G2Cdb::Gene report

Gene id
Gene symbol
Homo sapiens
flotillin 1
G00000130 (Mus musculus)

Databases (9)

Curated Gene
OTTHUMG00000031151 (Vega human gene)
ENSG00000137312 (Ensembl human gene)
10211 (Entrez Gene)
478 (G2Cdb plasticity & disease)
FLOT1 (GeneCards)
606998 (OMIM)
Marker Symbol
HGNC:3757 (HGNC)
Protein Expression
1393 (human protein atlas)
Protein Sequence
O75955 (UniProt)

Literature (41)

Pubmed - other

  • Flotillins are involved in the polarization of primitive and mature hematopoietic cells.

    Rajendran L, Beckmann J, Magenau A, Boneberg EM, Gaus K, Viola A, Giebel B and Illges H

    Systems and Cell Biology of Neurodegeneration, Department of Psychiatry Research, University of Zurich, Zurich, Switzerland. rajendran@bli.uzh.ch

    Background: Migration of mature and immature leukocytes in response to chemokines is not only essential during inflammation and host defense, but also during development of the hematopoietic system. Many molecules implicated in migratory polarity show uniform cellular distribution under non-activated conditions, but acquire a polarized localization upon exposure to migratory cues.

    Here, we present evidence that raft-associated endocytic proteins (flotillins) are pre-assembled in lymphoid, myeloid and primitive hematopoietic cells and accumulate in the uropod during migration. Furthermore, flotillins display a polarized distribution during immunological synapse formation. Employing the membrane lipid-order sensitive probe Laurdan, we show that flotillin accumulation in the immunological synapse is concomittant with membrane ordering in these regions.

    Conclusions: Together with the observation that flotillin polarization does not occur in other polarized cell types such as polarized epithelial cells, our results suggest a specific role for flotillins in hematopoietic cell polarization. Based on our results, we propose that in hematopoietic cells, flotillins provide intrinsic cues that govern segregation of certain microdomain-associated molecules during immune cell polarization.

    PloS one 2009;4;12;e8290

  • High-density SNP screening of the major histocompatibility complex in systemic lupus erythematosus demonstrates strong evidence for independent susceptibility regions.

    Barcellos LF, May SL, Ramsay PP, Quach HL, Lane JA, Nititham J, Noble JA, Taylor KE, Quach DL, Chung SA, Kelly JA, Moser KL, Behrens TW, Seldin MF, Thomson G, Harley JB, Gaffney PM and Criswell LA

    Division of Epidemiology, School of Public Health, University of California Berkeley, Berkeley, California, USA.

    A substantial genetic contribution to systemic lupus erythematosus (SLE) risk is conferred by major histocompatibility complex (MHC) gene(s) on chromosome 6p21. Previous studies in SLE have lacked statistical power and genetic resolution to fully define MHC influences. We characterized 1,610 Caucasian SLE cases and 1,470 parents for 1,974 MHC SNPs, the highly polymorphic HLA-DRB1 locus, and a panel of ancestry informative markers. Single-marker analyses revealed strong signals for SNPs within several MHC regions, as well as with HLA-DRB1 (global p = 9.99 x 10(-16)). The most strongly associated DRB1 alleles were: *0301 (odds ratio, OR = 2.21, p = 2.53 x 10(-12)), *1401 (OR = 0.50, p = 0.0002), and *1501 (OR = 1.39, p = 0.0032). The MHC region SNP demonstrating the strongest evidence of association with SLE was rs3117103, with OR = 2.44 and p = 2.80 x 10(-13). Conditional haplotype and stepwise logistic regression analyses identified strong evidence for association between SLE and the extended class I, class I, class III, class II, and the extended class II MHC regions. Sequential removal of SLE-associated DRB1 haplotypes revealed independent effects due to variation within OR2H2 (extended class I, rs362521, p = 0.006), CREBL1 (class III, rs8283, p = 0.01), and DQB2 (class II, rs7769979, p = 0.003, and rs10947345, p = 0.0004). Further, conditional haplotype analyses demonstrated that variation within MICB (class I, rs3828903, p = 0.006) also contributes to SLE risk independent of HLA-DRB1*0301. Our results for the first time delineate with high resolution several MHC regions with independent contributions to SLE risk. We provide a list of candidate variants based on biologic and functional considerations that may be causally related to SLE risk and warrant further investigation.

    Funded by: NCRR NIH HHS: M01 RR000079, P20 RR020143, RR20143; NIAID NIH HHS: AI063274, AI24717, AI31584, AI53747, AI62629, N01AI40076, R01 AI024717, R01 AI031584, R01 AI063274, R21 AI053747, R37 AI024717, R56 AI063274, U19 AI062629; NIAMS NIH HHS: AR02175, AR043274, AR052125, AR052300, AR19084, AR22804, AR42460, AR48940, K24 AR002175, N01AR62277, P30 AR053483, P50 AR048940, R01 AR042460, R01 AR043274, R01 AR052125, R01 AR052300; NIDCR NIH HHS: DE15223, R01 DE015223

    PLoS genetics 2009;5;10;e1000696

  • Hetero-oligomerization of reggie-1/flotillin-2 and reggie-2/flotillin-1 is required for their endocytosis.

    Babuke T, Ruonala M, Meister M, Amaddii M, Genzler C, Esposito A and Tikkanen R

    Institute of Biochemistry, University of Giessen, Friedrichstrasse 24, 35392 Giessen, Germany.

    Reggie-1/flotillin-2 and reggie-2/flotillin-1 are membrane raft associated proteins which have been implicated in growth factor signaling, phagocytosis, regulation of actin cytoskeleton and membrane trafficking. Membrane and raft association of reggies is mediated by myristoylation, palmitoylation and oligomerization. We have shown that upon EGF stimulation of cells, reggie-1 is tyrosine phosphorylated by Src kinase and endocytosed into late endosomes. Here we have analyzed the mechanism of the EGF-stimulated endocytosis of reggies in more detail and show that the Src-mediated phosphorylation of reggie-1 is not the driving force for endocytosis. However, hetero-oligomerization with reggie-2 is necessary for the translocation of reggie-1, which does not take place in the absence of reggie-2. In addition, the Y163F mutant of reggie-1, which is not capable of undergoing endocytosis, oligomerizes poorly with reggie-2. EGF stimulation results in changes in the size but not in the stoichiometry of the reggie hetero-oligomers, and reggie-1 oligomer size is decreased by knockdown of reggie-2. Based on our findings, we propose a model according to which reggie hetero-oligomers are dynamic, and changes in the size of the hetero-oligomers result in endocytosis of the complex from the plasma membrane.

    Cellular signalling 2009;21;8;1287-97

  • Endocytosis of flotillin-1 and flotillin-2 is regulated by Fyn kinase.

    Riento K, Frick M, Schafer I and Nichols BJ

    MRC Laboratory of Molecular Biology, Cambridge CB2 0QH, UK.

    Flotillin-1 and flotillin-2 co-assemble into plasma membrane microdomains that are involved in the endocytosis of molecules such as glycosyl phosphatidylinositol (GPI)-linked proteins. Previous studies suggest that budding of flotillin microdomains from the plasma membrane is a tightly regulated process. Here, we demonstrate that endocytosis of flotillins is regulated by the Src family kinase Fyn. The Src kinase inhibitor PP2 prevents EGF-induced flotillin internalisation, and EGF-induced internalisation does not occur in SYF cells lacking Src, Yes and Fyn. Expression of Fyn, but not Src or Yes, restores EGF-induced internalisation in SYF cells. Expression of an active form of Fyn but not other Src kinases is sufficient to induce redistribution of flotillins from the plasma membrane to late endosomes and lysosomes. Using two partial Fyn constructs that form a functional kinase upon addition of rapamycin to cells, we show that flotillin internalisation from the plasma membrane occurs shortly after Fyn activation. Tyr160 in flotillin-1 and Tyr163 in flotillin-2 are directly phosphorylated by Fyn, and mutation of these residues to phenylalanine prevents Fyn-induced flotillin internalisation. Uptake of the GPI-linked protein CD59 is reduced by expression of the phenylalanine-mutated flotillins. These data establish uptake of flotillin microdomains as a tyrosine-kinase-regulated endocytic process.

    Funded by: Medical Research Council: MC_U105178778

    Journal of cell science 2009;122;Pt 7;912-8

  • Flotillin-1 stabilizes caveolin-1 in intestinal epithelial cells.

    Vassilieva EV, Ivanov AI and Nusrat A

    Epithelial Pathobiology Research Unit, Department of Pathology and Laboratory Medicine, Emory University, Whitehead Research Building, 615 Michael Street, Atlanta, Georgia 30322, USA.

