Helicobacter pylori Neutrophil-Activating Protein Directly Interacts with and Activates Toll-like Receptor 2 to Induce the Secretion of Interleukin-8 from Neutrophils and ATRA-Induced Differentiated HL-60 Cells

Helicobacter pylori neutrophil-activating protein (HP-NAP)-induced production of reactive oxygen species (ROS) by neutrophils and monocytes is regulated by pertussis toxin (PTX)-sensitive G proteins, whereas HP-NAP-induced cytokine secretion by monocytes is mediated by Toll-like receptor 2 (TLR2). However, it is unclear whether TLR2 participates in HP-NAP-induced cytokine secretion by neutrophils. Here, all-trans retinoic acid (ATRA)-induced differentiated HL-60 cells were first employed as a neutrophil model to investigate the molecular mechanisms underlying neutrophil responses to HP-NAP. HP-NAP-induced ROS production in ATRA-induced differentiated HL-60 cells is mediated by the PTX-sensitive heterotrimeric G protein-dependent activation of extracellular signal-regulated kinase 1/2 and p38-mitogen-activated protein kinase, which is consistent with the findings reported for human neutrophils. Next, whether TLR2 participated in HP-NAP-induced secretion of interleukin-8 (IL-8) was investigated in neutrophils and ATRA-induced differentiated HL-60 cells. In both cells, TLR2 participated in HP-NAP-induced IL-8 secretion but not HP-NAP-induced ROS production. Interestingly, PTX-sensitive G proteins also contributed to the HP-NAP-induced secretion of IL-8 from neutrophils and the differentiated HL-60 cells. Our ELISA-based binding assay further revealed the competitive binding of Pam₃CSK₄, a TLR2 agonist, and HP-NAP to TLR2, which suggests the presence of specific and direct interactions between HP-NAP and TLR2. Thus, HP-NAP directly interacts with and activates TLR2 to induce IL-8 secretion in neutrophils and ATRA-induced differentiated HL-60 cells.