Lipopolysaccharide induces actin reorganization and tyrosine phosphorylation of pyk2 and paxillin in monocytes and macrophages

The bacterial endotoxin LPS is a potent stimulator of monocyte and macropha ge activation and induces adhesion of monocytes, Morphological changes in r esponse to LPS have not been characterized in detail, however, nor have the signaling pathways mediating LPS-induced adhesion been elucidated. We have found that LPS rapidly induced adhesion and spreading of peripheral blood monocytes, and that this was inhibited by the Src family kinase inhibitor P P1 and the phosphatidylinositide 3-kinase inhibitor LY294002, LPS also stim ulated actin reorganization, leading to the formation of filopodia, lamelli podia, and membrane ruffles in Bad mouse macrophages. Proline-rich tyrosine kinase 2 (Pyk2), a tyrosine kinase related to focal adhesion kinase, and p axillin, a cytoskeletal protein that interacts with Pyk2, were both tyrosin e phosphorylated in response to LPS in monocytes and macrophages. Both tyro sine phosphorylation events were inhibited by PP1 and LY294002, Adhesion al so stimulated tyrosine phosphorylation of Pyk2 and paxillin in monocytes, a nd this was further enhanced by LPS, Finally, Pyk2 and paxillin colocalized within membrane ruffles in LPS-stimulated cells. These results indicate th at LPS stimulation of monocytes and macrophages results in rapid morphologi cal changes and suggest that Pyk2 and/or paxillin play a role in this respo nse.