Gastrokine 1 inhibits the carcinogenic potentials of Helicobacter pylori CagA

Molecular Mechanisms and Treatment Strategies for Helicobacter pylori-Induced Gastric Carcinogenesis and Mucosa-Associated Lymphoid Tissue (MALT) Lymphoma

Helicobacter pylori has been classified as a class I carcinogen by WHO because of its primary involvement in the development of gastric cancer and mucosa-associated lymphoid tissue (MALT) lymphoma. This review focuses on understanding the molecular pathophysiological mechanisms that operate within intracellular transduction pathways and their relevance in the treatment strategies for the two main diseases caused by H. pylori. H. pylori virulence factors such as cytotoxin-associated gene A and vacuolating cytotoxin A genotypes, inflammatory mediators, H. pylori-induced microRNA deregulation, alterations in autophagy proteins and regulators, and changes in DNA methylation are some of the molecular mechanisms that play essential roles in H. pylori infection and gastric carcinogenesis. The discovery of novel treatment strategies that target the deregulated intracellular transduction pathways in gastric carcinogenesis and MALT lymphoma is critical. H. pylori eradication (HPE) is not limited to H. pylori-dependent low-grade MALT lymphoma and may be used in patients with high-grade diffuse large B-cell lymphoma (DLBCL) (de novo or DLBCL-MALT lymphoma). The loss of H. pylori dependency and high-grade transformation appear to be distinct events in the progression of gastric lymphoma. Interestingly, patients with H. pylori-positive gastric DLBCL without histological evidence of MALT lymphoma (pure gastric DLBCL) may respond to HPE therapy.

High expression of TRIP13 is associated with tumor progression in H. pylori infection induced gastric cancer

BACKGROUND/OBJECTIVE

H. pylori is a recognized bacterial carcinogen in the world to cause gastric cancer (GC). However, the molecular mechanism of H. pylori infection-induced GC is not completely clear. Thus, there is an urgent need to reveal the precise mechanisms regulating cancer development due to H. pylori infection.

METHODS

GEO microarray databases and TCGA databases were extracted for the analysis of different expression genes (DEGs). Then, Kaplan-Meier Plotter was used for prognostic analysis. Functional enrichment analysis of TRIP13 was performed by metascape database and TIMER database. Specific role of TRIP13 in GC with H. pylori infection was confirmed by CCK8, cell cycle analysis and WB.

RESULTS

A total 10 DEGs were substantially elevated in GC and H. pylori+ tissues and might be associated with H. pylori infection in GC and only the highly expressed TRIP13 was statistically associated with poor prognosis in GC patients. Meanwhile, TRIP13 were upregulated in both CagA-transfected epithelial cells and GC cells. And TRIP13 deficiency inhibited cell proliferation and arrested the cell cycle at the G1 phase.

CONCLUSION

Our study suggested that high expression of TRIP13 can promote the proliferation, cell cycle in GC cells, which could be used as a biomarker for H. pylori infection GC.

Helicobacter pylori CagA promotes immune evasion of gastric cancer by upregulating PD-L1 level in exosomes

Cytotoxin-associated gene A (CagA) of Helicobacter pylori (Hp) may promote immune evasion of Hp-infected gastric cancer (GC), but potential mechanisms are still under explored. In this study, the positive rates of CagA and PD-L1 protein in tumor tissues and the high level of exosomal PD-L1 protein in plasma exosomes were significantly associated with the elevated stages of tumor node metastasis (TNM) in Hp-infected GC. Moreover, the positive rate of CagA was positively correlated with the positive rate of PD-L1 in tumor tissues and the level of PD-L1 protein in plasma exosomes, and high level of exosomal PD-L1 might indicate poor prognosis of Hp-infected GC. Mechanically, CagA increased PD-L1 level in exosomes derived from GC cells by inhibiting p53 and miRNA-34a, suppressing proliferation and anticancer effect of CD8+ T cells. This study provides sights for understanding immune evasion mediated by PD-L1. Targeting CagA and exosomal PD-L1 may improve immunotherapy efficacy of Hp-infected GC.

Hierarchical clustering identifies oxidative stress-related subgroups for the prediction of prognosis and immune microenvironment in gastric cancer

Background

Gastric cancer (GC) is a prevalent malignancy of the digestive tract globally, demonstrating a substantial occurrence of relapse and metastasis, alongside the absence of efficacious treatment. Tumor progression and the development of cancer are linked to oxidative stress. Our objective was twofold: first, to determine distinct subcategories based on oxidative stress in GC patients, and second, to establish oxidative stress-related genes that would aid in stratifying the risk for GC patients.

Methods

TCGA-STAD and GSE84437 datasets were utilized to obtain the mRNA expression profiles and corresponding clinical information of GC patients. Through consensus clustering analysis, distinct subgroups related to oxidative stress were identified. To uncover the underlying mechanisms, GSEA and GSVA were performed. xCell, CIBERSORT, MCPCounter, and TIMER algorithms were employed to evaluate the immune microenvironment and immune status of the different GC subtypes. A prognostic risk model was developed using the TCGA-STAD dataset and substantiated using the GSE84437 dataset. Furthermore, qRT-PCR was employed to validate the expression of genes associated with prognosis.

Results

Two distinct subtypes of oxidative stress were discovered, with markedly different survival rates. The C1 subtype demonstrated an activated immune signal pathway, a significant presence of immune cell infiltration, high immune score, and a high microenvironment score, indicating a poor prognosis. Moreover, a prognostic signature related to oxidative stress (IMPACT and PXDN) was able to accurately estimate the likelihood of survival for patients with gastric cancer. A nomogram incorporating the patients' gender, age, and risk score was able to predict survival in gastric cancer patients. Additionally, the expression of IMPACT and PXDN showed a strong correlation with overall survival and the infiltration of immune cells.

