Structure of the F‐spondin domain of mindin,an integrin ligand and pattern recognition molecule

Mindin (spondin‐2) is an extracellular matrix protein of unknown structure that is required for efficient T‐cell priming by dendritic cells. Additionally, mindin functions as a pattern recognition molecule for initiating innate immune responses. These dual functions are mediated by interactions with integrins and microbial pathogens, respectively. Mindin comprises an N‐terminal F‐spondin (FS) domain and C‐terminal thrombospondin type 1 repeat (TSR). We determined the structure of the FS domain at 1.8‐Å resolution. The structure revealed an eight‐stranded antiparallel β‐sandwich motif resembling that of membrane‐targeting C2 domains, including a bound calcium ion. We demonstrated that the FS domain mediates integrin binding and identified the binding site by mutagenesis. The mindin FS domain therefore represents a new integrin ligand. We further showed that mindin recognizes lipopolysaccharide (LPS) through its TSR domain, and obtained evidence that C‐mannosylation of the TSR influences LPS binding. Through these dual interactions, the FS and TSR domains of mindin promote activation of both adaptive and innate immune responses.     

A novel NOD1‐ and CagA‐independent pathway of interleukin‐8 induction mediated by the Helicobacter pylori type IV secretion system

The type IV secretion system (T4SS) of Helicobacter pylori triggers massive inflammatory responses during gastric infection by mechanisms that are poorly understood. Here we provide evidence for a novel pathway by which the T4SS structural component, CagL, induces secretion of interleukin‐8 (IL‐8) independently of CagA translocation and peptidoglycan‐sensing nucleotide‐binding oligomerization domain 1 (NOD1) signalling. Recombinant CagL was sufficient to trigger IL‐8 secretion, requiring activation of α₅β₁ integrin and the arginine–glycine–aspartate (RGD) motif in CagL. Mutation of the encoded RGD motif to arginine‐glycine‐alanine (RGA) in the cagL gene of H. pylori abrogated its ability to induce IL‐8. Comparison of IL‐8 induction between H. pylori ΔvirD4 strains bearing wild‐type or mutant cagL indicates that CagL‐dependent IL‐8 induction can occur independently of CagA translocation. In line with this notion, exogenous CagL complemented H. pylori ΔcagL mutant in activating NF‐κB and inducing IL‐8 without restoring CagA translocation. The CagA translocation‐independent, CagL‐dependent IL‐8induction involved host signalling via integrin α₅β₁, Src kinase, the mitogen‐activated protein kinase (MAPK) pathway and NF‐κB but was independent of NOD1. Our findings reveal a novel pathway whereby CagL, via interaction with host integrins, can trigger pro‐inflammatory responses independently of CagA translocation or NOD1 signalling.     

Activated α2 macroglobulin induces matrix metalloproteinase 9 expression by low‐density lipoprotein receptor‐related protein 1 through MAPK‐ERK1/2 and NF‐κB activation in macrophage‐derived cell lines

Macrophages under certain stimuli induce matrix metalloproteinase 9 (MMP‐9) expression and protein secretion through the activation of MAPK‐ERK and NF‐κB signaling pathways. Previously, we demonstrated that activated α₂‐macroglulin (α₂M*) through the interaction with its receptor low‐density lipoprotein receptor‐related protein 1 (LRP1) induces macrophage proliferation mediated by the activation of MAPK‐ERK1/2. In the present work, we examined whether α₂M*/LRP1interaction could induce the MMP‐9 production in J774 and Raw264.7 macrophage‐derived cell lines. It was shown that α₂M* promoted MMP‐9 expression and protein secretion by LRP1 in both macrophage‐derived cell lines, which was mediated by the activation of MAPK‐ERK1/2 and NF‐κB. Both intracellular signaling pathways activated by α₂M* were effectively blocked by calphostin‐C, suggesting involvement of PKC. In addition, we demonstrate that α₂M* produced extracellular calcium influx via LRP1. However, when the intracellular calcium mobilization was inhibited by BAPTA‐AM, the α₂M*‐induced MAPK‐ER1/2 activation was fully blocked in both macrophage cell lines. Finally, using specific pharmacological inhibitors for PKC, Mek1, and NF‐κB, it was shown that the α₂M*‐induced MMP‐9 protein secretion was inhibited, indicating that the MMP production promoted by the α₂M*/LRP1 interaction required the activation of both signaling pathways. These findings may prove useful in the understanding of the macrophage LRP1 role in the vascular wall during atherogenic plaque progression. J. Cell. Biochem. 111: 607–617, 2010. © 2010 Wiley‐Liss, Inc.     

