Bacterial Pathogen Helicobacter Pylori Research Articles

Methylome evolution suggests lineage-dependent selection in the gastric pathogen Helicobacter pylori

The bacterial pathogen Helicobacter pylori, the leading cause of gastric cancer, is genetically highly diverse and harbours a large and variable portfolio of restriction-modification systems. Our understanding of the evolution and function of DNA methylation in bacteria is limited. Here, we performed a comprehensive analysis of the methylome diversity in H. pylori, using a dataset of 541 genomes that included all known phylogeographic populations. The frequency of 96 methyltransferases and the abundance of their cognate recognition sequences were strongly influenced by phylogeographic structure and were inter-correlated, positively or negatively, for 20% of type II methyltransferases. Low density motifs were more likely to be affected by natural selection, as reflected by higher genomic instability and compositional bias. Importantly, direct correlation implied that methylation patterns can be actively enriched by positive selection and suggests that specific sites have important functions in methylation-dependent phenotypes. Finally, we identified lineage-specific selective pressures modulating the contraction and expansion of the motif ACGT, revealing that the genetic load of methylation could be dependent on local ecological factors. Taken together, natural selection may shape both the abundance and distribution of methyltransferases and their specific recognition sequences, likely permitting a fine-tuning of genome-encoded functions not achievable by genetic variation alone.

RNase R is associated in a functional complex with the RhpA DEAD-box RNA helicase in Helicobacter pylori.

Ribonucleases are central players in post-transcriptional regulation, a major level of gene expression regulation in all cells. Here, we characterized the 3′-5′ exoribonuclease RNase R from the bacterial pathogen Helicobacter pylori. The ‘prototypical’ Escherichia coli RNase R displays both exoribonuclease and helicase activities, but whether this latter RNA unwinding function is a general feature of bacterial RNase R had not been addressed. We observed that H. pylori HpRNase R protein does not carry the domains responsible for helicase activity and accordingly the purified protein is unable to degrade in vitro RNA molecules with secondary structures. The lack of RNase R helicase domains is widespread among the Campylobacterota, which include Helicobacter and Campylobacter genera, and this loss occurred gradually during their evolution. An in vivo interaction between HpRNase R and RhpA, the sole DEAD-box RNA helicase of H. pylori was discovered. Purified RhpA facilitates the degradation of double stranded RNA by HpRNase R, showing that this complex is functional. HpRNase R has a minor role in 5S rRNA maturation and few targets in H. pylori, all included in the RhpA regulon. We concluded that during evolution, HpRNase R has co-opted the RhpA helicase to compensate for its lack of helicase activity.

How host regulation of Helicobacter pylori-induced gastritis protects against peptic ulcer disease and gastric cancer.

The bacterial pathogen Helicobacter pylori is the etiological agent of a range of gastrointestinal pathologies including peptic ulcer disease and the major killer, gastric adenocarcinoma. Infection with this bacterium induces a chronic inflammatory response in the gastric mucosa (gastritis). It is this gastritis that, over decades, eventually drives the development of H. pylori-associated disease in some individuals. The majority of studies investigating H. pylori pathogenesis have focused on factors that promote disease development in infected individuals. However, an estimated 85% of those infected with H. pylori remain completely asymptomatic, despite the presence of pathogenic bacteria that drive a chronic gastritis that lasts many decades. This indicates the presence of highly effective regulatory processes in the host that, in most cases, keeps a check on inflammation and protect against disease. In this minireview we discuss such known host factors and how they prevent the development of H. pylori-associated pathologies.

RNase J depletion leads to massive changes in mRNA abundance in Helicobacter pylori

ABSTRACTDegradation of RNA as an intermediate message between genes and corresponding proteins is important for rapid attenuation of gene expression and maintenance of cellular homeostasis. This process is controlled by ribonucleases that have different target specificities. In the bacterial pathogen Helicobacter pylori, an exo- and endoribonuclease RNase J is essential for growth. To explore the role of RNase J in H. pylori, we identified its putative targets at a global scale using next generation RNA sequencing. We found that strong depletion for RNase J led to a massive increase in the steady-state levels of non-rRNAs. mRNAs and RNAs antisense to open reading frames were most affected with over 80% increased more than 2-fold. Non-coding RNAs expressed in the intergenic regions were much less affected by RNase J depletion. Northern blotting of selected messenger and non-coding RNAs validated these results. Globally, our data suggest that RNase J of H. pylori is a major RNase involved in degradation of most cellular RNAs.