    Flotillins and caveolins represent two types of resident proteins associated with lipid rafts in mammalian cells, however, their possible cross-talk in regulating lipid raft functions remains poorly understood. In this report, we observed that siRNA-mediated down-regulation of flotillin-1 expression which disrupted lipid raft-mediated endocytosis of BODIPY FL C(5)-lactosylceramide also substantially decreased caveolin-1 level in SK-CO15 human intestinal epithelial cells. The decrease in caveolin-1 expression appeared to be specific for flotillin-1 knock-down and was not observed after down-regulation of flotillin-2. The decrease in caveolin-1 level in flotillin-1-depleted cells was not due to suppression of its mRNA synthesis and was not mimicked by cholesterol depletion of SK-CO15 cells. Furthermore, flotillin-1 dependent down-regulation of caveolin-1 was reversed after cell exposure to lysosomal inhibitor, chloroquine but not proteosomal inhibitor, MG262. Our data suggest that flotillin-1 regulates caveolin-1 level by preventing its lysosomal degradation in intestinal epithelial cells.

    Funded by: NIDDK NIH HHS: DK-59888, R01 DK059888, R01 DK059888-09

    Biochemical and biophysical research communications 2009;379;2;460-5

  • Flotillins interact with PSGL-1 in neutrophils and, upon stimulation, rapidly organize into membrane domains subsequently accumulating in the uropod.

    Rossy J, Schlicht D, Engelhardt B and Niggli V

    Department of Pathology, University of Bern, Bern, Switzerland.

    Background: Neutrophils polarize and migrate in response to chemokines. Different types of membrane microdomains (rafts) have been postulated to be present in rear and front of polarized leukocytes and disruption of rafts by cholesterol sequestration prevents leukocyte polarization. Reggie/flotillin-1 and -2 are two highly homologous proteins that are ubiquitously enriched in detergent resistant membranes and are thought to shape membrane microdomains by forming homo- and hetero-oligomers. It was the goal of this study to investigate dynamic membrane microdomain reorganization during neutrophil activation.

    We show now, using immunofluorescence staining and co-immunoprecipitation, that endogenous flotillin-1 and -2 colocalize and associate in resting spherical and polarized primary neutrophils. Flotillins redistribute very early after chemoattractant stimulation, and form distinct caps in more than 90% of the neutrophils. At later time points flotillins accumulate in the uropod of polarized cells. Chemotactic peptide-induced redistribution and capping of flotillins requires integrity and dynamics of the actin cytoskeleton, but does not involve Rho-kinase dependent signaling related to formation of the uropod. Both flotillin isoforms are involved in the formation of this membrane domain, as uropod location of exogenously expressed flotillins is dramatically enhanced by co-overexpression of tagged flotillin-1 and -2 in differentiated HL-60 cells as compared to cells expressing only one tagged isoform. Flotillin-1 and -2 associate with P-selectin glycoprotein ligand 1 (PSGL-1) in resting and in stimulated neutrophils as shown by colocalization and co-immunoprecipitation. Neutrophils isolated from PSGL-1-deficient mice exhibit flotillin caps to the same extent as cells isolated from wild type animals, implying that PSGL-1 is not required for the formation of the flotillin caps. Finally we show that stimulus-dependent redistribution of other uropod-located proteins, CD43 and ezrin/radixin/moesin, occurs much slower than that of flotillins and PSGL-1.

    These results suggest that flotillin-rich actin-dependent membrane microdomains are importantly involved in neutrophil uropod formation and/or stabilization and organize uropod localization of PSGL-1.

    PloS one 2009;4;4;e5403

  • Multiple genetic variants along candidate pathways influence plasma high-density lipoprotein cholesterol concentrations.

    Lu Y, Dollé ME, Imholz S, van 't Slot R, Verschuren WM, Wijmenga C, Feskens EJ and Boer JM

    Division of Human Nutrition, Wageningen University, Wageningen, The Netherlands. kevin.lu@wur.nl

    The known genetic variants determining plasma HDL cholesterol (HDL-C) levels explain only part of its variation. Three hundred eighty-four single nucleotide polymorphisms (SNPs) across 251 genes based on pathways potentially relevant to HDL-C metabolism were selected and genotyped in 3,575 subjects from the Doetinchem cohort, which was examined thrice over 11 years. Three hundred fifty-three SNPs in 239 genes passed the quality-control criteria. Seven SNPs [rs1800777 and rs5882 in cholesteryl ester transfer protein (CETP); rs3208305, rs328, and rs268 in LPL; rs1800588 in LIPC; rs2229741 in NRIP1] were associated with plasma HDL-C levels with false discovery rate (FDR) adjusted q values (FDR_q) < 0.05. Five other SNPs (rs17585739 in SC4MOL, rs11066322 in PTPN11, rs4961 in ADD1, rs6060717 near SCAND1, and rs3213451 in MBTPS2 in women) were associated with plasma HDL-C levels with FDR_q between 0.05 and 0.2. Two less well replicated associations (rs3135506 in APOA5 and rs1800961 in HNF4A) known from the literature were also observed, but their significance disappeared after adjustment for multiple testing (P = 0.008, FDR_q = 0.221 for rs3135506; P = 0.018, FDR_q = 0.338 for rs1800961, respectively). In addition to replication of previous results for candidate genes (CETP, LPL, LIPC, HNF4A, and APOA5), we found interesting new candidate SNPs (rs2229741 in NRIP1, rs3213451 in MBTPS2, rs17585739 in SC4MOL, rs11066322 in PTPN11, rs4961 in ADD1, and rs6060717 near SCAND1) for plasma HDL-C levels that should be evaluated further.

    Journal of lipid research 2008;49;12;2582-9

  • Toward a confocal subcellular atlas of the human proteome.

    Barbe L, Lundberg E, Oksvold P, Stenius A, Lewin E, Björling E, Asplund A, Pontén F, Brismar H, Uhlén M and Andersson-Svahn H

    Department of Biotechnology, AlbaNova University Center, Royal Institute of Technology, SE-106 91 Stockholm, Sweden.

    Information on protein localization on the subcellular level is important to map and characterize the proteome and to better understand cellular functions of proteins. Here we report on a pilot study of 466 proteins in three human cell lines aimed to allow large scale confocal microscopy analysis using protein-specific antibodies. Approximately 3000 high resolution images were generated, and more than 80% of the analyzed proteins could be classified in one or multiple subcellular compartment(s). The localizations of the proteins showed, in many cases, good agreement with the Gene Ontology localization prediction model. This is the first large scale antibody-based study to localize proteins into subcellular compartments using antibodies and confocal microscopy. The results suggest that this approach might be a valuable tool in conjunction with predictive models for protein localization.

    Molecular & cellular proteomics : MCP 2008;7;3;499-508

  • Novel interaction partners of Bardet-Biedl syndrome proteins.

    Oeffner F, Moch C, Neundorf A, Hofmann J, Koch M and Grzeschik KH

    Center of Human Genetics, University of Marburg, 35037 Marburg, Germany. oeffner@staff.uni-marburg.de

    Bardet-Biedl syndrome (BBS) is a rare, developmental disorder characterized by six major symptoms: rod-cone dystrophy, obesity, polydactyly, renal abnormalities, learning difficulties, and hypogonadism. Secondary features include cardiac and hepatic anomalies, metabolic disturbancies, and hearing loss. BBS is genetically heterogeneous with 12 disease genes (BBS1-BBS12) described thus far. Current data suggest a functional disturbance in ciliary function and intraflagellar transport being associated with the phenotype. However, the precise functions of the BBS proteins have yet to be elucidated. This study focuses on the detection of protein factors interacting with BBS proteins. Applying yeast two-hybrid (Y2H) technology we found a series of novel, functionally potentially plausible binding partners of BBS1, BBS2, BBS4, and BBS7. Protein interactions were supported by coimmunoprecipitation analyses (ALDOB, EPAS1) and substantiated by colocalization studies at the subcellular level (ALDOB, EXOC7, FLOT1, KRT18, PAX2). Our work provides new insights into the understanding of BBS interactions and thus their biological function.

    Cell motility and the cytoskeleton 2008;65;2;143-55

  • Flotillin and RacH modulate the intracellular immunity of Dictyostelium to Mycobacterium marinum infection.

    Hagedorn M and Soldati T

    Départment de Biochimie, Faculté des Sciences, Université de Genève, Sciences II, 30 quai Ernest Ansermet, CH-1211-Genève-4, Switzerland.

