The overmethylated genes in Helicobacter pylori-infected gastric mucosa are demethylated in gastric cancers

Species-specific role of gene-adjacent retroelements in human and mouse gastric carcinogenesis

Helicobacter pylori (HP) infection promotes the recruitment of bone marrow stem cells into chronic gastritis lesions. Some of these marrow stem cells can differentiate into gastric epithelial cells and neoplastic cells. We propose that HP-associated methylation could stabilize trans-differentiation of marrow-derived stem cells and that an unstable methylation status is associated with a risk of gastric cancer. Pathobiologic behavior of experimental mouse gastric cancer is mild compared to invasive and metastatic human gastric cancer. Differences in epigenetic stabilization of adult cell phenotypes between humans and mice could provide a foundation to explore the development of invasive and metastatic gastric cancer. Retroelements are highly repetitive sequences that play an essential role in the generation of species diversity. In this review, we analyzed retroelements adjacent to human and mouse housekeeping genes and proposed a possible epigenetic mechanism for HP-associated carcinogenesis.

Aberrant methylation patterns in cancer: a clinical view

Epigenetic mechanisms, such as DNA methylation, DNA hydroxymethylation, post-translational modifications (PTMs) of histone proteins affecting nucleosome remodelling, and regulation by small and large non-coding RNAs (ncRNAs) work in concert with cis and trans acting elements to drive appropriate gene expression. Advances in detection methods and development of dedicated platforms and methylation arrays resulted in an explosion of information on aberrantly methylated sequences linking deviations in epigenetic landscape with the initiation and progression of complex diseases. Here, we consider how DNA methylation changes in malignancies, such as breast, pancreatic, colorectal, and gastric cancer could be exploited for the purpose of developing specific diagnostic tools. DNA methylation changes can be applicable as biomarkers for detection of malignant disease in easily accessible tissues. Methylation signatures are already proving to be an important marker for determination of drug sensitivity. Even more, promoter methylation patterns of some genes, such as MGMT, SHOX2, and SEPT9, have already been translated into commercial clinical assays aiding in patient assessment as adjunct diagnostic tools. In conclusion, the changes in DNA methylation patterns in tumour cells are slowly gaining entrance into routine diagnostic tests as promising biomarkers and as potential therapeutic targets.

Proteomic analysis of Helicobacter pylori from patients with different gastric diseases in different regions of Jiangsu

AIM: To perform a proteomic analysis of Helicobacter pylori (H. pylori) from patients with different gastric diseases in different regions of Jiangsu.

METHODS: H. pylori strains were isolated from the endoscopic biopsy specimens of gastric mucosa of patients with gastritis or gastric cancer from areas of high (Taizhou) and low (Suzhou) incidence of gastric cancer, and whole-cell proteins of H. pylori were extracted and characterized by 2-dimensional electrophoresis (DE). Different protein spots were analyzed using PDQuest analysis software, identified by electrospray ionization quadruple time-of-flight mass spectrometry (ESI-Q-TOF-MS), and searched using the Mascot database.

RESULTS: Nine differentially expressed proteins were identified, including four up-regulated in gastric cancer (superoxide dismutase, urease subunit alpha, chaperone protein dnaK and DNA-directed RNA polymerase subunit alpha), two up-regulated in chronic gastritis (urease subunit alpha and nucleoside diphosphate kinase), and three only expressed in strains from one region (S-ribosyl homocysteine lyase, inorganic pyrophosphatase and 60 × 10³ chaperonin).

CONCLUSION: There are proteomic differences between H. pylori isolates from patients with gastritis and gastric cancer in areas of high and low incidents of gastric cancer. The protein spots overexpressed in gastric cancer in the area with high incidence of gastric cancer are more than those in the area with low incidence of gastric cancer.

Age-related methylation patterning of housekeeping genes and tissue-specific genes is distinct between the stomach antrum and body

AIM

The methylation-variable sites around CpG islands are frequently overmethylated in Helicobacter pylori-infected stomachs. Age-related patterns of the overmethylation changes were compared between the fast-growing antrum cells and the slow-growing body cells.

MATERIALS & METHODS

A total of 316 H. pylori-positive tissues and 380 H. pylori-negative tissues were obtained by endoscopic biopsy. The methylation-variable sites of ten housekeeping genes and nine tissue-specific genes were semiquantitatively analyzed, based on the ten-level classification of methylation-specific PCR intensity. The overmethylated genes were scored when their methylation levels were higher than an intermediate level of each gene common in the H. pylori-negative mucosa.

