CagA orchestrates eEF1A1 and PKCδ to induce interleukin-6 expression in Helicobacter pylori-infected gastric epithelial cells

Background: Helicobacter pylori colonises the stomach of approximately 50% of the global population. Cytotoxin-associated gene A protein (CagA) is one of the important virulent factors responsible for the increased inflammation and increases the risk of developing peptic ulcers and gastric carcinoma. The cytokine interleukin-6 (IL-6) has particularly important roles in the malignant transformation of gastric and intestinal epithelial cells as it is upregulated in H. pylori-infected gastric mucosa. In this study, we investigated the underlying mechanisms of CagA-induced IL-6 up-regulation during H. pylori infection. AGS cells, a human gastric adenocarcinoma cell line, lacking eEF1A1 were infected with CagA(+) H. pylori (NCTC11637), CagA(-) H. pylori (NCTC11637 Delta cagA), or transduced by Ad-cagA/Ad-GFP. The expression and production of IL-6 were measured by quantitative real-time reverse transcription polymerase chain reaction and enzyme-linked immunosorbent assay, respectively. The interactions among CagA, eukaryotic translation elongation factor 1-alpha 1 (eEF1A1), protein kinase C delta (PKC delta), and signal transducer and activator of transcription 3 (STAT3) were determined by western blot or co-immunoprecipitation. Results: During H. pylori infection, CagA-M (residues 256-871aa) was found to interact with eEF1A1-I (residues 1-240aa). NCTC11637 increased the expression of IL-6 in AGS cells compared with NCTC11637 Delta cagA whereas knockdown of eEF1A1 in AGS cells completely abrogated these effects. Moreover, the CagA-eEF1A1 complex promoted the expression of IL-6 in AGS cells. CagA and eEF1A1 cooperated to mediate the expression of IL-6 by affecting the activity of p-STAT(S727) in the nucleus. Further, CagA-eEF1A1 affected the activity of STAT3 by recruiting PKC delta. However, blocking PKC delta inhibited the phosphorylation of STAT3(S727) and induction of IL-6 by CagA. Conclusions: CagA promotes the expression of IL-6 in AGS cells by recruiting PKC delta through eEF1A1 in the cytoplasm to increase the phosphorylation of STAT3(S727) in the nucleus. These findings provide new insights into the function of CagA-eEF1A1 interaction in gastric adenocarcinoma.