    Mycobacterium marinum, a close relative of Mycobacterium tuberculosis, provides a useful model to study the pathogenesis of tuberculosis in genetically tractable model organisms. Using the amoeba Dictyostelium discoideum as a host, we show that expression of the M. marinum protein MAG24-1 is crucial to interfere with phagosome maturation. We find that two host proteins - the flotillin homologue vacuolin and p80, a predicted copper transporter - accumulate at the vacuole during pathogen replication until it finally ruptures and the bacteria are released into the host cytosol. Flotillin-1 accumulation at the replication niche and its rupture were also observed in human peripheral blood monocytes. By infecting various Dictyostelium mutants, we show that the absence of one of the two Dictyostelium vacuolin isoforms renders the host more immune to M. marinum. Conversely, the absence of the small GTPase RacH renders the host more susceptible to M. marinum proliferation but inhibits its cell-to-cell spreading.

    Cellular microbiology 2007;9;11;2716-33

  • Coassembly of flotillins induces formation of membrane microdomains, membrane curvature, and vesicle budding.

    Frick M, Bright NA, Riento K, Bray A, Merrified C and Nichols BJ

    Medical Research Council Laboratory of Molecular Biology, Cambridge, UK.

    Endocytosis has a crucial role in many cellular processes. The best-characterized mechanism for endocytosis involves clathrin-coated pits [1], but evidence has accumulated for additional endocytic pathways in mammalian cells [2]. One such pathway involves caveolae, plasma-membrane invaginations defined by caveolin proteins. Plasma-membrane microdomains referred to as lipid rafts have also been associated with clathrin-independent endocytosis by biochemical and pharmacological criteria [3]. The mechanisms, however, of nonclathrin, noncaveolin endocytosis are not clear [4, 5]. Here we show that coassembly of two similar membrane proteins, flotillin1 and flotillin2 [6-8], is sufficient to generate de novo membrane microdomains with some of the predicted properties of lipid rafts [9]. These microdomains are distinct from caveolin1-positive caveolae, are dynamic, and bud into the cell. Coassembly of flotillin1 and flotillin2 into microdomains induces membrane curvature, the formation of plasma-membrane invaginations morphologically similar to caveolae, and the accumulation of intracellular vesicles. We propose that flotillin proteins are defining structural components of the machinery that mediates a clathrin-independent endocytic pathway. Key attributes of this machinery are the dependence on coassembly of both flotillins and the inference that flotillin microdomains can exist in either flat or invaginated states.

    Funded by: Medical Research Council: MC_U105178778

    Current biology : CB 2007;17;13;1151-6

  • The lipid raft proteins flotillins/reggies interact with Galphaq and are involved in Gq-mediated p38 mitogen-activated protein kinase activation through tyrosine kinase.

    Sugawara Y, Nishii H, Takahashi T, Yamauchi J, Mizuno N, Tago K and Itoh H

    Laboratory of Signal Transduction, Department of Cell Biology, Graduate School of Biological Sciences, Nara Institute of Science and Technology, 8916-5 Takayama, Ikoma, Nara 630-0192, Japan.

    The heterotrimeric G protein alpha q subunit (Galphaq) mediates a variety of cell functions by activating the effector molecule phospholipase Cbeta. Galphaq activity is regulated by G protein betagamma subunits, G protein-coupled receptors, RGS proteins, and Ric-8. In this study, we identified the lipid raft resident proteins, flotillin-1/reggie-2 and flotillin-2/reggie-1, as Galphaq-binding proteins. The interactions of Galphaq and flotillins were independent of the nucleotide-binding state of Galphaq, and the N-terminal portion of flotillins was critical for the interaction. A short interfering RNA-mediated knockdown of flotillins, particularly flotillin-2, attenuated the UTP-induced activation of p38 mitogen-activated protein kinase (MAPK) but not that of ERK1/2. The activation of p38 MAPK was inhibited by the Src family tyrosine kinase inhibitor PP2 and the cholesterol-depleting agent methyl-beta-cyclodextrin, which is generally used for the disruption of lipid rafts. In contrast, the activation of ERK1/2 was not inhibited by these compounds. These lines of evidence suggested that a Gq-coupled receptor activates specifically p38 MAPK through lipid rafts and Src kinase activation, in which flotillins positively modulate the Gq signaling.

    Cellular signalling 2007;19;6;1301-8

  • Arginase-flotillin interaction brings arginase to red blood cell membrane.

    Jiang M, Ding Y, Su Y, Hu X, Li J and Zhang Z

    Department of Physiology and Biophysics, School of Life Sciences, Fudan University, Shanghai 200433, China.

    Flotillin-1 and arginase are both up-regulated in red blood cell membrane of type 2 diabetic patients. For studying why the soluble arginase can bind to the membrane and whether such binding would modify arginase activity, the arginase1 and related proteins were cloned and expressed. The results showed that flotillin-1 can interact with arginase1, and hence arginase activity was up-regulated by 26.8%. It was estimated that about 61% of arginase1 is bound to the membrane mediated by flotillin-1. The arginase activity in diabetic patients was significantly higher than that of the controls (752.4+/-38.5 U/mg protein vs 486.7+/-28.7 U/mg protein).

    FEBS letters 2006;580;28-29;6561-4

  • Proteomic and bioinformatic characterization of the biogenesis and function of melanosomes.

    Chi A, Valencia JC, Hu ZZ, Watabe H, Yamaguchi H, Mangini NJ, Huang H, Canfield VA, Cheng KC, Yang F, Abe R, Yamagishi S, Shabanowitz J, Hearing VJ, Wu C, Appella E and Hunt DF

    Department of Chemistry, University of Virginia, Charlottesville, Virginia 22904, USA.

    Melanin, which is responsible for virtually all visible skin, hair, and eye pigmentation in humans, is synthesized, deposited, and distributed in subcellular organelles termed melanosomes. A comprehensive determination of the protein composition of this organelle has been obstructed by the melanin present. Here, we report a novel method of removing melanin that includes in-solution digestion and immobilized metal affinity chromatography (IMAC). Together with in-gel digestion, this method has allowed us to characterize melanosome proteomes at various developmental stages by tandem mass spectrometry. Comparative profiling and functional characterization of the melanosome proteomes identified approximately 1500 proteins in melanosomes of all stages, with approximately 600 in any given stage. These proteins include 16 homologous to mouse coat color genes and many associated with human pigmentary diseases. Approximately 100 proteins shared by melanosomes from pigmented and nonpigmented melanocytes define the essential melanosome proteome. Proteins validated by confirming their intracellular localization include PEDF (pigment-epithelium derived factor) and SLC24A5 (sodium/potassium/calcium exchanger 5, NCKX5). The sharing of proteins between melanosomes and other lysosome-related organelles suggests a common evolutionary origin. This work represents a model for the study of the biogenesis of lysosome-related organelles.

    Funded by: NCRR NIH HHS: RR01744; NHGRI NIH HHS: U01-HG02712; NICHD NIH HHS: HD40179; NIGMS NIH HHS: GM 37537

    Journal of proteome research 2006;5;11;3135-44

  • The intracellular domain of amyloid precursor protein interacts with flotillin-1, a lipid raft protein.

    Chen TY, Liu PH, Ruan CT, Chiu L and Kung FL

    School of Pharmacy, National Taiwan University, Taipei 10051, Taiwan, ROC.

    Amyloid beta (Abeta) is a pathological hallmark of Alzheimer's disease (AD). It is derived from the amyloid precursor protein (APP) by two sequential proteolytic cleavages, which also generate the APP intracellular domain (AICD). The precise cellular function(s) of AICD still remain obscure. To elucidate the roles of AICD in the development of AD, a yeast two-hybrid system was used to screen a human brain cDNA library for proteins interacting directly with AICD. One of the potential AICD-interacting proteins identified from our screening result is a lipid raft-associated protein, flotillin-1. The interaction was confirmed by glutathione S-transferase pull-down and coimmunoprecipitation studies. Since lipid raft has been suggested to play an important role in signal transduction as well as the pathogenic development of neurodegenerative diseases, it is proposed that flotillin-1 may recruit APP to lipid rafts and therefore participate in the localization and processing of APP.

    Biochemical and biophysical research communications 2006;342;1;266-72

  • Flotillin-1 defines a clathrin-independent endocytic pathway in mammalian cells.

    Glebov OO, Bright NA and Nichols BJ

    MRC Laboratory of Molecular Biology, Hills Road, Cambridge CB2 2QH, UK.

