ICAM-1-mediated leukocyte adhesion is critical for the activation of endothelial LSP1.
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.
['Hossain|Mokarram|M|', 'Qadri|Syed M|SM|', 'Su|Yang|Y|', 'Liu|Lixin|L|']
D000818:Animals D018821:CD18 Antigens D002135:Calcium-Binding Proteins D002448:Cell Adhesion D002460:Cell Line D054426:Chemokine CXCL2 D042783:Endothelial Cells D007093:Imidazoles D018799:Intercellular Adhesion Molecule-1 D020935:MAP Kinase Signaling System D051379:Mice D057507:Mice, 129 Strain D018345:Mice, Knockout D008840:Microfilament Proteins D055806:Microvessels D009504:Neutrophils D010766:Phosphorylation D011499:Protein Processing, Post-Translational D011725:Pyridines D057705:Transendothelial and Transepithelial Migration D014409:Tumor Necrosis Factor-alpha D048051:p38 Mitogen-Activated Protein Kinases
adhesion LSP1 endothelial cells neutrophils p38 MAPK ICAM-1