Helicobacter pylori infection reduces disease severity in an experimental model of multiple sclerosis.

Recent research has demonstrated that infection with the bacterial pathogen Helicobacter pylori is less common amongst patients with multiple sclerosis (MS), an inflammatory demyelinating disease of the central nervous system (CNS). We aimed to compare the prevalence of H. pylori amongst MS patients and healthy controls, and also investigated the impact of this infection on an animal model for MS, experimental autoimmune encephalomyelitis (EAE). The H. pylori status of 71 MS patients and 42 healthy controls was determined by serology. Groups of C57BL/6 mice were infected with H. pylori, or given diluent alone as a placebo, prior to inducing EAE. Clinical scores were assessed for all mice, and spleens and spinal cord tissue were harvested. CD4+ T cell subsets were quantified by flow cytometry, and T cell proliferation assays were performed. In MS patients the seroprevalence of H. pylori was half that of healthy controls (p = 0.018). Over three independent experiments, prior H. pylori infection had a moderate effect in reducing the severity of EAE (p = 0.012). In line with this, the antigen-specific T cell proliferative responses of infected animals were significantly reduced (p = 0.001), and there was a fourfold reduction in the number of CD4+ cells in the CNS. CD4+ populations in both the CNS and the spleens of infected mice also contained greatly reduced proportions of IFNγ+, IL-17+, T-bet+, and RORγt+ cells, but the proportions of Foxp3+ cells were equivalent. There were no differences in the frequency of splenic CD4+cells expressing markers of apoptosis between infected and uninfected animals. H. pylori was less prevalent amongst MS patients. In mice, the infection exerted some protection against EAE, inhibiting both Th1 and Th17 responses. This could not be explained by the presence of increased numbers of Foxp3+ regulatory T cells, or T cell apoptosis. This is the first direct experimental evidence showing that H. pylori may provide protection against inflammatory demyelination in the CNS.

Effective treatment of allergic airway inflammation with Helicobacter pylori immunomodulators requires BATF3-dependent dendritic cells and IL-10.

The prevalence of allergic asthma and other atopic diseases has reached epidemic proportions in large parts of the developed world. The gradual loss of the human indigenous microbiota has been held responsible for this trend. The bacterial pathogen Helicobacter pylori is a constituent of the normal gastric microbiota whose presence has been inversely linked to allergy and asthma in humans and experimental models. Here we show that oral or i.p. tolerization with H. pylori extract prevents the airway hyperresponsiveness, bronchoalveolar eosinophilia, pulmonary inflammation, and Th2 cytokine production that are hallmarks of allergen-induced asthma in mice. Asthma protection is not conferred by extracts from other enteropathogens and requires a heat-sensitive H. pylori component and the DC-intrinsic production of IL-10. The basic leucine zipper ATF-like 3 (BATF3)-dependent CD103(+)CD11b(-) dendritic cell lineage is enriched in the lungs of protected mice and strictly required for protection. Two H. pylori persistence determinants, the γ-glutamyl-transpeptidase GGT and the vacuolating cytotoxin VacA, are required and sufficient for asthma protection and can be administered in purified form to prevent asthma. In conclusion, we provide preclinical evidence for the concept that the immunomodulatory properties of H. pylori can be exploited for tolerization strategies aiming to prevent allergen-induced asthma.

Natural products and food components with anti-Helicobacter pylori activities.