    Previous studies provide evidence for an endocytic mechanism in mammalian cells that is distinct from both clathrin-coated pits and caveolae, and is not inhibited by overexpression of GTPase-null dynamin mutants. This mechanism, however, has been defined largely in these negative terms. We applied a ferro-fluid-based purification of endosomes to identify endosomal proteins. One of the proteins identified in this way was flotillin-1 (also called reggie-2). Here, we show that flotillin-1 resides in punctate structures within the plasma membrane and in a specific population of endocytic intermediates. These intermediates accumulate both glycosylphosphatidylinositol (GPI)-linked proteins and cholera toxin B subunit. Endocytosis in flotillin-1-containing intermediates is clathrin-independent. Total internal reflection microscopy and immuno-electron microscopy revealed that flotillin-1-containing regions of the plasma membrane seem to bud into the cell, and are distinct from clathrin-coated pits and caveolin-1-positive caveolae. Flotillin-1 small interfering RNA (siRNA) inhibited both clathrin-independent uptake of cholera toxin and endocytosis of a GPI-linked protein. We propose that flotillin-1 is one determinant of a clathrin-independent endocytic pathway in mammalian cells.

    Funded by: Medical Research Council: MC_U105178778

    Nature cell biology 2006;8;1;46-54

  • Identification of flotillin-1 as a protein interacting with myocilin: implications for the pathogenesis of primary open-angle glaucoma.

    Joe MK, Sohn S, Choi YR, Park H and Kee C

    Department of Ophthalmology, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Republic of Korea.

    Mutations in MYOC gene encoding myocilin are responsible for primary open-angle glaucoma (POAG). In order to search for protein(s) that can interact with myocilin, we screened a human skeletal muscle cDNA library using yeast two-hybrid system and identified flotillin-1, a structural protein of lipid raft that is detergent-resistant and a liquid ordered microdomain, as a protein interacting with myocilin. The interaction was confirmed by in vitro glutathione S-transferase pulldown and in vivo co-immunoprecipitation studies. In yeast two-hybrid assay, the C-terminus of myocilin, an olfactomedin-like domain in which most mutations related to POAG are scattered, was found to be necessary and sufficient for the interaction. However, myocilins with mutations such as G364V, K423E, and Y437H on the domain failed to interact with flotillin-1. Although the physiological significance of the interaction has yet to be elucidated, our results showed that the alteration of the interaction by mutations in MYOC might be a key factor of the pathogenesis of POAG.

    Biochemical and biophysical research communications 2005;336;4;1201-6

  • Towards a proteome-scale map of the human protein-protein interaction network.

    Rual JF, Venkatesan K, Hao T, Hirozane-Kishikawa T, Dricot A, Li N, Berriz GF, Gibbons FD, Dreze M, Ayivi-Guedehoussou N, Klitgord N, Simon C, Boxem M, Milstein S, Rosenberg J, Goldberg DS, Zhang LV, Wong SL, Franklin G, Li S, Albala JS, Lim J, Fraughton C, Llamosas E, Cevik S, Bex C, Lamesch P, Sikorski RS, Vandenhaute J, Zoghbi HY, Smolyar A, Bosak S, Sequerra R, Doucette-Stamm L, Cusick ME, Hill DE, Roth FP and Vidal M

    Center for Cancer Systems Biology and Department of Cancer Biology, Dana-Farber Cancer Institute, Harvard Medical School, 44 Binney Street, Boston, Massachusetts 02115, USA.

    Systematic mapping of protein-protein interactions, or 'interactome' mapping, was initiated in model organisms, starting with defined biological processes and then expanding to the scale of the proteome. Although far from complete, such maps have revealed global topological and dynamic features of interactome networks that relate to known biological properties, suggesting that a human interactome map will provide insight into development and disease mechanisms at a systems level. Here we describe an initial version of a proteome-scale map of human binary protein-protein interactions. Using a stringent, high-throughput yeast two-hybrid system, we tested pairwise interactions among the products of approximately 8,100 currently available Gateway-cloned open reading frames and detected approximately 2,800 interactions. This data set, called CCSB-HI1, has a verification rate of approximately 78% as revealed by an independent co-affinity purification assay, and correlates significantly with other biological attributes. The CCSB-HI1 data set increases by approximately 70% the set of available binary interactions within the tested space and reveals more than 300 new connections to over 100 disease-associated proteins. This work represents an important step towards a systematic and comprehensive human interactome project.

    Funded by: NCI NIH HHS: R33 CA132073; NHGRI NIH HHS: P50 HG004233, R01 HG001715, RC4 HG006066, U01 HG001715; NHLBI NIH HHS: U01 HL098166

    Nature 2005;437;7062;1173-8

  • A human protein-protein interaction network: a resource for annotating the proteome.

    Stelzl U, Worm U, Lalowski M, Haenig C, Brembeck FH, Goehler H, Stroedicke M, Zenkner M, Schoenherr A, Koeppen S, Timm J, Mintzlaff S, Abraham C, Bock N, Kietzmann S, Goedde A, Toksöz E, Droege A, Krobitsch S, Korn B, Birchmeier W, Lehrach H and Wanker EE

    Max Delbrueck Center for Molecular Medicine, 13092 Berlin-Buch, Germany.

    Protein-protein interaction maps provide a valuable framework for a better understanding of the functional organization of the proteome. To detect interacting pairs of human proteins systematically, a protein matrix of 4456 baits and 5632 preys was screened by automated yeast two-hybrid (Y2H) interaction mating. We identified 3186 mostly novel interactions among 1705 proteins, resulting in a large, highly connected network. Independent pull-down and co-immunoprecipitation assays validated the overall quality of the Y2H interactions. Using topological and GO criteria, a scoring system was developed to define 911 high-confidence interactions among 401 proteins. Furthermore, the network was searched for interactions linking uncharacterized gene products and human disease proteins to regulatory cellular pathways. Two novel Axin-1 interactions were validated experimentally, characterizing ANP32A and CRMP1 as modulators of Wnt signaling. Systematic human protein interaction screens can lead to a more comprehensive understanding of protein function and cellular processes.

    Cell 2005;122;6;957-68

  • Expression, purification, and characterization of recombinant human flotillin-1 in Escherichia coli.

    Ding Y, Jiang M, Jiang W, Su Y, Zhou H, Hu X and Zhang Z

    Department of Physiology and Biophysics, School of Life Sciences, Fudan University, Shanghai, China.

    Human flotillin-1 (reggie-2), a major hydrophobic protein of biomembrane microdomain lipid rafts, was cloned and expressed in Escherichia coli with four different fusion tags (hexahistidine, glutathione S-transferase, NusA, and thioredoxin) to increase the yield. The best expressed flotillin-1 with thioredoxin tag was solubilized from inclusion bodies, first purified by immobilized metal affinity column under denaturing condition and direct refolded on column by decreasing urea gradient method. The thioredoxin tag was cleaved by thrombin, and the flotillin-1 protein was further purified by anion exchanger and gel filtration column. The purified protein was verified by denaturing gel electrophoresis and Western blot. The typical yield was 3.4 mg with purity above 98% from 1L culture medium. Using pull-down assay, the interaction of both the recombinant flotillin-1 and the native flotillin-1 from human erythrocyte membranes with c-Cbl-associated protein or neuroglobin was confirmed, which demonstrated that the recombinant proteins were functional active. This is the first report describing expression, purification, and characterization of active recombinant raft specific protein in large quantity and highly purity, which would facilitate further research such as X-ray crystallography.

    Protein expression and purification 2005;42;1;137-45

  • Yeast two-hybrid identification of prostatic proteins interacting with human sex hormone-binding globulin.

    Pope SN and Lee IR

    School of Biomedical Sciences, Curtin University of Technology, G.P.O. Box U1987, Perth, WA 6845, Australia.

    Yeast two-hybrid (Y2H) screening of a prostate cDNA library with the cDNA for sex hormone-binding globulin (SHBG) has been used to identify proteins through which SHBG may exert autocrine or paracrine effects on sex steroid target tissues. The library screen gave 230 positive interactions of which around 60 have been sequenced. Of the proteins identified to date from database (BLAST) searches of these sequences, SHBG is one of those occurring most frequently. Amongst the proteins of interest are the membrane-associated proteins flotillin-1 and PRV-1, the enzymes cathepsin D, kallikrein 4 and acid phosphatase, various metallothioneins and translation elongation factor 1 alpha. The significance of the interaction of SHBG with these proteins is discussed.

    The Journal of steroid biochemistry and molecular biology 2005;94;1-3;203-8

  • Association of ABCA1 with syntaxin 13 and flotillin-1 and enhanced phagocytosis in tangier cells.

    Bared SM, Buechler C, Boettcher A, Dayoub R, Sigruener A, Grandl M, Rudolph C, Dada A and Schmitz G

    Institute of Clinical Chemistry and Laboratory Medicine, University of Regensburg, 93040 Regensburg, Germany.

