Activation of Nod2 signaling upon norovirus infection enhances antiviral immunity and susceptibility to colitis

Over 90% of epidemic non-bacterial gastroenteritis are caused by human noroviruses (NoVs), which persist in a substantial subset of people allowing their spread worldwide. This has led to a significant number of endemic cases and up to 70,000 children deaths in developing countries. NoVs are primarily transmitted through the fecal-oral route. To date, studies have focused on the influence of the gut microbiota on enteric viral clearance by mucosal immunity. In this study, the use of mouse norovirus S99 (MNoV_S99) and CR6 (MNoV_CR6), two persistent strains, allowed us to provide evidence that the norovirus-induced exacerbation of colitis severity relied on bacterial sensing by nucleotide-binding oligomerization domain 2 (Nod2). Consequently, Nod2-deficient mice showed reduced levels of gravity of Dextran sodium sulfate (DSS)-induced colitis with both viral strains. And MNoV_CR6 viremia was heightened in Nod2-/- mice in comparison with animals hypomorphic for Atg16l1, which are prone to aggravated inflammation under DSS. Accordingly, the infection of macrophages derived from WT mice promoted the phosphorylation of Signal Transducer and Activator of Transcription 1 (STAT1) and NOD2's expression levels. Higher secretion of Tumor Necrosis Factor alpha (TNFα ) following NOD2 activation and better viral clearance were measured in these cells. By contrast, reduced levels of pSTAT1 and blunted downstream secretion of TNFα were found in Nod2-deficient macrophages infected by MNoV_S99. Hence, our results uncover a previously unidentified virus-host-bacterial interplay that may represent a novel therapeutic target for treating noroviral origin gastroenteritis that may be linked with susceptibility to several common illnesses such as Crohn's disease.

Persistence and dynamics of fluorescent Lactobacillus plantarum in the healthy versus inflamed gut

The gastrointestinal tract is the main ecological niche in which Lactobacillus strains may provide health benefits in mammals. There is currently a need to characterize host-microbe interactions in space and time by tracking these bacteria in vivo. We combined noninvasive whole-body imaging with ex vivo fluorescence confocal microscopy imaging to monitor the impact of intestinal inflammation on the persistence of orally administered Lactobacillus plantarum NCIMB8826 in healthy and inflamed mouse colons. We developed fluorescent L. plantarum strains and demonstrated that mCherry is the best system for in vivo imaging and ex vivo fluorescence confocal microscopy of these bacteria. We also used whole-body imaging to show that this anti-inflammatory, orally administered strain persists for longer and at higher counts in the inflamed colon than in the healthy colon. We confirmed these results by the ex vivo confocal imaging of colons from mice with experimental colitis for 3 days after induction. Moreover, extended orthogonal view projections enabled us to localize individual L. plantarum in sites that differed for healthy versus inflamed guts. In healthy colons, orally administered bacteria were localized in the lumen (in close contact with commensal bacteria) and sometimes in the crypts (albeit very rarely in contact with intestinal cells). The bacteria were observed within and outside the mucus layer. In contrast, L. plantarum bacteria in the inflamed colon were mostly located in the lumen and (in less inflamed areas) within the mucus layer. In more intensely inflamed areas (i.e., where the colon had undergone structural damage), the L. plantarum were in direct contact with damaged epithelial cells. Taken as a whole, our results show that fluorescently labeled L. plantarum can be used to study the persistence of these bacteria in inflamed guts using both noninvasive whole-body imaging and ex vivo fluorescence confocal microscopy.

