Evaluation of Global Genome Methylation in Gastritis Lesion and its Correlation With Clinicopatological Findings

Abstract

Global genome hypomethylation as an epigenetic phenomenon may induce (pre)neoplastic transformation through inducing chromosomal and genomic instability and activating oncogenes. Global genome hypomethylation has a fundamental role in early stages of tumorigenesis but little is known about this epigenetic event in gastric precancerous lesions such as gastritis. Therefore, we decided to evaluate this issue in gastritis lesion for obtaining new insight toward molecular biology of gastric cancer. Here we used a technique composed of restriction enzyme digestion and pyrosequencing known as luminometric methylation assay to evaluate this issue. DNA obtained from normal and gastritis lesions was digested with HpaII (sensitive to methylation in its cut site) and MspI (insensitive). Overhangs resulting from these enzymes then fill in by polymerase extension assay using pyrosequencing instrument. Nucleotide incorporation during polymerase extension generates light, which expresses as pick in the pyrogram. By comparing the height of picks obtained form both enzymes it can be possible to evaluate and compare global genome methylation level of gastritis and normal tissues. If the target site is fully methylated, the HpaII/MspI (their pick height) will approach zero. If not, this ratio will be around 1. In the other conditions this ratio varies between 0 and 1. Comparing the ratio of normal and gastritis sample, it can be inferred whether or not gastritis is hypomethylated. This study was performed on 83 gastritis and normal adjacent tissues. The patients included 34 male and 49 female and were 15 to 83 years old. According to our study, gastritis tissue was hypomethylated more than the normal tissue (p = 0.028). Global genome methylation has no significant correlation with MSI, pathological findings, age, and gender. We conclude that global genome hypomethylation occurs in the gastritis level. This reduction probably continues in the next steps toward gastric cancer and may induce other epigenetic and/or genetic changes (such as MSI) that promote carcinogenesis.

Profile and Frequency of p53 Gene Alterations in Gastritis Lesions from Iran

“…This transition has been linked to N-nitrosamines which are present in many foods [37,38] and to spontaneous deamination of methylcytosine [39]. The probable explanation for the low frequency of CpG-related G:C>A:T transition is that the genome in the gastritis stage undergoes global hypomethylation as seen in our previous work on gastritis [40]. This hypomethylation of the genome largely affects the intergene region of the DNA [41].…”

Correlation between global genome methylation and mutation at CpG codons of p53 gene

“…All samples expressed p53 and mismatch repair proteins (MLH1, MSH2 and MSH6). Also, most patients (89%) were Helicobacter pylori positive …”

“…In this study, we used a luminometric methylation assay following the CpG methylation‐sensitive restriction enzyme Hpa II and its methylation‐insensitive isoschizomer Msp I in the sequence CCGG . Briefly, extracted DNA was cleaved with Hpa II + Eco RI or Msp I + Eco RI in two separate reactions at 37°C for 4 h. Then, the samples were placed in a PSQ 96MA system (Biotage, Uppsala, Sweden).…”

Global DNA hypomethylation is an early event inHelicobacter pylori-related gastric carcinogenesis

“…Global DNA hypomethylation is generally considered one of the hallmarks of cancer cells because the genes vulnerable to aberrant hypermethylation usually are overlapped by the genes targeted by hypomethylation 23 24. Therefore, assessing global DNA methylation rather than the methylation status of a single gene may contribute to predict the individual susceptibility to develop GC.…”