RESULTS

The age-dependent methylation level of the inactive APC gene observed similarly in the antrum and the body was used as an age standard of methylation variation in a biopsy tissue. The overmethylation of housekeeping genes and stomach-specific genes rapidly increased to a high plateau frequency in the young-aged APC methylation cases (mean age: 43 years) in the H. pylori-positive antrum. In the H. pylori-positive body, most of the overmethylated housekeeping genes slowly increased to a peak frequency in the middle-aged APC methylation cases (mean age: 53 years). The housekeeping gene pairs showed high correlations (Spearman's correlation coefficient > 0.4) in both the antrum and the body.

CONCLUSION

The overmethylation of housekeeping genes rapidly and slowly increased to a high frequency in concordance with a rapid and slow growth of epithelial cells in the H. pylori-infected stomach.

Epigenetic implication of gene-adjacent retroelements in Helicobacter pylori-infected adults

A chronic inflammatory condition of gastric mucosa can facilitate the influx of new stem cells into the stomach. Epigenetic codes, such as DNA methylation, may be responsible for the stable maintenance of epigenetic phenotypes established in the new stomach-adapted stem cells. A number of hypotheses have been made for the role of CpG-island methylation, which is common in the Helicobacter pylori-infected stomach. However, they could not explain the plausible role of CpG-island methylation in the re-establishment of epigenetic phenotypes. These islands are highly repetitive sequences densely methylated throughout the human genome, the so-called parasitic retroelements, which expand a number of cDNA copies with reverse transcriptase. The densely methylated retroelements adjacent to the host genes can form the transitional-CpG sites around gene-control regions that are barely methylated. This review focuses on the putative role of transitional CpG methylation in the adaptive differentiation of new stem cells in the H. pylori-infected stomach.

Helicobacter pylori induces demethylation of the Calmodulin gene promoter in gastric cancer cells

AIM: To explore the expression of Calmodulin (CaM) gene in gastric cancer tissue and the relationship between the methylation level of the CaM gene promoter and Helicobacter pylori (H. pylori) infection.

METHODS: The expression of the CaM gene in 30 cases of gastric cancer and matched tumor-adjacent gastric tissue and metastatic lymph nodes was assessed by real-time fluorescence quantitative PCR. The relationship between CaM gene expression and H. pylori infection was analyzed. Methylation of CpG islands in the CaM gene promoter was measured by bisulfite modified sequencing method in gastric cancer cells infected with H. pylori and stably transfected with the H. pylori cytotoxin-associated protein A (cagA) gene.

RESULTS: The relative expression level of the CaM gene in cancer tissue was 2.08 times higher than that in tumor-adjacent gastric tissue (P < 0.05). The relative expression level of the CaM gene in H. pylori-positive gastric cancer was 6.11 times higher than that in the H. pylori-negative group (P < 0.05). The demethylation at -276 bp in the CaM gene promoter was detected in H. pylori-infected and cagA-overexpressed gastric cancer cells.

CONCLUSION: H. pylori, though secreting the virulence factor CagA, up-regulates the expression of the CaM gene in gastric cancer possibly by inducing the demethylation of the CaM promoter.

The gene-reduction effect of chromosomal losses detected in gastric cancers

Background

The level of loss of heterozygosity (LOH) that reduces a gene dose and exerts a cell-adverse effect is known to be a parameter for the genetic staging of gastric cancers. This study investigated if the cell-adverse effect induced with the gene reduction was a rate-limiting factor for the LOH events in two distinct histologic types of gastric cancers, the diffuse- and intestinal-types.

Methods

The pathologic specimens obtained from 145 gastric cancer patients were examined for the level of LOH using 40 microsatellite markers on eight cancer-associated chromosomes (3p, 4p, 5q, 8p, 9p, 13q, 17p and 18q).

Results

Most of the cancer-associated chromosomes were found to belong to the gene-poor chromosomes and to contain a few stomach-specific genes that were highly expressed. A baseline-level LOH involving one or no chromosome was frequent in diffuse-type gastric cancers. The chromosome 17 containing a relatively high density of genes was commonly lost in intestinal-type cancers but not in diffuse-type cancers. A high-level LOH involving four or more chromosomes tended to be frequent in the gastric cancers with intestinal and mixed differentiation. Disease relapse was common for gastric cancers with high-level LOH through both the hematogenous (38%) and non-hematogenous (36%) routes, and for the baseline-level LOH cases through the non-hematogenous route (67%).

Conclusions

The cell-adverse effect of gene reduction is more tolerated in intestinal-type gastric cancers than in diffuse-type cancers, and the loss of high-dose genes is associated with hematogenous metastasis.