Oxidized low density lipoprotein inhibits interleukin-12 production in lipopolysaccharide-activated mouse macrophages via direct interactions between peroxisome proliferator-activated receptor-gamma and nuclear factor-kappa B

Lipopolysaccharide (LPS) increases the production of interleukin-12 (IL-12) from mouse macrophages via a kappaB site within the IL-12 p40 promoter. In this study, we found that oxidized low density lipoprotein (oxLDL) inhibited this LPS-stimulated production of IL-12 in a dose-dependent manner while native LDL did not. OxLDL inhibited p40 promoter activation in monocytic RAW264.7 cells transiently transfected with p40 promoter/reporter constructs, and the repressive effect mapped to a region in the p40 promoter containing a binding site for nuclear factor-kappaB (NF-kappaB) (p40-kappaB). Activation of macrophages by LPS in the presence of oxLDL resulted in markedly reduced binding to the kappaB site, as demonstrated by the electrophoretic mobility shift assays. In contrast, native LDL did not inhibit the IL-12 p40 promoter activation and NF-kappaB binding to the kappaB sites, suggesting that oxidative modification of LDL was crucial for the inhibition of NF-kappaB-mediated IL-12 production. 9-Hydroxyoctadecadienoic acid, a major oxidized lipid component of oxLDL, significantly inhibited IL-12 production in LPS-stimulated mouse macrophages and also suppressed NF-kappaB-mediated activation in IL-12 p40 promoter. The NF-kappaB components p50 and p65 directly bound peroxisome proliferator-activated receptor-gamma (PPAR-gamma) in vitro. In cotransfections of CV-1 and HeLa cells, PPAR-gamma inhibited the NF-kappaB transactivation in an oxLDL-dependent manner. From these results, we propose that oxLDL-mediated suppression of the IL-12 production from LPS-activated mouse macrophages may, at least in part, involve both inhibition of the NF-kappaB-DNA interactions and physical interactions between NF-kappaB and PPAR-gamma.     

p47phox participates in activation of RelA in endothelial cells

Activation of endothelial cell NF-kappaB by interleukin (IL)-1 constitutes an event critical to the progression of the innate immune response. In this context, oxidants have been associated with NF-kappaB activation, although the molecular source and mechanism of targeting have remained obscure. We found that RelA, essential for NF-kappaB activation by IL-1, was associated with the NADPH oxidase adapter protein p47(phox) in yeast two-hybrid, coprecipitation, and in vitro binding studies. RelA and p47-GFP also colocalized in endothelial cells in focal submembranous dorsoventral protrusions. Overexpression of p47(phox) synergized with IL-1beta in the activation of an artificial kappaB-luciferase reporter and specifically augmented IL-1beta-induced RelA transactivation activity. p47(phox) overexpression also greatly increased IL-1beta-stimulated RelA phosphorylation, whereas it had no effect on I-kappaB degradation or on RelA nuclear translocation or kappaB binding. The tandem SH3 domains of p47(phox) were found to associate with a proline-rich mid-region of RelA (RelA-PR) located between the Rel homology and transactivation domains. The RelA-PR peptide blocked interaction of p47(phox) and RelA, and ectopic expression of RelA-PR abrogated IL-1beta-induced transactivation of the NF-kappaB-dependent E-selectin promoter. Further, suppression of NADPH oxidase function through the inhibitor diphenylene iodonium, the superoxide dismutase mimetic Mn(III) tetrakis(4-benzoic acid)porphyrin (MnTBAP), or expression of a dominant interfering mutant of a separate NADPH oxidase subunit (p67(V204A)) decreased IL-1beta-induced E-selectin promoter activation, suggesting that p47(phox) facilitates NF-kappaB activation through linkage with the NADPH oxidase. IL-1beta rapidly increased tyrosine phosphorylation of IL-1 type I receptor-associated proteins, suggesting that oxidants may operate through inactivation of local protein-tyrosine phosphatases in the proximal IL-1beta signaling pathway leading to RelA activation.     

Activation of Phosphatidylinositol 3-Kinase in Response to Interleukin-1 Leads to Phosphorylation and Activation of the NF-κB p65/RelA Subunit

The work of Reddy et al. (S. A. Reddy, J. A. Huang, and W. S. Liao, J. Biol. Chem. 272:29167-29173, 1997) reveals that phosphatidylinositol 3-kinase (PI3K) plays a role in transducing a signal from the occupied interleukin-1 (IL-1) receptor to nuclear factor kappaB (NF-kappaB), but the underlying mechanism remains to be determined. We have found that IL-1 stimulates interaction of the IL-1 receptor accessory protein with the p85 regulatory subunit of PI3K, leading to the activation of the p110 catalytic subunit. Specific PI3K inhibitors strongly inhibit both PI3K activation and NF-kappaB-dependent gene expression but have no effect on the IL-1-stimulated degradation of IkappaBalpha, the nuclear translocation of NF-kappaB, or the ability of NF-kappaB to bind to DNA. In contrast, PI3K inhibitors block the IL-1-stimulated phosphorylation of NF-kappaB itself, especially the p65/RelA subunit. Furthermore, by using a fusion protein containing the p65/RelA transactivation domain, we found that overexpression of the p110 catalytic subunit of PI3K induces p65/RelA-mediated transactivation and that the specific PI3K inhibitor LY294,002 represses this process. Additionally, the expression of a constitutively activated form of either p110 or the PI3K-activated protein kinase Akt also induces p65/RelA-mediated transactivation. Therefore, IL-1 stimulates the PI3K-dependent phosphorylation and transactivation of NF-kappaB, a process quite distinct from the liberation of NF-kappaB from its cytoplasmic inhibitor IkappaB.     

