Granulocyte-macrophage colony-stimulating factor and IL-5 activate mitogen-activated protein kinase through Jak2 kinase and phosphatidylinositol 3-kinase in human eosinophils.

Mitogen-activated protein (MAP) kinases are activated by the sequential activation of Ras, Raf, and MEK (MAP kinase kinase) and regulate a wide variety of cell functions. To determine the kinase cascade for granulocyte-macrophage colony-stimulating factor (GM-CSF)- and IL-5-induced MAP kinase activation in eosinophils, we studied the effect of inhibitors of Jak2 kinase, tyrosine kinases, phosphatidylinositol 3-kinase, and protein kinase C on GM-CSF- and IL-5-induced MAP kinase activation in human eosinophils. GM-CSF and IL-5 activated 40, 42, and 44 kilodalton MAP kinase isoforms in eosinophils. This was indicated by the electrophoretic mobility shift of the three isoforms of MAP kinase in immunoblotting with anti-MAP kinase antibody and also by in-gel MAP kinase assay. MAP kinase activation was time- and dose-dependent, becoming maximal 3 to 15 minutes after stimulation. A Jak2 kinase inhibitor AG-490, a tyrosine kinase inhibitor genistein, and a phosphatidylinositol 3-kinase inhibitor wortmannin inhibited GM-CSF- and IL-5-induced MAP kinase activation in eosinophils, whereas a protein kinase C inhibitor staurosporine had a weak inhibitory effect. Furthermore, AG-490 and genistein prevented GM-CSF-induced tyrosine phosphorylation of Jak2 kinase in eosinophils. Taken together, these results indicate that GM-CSF and IL-5 activate MAP kinases through the signaling pathway of Jak2 kinase-tyrosine phosphorylated beta chain-phosphatidylinositol 3-kinase-Ras in eosinophils.