Conclusion

Based on signatures related to oxidative stress, we developed an innovative system for categorizing patients with GC. This stratification enables accurate prognostication of individuals with GC.

Reactive Oxygen Species and H. pylori Infection: A Comprehensive Review of Their Roles in Gastric Cancer Development

Gastric cancer (GC) is the fifth most common cancer worldwide and makes up a significant component of the global cancer burden. Helicobacter pylori (H. pylori) is the most influential risk factor for GC, with the International Agency for Research on Cancer classifying it as a Class I carcinogen for GC. H. pylori has been shown to persist in stomach acid for decades, causing damage to the stomach's mucosal lining, altering gastric hormone release patterns, and potentially altering gastric function. Epidemiological studies have shown that eliminating H. pylori reduces metachronous cancer. Evidence shows that various molecular alterations are present in gastric cancer and precancerous lesions associated with an H. pylori infection. However, although H. pylori can cause oxidative stress-induced gastric cancer, with antioxidants potentially being a treatment for GC, the exact mechanism underlying GC etiology is not fully understood. This review provides an overview of recent research exploring the pathophysiology of H. pylori-induced oxidative stress that can cause cancer and the antioxidant supplements that can reduce or even eliminate GC occurrence.

Helicobacter Pylori Infection Induces Intestinal Dysbiosis That Could Be Related to the Onset of Atherosclerosis

Cardiovascular diseases represent one of the first causes of death around the world, and atherosclerosis is one of the first steps in the development of them. Although these problems occur mainly in elderly, the incidence in younger people is being reported, and an undetermined portion of patients without the classic risk factors develop subclinical atherosclerosis at earlier stages of life. Recently, both the H. pylori infection and the intestinal microbiota have been linked to atherosclerosis. The mechanisms behind those associations are poorly understood, but some of the proposed explanations are (a) the effect of the chronic systemic inflammation induced by H. pylori, (b) a direct action over the endothelial cells by the cytotoxin associated gene A protein, and (c) alterations of the lipid metabolism and endothelial dysfunction induced by H. pylori infection. Regarding the microbiota, several studies show that induction of atherosclerosis is related to high levels of Trimethylamine N-oxide. In this review, we present the information published about the effects of H. pylori over the intestinal microbiota and their relationship with atherosclerosis and propose a hypothesis to explain the nature of these associations. If H. pylori contributes to atherosclerosis, then interventions for eradication and restoration of the gut microbiota at early stages could represent a way to prevent disease progression.

Association of Helicobacter pylori Infection and Host Cytokine Gene Polymorphism with Gastric Cancer

The global cancer burden of new cases of various types rose with millions of death in 2018. Based on the data extracted by GLOBOCAN 2018, gastric cancer (GC) is the third leading cause of mortality related to cancer across the globe. Carcinogenic or oncogenic infections associated with Helicobacter pylori (Hp) are regarded as one of the essential risk factors for GC development. It contributes to the increased production of cytokines that cause inflammation prior to their growth in the host cells. Hp infections and specific types of polymorphisms within the host cells encoding cytokines are significant contributors to the host's increased susceptibility in terms of the development of GC. Against the backdrop of such an observation is that only a small portion of the cells infected can become malignant. The diversities are a consequence of the differences in the pathogenic pathway of the Hp, susceptibility of the host, environmental conditions, and interplay between these factors. It is evident that hosts carrying cytokine genes with high inflammatory levels and polymorphism tend to exhibit an increased risk of development of GC, with special emphasis being placed on the host cytokines gene polymorphisms.

Metformin attenuates synergic effect of diabetes mellitus and Helicobacter pylori infection on gastric cancer cells proliferation by suppressing PTEN expression

It has been reported that CagA of Helicobacter pylori reduced PTEN expression by enhancing its promoter methylation. Furthermore, diabetes mellitus (DM) may also promote the methylation status of PTEN, a tumour suppressor gene in gastric cancer (GC). It is intriguing to explore whether DM may strengthen the tumorigenic effect of H pylori (HP) by promoting the methylation of PTEN promoter and whether the administration of metformin may reduce the risk of GC by suppressing the methylation of PTEN promoter. In this study, we enrolled 107 GC patients and grouped them as HP(-)DM(-) group, HP(+)DM(-) group and HP(+)DM(+) group. Bisulphite sequencing PCR evaluated methylation of PTEN promoter. Quantitative real-time PCR, immunohistochemistry and Western blot, immunofluorescence, flow cytometry and MTT assay were performed accordingly. DNA methylation of PTEN promoter was synergistically enhanced in HP(+)DM(+) patients, and the expression of PTEN was suppressed in HP(+)DM(+) patients. Cell apoptosis was decreased in HP(+)DM(+) group. Metformin showed an apparent effect on restoring CagA-induced elevation of PTEN promoter methylation, thus attenuating the PTEN expression. The reduced PTEN level led to increased proliferation and inhibited apoptosis of HGC-27 cells. In this study, we collected GC tumour tissues from GC patients with or without DM/HP to compare their PTEN methylation and expression while testing the effect of metformin on the methylation of PTEN promoter. In summary, our study suggested that DM could strengthen the tumorigenic effect of HP by promoting the PTEN promoter methylation, while metformin reduces GC risk by suppressing PTEN promoter methylation.

