Helicobacter pylori Might Induce TGF-β1-Mediated EMT by Means of cagE

Cytolethal Distending Toxin Modulates Cell Differentiation and Elicits Epithelial to Mesenchymal Transition

BACKGROUND

The bacterial genotoxin, cytolethal distending toxin (CDT), causes DNA damage in host cells, a risk factor for carcinogenesis. Previous studies have shown that CDT induces phenotypes reminiscent of epithelial to mesenchymal transition (EMT), a process involved in cancer initiation and progression.

METHODS

We investigated different steps of EMT in response to Helicobacter hepaticus CDT and its active CdtB subunit using in vivo and in vitro models.

RESULTS

Most of the steps of the EMT process were induced by CDT/CdtB and observed throughout the study in murine and epithelial cell culture models. CdtB induced cell-cell junction disassembly, causing individualization of cells and acquisition of a spindle-like morphology. The key transcriptional regulators of EMT (SNAIL and ZEB1) and some EMT markers were upregulated at both RNA and protein levels in response to CDT/CdtB. CdtB increased the expression and proteolytic activity of matrix metalloproteinases, as well as cell migration. A range of these results were confirmed in Helicobacter hepaticus-infected and xenograft murine models. In addition, colibactin, a genotoxic metabolite produced by Escherichia coli, induced EMT-like effects in cell culture.

CONCLUSIONS

Overall, these data show that infection with genotoxin-producing bacteria elicits EMT process activation, supporting their role in tumorigenesis.

Comprehensive insight into altered host cell-signaling cascades upon Helicobacter pylori and Epstein-Barr virus infections in cancer

Cancer is characterized by mutagenic events that lead to disrupted cell signaling and cellular functions. It is one of the leading causes of death worldwide. Literature suggests that pathogens, mainly Helicobacter pylori and Epstein-Barr virus (EBV), have been associated with the etiology of human cancer. Notably, their co-infection may lead to gastric cancer. Pathogen-mediated DNA damage could be the first and crucial step in the carcinogenesis process that modulates numerous cellular signaling pathways. Altogether, it dysregulates the metabolic pathways linked with cell growth, apoptosis, and DNA repair. Modulation in these pathways leads to abnormal growth and proliferation. Several signaling pathways such RTK, RAS/MAPK, PI3K/Akt, NFκB, JAK/STAT, HIF1α, and Wnt/β-catenin are known to be altered in cancer. Therefore, this review focuses on the oncogenic roles of H. pylori, EBV, and its associated signaling cascades in various cancers. Scrutinizing these signaling pathways is crucial and may provide new insights and targets for preventing and treating H. pylori and EBV-associated cancers.

Persistence Infection of TGEV Promotes Enterococcus faecalis Infection on IPEC-J2 Cells

Transmissible gastroenteritis virus (TGEV) is a coronavirus causing diarrhea with high incidence in swine herds. Its persistent infection might lead to epithelial-mesenchymal transition (EMT) of swine intestinal epithelial cells, followed by subsequent infections of other pathogens. Enterococcus faecalis (E. faecalis) is a member of the enteric microorganisms and an opportunistic pathogen. There is no report of secondary E. faecalis infection to TGEV, even though they both target to the intestinal tracts. To investigate the interactions between TGEV and E. faecalis, we set up an in vitro infection model by the swine IPEC-J2 cells. Dynamic changes of cell traits, including EMT and cell motility, were evaluated through qPCR, Western blot, electronic microscopy, scratch test, Transwell migration test and invasion test, respectively. The adhesion and invasion tests of E. faecalis were taken to verify the impact of the preceding TGEV infection. The cell morphology and molecular marker evaluation results showed that the TGEV persistent infection induced EMT on IPEC-J2 cells; increased cellular motility and invasion potential were also observed. Spontaneously, the expression levels of fibronectin (FN) and the membrane protein integrin-α5, which are dominant bacterial receptors on IPEC-J2 cells, were upgraded. It indicated that the bacteria E. faecalis adhered to IPEC-J2 cells through the FN receptor, and then invaded the cells by binding with the integrin-α5, suggesting that both molecules were critical for the adhesion and invasion of E. faecalis to IPEC-J2 cells. Additionally, it appeared that E. faecalis alone might trigger certain EMT phenomena, implying a vicious circle might occur. Generally, bacterial and viral co-infections are frustrating yet common in both human and veterinary medicines, and our observations on enteric TGEV and E. faecalis interactions, especially the diversity of bacterial invasion strategies, might provide new insights into the mechanisms of E. faecalis pathogenicity.

