H. pylori, whose infection increases tumor invasiveness and metastasis, is generally labelled as the strongest risk factor for the development of gastric cancer. It appears not to be a coincidence that there is also an overexpression of CXCR4 and an obvious involvement in gastric cancer metastasis. The aim of this study attempts to investigate and further to establish a link between them. With H. pylori being a potent inducer of TNF-alpha, whether TNF-alpha, a tumor promoter, is involved in the induction of CXCR4 expression by H. pylori was also under research in this study.

Expression of CXCR4, TNF-alpha, IL-6 and IL-1beta mRNA was determined by real-time PCR. CXCR4 protein expression was detected by Western blotting. Concentrations of TNF-alpha, IL-6 and IL-1beta in cell culture supernatants were measured using the Quantikine Elisa kit. To abrogate TNF-alpha expression in SGC-7901 cells, TNF-alpha RNAi plasmid was used to transfect them.

Levels of CXCR4 and TNF-alpha mRNA were significantly higher in H. pylori-positive gastric cancers (n=19) compared to H. pylori-negative ones (n=15). A subsequently Spearman's rank correlation test showed there was a positive correlation between the level of CXCR4 mRNA and that of TNF-alpha in 34 primary gastric cancers. Other results followed: Expression of CXCR4 and TNF-alpha was upregulated in gastric cancer cell MKN45 and HGC27 after infection with H. pylori 26695 (cag PAI+) or Tx30a (cag PAI-); The induction of CXCR4 expression by H. pylori was inhibited significantly by a neutralizing TNF-alpha antibody, infliximab; CXCR4 expression was upregulated by MKN45 after treatment with exogenous TNF-alpha or co-culture with macrophage, and was downregulated in HGC27 after transfection with TNF-alpha RNAi plasmid. There was a significant increase in the migration of MKN45 cells treated with H. pylori 26695, and a strong inhibition when AMD 3100, a CXCR4 antagonist, or infliximab, was added.

Our findings demonstrated that H. pylori upregulates CXCR4 expression in gastric cancer through TNF-alpha.

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