Interleukin-8 regulation of the Ras/Raf/mitogen-activated protein kinase pathway in human neutrophils.
Interleukin-8 (IL-8), the prototypic member of the CXC subfamily of chemokines, induces in neutrophils chemotaxis, the respiratory burst, granule release, and increased cell adhesion. The IL-8 receptor is a seven-transmembrane spanning receptor coupled to specific heterotrimeric G proteins including Gi and G16. IL-8 stimulation of its receptor on neutrophils activates Ras GTP loading and the mitogen-activated protein kinase (MAPK) pathway including Raf-1 and B-Raf. The properties of IL-8 stimulation of the MAPK pathway differ from those observed for chemoattractants such as C5a. Even though Ras GTP loading is similar for IL-8 and C5a, the maximal activation of Raf-1 and B-Raf is approximately 2-fold and 3-7-fold, respectively, less for IL-8 than that observed for C5a. Raf-1 activation is rapid but transient, returning to near basal levels by 10 min. B-Raf activation is slower in onset and does not return to basal levels for nearly 30 min. IL-8 activation of MAPK follows a time course suggesting an involvement of both Raf-1 and B-Raf. Surprisingly, wortmannin, at low concentrations, inhibits Raf-1, B-Raf, and MAPK activation in response to IL-8 and C5a demonstrating a role for phosphatidylinositol 3-kinase in the activation of Raf kinases in G protein-coupled receptor systems in human neutrophils. Furthermore, wortmannin inhibits IL-8 stimulated granule release and neutrophil adherence. These findings demonstrate the control of Raf kinases, the MAPK pathway and specific neutrophil functions by phosphatidylinositol 3-kinase enzymes.
Knall
C
C
Division of Basic Sciences, National Jewish Center for Immunology and Respiratory Medicine, Denver, Colorado 80206, USA. knallc@njc.org
Young
S
S
Nick
J A
JA
Buhl
A M
AM
Worthen
G S
GS
Johnson
G L
GL
D000730:Androstadienes / Q000494:pharmacology; D002448:Cell Adhesion; D015936:Complement C5a / Q000378:metabolism; D004789:Enzyme Activation; D006160:Guanosine Triphosphate / Q000378:metabolism; D006801:Humans; D016209:Interleukin-8 / Q000378:metabolism*; D007700:Kinetics; D009504:Neutrophils / Q000166:cytology / Q000201:enzymology*; D019869:Phosphatidylinositol 3-Kinases; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000037:antagonists & inhibitors / Q000378:metabolism; D047428:Protein Kinase Inhibitors; D011494:Protein Kinases / Q000378:metabolism*; D015398:Signal Transduction; D000077191:Wortmannin; D018631:ras Proteins / Q000378:metabolism
D000730:Androstadienes; D016209:Interleukin-8; D047428:Protein Kinase Inhibitors; D015936:Complement C5a; D006160:Guanosine Triphosphate; D011494:Protein Kinases; D019869:Phosphatidylinositol 3-Kinases; D017853:Phosphotransferases (Alcohol Group Acceptor); D018631:ras Proteins; D000077191:Wortmannin