Helicobacter pylori infection induces stem cell-like properties in Correa cascade of gastric cancer

Gastric cancer (GC) is the fourth leading cause of cancer-related death. Its poor prognosis is attributed to unclear pathogenesis. Currently, the most widely accepted model for elucidating the mechanism of GC is the Correa cascade, which covers several histological lesions of the gastric mucosa. GC stem cells (CSCs) are crucial for oncogenesis in the Correa cascade and GC progression. As Helicobacter pylori (H. pylori) is the etiological factor in the Correa cascade, growing evidence suggests that enhancement of gastric stem cell-like properties and increase in CSCs correlate with H. pylori infection. In this paper, we review recent studies that present pathogenic mechanisms by which H. pylori induces gastric stem cell-like properties and CSCs, which may supplement the existing Correa model of GC. First, the dysfunction of developmental signaling pathways associated with H. pylori infection leads to the enhancement of gastric stemness. Second, H. pylori infection promotes alteration of the gastric mucosal microenvironment. In addition, epithelial-mesenchymal transition (EMT) may contribute to H. pylori-induced gastric stemness. Taken together, understanding these pathogeneses will provide potential therapeutic targets for the treatment of CSCs and malignant GC in H. pylori induced-Correa cascade of GC.

MicroRNA‑181a promotes epithelial‑mesenchymal transition in esophageal squamous cell carcinoma via the TGF‑β/Smad pathway

Esophageal squamous cell carcinoma (ESCC) is one of the most debilitating and invasive tumors. Although previous reports have demonstrated the critical role microRNA-181a (miR-181a) serves in the progression of ESCC, how miR-181a induces epithelial-mesenchymal transition (EMT) remains to be elucidated. In the present study, the expression profiles of TGF-β1 and Smad4 proteins in 88 patients with ESCC and 21 adjacent non-cancerous tissues were analyzed using immunohistochemistry. The expression of miR-181a in ESCC cells (ECA109 and TE-1) and HEEC was analyzed using reverse transcription-quantitative polymerase chain reaction (RT-qPCR). The role of miR-181a in ESCC was analyzed using miR-181a mimics and inhibitor in the same system. Migration, proliferation and apoptosis of cells were assessed using wound-healing assays and cell proliferation assays and flow cytometry, respectively. The expression levels of TGF-β1 and Smad4 in ESCC cell lines transfected with miR-181a mimics and inhibitor were measured using RT-qPCR and western blotting. The expression of E-cadherin and vimentin was also assessed following transfection. The findings demonstrated that expression of TGF-β1 was upregulated, in contrast to Smad4 expression which was downregulated. Expression levels of Smad4 affected the prognosis of patients with ESCC. Higher expression of miR-181a promoted migration and proliferation but inhibited apoptosis of ESCC cells. miR-181a promoted EMT by modulating Smad4 expression in ESCC cells. Overall, these findings revealed that miR-181a induced EMT in ESCC via the TGF-β/Smad pathway in ESCC. Consequently, miR-181a is a potential novel target against ESCC.

Gut Microbiota and Colon Cancer: A Role for Bacterial Protein Toxins?

Accumulating evidence indicates that the human intestinal microbiota can contribute to the etiology of colorectal cancer. Triggering factors, including inflammation and bacterial infections, may favor the shift of the gut microbiota from a mutualistic to a pro-carcinogenic configuration. In this context, certain bacterial pathogens can exert a pro-tumoral activity by producing enzymatically-active protein toxins that either directly induce host cell DNA damage or interfere with essential host cell signaling pathways involved in cell proliferation, apoptosis, and inflammation. This review is focused on those toxins that, by mimicking carcinogens and cancer promoters, could represent a paradigm for bacterially induced carcinogenesis.

