在胃幽門螺旋桿菌誘發TRAIL引起人類胃上皮細胞凋亡中casein kinase 2 的角色

Abstract

Helicobacter pylori (H. pylori), is a common pathogen of humans that causes chronic gastritis, peptic ulcer and gastric adenocarcinoma. However, the mechanisms by which H. pylori mediates pathogenesis are still unclear. Studies have shown that the enhanced gastric epithelial cell apoptosis observed during infection with H. pylori was significant in the pathogenesis of gastritis. The virulence factors produced by H. pylori and activation of immune response by host also contribute to gastric epithelium damage. Previous studies of our laboratory demonstrated that when direct contacting with gastric epithelial cells, H. pylori could sensitize human gastric epithelial cell line to be susceptible to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptosis. TRAIL death signal transduction in human gastric epithelial cells was modulated by H. pylori. After co-cultured with H. pylori and treated with TRAIL, caspase-8 activation was enhanced and the enhanced caspase-8 activation was sufficient to lead downstream Bid, caspase-9 and caspase-3 cleavage and finally break the resistant to TRAIL-induced apoptosis. However, the mechanism of H. pylori modulate TRAIL death signaling is still not clear. We hypothesize that the carbohydrate molecules that cover the cell surface may play a role in H. pylori-induced TRAIL sensitivity during H. pylori contact to gastric epithelial cell surface. In order to study the role of cell surface carbohydrate molecules in regulation of H. pylori-induced TRAIL sensitivity, we use different carbohydrates adding to the in vitro co-culture system. We demonstrated that heparan sulfate could inhibit H. pylori-induced TRAIL sensitivity, but not the binding of H. pylori to cell surface. These results indicated that H. pylori sensitize gastric epithelial cells to TRAIL-induced apoptosis might through the interaction with cell surface heparan sulfate. Recent studies have shown casein kinase II (CK2), a highly conserved, ubiquitous and constitutively active serine/threonine kinase, could protect cancer cell from TRAIL-induced apoptosis. Since the CK2 activity is found low in TRAIL-sensitive cancer cell lines but high in TRAIL-resistant cancer cell lines. Inhibition of CK2 phosphorylation events result in dramatic sensitization of tumor cells to TRAIL-induced apoptosis but not normal cells. Studies also shown CK2 inhibition increase the level of recruitment of procaspase-8 to the death-inducing signaling complex (DISC) and induce rapid caspase-8,-9, -3 cleavage after TRAIL treatment. We hypothesize that H. pylori sensitize gastric epithelial cells to TRAIL-induced apoptosis may through modulation CK2 activity. In order to study the role of CK2 in regulation of H. pylori-induced TRAIL sensitivity, we use CK2 specific inhibitor, DRB, to inhibit the phosphorylation events of CK2 in human gastric epithelial cell line, AGS cells. We demonstrated that inhibition of CK2 activity could sensitize AGS to TRAIL-induced apoptosis, indicating a role of CK2 in protecting AGS cells from TRAIL-induced apoptosis. Western blotting also demonstrated that caspase-8 cleavage was enhanced by DRB and TRAIL treatment and this phenomenon was similar to co-culture with H. pylori, suggesting that H. pylori sensitize AGS cells to TRAIL-induced apoptosis through modulating CK2 activity. We use Western blotting and CK2 kinase assay to clarify the interaction between H. pylori and CK2. But the CK2 protein expression level and kinase activity did not show difference before and after co-cultured with H. pylori. These result demonstrated that CK2 is not the molecule that participates in the downstream of H. pylori-induced TRAIL sensitivity.