Abstract
Highly virulent Helicobacter pylori cause proinflammatory signaling inducing the transcriptional activation and secretion of cytokines such as IL-8 in epithelial cells. Responsible in part for this signaling is the cag pathogenicity island (cagPAI) that codetermines the risk for pathological sequelae of an H. pylori infection such as gastric cancer. The Cag type IV secretion system (CagT4SS), encoded on the cagPAI, can translocate various molecules into cells, the effector protein CagA, peptidoglycan metabolites and DNA. Although these transported molecules are known to contribute to cellular responses to some extent, a major part of the cagPAI-induced signaling leading to IL-8 secretion remains unexplained. We report here that biosynthesis of heptose-1,7-bisphosphate (HBP), an important intermediate metabolite of LPS inner heptose core, contributes in a major way to the H. pylori cagPAI-dependent induction of proinflammatory signaling and IL-8 secretion in human epithelial cells. Mutants defective in the genes required for synthesis of HBP exhibited a more than 95% reduction of IL-8 induction and impaired CagT4SS-dependent cellular signaling. The loss of HBP biosynthesis did not abolish the ability to translocate CagA. The human cellular adaptor TIFA, which was described before to mediate HBP-dependent activity in other Gram-negative bacteria, was crucial in the cagPAI- and HBP pathway-induced responses by H. pylori in different cell types. The active metabolite was present in H. pylori lysates but not enriched in bacterial supernatants. These novel results advance our mechanistic understanding of H. pylori cagPAI-dependent signaling mediated by intracellular pattern recognition receptors. They will also allow to better dissect immunomodulatory activities by H. pylori and to improve the possibilities of intervention in cagPAI- and inflammation-driven cancerogenesis.
Highlights
The successful bacterial gastric colonizer and human pathogen Helicobacter pylori has conquered a largely uninhabitable niche, the human stomach mucosa, where it persists in about 50% of the world’s population
We report here that HBP, an intermediate metabolite in LPS core heptose biosynthesis, is translocated into host cells dependent on the CagT4SS, and is a major factor leading to the activation of cellular responses
The knowledge of this specific response pathway is a major advance in understanding CagT4SS-dependent signaling and will enable us to understand better how H. pylori modulates the immune response repertoire in its human host
Summary
The successful bacterial gastric colonizer and human pathogen Helicobacter pylori has conquered a largely uninhabitable niche, the human stomach mucosa, where it persists in about 50% of the world’s population. The changing niche and the individual host phenotypes require that the bacterial host interaction repertoire adjusts itself upon each transmission event and during a lifetime of persistence in one evolving host individual [11] To achieve this purpose in an unusually efficient manner, H. pylori has developed several arms of modulating its host interactions: within the stomach and upon transmission, H. pylori can change its genetic repertoire by a high mutation rate [12] and an even higher propensity to recombine and shuffle its DNA during mixed infection [13]. Even within one host stomach, cagPAI genes, the expression of cagPAI components or cagPAI-dependent cell activation phenotypes can vary Examples for this variation have been identified in CagA and CagY [35;36]
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