Toll‐like receptor‐mediated tyrosine phosphorylation of paxillin via MyD88‐dependent and ‐independent pathways

AbstractToll‐like receptor (TLR)‐mediated recognition of pathogens represents one of the most important mechanisms of innate immunity. A proximal signaling event of TLR is the direct binding of an adaptor protein MyD88 to TLR and recruitment of the IL‐1R‐associated kinase (IRAK). In the present study, we examined the effect of several TLR ligands on protein tyrosine phosphorylation in rat macrophages. Macrophage‐activating lipopeptide‐2 kDa (MALP2) and lipoarabinomannan were used as activators of TLR2, while lipopolysaccharides (LPS) and lipoteichoic acid were used as TLR4 ligands. All these ligands induced tyrosine phosphorylation of proline‐rich tyrosine kinase 2 (Pyk2) and its substrate paxillin, an integrin‐associated focal adhesion adaptor protein, in the macrophages. PP2, an inhibitor of Src family tyrosine kinases, prevented the TLR‐induced phosphorylation of paxillin and Pyk2 without affecting TLR‐induced IRAK activation. MALP2 failed to induce paxillin phosphorylation in the macrophages from MyD88‐knockout mice. In contrast, the effect of LPS weakened, but was still observed even in the MyD88‐deficient cells. Thus, TLR regulate the function of paxillin in an Src family‐dependent mechanism through both MyD88‐dependent and MyD88‐independent pathways.