Integrated analysis identifies oxidative stress genes associated with progression and prognosis in gastric cancer

Oxidative stress (OS) reactions are reported to be associated with oncogenesis and tumor progression. However, little is known about the potential diagnostic value of OS in gastric cancer (GC). This study identified hub OS genes associated with the prognosis and progression of GC and illustrated the underlying mechanisms. The transcriptome data and corresponding GC clinical information were collected from The Cancer Genome Atlas (TCGA) database. Aberrantly expressed OS genes between tumors and adjacent normal tissues were screened, and 11 prognosis-associated genes were identified with a series of bioinformatic analyses and used to construct a prognostic model. These genes were validated in the Gene Expression Omnibus (GEO) database. Furthermore, weighted gene co-expression network analysis (WGCNA) was subsequently conducted to identify the most significant hub genes for the prediction of GC progression. Analysis revealed that a good prognostic model was constructed with a better diagnostic accuracy than other clinicopathological characteristics in both TCGA and GEO cohorts. The model was also significantly associated with the overall survival of patients with GC. Meanwhile, a nomogram based on the risk score was established, which displayed a favorable discriminating ability for GC. In the WGCNA analysis, 13 progression-associated hub OS genes were identified that were also significantly associated with the progression of GC. Furthermore, functional and gene ontology (GO) analyses were performed to reveal potential pathways enriched with these genes. These results provide novel insights into the potential applications of OS-associated genes in patients with GC.

Uptake and tumor-suppressive pathways of exosome-associated GKN1 protein in gastric epithelial cells

BACKGROUND

Gastrokine 1 (GKN1) is a stomach-specific tumor suppressor that is secreted into extracellular space as an exosomal cargo protein. The objective of this study was to investigate the uptake and tumor-suppressive pathways of exosome-associated GKN1 protein in gastric epithelial cells.

METHODS

Immunofluorescent and Western blot analysis were used to investigate gastric-specific uptake of HFE-145-derived exosomes. Binding affinity of HFE-145 derived exosomes with integrin proteins was examined using protein microarray chip. Tumor suppressor activities of exosome-carrying GKN1 protein were analyzed using transwell co-culture, MTT assay, BrdU incorporation, immunoprecipitation, and Western blot analysis.

RESULTS

HFE-145-derived exosomes were internalized only into HFE-145 gastric epithelial cells and gastric cancer cells. Gastric-specific uptake of stomach-derived exosomes required integrin α6 and αX proteins. Clathrin and macropinocytosis increased the uptake of exosomes into gastric epithelial cells, whereas caveolin inhibited the uptake of exosomes. Transwell co-culture of AGS cells with HFE-145 cells markedly inhibited viability and proliferation of AGS cells. Following uptake of HFE-145-derived exosomes in recipient cells, GKN1 protein bound to HRas and inhibited the binding of HRas to b-Raf and c-Raf which subsequently downregulated HRas/Raf/MEK/ERK signaling pathways in AGS, MKN1 cells, and MKN1-derived xenograft tumor tissues. In addition, exosomal GKN1 protein suppressed both migration and invasion of gastric cancer cells by inhibiting epithelial-mesenchymal transition.

CONCLUSIONS

Gastric-specific uptake of exosomes derived from gastric epithelial cells requires integrin α6 and αX proteins in both gastric epithelial cells and exosomes. Exosomal GKN1 protein inhibits gastric carcinogenesis by downregulating HRas/Raf/MEK/ERK signaling pathways.

Helicobacter pylori infection leads to KLF4 inactivation in gastric cancer through a TET1-mediated DNA methylation mechanism

Krüppel-like factor 4 (KLF4) has a tumor suppressor role in the progression of gastric cancer (GC), and inhibition or loss of KLF4 expression was identified in GC. The aim of this study was to explore the new molecular mechanism of KLF4 inactivation in gastric cancer. Herein, we report that Helicobacter pylori infection or Cag pathogenicity island protein A (CagA) gene transduction resulted in KLF4 expression downregulation and promoted gastric epithelial cell and gastric cancel cell proliferation, migration, and colony formation. Mechanistically, we found that CagA gene transduction led to DNA methylation of the KLF4 promoter, an effect that was relevant to the significant downregulation of TET1 expression. Causally, knockdown of TET1 expression decreased KLF4 expression, whereas overexpression of TET1 had the opposite effect. Clinically, we found that KLF4 expression and the 5-hmC levels were lower in GC cells with H pylori infection than in GC cells without H pylori infection. Thus, our study not only sheds new light on how H pylori infection promotes the progression of GC but also elucidates a novel mechanism of KLF4 inactivation in GC pathogenesis. During pathogenesis, an alteration in the H pylori/CagA-TET1-KLF4 signaling pathway plays a critical role, suggesting that this pathway may be a prospective target for gastric carcinoma intervention and therapy.

Helicobacter pylori inhibits GKN1 expression via the CagA/p-ERK/AUF1 pathway

BACKGROUND

Recent studies have shown that gastrokine 1 (GKN1), an important tumor suppressor gene, is downregulated in Helicobacter pylori (H. pylori) infected gastric mucosa and gastric cancer. However, the underlying mechanism is poorly understood. Herein, we investigated the potential mechanism of H. pylori-induced GKN1 downregulation.

