ABSTRACT
Monocyte chemoattractant protein-1 (MCP-1) is an essential cytokine for the migration of monocytes into vessels, and is also involved in the pathogenesis of atherosclerosis. In this study, we investigated the importance of janus kinase 2 (JAK2) and the function of the Akt and glycogen synthase kinase-3ß (GSK3ß) pathway in toll-like receptor (TLR2)-mediated MCP-1 expression. The TLR2 agonist, Pam3CSK4, induced MCP-1 expression in the Raw264.7 cell line. The induction of MCP-1 was seen in the bone marrow-derived macrophages of wild-type mice but not in TLR2 knockout mice. The TLR2-mediated MCP-1 induction was myeloid differentiation primary response gene 88 (MyD88)-independent. By contrast, the inactivation of JAK2 attenuated TLR2-mediated MCP-1 expression. The JAK inhibitor suppressed the phosphorylation of GSK3ß as well as Akt by Pam3CSK4 stimulation. While the inactivation of Akt by LY294002 suppressed TLR2-mediated MCP-1 induction, the inactivation of GSK3ß by LiCl potentiated TLR2-mediated MCP-1 induction. Furthermore, Akt inhibitor suppressed TLR2-mediated phosphorylation of GSK3ß. Taken together, these results suggest that a MyD88-independent pathway exists in TLR2 signaling; the JAK2-Akt-GSK3ß pathway is a novel MyD88-independent pathway for MCP-1 induction.
Subject(s)
Chemokine CCL2/metabolism , Glycogen Synthase Kinase 3/metabolism , Janus Kinase 2/metabolism , Proto-Oncogene Proteins c-akt/metabolism , Signal Transduction , Toll-Like Receptor 2/metabolism , Animals , Cell Line, Tumor , Chromones/pharmacology , Glycogen Synthase Kinase 3 beta , Janus Kinase 2/antagonists & inhibitors , Lipopeptides/pharmacology , Lithium Chloride/pharmacology , Mice , Mice, Knockout , Morpholines/pharmacology , Myeloid Differentiation Factor 88/metabolism , Phosphorylation , Signal Transduction/drug effects , Toll-Like Receptor 2/agonists , Toll-Like Receptor 2/geneticsABSTRACT
Synthetic oligodeoxynucleotides (ODNs) with the CpG-motifs are recognized by toll-like receptor 9 (TLR9), which elicits an immune response. Serum starvation of Raw264.7 cells increased tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) expression. However, treatment with CpG ODN reduced TRAIL expression as well as apoptosis by serum starvation. In serum starved cells, TLR9 inhibitors recovered the decreasing TRAIL expression and sub-G1 accumulation by CpG ODN. CpG ODN-regulated anti-apoptotic signals which were dependent on the Akt-FoxO3a signaling pathway. CpG ODNs activated Akt and inactivated FoxO3a in serum starved cells. Knockdown of FoxO3a by siRNA decreased TRAIL expression and apoptosis in serum-starved cells. In contrast, FoxO3a overexpression increased apoptosis by serum starvation, and CpG ODNs blocked these effects through TRAIL expression. LY294002, a PI3K-Akt inhibitor, blocked the CpG ODN effect of TRAIL expression and the sub-G1 population in serum starved cells. In contrast, overexpression of wild-type Akt reduced additional sub-G1 cells both in non-CpG ODN- and CpG ODN-treated cells. Taken together, these results demonstrate the involvement of Akt-FoxO3a signaling in TLR9-mediated downregulation of TRAIL and anti-apoptotic signals.
