title: Asymmetric localization of flotillins/reggies in preassembled platforms confers inherent polarity to hematopoietic cells.
abstract: Hematopoietic cells have long been defined as round, nonpolar cells that show uniform distribution of cell surface-associated molecules. However, recent analyses of the immunological synapse and the importance of lipid microdomains in signaling have shed new light on the aspect of lymphocyte polarization during the activation processes, but none of the molecules implicated so far in either the activation process or the microdomain residency are known to have a preferential localization in nonactivated cells. Chemical crosslinking and fluorescence resonance energy transfer methods have allowed the visualization of certain glycosylphosphatidylinositol-anchored proteins in lipid rafts but so far no microdomain resident protein has been shown to exist as visible stable platforms in the membrane. We report here that two lipid microdomain resident proteins, flotillins/reggies, form preassembled platforms in hematopoietic cells. These platforms recruit signaling molecules upon activation through lipid rafts. The preassembled platforms significantly differ from the canonical cholesterol-dependent "lipid rafts," as they are resistant to cholesterol-disrupting agents. Most evidence for the functional relevance of microdomains in living cells remains indirect. Using laser scanning confocal microscopy, we show that these proteins exist as stable, microscopically patent domains localizing asymmetrically to one pole of the cell. We present evidence that the asymmetric concentration of these microdomain resident proteins is built up during cytokinesis.
authors.affiliation: Division of Immunology, Department of Biology, University of Konstanz, 78457 Konstanz, Germany.
authors.forename: Lawrence
authors.initials: L
authors.lastname: Rajendran
authors.forename: Madhan
authors.initials: M
authors.lastname: Masilamani
authors.forename: Samuel
authors.initials: S
authors.lastname: Solomon
authors.forename: Ritva
authors.initials: R
authors.lastname: Tikkanen
authors.forename: Claudia A O
authors.initials: CA
authors.lastname: Stuermer
authors.forename: Helmut
authors.initials: H
authors.lastname: Plattner
authors.forename: Harald
authors.initials: H
authors.lastname: Illges
mesh_terms: D015703:Antigens, CD / Q000032:analysis; D001402:B-Lymphocytes / Q000378:metabolism / Q000648:ultrastructure*; D002455:Cell Division; D016764:Cell Polarity / Q000502:physiology*; D002772:Cholera Toxin / Q000494:pharmacology; D002784:Cholesterol / Q000032:analysis; D003505:Cyclodextrins / Q000494:pharmacology; D003902:Detergents / Q000494:pharmacology; D049452:Green Fluorescent Proteins; D006801:Humans; D007476:Ionophores / Q000494:pharmacology; D019169:Jurkat Cells / Q000378:metabolism / Q000648:ultrastructure; D008164:Luminescent Proteins / Q000032:analysis; D008213:Lymphocyte Activation / Q000502:physiology*; D008563:Membrane Lipids / Q000032:analysis; D021962:Membrane Microdomains / Q000737:chemistry / Q000187:drug effects / Q000502:physiology*; D008565:Membrane Proteins / Q000032:analysis / Q000502:physiology*; D015739:Nocodazole / Q000494:pharmacology; D017830:Octoxynol / Q000494:pharmacology; D011993:Recombinant Fusion Proteins / Q000032:analysis; D013601:T-Lymphocytes / Q000378:metabolism / Q000648:ultrastructure*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014407:Tumor Cells, Cultured / Q000378:metabolism / Q000648:ultrastructure; D047392:beta-Cyclodextrins
chemical_list: D015703:Antigens, CD; D003505:Cyclodextrins; D003902:Detergents; D007476:Ionophores; D008164:Luminescent Proteins; D008563:Membrane Lipids; D008565:Membrane Proteins; D011993:Recombinant Fusion Proteins; D047392:beta-Cyclodextrins; C106354:flotillins; C108732:methyl-beta-cyclodextrin; D049452:Green Fluorescent Proteins; D017830:Octoxynol; D002772:Cholera Toxin; D002784:Cholesterol; D013755:Tetradecanoylphorbol Acetate; D015739:Nocodazole