CD11b/CD18 Acts in Concert with CD14 and Toll-Like Receptor (TLR) 4 to Elicit Full Lipopolysaccharide and Taxol-Inducible Gene Expression

Abstract

Overproduction of inflammatory mediators by macrophages in response to Gram-negative LPS has been implicated in septic shock. Recent reports indicate that three membrane-associated proteins, CD14, CD11b/CD18, and Toll-like receptor (TLR) 4, may serve as LPS recognition and/or signaling receptors in murine macrophages. Therefore, the relative contribution of these proteins in the induction of cyclooxygenase 2 (COX-2), IL-12 p35, IL-12 p40, TNF-α, IFN-inducible protein (IP)-10, and IFN consensus sequence binding protein (ICSBP) genes in response to LPS or the LPS-mimetic, Taxol, was examined using macrophages derived from mice deficient for these membrane-associated proteins. The panel of genes selected reflects diverse macrophage effector functions that contribute to the pathogenesis of septic shock. Induction of the entire panel of genes in response to low concentrations of LPS or Taxol requires the participation of both CD14 and TLR4, whereas high concentrations of LPS or Taxol elicit the expression of a subset of LPS-inducible genes in the absence of CD14. In contrast, for optimal induction of COX-2, IL-12 p35, and IL-12 p40 genes by low concentrations of LPS or by all concentrations of Taxol, CD11b/CD18 was also required. Mitigated induction of COX-2, IL-12 p35, and IL-12 p40 gene expression by CD11b/CD18-deficient macrophages correlated with a marked inhibition of NF-κB nuclear translocation and mitogen-activated protein kinase (MAPK) activation in response to Taxol and of NF-κB nuclear translocation in response to LPS. These findings suggest that for expression of a full repertoire of LPS-/Taxol-inducible genes, CD14, TLR4, and CD11b/CD18 must be coordinately engaged to deliver optimal signaling to the macrophage.

Paclitaxel (Taxol) upregulates expression of functional interleukin-6 in human ovarian cancer cells through multiple signaling pathways

“…At pharmacologically low concentrations (exemplified by 1 mM in this study), the JNK signaling pathway was the major stimulator of IL-6 gene regulation. However, at suprapharmacologically high concentrations (exemplified by 50 mM in this study), paclitaxel exerted LPS-like effects likely through the TLR4 signaling pathway as reported previously (Kawasaki et al, 2000(Kawasaki et al, , 2003Perera et al, 2001). Elucidation of the signaling networks that are differentially initiated by low concentrations or by high concentrations of paclitaxel and the verification of specific inhibitors against key molecules inside the networks may help us in developing a better chemotherapeutic strategy in treatment of ovarian cancer with paclitaxel.…”

“…Taken together, these results indicated that two pathways ( Figure 7) are involved in the upregulation of IL-6 by treatment with paclitaxel: (a) at low, pharmacological concentrations (exemplified by 1 mM in this study), the JNK signaling pathway was the major stimulator of IL-6 gene regulation, and (b) at high, suprapharmacological concentrations (exemplified by 50 mM in this study), paclitaxel exerted LPS-like effects, which were most likely carried out through the TLR4 signaling pathway as reported previously (Kawasaki et al, 2000(Kawasaki et al, , 2003Perera et al, 2001). …”

“…Results of this study demonstrated that paclitaxel in this range of concentrations activated IL-6 through the activation of JNK signaling pathway but not through the LPS-like activity of paclitaxel. First, the 1 mM concentration of paclitaxel used in this study was much lower than that reportedly (3-140 mM) effective for upregulation of IL1alpha, IL-1 beta, IL-8 and TNF-alpha (Ding et al, 1990;Lee et al, 1996;Lanni et al, 1997;Kawasaki et al, 2000Kawasaki et al, , 2003Perera et al, 2001;Takeda et al, 2003). Second, no upregulation of TLR4, MyD88, or NF-IL6 in terms of mRNA levels in BR cells treated with 1 mM paclitaxel was noted (Figure 6a).…”

“…Lipopolysaccharidelike effects of paclitaxel were thought to be conveyed through TNF receptor (Ding et al, 1990) or TLR-4 (Kawasaki et al, 2000(Kawasaki et al, , 2003Perera et al, 2001). Microtubule cytoskeleton dysfunction has been shown to activate NF-kB (Rosette and Karin, 1995; Das and Mechanisms of IL-6 upregulation by paclitaxel T-H Wang et al White, 1997).…”

“…More recently, Toll-like receptor 4 (TLR4) on murine macrophage has been shown to be the receptor for paclitaxel (Kawasaki et al, 2000(Kawasaki et al, , 2003Perera et al, 2001). Paclitaxel, notably at 5-30 mM, was thus proposed as a TLR4 ligand (Takeda et al, 2003).…”