title: Sequestration of epidermal growth factor receptors in non-caveolar lipid rafts inhibits ligand binding.
abstract: Cholesterol depletion has been shown to increase mitogen-activated protein kinase activation in response to stimulation with epidermal growth factor (EGF) (Furuchi, T., and Anderson, R. G. W. (1998) J. Biol. Chem. 273, 21099-21104). However, the underlying mechanisms are unknown. We show that cholesterol depletion increases EGF binding, whereas cholesterol loading lowers EGF binding. Based on binding analyses, we demonstrate that the observed changes in EGF binding are caused by alterations in the number of EGF receptors available for ligand binding, whereas the affinity of the receptor for EGF remains unaltered. We also show by immunofluorescence that in unstimulated cells the EGF receptor is localized in non-caveolar lipid rafts containing the ganglioside GM1 and that patching of these rafts by cholera toxin B-chain causes co-patching of EGF receptors. Experiments with solubilization in different detergents at 4 degrees C show that the association of the EGF receptor with these rafts is sensitive to Triton X-100 extraction but insensitive to extraction with another non-ionic detergent, Brij 58. Furthermore, experiments with cholesterol-depleted cells show that the association is cholesterol-dependent. We propose that non-caveolar lipid rafts function as negative regulators of EGF receptor signaling by sequestering a fraction of the EGF receptors in a state inaccessible for ligand binding.
authors.affiliation: Structural Cell Biology Unit, Department of Medical Anatomy, the Panum Institute, University of Copenhagen, DK-2200 Copenhagen N, Denmark.
authors.forename: Kirstine
authors.initials: K
authors.lastname: Roepstorff
authors.forename: Peter
authors.initials: P
authors.lastname: Thomsen
authors.forename: Kirsten
authors.initials: K
authors.lastname: Sandvig
authors.forename: Bo
authors.initials: B
authors.lastname: van Deurs
mesh_terms: D002460:Cell Line; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D002592:Cetomacrogol / Q000494:pharmacology; D002784:Cholesterol / Q000378:metabolism*; D003902:Detergents / Q000494:pharmacology; D066246:ErbB Receptors / Q000378:metabolism*; D005677:G(M1) Ganglioside / Q000378:metabolism; D006801:Humans; D008024:Ligands; D011485:Protein Binding
chemical_list: D003902:Detergents; D008024:Ligands; D005677:G(M1) Ganglioside; D002592:Cetomacrogol; D002784:Cholesterol; D066246:ErbB Receptors