Helicobacter pylori induces interleukin-8 secretion by toll-like receptor 2- and toll-like receptor 5-dependent and -independent pathways

Helicobacter pylori is an important human pathogen that causes gastritis and is strongly associated with gastric ulcers, gastric adenocarcinomas, and mucosa-associated lymphoid tissue lymphomas. In response to H. pylori, interleukin-8 (IL-8) is secreted from host cells to attract components of the innate and adaptive immune systems to the site of infection. Toll-like receptor 2 (TLR2) and TLR5 have been shown to recognize H. pylori and to initiate signaling pathways that result in enhanced activation of NF-kappaB. Here, we evaluated the contribution of mitogen-activated protein kinase signaling pathways to TLR2-dependent and TLR5-dependent secretion of IL-8. Secretion of IL-8 from H. pylori-infected HEK293 cells was augmented by the expression of TLR2 or TLR5. While H. pylori infection resulted in the activation of ERK, JNK, and p38, the enhanced IL-8 secretion from TLR2- and TLR5-expressing cells coincided with increased p38 activation and phosphorylation of the transcription factor ATF2. When p38 activity was inhibited in TLR2- or TLR5-expressing cells, H. pylori-dependent IL-8 secretion returned to the level observed in infected parental HEK293 cells that did not express TLR2 or TLR5; inhibition of p38 had no effect on IL-8 secretion from infected parental HEK cells. In contrast, inhibition of JNK and/or ERK resulted in substantially less IL-8 secretion from infected cells, independent of TLR2 or TLR5 expression. Based on these data, we propose that H. pylori induces IL-8 secretion through a dual mechanism that includes a TLR2/5-independent component involving the activities of JNK and ERK and a TLR2/5-dependent component that requires p38 activity.