Involvement of Cyclooxygenase-2–Prostaglandin E2 Pathway in Interleukin-8 Production in Gastric Cancer Cells

Prostaglandin E2 (PGE2) is thought to play an important role in both inflammatory and anti-inflammatory effects. The effect of PGE2 on the proinflammatory chemokine interleukin-8 (IL-8) in the gastric epithelial cells has not been defined yet. A gastric cancer cell line (MKN45) and primary gastric fibroblasts were cocultured with Helicobacter pylori standard strain (NCTC11637). The expressions of IL-8 and cyclooxygenase 2 (COX-2) mRNA were examined by reverse transcription polymerase chain reaction (RT-PCR) amplification. The amount of IL-8 antigen secreted by the MKN45 cells and gastric fibroblasts was measured by enzyme-linked immunosorbent assay (ELISA). We examined the effects of H pylori stimulation on IL-8 and COX-2 expression levels and the effects of COX-2 inhibitor on H pylori-induced IL-8 production in the MKN45 cells and gastric fibroblasts. Furthermore, we examined the expressions of subtypes of PGE2 receptors, the effects of arachidonic acid and PGE2 on IL-8 production, and the effects of PGE2 on the total cellular cyclic adenosine monophosphate (cAMP) in MKN45 cells. MKN45 cells and gastric fibroblasts expressed IL-8 and COX-2 mRNA under stimulation with H pylori. The MKN45 cells produced IL-8 and PGE2 antigen into the culture medium with H pylori stimulation, and the production level of IL-8 and PGE2 antigen decreased significantly with COX-2 inhibitor pretreatment (concentration: 50 μM). On the other hand, the gastric fibroblasts strongly produced IL-8 antigen even in the unstimulated condition, and the amount of IL-8 antigen was not affected by H pylori stimulation and/or COX-2 inhibitor pretreatment. The MKN45 cells expressed IL-8 mRNA and released IL-8 antigen slightly, and the expression level of IL-8 mRNA and the amount of IL-8 antigen increased significantly with PGE2 treatment in a dose-dependent manner. PGE2-induced IL-8 production was inhibited by pretreatment with EP2 and EP4 antagonists. The MKN45 cells expressed EP2 and EP4 subtypes of PGE2 receptors, and these expression levels were not affected by H pylori stimulation or PGE2 treatment. The amount of IL-8 antigen increased slightly, but not significantly, with arachidonic acid treatment. PGE2 treatment for 15 minutes increased the total cellular cAMP in the MKN45 cells. These results suggest that the COX-2–PGE2 pathway may be involved in IL-8 production in gastric epithelial cells.