Apoptosis or Cell Survival: c-Abl in Helicobacter pylori-infected epithelial cells

To further our understanding of the Helicobacter pylori (Hp)-dependent pathogenesis leading to inflammation and neoplasia, we will investigate the molecular mechanism of how Hp promotes cellular survival and migration while preventing apoptosis. In our previous work, we identified threonine 735 phosphorylation of c-Abl (c-AblT735 ) in Hp-infected gastric epithelial cells as a crucial step in these processes, but the molecular mechanisms of this novel cross-talk are still unknown. Based on our data, we will investigate the molecular mechanism of phosphorylated c- AblT735 in the prevention of apoptosis and induction of survival and enhanced migration of Hp-infected gastric epithelial cells. Functional consequences of c-Abl-dependent signal transduction pathways will be examined in the Mongolian gerbil animal model which is well established for Hp infections and pathogenesis. Since c-Abl already represents an attractive target molecule in drug intervention in certain neoplasia, increasing knowledge of c-Abl signaling obtained from this proposed project may also uncover novel strategies in therapeutic intervention of H. pylori-related diseases.

Growth, death and migration of epithelial cells are strictly regulated processes. The human pathogen and class-I carcinogen Helicobacter pylori (H. pylori) can directly interfere with these processes with drastic consequences for the bacterial pathogenesis. In this project, the molecular and cellular mechanisms of the non-receptor tyrosine kinase c-Abl in epithelial cells and B cells were analyzed, which can contribute to the induction of H. pylori-dependent gastric cancer and MALT lymphoma. Previously, we have shown that c-Abl directly phosphorylates the oncoprotein cytotoxin-associated gene A (CagA) which is injected by H. pylori into infected host cells and is a key player in H. pylori pathogenesis. In this project, we have shown that c-Abl in cooperation with Src family kinases mediated a hierarchically structured phosphorylation of CagA in epithelial cells. In comparison to epithelial cells, this strict hierarchy was not observed in B cells. In B cells, H. pylori stimulated c-Abl kinase activity at very early time points of infection. Phosphorylation of CagA was partially inhibited by the c-Abl inhibitor STI-571 and completely after the addition of the Src/Abl inhibitor Dasatinib. Further, STI-571 significantly inhibited cell death of the B cell line Mec1.In the main part of the project, we investigated the activity and subcellular localization of c- Abl in vitro and in vivo and aimed to unravel the contribution of c-Abl in CagA-dependent and -independent pathways. H. pylori induced c-Abl tyrosine phosphorylation, which is necessary for full kinase activity. Furthermore, we identified PKC as a novel kinase for c-Abl threonine 735 phosphorylation. pAblT735 interacted with 14-3-3 proteins which caused cytoplasmic retention of c-Abl, where it potentiated H. pylori-mediated cell elongation and migration. Further, the nuclear exclusion of pAblT735 attenuated caspase-dependent cell death. Importantly, in human biopsies from patients suffering from H. pylori-mediated gastritis c-Abl expression and pAblT735 phosphorylation were drastically enhanced as compared to type C gastritis patients or healthy individuals. Finally, pharmacological c-Abl inhibition confirmed that c-Abl plays an important role in H. pylori pathogenesis in a murine animal model in vivo. This novel mechanism suggests c-Abl as a candidate target for pharmacological treatment of H. pylori-associated gastric disease.