Abstract
BackgroundCampylobacter jejuni is one of the most important bacterial pathogens causing food-borne illness worldwide. Crossing the intestinal epithelial barrier and host cell entry by C. jejuni is considered the primary reason of damage to the intestinal tissue, but the molecular mechanisms as well as major bacterial and host cell factors involved in this process are still widely unclear.ResultsIn the present study, we characterized the serine protease HtrA (high-temperature requirement A) of C. jejuni as a secreted virulence factor with important proteolytic functions. Infection studies and in vitro cleavage assays showed that C. jejuni’s HtrA triggers shedding of the extracellular E-cadherin NTF domain (90 kDa) of non-polarised INT-407 and polarized MKN-28 epithelial cells, but fibronectin was not cleaved as seen for H. pylori’s HtrA. Deletion of the htrA gene in C. jejuni or expression of a protease-deficient S197A point mutant did not lead to loss of flagella or reduced bacterial motility, but led to severe defects in E-cadherin cleavage and transmigration of the bacteria across polarized MKN-28 cell layers. Unlike other highly invasive pathogens, transmigration across polarized cells by wild-type C. jejuni is highly efficient and is achieved within a few minutes of infection. Interestingly, E-cadherin cleavage by C. jejuni occurs in a limited fashion and transmigration required the intact flagella as well as HtrA protease activity, but does not reduce transepithelial electrical resistance (TER) as seen with Salmonella, Shigella, Listeria or Neisseria.ConclusionThese results suggest that HtrA-mediated E-cadherin cleavage is involved in rapid crossing of the epithelial barrier by C. jejuni via a very specific mechanism using the paracellular route to reach basolateral surfaces, but does not cleave the fibronectin receptor which is necessary for cell entry.
Highlights
Infections with pathogenic food-borne bacteria constitute one of the leading causes of morbidity and mortality in humans
HtrA protease is conserved in H. pylori and C. jejuni Recently, HtrA of the gastric pathogen H. pylori was reported to be secreted into the cell culture supernatant, where it can cleave the ectodomain of the host cell adhesion protein and tumour-suppressor E-cadherin, and degrades fibronectin [32]
Motility assays revealed that both C. jejuni wt and htrA mutant strains were highly motile, suggesting that mutation of htrA does not significantly affect this important pathogenicity property of the bacteria (Figure 2)
Summary
Infections with pathogenic food-borne bacteria constitute one of the leading causes of morbidity and mortality in humans. After ingestion by a human host, these bacteria use their flagella-driven motility to colonize the epithelial cells of the ileum and colon. They can interfere with normal functions in the intestinal tract, leading to diseases associated with fever, malaise, abdominal pain and watery diarrhoea [2,3]. There is increasing evidence showing that C. jejuni disturbs the normal absorptive capacity of the human intestine by damaging epithelial cell functions, either by cell invasion, the production of pathogenicity-associated factors or indirectly by triggering inflammatory responses [3,6,7,8]. Campylobacter jejuni is one of the most important bacterial pathogens causing food-borne illness worldwide. Crossing the intestinal epithelial barrier and host cell entry by C. jejuni is considered the primary reason of damage to the intestinal tissue, but the molecular mechanisms as well as major bacterial and host cell factors involved in this process are still widely unclear
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