Platelet-activating factor induces TLR4 expression in intestinal epithelial cells: implication for the pathogenesis of necrotizing enterocolitis.

Necrotizing enterocolitis (NEC) is a leading cause of morbidity and mortality in neonatal intensive care units, however its pathogenesis is not completely understood. We have previously shown that platelet activating factor (PAF), bacteria and TLR4 are all important factors in the development of NEC. Given that Toll-like receptors (TLRs) are expressed at low levels in enterocytes of the mature gastrointestinal tract, but were shown to be aberrantly over-expressed in enterocytes in experimental NEC, we examined the regulation of TLR4 expression and signaling by PAF in intestinal epithelial cells using human and mouse in vitro cell lines, and the ex vivo rat intestinal loop model. In intestinal epithelial cell (IEC) lines, PAF stimulation yielded upregulation of both TLR4 mRNA and protein expression and led to increased IL-8 secretion following stimulation with LPS (in an otherwise LPS minimally responsive cell line). PAF stimulation resulted in increased human TLR4 promoter activation in a dose dependent manner. Western blotting and immunohistochemical analysis showed PAF induced STAT3 phosphorylation and nuclear translocation in IEC, and PAF-induced TLR4 expression was inhibited by STAT3 and NFκB Inhibitors. Our findings provide evidence for a mechanism by which PAF augments inflammation in the intestinal epithelium through abnormal TLR4 upregulation, thereby contributing to the intestinal injury of NEC.

Lipopolysaccharide-induced apoptosis in transformed bovine brain endothelial cells and human dermal microvessel endothelial cells: the role of JNK.

Stimulation of transformed bovine brain endothelial cells (TBBEC) with LPS leads to apoptosis while human microvessel endothelial cells (HMEC) need the presence of cycloheximide (CHX) with LPS to induce apoptosis. To investigate the molecular mechanism of LPS-induced apoptosis in HMEC or TBBEC, we analyzed the involvement of MAPK and PI3K in TBBEC and HMEC. LPS-induced apoptosis in TBBEC was hallmarked by the activation of caspase 3, caspase 6, and caspase 8 after the stimulation of LPS, followed by poly(ADP-ribose) polymerase cleavage and lactate dehydrogenase release. We also observed DNA cleavage determined by TUNEL staining in TBBEC treated with LPS. Herbimycin A, a tyrosine kinase inhibitor, and SP600125, a JNK inhibitor, suppressed the activation of caspases and lactate dehydrogenase release. Moreover, a PI3K inhibitor (LY294002) suppressed activation of caspases and combined treatment with both SP600125 and LY294002 completely inhibited the activation of caspases. These results suggest that the JNK signaling pathway through the tyrosine kinase and PI3K pathways is involved in the induction of apoptosis in LPS-treated TBBEC. On the other hand, we observed sustained JNK activation in HMEC treated with LPS and CHX, and neither ERK1/2 nor AKT were activated. The addition of SP600125 suppressed phosphorylation of JNK and the activation of caspase 3 in HMEC treated with LPS and CHX. These results suggest that JNK plays an important role in the induction of apoptosis in endothelial cells.

ERCC5 is a novel biomarker of ovarian cancer prognosis.

PURPOSE: To identify a biomarker of ovarian cancer response to chemotherapy. PATIENTS AND METHODS Study: participants had epithelial ovarian cancer treated with surgery followed by platinum-based chemotherapy. DNA and RNA were isolated from frozen tumors and normal DNA was isolated from matched peripheral blood. A whole-genome loss of heterozygosity (LOH) analysis was performed using a high-density oligonucleotide array. Candidate genomic areas that predicted enhanced response to chemotherapy were identified with Cox proportional hazards methods. Gene expression analyses were performed through microarray experiments. Candidate genes were tested for independent effects on survival using Cox proportional hazards models, Kaplan-Meier survival curves, and the log-rank test. RESULTS: Using a whole-genome approach to study the molecular determinants of ovarian cancer response to platinum-based chemotherapy, we identified LOH of a 13q region to predict prolonged progression-free survival (PFS; hazard ratio, 0.23; P = .006). ERCC5 was identified as a candidate gene in this region because of its known function in the nucleotide excision repair pathway, the unique DNA repair pathway that removes platinum-DNA adducts. We found LOH of the ERCC5 gene locus and downregulation of ERCC5 gene expression to predict prolonged PFS. Integration of genomic and gene expression data shows a correlation between 13q LOH and ERCC5 gene downregulation. CONCLUSION: ERCC5 is a novel biomarker of ovarian cancer prognosis and a potential therapeutic target of ovarian cancer response to platinum chemotherapy.

Ubiquitination and de-ubiquitination: role in regulation of signaling by Toll-like receptors.

Signaling by Toll-like receptors (TLRs) has attracted accelerating attention over the past decade because of the central role of TLR signaling in both innate and adaptive immunity. In addition, TLR signaling is now increasingly implicated in a remarkably wide range of diseases that are either caused, or accompanied, by dysregulated inflammation. Much has been learned about the basic signaling framework and participants, as well as how signaling is turned off and fine-tuned. Here, we summarize key aspects of TLR signaling, focusing on interaction with the anti-inflammatory TGF-beta signaling network. We propose that ubiquitination and de-ubiquitination of TLR pathway components may be a mechanism by which predominantly anti-inflammatory input is integrated into the host response to fine-tune inflammation in accordance with the needs of host defenses.