The BAFFling function of Syk in B‐cell homeostasis

The TNF receptor family member BAFFR is essential for providing mature B cells with pro‐survival signals and has recently been claimed to transduce these, though not exclusively, via a Syk‐dependent signaling hub that feeds into ERK/AKT activation. In this issue of The EMBO Journal, Hobeika et al (2015) describe a synergistic pro‐survival scenario involving BAFFR and CD19, which remains functional under Syk null conditions and is able to maintain mature B‐cell survival. The authors hence propose a BAFFR‐/CD19‐driven mechanism to act in parallel with homeostatic NF‐κB/AKT activation in non‐stimulated B cells.     

Dioscorealide B suppresses LPS‐induced nitric oxide production and inflammatory cytokine expression in RAW 264.7 macrophages: The inhibition of NF‐κB and ERK1/2 activation

Dioscorealide B (DB), a naphthofuranoxepin has been purified from an ethanolic extract of the rhizome of Dioscorea membranacea Pierre ex Prain & Burkill which has been used to treat inflammation and cancer in Thai Traditional Medicine. Previously, DB has been reported to have anti‐inflammatory activities through reducing nitric oxide (NO) and tumor necrosis factor‐α (TNF‐α) production in lipopolysaccharides (LPS)‐induced RAW 264.7 macrophage cells. In this study, the mechanisms of DB on LPS‐induced NO production and cytokine expression through the activation of nuclear factor‐κB (NF‐κB) and ERK1/2 are demonstrated in RAW 264.7 cells. Through measurement with Griess's reagent, DB reduced NO level with an IC₅₀ value of 2.85 ± 0.62 µM that was due to the significant suppression of LPS‐induced iNOS mRNA expression as well as IL‐1β, IL‐6, and IL‐10 mRNA at a concentration of 6 µM. At the signal transduction level, DB significantly inhibited NF‐κB binding activity, as determined using pNFκB‐Luciferase reporter system, which action resulted from the prevention of IκBα degradation. In addition, DB in the range of 1.5–6 µM significantly suppressed the activation of the ERK1/2 protein. In conclusion, the molecular mechanisms of DB on the inhibition of NO production and mRNA expression of iNOS, IL‐1β, IL‐6, and IL‐10 were due to the inhibition of the upstream kinases activation, which further alleviated the NF‐κB and MAPK/ERK signaling pathway in LPS‐induced RAW264.7 macrophage cells. J. Cell. Biochem. 109: 1057–1063, 2010. © 2010 Wiley‐Liss, Inc.     

α1 adrenoceptor activation by norepinephrine inhibits LPS‐induced cardiomyocyte TNF‐α production via modulating ERK1/2 and NF‐κB pathway

Cardiomyocyte tumour necrosis factor α (TNF‐α) production contributes to myocardial depression during sepsis. This study was designed to observe the effect of norepinephrine (NE) on lipopolysaccharide (LPS)‐induced cardiomyocyte TNF‐α expression and to further investigate the underlying mechanisms in neonatal rat cardiomyocytes and endotoxaemic mice. In cultured neonatal rat cardiomyocytes, NE inhibited LPS‐induced TNF‐α production in a dose‐dependent manner. α₁‐ adrenoceptor (AR) antagonist (prazosin), but neither β₁‐ nor β₂‐AR antagonist, abrogated the inhibitory effect of NE on LPS‐stimulated TNF‐α production. Furthermore, phenylephrine (PE), an α₁‐AR agonist, also suppressed LPS‐induced TNF‐α production. NE inhibited p38 phosphorylation and NF‐κB activation, but enhanced extracellular signal‐regulated kinase 1/2 (ERK1/2) phosphorylation and c‐Fos expression in LPS‐treated cardiomyocytes, all of which were reversed by prazosin pre‐treatment. To determine whether ERK1/2 regulates c‐Fos expression, p38 phosphorylation, NF‐κB activation and TNF‐α production, cardiomyocytes were also treated with U0126, a selective ERK1/2 inhibitor. Treatment with U0126 reversed the effects of NE on c‐Fos expression, p38 mitogen‐activated protein kinase (MAPK) phosphorylation and TNF‐α production, but not NF‐κB activation in LPS‐challenged cardiomyocytes. In addition, pre‐treatment with SB202190, a p38 MAPK inhibitor, partly inhibited LPS‐induced TNF‐α production in cardiomyocytes. In endotoxaemic mice, PE promoted myocardial ERK1/2 phosphorylation and c‐Fos expression, inhibited p38 phosphorylation and IκBα degradation, reduced myocardial TNF‐α production and prevented LPS‐provoked cardiac dysfunction. Altogether, these findings indicate that activation of α₁‐AR by NE suppresses LPS‐induced cardiomyocyte TNF‐α expression and improves cardiac dysfunction during endotoxaemia via promoting myocardial ERK phosphorylation and suppressing NF‐κB activation.     

