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

Abstract

Toll-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.

Cardiomyocyte Apoptosis Triggered by RAFTK/pyk2 via Src Kinase Is Antagonized by Paxillin

“…RAFTK/pyk2 activity and/or paxillin phosphorylation depends upon Src (35,41) because Src kinase inhibitors prevent increased phosphorylation of RAFTK/pyk2 as well as paxillin (42). Our results are consistent with RAFTK/pyk2-mediated loss of paxillin promoting apoptotic signaling by promotion of Src kinase activity.…”

Cross Talk between MyD88 and Focal Adhesion Kinase Pathways

“…We further demonstrated that other TLR ligands may also induce FAK phosphorylation at Tyr 397 and require FAK for cytokine release because comparable results have been obtained with the TLR2 ligand Pam 3 CSK 4 (data not shown). Also, our findings extend to FAK the observation that TLR2 and TLR4 agonists induced tyrosine phosphorylation of the prolinerich tyrosine kinase 2 (Pyk2), which in turn increases tyrosine phosphorylation of paxillin, an adaptor protein involved in integrin signaling and binding to Pyk2, vinculin, and FAK, through MyD88-dependent and -independent pathways (19). However, in our experiments, MyD88 does not seem to be essential for FAK autophosphorylation because this kinase is phosphorylated in MyD88 Ϫ/Ϫ macrophages activated with either LPS or protein I/II.…”

MyD88 Adapter-like (Mal) Is Phosphorylated by Bruton's Tyrosine Kinase during TLR2 and TLR4 Signal Transduction

“…Phosphatase treatment established that the slower migrating form of Mal represented tyrosine-phosphorylated Mal. A role for tyrosine phosphorylation has previously been ascribed to the TLR2 and TLR4 signaling pathway (32,33). In this study, MALP-2 and LPS rapidly triggered tyrosine phosphorylation of endogenous Mal in THP-1 cells.…”