Rubrolone production by Dactylosporangium vinaceum: biosynthesis, modulation and possible biological function

Rare actinomycetes are likely treasure troves for bioactive natural products, and it is therefore important that we enrich our understanding of biosynthetic potential of these relatively understudied bacteria. Dactylosporangium are a genus of such rare Actinobacteria that are known to produce a number of important antibacterial compounds, but for which there are still no fully assembled reference genomes, and where the extent of encoded biosynthetic capacity is not defined. Dactylosporangium vinaceum (NRRL B-16297) is known to readily produce a deep wine red-coloured diffusible pigment of unknown origin, and it was decided to define the chemical identity of this natural product pigment, and in parallel use whole genome sequencing and transcriptional analysis to lay a foundation for understanding the biosynthetic capacity of these bacteria. Results show that the produced pigment is made of various rubrolone conjugates, the spontaneous product of the reactive pre-rubrolone, produced by the bacterium. Genome and transcriptome analysis identified the highly expressed biosynthetic gene cluster (BGC) for pre-rubrolone. Further analysis of the fully assembled genome found it to carry 24 additional BGCs, of which the majority were poorly transcribed, confirming the encoded capacity of this bacterium to produce natural products but also illustrating the main bottleneck to exploiting this capacity. Finally, analysis of the potential environmental role of pre-rubrolone found it to react with a number of amine containing antibiotics, antimicrobial peptides and siderophores pointing to its potential role as a "minesweeper" of xenobiotic molecules in the bacterial environment. KEY POINTS: • D. vinaceum encodes many BGC, but the majority are transcriptionally silent. • Chemical screening identifies molecules that modulate rubrolone production. • Pre-rubrolone is efficient at binding and inactivating many natural antibiotics.

Vimentin-ERK Signaling Uncouples Slug Gene Regulatory Function

Epithelial-mesenchymal transition (EMT) in cells is a developmental process adopted during tumorigenesis that promotes metastatic capacity. In this study, we advance understanding of EMT control in cancer cells with the description of a novel vimentin-ERK axis that regulates the transcriptional activity of Slug (SNAI2). Vimentin, ERK, and Slug exhibited overlapping subcellular localization in clinical specimens of triple-negative breast carcinoma. RNAi-mediated ablation of these gene products inhibited cancer cell migration and cell invasion through a laminin-rich matrix. Biochemical analyses demonstrated direct interaction of vimentin and ERK, which promoted ERK activation and enhanced vimentin transcription. Consistent with its role as an intermediate filament, vimentin acted as a scaffold to recruit Slug to ERK and promote Slug phosphorylation at serine-87. Site-directed mutagenesis established a requirement for ERK-mediated Slug phosphorylation in EMT initiation. Together, these findings identified a pivotal step in controlling the ability of Slug to organize hallmarks of EMT.

Tensin-4-dependent MET stabilization is essential for survival and proliferation in carcinoma cells

Inappropriate MET tyrosine kinase receptor signaling is detected in almost all types of human cancer and contributes to malignant growth and MET dependency via proliferative and antiapoptotic activities. Independently, Tensin-4 (TNS4) is emerging as a putative oncogene in many cancer types, but the mechanisms of TNS4 oncogenic activity are not well established. Here, we demonstrate that TNS4 directly interacts with phosphorylated MET via the TNS4 SH2-domain to positively regulate cell survival, proliferation, and migration, through increased MET protein stability. In addition, TNS4 interaction with β1-integrin cytoplasmic tail positively regulates β1-integrin stability. Loss of TNS4 or disruption of MET-TNS4 interaction triggers MET trafficking toward the lysosomal compartment that is associated with excessive degradation of MET and triggers MET-addicted carcinoma cell death in vitro and in vivo. Significant correlation between MET and TNS4 expression in human colon carcinoma and ovarian carcinoma suggests TNS4 plays a critical role in MET stability in cancer.

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A direct interaction is identified between MET and Tensin-4

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TNS4 protects MET from degradation, thus promoting its oncogenic activity

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TNS4 and MET are significantly coexpressed in human carcinomas

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Loss of TNS4 inhibits survival of MET-dependent tumors

Distinct c-Met activation mechanisms induce cell rounding or invasion through pathways involving integrins, RhoA and HIP1

