Myeloid Differentiation Factor 88-dependent Post-transcriptional Regulation of Cyclooxygenase-2 Expression by CpG DNA

Abstract

The immune stimulatory unmethylated CpG motifs present in bacterial DNA (CpG DNA) induce expression of cyclooxygenase-2 (cox-2). The present study demonstrates that CpG DNA can up-regulate cox-2 expression by post-transcriptional mechanisms in RAW264.7 cells. To determine the CpG DNA-mediated signaling pathway that post-transcriptionally regulates cox-2 expression, a cox-2 translational reporter (COX2-3-UTR-luciferase) was generated by inserting sequences within the 3-untranslated region (UTR) of cox-2 to the 3 end of the luciferase gene under control of the SV40 promoter. CpG DNA-induced COX2-3-UTR-luciferase activity was completely inhibited by an endosomal acidification inhibitor chloroquine, a Toll-like receptor 9 antagonist inhibitory CpG DNA, or overexpression of a dominant negative (DN) form of MyD88. However, overexpression of DN-IRAK-1 or DN-TRAF6 resulted in substantial, but not complete, inhibition of the CpG DNA-induced COX2-3-UTR-luciferase activity. Activation of all three MAPKs (ERK, p38, and JNK) was required for optimal COX2-3-UTR-luciferase activity induced by CpG DNA.

Dendritic cells from HIV-1 infected individuals are less responsive to toll-like receptor (TLR) ligands

“…We also observed higher constitutive levels of COX-2 in mDC from HIV-1 infected individuals. COX-2 is up-regulated by TLR agonists such as CpG ODN and LPS in a MyD88-dependent signaling pathway (22)(23)(24). In these studies we demonstrate direct modulation of COX-2 expression in mDC using TLR4, TLR7/8, and TLR8 agonists.…”

“…COX-2 expression is regulated through the MyD88 dependent pathway (22,23) and is induced by pathogens, microbes and synthetic TLR agonists including CpG DNA (TLR9) and lipopolysaccharides (LPS, TLR4) (24). Continuous antigenic stimulation and inflammation observed during chronic infections, including HIV-1, may inhibit effector T cell function through COX-2 expression and the production of prostaglandins (25).…”

CpG DNA Prevents Liver Injury and Shock-mediated Death by Modulating Expression of Interleukin-1 Receptor-associated Kinases

“…Involvement of IRAK-1 and IRAK-M in TLR signal transduction and TLR-mediated induction of macrophage hyporesponsiveness has previously been reported. Overexpression of the dominant negative (DN) form of IRAK1 inhibits CpG DNA-mediated NF-B and AP-1 activation in macrophages (33,45). LPS-and R848 (TLR7 ligand)-mediated production of proinflammatory cytokines and activation of MAPKs and NF-B are partially impaired in IRAK-1 Ϫ/Ϫ macrophages, and CpG DNA-mediated type I interferon production is completely impaired in IRAK-1 Ϫ/Ϫ plasmatoid dendritic cells (50).…”

“…S-ODN had no detectable endotoxins by Limulus assay. The sequences of S-ODN used are previously reported (33). LPS (Salmonella minnesota Re 595) and D-galactosamine (D-GalN) were purchased from Sigma.…”

CpG DNA-mediated Induction of Acute Liver Injury in d-Galactosamine-sensitized Mice

“…This recruitment of MyD88 to toll/IL-1 receptor domains of TLR9 initiates a signaling pathway that sequentially involves IL-1R-associated kinase (IRAK) family proteins and tumor necrosis factor-␣ receptorassociated factor (TRAF) 6 and TRAF3 (10,(15)(16)(17)(18). This TLR9/MyD88-mediated signaling pathway is essential for the CpG DNA-induced activation of NF-B, interferon regulatory factors 5 and 7, small GTPase family protein Ras, mitogen-activated protein kinases, including c-Jun N-terminal kinase, p38, and extracellular signal-regulated kinase, and subsequent production of proinflammatory cytokines, chemokines, and modulators in innate immune cells (10,15,(17)(18)(19)(20)(21)(22)(23)(24)(25).…”