that EGFR-ErbB2 dimers were fully functional. Our results strongly suggest that high-affinity binding of EGF and EGFR-ErbB2 heterodimerization are regulated by different mechanisms.
authors.affiliation: Institute of Pathology, University of Oslo, The National Hospital, N-0027 Oslo, Norway.
authors.forename: L E
authors.initials: LE
authors.lastname: Johannessen
authors.forename: K E
authors.initials: KE
authors.lastname: Haugen
authors.forename: A C
authors.initials: AC
authors.lastname: østvold
authors.forename: E
authors.initials: E
authors.lastname: Stang
authors.forename: I H
authors.initials: IH
authors.lastname: Madshus
mesh_terms: D019281:Dimerization; D034281:Dynamins; D004705:Endocytosis; D004815:Epidermal Growth Factor / Q000378:metabolism*; D066246:ErbB Receptors / Q000378:metabolism*; D020558:GTP Phosphohydrolases / Q000096:biosynthesis; D006367:HeLa Cells; D006801:Humans; D019606:Phosphoamino Acids / Q000032:analysis; D010766:Phosphorylation; D011485:Protein Binding; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000378:metabolism*; D019311:Staurosporine / Q000494:pharmacology; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
chemical_list: D034281:Dynamins; D004815:Epidermal Growth Factor; D066246:ErbB Receptors; D020558:GTP Phosphohydrolases; D019606:Phosphoamino Acids; D018719:Erb-b2 Receptor Tyrosine Kinases; D019311:Staurosporine; D013755:Tetradecanoylphorbol Acetate