The src family-selective tyrosine kinase inhibitor PP1 blocks LPS and IFN-gamma-mediated TNF and iNOS production in murine macrophages

Tyrosine phosphorylation pathways are essential components of the process o f macrophage activation and the resultant production of inflammatory mediat ors such as tumor necrosis factor (TNF) and nitric oxide (NO). Several line s of evidence suggest that members of the src family of protein tyrosine ki nases play important roles in macrophage activation by gram-negative bacter ial lipopolysaccharide (LPS) or the cytokine interferon-gamma (IFN-gamma), but targeted disruption of three members of the src family (hck, fgr, and l yn) in mice failed to demonstrate a requirement for these particular kinase s in macrophage activation, We report that the pyrazolopyrimidine PP1, a sr c family-selective tyrosine kinase inhibitor, potently inhibits the product ion of TNF and inducible nitric oxide synthase (iNOS) in RAW 264.7 murine m acrophages stimulated with LPS, rIFN-gamma, or LPS + rIFN-gamma. Furthermor e, the tested concentrations of PP1 inhibit LPS- and rIFN-gamma-mediated ty rosine phosphorylation of the hck tyrosine kinase and its putative substrat e, vav, but fail to block rIFN-gamma-mediated JAK2 tyrosine phosphorylation . These findings provide additional support for a model of macrophage activ ation involving one or more src-related kinases. Selective inhibitors of th is signaling pathway should be studied in animal models of sepsis.