N‐methyl‐N‐nitrosourea induces retinal degeneration in the rat via the inhibition of NF‐κB activation

Retinitis pigmentosa (RP) is a group of inherited neurodegenerative diseases characterized by the loss of photoreceptor cells through apoptosis. N‐methyl‐N‐nitrosourea (MNU) is an alkylating toxicant that induces photoreceptor cell death resembling hereditary RP. This study aimed to investigate the role of nuclear factor κB (NF‐κB) in MNU‐induced photoreceptor degeneration. Adult rats received a single intraperitoneal injection of MNU (60 mg/kg bodyweight). Hematoxylin and eosin staining demonstrated progressive outer nuclear layer (ONL) loss after MNU treatment. Transmission electron microscopy revealed nuclear pyknosis, chromatin margination in the photoreceptors, increased secondary lysosomes, and lobulated retinal‐pigmented epithelial cells in MNU‐treated rats. Numerous photoreceptor cells in the ONL showed positive TUNEL staining and apoptosis rate peaked at 24 hours. Enhanced depth imaging spectral‐domain optical coherence tomography showed ONL thinning and decreased choroid thickness. Electroretinograms showed decreased A wave amplitude that predominated in scotopic conditions. Western blot analysis showed that nuclear IκBα level increased, whereas nuclear NF‐κB p65 decreased significantly in the retinas of MNU‐treated rats. These findings indicate that MNU leads to selective photoreceptor degradation, and this is associated with the inhibition of NF‐κB activation.     

5′‐N‐ethylcarboxamide induces IL‐6 expression via MAPKs and NF‐κB activation through Akt,Ca2+/PKC,cAMP signaling pathways in mouse embryonic stem cells

Many studies suggest that adenosine modulates cell responses in a wide array of tissues through potent and selective regulation of cytokine production. This study examined the effects of adenosine on interleukin (IL)‐6 expression and its related signal pathways in mouse embryonic stem (ES) cells. In this study, the adenosine analogue 5′‐N‐ethylcarboxamide (NECA) increased IL‐6 protein expression level. Mouse ES cells expressed the A₁, A_2A, A_2B, and A₃ adenosine receptors (ARs), whose expression levels were increased by NECA and NECA‐induced increase of IL‐6 mRNA expression or secretion level was inhibited by the non‐specific AR inhibitor, caffeine. NECA increased Akt and protein kinase C (PKC) phosphorylation, intracellular Ca²⁺ and cyclic adenosine monophosphate (cAMP) levels, which were blocked by caffeine. On the other hand, NECA‐induced IL‐6 secretion was partially inhibited by Akt inhibitor, bisindolylmaleimide I (PKC inhibitor), SQ 22536 (adenylate cyclate inhibitor) and completely blocked by the 3 inhibitor combination treatment. In addition, NECA increased mitogen activated protein kinase' (MAPK) phosphorylation, which were partially inhibited by the Akt inhibitor, bisindolylmaleimide I, and SQ 22536 and completely blocked by the 3 inhibitor combination treatment. NECA‐induced increases of IL‐6 protein expression and secretion levels were inhibited by MAPK inhibition. NECA‐induced increase of nuclear factor (NF)‐κB phosphorylation was inhibited by MAPK inhibitors. NECA also increased cAMP response element‐binding protein (CREB) phosphorylation, which was blocked by MAPK or NF‐κB inhibitors. Indeed, NECA‐induced increase of IL‐6 protein expression and secretion was blocked by NF‐κB inhibitors. In conclusion, NECA stimulated IL‐6 expression via MAPK and NF‐κB activation through Akt, Ca²⁺/PKC, and cAMP signaling pathways in mouse ES cells. J. Cell. Physiol. 219: 752–759, 2009. © 2009 Wiley‐Liss, Inc.     

Central role of PAFR signalling in ExoU‐induced NF‐κB activation

ExoU is an important virulence factor in acute Pseudomonas aeruginosa infections. Here, we unveiled the mechanisms of ExoU‐driven NF‐κB activation by using human airway cells and mice infected with P. aeruginosa strains. Several approaches showed that PAFR was crucially implicated in the activation of the canonical NF‐κB pathway. Confocal microscopy of lungs from infected mice revealed that PAFR‐dependent NF‐κB activation occurred mainly in respiratory epithelial cells, and reduced p65 nuclear translocation was detected in mice PAFR?/? or treated with the PAFR antagonist WEB 2086. Several evidences showed that ExoU‐induced NF‐κB activation regulated PAFR expression. First, ExoU increased p65 occupation of PAFR promoter, as assessed by ChIP. Second, luciferase assays in cultures transfected with different plasmid constructs revealed that ExoU promoted p65 binding to the three κB sites in PAFR promoter. Third, treatment of cell cultures with the NF‐κB inhibitor Bay 11–7082, or transfection with IκBα negative‐dominant, significantly decreased PAFR mRNA. Finally, reduction in PAFR expression was observed in mice treated with Bay 11–7082 or WEB 2086 prior to infection. Together, our data demonstrate that ExoU activates NF‐κB by PAFR signalling, which in turns enhances PAFR expression, highlighting an important mechanism of amplification of response to this P. aeruginosa toxin.