    The ATP-binding cassette transporter A1 (ABCA1) facilitates the cellular release of cholesterol and choline-phospholipids to apolipoprotein A-I (apoA-I) and several studies indicate that vesicular transport is associated with ABCA1 function. Syntaxins play a major role in vesicular fusion and have also been demonstrated to interact with members of the ABC-transporter family. Therefore, we focused on the identification of syntaxins that directly interact with ABCA1. The expression of syntaxins and ABCA1 in cultured human monocytes during M-CSF differentiation and cholesterol loading was investigated and syntaxins 3, 6, and 13 were found induced in foam cells together with ABCA1. Immunoprecipitation experiments revealed a direct association of syntaxin 13 and full-length ABCA1, whereas syntaxin 3 and 6 failed to interact with ABCA1. The colocalization of ABCA1 and syntaxin 13 was also shown by immunofluorescence microscopy. Silencing of syntaxin 13 by small interfering RNA (siRNA) led to reduced ABCA1 protein levels and hence to a significant decrease in apoA-I-dependent choline-phospholipid efflux. ABCA1 is localized in Lubrol WX-insoluble raft microdomains in macrophages and syntaxin 13 and flotillin-1 were also detected in these detergent resistant microdomains along with ABCA1. Syntaxin 13, flotillin-1, and ABCA1 were identified as phagosomal proteins, indicating the involvement of the phagosomal compartment in ABCA1-mediated lipid efflux. In addition, the uptake of latex phagobeads by fibroblasts with mutated ABCA1 was enhanced when compared with control cells and the recombinant expression of functional ABCA1 normalized the phagocytosis rate in Tangier fibroblasts. It is concluded that ABCA1 forms a complex with syntaxin 13 and flotillin-1, residing at the plasma membrane and in phagosomes that are partially located in raft microdomains.

    Molecular biology of the cell 2004;15;12;5399-407

  • D1 dopamine receptor signaling involves caveolin-2 in HEK-293 cells.

    Yu P, Yang Z, Jones JE, Wang Z, Owens SA, Mueller SC, Felder RA and Jose PA

    Department of Pediatrics, Georgetown University School of Medicine, Washington, D.C., USA. yup@georgetown.edu

    Background: Dopamine receptors in the kidney, especially those belonging to the D1-like receptor family, are important in the regulation of renal function and blood pressure. Because of increasing evidence that G protein-coupled receptors (GPCRs) are associated with caveolae and lipid rafts, we tested the hypothesis that the D1 dopamine receptor (D1R) and signaling molecules are regulated by caveolin in caveolae or lipid rafts.

    Methods: Six experimental approaches were used: (1) construction of tagged human D1Rs (hD1Rs) and transfectants; (2) cell culture [human embryonic kidney (HEK)-293 and immortalized rat renal proximal tubule cells] and biotinylation; (3) cell fractionation by sucrose gradient centrifugation; (4) immunoprecipitation and immunoblotting; (5) immunofluorescence and confocal microscopy; and (6) adenylyl cyclase assays.

    Results: hD1Rs, heterologously expressed in HEK-293 cells, formed protein species with molecular mass ranging from 50 to 250 kD, and were localized in lipid rafts and nonraft plasma membranes. The hD1Rs cofractionated with caveolin-2, G protein subunits, and several signaling molecules. Both exogenously expressed hD1Rs and endogenously expressed rat D1Rs colocalized and coimmunoprecipitated with caveolin-2. A D1R agonist (fenoldopam) increased the amount of caveolin-2beta associated with hD1Rs and activated adenylyl cyclase to a greater extent in lipid rafts than in nonraft plasma membranes. Reduction in the expression of caveolin-2 with antisense oligonucleotides attenuated the stimulatory effect of fenoldopam on cyclic adenosine monophosphate (cAMP) accumulation.

    Conclusion: The majority of hD1Rs are distributed in lipid rafts. Heterologously and endogenously expressed D1Rs in renal cells are associated with and regulated by caveolin-2.

    Funded by: NCI NIH HHS: 2P30-CA-51008; NCRR NIH HHS: 1S10 RR15768-01; NHLBI NIH HHS: HL23081, HL68686, HL74940; NIDDK NIH HHS: DK39308, DK52612

    Kidney international 2004;66;6;2167-80

  • The status, quality, and expansion of the NIH full-length cDNA project: the Mammalian Gene Collection (MGC).

    Gerhard DS, Wagner L, Feingold EA, Shenmen CM, Grouse LH, Schuler G, Klein SL, Old S, Rasooly R, Good P, Guyer M, Peck AM, Derge JG, Lipman D, Collins FS, Jang W, Sherry S, Feolo M, Misquitta L, Lee E, Rotmistrovsky K, Greenhut SF, Schaefer CF, Buetow K, Bonner TI, Haussler D, Kent J, Kiekhaus M, Furey T, Brent M, Prange C, Schreiber K, Shapiro N, Bhat NK, Hopkins RF, Hsie F, Driscoll T, Soares MB, Casavant TL, Scheetz TE, Brown-stein MJ, Usdin TB, Toshiyuki S, Carninci P, Piao Y, Dudekula DB, Ko MS, Kawakami K, Suzuki Y, Sugano S, Gruber CE, Smith MR, Simmons B, Moore T, Waterman R, Johnson SL, Ruan Y, Wei CL, Mathavan S, Gunaratne PH, Wu J, Garcia AM, Hulyk SW, Fuh E, Yuan Y, Sneed A, Kowis C, Hodgson A, Muzny DM, McPherson J, Gibbs RA, Fahey J, Helton E, Ketteman M, Madan A, Rodrigues S, Sanchez A, Whiting M, Madari A, Young AC, Wetherby KD, Granite SJ, Kwong PN, Brinkley CP, Pearson RL, Bouffard GG, Blakesly RW, Green ED, Dickson MC, Rodriguez AC, Grimwood J, Schmutz J, Myers RM, Butterfield YS, Griffith M, Griffith OL, Krzywinski MI, Liao N, Morin R, Morrin R, Palmquist D, Petrescu AS, Skalska U, Smailus DE, Stott JM, Schnerch A, Schein JE, Jones SJ, Holt RA, Baross A, Marra MA, Clifton S, Makowski KA, Bosak S, Malek J and MGC Project Team

    The National Institutes of Health's Mammalian Gene Collection (MGC) project was designed to generate and sequence a publicly accessible cDNA resource containing a complete open reading frame (ORF) for every human and mouse gene. The project initially used a random strategy to select clones from a large number of cDNA libraries from diverse tissues. Candidate clones were chosen based on 5'-EST sequences, and then fully sequenced to high accuracy and analyzed by algorithms developed for this project. Currently, more than 11,000 human and 10,000 mouse genes are represented in MGC by at least one clone with a full ORF. The random selection approach is now reaching a saturation point, and a transition to protocols targeted at the missing transcripts is now required to complete the mouse and human collections. Comparison of the sequence of the MGC clones to reference genome sequences reveals that most cDNA clones are of very high sequence quality, although it is likely that some cDNAs may carry missense variants as a consequence of experimental artifact, such as PCR, cloning, or reverse transcriptase errors. Recently, a rat cDNA component was added to the project, and ongoing frog (Xenopus) and zebrafish (Danio) cDNA projects were expanded to take advantage of the high-throughput MGC pipeline.

    Funded by: PHS HHS: N01-C0-12400

    Genome research 2004;14;10B;2121-7

  • Human neuroglobin interacts with flotillin-1, a lipid raft microdomain-associated protein.

    Wakasugi K, Nakano T, Kitatsuji C and Morishima I

    Department of Molecular Engineering, Graduate School of Engineering, Kyoto University, Kyoto, Japan. kei@wakasugi.mbox.media.kyoto-u.ac.jp

    Neuroglobin (Ngb) is a newly discovered vertebrate globin that is expressed in the brain and that can reversibly bind oxygen. It has been reported that Ngb levels increase in neurons in response to oxygen deprivation, and that it protects neurons from hypoxia. However, the mechanism of this neuroprotection remains unclear. Recently, we found that oxidized human Ngb bound to the alpha-subunits of heterotrimeric G proteins (Galpha) and acted as a guanine nucleotide dissociation inhibitor for Galpha. To identify other Ngb-binding proteins, we herein screened a human brain cDNA library by using a yeast two-hybrid system. Among the plasmids isolated from positive clones, one contained an insert with 100% sequence identity to human flotillin-1. The interaction of Ngb with flotillin-1 was confirmed by glutathione S-transferase pull-down experiments. Since Galpha exists within lipid rafts critical for signal transduction and flotillin-1 recruits signaling proteins to lipid rafts, flotillin-1 might recruit Ngb to lipid rafts as a means of preventing neuronal death.

    Biochemical and biophysical research communications 2004;318;2;453-60

  • Recruitment of Pyk2 and Cbl to lipid rafts mediates signals important for actin reorganization in growing neurites.

