Mitogen-activated protein kinases and NF-kB regulate Helicobacter pylori-mediated interleukin-8 release from macrophages

Abstract

Gastric infection as well as inflammation caused by Helicobacter pylori activates the production of cytokines/chemokines by mononuclear cells. IL-8 is one of the major inflammatory chemokines. Since H. pylori does not invade mucosal tissue, we observed the effect of the water extract of H. pylori (HPE) containing shed factors on the production of interleukin (IL-8) by human peripheral blood monocytes and the human monocyte cell line THP-1. HPE treatment induced activation of mitogen-activated protein (MAP) kinases (ERK, p38 and JNK), an effect which was not dependent on the presence of the cag pathogenicity island. p38 MAPK activation was sustained. The specific inhibitors, U0126 (for ERK½ signalling) and SB203580 (for p38 MAPK signalling), both abrogated IL-8 secretion from HPE-treated THP-1. Dominant-negative mutants of the upstream kinases MEK1, MKK6 and MKK7 also inhibited IL-8 secretion pointing to a role of all three MAP kinases in HPE-mediated IL-8 release. The inhibitory effects of polymyxin B and anti-CD14 antibody suggested that the effect of HPE on MAPKs was mediated by H. pylori lipopolysaccharide (LPS). By analysis of IL-8- promoter-driven luciferase gene expression, we observed that the effects of HPE-induced NF-kB activation and MAPK signalling were mediated at the level of the IL-8 promoter. While ERK½ activation could be linked to enhanced DNA-binding of AP-1, p38 MAPK signalling did not affect AP-1 DNA binding. Taken together these results provide the first evidence that LPS from H. pylori stimulates IL-8 release from cells of the monocytic lineage through activation of NF-kB and signalling along MAPK cascades. The stimulation of MAP kinase signalling in macrophages by LPS of H. pylori amplifies the inflammatory response associated with gastric H. pylori infection and needs to be taken into consideration while developing therapeutics based on these signalling pathways.