MATERIALS AND METHODS

GKN1 and AU-rich element RNA-binding factor 1 (AUF1) expressions were assessed by quantitative real-time PCR, Western blot, or immunohistochemistry in H. pylori-infected tissues and H. pylori co-cultured cell lines. The regulation of AUF1 on GKN1 was determined by RNA pulldown assay, RNA immunoprecipitation, mRNA turnover, and luciferase activity assays. The involvement of phosphorylated extra-cellular signal-regulated kinase (p-ERK) or CagA in H. pylori-induced AUF1 expression was verified using p-ERK inhibitor or CagA knockout H. pylori. In addition, the cell proliferation and migration capacities of AUF1-knockdown cells were investigated.

RESULTS

GKN1 expression progressively decreased from H. pylori-infected gastritis to gastric cancer tissues. H. pylori co-culture also induced significant GKN1 reduction in GES-1 and BGC-823 cells. Besides, the mRNA level of GKN1 and AUF1 in human gastric mucosa showed negative correlation significantly. AUF1 knockdown resulted in upregulation of GKN1 expression and promoted GKN1 mRNA decay by binding the 3' untranslated region of GKN1 mRNA H. pylori-induced AUF1 expression was associated with p-ERK activation and CagA. Furthermore, knockdown of AUF1 significantly inhibited cell viability, migration ability, and arrested fewer cells in S-phase.

CONCLUSION

Our data demonstrated that H. pylori infection downregulated GKN1 expression via the CagA/p-ERK/AUF1 pathway. AUF1 promoted gastric cancer at least partly through downregulating GKN1, which presented a novel potential target for the treatment of gastric cancer.

Epigenetic downregulation of MUC17 by H. pylori infection facilitates NF-κB-mediated expression of CEACAM1-3S in human gastric cancer

BACKGROUND AND AIMS

Helicobacter pylori invades the mucosal barrier and infects the mucins of gastric epithelial cells. However, whether gastric carcinogenesis caused by H. pylori infection involves the membrane-bound mucins is unclear. This study explored the role of mucin 17 (MUC17) in gastric cancer (GC) associated with H. pylori infection.

METHODS

The expression of MUC17 and carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1) was examined in human GC cells and tissues with H. pylori infection. Gain- and loss-of-function assays were performed to assess the role of MUC17 in regulating CEACAM1 in H. pylori-infected GC cells.

RESULTS

MUC17 was downregulated in H. pylori-infected GC cells and tissues in association with poor survival of GC patients. Downregulation of MUC17 was attributable to MUC17 promoter methylation mediated by DNA methyltransferase 1 (DNMT1) H. pylori-enhanced GC cell proliferation and colony formation associated with MUC17 downregulation. Gain- and loss-of-function assays showed that MUC17 inhibited the H. pylori-enhanced GC cell growth by preventing the translocation of H. pylori CagA into GC cells. Moreover, MUC17 downregulated the expression of CEACAM1 variant 3S (CEACAM1-3S) in GC cells and tissues with H. pylori infection. Additionally, MUC17 downregulated CEACAM1 promoter activity via attenuation of NF-κB activation in GC cells.

CONCLUSIONS

MUC17 was epigenetically downregulated in GC with H. pylori infection. MUC17 inhibited H. pylori CagA translocation via attenuation of NF-κB-mediated expression of CEACAM1-3S in GC cells. Thus, MUC17 may serve as a valuable prognostic biomarker for H. pylori-associated GC.

Regulation of GKN1 expression in gastric carcinogenesis: A problem to resolve (Review)

Gastrokine 1 (GKN1) is a protein expressed on the surface mucosa cells of the gastric antrum and fundus, which contributes to maintaining gastric homeostasis, inhibits inflammation and is a tumor suppressor. The expression of GKN1 decreases in mucosa that are either inflamed or infected by Helicobacter pylori, and is absent in gastric cancer. The measurement of circulating GKN1 concentration, the protein itself, or the mRNA in gastric tissue may be of use for the early diagnosis of cancer. The mechanisms that modulate the deregulation or silencing of GKN1 expression have not been completely described. The modification of histones, methylation of the GKN1 promoter, or proteasomal degradation of the protein have been detected in some patients; however, these mechanisms do not completely explain the absence of GKN1 or the reduction in GKN1 levels. Only NKX6.3 transcription factor has been shown to be a positive modulator of GKN1 transcription, although others also have an affinity with sequences in the promoter of this gene. While microRNAs (miRNAs) are able to directly or indirectly regulate the expression of genes at the post‑transcriptional level, the involvement of miRNAs in the regulation of GKN1 has not been reported. The present review analyzes the information reported on the determination of GKN1 expression and the regulation of its expression at the transcriptional, post‑transcriptional and post‑translational levels; it proposes an integrated model that incorporates the regulation of GKN1 expression via transcription factors and miRNAs in H. pylori infection.

Reactive Oxygen Species Are Involved in the Development of Gastric Cancer and Gastric Cancer-Related Depression through ABL1-Mediated Inflammation Signaling Pathway

Background

The mechanisms of crosstalk between depression and gastric cancer (GC) remain ill defined. Given that reactive oxygen species (ROS) is involved in the pathophysiology of both GC and depression, we try to explore the activities of ROS in the development of GC and GC-related depression.

Methods

110 patients with newly diagnosed GC were recruited in our study. The clinical characteristics of these patients were recorded. Inflammation and oxidative stress markers were detected by ELISA. The depression status of patients with GC was assessed during follow-up. The association between ROS, ABL1, and inflammation factors was evaluated in H₂O₂-treated GC cell lines and The Cancer Genome Atlas (TCGA) database. The effect of ABL1 on inflammation was detected with Imatinib/Nilotinib-treated GC cell lines. A chronic mild stress- (CMS-) induced patient-derived xenograft (PDX) mice model was established to assess the crosstalk between depression and GC.