    Haglund K, Ivankovic-Dikic I, Shimokawa N, Kruh GD and Dikic I

    Institute for Biochemistry II, Building 75, Goethe University Medical School, Theodor-Stern-Kai 7, 60590 Frankfurt am Main, Germany.

    Protein tyrosine kinase Pyk2 and multifunctional adaptor protein Cbl are implicated in the regulation of the cytoskeleton in several cell types. We report that Pyk2 and Cbl form a signaling complex that is translocated to lipid rafts and is enriched in growth cones of differentiating PC12 cells following growth factor stimulation. We found that Pyk2 and Cbl interacted with the adaptor protein ArgBP2, which also bound to flotillin-1, a component of lipid raft microdomains. These interactions contributed to recruitment of the Pyk2/Cbl complex to lipid raft compartments. In addition, Pyk2, Cbl and ArgBP2 were found co-localized with actin in axons and growth cones of differentiated PC12 cells. Moreover, co-expression of Pyk2, ArgBP2 and Cbl facilitated growth factor-induced formation of lamellipodia at the tip of neurites. Formation of these growth cone lamellipodia was dependent on intact lipid rafts and the Cbl-associated effectors Crk and phosphatidylinositol 3 (PI 3)-kinase. Our results indicate that recruitment of Pyk2/Cbl complexes to lipid rafts participates in growth factor-induced regulation of the actin cytoskeleton in growing neurites.

    Journal of cell science 2004;117;Pt 12;2557-68

  • Flotillin-1 in the substantia nigra of the Parkinson brain and a predominant localization in catecholaminergic nerves in the rat brain.

    Jacobowitz DM and Kallarakal AT

    Laboratory of Clinical Science, NIMH, NIH, Bethesda, MD 20892, USA. dwj@helix.nih.gov

    The substantia nigra cells of a normal and Parkinson's disease human brain were obtained by the micropunch procedure and total RNA was isolated. Differential display RT-PCR of the total RNA revealed differentially expressed cDNAs that were identified by sequencing. This resulted in the identification of a panel of known and unknown differentially expressed genes. Complex I (NADH ubiquinone oxidoreductase) and Complex IV (cytochrome oxidase) whose expressions are decreased in Parkinson's disease were reduced in the Parkinson brain. Of the various differentially expressed genes, flotillin-1, also known as reggie-2, was of great interest to us. It is a relatively new protein which is an integral membrane component of lipid rafts and has been implicated in signal transduction pathway events. In situ hybridization histochemical studies with human and rat brain sections revealed the presence of this mRNA in discrete neuronal (and possibly glial) cells of the substantia nigra, locus coeruleus, cortex, hippocampus, hypothalamus, thalamus, motor nuclei, nucleus basalis, raphe nucleus, and other brain regions. Immunohistochemical studies revealed that flotillin-1 is not present in all the regions where the message was found. In the rat brain, the most prominent observation was the revelation of all catecholamine cells (dopamine, norepinephrine, epinephrine) by the flotillin-1 antibody (1:100 dilution). At a more concentrated dilution (1:10) other neuronal cells (e.g., cortex, thalamus, hindbrain) were observed. At both dilutions dense dopaminergic fibers were observed in the rat caudate-putamen, nigrostriatal tract, and substantia nigra. It is significant that there is an increased gene expression of flotillin-1 in the Parkinson substantia nigra/ventral tegmental area. The role of flotillin in these cells is unclear although it is interesting that the reggie-2/flotillin-1 gene was upregulated during retinal axon regeneration in the goldfish visual pathway (Schulte et al., Development 124:577-87, 1997) which suggests that flotillin-1/reggie-2 might play a role in axonal growth from the remaining substantia nigra cells of the Parkinson brain.

    Neurotoxicity research 2004;6;4;245-57

  • [Lipid rafts, flotillin-1 and Alzheimer disease].

    Girardot N, Allinquant B and Duyckaerts C

    Laboratoire de Neuropathologie Raymond Escourolle et Inserm U106, Hôpital de La Salpêtrière, Paris.

    A beta peptide accumulates in the extracellular space during Alzheimer's disease. It is the cleavage product of APP (Amyloid Precursor Protein), a large transmembrane protein. After ultracentrifugation, APP is found in a low-density fraction, enriched in cholesterol. These properties are characteristic of lipid rafts, which are microdomains that "float" like rafts on the plasma membrane. We have confirmed the presence of cholesterol in the core of the senile plaque, using the fluorescent probe filipin. In addition, we have shown that flotillin-1, a marker of rafts, accumulated in lysosomes of neurons in Alzheimer's disease. In most cases (76% of the flotillin-1 positive neurons), the accumulation was associated with the presence of neurofibrillary tangles. Our data suggest that the A beta peptide, which is poorly soluble in water, is actually linked with cholesterol, possibly from cellular membranes, in the extracellular space.

    Journal de la Societe de biologie 2003;197;3;223-9

  • Glycosylphosphatidyl inositol-anchored proteins and fyn kinase assemble in noncaveolar plasma membrane microdomains defined by reggie-1 and -2.

    Stuermer CA, Lang DM, Kirsch F, Wiechers M, Deininger SO and Plattner H

    Department of Biology, University of Konstanz, 78467 Konstanz, Germany. claudia.stuermer@uni.konstanz.de

    Using confocal laser scanning and double immunogold electron microscopy, we demonstrate that reggie-1 and -2 are colocalized in < or =0.1-microm plasma membrane microdomains of neurons and astrocytes. In astrocytes, reggie-1 and -2 do not occur in caveolae but clearly outside these structures. Microscopy and coimmunoprecipitation show that reggie-1 and -2 are associated with fyn kinase and with the glycosylphosphatidyl inositol-anchored proteins Thy-1 and F3 that, when activated by antibody cross-linking, selectively copatch with reggie. Jurkat cells, after cross-linking of Thy-1 or GM1 (with the use of cholera toxin), exhibit substantial colocalization of reggie-1 and -2 with Thy-1, GM1, the T-cell receptor complex and fyn. This, and the accumulation of reggie proteins in detergent-resistant membrane fractions containing F3, Thy-1, and fyn imparts to reggie-1 and -2 properties of raft-associated proteins. It also suggests that reggie-1 and -2 participate in the formation of signal transduction centers. In addition, we find reggie-1 and -2 in endolysosomes. In Jurkat cells, reggie-1 and -2 together with fyn and Thy-1 increase in endolysosomes concurrent with a decrease at the plasma membrane. Thus, reggie-1 and -2 define raft-related microdomain signaling centers in neurons and T cells, and the protein complex involved in signaling becomes subject to degradation.

    Molecular biology of the cell 2001;12;10;3031-45

  • The sorbin homology domain: a motif for the targeting of proteins to lipid rafts.

    Kimura A, Baumann CA, Chiang SH and Saltiel AR

    Department of Internal Medicine and Physiology, Life Sciences Institute, University of Michigan Medical Center, Ann Arbor, MI 48109, USA.

    On phosphorylation of Cbl, the c-Cbl-associated protein (CAP)/Cbl complex dissociates from the insulin receptor and translocates to a lipid raft membrane fraction to form a ternary complex with flotillin. Deletion analyses of the CAP gene identified a 115-aa region responsible for flotillin binding. This region is homologous to the peptide sorbin and is referred to as the sorbin homology (SoHo) domain. This domain is present in two other proteins, vinexin and ArgBP2. Vinexin also interacted with flotillin, and deletion of its SoHo domain similarly blocked flotillin binding. The overexpression of a CAP mutant in which the SoHo domain had been deleted (CAPDeltaSoHo) prevented the translocation of Cbl to lipid rafts and subsequently blocked the recruitment of CrkII and C3G. Moreover, overexpression of CAPDeltaSoHo prevented the stimulation of glucose transport and GLUT4 translocation by insulin. These results suggest a mechanism for localization of signaling proteins to the lipid raft that mediates the compartmentalization of crucial signal transduction pathways.

    Proceedings of the National Academy of Sciences of the United States of America 2001;98;16;9098-103

  • Stomatin, flotillin-1, and flotillin-2 are major integral proteins of erythrocyte lipid rafts.

    Salzer U and Prohaska R

    Institute of Medical Biochemistry, University of Vienna, Vienna Biocenter, Vienna, Austria.

    Lipid rafts are sphingolipid- and cholesterol-rich membrane microdomains that are insoluble in nonionic detergents, have a low buoyant density, and preferentially contain lipid-modified proteins, like glycosyl phosphatidylinositol (GPI)-anchored proteins. The lipid rafts were isolated from human erythrocytes and major protein components were identified. Apart from the GPI-anchored proteins, the most abundant integral proteins were found to be the distantly related membrane proteins stomatin (band 7.2b), flotillin-1, and flotillin-2. Flotillins, already described as lipid raft components in neurons and caveolae-associated proteins in A498 kidney cells, have not been recognized as red cell components yet. In addition, it was shown that the major cytoskeletal proteins, spectrin, actin, band 4.1, and band 4.2, are partly associated with the lipid rafts. Stomatin and the flotillins are present as independently organized high-order oligomers, suggesting that these complexes act as separate scaffolding components at the cytoplasmic face of erythrocyte lipid rafts.

