Analysis of signal transduction pathways in human eosinophils activated by chemoattractants and the T-helper 2-derived cytokines interleukin-4 and interleukin-5.
Activation and recruitment of eosinophils in allergic inflammation is in part mediated by chemoattractants and T-helper 2 (Th2)-derived cytokines. However, little is known concerning the signal transduction mechanisms by which this activation occurs. We have investigated tyrosine kinase-mediated activation of phosphatidylinositol 3-kinase (PI3K) and compared this with the activation of the p21ras-ERK signaling pathway in human eosinophils. The related cytokines interleukin-3 (IL-3), IL-5, and granulocyte-macrophage colony-stimulating factor (GM-CSF), all induced PI3K activity detected in antiphosphotyrosine immunoprecipitates. Furthermore, the chemoattractants platelet-activating factor (PAF), RANTES, and C5a were also able to induce phosphotyrosine-associated PI3K activity. Protein kinase B (PKB) is a downstream target of PI3K activation by growth factors. Induction of PKB phosphorylation in human eosinophils was transiently induced on activation with the cytokines IL-4 and IL-5, as well as the chemoattractants PAF, C5a, and RANTES showing a broad activation profile. Surprisingly, analysis of the activation of the mitogen-activated protein (MAP) kinases p44(ERK1) and p42(ERK2), showed that ERK2, but not ERK1, was transiently activated in human eosinophils after stimulation with IL-5 or PAF. Activation kinetics correlated with activation of p21ras by both cytokines and chemoattractants as measured by a novel assay for guanosine triphosphate (GTP)-loading. Finally, using specific inhibitors of both the p21ras-ERK and PI3K signaling pathways, a role was demonstrated for PI3K, but not p21ras-ERK, in activation of the serum-treated zymosan (STZ)-mediated respiratory burst in IL-5 and PAF-primed eosinophils. In summary, these data show that in human eosinophils, Th2-derived cytokines differentially activate both PI3K and MAP kinase signal transduction pathways with distinct functional consequences showing complex regulation of eosinophil effector functions.
Coffer
P J
PJ
Department of Pulmonary Diseases, University Hospital Utrecht, Utrecht, The Netherlands.
Schweizer
R C
RC
Dubois
G R
GR
Maikoe
T
T
Lammers
J W
JW
Koenderman
L
L
D002478:Cells, Cultured; D002630:Chemotactic Factors / Q000494:pharmacology*; D004789:Enzyme Activation / Q000187:drug effects; D004804:Eosinophils / Q000378:metabolism*; D016178:Granulocyte-Macrophage Colony-Stimulating Factor / Q000494:pharmacology*; D006801:Humans; D015847:Interleukin-4 / Q000494:pharmacology*; D015848:Interleukin-5 / Q000494:pharmacology*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects*; D018418:Th2 Cells / Q000378:metabolism*
D002630:Chemotactic Factors; D015848:Interleukin-5; D015847:Interleukin-4; D016178:Granulocyte-Macrophage Colony-Stimulating Factor; D019869:Phosphatidylinositol 3-Kinases