7a). It was found that incubation with FSL-1 induced down-regulation of the surface expression level of TLR2 (Fig. 8a,b), suggesting that FSL-1 stimulation is required for TLR2 internalization. We speculated that receptor(s) selleck that mediate(s) the uptake of FSL-1 are CD36 and CD14, because they function as co-receptors for the recognition of a mycoplasmal diacylated lipopeptide, MALP-2,32 and a triacylated

lipopeptide, Pam3CSK4,16,33 by TLR2. Therefore, experiments were carried out to determine the roles of CD14 and CD36 in the uptake of FSL-1 by using HEK293WT, HEK293/CD14, HEK293/CD36, HEK293/TLR2, HEK293/CD14/TLR2 or HEK293/CD36/TLR2. They were incubated with FITC-FSL-1 for 2 hr and then examined for the uptake of FSL-1 by CLSM and FCM (Fig. 9). It was clearly demonstrated that FSL-1 internalization occurs in both HEK293/CD14 (Fig. 9b) and HEK293/CD36 (Fig. 9c) but not in HEK293WT (Fig. 9a) and HEK293/TLR2 (Fig. 9d). In addition, co-transfection of TLR2 had no effect on the uptake of FSL-1 by HEK293/CD14 (Fig. 9b,e) selleck chemical and HEK293/CD36 (Fig. 9c,f). These results demonstrated that both CD14 and CD36 are responsible for the uptake of FSL-1. To further confirm the involvement of CD14 and CD36 in FSL-1 uptake, the experiments

were carried out to investigate the effects of knockdown of CD14 and CD36 on FSL-1 uptake. The gene silencing of CD14 and CD36 were attempted by transfecting their specific siRNAs into HEK293/CD14 and 3-mercaptopyruvate sulfurtransferase HEK293/CD36, respectively. FCM analysis revealed that the level of both CD14 and CD36 was significantly down-regulated by siRNA transfection (Fig. 10a,b). Then, the effects of transfection of these siRNAs on the level of FSL-1 uptake were determined. It was found that the internalization level was down-regulated in both HEK293/CD14 by CD14 siRNA transfection and HEK293/CD36 by CD36 siRNA transfection. Hence, down-regulation of CD14 and CD36 expression was correlated with a decrease in the level of FSL-1 uptake, suggesting that CD14 and CD36 are responsible for the uptake of FSL-1. Then,

the effect of co-transfection of CD14 and CD36 on the uptake of FSL-1 was examined. No synergistic effect by co-transfection was observed, suggesting that FSL-1 uptake mediated by these molecules occurs independently (Fig. 11). This study demonstrated that the diacylated lipopeptide FSL-1 was incorporated into mammalian cells through a clathrin-dependent endocytic pathway in which CD14 and CD36 were involved. First we thought TLR2 is involved in the FSL-1 uptake, because TLR2 is a receptor for FSL-1. However, TLR2 was not co-localized with FSL-1 in the cytosol of macrophages (Fig 7a) and FSL-1 was internalized into PMφs from TLR2−/− mice (Fig. 7c,e). These results suggest the TLR2 is not involved in the FSL-1 uptake. This unique finding is supported by the recent findings of Triantafilou et al.