title: The high-affinity immunoglobulin-E receptor (FcepsilonRI) is endocytosed by an AP-2/clathrin-independent, dynamin-dependent mechanism.
abstract: Aggregation of the high-affinity immunoglobulin E (IgE) receptor (FcepsilonRI), expressed on mast cells and basophils, initiates the immediate hypersensitivity reaction. Aggregated FcepsilonRI has been reported to rapidly migrate to lipid rafts in RBL-2H3 cells. We confirmed that aggregated FcepsilonRI is found in the lipid raft fractions of cellular lysates. Furthermore, we show that the cross-linked FcepsilonRI remains associated with detergent-resistant structures upon internalization. Previous morphological studies have reported that aggregated FepsiloncRI is endocytosed via clathrin-coated pits, which in general are not lipid raft associated. To address this apparent discrepancy, we employed siRNA to suppress expression of components of the clathrin-mediated internalization machinery, namely, clathrin heavy chain, and the AP-2 (alpha-adaptin or mu2-subunit). Transferrin receptor (TfR) is endocytosed by a clathrin-mediated process and, as expected, each transfected siRNA caused a two to threefold elevation of TfR surface expression and almost completely inhibited its endocytosis. In contrast, there was no effect on surface expression levels of FcepsilonRI nor on the endocytosis of the dinitrophenyl-human serum albumin (DNP-HSA)/IgE/FcepsilonRI complex. On the contrary, internalization of DNP-HSA/IgE/FcepsilonRI was inhibited by overexpression of a dominant-negative dynamin mutant. We conclude that internalization of cross-linked FcRI does not require the AP-2/clathrin complex but is dynamin-dependent and may be lipid raft mediated.
authors.affiliation: Receptor Cell Biology Section, Laboratory of Allergic Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Rockville, MD 20852, USA.
authors.forename: Gul'nar
authors.initials: G
authors.lastname: Fattakhova
authors.forename: Madhan
authors.initials: M
authors.lastname: Masilamani
authors.forename: Francisco
authors.initials: F
authors.lastname: Borrego
authors.forename: Alasdair M
authors.initials: AM
authors.lastname: Gilfillan
authors.forename: Dean D
authors.initials: DD
authors.lastname: Metcalfe
authors.forename: John E
authors.initials: JE
authors.lastname: Coligan
mesh_terms: D000818:Animals; D001483:Base Sequence; D002460:Cell Line; D033922:Clathrin Heavy Chains / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D003432:Cross-Linking Reagents; D034281:Dynamins / Q000235:genetics / Q000378:metabolism*; D004705:Endocytosis; D021962:Membrane Microdomains / Q000378:metabolism; D009154:Mutation; D034741:RNA, Small Interfering / Q000235:genetics; D051381:Rats; D017455:Receptors, IgE / Q000378:metabolism*; D011990:Receptors, Transferrin / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D050656:Transcription Factor AP-2 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D014162:Transfection
chemical_list: D003432:Cross-Linking Reagents; D034741:RNA, Small Interfering; D017455:Receptors, IgE; D011990:Receptors, Transferrin; D011993:Recombinant Fusion Proteins; D050656:Transcription Factor AP-2; D033922:Clathrin Heavy Chains; D034281:Dynamins