Abstract
BackgroundDeregulated 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.Methodsc-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.ResultsHere, 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-β-D-manno-heptose-1,7-bisphosphate (βHBP) 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.ConclusionsIn 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.
Highlights
Deregulated c-Abl activity has been intensively studied in a variety of solid tumors and leukemia
Helicobacter pylori (Hp) regulates c-Abl tyrosine and threonine phosphorylation via different signaling pathways c-Abl plays a well documented crucial role in Hp pathogenesis, the complex network of kinase regulation has not been investigated in detail
This could be detected in MKN28 (Additional file 2: Figure S1B) and MCF-7 cells (Additional file 2: Fig. S1C), which have been established as suitable Hp infection models [46]
Summary
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). Helicobacter pylori (Hp) is a human class-I carcinogen that exclusively colonizes the gastric epithelium of approximately 50% of the world’s population. Persistent infections with Hp are considered as the main factor responsible for chronic gastritis, ulceration, lymphoma of the MALT system and gastric cancer [1, 2]. Gastric cancer can be distinguished in cardia (gastro-esophageal junction) and non-cardia adenocarcinomas caused by altered cell proliferation, survival, apoptosis and (epigenetic) modifications of tumor suppressor genes (cdh, tp53, kras, etc.) [3, 4]. Hp-mediated tumorigenesis and gastric cancer progression involve a complex network of signaling cascades which allows persistent colonization and causes the induction of inflammatory and carcinogenic responses
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