Helicobacter pylori cagE, cagG, and cagM can be a prognostic marker for intestinal and diffuse gastric cancer

It is known that Helicobacter pylori is the main cause of peptic ulceration and gastric cancer. However, there is a lack of information on whether H. pylori strains may differ in gastric cancer histological subtypes. This study aimed to investigate different H. pylori strains considering six cag Pathogenicity Island - cagPAI genes (cagA, cagE, cagG, cagM, cagT, and virb11), and vacuolating cytotoxin - vacA alleles, and their relation to gastric cancer histologic subtypes. For this purpose, tumor samples from 285 patients with gastric carcinoma were used. H. pylori infection and genotypes were determined by polymerase chain reaction (PCR). H. pylori was detected in 93.9% of gastric tumors. For comparative analyzes between histopathological subtypes considering H. pylori cagPAI genes the strains were grouped according to the vacA s1/s2 alleles. In the vacAs1 group, the strains cagA(-)cagE(+), cagA(+)cagE(+)cagG(+), cagA(+)cagM(+), or only cagE(+) strains were more frequent in the intestinal subtype (P = .009; P = .024; P = .046, respectively). In contrast, cagM(+)cagG(+)cagA(-) and cagE(-) were associated with diffuse tumors (P = .036), highlighting the presence of cagE in the development of intestinal tumors, and the presence of cagG and absence of cagE in diffuse tumors. Furthermore, WEKA software and Decision Tree (CART) analyses confirmed these findings, in which cagE presence was associated with intestinal tumors, and cagE absence and cagG(+) with diffuse tumors. In conclusion our results showed that vacAs1 (cagG + cagM) strains, mainly cagG positive with cagE absence, were relevant in the studied population for the diffuse outcome, while the presence of cagE was relevant for the intestinal outcome. These findings suggest the relevance of these H. pylori genes as potential markers for gastric cancer histological outcomes.

The Escherichia coli protein toxin cytotoxic necrotizing factor 1 induces epithelial mesenchymal transition

Some toxigenic bacteria produce protein toxins with carcinogenic signatures, which either directly damage DNA or stimulate signalling pathways related to cancer. So far, however, only a few of them have been proved to favour the induction or progression of cancer. In this work, we report that the Rho-activating Escherichia coli protein toxin, cytotoxic necrotising factor 1 (CNF1), induces epithelial to mesenchymal transition (EMT) in intestinal epithelial cells. EMT is a crucial step in malignant tumour conversion and invasiveness. In the case of CNF1, it occurs by up-regulation of the transcription factors ZEB1 and Snail1, delocalisation of E-cadherin and β-catenin, activation of the serine/threonine kinase mTOR, accelerated wound healing, and invasion. However, our results highlight that nontransformed epithelial cells entail the presence of inflammatory factors, in addition to CNF1, to acquire a mesenchymal-like behaviour. All this suggests that the surrounding microenvironment, as well as the cell type, dramatically influences the CNF1 ability to promote carcinogenic traits.

Chemoprevention of gastric cancer by Helicobacter pylori eradication and its underlying mechanism

