Bacterial CagA protein compromises tumor suppressor mechanisms in gastric epithelial cells
Manikandan Palrasu, … , Richard M. Peek Jr., Alexander I. Zaika
Manikandan Palrasu, … , Richard M. Peek Jr., Alexander I. Zaika
Published April 6, 2020
Citation Information: J Clin Invest. 2020;130(5):2422-2434. https://doi.org/10.1172/JCI130015.
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Research Article Gastroenterology

Bacterial CagA protein compromises tumor suppressor mechanisms in gastric epithelial cells

Abstract

Approximately half of the world’s population is infected with the stomach pathogen Helicobacter pylori. Infection with H. pylori is the main risk factor for distal gastric cancer. Bacterial virulence factors, such as the oncoprotein CagA, augment cancer risk. Yet despite high infection rates, only a fraction of H. pylori–infected individuals develop gastric cancer. This raises the question of defining the specific host and bacterial factors responsible for gastric tumorigenesis. To investigate the tumorigenic determinants, we analyzed gastric tissues from human subjects and animals infected with H. pylori bacteria harboring different CagA status. For laboratory studies, well-defined H. pylori strain B128 and its cancerogenic derivative strain 7.13, as well as various bacterial isogenic mutants were employed. We found that H. pylori compromises key tumor suppressor mechanisms: the host stress and apoptotic responses. Our studies showed that CagA induces phosphorylation of XIAP E3 ubiquitin ligase, which enhances ubiquitination and proteasomal degradation of the host proapoptotic factor Siva1. This process is mediated by the PI3K/Akt pathway. Inhibition of Siva1 by H. pylori increases survival of human cells with damaged DNA. It occurs in a strain-specific manner and is associated with the ability to induce gastric tumor.

Authors

Manikandan Palrasu, Elena Zaika, Wael El-Rifai, Monica Garcia-Buitrago, Maria Blanca Piazuelo, Keith T. Wilson, Richard M. Peek Jr., Alexander I. Zaika

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Figure 3

H.pylori causes rapid degradation of Siva1 protein in genotoxic conditions.

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H.pylori causes rapid degradation of Siva1 protein in genotoxic conditi...
(A) Western blot analysis of Siva1 and pH2AX(S139) proteins in DNA-damaged cells. AGS cells were treated with DNA damaging drug camptothecin (50 nM) for 6 hours. Drug was then removed and cells were supplemented with either conditional media or cocultured with H. pylori strain 7.13 for the indicated time. The graph panel shows quantification of Siva1 protein by densitometry, normalized to actin. Expression of Siva1 protein in untreated cells was arbitrarily set at 1. Upper panels show the experimental design. (B) Western blot analysis of Siva1 protein in infected HCT116 cells with different p53 status. Isogenic HCT116 p53+/+ and HCT116 p53−/− cells were cocultured with H. pylori strain 7.13 for 6 hours and analyzed by Western blotting. The graph panels show quantification of Siva1 protein by densitometry, normalized to actin. Expression of Siva1 protein in uninfected cells was arbitrarily set at 1. Statistical significance was calculated using unpaired 2-tailed t tests. Data are displayed as mean ± SE and are representative of 3 independent experiments. ***P < 0.001.