The bacterial pathogen Helicobacter pylori (H. pylori) colonizes in over half of the world's population. H. pylori that establishes life-long infection in the stomach is definitely associated with gastro-duodenal diseases and a wide variety of non-gastrointestinal tract conditions such as immune thrombocytopenia. Triple therapy which consists of a proton pump inhibitor and combinations of two antibiotics (amoxicillin, clarithromycin or amoxicillin, metronidazol) is commonly used for H. pylori eradication. Recently, the occurrence of drug-resistant H. pylori and the adverse effect of antibiotics have severely weakened eradication therapy. Generally antibiotics induce the disturbance of human gastrointestinal microflora. Furthermore, there are inappropriate cases of triple therapy such as allergy to antibiotics, severe complications (liver and/or kidney dysfunction), the aged and people who reject the triple therapy. These prompt us to seek alterative agents instead of antibiotics and to develop more effective and safe therapy with these agents. The combination of these agents actually may result in lower a dose of antibiotics. There are many reports world-wide that non-antibiotic substances from natural products potentially have an anti-H. pylori agent. We briefly review the constituents derived from nature that fight against H. pylori in the literature with our studies.

Association of Neutrophil to Lymphocyte Ratio With Presence and Severity of Gastritis Due toHelicobacter pyloriInfection

Infection with the bacterial pathogen Helicobacter pylori (HP) clearly results in chronic mucosal inflammation in the stomach and duodenum, which, in turn, might lead to abnormalities in gastroduodenal motility and sensitivity and is the most frequent cause of dyspepsia and peptic disease. Some studies have shown that there was a correlation between low-grade inflammation as C-reactive protein (CRP) and HP infection. The aim of this study was to investigate the relationship between the presence of gastritis due to HP infection and neutrophil/lymphocyte ratio (NLR), a simple and reliable indicator of inflammation. Fifty patients met the HP criteria and half of them have had severe symptoms and upper endoscopy showed atrophic gastritis, and fifty age- and sex-matched control subjects with gastritis without HP infection were included in this randomized controlled trial. Patients were diagnosed to have HP according to the use of urea breath testing (UBT) and multiple biopsies. NLR was calculated from complete blood count at the time of diagnosis and before initiating the treatment to all groups. Patients with HP infection had significantly higher NLR compared to those without HP. Moreover, the patients with symptomatic HP and grade 4 gastritis had higher NLR than those asymptomatic with past history of peptic disease (P 0.007 and P 0.068, respectively). Although NLR increased as the severity of gastritis and HP symptoms increased (r = 0.564, P < 0.001), Receiver operating characteristic (ROC) Curve analysis was performed. The cut-off level for NLR with optimal sensitivity and specificity was calculated as 1.82 (area under curve [AUC] = 0.825 [0.753-0.884], P < 0.001). The present study indicated, for the first time, a significant correlation between HP infection and inflammation on the basis of NLR, a simple and reliable indicator of inflammation. Furthermore, there is an increase in NLR as the severity of gastritis with HP increases. This elevated ratio gets normalized with treatment.

Histo-blood group antigens: a common niche for norovirus and rotavirus

Noroviruses (NoVs) and rotaviruses (RVs), the two most important causes of viral acute gastroenteritis, are found to recognise histo-blood group antigens (HBGAs) as receptors or ligands for attachment. Human HBGAs are highly polymorphic containing ABO, secretor and Lewis antigens. In addition, both NoVs and RVs are highly diverse in how they recognise these HBGAs. Structural analysis of the HBGA-binding interfaces of NoVs revealed a conserved central binding pocket (CBP) interacting with a common major binding saccharide (MaBS) of HBGAs and a variable surrounding region interacting with additional minor binding saccharides. The conserved CBP indicates a strong selection of NoVs by the host HBGAs, whereas the variable surrounding region explains the diverse recognition patterns of different HBGAs by NoVs and RVs as functional adaptations of the viruses to human HBGAs. Diverse recognition of HBGAs has also been found in bacterial pathogen Helicobacter pylori. Thus, exploratory research into whether such diverse recognitions also occur for other viral and bacterial pathogens that recognise HBGAs is warranted.

