Spermine Oxidase Mediates the Gastric Cancer Risk Associated With Helicobacter pylori CagA

Abstract

BACKGROUND & AIMS Helicobacter pylori-induced gastric carcinogenesis has been linked to the microbial oncoprotein CagA. Spermine oxidase (SMO) metabolizes the polyamine spermine into spermidine and generates H2O2 that causes apoptosis and DNA damage. We determined if pathogenic effects of CagA are attributable to SMO. METHODS Levels of SMO, apoptosis, and DNA damage (8-oxoguanosine) were measured in gastric epithelial cell lines infected with cagA+ or cagA− H. pylori strains, or transfected with a CagA expression plasmid, in the absence or presence of SMO small interfering RNA, or an SMO inhibitor. The role of CagA in induction of SMO and DNA damage was assessed in H. pylori-infected gastritis tissues from humans, gerbils, and both wild-type and hypergastrinemic INS-GAS mice, using immunohistochemistry and flow cytometry. RESULTS cagA+ strains or ectopic expression of CagA, but not cagA− strains, led to increased levels of SMO, apoptosis, and DNA damage in gastric epithelial cells, and knockdown or inhibition of SMO blocked apoptosis and DNA damage. There was increased SMO expression, apoptosis, and DNA damage in gastric tissues from humans infected with cagA+, but not cagA− strains. In gerbils and mice, DNA damage was CagA-dependent and present in cells that expressed SMO. Gastric epithelial cells with DNA damage that were negative for markers of apoptosis accounted for 42–69% of cells in gerbils and INS-GAS mice with dysplasia and carcinoma. CONCLUSIONS By inducing SMO, H. pylori CagA generates cells with oxidative DNA damage, and a subpopulation of these cells are resistant to apoptosis and thus at high risk for malignant transformation.

Induction of COX-2 expression by Helicobacter pylori is mediated by activation of epidermal growth factor receptor in gastric epithelial cells

“…The most abundant PG produced by COX-2 in gastric cancer is PGE 2 (22). PGE 2 binds to four subtypes of receptors (EP 1 -EP 4 ) and promotes tumor growth by stimulating cell proliferation, promoting angiogenesis, inhibiting apoptosis, inducing invasion, and suppressing immune activation (25).…”

Spermine oxidase, a polyamine catabolic enzyme that linksHelicobacter pyloriCagA and gastric cancer risk

“…These data were confirmed by flow cytometry of isolated gastric epithelial cells from human tissues. 24 We also showed that in C57BL/6 mice chronically infected with H. pylori PMSS1, a strain that maintains the ability to translocate CagA into gastric epithelial cells after in vivo passage, 32 there were increased levels of SMO protein in gastric epithelial cells when assessed by flow cytometry. 24 In contrast, mice infected with a PMSS1 cagE -mutant exhibited no significant increase in SMO expression in gastric epithelial cells.…”

“…31 We found higher levels of CagA protein in ImSt cells co-cultured with 7.13, compared with its non-carcinogenic parental strain B128. 24 Co-culture of 7.13 with ImSt cells resulted in higher levels of SMO mRNA expression compared with coculture with B128, and the 7.13 cagA -mutant failed to increase SMO mRNA levels. Similarly, when assessed by western blotting or flow cytometry, H. pylori strain 7.13 significantly upregulated SMO protein levels, which were induced to a lesser degree with B128, and the 7.13 cagA -strain did not increase SMO protein expression.…”

“…24 CagA is an H. pylori bacterial effector protein that is translocated by the type IV cag secretion system. 25,26 Animal, cell culture, and epidemiological studies have provided evidence for the importance of CagA in H. pylori pathogenesis.…”

“…24 In order to address the role of CagA in SMO induction and its biological effects, we used conditionally-immortalized mouse stomach (ImSt) non-cancerous gastric epithelial cells that express a temperaturesensitive SV40 large T antigen under an IFN-c promoter, such that cells exhibit a normal phenotype when cultured without IFN-c at the non-permissive temperature of 37°C. 30 These cells were exposed to H. pylori strain 7.13, an oncogenic strain shown to cause gastric cancer in gerbils; the non-carcinogenic parental strain B128 (a clinical isolate); and the cagA isogenic mutant of 7.13 (7.13 cagA -).…”