Reactive Oxygen and Nitrogen Species Differentially Regulate Toll-Like Receptor 4-Mediated Activation of NF-κB and Interleukin-8 Expression

Abstract

Toll-like receptor 4 (TLR4) has been identified as a transmembrane protein involved in the host innate immune response to gram-negative bacterial lipopolysaccharide (LPS). Upon activation by LPS recognition, the TIR domain of TLR4 signals through MyD88 to activate the nuclear factor B (NF-B) pathway, a critical regulator of many proinflammatory genes, including interleukin-8 (IL-8). Emerging evidence suggests that reactive oxygen species (ROS) can contribute to diverse signaling pathways, including the LPS-induced cascade. In the present study we investigated the role of ROS in TLR-mediated signaling. Purified Escherichia coli LPS, a highly specific TLR4 agonist, elicited an oxidative burst in the monocyte-like cell line THP-1 in a time-and dose-dependent manner. This oxidative burst was shown to be dependent on the presence of TLR4 through transfection studies in HEK cells, which do not normally express this protein, and with bone marrow-derived macrophages from C3H/HeJ mice, which express a mutated TLR4 protein. LPS-stimulated IL-8 expression could be blocked by the antioxidants N-acetyl-L-cysteine and dimethyl sulfoxide at both the protein and mRNA levels. These antioxidants also blocked LPS-induced IL-8 promoter transactivation as well as the nuclear translocation of NF-B. These data provide evidence that ROS regulate immune signaling through TLR4 via their effects on NF-B activation.

ATR-dependent radiation-induced γH2AX foci in bystander primary human astrocytes and glioma cells

“…a protein) produced by targeted cells and passed on through the medium or the induction of a (secondary) bystander signal in the Mechanisms of bystander cH2AX foci induction S Burdak-Rothkamm et al bystander cells themselves. As some cytokines can be induced by increased ROS levels (Bellocq et al, 1999;Ayache et al, 2002;Hsu and Wen, 2002;Kosmidou et al, 2002;Hwang et al, 2004;Ryan et al, 2004), they are likely candidates for a secondary bystander signal. Furthermore, some of these cytokines (e.g.…”

“…The involvement of soluble factors like reactive oxygen species (ROS) (Azzam et al, 2002;Shao et al, 2003aShao et al, , 2005, nitric oxide (NO) (Shao et al, 2003b(Shao et al, , 2005Sokolov et al, 2005) and cytokines released from irradiated cells as well as gap junction intercellular communication (Azzam et al, 2001;Shao et al, 2003a;Mitchell et al, 2004;Sokolov et al, 2005) have recently been reported. Most interestingly, several cytokines can be induced by ROS and NO/NOS (Ayache et al, 2002;Hsu and Wen, 2002;Kosmidou et al, 2002;Hwang et al, 2004;Ryan et al, 2004) providing a possible link between different factors potentially involved in bystander signalling. End points used for the study of bystander effects in vitro have included micronuclei formation (Azzam et al, 2002;Kashino et al, 2004;Shao et al, 2004), gene mutations and genomic instability (Zhou et al, 2000), gene expression changes (Azzam et al, 2002;Yang et al, 2005), transformation (Sawant et al, 2001), proliferation (Gerashchenko and Howell, 2003), cell survival, apoptosis (Belyakov et al, 2002;Lyng et al, 2002), cell cycle arrest (Azzam et al, 2000) and most recently the induction of gH2AX foci in bystander cells (Hu et al, 2005;Sokolov et al, 2005;Yang et al, 2005).…”

MyD88 and Src Are Differentially Regulated in Kupffer Cells of Males and Proestrus Females Following Hypoxias

“…The increased release of these immunomodulators is significant and correlates with immunosuppression in males, but not in proestrus females, following hypoxia (11). Earlier studies have demonstrated the expression of TLR in macrophages and their involvement in the intracellular signaling cascade for the generation of immune modulators, TNF-α, IL-6, and iNOS (6,7,36,37). In this study, we examined the expression of TLR4, the downstream signaling pathway, and release of the cytokine IL-6 by Kupffer cells from male and proestrus female mice to determine whether intracellular signaling differs significantly and reflects a divergent hypoxic effect.…”

Oxidative Stress: Noxious but Also Vital

“…In the innate immune system, mononuclear monocytes/macrophages eliminate pathogen, antigen and cellular components through generation of ROS/RNS [149]. When there is an imbalance in the equilibrium between oxidative/nitrosative stress and cellular requirements, the stress can generates pathological complications.…”

“…The inflammatory mechanism involves synovial cellular infiltrate and peripheral blood inflammatory cells following by polymorphonuclear neutrophils and lymphocytes culminating in the joint damage [150,151]. The signaling cascade occurs via activation of NFkB for synthesizing pro-inflammatory cytokines and chemokines [149]. The Th1 cytokines are one of the most important because can provide the development of autoimmune disorders.…”