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

Tyrosine phosphorylation pathways are essential components of the process of macrophage activation and the resultant production of inflammatory mediators such as tumor necrosis factor (TNF) and nitric oxide (NO). Several lines of evidence suggest that members of the src family of protein tyrosine kinases play important roles in macrophage activation by gram-negative bacterial lipopolysaccharide (LPS) or the cytokine interferon-gamma (IFN-gamma), but targeted disruption of three members of the src family (hck, fgr, and lyn) in mice failed to demonstrate a requirement for these particular kinases in macrophage activation, We report that the pyrazolopyrimidine PP1, a src family-selective tyrosine kinase inhibitor, potently inhibits the production of TNF and inducible nitric oxide synthase (iNOS) in RAW 264.7 murine macrophages stimulated with LPS, rIFN-gamma, or LPS + rIFN-gamma. Furthermore, the tested concentrations of PP1 inhibit LPS- and rIFN-gamma-mediated tyrosine phosphorylation of the hck tyrosine kinase and its putative substrate, vav, but fail to block rIFN-gamma-mediated JAK2 tyrosine phosphorylation. These findings provide additional support for a model of macrophage activation involving one or more src-related kinases. Selective inhibitors of this signaling pathway should be studied in animal models of sepsis.