Tyrosine phosphorylation of Vav stimulates IL-6 production in mast cells by a Rac/c-Jun N-terminal kinase-dependent pathway

This study investigates whether the guanine nucleotide exchange activity of Vav is linked to cytokine production in mast cells, Overexpression of Vav in the RBL-2H3 mast cell line resulted in the constitutive tyrosine phospho rylation and activation of Vav, We analyzed the functional effect of Vav ov erexpression on cytokine production. IL-2 and IL-6 mRNA levels were dramati cally increased in Vav-overexpressing cells and correlated with increased N F-AT activity. Little or no effect was observed on the mRNA levels of IL-3, IL-4, GM-CSF, TNF-alpha, and TGF-beta, Fc epsilon RI engagement did not fu rther enhance IL-2 and IL-6 mRNA levels and only slightly enhanced NF-AT ac tivity, but dramatically increased the mRNA levels of other tested cytokine s. To understand the signal transduction required, we focused primarily on IL-6 induction by measuring mitogen-activated protein kinase activity and a nalyzing the effects of mutant or dominant negative forms of Vav, Rad, and c-Jun N-terminal kinase-1 (JNK1), Vav overexpression resulted in the consti tutive activation of JNK1 with little or no effect on p38 mitogen-activated protein kinase and ERK2, This was dependent on Vav-mediated activation of Rad as a Dbl domain-mutated Vav, inactive Rac N17, and inactive JNK1 do,m-r egulated the Vav-induced JNK1 or IL-6 responses. Vav expression, but not ex pression of domain-mutated Vav, increased IL-6 secretion from nonimmortaliz ed bone marrow-derived mast cells upon FceRI engagement. We conclude that V av phosphorylation contributes to IL-6 induction in mast cells.