Albumin mediates the transcytosis of myeloperoxidase by means of caveolae in endothelial cells.
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.
Tiruppathi
Chinnaswamy
C
Department of Pharmacology, College of Medicine, University of Illinois, Chicago, IL 60612, USA. tiruc@uic.edu
Naqvi
Tabassum
T
Wu
Yubin
Y
Vogel
Stephen M
SM
Minshall
Richard D
RD
Malik
Asrar B
AB
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
D000418:Albumins; D007457:Iodine Radioisotopes; D009195:Peroxidase