Results

Depression was correlated with poor prognosis of patients with GC. GC patients with depression were under a high level of oxidative status as well as dysregulated inflammation. In the CMS-induced GC PDX mice model, CMS could facilitate the development of GC. Additionally, tumor bearing could induce depressive-like behaviors of mice. With the treatment of ROS, the activities of ABL1 and inflammatory signaling were enhanced both in vitro and in vivo, and blocking the activities of ABL1 inhibited inflammatory signaling.

Conclusions

ROS-activated ABL1 mediates inflammation through regulating NF-κB1 and STAT3, which subsequently leads to the development of GC and GC-related depression.

The role and diagnostic potential of gastrokine 1 in gastric cancer

Introduction

Gene for gastrokine 1 (GKN1) was identified as one of the most significant in gastric cancer and indicated as a potential therapeutic target.

Aim

The aim was a review of literature reports concerning the role and diagnostic potential of GKN1 in gastric cancer.

Materials and methods

PubMED database was searched for sources using the following keywords: gastrokine 1/GKN1/AMP-18 and gastric cancer, Helicobacter pylori, aspirin, nonsteroidal anti-inflammatory drugs. Preference was given to the sources which were published within the past 10 years.

Conclusion

GKN1 is a stomach-specific protein, and its role consists of maintaining mucosal integrity as well as the replenishment of the surface lumen epithelial cells layer. The evaluation of GKN1 expression seems to be a useful indicator of the presence of neoplastic or inflammatory lesions in the gastric mucosa. GKN1 expression is decreased in gastric tumor tissues and derived cell lines and its upregulation in cell lines of gastric cancer induces cells apoptosis. The mechanism by which GKN1 is inactivated in gastric cancer cells is still not fully understood. The future diagnostic capabilities of gastric cancer concern the assessment of serum GKN1 concentration by means of ELISA method. Serum GKN1 concentration is not related to patients’ sex. Moreover, the measurement of GKN1 concentration is possible only after the incubation of samples at 70°C for 10 minutes. Nevertheless, the aspect of quantitative serum GKN1 evaluation is new in the context of available literature and requires further studies.

Role of abnormal microRNA expression in Helicobacter pylori associated gastric cancer

Epidemiological studies have shown that Helicobacter pylori (HP) infection is a risk factor for gastric cancer (GC). HP infection may induce the release of pro-inflammatory mediators, and abnormally increase the level of reactive oxygen species (ROS), nitric oxide (NO), and cytokines in mucosal epithelial cells of the stomach. However, the specific mechanism underlying the pathogenesis of HP-associated GC is still poorly understood. Recent studies have revealed that abnormal microRNA expression may affect the proliferation, differentiation, and apoptosis of mucosal epithelial cells of the stomach to further influence GC occurrence, development, and metastasis. Herein, we summarize the role of abnormal microRNAs in the regulation of HP-associated GC progression. Abnormal microRNA expression in HP-positive GC may be a biomarker for GC diagnosis, occurrence, and development as well as its targeted treatment and prognosis.

NKX6.3 protects against gastric mucosal atrophy by downregulating β-amyloid production

BACKGROUND

Atrophic gastritis is characterized by loss of appropriate glands and reduction in gastric secretory function due to chronic inflammatory processes in gastric mucosa. Moreover, atrophic gastritis is considered as a precancerous condition of gastric cancer. However, little is known about the molecular mechanism underlying gastric mucosal atrophy and its contribution to gastric carcinogenesis. Thus, we hypothesized that transcription factor NKX6.3 might be involved in maintaining gastric epithelial homeostasis by regulating amyloid β (Aβ) production.

AIM

To determine whether NKX6.3 might protect against gastric mucosal atrophy by regulating Aβ production.

METHODS

We identified NKX6.3 depletion induced cell death by cell count and Western blot assay. Production and mechanism of Aβ oligomer were analyzed by enzyme-linked immunosorbent assay, Western blot, immunoprecipitation, real-time quantitative polymerase chain reaction and immunofluorescence analysis. We further validated the correlation between expression of NKX6.3, Helicobacter pylori CagA, Aβ oligomer, apolipoprotein E (ApoE), and β-secretase 1 (Bace1) in 55 gastric mucosae.

RESULTS

NKX6.3 depletion increased both adherent and floating cell populations in HFE-145 cells. Expression levels of cleaved caspase-3, -9, and poly ADP ribose polymerase were elevated in floating HFE-145^shNKX6.3 cells. NKX6.3 depletion produced Aβ peptide oligomers, and increased expression of ApoE, amyloid precursor protein, Aβ, Bace1, low-density lipoprotein receptor, nicastrin, high mobility group box1, and receptor for advanced glycosylation end product proteins. In immunoprecipitation assay, γ-secretase complex was stably formed only in HFE-145^shNKX6.3 cells. In gastric mucosae with atrophy, expression of Aβ peptide oligomer, ApoE, and Bace1 was detected and inversely correlated with NKX6.3 expression. Treatment with recombinant Aβ 1-42 produced Aβ oligomeric forms and decreased cell viability in HFE-145^shNKX6.3 cells. Additionally, NKX6.3 depletion increased expression of inflammatory cytokines and cyclooxygenase-2.

CONCLUSION

NKX6.3 inhibits gastric mucosal atrophy by regulating Aβ accumulation and inflammatory reaction in gastric epithelial cells.

