In this way, we could show that NF-κB dimers induced by h-S100A9 contained more of the p50 NF-κB isoform, suggesting different NF-κB isoform formation in cells stimulated by h-S100A9 and LPS, respectively (Fig. 5b). In

summary from these data we can conclude that h-S100A9 and LPS exerted their pro-inflammatory effects in a qualitatively different way. We suggest that this may be a result of the formation of different NF-κB isoforms in the stimulated cells. We wanted to determine which cell-surface receptors might contribute to the m-S100A9-induced response. Previous reports have indicated that S100A9 could interact both with RAGE[23, 36-38] and TLR4.[30] To determine whether m-S100A9 would induce cytokine responses via these PF-02341066 mouse receptors, we prepared BM-DC from TLR4-KO and RAGE-KO mice and stimulated them with either m-S100A9 or LPS. As shown in Fig. 6(a), the secretion of TNF-α, IL-6 and IL-1β triggered by LPS and by m-S100A9 was completely absent in TLR4-KO BM-DC, whereas IL-1β (> 50%) but not TNF-α secretion was inhibited in RAGE-KO BM-DC. check details We also observed a weak inhibition of IL-6 secretion in RAGE-KO BM-DC stimulated with both m-S100A9 and LPS. Taken together, these data

suggest that m-S100A9 was able to interact with both RAGE and TLR4 receptors. Most importantly, whereas TLR4 seems to be crucial for the induction of all cytokines, RAGE was involved mainly in IL-1β secretion. This result was further confirmed by analysing NO secretion in TLR4-KO and RAGE-KO BM-DC. The NO secretion triggered by m-S100A9 completely disappeared in TLR4-KO BM-DC, but it was not affected in RAGE-KO BM-DC (Fig. 6b). It is well established that TLR4 can be internalized in cells

upon triggering. The TRIF (TIR-domain-containing adapter-inducing interferon-β)-mediated type-1 interferon stimulation via TLR4-stimulation involves receptor internalization. Recent results also suggested the possibility that even the MyD88-dependent pathway might need TLR4 internalization.[39-41] To test whether h-S100A9-mediated stimulation would involve receptor internalization, RAS p21 protein activator 1 we tried to inhibit endosomal signalling using chloroquine. This molecule is a weak base, blocking endosome maturation[42] and clathrin-mediated internalization.[43] Secretion of TNF-α measured after pre-treatment of THP-1 with 10 μm chloroquine was significantly reduced in h-S100A9-stimulated cells but not in LPS-stimulated cells (Fig. 7a). These data suggested that h-S100A9-induced triggering, but not LPS-induced triggering, may need receptor internalization to promote cytokine secretion. To corroborate our previous finding, we incubated A488-labelled h-S100A9 for 30 min at 37° with THP-1 cells.