Differential Proteomics of Helicobacter pylori Associated with Autoimmune Atrophic Gastritis

Atrophic autoimmune gastritis (AAG) is a condition of chronic inflammation and atrophy of stomach mucosa, for which development can be partially triggered by the bacterial pathogen Helicobacter pylori (HP). HP can cause a variety of gastric diseases, such as duodenal ulcer (DU) or gastric cancer (GC). In this study, a comparative proteomic approach was used by two-dimensional fluorescence difference gel electrophoresis (DIGE) to identify differentially expressed proteins of HP strains isolated from patients with AAG, to identify markers of HP strain associated with AAG. Proteome profiles of HP isolated from GC or DU were used as a reference to compare proteomic levels. Proteomics analyses revealed 27 differentially expressed spots in AAG-associated HP in comparison with GC, whereas only 9 differential spots were found in AAG-associated HP profiles compared with DU. Proteins were identified after matrix-assisted laser desorption ionization (MALDI)-TOF and peptide mass fingerprinting. Some AAG-HP differential proteins were common between DU- and GC-HP (peroxiredoxin, heat shock protein 70 [HSP70], adenosine 5'-triphosphate [ATP] synthase subunit α, flagellin A). Our results presented here may suggest that comparative proteomes of HP isolated from AAG and DU share more common protein expression than GC and provide subsets of putative AAG-specific upregulated or downregulated proteins that could be proposed as putative markers of AAG-associated HP. Other comparative studies by two-dimensional maps integrated with functional genomics of candidate proteins will undoubtedly contribute to better decipher the biology of AAG-associated HP strains.

Up-regulation of neutrophil activating protein in Helicobacter pylori under high-salt stress: Structural and phylogenetic comparison with bacterial iron-binding ferritins

It is generally accepted that most gastrointestinal diseases are probably caused by the bacterial pathogen Helicobacter pylori (H. pylori). In this study we have focused on the comparison of protein expression profiles of H. pylori grown under normal and high-salt conditions by a proteomics approach. We have identified about 190 proteins whose expression levels changed after growth at high salt concentration. Among these proteins, neutrophil-activating protein (NapA) was found to be consistently up-regulated under osmotic stress brought by high salts. We have investigated the effect of high salt on secondary and tertiary structures of NapA by circular dichroism spectroscopy followed by analytical ultracentrifugation to monitor the change of quaternary structure of recombinant NapA with increasing salt concentration. The loss of iron-binding activity of NapA coupled with noticeable energetic variation in protein association of NapA as revealed by isothermal titration calorimetry was found under high salt condition. The phylogenetic tree analysis based on sequence comparison of 16 protein sequences encompassing NapA proteins and ferritin of H. pylori and other prokaryotic organisms pointed to the fact that all H. pylori NapA proteins of human origin are more homologous to NapA of Helicobacter genus than to other bacterial NapA. Based on computer modeling, NapA proteins from H. pylori of human isolates are found more similar to ferritin from H. pylori than to NapA from other species of bacteria. Taken together, these results suggested that divergent evolution of NapA and ferritin possessing dissimilar and diverse sequences follows a path distinct from that of convergent evolution of NapA and ferritin with similar dual functionality of iron-binding and ferroxidase activities.

Inhibition ofHelicobacter pyloriCagA-Induced Pathogenesis by Methylantcinate B fromAntrodia camphorata

The bacterial pathogen Helicobacter pylori (Hp) is the leading risk factor for the development of gastric cancer. Hp virulence factor, cytotoxin-associated gene A (CagA) interacted with cholesterol-enriched microdomains and leads to induction of inflammation in gastric epithelial cells (AGS). In this study, we identified a triterpenoid methylantcinate B (MAB) from the medicinal mushroom Antrodia camphorata which inhibited the translocation and phosphorylation of CagA and caused a reduction in hummingbird phenotype in HP-infected AGS cells. Additionally, MAB suppressed the Hp-induced inflammatory response by attenuation of NF-κB activation, translocation of p65 NF-κB, and phosphorylation of IκB-α, indicating that MAB modulates CagA-mediated signaling pathway. Additionally, MAB also suppressed the IL-8 luciferase activity and its secretion in HP-infected AGS cells. On the other hand, molecular structure simulations revealed that MAB interacts with CagA similarly to that of cholesterol. Moreover, binding of cholesterol to the immobilized CagA was inhibited by increased levels of MAB. Our results demonstrate that MAB is the first natural triterpenoid which competes with cholesterol bound to CagA leading to attenuation of Hp-induced pathogenesis of epithelial cells. Thus, this study indicates that MAB may have a scope to develop as a therapeutic candidate against Hp CagA-induced inflammation.