The cascade of gastric cancer, a leading cause of cancer incidence and mortality, is multifactorial. Helicobacter pylori (HP) infection plays a major role in gastric cancer (GC), and there has been an accumulation of data regarding the chemopreventive effect of HP eradication. However, it remains unclear how HP infection causes GC and how HP eradication prevents GC. To clarify this issue, the following approaches were performed in this review article. First, how HP-induced atrophic gastritis (AG) and intestinal metaplasia (IM) provoke the development of GC is shown, followed by how long HP eradication takes to induce a reversible change in AG and IM. Second, epigenetic studies of PTPN6, MOS, DCC, CRK, and VAV1 were performed in noncancerous gastric specimens in terms of HP status. Among these genes, MOS was found to be a possible surrogate marker for GC development. HP eradication decreased aberrant DNA methylation in a gene-specific manner, and MOS played a role in metachronous gastric neoplasms. Third, transforming growth factor-β1 (TGF-β1) and TGF-β1-induced epithelial-mesenchymal transition (EMT) markers were investigated in gastric mucosa. HP infection triggered the TGF-β1-induced EMT pathway and caused the emergence of GC stem cells, such as CD44v8-10. When HP was eradicated, these two pathways were inhibited. Finally, a 2222 cohort study showed that HP eradication significantly decreased the risk of noncardiac GC. Taken together, HP eradication is effective as a primary GC prevention method, and its underlying mechanism includes reversibility of AG and IM, methylation, EMT, and stem cells.

MiR-181a, a new regulator of TGF-β signaling, can promote cell migration and proliferation in gastric cancer

Transforming growth factor-beta (TGF-β) signaling pathway plays pivotal roles in various types of cancer. TGF-β receptor 2 (TGFβR2) contains a kinase domain that phosphorylates and activates the downstream of the TGF-β signaling pathway. Our previous microarray analysis revealed marked changes in miR-181a expression in gastric cancers, and the bioinformatics analysis suggested that miR-181a negatively regulated TGFβR2. In order to verify the effect of miR-181a on TGFβR2 and clarify the influence of miR-181a on the migration and proliferation of gastric cancer, studies in gastric cancer cell lines and xenograft mouse models were carried out. We found that a reduced expression of TGFβR2 and an increased expression miR-181a in gastric cancer tissues compared to adjacent noncancerous tissues. A luciferase reporter assay confirmed that TGFβR2 was a target of miR-181a. In addition, we found that miR-181a mimics, which increased the level of miR-181a, downregulated the expression of TGFβR2 in the gastric cancer cell line SGC-7901. Moreover, both the overexpression of miR-181a and the downregulation of TGFβR2 promoted the migration and proliferation of SGC-7901 cells. Conversely, SGC-7901 cell migration and proliferation were inhibited by the downregulation of miR-181a and the overexpression of TGFβR2. Furthermore, the increased expression of miR-181a and the decreased expression of TGFβR2 also enhanced the tumor growth in mice bearing gastric cancer. Our results herein indicated that miR-181a promoted the migration and proliferation of gastric cancer cells by downregulating TGFβR2 at the posttranscriptional level. The present study suggests that miR-181a is a novel negative regulator of TGFβR2 in the TGF-β signaling pathway and thus represents a potential new therapeutic target for gastric cancer.

Mechanisms of Inflammasome Signaling, microRNA Induction and Resolution of Inflammation by Helicobacter pylori

Inflammasome-controlled transcription and subsequent cleavage-mediated activation of mature IL-1β and IL-18 cytokines exemplify a crucial innate immune mechanism to combat intruding pathogens. Helicobacter pylori represents a predominant persistent infection in humans, affecting approximately half of the population worldwide, and is associated with the development of chronic gastritis, peptic ulcer disease, and gastric cancer. Studies in knockout mice have demonstrated that the pro-inflammatory cytokine IL-1β plays a central role in gastric tumorigenesis. Infection by H. pylori was recently reported to stimulate the inflammasome both in cells of the mouse and human immune systems. Using mouse models and in vitro cultured cell systems, the bacterial pathogenicity factors and molecular mechanisms of inflammasome activation have been analyzed. On the one hand, it appears that H. pylori-stimulated IL-1β production is triggered by engagement of the immune receptors TLR2 and NLRP3, and caspase-1. On the other hand, microRNA hsa-miR-223-3p is induced by the bacteria, which controls the expression of NLRP3. This regulating effect by H. pylori on microRNA expression was also described for more than 60 additionally identified microRNAs, indicating a prominent role for inflammatory and other responses. Besides TLR2, TLR9 becomes activated by H. pylori DNA and further TLR10 stimulated by the bacteria induce the secretion of IL-8 and TNF, respectively. Interestingly, TLR-dependent pathways can accelerate both pro- and anti-inflammatory responses during H. pylori infection. Balancing from a pro-inflammation to anti-inflammation phenotype results in a reduction in immune attack, allowing H. pylori to persistently colonize and to survive in the gastric niche. In this chapter, we will pinpoint the role of H. pylori in TLR- and NLRP3 inflammasome-dependent signaling together with the differential functions of pro- and anti-inflammatory cytokines. Moreover, the impact of microRNAs on H. pylori-host interaction will be discussed, and its role in resolution of infection versus chronic infection, as well as in gastric disease development.

