title: Albumin mediates the transcytosis of myeloperoxidase by means of caveolae in endothelial cells.
abstract: Myeloperoxidase (MPO), the phagocyte hemoprotein involved in neutrophil host defense and consuming nitric oxide (*NO), induces the nitration of extracellular matrix proteins and tissue remodeling subsequent to its transcytosis across the endothelial barrier. We addressed the role of an interaction of MPO with albumin as a requirement for MPO transport across the endothelium. Matrix-assisted laser desorption/ionization MS analysis of 80- and 60-kDa proteins purified from human lung tissue [with a human serum albumin (HSA)-affinity column] identified these albumin-binding proteins as MPO and MPO-heavy chain. A peptide corresponding to the MPO-heavy chain residues 425-454 demonstrated high-affinity binding to HSA. Replacement of the positively charged residues, R and K with G, prevented the binding of HSA to the peptide. We observed that albumin increased the binding of (125)I-MPO to lung microvascular endothelial cells by 2-fold and the rate of transendothelial flux of (125)I-MPO in cultured monolayers and intact vessels. Disruption of caveolae with cyclodextrin prevented the albumin-induced increase in transendothelial flux of (125)I-MPO. We also observed by confocal imaging that albumin induced the rapid internalization of MPO and its colocalization with albumin-labeled vesicles. MPO colocalized with the caveolae markers cholera toxin subunit B and caveolin 1 in the endocytosed vesicles. Thus, transcytosis of MPO by caveolae induced by its charge-dependent interaction with albumin is an important means of delivering MPO to the subendothelial space. Albumin-mediated transport of MPO may thereby regulate NO bioavailability and formation of NO-derived oxidants in the vessel wall.
authors.affiliation: Department of Pharmacology, College of Medicine, University of Illinois, Chicago, IL 60612, USA. tiruc@uic.edu
authors.forename: Chinnaswamy
authors.initials: C
authors.lastname: Tiruppathi
authors.forename: Tabassum
authors.initials: T
authors.lastname: Naqvi
authors.forename: Yubin
authors.initials: Y
authors.lastname: Wu
authors.forename: Stephen M
authors.initials: SM
authors.lastname: Vogel
authors.forename: Richard D
authors.initials: RD
authors.lastname: Minshall
authors.forename: Asrar B
authors.initials: AB
authors.lastname: Malik
mesh_terms: D000418:Albumins / Q000378:metabolism*; D021941:Caveolae / Q000378:metabolism*; D002846:Chromatography, Affinity; D042783:Endothelial Cells / Q000378:metabolism*; D006801:Humans; D007457:Iodine Radioisotopes; D009195:Peroxidase / Q000378:metabolism*; D021381:Protein Transport / Q000502:physiology
chemical_list: D000418:Albumins; D007457:Iodine Radioisotopes; D009195:Peroxidase