    Blood 2001;97;4;1141-3

  • Flotillin-1: gene structure: cDNA cloning from human lung and the identification of alternative polyadenylation signals.

    Edgar AJ and Polak JM

    Department of Histochemistry, Division of Investigative Science, Commonwealth Building, Hammersmith Campus, Imperial College School of Medicine, Du Cane Road, London W12 0NN, UK. alasdair.edgar@ic.ac.uk

    To identify changes in gene expression associated with emphysema, differential display was used to compare RNA extracted from emphysematous lung with that of unused donor tissue taken at the time of transplant. Two expressed clones with sequence homology to the 3' UTR of the murine flotillin-1 cDNA were identified. Flotillin-1 is a plasma membrane protein, which has been associated with detergent-insoluble glycolipid-rich domains and the formation of caveolae. One clone was 95 bp longer than the other. It arose from the use of a second polyadenylation signal and its existence was not due to differential expression nor to polymorphisms in the human flotillin-1 sequence. The 1839 bp human flotillin-1 sequence was completed by 5' RACE from a lung cDNA library. The human mRNA has a 1.9 kbase transcript being highly expressed in brain, heart and lung. The single copy flotillin-1 gene is located at 6p21.3 in the MHC class I region and consists of 13 exons over 15 kb. The ORF encodes a 427 residue protein with a molecular mass 47355 Da, and an isoelectric point 7.08. Human flotillin-1 has a 98% identity with the murine protein and a 47% identity with human flotillin-2. Flotillin-1 belongs to the Band 7.2/stomatin protein family, possessing a hydrophobic N-terminal region, predicted to form a single, outside to inside, transmembrane domain. The long central alpha-helical domain may form a coiled-coil. We have isolated and characterised a cDNA encoding the human flotillin-1 gene, which may play an important role in raft formation.

    The international journal of biochemistry & cell biology 2001;33;1;53-64

  • Cloning and functional analysis of cDNAs with open reading frames for 300 previously undefined genes expressed in CD34+ hematopoietic stem/progenitor cells.

    Zhang QH, Ye M, Wu XY, Ren SX, Zhao M, Zhao CJ, Fu G, Shen Y, Fan HY, Lu G, Zhong M, Xu XR, Han ZG, Zhang JW, Tao J, Huang QH, Zhou J, Hu GX, Gu J, Chen SJ and Chen Z

    Shanghai Institute of Hematology (SIH), Rui Jin Hospital affiliated with Shanghai Second Medical University, Shanghai 200025, China.

    Three hundred cDNAs containing putatively entire open reading frames (ORFs) for previously undefined genes were obtained from CD34+ hematopoietic stem/progenitor cells (HSPCs), based on EST cataloging, clone sequencing, in silico cloning, and rapid amplification of cDNA ends (RACE). The cDNA sizes ranged from 360 to 3496 bp and their ORFs coded for peptides of 58-752 amino acids. Public database search indicated that 225 cDNAs exhibited sequence similarities to genes identified across a variety of species. Homology analysis led to the recognition of 50 basic structural motifs/domains among these cDNAs. Genomic exon-intron organization could be established in 243 genes by integration of cDNA data with genome sequence information. Interestingly, a new gene named as HSPC070 on 3p was found to share a sequence of 105bp in 3' UTR with RAF gene in reversed transcription orientation. Chromosomal localizations were obtained using electronic mapping for 192 genes and with radiation hybrid (RH) for 38 genes. Macroarray technique was applied to screen the gene expression patterns in five hematopoietic cell lines (NB4, HL60, U937, K562, and Jurkat) and a number of genes with differential expression were found. The resource work has provided a wide range of information useful not only for expression genomics and annotation of genomic DNA sequence, but also for further research on the function of genes involved in hematopoietic development and differentiation.

    Genome research 2000;10;10;1546-60

  • CAP defines a second signalling pathway required for insulin-stimulated glucose transport.

    Baumann CA, Ribon V, Kanzaki M, Thurmond DC, Mora S, Shigematsu S, Bickel PE, Pessin JE and Saltiel AR

    Department of Physiology, University of Michigan School of Medicine, Ann Arbor, Michigan 48109, USA.

    Insulin stimulates the transport of glucose into fat and muscle cells. Although the precise molecular mechanisms involved in this process remain uncertain, insulin initiates its actions by binding to its tyrosine kinase receptor, leading to the phosphorylation of intracellular substrates. One such substrate is the Cbl proto-oncogene product. Cbl is recruited to the insulin receptor by interaction with the adapter protein CAP, through one of three adjacent SH3 domains in the carboxy terminus of CAP. Upon phosphorylation of Cbl, the CAP-Cbl complex dissociates from the insulin receptor and moves to a caveolin-enriched, triton-insoluble membrane fraction. Here, to identify a molecular mechanism underlying this subcellular redistribution, we screened a yeast two-hybrid library using the amino-terminal region of CAP and identified the caveolar protein flotillin. Flotillin forms a ternary complex with CAP and Cbl, directing the localization of the CAP-Cbl complex to a lipid raft subdomain of the plasma membrane. Expression of the N-terminal domain of CAP in 3T3-L1 adipocytes blocks the stimulation of glucose transport by insulin, without affecting signalling events that depend on phosphatidylinositol-3-OH kinase. Thus, localization of the Cbl-CAP complex to lipid rafts generates a pathway that is crucial in the regulation of glucose uptake.

    Nature 2000;407;6801;202-7

  • Gene expression profiling in the human hypothalamus-pituitary-adrenal axis and full-length cDNA cloning.

    Hu RM, Han ZG, Song HD, Peng YD, Huang QH, Ren SX, Gu YJ, Huang CH, Li YB, Jiang CL, Fu G, Zhang QH, Gu BW, Dai M, Mao YF, Gao GF, Rong R, Ye M, Zhou J, Xu SH, Gu J, Shi JX, Jin WR, Zhang CK, Wu TM, Huang GY, Chen Z, Chen MD and Chen JL

    Rui-Jin Hospital, Shanghai Institute of Endocrinology, Shanghai Second Medical University, China.

    The primary neuroendocrine interface, hypothalamus and pituitary, together with adrenals, constitute the major axis responsible for the maintenance of homeostasis and the response to the perturbations in the environment. The gene expression profiling in the human hypothalamus-pituitary-adrenal axis was catalogued by generating a large amount of expressed sequence tags (ESTs), followed by bioinformatics analysis (http://www.chgc.sh.cn/ database). Totally, 25,973 sequences of good quality were obtained from 31,130 clones (83.4%) from cDNA libraries of the hypothalamus, pituitary, and adrenal glands. After eliminating 5,347 sequences corresponding to repetitive elements and mtDNA, 20,626 ESTs could be assembled into 9, 175 clusters (3,979, 3,074, and 4,116 clusters in hypothalamus, pituitary, and adrenal glands, respectively) when overlapping ESTs were integrated. Of these clusters, 2,777 (30.3%) corresponded to known genes, 4,165 (44.8%) to dbESTs, and 2,233 (24.3%) to novel ESTs. The gene expression profiles reflected well the functional characteristics of the three levels in the hypothalamus-pituitary-adrenal axis, because most of the 20 genes with highest expression showed statistical difference in terms of tissue distribution, including a group of tissue-specific functional markers. Meanwhile, some findings were made with regard to the physiology of the axis, and 200 full-length cDNAs of novel genes were cloned and sequenced. All of these data may contribute to the understanding of the neuroendocrine regulation of human life.

    Proceedings of the National Academy of Sciences of the United States of America 2000;97;17;9543-8

  • Flotillin 2 is distinct from epidermal surface antigen (ESA) and is associated with filopodia formation.

    Hazarika P, Dham N, Patel P, Cho M, Weidner D, Goldsmith L and Duvic M

    Department of Dermatology, University of Texas Medical School and Department of Medical Specialties, Section of Dermatology, MD Anderson Cancer Center, Houston, Texas 77030, USA.