Penicillin‑binding protein 1A mutation‑positive Helicobacter pylori promotes epithelial‑mesenchymal transition in gastric cancer via the suppression of microRNA‑134

Evidence suggests that Helicobacter pylori (H. pylori) is not only the main cause of gastric cancer (GC), but is also closely associated with its metastasis. One of the major virulence factors in H. pylori is the cytotoxin-associated gene A (CagA). With the growing proportion of amoxicillin-resistant H. pylori strains, the present study aimed to explore the effects of CagA- and penicillin-binding protein 1A (PBP1A) mutation-positive H. pylori (H. pylori_CagA+/P+) on GC cells, and its clinical significance. The clinical significance of H. pylori_CagA+/P+ infection was analyzed in patients with GC. In vitro, GC cells were infected with H. pylori_CagA+/P+ to investigate whether it was involved in the epithelial-mesenchymal transition (EMT) of SGC-7901 cells using immunofluorescence and western blot analysis. The results of clinical analysis demonstrated that, although CagA-negative H. pylori infection had no significant association with the characteristics of patients with GC, H. pylori_CagA+/P+ infection was significantly associated with various clinicopathological parameters, including invasion depth, lymphatic metastasis and distant metastasis. In vitro, the results indicated that H. pylori_CagA+/P+ promoted proliferation, invasion and EMT of SGC-7901 cells. MicroRNA (miR)-134 was downregulated in H. pylori_CagA+/P+ infected tissues compared with in those with H. pylori_CagA+/P- infection. miR-134 overexpression significantly reversed H. pylori_CagA+/P+ infection-associated cell proliferation, invasion and EMT. Furthermore, the results revealed that Forkhead box protein M1 (FoxM1) was a direct target of miR-134, and FoxM1 knockdown impeded H. pylori_CagA+/P+-induced EMT. In conclusion, the present study demonstrated that miR-134 may suppress the proliferation, invasion and EMT of SGC-7901 cells by targeting FoxM1, and may serve a protective role in the process of H. pylori_CagA+/P+-induced GC. These findings may lead to an improved understanding of H. pylori_CagA+/P+-associated poor clinical characteristics in patients with GC.

Multiple genetic mutations caused by NKX6.3 depletion contribute to gastric tumorigenesis

NKX family members are involved in a variety of developmental processes such as cell fate determination in the central nervous system, gastrointestinal tract, and pancreas. However, whether NKX6.3 contributes to gastric carcinogenesis remains unclear. The objective of this study was to examine roles of NKX6.3 depletion in mutagenesis and gastric carcinogenesis, focusing on its effects on genetic alterations and expression of genes. Our results revealed that NKX6.3 depletion induced multiple genetic mutations in coding regions, including high frequency of point mutations such as cytosine-to-thymine and guanine-to-adenine transitions caused by aberrant expression of AICDA/APOBEC family in human gastric epithelial cells. Interestingly, NKX6.3 downregulated AICDA/APOBEC family, NFκB, and CBFβ genes by acting as a transcription factor while inhibiting deaminase activity in gastric epithelial cells. Functional relevance of NKX6.3 was validated in xenograft mice injected with NKX6.3 depleting cells. NKX6.3 depletion resulted in tumor formation and mutations of tumor-associated genes, including p53 and E-cadherin. Moreover, expression levels of NKX6.3 and its target genes were analyzed in tumors derived from mice implanted with NKX6.3 depleting cells and tissue samples of gastric cancer patients. Our results indicate that NKX6.3 depletion in gastric epithelial cells activates AICDA/APOBEC family, leading to accumulation of genetic mutations and eventually driving the development of gastric cancers.

Evaluation of GKN1 and GKN2 gene expression as a biomarker of gastric cancer

AIM

The aim of this study was to investigate the expression of GKN1 and GKN2 genes as probable biomarkers for gastric cancer.

BACKGROUND

Gastric cancer is a multifactorial process characterized by the uncontrolled growth and dissemination of abnormal cells. Survival rates of gastric cancer tend to be poor, a plausible explanation is a combination of a late-stage diagnosis and limited access to treatment. In this regard, finding relevant and measurable biomarkers is urgently needed.

METHODS

27 samples of gastric cancer tissues were enrolled into this study, according to their pathological responses. The alteration of genes expression were evaluated by Real-Time PCR technique.

RESULTS

Our findings showed the significant reduction of Gastrokin-1 and Gastrokine-2 genes expression in the cancerous specimens in comparison with the normal tissues. (P = 0.008 and P = 0.004 respectively).

CONCLUSION

Our findings showed the significant reduction of Gastrokin-1 and Gastrokine-2 genes expression in the cancerous specimens in comparison with the normal tissues. (P = 0.008 and P = 0.004 respectively).

Helicobacter pylori CagA protein activates Akt and attenuates chemotherapeutics-induced apoptosis in gastric cancer cells

