The Epithelial avb3-Integrin Boosts the MYD88- Dependent TLR2 Signaling in Response to Viral and Bacterial Components

TLR2 is a cell surface receptor which elicits an immediate response to a wide repertoire of bacteria and viruses. Its response is usually thought to be proinflammatory rather than an antiviral. In monocytic cells TLR2 cooperates with coreceptors, e.g. CD14, CD36 and aMb2-integrin. In an earlier work we showed that avb3-integrin acts in concert with TLR2 to elicit an innate response to HSV, and to lipopolysaccharide. This response is characterized by production of IFN-a and-b, a specific set of cytokines, and NF-kB activation. We investigated the basis of the cooperation between avb3-integrin and TLR2. We report that b3-integrin participates by signaling through Y residues located in the C-tail, known to be involved in signaling activity. avb3-integrin boosts the MYD88-dependent TLR2 signaling and IRAK4 phosphorylation in 293T and in epithelial, keratinocytic and neuronal cell lines. The replication of ICP0minus HSV is greatly enhanced by DN versions of MYD88, of Akt – a hub of this pathway, or by b3integrin-silencing. avb3-integrin enables the recruitment of TLR2, MAL, MYD88 at lipid rafts, the platforms from where the signaling starts. The PAMP of the HSV-induced innate response is the gH/gL virion glycoprotein, which interacts with avb3-integrin and TLR2 independently one of the other, and cross-links the two receptors. Given the preferential distribution of avb3-integrin to epithelial cells, we propose that avb3-integrin serves as coreceptor of TLR2 in these cells. The results open the possibility that TLR2 makes use of coreceptors in a variety of cells to broaden its spectrum of activity and tissue specificity