Bruton's tyrosine kinase is required for lipopolysaccharide-induced tumor necrosis factor at production

Lipopolysaccharide (LPS), a product of Gram-negative bacteria, is potent mediator of tumor necrosis factor (TNF)alpha production by myeloid/macrophage cells. Inhibitors capable of blocking the signaling events that result in TNFalpha production could provide useful therapeutics for treating septic shock and other inflammatory diseases. Broad spectrum tyrosine inhibitors are known to inhibit TNFalpha production, however, no particular family of tyrosine kinases has been shown to be essential for this process. Here we show that the Bruton's tyrosine kinase (Btk)-deficient mononuclear cells from X-linked agammaglobulinemia patients have impaired LPS-induced TNFalpha production and that LPS rapidly induces Btk kinase activity in normal monocytes. In addition, adenoviral overexpression of Btk in normal human monocytes enhanced TNFalpha production. We examined the role of Btk in TNFalpha production using luciferase reporter adenoviral constructs and have established that overexpression of Btk results in the stabilization of TNFalpha mRNA via the 3' untranslated region. Stimulation with LPS also induced the activation of related tyrosine kinase, Tec, suggesting that the Tec family kinases are important components for LPS-induced TNFalpha production. This study provides the first clear evidence that tyrosine kinases of the Tec family, in particular Btk, are key elements of LPS-induced TNFalpha production and consequently may provide valuable therapeutic targets for intervention in inflammatory conditions.