DNA Hypermethylation Downregulates Telomerase Reverse Transcriptase (TERT) during H. pylori-Induced Chronic Inflammation.

Françoise I Bussière,Vania Camilo,Lionel Costa,Hilde De Reuse,Julien Fernandes,Giulia Nigro,Eliette Touati,Laurence Fiette,Valérie Michel

doi:10.1155/2019/5415761

Abstract

Helicobacter pylori infection causes chronic gastritis and is the major risk factor of gastric cancer. H. pylori induces a chronic inflammation-producing reactive oxygen species (ROS) which is a source of chromosome instabilities and contributes to the development of malignancy. H. pylori also promotes DNA hypermethylation, known to dysregulate essential genes that maintain genetic stability. The maintenance of telomere length by telomerase is essential for chromosome integrity. Telomerase reverse transcriptase (TERT) is the catalytic component of telomerase activity and an important target during host-pathogen interaction. We aimed to investigate the consequences of H. pylori on the regulation of TERT gene expression and telomerase activity. In vitro, hTERT mRNA levels and telomerase activity were analysed in H. pylori-infected human gastric epithelial cells. In addition, C57BL/6 and INS-GAS mice were used to investigate the influence of H. pylori-induced inflammation on TERT levels. Our data demonstrated that, in vitro, H. pylori inhibits TERT gene expression and decreases the telomerase activity. The exposure of cells to lycopene, an antioxidant compound, restores TERT levels in infected cells, indicating that ROS are implicated in this downregulation. In vivo, fewer TERT-positive cells are observed in gastric tissues of infected mice compared to uninfected, more predominantly in the vicinity of large aggregates of lymphocytes, suggesting an inflammation-mediated regulation. Furthermore, H. pylori appears to downregulate TERT gene expression through DNA hypermethylation as shown by the restoration of TERT transcript levels in cells treated with 5′-azacytidine, an inhibitor of DNA methylation. This was confirmed in infected mice, by PCR-methylation assay of the TERT gene promoter. Our data unraveled a novel way for H. pylori to promote genome instabilities through the inhibition of TERT levels and telomerase activity. This mechanism could play an important role in the early steps of gastric carcinogenesis.

Highlights

Helicobacter pylori is a gastric pathogen that infects half of the human population worldwide. is bacterium is responsible for chronic inflammation and gastroduodenal diseases, including gastric adenocarcinoma and mucosaassociated lymphoid tissue (MALT) lymphoma [1, 2]
H. pylori is an efficient inducer of DNA damage such as DNA double-strand breaks Journal of Oncology (DSBs) and mutations in the nuclear and mitochondrial DNA [6,7,8,9]. e genotoxic activity of H. pylori infection is largely associated with chronic inflammation of the gastric mucosa and the resulting oxidative stress, leading to a harmful environment for the host and promotion of carcinogenesis [10]
We examined the consequences of H. pylori infection on telomerase activity using the Telomeric Repeat Amplification Protocol (TRAP) assay [34], which allows the ability of the telomerase to add telomeric repeats at the 3′end of an oligonucleotide substrate to be determined

Summary

Introduction

Helicobacter pylori is a gastric pathogen that infects half of the human population worldwide. is bacterium is responsible for chronic inflammation and gastroduodenal diseases, including gastric adenocarcinoma and mucosaassociated lymphoid tissue (MALT) lymphoma [1, 2]. Prolonged inflammation and long-term persistence of H. pylori contribute to gastric carcinogenesis, via dysregulation of signaling pathways, cell proliferation, and chromosome instability [4, 5]. E genotoxic activity of H. pylori infection is largely associated with chronic inflammation of the gastric mucosa and the resulting oxidative stress, leading to a harmful environment for the host and promotion of carcinogenesis [10]. Oxidative stress is a source of DNA damage and telomere shortening [11]. H. pylori is a source of aberrant DNA methylation in the host cells [5, 13]. We reported that H. pylori inhibits the expression of the transcription factors USF1 and USF2 (upstream stimulating factors 1 and 2) genes, by DNA hypermethylation of their promoter region [14]. USF1 and USF2 regulate among others the transcription of TERT coding for the telomerase reverse transcriptase (TERT), the major component of telomerase [15, 16]

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