title: Spatial segregation of transport and signalling functions between human endothelial caveolae and lipid raft proteomes.
abstract: Lipid rafts and caveolae are biochemically similar, specialized domains of the PM (plasma membrane) that cluster specific proteins. However, they are morphologically distinct, implying different, possibly complementary functions. Two-dimensional gel electrophoresis preceding identification of proteins by MS was used to compare the relative abundance of proteins in DRMs (detergent-resistant membranes) isolated from HUVEC (human umbilical-vein endothelial cells), and caveolae immunopurified from DRM fractions. Various signalling and transport proteins were identified and additional cell-surface biotinylation revealed the majority to be exposed, demonstrating their presence at the PM. In resting endothelial cells, the scaffold of immunoisolated caveolae consists of only few resident proteins, related to structure [CAV1 (caveolin-1), vimentin] and transport (V-ATPase), as well as the GPI (glycosylphosphatidylinositol)-linked, surface-exposed protein CD59. Further quantitative characterization by immunoblotting and confocal microscopy of well-known [eNOS (endothelial nitric oxide synthase) and CAV1], less known [SNAP-23 (23 kDa synaptosome-associated protein) and BASP1 (brain acid soluble protein 1)] and novel [C8ORF2 (chromosome 8 open reading frame 2)] proteins showed different subcellular distributions with none of these proteins being exclusive to either caveolae or DRM. However, the DRM-associated fraction of the novel protein C8ORF2 (approximately 5% of total protein) associated with immunoseparated caveolae, in contrast with the raft protein SNAP-23. The segregation of caveolae from lipid rafts was visually confirmed in proliferating cells, where CAV1 was spatially separated from eNOS, SNAP-23 and BASP1. These results provide direct evidence for the previously suggested segregation of transport and signalling functions between specialized domains of the endothelial plasma membrane.
authors.affiliation: Department of Medical Biochemistry, Academic Medical Center K1-114, Meibergdreef 15, University of Amsterdam, 1105 AZ, Amsterdam, The Netherlands.
authors.forename: Richard R
authors.initials: RR
authors.lastname: Sprenger
authors.forename: Ruud D
authors.initials: RD
authors.lastname: Fontijn
authors.forename: Jan
authors.initials: J
authors.lastname: van Marle
authors.forename: Hans
authors.initials: H
authors.lastname: Pannekoek
authors.forename: Anton J G
authors.initials: AJ
authors.lastname: Horrevoets
mesh_terms: D021941:Caveolae / Q000737:chemistry / Q000378:metabolism*; D051242:Caveolin 1 / Q000378:metabolism; D002478:Cells, Cultured; D042783:Endothelial Cells / Q000378:metabolism* / Q000648:ultrastructure; D006801:Humans; D021962:Membrane Microdomains / Q000737:chemistry / Q000378:metabolism*; D008565:Membrane Proteins / Q000378:metabolism; D009419:Nerve Tissue Proteins / Q000378:metabolism; D052250:Nitric Oxide Synthase Type III / Q000378:metabolism; D010455:Peptides / Q000378:metabolism; D021381:Protein Transport / Q000502:physiology*; D020543:Proteome / Q000378:metabolism*; D050766:Qb-SNARE Proteins / Q000378:metabolism; D050767:Qc-SNARE Proteins / Q000378:metabolism; D012097:Repressor Proteins / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology*
chemical_list: C104089:BASP1 protein, human; D051242:Caveolin 1; C121703:ERLIN2 protein, human; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D010455:Peptides; D020543:Proteome; D050766:Qb-SNARE Proteins; D050767:Qc-SNARE Proteins; D012097:Repressor Proteins; C100493:SNAP23 protein, human; C496314:NOS3 protein, human; D052250:Nitric Oxide Synthase Type III