Sa1865 Helicobacter pylori Induces Phosphorylation of Epidermal Growth Factor Receptor via p38/ERK Activation in Gastric Epithelial Cells in Heparin Binding-Epidermal Growth Factor Independent Manner

Abstract

Helicobacter pylori is the strongest known risk factor for gastric adenocarcinoma; however, most infected individuals never develop this malignancy. H. pylori strains harboring the cag pathogenicity island, which encodes CagA and a type IV secretion system (T4SS), augment cancer risk. In conjunction with bacterial determinants, environmental conditions such as iron deficiency influence disease outcomes. We previously reported that iron depletion accelerates the development of H. pylori-induced carcinogenesis in a cagA-dependent manner and that CagA is necessary for H. pylori survival in vitro and in vivo under iron-deficient conditions. To define mechanisms that regulate these CagA-dependent phenotypes, we infected Mongolian gerbils with the carcinogenic cag+ H. pylori strain 7.13, or a 7.13 cagAisogenic mutant under iron-replete or iron-depleted conditions. Localization, distribution, and morphology of H. pylori were assessed six weeks post-infection by immunofluorescence and in vivo confocal microscopy. Under iron-replete conditions, the H. pylori cagAisogenic mutant exhibited an elongated and spiral-like morphology similar to wild-type strain 7.13; however, iron depletion induced shortened, rounded, and coccoid morphologies in the cagAmutant, but not the wild-type strain. To investigate this phenotype in greater depth, scanning electron microscopy was performed on gerbil gastric tissue sections, which confirmed aberrant coccoid morphology of cagA-deficient strains only under iron-depleted conditions. To directly assess the effects of iron depletion on this phenotype, wild-type H. pylori strain 7.13 and the cagAisogenic mutant were grown in vitro under iron-replete or iron-restricted conditions. Wild-type strain 7.13 maintained a characteristic spiral morphology under iron-replete and iron-restricted conditions; however, consistent with our in vivo observations, conditions of iron restriction induced a coccoid-like morphology in the 7.13 cagAmutant strain, which was abrogated following the addition of exogenous iron. These data demonstrate that loss of cagA alters H. pylori morphology in an iron-dependent manner, which is reversible following iron supplementation. Collectively, these phenotypes likely contribute to impaired growth and colonization observed with the cagAisogenic mutant under iron-depleted conditions in vivo and implicate CagA and the type IV secretion system as mediators of nutrient acquisition and survival under austere conditions within the gastric niche.