Helicobacter pylori targets dendritic cells to induce immune tolerance, promote persistence and confer protection against allergic asthma

The bacterial pathogen Helicobacter pylori is predominantly known for its tight association with peptic ulcer disease and gastric cancer. However, recent evidence suggests that chronic infection with H. pylori may also be beneficial to the host by conferring protection against allergies, asthma and inflammatory bowel diseases. The protective effects of H. pylori depend on highly suppressive regulatory T-cells. In this addendum, we summarize results showing that H. pylori infection efficiently re-programs dendritic cells (DCs) toward a tolerance-promoting phenotype; their “tolerogenic” activity requires inflammasome activation and the secretion of interleukin-18. H. pylori-experienced DCs fail to induce T-cell effector functions, but efficiently induce FoxP3 expression in naive T-cells in vitro and in vivo. The experimental depletion of DCs breaks tolerance and results in improved infection control, but also in aggravated T-cell-driven immunopathology. In summary, we propose that H. pylori evades adaptive immune responses by re-programming DCs in favor of tolerance over immunity.

A minimal bacterial RNase J-based degradosome is associated with translating ribosomes

Protein complexes directing messenger RNA (mRNA) degradation are present in all kingdoms of life. In Escherichia coli, mRNA degradation is performed by an RNA degradosome organized by the major ribonuclease RNase E. In bacteria lacking RNase E, the existence of a functional RNA degradosome is still an open question. Here, we report that in the bacterial pathogen Helicobacter pylori, RNA degradation is directed by a minimal RNA degradosome consisting of Hp-RNase J and the only DExD-box RNA helicase of H. pylori, RhpA. We show that the protein complex promotes faster degradation of double-stranded RNA in vitro in comparison with Hp-RNase J alone. The ATPase activity of RhpA is stimulated in the presence of Hp-RNase J, demonstrating that the catalytic capacity of both partners is enhanced upon interaction. Remarkably, both proteins are associated with translating ribosomes and not with individual 30S and 50S subunits. Moreover, Hp-RNase J is not recruited to ribosomes to perform rRNA maturation. Together, our findings imply that in H. pylori, the mRNA-degrading machinery is associated with the translation apparatus, a situation till now thought to be restricted to eukaryotes and archaea.

Regulation of p53 by Helicobacter pylori

Regulation of p53 by <i>Helicobacter pylori</i>

Abstract B28: Exploring the host immune response to understand the existence of Helicobacter-induced gastric cancer disparity.