Infection with cagA-positive Helicobacter pylori is associated with a higher risk of gastric cancer. The cagA gene product, CagA, is translocated into gastric epithelial cells and perturbs host cellular biological functions. Etoposide, a topoisomerase II inhibitor widely used to couple DNA damage to apoptosis, is a common cytotoxic agent used for advanced gastric cancer. We investigate the effect of CagA on etoposide-induced apoptosis in gastric cancer cells to elucidate whether CagA play a role in gastric carcinogenesis via impairing DNA damage-dependent apoptosis. AGS cell lines stably expressing CagA isolated from H. pylori 26695 strain were established. In the presence of etoposide, viability of parental AGS cells was decreased in a time-and dose-dependent manner, whereas CagA-expressing AGS cells were less susceptible to etoposide induced cell-killing effect. Suppression of etoposide-induced apoptosis was shown in CagA-expressing but not in parental AGS cells by DNA fragmentation, cell cycle, and annexin-V assays. This inhibitory effect of etoposide-induced apoptosis conferred by CagA was also demonstrated in SCM1 and MKN45 gastric cancer cell lines, with two additional chemotherapeutics, 5-FU and cisplatin. The effect of Akt activation on inhibition of etoposide-induced cytotoxicity by CagA was also evaluated. CagA expression and etoposide administration activate Akt in a dose-dependent manner. Enhancement of etoposide cytotoxicity by a PI-3-kinase inhibitor, LY294002, was evident in parental but was attenuated in CagA-expressing AGS cells. CagA may activate Akt, either in the absence or presence of etoposide, potentially contributing to gastric carcinogenesis associated with H. pylori infection and therapeutic resistance by impairing DNA damage-dependent apoptosis.

CagA promotes proliferation and inhibits apoptosis of GES-1 cells by upregulating TRAF1/4-1BB

Cytotoxin-associated gene A (CagA) is one of the most important virulence factors of Helicobacter pylori, and serves a role in H. pylori‑mediated tumorigenesis in gastric cancer. However, the underlying molecular mechanism remains to be elucidated. The present study aimed to investigate the effects of CagA on the proliferation and apoptosis of GES‑1 cells, and the underlying mechanism. A CagA eukaryotic expression plasmid was constructed and transfected into GES‑1 cells. The mRNA and protein levels of CagA, tumor necrosis factor receptor‑associated factor 1 (TRAF1) and tumor necrosis factor receptor superfamily member 9 (4‑1BB) were determined using the reverse transcription‑quantitative polymerase chain reaction and western blot analysis, respectively. Western blot and ELISA analysis was used to detect the release of interleukin (IL)‑8. An MTT assay and flow cytometric analysis was used to assess cell viability and apoptosis, respectively. Ectopic expression of CagA markedly increased TRAF1 and 4‑1BB mRNA and protein levels in GES‑1 cells. CagA increased the expression and release of IL‑8 in GES‑1 cells. The expression of CagA significantly promoted the proliferation (P<0.05) and inhibited the apoptosis (P<0.05) of GES‑1 cells. In conclusion, CagA upregulated TRAF1/4‑1BB, thereby promoting the proliferation and inhibiting the apoptosis of GES-1 cells.

NKX6.3 Regulates Reactive Oxygen Species Production by Suppressing NF-kB and DNMT1 Activities in Gastric Epithelial Cells

NKX6.3 plays an important role in gastric epithelial differentiation and also acts as a gastric tumor suppressor. The specific aim of this study was to determine whether NKX6.3 contributes to gastric mucosal barrier function by regulating reactive oxygen species (ROS) production. NKX6.3 reduced ROS production and regulated expression of anti-oxidant genes, including Hace1. In addition, NKX6.3 reduced DNMT1 expression and activity by down-regulating NF-kB family gene transcription. Silencing of Hace1 recovered ROS production, whereas knock-down of DNMT1 and NF-kB reduced ROS production and induced Hace1 expression by hypomethylating its promoter region. In addition, NKX6.3 inhibited CagA effects on cell growth, ROS production, and NF-kB and DNMT1 activity. In gastric mucosae and cancers, NKX6.3 and Hace1 expression was significantly reduced. The NKX6.3 expression was positively correlated with Hace1 and Nrf2 genes, but negatively correlated with DNMT1. Hypermethylation of Hace1 gene was observed only in gastric mucosae with H. pylori, atrophy and intestinal metaplasia. Thus, these results suggest that NKX6.3 inhibits ROS production by inducing the expression of Hace1 via down-regulating NF-kB and DNMT1 activity in gastric epithelial cells.

NKX6.3 controls gastric differentiation and tumorigenesis

NKX6.3 transcription factor is known to be an important regulator in gastric mucosal epithelial differentiation. The present study aimed to investigate whether NKX6.3 acts as an essential tumor suppressor in gastric carcinogenesis. Absent or reduced protein expression and decreased DNA copy number and mRNA transcript of the NKX6.3 gene were frequently observed in gastric cancers. Overexpression of NKX6.3 in AGSNKX6.3 and MKN1NKX6.3 cells markedly arrested cell proliferation by inhibiting cell cycle progression and induced apoptosis through both death receptor- and mitochondrial-pathways. In addition, stable NKX6.3 transfectants increased the expression of gastric differentiation markers, including SOX2 and Muc5ac, and decreased the expression of intestinal differentiation markers, CDX2 and Muc2. In ChIP-cloning and sequencing analyses, NKX6.3 coordinated a repertoire of target genes, some of which are clearly associated with cell cycle, differentiation and death. In particular, NKX6.3 transcriptional factor was found to bind specifically to the upstream sequences of GKN1, a gastric-specific tumor suppressor, and dramatically increase expression of the latter. Furthermore, there was a positive correlation between NKX6.3 and GKN1 expression in non-cancerous gastric mucosae. Thus, these data suggest that NKX6.3 may control the fate of gastric mucosal cells and function as a gastric tumor suppressor.

Molecular mechanisms of gastric cancer initiation and progression by Helicobacter pylori

PURPOSE OF REVIEW

Infection with the Gram-negative, microaerophilic pathogen Helicobacter pylori results in gastric cancer in a subset of infected individuals. As such, H. pylori is the only WHO classified bacterial class I carcinogen. Numerous studies have identified mechanisms by which H. pylori alters host cell signaling pathways to cause disease. The purpose of this review is to highlight recent studies that explore mechanisms associated with induction of gastric cancer.