    ECS-1, a monoclonal antibody (MoAb) raised to cultured human keratinocytes, stains the intercellular glycocalyx with a pemphigus-like pattern and recognizes a 35-kDa epidermal surface antigen (ESA) on Western blotting of keratinocyte extracts. When ECS-1 MoAb was used to screen a keratinocyte expression library, a unique cDNA was identified that predicted a 42-kDa globular protein of unknown function. This putative ESA was conserved between mice and humans and was encoded by a gene on chromosome 17q11-12 in linkage with neurofibromin. Homology between the cDNA sequence has been reported with flotillin 1, a caveolae associated protein, as well as Reggie 1 and 2, neuronal proteins expressed during axonal regeneration present in activated GPI-anchored cell adhesion molecules in non-caveolar-associated micropatches. In order to determine whether the cDNA predicted protein and ECS-1 antigen were identical, we compared ECS-1 with the immunoreactivity of a new antibody raised to the cDNA fusion protein in epidermis and cultured cells. The cDNA fusion protein was expressed in bacteria and in cos cells with his, FLAG, and EGFP reporter tags and by stable transfection as an EGFP fusion protein. The fusion protein and native protein of 42 kDa were detected by the new antibody, but not by the original ECS-1. Thus, the ECS-1 antigen, ESA (35 kDa), is clearly distinct from the protein predicted by the cDNA (renamed flotillin 2). Stable transfection of ESA/flotillin 2 fusion protein in cos cells induced filopodia formation and changed epithelial cells to a neuronal appearance. Thus, the function of flotillin 2 may resemble that of the goldfish optic nerve neuronal regeneration proteins, Reggie 1 and 2.

    Funded by: NCI NIH HHS: CA-16672-22

    Journal of cellular biochemistry 1999;75;1;147-59

  • Flotillins/cavatellins are differentially expressed in cells and tissues and form a hetero-oligomeric complex with caveolins in vivo. Characterization and epitope-mapping of a novel flotillin-1 monoclonal antibody probe.

    Volonte D, Galbiati F, Li S, Nishiyama K, Okamoto T and Lisanti MP

    Department of Molecular Pharmacology and The Albert Einstein Cancer Center, Albert Einstein College of Medicine, Bronx, New York 10461, USA.

    Caveolae are vesicular organelles that represent a subcompartment of the plasma membrane. Caveolins and flotillins are two families of mammalian caveolae-associated integral membrane proteins. However, it remains unknown whether flotillins interact with caveolin proteins to form a stable caveolar complex or if expression of flotillins can drive vesicle formation. Here, we examine the cell type and tissue-specific expression of the flotillin gene family. For this purpose, we generated a novel monoclonal antibody probe that recognizes only flotillin-1. A survey of cell and tissue types demonstrates that flotillins 1 and 2 have a complementary tissue distribution. At the cellular level, flotillin-2 was ubiquitously expressed, whereas flotillin-1 was most abundant in A498 kidney cells, muscle cell lines, and fibroblasts. Using three different models of cellular differentiation, we next examined the expression of flotillins 1 and 2. Taken together, our data suggest that the expression levels of flotillins 1 and 2 are independently regulated and does not strictly correlate with known expression patterns of caveolin family members. However, when caveolins and flotillins are co-expressed within the same cell, as in A498 cells, they form a stable hetero-oligomeric "caveolar complex." In support of these observations, we show that heterologous expression of murine flotillin-1 in Sf21 insect cells using baculovirus-based vectors is sufficient to drive the formation of caveolae-like vesicles. These results suggest that flotillins may participate functionally in the formation of caveolae or caveolae-like vesicles in vivo. Thus, flotillin-1 represents a new integral membrane protein marker for the slightly larger caveolae-related domains (50-200 nm) that are observed in cell types that fail to express caveolin-1. As a consequence of these findings, we propose the term "cavatellins" be used (instead of flotillins) to describe this gene family.

    Funded by: NCI NIH HHS: CA-71326, F32 CA071326, R01-CA-80250; NIMH NIH HHS: MH-56036

    The Journal of biological chemistry 1999;274;18;12702-9

  • Construction and characterization of a full length-enriched and a 5'-end-enriched cDNA library.

    Suzuki Y, Yoshitomo-Nakagawa K, Maruyama K, Suyama A and Sugano S

    International and Interdisciplinary Studies, The University of Tokyo, Japan.

    Using 'oligo-capped' mRNA [Maruyama, K., Sugano, S., 1994. Oligo-capping: a simple method to replace the cap structure of eukaryotic mRNAs with oligoribonucleotides. Gene 138, 171-174], whose cap structure was replaced by a synthetic oligonucleotide, we constructed two types of cDNA library. One is a 'full length-enriched cDNA library' which has a high content of full-length cDNA clones and the other is a '5'-end-enriched cDNA library', which has a high content of cDNA clones with their mRNA start sites. The 5'-end-enriched library was constructed especially for isolating the mRNA start sites of long mRNAs. In order to characterize these libraries, we performed one-pass sequencing of randomly selected cDNA clones from both libraries (84 clones for the full length-enriched cDNA library and 159 clones for the 5'-end-enriched cDNA library). The cDNA clones of the polypeptide chain elongation factor 1 alpha were most frequently (nine clones) isolated, and more than 80% of them (eight clones) contained the mRNA start site of the gene. Furthermore, about 80% of the cDNA clones of both libraries whose sequence matched with known genes had the known 5' ends or sequences upstream of the known 5' ends (28 out of 35 for the full length-enriched library and 51 out of 62 for the 5'-end-enriched library). The longest full-length clone of the full length-enriched cDNA library was about 3300 bp (among 28 clones). In contrast, seven clones (out of the 51 clones with the mRNA start sites) from the 5'-end-enriched cDNA library came from mRNAs whose length is more than 3500 bp. These cDNA libraries may be useful for generating 5' ESTs with the information of the mRNA start sites that are now scarce in the EST database.

    Gene 1997;200;1-2;149-56

  • Flotillin and epidermal surface antigen define a new family of caveolae-associated integral membrane proteins.

    Bickel PE, Scherer PE, Schnitzer JE, Oh P, Lisanti MP and Lodish HF

    Whitehead Institute for Biomedical Research, Cambridge, Massachusetts 02142-1479, USA.

    Caveolae are plasmalemmal microdomains that are involved in vesicular trafficking and signal transduction. We have sought to identify novel integral membrane proteins of caveolae. Here we describe the identification and molecular cloning of flotillin. By several independent methods, flotillin behaves as a resident integral membrane protein component of caveolae. Furthermore, we have identified epidermal surface antigen both as a flotillin homologue and as a resident caveolar protein. Significantly, flotillin is a marker for the Triton-insoluble, buoyant membrane fraction in brain, where to date mRNA species for known caveolin gene family members have not been detected.

    Funded by: NHLBI NIH HHS: HL43278; NIDDK NIH HHS: DK02219, DK47618; ...

    The Journal of biological chemistry 1997;272;21;13793-802

  • Oligo-capping: a simple method to replace the cap structure of eukaryotic mRNAs with oligoribonucleotides.

    Maruyama K and Sugano S

    Institute of Medical Science, University of Tokyo, Japan.

    We have devised a method to replace the cap structure of a mRNA with an oligoribonucleotide (r-oligo) to label the 5' end of eukaryotic mRNAs. The method consists of removing the cap with tobacco acid pyrophosphatase (TAP) and ligating r-oligos to decapped mRNAs with T4 RNA ligase. This reaction was made cap-specific by removing 5'-phosphates of non-capped RNAs with alkaline phosphatase prior to TAP treatment. Unlike the conventional methods that label the 5' end of cDNAs, this method specifically labels the capped end of the mRNAs with a synthetic r-oligo prior to first-strand cDNA synthesis. The 5' end of the mRNA was identified quite simply by reverse transcription-polymerase chain reaction (RT-PCR).

    Gene 1994;138;1-2;171-4

Gene lists (6)

Gene List Source Species Name Description Gene count
L00000009 G2C Homo sapiens Human PSD Human orthologues of mouse PSD adapted from Collins et al (2006) 1080
L00000016 G2C Homo sapiens Human PSP Human orthologues of mouse PSP adapted from Collins et al (2006) 1121
L00000059 G2C Homo sapiens BAYES-COLLINS-HUMAN-PSD-CONSENSUS Human cortex PSD consensus 748
L00000061 G2C Homo sapiens BAYES-COLLINS-MOUSE-PSD-CONSENSUS Mouse cortex PSD consensus (ortho) 984
L00000069 G2C Homo sapiens BAYES-COLLINS-HUMAN-PSD-FULL Human cortex biopsy PSD full list 1461
L00000071 G2C Homo sapiens BAYES-COLLINS-MOUSE-PSD-FULL Mouse cortex PSD full list (ortho) 1556
© G2C 2014. The Genes to Cognition Programme received funding from The Wellcome Trust and the EU FP7 Framework Programmes:
EUROSPIN (FP7-HEALTH-241498), SynSys (FP7-HEALTH-242167) and GENCODYS (FP7-HEALTH-241995).

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