title: ICAM-1-mediated leukocyte adhesion is critical for the activation of endothelial LSP1.
abstract: Leukocyte-endothelial interaction triggers signaling events in endothelial cells prior to transendothelial migration of leukocytes. Leukocyte-specific protein 1 (LSP1), expressed in endothelial cells, plays a pivotal role in regulating subsequent recruitment steps following leukocyte adhesion. In neutrophils, LSP1 is activated by phosphorylation of its serine residues by molecules downstream of p38 MAPK and PKC. Whether leukocyte adhesion to endothelial cells is required for endothelial LSP1 activation remains elusive. In addition, discrepancies in the functions of endothelial and leukocyte LSP1 in leukocyte adhesion prevail. We demonstrate that adhesion of wild-type (Lsp1(+/+)) neutrophils to LSP1-deficient (Lsp1(-/-)) endothelial cells was significantly reduced compared with adhesion to Lsp1(+/+) endothelial cells. Immunoblotting revealed increased phosphorylated endothelial LSP1 in the presence of adherent Lsp1(-/-) neutrophils [stimulated by macrophage inflammatory protein-2 (CXCL2), TNF-α, or thapsigargin], but not cytokine or chemokine alone. Pharmacological inhibition of p38 MAPK by SB-203580 (10 μM) significantly blunted the phosphorylation of endothelial LSP1. Functionally blocking endothelial ICAM-1 or neutrophil β2-integrins diminished neutrophil adhesion and phosphorylation of endothelial LSP1. The engagement of endothelial ICAM-1 cross-linking, which mimics leukocyte adhesion, resulted in phosphorylation of endothelial LSP1. In neutrophil-depleted Lsp1(+/+) mice, administration of ICAM-1 cross-linking antibody resulted in increased phosphorylation of LSP1 and p38 MAPK in TNF-α-stimulated cremaster muscle. In conclusion, endothelial LSP1 participates in leukocyte adhesion in vitro, and leukocyte adhesion through ICAM-1 fosters the activation of endothelial LSP1, an effect at least partially mediated by the activation of p38 MAPK. Endothelial LSP1, in contrast to neutrophil LSP1, is not phosphorylated by cytokine or chemokine stimulation alone.
authors: Department of Pharmacology, College of Medicine, University of Saskatchewan, Saskatoon, Saskatchewan, Canada.
authors: Mokarram
authors: M
authors: Hossain
authors: Syed M
authors: SM
authors: Qadri
authors: Yang
authors: Y
authors: Su
authors: Lixin
authors: L
authors: Liu
mesh_terms: D000818:Animals; D018821:CD18 Antigens / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000378:metabolism*; D002448:Cell Adhesion; D002460:Cell Line; D054426:Chemokine CXCL2 / Q000502:physiology; D042783:Endothelial Cells / Q000378:metabolism*; D007093:Imidazoles / Q000494:pharmacology; D018799:Intercellular Adhesion Molecule-1 / Q000378:metabolism*; D020935:MAP Kinase Signaling System / Q000187:drug effects; D051379:Mice; D057507:Mice, 129 Strain; D018345:Mice, Knockout; D008840:Microfilament Proteins; D055806:Microvessels / Q000166:cytology; D009504:Neutrophils / Q000502:physiology*; D010766:Phosphorylation; D011499:Protein Processing, Post-Translational; D011725:Pyridines / Q000494:pharmacology; D057705:Transendothelial and Transepithelial Migration; D014409:Tumor Necrosis Factor-alpha / Q000502:physiology; D048051:p38 Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism
chemical_list: D018821:CD18 Antigens; D002135:Calcium-Binding Proteins; D054426:Chemokine CXCL2; C404915:Cxcl2 protein, mouse; C090509:Icam1 protein, mouse; D007093:Imidazoles; C057701:Lsp1 protein, mouse; D008840:Microfilament Proteins; D011725:Pyridines; D014409:Tumor Necrosis Factor-alpha; D018799:Intercellular Adhesion Molecule-1; D048051:p38 Mitogen-Activated Protein Kinases; C093642:SB 203580
keywords: ICAM-1; LSP1; adhesion; endothelial cells; neutrophils; p38 MAPK