Many carcinomas have acquired oncogenic mechanisms for activating c-Met, including c-Met overexpression and excessive autocrine or paracrine stimulation with hepatocyte growth factor (HGF). However, the biological outcome of c-Met activation through these distinct modes remains ambiguous. Here, we report that HGF-mediated c-Met stimulation triggers a mesenchymal-type collective cell invasion. By contrast, the overexpression of c-Met promotes cell rounding. Moreover, in a high-throughput siRNA screen that was performed using a library of siRNAs against putative regulators of integrin activity, we identified RhoA and the clathrin-adapter protein HIP1 as crucial c-Met effectors in these morphological changes. Transient RhoA activation was necessary for the HGF-induced invasion, whereas sustained RhoA activity regulated c-Met-induced cell rounding. In addition, c-Met-induced cell rounding correlated with the phosphorylation of filamin A and the downregulation of active cell-surface integrins. By contrast, a HIP1-mediated increase in β1-integrin turnover was required for the invasion triggered by HGF. Taken together, our results indicate that c-Met induces distinct cell morphology alterations depending on the stimulus that activates c-Met.

Caspase-generated fragment of the Met receptor favors apoptosis via the intrinsic pathway independently of its tyrosine kinase activity

The receptor tyrosine kinase Met and its ligand, the hepatocyte growth factor, are essential to embryonic development, whereas the deregulation of Met signaling is associated with tumorigenesis. While ligand-activated Met promotes survival, caspase-dependent generation of the p40 Met fragment leads to apoptosis induction - hallmark of the dependence receptor. Although the survival signaling pathways induced by Met are well described, the pro-apoptotic signaling pathways are unknown. We show that, although p40 Met contains the entire kinase domain, it accelerates apoptosis independently of kinase activity. In cell cultures undergoing apoptosis, the fragment shows a mitochondrial localization, required for p40 Met-induced cell death. Fulminant hepatic failure induced in mice leads to the generation of p40 Met localized also in the mitochondria, demonstrating caspase cleavage of Met in vivo. According to its localization, the fragment induces mitochondrial permeabilization, which is inhibited by Bak silencing and Bcl-xL overexpression. Moreover, Met silencing delays mitochondrial permeabilization induced by an apoptotic treatment. Thus, the Met-dependence receptor in addition to its well-known role in survival signaling mediated by its kinase activity, also participates in the intrinsic apoptosis pathway through the generation of p40 Met - a caspase-dependent fragment of Met implicated in the mitochondrial permeabilization process.

Shedding-generated Met receptor fragments can be routed to either the proteasomal or the lysosomal degradation pathway

The receptor tyrosine kinase Met and its ligand, the hepatocyte growth factor/scatter factor, are essential for embryonic development, whereas deregulation of Met signaling pathways is associated with tumorigenesis and metastasis. The presenilin-regulated intramembrane proteolysis (PS-RIP) is involved in ligand-independent downregulation of Met. This proteolytic process involves shedding of the Met extracellular domain followed by γ-secretase cleavage, generating labile intracellular fragments degraded by the proteasome. We demonstrate here that upon shedding both generated Met N- and C-terminal fragments are degraded directly in the lysosome, with C-terminal fragments escaping γ-secretase cleavage. PS-RIP and lysosomal degradation are complementary, because their simultaneous inhibition induces synergistic accumulation of fragments. Met N-terminal fragments associate with the high-affinity domain of HGF/SF, confirming its decoy activity which could be reduced through their routing to the lysosome at the expense of extracellular release. Finally, the DN30 monoclonal antibody inducing Met shedding promotes receptor degradation through induction of both PS-RIP and the lysosomal pathway. Thus, we demonstrate that Met shedding initiates a novel lysosomal degradation which participates to ligand-independent downregulation of the receptor.

Met degradation: more than one stone to shoot a receptor down

The receptor tyrosine kinase Met and its high-affinity ligand, the hepatocyte growth factor/scatter factor (HGF/SF), are essential to embryonic development. Deregulation of their signaling is associated with tumorigenesis and metastasis, notably through receptor overexpression. It is thus important to understand the mechanisms controlling Met expression. The ligand-dependent internalization of Met and its subsequent degradation in the lysosomal compartment are well described. This process is known to attenuate downstream Met signaling pathways. Yet internalized Met takes part directly in intracellular signaling by chaperoning signaling factors in the course of its trafficking. Furthermore, recent studies describe various new degradation mechanisms of membrane-anchored Met, involving proteolytic cleavages or association with novel partners. Although all these degradations are ligand-independent, they share, to different extents, some common features with canonical HGF/SF-dependent degradation. Interestingly, activated Met variants display resistance to degradation, suggesting defective degradation is involved in tumorigenesis. Conversely, forced degradation of Met through reinduction of one or more degradation pathways is a promising therapeutic strategy.

