Signal transduction for interleukin‐3‐dependent leukotriene synthesis in normal human basophils: opposing role of tyrosine kinase and protein kinase C

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Abstract
The intracellular signaling pathways regulating the synthesis of leukotrienes by myeloid cells are largely unknown. In addition, the signal transduction mechanisms utilized by the cytokine receptor family are still poorly understood. The fact that in mature human basophils the synthesis of leukotriene C4 (LTC4) induced by C5a is strictly dependent on a short preincubation with the cytokine interleukin-3 (IL-3), allowed us to investigate the metabolic requirements for LTC4 synthesis, and also to provide some information on early signal transduction mechanisms of IL-3 in these differentiated, non-dividing blood leukocytes. IL-3 itself does not alter intracellular free calcium concentration ([Ca2+]i) in basophils, whereas C5a induces a transient rise independent of IL-3 pretreatment, indicating that the priming effect of IL-3 cannot be explained by alterations in [Ca2+]i changes. The protein kinase C inhibitor staurosporine did not inhibit C5a-induced histamine release nor IL-3-dependent LTC4 formation in contrast to the IgE receptor-dependent basophil response. Activation of protein kinase C (PKC) by phorbol-12-myristate-13-acetate (PMA) induced histamine release without leukotriene formation. PMA-treated basophils did not produce LTC4 in response to C5a. Rather, PMA blocked the IL-3 effect on C5a-induced LTC4 synthesis. Only the C5a signal but not the IL-3 effect was pertussis toxin sensitive. Two unrelated tyrosine kinase inhibitors, tyrphostin RG-50864 and herbimycin A, were both very efficient blockers of IL-3-dependent lipid mediator formation whereas C5a-induced histamine release was preserved. Thus LTC4 formation does not require activation of a staurosporine-sensitive serine/threonine kinase. To the contrary, IL-3-dependent LTC4 formation appears to be regulated by serine/threonine and tyrosine phosphorylation in an antagonistic manner.

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