RECENT FINDINGS

Over the last year and a half, new mechanisms contributing to the etiology of H. pylori-associated gastric cancer development have been discovered. In addition to utilizing the oncogenic CagA toxin to alter host cell signaling pathways, H. pylori also induces host DNA damage and alters DNA methylation to perturb downstream signaling. Furthermore, H. pylori activates numerous host cell pathways and proteins that result in epithelial-to-mesenchymal transition and induction of cell survival and proliferation.

SUMMARY

Mounting evidence suggests that H. pylori promotes gastric carcinogenesis using a multifactorial approach. Intriguingly, many of the targeted pathways and mechanisms show commonality with diverse forms of cancer.

Inactivation of NKX6.3 in the stomach leads to abnormal expression of CDX2 and SOX2 required for gastric-to-intestinal transdifferentiation

Intestinal metaplasia in gastric mucosa is considered a preneoplastic lesion that progresses to gastric cancer. However, the molecular networks underlying this lesion formation are largely unknown. NKX6.3 is known to be an important regulator in gastric mucosal epithelial differentiation. In this study, we characterized the effects of NKX6.3 that may contribute to gastric intestinal metaplasia. NKX6.3 expression was significantly reduced in gastric mucosae with intestinal metaplasia. The mRNA expression levels of both NKX6.3 and CDX2 predicted the intestinal metaplasia risk, with an area under the receiver operating characteristic curve value of 0.9414 and 0.9971, respectively. Notably, the NKX6.3 expression level was positively and inversely correlated with SOX2 and CDX2, respectively. In stable AGS(NKX6.3) and MKN1(NKX6.3) cells, NKX6.3 regulated the expression of CDX2 and SOX2 by directly binding to the promoter regions of both genes. Nuclear NKX6.3 expression was detected only in gastric epithelial cells without intestinal metaplasia. Furthermore, NKX6.3-induced TWSG1 bound to BMP4 and inhibited BMP4-binding activity to BMPR-II. These data suggest that NKX6.3 might function as a master regulator of gastric differentiation by affecting SOX2 and CDX2 expression and the NKX6.3 inactivation may result in intestinal metaplasia in gastric epithelial cells.

Helicobacter pylori and microRNAs: Relation with innate immunity and progression of preneoplastic conditions

The accepted paradigm for intestinal-type gastric cancer pathogenesis is a multistep progression from chronic gastritis induced by Helicobacter pylori (H. pylori) to gastric atrophy, intestinal metaplasia, dysplasia and ultimately gastric cancer. The genetic and molecular mechanisms underlying disease progression are still not completely understood as only a fraction of colonized individuals ever develop neoplasia suggesting that bacterial, host and environmental factors are involved. MicroRNAs are noncoding RNAs that may influence H. pylori-related pathology through the regulation of the transcription and expression of various genes, playing an important role in inflammation, cell proliferation, apoptosis and differentiation. Indeed, H. pylori have been shown to modify microRNA expression in the gastric mucosa and microRNAs are involved in the immune host response to the bacteria and in the regulation of the inflammatory response. MicroRNAs have a key role in the regulation of inflammatory pathways and H. pylori may influence inflammation-mediated gastric carcinogenesis possibly through DNA methylation and epigenetic silencing of tumor suppressor microRNAs. Furthermore, microRNAs influenced by H. pylori also have been found to be involved in cell cycle regulation, apoptosis and epithelial-mesenchymal transition. Altogether, microRNAs seem to have an important role in the progression from gastritis to preneoplastic conditions and neoplastic lesions and since each microRNA can control the expression of hundreds to thousands of genes, knowledge of microRNAs target genes and their functions are of paramount importance. In this article we present a comprehensive review about the role of microRNAs in H. pylori gastric carcinogenesis, identifying the microRNAs downregulated and upregulated in the infection and clarifying their biological role in the link between immune host response, inflammation, DNA methylation and gastric carcinogenesis.

The role of gastrokine 1 in gastric cancer

Homeostatic imbalance between cell proliferation and death in gastric mucosal epithelia may lead to gastritis and gastric cancer. Despite abundant gastrokine 1 (GKN1) expression in the normal stomach, the loss of GKN1 expression is frequently detected in gastric mucosa infected with Helicobacter pylori, as well as in intestinal metaplasia and gastric cancer tissues, suggesting that GKN1 plays an important role in gastric mucosal defense, and the gene functions as a gastric tumor suppressor. In the stomach, GKN1 is involved in gastric mucosal inflammation by regulating cytokine production, the nuclear factor-κB signaling pathway, and cyclooxygenase-2 expression. GKN1 also inhibits the carcinogenic potential of H. pylori protein CagA by binding to it, and up-regulates antioxidant enzymes. In addition, GKN1 reduces cell viability, proliferation, and colony formation by inhibiting cell cycle progression and epigenetic modification by down-regulating the expression levels of DNMT1 and EZH2, and DNMT1 activity, and inducing apoptosis through the death receptor-dependent pathway. Furthermore, GKN1 also inhibits gastric cancer cell invasion and metastasis via coordinated regulation of epithelial mesenchymal transition-related protein expression, reactive oxygen species production, and PI3K/Akt signaling pathway activation. Although the modes of action of GKN1 have not been clearly described, recent limited evidence suggests that GKN1 acts as a gastric-specific tumor suppressor. This review aims to discuss, comment, and summarize the recent progress in the understanding of the role of GKN1 in gastric cancer development and progression.