1,25-Dihydroxyvitamin D3 protects human pancreatic islets against cytokine-induced apoptosis via down-regulation of the Fas receptor

Beta cell loss occurs at the onset of type 1 diabetes and after islet graft. It results from the dysfunction and destruction of beta cells mainly achieved by apoptosis. One of the mediators believed to be involved in beta cell apoptosis is Fas, a transmembrane cell surface receptor transducing an apoptotic death signal and contributing to the pathogenesis of several autoimmune diseases. Fas expression is particularly induced in beta cells by inflammatory cytokines secreted by islet-infiltrating mononuclear cells and makes cells susceptible to apoptosis by interaction with Fas-ligand expressing cells. We have previously demonstrated that 1,25(OH)2D3, the active metabolite of vitamin D, known to exhibit immunomodulatory properties and prevent the development of type 1 diabetes in NOD mice, is efficient against apoptosis induced by cytokines in human pancreatic islets in vitro. The effects were mainly mediated by the inactivation of NF-kappa-B. In this study we demonstrated that 1,25(OH)2D3 was also able to counteract cytokine-induced Fas expression in human islets both at the mRNA and protein levels. These results were reinforced by our microarray analysis highlighting the beneficial effects of 1,25(OH)2D3 on death signals induced by Fas activation. Our results provides additional evidence that 1,25(OH)2D3 may be an interesting tool to help prevent the onset of type 1 diabetes and improve islet graft survival.

Endocrine pancreatic tissue plasticity in obese humans is associated with cytoplasmic expression of PBX-1 in pancreatic ductal cells

In vivo lineage tracing experiments in mice have recently cast doubt on the potential islet neogenesis from ductal precursors in adult mammals. We examined, in human obesity, a model for pancreatic endocrine tissue plasticity, the gene and protein expression of PBX-1-a transcription factor expressed in regenerating rat ductules and potentially implicated in the pancreatic development, alone or in association with PDX-1. When comparing gene expression, by quantitative real-time RT-PCR, in pancreatic exocrine tissue from obese non-diabetic subjects with increased islet mass, we found that Pbx-1 and Pdx-1 were up-regulated (5.9+/-1.2 and 2.4+/-0.6 versus non-obese). Immunohistochemistry confirmed PBX-1 over-expression and its cytoplasmic sequestration in ductal cells of obese subjects, associated with pronounced islet neogenesis (cytokeratin 19/chromogranin A double labeling). cDNA microarray analysis also showed up-regulation of other genes implicated in islet regeneration, including betacellulin, laminin, TGFa, NeuroD1, Pax6, substantiating the role of the islet neogenesis pathway in human obesity.

Expression of progenitor cell markers during expansion of sorted human pancreatic beta cells

