Phosphatidylinositol-3 kinase regulates p21ras activation during IgE-mediated stimulation of human basophils.
Cross-linking of IgE or a bacterial product (f-Met-Leu-Phe; FMLP) induces the release of leukotriene C4 (LTC4) and histamine in human basophils. However, the signaling mechanisms in human basophils are only partially understood. It has been demonstrated that extracellular signal-regulated kinases (ERK1/2) specifically regulate the pathway for LTC4 generation, but not for histamine release and interleukin-4 production. More recent studies have suggested that tyrosine kinase (syk)-mediated phosphorylation of shc is responsible for the ras-ERK cascade via the formation of shc-Grb2-Sos2 following stimulation with anti-IgE antibody, but not FMLP, in human basophils. However, while characterizing the role of phosphatidylinositol (PI)-3 kinase in signaling pathways leading to basophil mediator release, it was noted that this pathway might also regulate p21ras activation. Anti-IgE antibody, but not FMLP, resulted in phosphorylation of p85 (regulatory subunit of PI3 kinase), suggesting activation of PI3 kinase. Inhibition of PI3 kinase by selective inhibitor (LY294002) abolished anti-IgE antibody- but not FMLP-induced phosphorylation of MEK1 (MAPK kinase/ERK kinase) and ERKs while inhibiting LTC4 generation as well as histamine release. IgE-mediated activation of ras (upstream of MEK-ERK) was also inhibited. But, further upstream, phosphorylation of syk and of shc and inducible association between shc and Grb2 were not affected. Furthermore, the IgE-mediated cytosolic calcium response ([Ca(++)](i)) was also diminished. These results suggest that functional responses may be dependent on the activity of PI3 kinase, which regulates at least 2 important signaling pathways: by regulating activation of ras for the MEK-ERK pathway and the increase in [Ca(++)](i).
Miura
K
K
Johns Hopkins Asthma and Allergy Center, Baltimore, MD 21224, USA.
MacGlashan
D W
DW
D001491:Basophils / Q000502:physiology*; D004789:Enzyme Activation; D006801:Humans; D007073:Immunoglobulin E / Q000494:pharmacology / Q000502:physiology*; D019869:Phosphatidylinositol 3-Kinases / Q000502:physiology*; D010766:Phosphorylation; D016283:Proto-Oncogene Proteins p21(ras) / Q000502:physiology*; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*
D007073:Immunoglobulin E; D019869:Phosphatidylinositol 3-Kinases; C501009:HRAS protein, human; D016283:Proto-Oncogene Proteins p21(ras)