Abstract Gastric cancer is the second most common cause of death from cancer worldwide, with approximately 800,000 deaths each year. The majority of human stomach tumors are associated with chronic infection with the bacterial pathogen Helicobacter pylori. In the U.S. gastric cancer incidences and mortality rates are higher among minority groups (African Americans, Asian/Pacific Islanders, Alaskan Natives, Hispanic-Latino) than whites. Accordingly, colonization rates of H. pylori are also higher in these groups with 75% for Alaska Natives, 62% for Mexican Americans, and 53% for non-Hispanic blacks compared to 26% for non-Hispanic whites, making H. pylori infection a disease that disproportionately afflicts minorities. The cause of this disparity is unknown. There is now considerable amount of confirmatory evidence that the host response to H. pylori is crucial in determining susceptibility to gastric cancer. Our objective was to study the role of the host innate immune response in Helicobacter disease progression to understand the existence of gastric cancer disparity. Specifically, we investigated the role of a key signaling molecule, myeloid differentiation primary response gene 88 (MyD88) in Helicobacter-induced gastric cancer. MyD88 is an adaptor protein that plays a central role in the innate and adaptive immune response. It is involved in inflammatory pathways of interleukin (IL) -1/IL-18 and Toll-like receptor signaling and is considered to be responsible for the chronic inflammation attributed to Helicobacter infection. Induction of chronic inflammation during infection with H. pylori is widely accepted to be the trigger for gastric carcinogenesis. We used a well-characterized animal model of gastric carcinogenesis that involves infection of C57BL/6 mice with H. felis, which is a close relative of the human pathogen H. pylori. Wild type (WT) and mice deficient in MyD88 (Myd88-/-) in the C57BL/6 background were infected with H. felis for 25 or 47 weeks and mouse stomachs processed for histology, immunohistochemistry, gene expression analysis, and apoptosis. Myd88-/- mice had a higher apoptotic index and progressed rapidly to neoplasia than WT mice. Microarray data showed differential gene expression between Helicobacter infected WT and Myd88-/- mice. At 25 weeks, Myd88-/- mice showed evidence of dysplasia, which was absent in WT mice. By 47 weeks, Myd88-/- mice had developed severe dysplasia, which is considered gastric cancer in situ while WT mice only showed early evidence of dysplasia. MyD88 deficiency therefore resulted in rapid progression to gastric dysplasia. In conclusion, our data show that in the absence of MyD88, infection with Helicobacter resulted in accelerated development of gastric cancer. These data suggest that the host immune response is a critical determinant of Helicobacter disease progression. Knowledge on the status of the immune responses during Helicobacter infection is the first step in understanding mechanisms of Helicobacter-induced carcinogenesis, which may lead to a better understanding of the existence of gastric cancer disparity. Citation Format: Kelly S. Doran, Ellese M. Carmona, Anirban Banerjee, Arnika Sharma, Marygorret Obonyo. Exploring the host immune response to understand the existence of Helicobacter-induced gastric cancer disparity. [abstract]. In: Proceedings of the Fifth AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2012 Oct 27-30; San Diego, CA. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2012;21(10 Suppl):Abstract nr B28.

Outer membrane biogenesis in Escherichia coli, Neisseria meningitidis, and Helicobacter pylori: paradigm deviations in H. pylori

The bacterial pathogen Helicobacter pylori is capable of colonizing the gastric mucosa of the human stomach using a variety of factors associated with or secreted from its outer membrane (OM). Lipopolysaccharide (LPS) and numerous OM proteins have been shown to be involved in adhesion and immune stimulation/evasion. Many of these factors are essential for colonization and/or pathogenesis in a variety of animal models. Despite this wide array of potential targets present on the bacterial surface, the ability of H. pylori to vary its OM profile limits the effectiveness of vaccines or therapeutics that target any single one of these components. However, it has become evident that the proteins comprising the complexes that transport the majority of these molecules to the OM are highly conserved and often essential. The field of membrane biogenesis has progressed remarkably in the last few years, and the possibility now exists for targeting the mechanisms by which β-barrel proteins, lipoproteins, and LPS are transported to the OM, resulting in loss of bacterial fitness and significant altering of membrane permeability. In this review, the OM transport machinery for LPS, lipoproteins, and outer membrane proteins (OMPs) are discussed. While the principal investigations of these transport mechanisms have been conducted in Escherichia coli and Neisseria meningitidis, here these systems will be presented in the genetic context of ε proteobacteria. Bioinformatic analysis reveals that minimalist genomes, such as that of Helicobacter pylori, offer insight into the smallest number of components required for these essential pathways to function. Interestingly, in the majority of ε proteobacteria, while the inner and OM associated apparatus of LPS, lipoprotein, and OMP transport pathways appear to all be intact, most of the components associated with the periplasmic compartment are either missing or are almost unrecognizable when compared to their E. coli counterparts. Eventual targeting of these pathways would have the net effect of severely limiting the delivery/transport of components to the OM and preventing the bacterium's ability to infect its human host.

