Multiple Signaling Molecules are Involved in Expression of CCL2 and IL-1β in Response to FSL-1, a Toll-Like Receptor 6 Agonist, in Macrophages

TLR6 forms a heterodimer with TLR2 and TLR4. While proinflammatory roles of TLR2 and TLR4 are well documented, the role of TLR6 in inflammation is poorly understood. In order to understand mechanisms of action of TLR6 in inflammatory responses, we investigated the effects of FSL-1, the TLR6 ligand, on expression of chemokine CCL2 and cytokine IL-1β and determined cellular factors involved in FSL-1-mediated expression of CCL2 and IL-1β in mononuclear cells. Exposure of human monocytic leukemia THP-1 cells to FSL-1 resulted not only in enhanced secretion of CCL2 and IL-1β, but also profound induction of their gene transcripts. Expression of CCL2 was abrogated by treatment with OxPAPC, a TLR-2/4 inhibitor, while treatment with OxPAPC resulted in partially inhibited expression of IL-1β. Treatment with FSL-1 resulted in enhanced phosphorylation of Akt and mitogen-activated protein kinases and activation of protein kinase C. Treatment with pharmacological inhibitors, including SB202190, SP6001250, U0126, Akt inhibitor IV, LY294002, GF109203X, and RO318220 resulted in significantly attenuated FSL-1-mediated upregulation of CCL2 and IL-1β. Our results indicate that activation of TLR6 will trigger inflammatory responses by upregulating expression of CCL2 and IL-1β via TLR-2/4, protein kinase C, PI3K-Akt, and mitogen-activated protein kinases.