Asthma exacerbations are often caused by rhinovirus (RV). We and others have shown that Toll-like receptor 2 (TLR2)， a membrane surface receptor that recognizes bacterial lipopeptides and lipoteichoic acid， is required and sufficient for RV-induced proinflammatory responses in vitro and in vivo. We hypothesized that viral protein-4 (VP4)， an internal capsid protein that is myristoylated upon viral replication and externalized upon viral binding， is a ligand for TLR2. Recombinant VP4 and myristoylated VP4 (MyrVP4) were purified by Ni-affinity chromatography. MyrVP4 was also purified from RV-A1B-infected HeLa cells by urea solubilization and anti-VP4 affinity chromatography. Finally， synthetic MyrVP4 wa... More
Asthma exacerbations are often caused by rhinovirus (RV). We and others have shown that Toll-like receptor 2 (TLR2)， a membrane surface receptor that recognizes bacterial lipopeptides and lipoteichoic acid， is required and sufficient for RV-induced proinflammatory responses in vitro and in vivo. We hypothesized that viral protein-4 (VP4)， an internal capsid protein that is myristoylated upon viral replication and externalized upon viral binding， is a ligand for TLR2. Recombinant VP4 and myristoylated VP4 (MyrVP4) were purified by Ni-affinity chromatography. MyrVP4 was also purified from RV-A1B-infected HeLa cells by urea solubilization and anti-VP4 affinity chromatography. Finally， synthetic MyrVP4 was produced by chemical peptide synthesis. MyrVP4-TLR2 interactions were assessed by confocal fluorescence microscopy， fluorescence resonance energy transfer (FRET)， and monitoring VP4-induced cytokine mRNA expression in the presence of anti-TLR2 and anti-VP4. MyrVP4 and TLR2 colocalized in TLR2-expressing HEK-293 cells， mouse bone marrow-derived macrophages， human bronchoalveolar macrophages， and human airway epithelial cells. Colocalization was absent in TLR2-null HEK-293 cells and blocked by anti-TLR2 and anti-VP4. Cy3-labeled MyrVP4 and Cy5-labeled anti-TLR2 showed an average fractional FRET efficiency of 0.24?±?0.05， and Cy5-labeled anti-TLR2 increased and unlabeled MyrVP4 decreased FRET efficiency. MyrVP4-induced chemokine mRNA expression was higher than that elicited by VP4 alone and was attenuated by anti-TLR2 and anti-VP4. Cytokine expression was similarly increased by MyrVP4 purified from RV-infected HeLa cells and synthetic MyrVP4. We conclude that， during RV infection， MyrVP4 and TLR2 interact to generate a proinflammatory response.
