Signal Transduction in Activation of Human Eosinophils: G Protein-Dependent and -Independent Pathways

Abstract

Degranulation of eosinophils and subsequent release of toxic granule proteins play a key role in allergic diseases such as bronchial asthma. We have previously shown that stimulation of eosinophils with immobilized secretory immunoglobulin A (sIgA) induced the phosphorylation of several proteins including 51-, 65-, 73-, 78-, 100-, 105- and 113-kD proteins. Pervanadate, a protein tyrosine phosphatase inhibitor, also induced at least 7 tyrosine phosphorylated proteins including those observed with immobilized sIgA. Pervanadate also induced inositol phosphate (IP) production and degranulation of eosinophils in a concentration-dependent manner. Eosinophil production of IP and degranulation as well as tyrosine phosphorylation of proteins induced by sIgA were completely inhibited by a tyrosine kinase inhibitor, genistein, and pertussis toxin (PTX), suggesting the involvement of both the PTX-sensitive guanine nucleotide-binding (G) protein and protein tyrosine kinases (PTK) in sIgA-induced activation of eosinophils. In contrast, PTX did not affect tyrosine phosphorylation induced by sIgA or pervanadate. Furthermore, pervanadate-induced IP production was partially inhibited by PTX. Finally, a phospholipase C-γ2 isoform was tyrosine phosphorylated by pervanadate, but not by sIgA. These findings suggest that at least two different pathways, i.e. PTK-mediated G protein-dependent or -independent PLC activation, are involved in the activation of human eosinophils.