A novel NOD1-and CagA-independent pathway of interleukin-8 induction mediated by the Helicobacter pylori type IV secretion system

The type IV secretion system (T4SS) of Helicobacter pylori triggers massive inflammatory responses during gastric infection by mechanisms that are poorly understood. Here we provide evidence for a novel pathway by which the T4SS structural component, CagL, induces secretion of interleukin-8 (IL-8) independently of CagA translocation and peptidoglycan-sensing nucleotide-binding oligomerization domain 1 (NOD1) signalling. Recombinant CagL was sufficient to trigger IL-8 secretion, requiring activation of 51 integrin and the arginineglycineaspartate (RGD) motif in CagL. Mutation of the encoded RGD motif to arginine-glycine-alanine (RGA) in the cagL gene of H.pylori abrogated its ability to induce IL-8. Comparison of IL-8 induction between H.pylori virD4 strains bearing wild-type or mutant cagL indicates that CagL-dependent IL-8 induction can occur independently of CagA translocation. In line with this notion, exogenous CagL complemented H.pylori cagL mutant in activating NF-B and inducing IL-8 without restoring CagA translocation. The CagA translocation-independent, CagL-dependent IL-8induction involved host signalling via integrin 51, Src kinase, the mitogen-activated protein kinase (MAPK) pathway and NF-B but was independent of NOD1. Our findings reveal a novel pathway whereby CagL, via interaction with host integrins, can trigger pro-inflammatory responses independently of CagA translocation or NOD1 signalling.