Integrin-nucleated Toll-like receptor (TLR) dimerization reveals subcellular targeting of TLRs and distinct mechanisms of TLR4 activation and signaling

Abstract Toll-like receptors (TLRs) are activated by microbial structures. To investigate the mechanisms of TLR activation, the 10 human TLRs were expressed as chimeras with the integrin αv and β5 subunits. Co-expression of the αv-TLR and β5-TLR chimeras in 293T cells generated 10 TLR homodimers, but only TLR4/4 could effectively activate NF-κB. TLR4 monomers also activated NF-κB but it was enhanced upon homodimerization. The TLR homodimers showed differential surface/intracellular expression. In TLR heterodimers, only TLR2/1 and TLR2/6 were potent in NF-κB activation. NF-κB activation by TLR2/1, TLR2/6 and the TLR4 monomer, but not TLR4/4, was completely inhibited by dominant negative MyD88, suggesting that TLR4 homodimers and monomers could activate NF-κB through different mechanisms.