Background and aims: Helicobacter pylori infection induces expression of proinflammatory cytokines such as interleukin (IL)-8 and tumour necrosis factor alpha (TNF-alpha) in gastric mucosa, and their genes have AP-1 binding sites in the promoter region. c-Fos is important for transactivation of AP-1 which has SRE in the promoter region. We conducted this study to confirm H pylori induced transactivation of these binding sites.
Methods: Transactivation of SRE and AP-1 was evaluated in human gastric cancer cells TMK1 and MKN45 by luciferase reporter assay in transient transfection. We compared the effects of coculture with four H pylori strains, a cag pathogenicity island (PAI) positive strain TN2, its isogenic vacA negative (TN2-DeltavacA) or cagE negative (TN2-DeltacagE) mutants, and a cag PAI negative clinical isolate T68. Phosphorylation of ERK1/2, JNK, and c-Jun was measured by immunoblot, induction of IL-8 secretion by ELISA, and the effects of MEK by inhibitor U0126.
Results: Both SRE and AP-1 were transactivated by coculture with TN2. Although TN2-DeltavacA induced comparable transactivation, TN2-DeltacagE and T68 showed decreased transactivation of SRE (65% and 51%) and AP-1 (71% and 54%, respectively, of TN2). Heat killed TN2 or indirect contact using a permeable membrane inhibited transactivation. Levels of phosphorylated ERK1/2, JNK, and c-Jun were increased by coculture with TN2. MEK inhibitor U0126 reduced TN2 induced transactivation of SRE and AP1, as well as secretion of IL-8, by 83%, 87%, and 53%, respectively, of TN2.
Conclusions: Transactivation of SRE and AP-1, through ERK/MAPK and JNK/SAPK cascades, respectively, was found in gastric cancer cells cocultured with H pylori. Direct contact with viable bacteria possessing intact cag PAI is a prerequisite for the onset of intracellular signalling leading to AP-1 transactivation.