Myc-mediated repression of microRNA-34a promotes high-grade transformation of B-cell lymphoma by dysregulation of FoxP1

AbstractGastric marginal zone B-cell lymphoma of MALT type (MALT lymphoma) arises in the context of chronic inflammation induced by the bacterial pathogen Helicobacter pylori. Although generally considered an indolent disease, MALT lymphoma may transform to gastric diffuse large B-cell lymphoma (gDLBCL) through mechanisms that remain poorly understood. By comparing microRNA expression profiles of gastric MALT lymphoma and gDLBCL, we have identified a signature of 27 deregulated microRNAs(miRNAs) that share the characteristic of being transcriptionally repressed by Myc. Myc overexpression was consequently detected in 80% of gDLBCL but only 20% of MALT lymphomas spotted on a tissue microarray. A highly similar signature of Myc-repressed miRNAs was further detected in nodal DLBCL. Small interfering RNA–mediated knock-down of Myc blocked proliferation of DLBCL cell lines. Of the Myc-repressed miRNAs down-regulated in malignant lymphoma, miR-34a showed the strongest antiproliferative properties when overexpressed in DLBCL cells. We could further attribute miR-34a's tumor-suppressive effects to deregulation of its target FoxP1. FoxP1 overexpression was detected in gDLBCL but not in gastric MALT lymphoma; FoxP1 knock-down efficiently blocked DLBCL proliferation. In conclusion, our results elucidate a novel Myc- and FoxP1-dependent pathway of malignant transformation and suggest miR-34a replacement therapy as a promising strategy in lymphoma treatment.

Epigenetic Silencing of MicroRNA-203 Dysregulates ABL1 Expression and Drives Helicobacter-Associated Gastric Lymphomagenesis

Gastric B-cell lymphoma of mucosa-associated lymphoid tissue (MALT lymphoma) develops in the chronically inflamed mucosa of patients infected with the bacterial pathogen Helicobacter pylori. Here we use patient material, primary gastric lymphoma cell cultures, and a preclinical model of the disease to examine the role of microRNA (miRNA)-mediated posttranscriptional regulation--focusing in particular on miR-203 and its target ABL1--in gastric MALT lymphomagenesis. Microarray-based miRNA expression profiling revealed a strong downregulation of the putative tumor suppressor miRNA miR-203 in human MALT lymphoma samples, which resulted from extensive promoter hypermethylation of the miR-203 locus and coincided with the dysregulation of the miR-203 target ABL1 in lymphoma biopsies compared with matched adjacent normal material from the same patients. Treatment of lymphoma B cells with demethylating agents led to increased miR-203 expression and the concomitant downregulation of ABL1, confirming the epigenetic regulation of this miRNA. Ectopic reexpression of miR-203 by transfection of a human lymphoma cell line or lentiviral transduction of explanted primary MALT lymphoma cells was sufficient to prevent tumor cell proliferation in vitro. Similarly, the treatment of primary MALT lymphoma cells with the ABL inhibitors imatinib and dasatinib prevented tumor cell growth. Finally, we show that the treatment of tumor-bearing mice with imatinib induces MALT lymphoma regression in a preclinical model of the disease, implicating ABL1 in MALT lymphoma progression. In summary, our results show that the transformation from gastritis to MALT lymphoma is epigenetically regulated by miR-203 promoter methylation and identify ABL1 as a novel target for the treatment of this malignancy.

Protective and pathogenic functions of T-cells are inseparable during the Helicobacter-host interaction.

Chronic infection with the bacterial pathogen Helicobacter pylori is closely linked to the development of gastric cancer. Experimental infection of the laboratory mouse strain C57Bl6 mimics the initiation and progression of the disease in humans. Using this model, we have identified a dual role for CD4+ IFN-gamma-secreting T-cells in the control of Helicobacter infection as well as in the induction of preneoplastic gastric pathology. High gastric expression of IFN-gamma was positively correlated with a low Helicobacter burden, and was essential for vaccine-induced protection; on the other hand, elevated levels of the cytokine also, either directly or indirectly, triggered the transformation of the normal gastric mucosa to atrophic, hyperplastic and metaplastic lesions. Based on similar patterns of gene expression changes induced by IFN-gamma in vivo and in cultured gastric epithelial cells, we hypothesize that IFN-gamma may act directly on epithelial cells to stimulate their hyperproliferation, and thus to predispose them to elevated mutation rates and an increased risk of malignant transformation.