2b). The dltA gene codes for one of the proteins
responsible for the d-alanylation of teichoic acids,28 and tagO codes for an enzyme responsible for the transfer of N-acetylglucosamine phosphate to the lipid carrier,28 an essential step in the synthesis of WTA. SA0614 and SA0615 code for proteins that compose a two-component system of S. aureus, which induces the expression of the dltABCD operon.29,30 On the basis of the results obtained with mutant strains deficient in these genes as well as with the ltaS mutant lacking LTA, we hypothesized that d-alanylated WTA is required for the TLR2-mediated phosphorylation of JNK in macrophages. To more directly determine the role of WTA, we prepared a fraction of S. aureus cell wall free from peptidoglycan and examined its action. This fraction was considered to be enriched in WTA based on the
content of phosphorus Nivolumab ic50 and the staining pattern in PAGE (left and middle panels in Fig. 2c): note that no appreciable signals were obtained in either assay with a fraction prepared from the tagO mutant lacking an enzyme essential for WTA synthesis, and that a difference in the migration of WTA prepared from the dltA mutant was probably attributable to a lack of d-alanine. In fact, WTA of the dltA mutant strain seemed to be devoid of d-alanine whereas that of the parental and lgt mutant strains retained selleck products it (right panel in Fig. 2c). This preparation of WTA has been shown to directly induce innate immune responses in an insect system (K. Kurokawa and B. L. Lee, unpublished data). When macrophages were incubated with these WTA preparations, the phosphorylation of JNK was not induced irrespective of the presence of bound d-alanine
Celecoxib in WTA (Fig. 2d), indicating that WTA does not serve as a ligand for TLR2. We next tested whether WTA influences the action of the TLR2 ligand. To this end, macrophages were incubated with Pam3Cys, a synthetic TLR2 ligand, in the presence and absence of WTA. However, the level of phosphorylated JNK was not altered by the addition of WTA (Fig. 2d). These results suggested that d-alanylated WTA does not directly act on TLR2 or TLR2 ligand but modulates the cell wall milieu for lipoproteins so that they effectively serve as a ligand for TLR2 to induce the phosphorylation of JNK. We next determined the level of superoxide production in S. aureus-incubated macrophages, which we previously showed to be inhibited by phosphorylated and thus activated JNK.10 The level of superoxide released from macrophages into the culture media was significantly higher on incubation with a mutant strain lacking the expression of dltA, tagO or lgt than with the parental strain (left panel in Fig. 3a).