Helicobacter pylori lipopolysaccharide alters ECL cell DNA synthesis via aCD14 receptor and polyamine pathway in Mastomys

Chronic Helicobacter pylori infection is associated with alterations in gas tric mucosal cell proliferation. Despite the recognition that bacterial lip opolysaccharide (LPS) is present in biologically active quantities in the g astric mucosa, the mechanisms by which it stimulates cells are largely unkn own. We have previously established a gastric enterochromaffin-like (ECL) c ell neoplasia model in the African rodent species Mastomys and identified t hat tumor ECL cell proliferation is associated with polyamine biosynthesis and ornithine decarboxylase (ODC) activity. In addition, we have shown that H. pylori LPS exhibits a specific mitogenic effect on naive ECL cells in v itro. The aim of this study was to evaluate whether H. pylori has a direct effect on tumor ECL cell proliferation in vitro and further to evaluate the possible molecular mechanisms for this effect. ECL cell neoplasia was gene rated in Mastomys by endogenous hypergastrinemia induced by H-2 blockade (l oxtidine 1 g/kg/day) and tumor ECL cells prepared. The DNA synthesis in 24- hour cultured tumor cells was measured by bromodeoxyuridine uptake and ODC activity by (CO2)-C-14 formation from C-14-ornithine. The putative LPS rece ptor, CD14, was evaluated by reverse-transcription polymerase chain reactio n. Our results demonstrated: (1) H. pylori LPS (10(-12) to 10(-7) M) stimul ated basal DNA synthesis (2.2-fold) with an estimated EC50 of 10(-10) M; (2 ) this proliferative response correlated with an increase in ODC activity ( 1.4-fold, EC50 similar to 10(-10) M) which could be inhibited by a specific ODC inhibitor, difluoromethyl ornithine, at 10(-9) M;(3) the CD14 receptor was identified in both naive and transformed ECL cells by reverse-transcri ption polymerase chain reaction, and (4) the effects of LPS were inhibited by blocking the CD14 receptor with its specific monoclonal antibody (1:100) . Thus, H. pylori LPS appears to influence tumor ECL cell proliferation by activation of the intracellular polyamine pathway and ODC activity via a CD 14 receptor on the ECL cell. Copyright (C) 2000 S. Karger AG, Basel.