Functional pancreatic beta cell mass is dynamic and although fully differentiated, beta cells are capable of reentering the cell cycle upon appropriate stimuli. Stimulating regeneration-competent cells in situ is clearly the most desirable way to restore damaged tissue. Regeneration by dedifferentiation and transdifferentiation is a potential source of cells exhibiting a more developmentally immature phenotype and a wide differentiation potential. In this context and to gain a better understanding of the transformation induced in human beta cells during forced in vitro expansion, we focused on identifying differences in gene expression along with phenotypical transformation between proliferating and quiescent human beta cells. FACS-purified beta cells from three different human pancreata were cultured during 3-4 months (8-10 subcultures) on HTB-9 cell matrix with hepatocyte growth factor. Gene expression profiling was performed on cells from each subculture on "in-house" pancreas-specific microarrays consisting of 218 genes and concomitant morphological transformations were studied by immunocytochemistry. Immunocytochemical studies indicated a shift from epithelial to neuroepithelial cell phenotype, including progenitor cell features such as protein gene product 9.5 (PGP 9.5), Reg, vimentin, and neurogenin 3 protein expression. The expression of 49 genes was downregulated, including several markers of endocrine differentiation while 76 were induced by cell expansion including several markers of progenitor cells. Their pattern also argues for the transdifferentiation of beta cells into progenitor cells, demonstrating neuroepithelial features and overexpressing both PBX1, a homeodomain protein that can bind as a heterodimer with PDX1 and could switch the nature of its transcriptional activity, and neurogenin 3, a key factor for the generation of endocrine islet cells. Our study of the machinery that regulates human beta cell expansion and dedifferentiation may help elucidate some of the critical genes that control the formation of adult pancreatic progenitor cells and hence design targets to modify their expression in view of the production of insulin-secreting cells.

Rapid purification of human ductal cells from human pancreatic fractions with surface antibody CA19-9

Generating human insulin-secreting cells for cell therapy of diabetes represents a highly competitive world challenge. Human ductal cells can give rise to islets in vivo and in vitro. The goal of this study was to devise a rapid sorting method to highly purify human ductal cells from pancreatic tissue using a pan-ductal membrane antibody carbohydrate antigen 19-9 (CA19-9). Human pancreatic sections confirmed antibody specificity. The human exocrine fraction (30% ductal cells) was sorted with magnetic bead technology or by FACS. Immunocytochemistry post-sorting determined ductal cell content. The manual magnetic bead technique resulted in 74%+/-2 (n = 4) CA19 positive cells. Whereas the automated AutoMACS technique (n = 5) yielded 92.6%+/-0.5 CA19-9 positive cells with only a minor beta cell contamination (0.2%+/-0.03); cell yield post-sorting was 12.9%+/-2.5 (1.69+/-0.41 x 10(6) cells) with 51.7%+6.5 (n = 5) viability post-sorting. The FACS (n = 6) resulted in 97.1%+/-0.82 CA19-9 positive cells, a cell yield of 25.5%+/-5.6 (5.03+/-1.0 x 10(6)), with 72.1%+/-6.1 viability post-sorting.

Non-esterified fatty acids are deleterious for human pancreatic islet function at physiological glucose concentration

AIMS/HYPOTHESIS

Whether excess glucose (glucotoxicity) and excess non-esterified fatty acids (lipotoxicity) act synergistically or separately to alter beta-cell function on Type 2 diabetes remains controversial. We examined the influence of non-esterified fatty acids, with or without concomitant increased glucose concentrations, on human islet function and on the expression of genes involved in lipid metabolism.

METHODS

Human islets isolated from non-diabetic and non-obese donors were cultured with 5.5, 16 or 30 mmol/l glucose, and when appropriate with 1 or 2 mmol/l non-esterified fatty acids. After 48 h, glucose-stimulated insulin secretion, insulin content, triglyceride content and expression of different genes were evaluated.

RESULTS

Non-esterified fatty acids decreased glucose-stimulated insulin secretion, insulin content and increased triglyceride content of human isolated islets, independently from the deleterious effect of glucose. Increased glucose concentrations also decreased glucose-stimulated insulin secretion and insulin content, but had no influence on triglyceride content. Glucose-stimulated insulin secretion of islets appeared to be significantly correlated with their triglyceride content. Glucose and non-esterified fatty acids modified the gene expression of carnitine palmitoyltransferase-I, acetyl-CoA carboxylase, acyl-CoA oxidase and uncoupling protein 2.

CONCLUSION/INTERPRETATION

In our model of isolated human islets, increased glucose and non-esterified fatty acids separately reproduced the two major beta-cell alterations observed in vivo, i.e. loss of glucose-stimulated insulin secretion and reduction in islet insulin content. Our results also suggest that this deleterious effect was, at least in part, mediated by modifications in lipid metabolism gene expression.