The study of H. pylori putative candidate factors for single- and multi-component vaccine development

Helicobacter pylori has grown to colonize inside the stomach of nearly half of the world's population, turning into the most prevalent infections in the universe. Medical care failures noticeably confirm the need for a vaccine to hinder or deal with H. pylori. This review is planned to discuss the most known factors as a vaccine candidate, including single (AhpC, BG, CagA, KatA, Fla, Hsp, HWC, Lpp, LPS, NAP, OMP, OMV, SOD, Tpx, Urease, VacA) and multi-component vaccines. Many promising results in the field of single and multivalent vaccine can be seen, but there is no satisfactory outcome and neither a prophylactic nor a therapeutic vaccine to treat or eradicate the infection in human has been acquired. Hence, selecting suitable antigen is an important factor as an appropriate adjuvant. Taken all together, the development of efficient anti-H. pylori vaccines relies on the fully understanding of the interactions between H. pylori and its host immune system. Therefore, more work should be done on epitope mapping, analysis of molecular structure, and determination of the antigen determinant region as well due to design a vaccine, preferably a multi-component vaccine to elicit specific CD4 T-cell responses that are required for H. pylori vaccine efficacy.

Emerging molecular basis of hematogenous metastasis in gastric cancer

Lymphatic metastasis is commonly observed in gastric cancer (GC), but hematogenous metastasis is more likely responsible for the cancer-related mortality. Since Stephen Paget first introduced the “seed and soil hypothesis” a century ago, growing evidence recognizes that numerous essential secreted factors and signaling pathway effectors participate in the pre-metastatic niche formation and distant organ metastasis. The cross-talk between GC cells and surrounding microenvironment may consist of a series of interrelated steps, including epithelial mesenchymal transition, intravasation into blood vessels, circulating tumor cell translocation, and secondary organ metastasis. Secreted factors including vascular endothelial growth factor (VEGF), matrix metalloproteinases and cancer-derived extracellular vesicles, especially exosomes, are essential in formation of premetastatic niche. Circulating tumor cells and microRNAs represent as ‘‘metastatic intermediates’’ between primary tumors and sites of dissemination. Many biomarkers have been identified as novel metastatic markers and prognostic effectors. In addition, molecular therapy has been designed to target biomarkers such as growth factors (human epidermal growth factor receptor 2, VEGF) and chemokines, although they have not clearly proven to be effective in inhibiting GC metastasis in clinical trials. In this review, we will systematically discuss the emerging molecules and their microenvironment in hematogenous metastasis of GC, which may help us to find new therapeutic strategies in the future.

Transforming growth factor-β: an important mediator in Helicobacter pylori-associated pathogenesis

Helicobacter pylori (H.pylori) is a Gram-negative, microaerophilic, helical bacillus that specifically colonizes the gastric mucosa. The interaction of virulence factors, host genetic factors, and environmental factors contributes to the pathogenesis of H. pylori-associated conditions, such as atrophic gastritis and intestinal metaplasia. Infection with H. pylori has recently been recognized as the strongest risk factor for gastric cancer. As a pleiotropic cytokine, transforming growth factor (TGF)-β regulates various biological processes, including cell cycle, proliferation, apoptosis, and metastasis. Recent studies have shed new light on the involvement of TGF-β signaling in the pathogenesis of H. pylori infection. This review focuses on the potential etiological roles of TGF-β in H. pylori-mediated gastric pathogenesis.