Neutrophil adhesion to endothelial cells induced by platelet factor 4 requires sequential activation of Ras, Syk, and JNK MAP kinases.
Signal transduction mechanisms associated with neutrophil activation by platelet factor 4 (PF4; CXCL4) are as yet poorly characterized. In a recent report, we showed that PF4-induced neutrophil functions (such as adhesion and secondary granule exocytosis) involve the activation of Src-kinases. By analyzing intracellular signals leading to adherence, we here demonstrate by several lines of evidence that in addition to Src-kinases, PF4 signaling involves the monomeric GTPase Ras, the tyrosine kinase Syk, and the MAP kinase JNK. Furthermore, on stimulation, GTPases Rac2 and RhoA were activated, and each was translocated to a different membrane compartment. As shown by inhibitor studies, Rac2 and JNK are located downstream of Syk and Ras. Most intriguingly, the latter 2 elements appear to control the activity of Rac2 and JNK independently of each other at different phases of the activation process. Although a first phase of Rac2 and JNK activation of up to 5 minutes is initiated by Ras, the second phase (5-30 minutes) depends predominantly on the activity of Syk. In summary, we describe that coordinated activity of Syk, Ras, and JNK mediates neutrophil adhesion to endothelial cells and that PF4 induces sequential activation of these elements.
Kasper
Brigitte
B
Department of Immunology and Cell Biology, Research Center Borstel, Parkallee 22a, D-23845 Borstel, Germany. bkasper@fz-borstel.de
Brandt
Ernst
E
Ernst
Martin
M
Petersen
Frank
F
D002448:Cell Adhesion / Q000187:drug effects / Q000502:physiology; D002462:Cell Membrane / Q000201:enzymology; D002478:Cells, Cultured; D018920:Coculture Techniques; D042783:Endothelial Cells / Q000166:cytology / Q000378:metabolism*; D005089:Exocytosis / Q000187:drug effects* / Q000502:physiology; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism; D048670:MAP Kinase Kinase 4 / Q000378:metabolism; D020935:MAP Kinase Signaling System / Q000187:drug effects* / Q000502:physiology; D018375:Neutrophil Activation / Q000187:drug effects* / Q000502:physiology; D009504:Neutrophils / Q000166:cytology / Q000201:enzymology*; D010978:Platelet Factor 4 / Q000378:metabolism / Q000494:pharmacology*; D021381:Protein Transport / Q000187:drug effects / Q000502:physiology; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D016283:Proto-Oncogene Proteins p21(ras) / Q000378:metabolism; D000072377:Syk Kinase
D047908:Intracellular Signaling Peptides and Proteins; D010978:Platelet Factor 4; D011505:Protein-Tyrosine Kinases; C000606896:SYK protein, human; D000072377:Syk Kinase; D048670:MAP Kinase Kinase 4; D016283:Proto-Oncogene Proteins p21(ras)