Inhibition of NF-IL6 activity by manassantin B, a dilignan isolated from Saururus chinensis, in phorbol myristate acetate-stimulated U937 promonocytic cells

Mannasantin B, a dilignan structurally related to manssantin A, is an inhibitor of NF-kappaB transactivation. In the present study, we found that it inhibited PMA-induced expression of IL-1beta, IL-1beta mRNA, and IL-1beta promoter activity in U937 cells with IC50 values of about 50 nM. It also inhibited NF-IL6- and NF-kappaB-induced activation of IL-1beta, with IC50 values of 78 nM and 1.6 microM, respectively, revealing a potent inhibitory effect on NF-IL6. Electrophoretic mobility shift assays showed that manassantin B had an inhibitory effect on DNA binding by NF-IL6, but not by NF-kappaB. Further analysis revealed that transactivation by NF-IL6 was also inhibited. Our results indicate that manassantin B suppresses expression of IL-1beta in promonocytic cells by inhibiting not only NF-kappaB but also NF-IL6 activity. Furthermore, our observations suggest that manassantin B may be clinically useful as a potent inhibitor of NF-IL6 activity.     

Estrogen receptor impairs interleukin-6 expression by preventing protein binding on the NF-kappaB site.

Interleukin-6 (IL-6) is a multifunctional cytokine thought to be a key factor in post-menopausal osteoporosis, given its ability to induce osteoclast maturation and its down regulation by estrogens. We have previously shown that the effects of TNFalphaand estradiol on the human IL-6 promoter were dependent on a region of the promoter containing a C/EBP site and a NF-kappaB site. To define the molecular mode of action of estrogens, we performed gel shift assays with this DNA fragment as a probe, and nuclear extracts from TNFalpha-induced HeLa, MCF7 and Saos2 cells. Several induced complexes specifically bound the probe. The use of various competitor DNA suggested that most of the complexes detected contained NF-kappaB factors, and that C/EBP site binding factors were important for the overall binding to the probe. Addition of in vitro translated human estrogen receptor (hER) impaired the binding of three complexes in HeLa cells and two complexes in MCF7 and Saos2 cells. Competition experiments suggested that the NF-kappaB site was necessary for the effect of hER. The use of antisera against NF-kappaB and C/EBP proteins showed that the target complexes of hER contained the c-rel proto-oncogene product and to a lesser extent, the RelA protein. Taken together, these data show that hER impairs TNFalphainduction of IL-6 by preventing c-rel and, to a lesser extent, RelA proteins binding to the NF-kappaB site of the IL-6 promoter.     

Impaired Bcl3 up-regulation leads to enhanced lipopolysaccharide-induced interleukin (IL)-23P19 gene expression in IL-10(-/-) mice

Genetic and biochemical analyses show that IL-23p19 plays a central role in mediating bacteria-induced colitis in interleukin-10-deficient (IL-10(-/-)) mice. The molecular mechanisms responsible for the dysregulated innate host response leading to enhanced IL-23 gene expression in IL-10(-/-) mice are poorly understood. In this study, we investigated the role of Bcl3 in controlling LPS-induced IL-23p19 gene expression in bone marrow-derived dendritic cells (BMDC) isolated from IL-10(-/-) mice. We report higher IL-23p19 mRNA accumulation and protein secretion in LPS-stimulated BMDC isolated from IL-10(-/-) compared with WT mice. Lipopolysaccharide (LPS)-induced B cell leukemia 3 (Bcl3) expression was strongly impaired (90% decrease) in IL-10(-/-) BMDC compared with WT BMDC. Chromatin immunoprecipitation demonstrated enhanced RelA binding to the IL-23p19 promoter in IL-10(-/-) compared with WT BMDC. Bcl3 overexpression decreased LPS-induced IL-23p19 gene expression in IL-10(-/-) BMDC, which correlated with enhanced NF-kappaB p50 binding and decreased RelA binding to the gene promoter. Conversely, Bcl3 knockdown enhanced LPS-induced IL-23p19 gene expression in WT BMDC. Moreover, LPS-induced IL-23p19 gene expression was significantly enhanced in Bcl3(-/-) BMDC compared with WT BMDC. In conclusion, enhanced LPS-induced IL-23p19 gene expression in IL-10(-/-) mice is due to impaired Bcl3 expression leading to diminished p50 and enhanced RelA recruitment to the IL-23p19 promoter.