Mastoparan, a G protein agonist peptide, differentially modulates TLR4- and TLR2-mediated signaling in human endothelial cells and murine macrophages.

Previous studies have implicated a role for heterotrimeric G protein-coupled signaling in B cells, monocytes, and macrophages stimulated with LPS and have shown that G proteins coimmunoprecipitate with membrane-bound CD14. In this study, we have extended these observations in human dermal microvessel endothelial cells (HMEC) that lack membrane-bound CD14 and in murine macrophages to define further the role of heterotrimeric G proteins in TLR signaling. Using the wasp venom-derived peptide, mastoparan, to disrupt G protein-coupled signaling, we identified a G protein-dependent signaling pathway in HMEC stimulated with TLR4 agonists that is necessary for the activation of p38 phosphorylation and kinase activity, NF-kappaB and IL-6 transactivation, and IL-6 secretion. In contrast, HMEC activation by TLR2 agonists, TNF-alpha, or IL-1beta was insensitive to mastoparan. In the murine macrophage cell line, RAW 264.7, and in primary murine macrophages, G protein dysregulation by mastoparan resulted in significant inhibition of LPS-induced signaling leading to both MyD88-dependent and MyD88-independent gene expression, while TLR2-mediated gene expression was not significantly inhibited. In addition to inhibition of TLR4-mediated MAPK phosphorylation in macrophages, mastoparan blunted IL-1R-associated kinase-1 kinase activity induced by LPS, but not by TLR2 agonists, yet failed to affect phosphorylation of Akt by phosphoinositol-3-kinase induced by either TLR2- or TLR4-mediated signaling. These data confirm the importance of heterotrimeric G proteins in TLR4-mediated responses in cells that use either soluble or membrane-associated CD14 and reveal a level of TLR and signaling pathway specificity not previously appreciated.

Endotoxin-tolerance to the cytotoxicity toward a macrophage-like cell line, J774.1, induced by lipopolysaccharide and cycloheximide: role of p38 MAPK in induction of the cytotoxicity.

Novel endotoxin-tolerance was observed to the cytotoxycity induced by lipopolysaccharide (LPS) and cycloheximide (CHX) in an LPS-treated macrophage-like cell line, J774.1; preincubation of macrophages with low doses of LPS alone for 90 min almost completely prevented the apoptotic death in the second incubation with LPS and CHX. The first challenge of LPS affected neither the subsequent LPS binding nor the expression of CD14. Instead, phosphorylation of mitogen-activated proteinkinase (MAP kinases) involving p38, extracellular signal-regulated kinase 1/2 (Erk1/Erk2) and c-jun N-terminal kinase (JNK) in the second incubation with LPS and CHX were suppressed, suggesting that this endotoxin-tolerance was caused by down-regulation of LPS-signaling pathway leading to MAP kinase activation. On the other hand, LPS-induced cytotoxicity seemed to depend on the sustained phosphorylation of p38 MAP kinase; the addition of SB202190, an inhibitor of p38 MAP kinase activity, in the first incubation with LPS caused induction of the cytotoxicity in the second incubation with LPS and CHX or CHX alone, under which conditions increased phosphorylation of p38 MAP kinase without that of Erk1/Erk2 or JNK was observed. These results suggest that down-regulation of the p38 MAP kinase cascade in the first incubation with LPS is linked to induction of endotoxin-tolerance to the cytotoxicity with higher doses of LPS and CHX.

Chlamydial heat shock protein 60 activates macrophages and endothelial cells through Toll-like receptor 4 and MD2 in a MyD88-dependent pathway.

Active inflammation and NF-kappaB activation contribute fundamentally to atherogenesis and plaque disruption. Accumulating evidence has implicated specific infectious agents including Chlamydia pneumoniae in the progression of atherogenesis. Chlamydial heat shock protein 60 (cHSP60) has been implicated in the induction of deleterious immune responses in human chlamydial infections and has been found to colocalize with infiltrating macrophages in atheroma lesions. cHSP60 might stimulate, enhance, and maintain innate immune and inflammatory responses and contribute to atherogenesis. In this study, we investigated the signaling mechanism of cHSP60. Recombinant cHSP60 rapidly activated NF-kappaB in human microvascular endothelial cells (EC) and in mouse macrophages, and induced human IL-8 promoter activity in EC. The inflammatory effect of cHSP60 was heat labile, thus excluding a role of contaminating LPS, and was blocked by specific anti-chlamydial HSP60 mAb. In human vascular EC which express Toll-like receptor 4 (TLR4) mRNA and protein, nonsignaling TLR4 constructs that act as dominant negative blocked cHSP60-mediated NF-kappaB activation. Furthermore, an anti-TLR4 Ab abolished cHSP60-induced cellular activation, whereas a control Ab had no effect. In 293 cells, cHSP60-mediated NF-kappaB activation required both TLR4 and MD2. A dominant-negative MyD88 construct also inhibited cHSP60-induced NF-kappaB activation. Collectively, our results indicate that cHSP60 is a potent inducer of vascular EC and macrophage inflammatory responses, which are very relevant to atherogenesis. The inflammatory effects are mediated through the innate immune receptor complex TLR4-MD2 and proceeds via the MyD88-dependent signaling pathway. These findings may help elucidate the mechanisms by which chronic asymptomatic chlamydial infection contribute to atherogenesis.