Helicobacter pylori CagA EPIYA Motif Variations Affect Metabolic Activity in B Cells.

BACKGROUND: Helicobacter pylori (Hp) colonizes the human stomach and can induce gastric cancer and mucosa-associated lymphoid tissue (MALT) lymphoma. Clinical observations suggest a role for the Hp virulence factor cytotoxin-associated gene A (CagA) in pathogenesis. The pathogenic activity of CagA is partly regulated by tyrosine phosphorylation of C-terminal Glu-Pro-Ile-Tyr-Ala (EPIYA) motifs in host cells. However, CagA differs considerably in EPIYA motifs, whose functions have been well characterized in epithelial cells. Since CagA is fragmented in immune cells, different CagA variants may exhibit undetected functions in B cells. METHODS: B cells were infected with Hp isolates and isogenic mutants expressing different CagA EPIYA variants. CagA translocation and tyrosine phosphorylation were investigated by Western blotting. Apoptosis was analyzed by flow cytometry and metabolic activity was detected by an MTT assay. RESULTS: Isogenic CagA EPIYA variants are equally well translocated into B cells, followed by tyrosine phosphorylation and cleavage. B cell apoptosis was induced in a CagA-independent manner. However, variants containing at least one EPIYA-C motif affected metabolic activity independently of phosphorylation or multiplication of EPIYA-C motifs. CONCLUSIONS: The diverse structure of CagA regulates B cell physiology, whereas B cell survival is independent of CagA.

Dissecting the Helicobacter pylori-regulated transcriptome of B cells.

Persistent infections with the bacterial group-I carcinogen Helicobacter pylori (H. pylori) have been associated with a broad range of gastric disorders, including gastritis, ulceration, gastric cancer or mucosa-associated lymphoid tissue (MALT) lymphoma. Pathogenesis of H. pylori requires a balance between immune tolerance and defense. Although H. pylori induces inflammatory responses, the immune system cannot eliminate the pathogen. The detailed molecular mechanisms of how H. pylori interferes with cells of the immune system, in particular infiltrated B cells, are not well investigated. Previously, it was shown that the bacterial effector and oncoprotein cytotoxin-associated gene A (CagA) is delivered into B cells followed by its tyrosine-phosphorylation. To investigate the functional consequences in B cells colonized by CagA-positive H. pylori, we analyzed the global transcriptome of H. pylori-infected Mec-1 cells by RNA sequencing. We found 889 differentially expressed genes (DEGs) and validated JUN, FOSL2, HSPA1B, SRC, CXCR3, TLR-4, TNF-α, CXCL8, CCL2, CCL4, MHC class I and MHC class II molecules by qPCR, western blot, flow cytometry and ELISA assays. The H. pylori-specific mRNA expression signature reveals a downregulation of inflammation- and migration-associated genes, whereas central signal transduction regulators of cell survival and death are upregulated.

Tyrosine Kinases in Helicobacter pylori Infections and Gastric Cancer.

Helicobacter pylori (H. pylori) has been identified as a leading cause of gastric cancer, which is one of the most frequent and malignant types of tumor. It is characterized by its rapid progression, distant metastases, and resistance to conventional chemotherapy. A number of receptor tyrosine kinases and non-receptor tyrosine kinases have been implicated in H. pylori-mediated pathogenesis and tumorigenesis. In this review, recent findings of deregulated EGFR, c-Met, JAK, FAK, Src, and c-Abl and their functions in H. pylori pathogenesis are summarized.

Helicobacter pylori-controlled c-Abl localization promotes cell migration and limits apoptosis.

BACKGROUND: Deregulated c-Abl activity has been intensively studied in a variety of solid tumors and leukemia. The class-I carcinogen Helicobacter pylori (Hp) activates the non-receptor tyrosine kinase c-Abl to phosphorylate the oncoprotein cytotoxin-associated gene A (CagA). The role of c-Abl in CagA-dependent pathways is well established; however, the knowledge of CagA-independent c-Abl processes is scarce. METHODS: c-Abl phosphorylation and localization were analyzed by immunostaining and immunofluorescence. Interaction partners were identified by tandem-affinity purification. Cell elongation and migration were analyzed in transwell-filter experiments. Apoptosis and cell survival were examined by FACS analyses and MTT assays. In mice experiments and human biopsies, the involvement of c-Abl in Hp pathogenesis was investigated. RESULTS: Here, we investigated the activity and subcellular localization of c-Abl in vitro and in vivo and unraveled the contribution of c-Abl in CagA-dependent and -independent pathways to gastric Hp pathogenesis. We report a novel mechanism and identified strong c-Abl threonine 735 phosphorylation (pAblT735) mediated by the type-IV secretion system (T4SS) effector D-glycero-ß-D-manno-heptose-1,7-bisphosphate (ßHBP) and protein kinase C (PKC) as a new c-Abl kinase. pAblT735 interacted with 14-3-3 proteins, which caused cytoplasmic retention of c-Abl, where it potentiated Hp-mediated cell elongation and migration. Further, the nuclear exclusion of pAblT735 attenuated caspase-8 and caspase-9-dependent apoptosis. Importantly, in human patients suffering from Hp-mediated gastritis c-Abl expression and pAblT735 phosphorylation were drastically enhanced as compared to type C gastritis patients or healthy individuals. Pharmacological inhibition using the selective c-Abl kinase inhibitor Gleevec confirmed that c-Abl plays an important role in Hp pathogenesis in a murine in vivo model. CONCLUSIONS: In this study, we identified a novel regulatory mechanism in Hp-infected gastric epithelial cells by which Hp determines the subcellular localization of activated c-Abl to control Hp-mediated EMT-like processes while decreasing cell death.