Phosphorylated Toll-Like Receptor 2 Interacts with Fyn and Cross-Talks with the Phosphorylation-Independent TLR2-Signaling Pathway

Following ligand stimulation, several Toll-like receptors (TLRs) are phosphorylated at tyrosine residues in their intracellular domains. However, the precise chain of events leading to tyrosine-phosphorylation-dependent TLR-mediated cytokine secretion has not been defined. We focused on elaborating the signaling pathway of tyrosine-phosphorylated TLR2. We demonstrated that two tyrosine residues in the intracellular domain of TLR2, Y616 and Y761, were important for cytokine secretion. We also showed that the src-kinase, Fyn, is constitutively associated with TLR2. TLR2-ligand stimulation increases the amount of phosphorylated Fyn and phosphorylated TLR2. The p85-PI3K complex together with PKC associated with TLR2 in a src-kinase dependent manner. We identified crosstalk between this complex and two components of the TLR2 tyrosine-phosphorylation-independent pathway, IRAK-1 and TRAF6. Our results demonstrate that the downstream events of ligand-stimulated TLR2, including activation of NF B and Erk1/2 as well as cytokine secretion, are src-kinase dependent.