"Molecular characterization of a novel host cell binding and invasion factor by the major foodborne pathogen Campylobacter jejuni"

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Food-borne infections by Campylobacter jejuni are the major cause of human bacterial gastroenteritis, and may be responsible for as many as 400-500 million cases worldwide every year. Disease outcomes vary from mild, non-inflammatory, self-limiting diarrhea to severe, inflammatory, bloody diarrhea and abdominal pain lasting for several weeks, but C. jejuni is also associated with more severe sequelae such as the development of reactive arthritis and peripheral neuropathies, the Miller-Fisher and Guillain-Barrè syndromes, in some individuals. Major challenges are the lack of effective control schemes for C. jejuni in the food chain and a relatively poor understanding of basic mechanisms underlying host-pathogen interactions. Despite the array of bacterial virulence factors reported in the past, their potential role in pathogenesis is often controverse in the literature and still not fully clear. For example, it remained widely unknown which of the proposed C. jejuni factors are typical adhesins or not, and which disease-related signaling pathways are regulated by these factors. Recently, we have identified a novel C. jejuni virulence factor directly interacting with host cells, high temperature requirement A (HtrA), a surface exposed serine protease. Having established a series of important molecular tools and methods in our previous studies, this proposal is designed to gain a detailed understanding of the molecular mechanisms underlying specific HtrA functions in cell adhesion, invasion and host signaling during infection with C. jejuni in vitro and in vivo. In particular, we have identified an arginine-glycine-aspartate (RGD) motif in HtrA, and our preliminary data indicate that this motif is surface-exposed and crucial for cell binding and invasion by C. jejuni. We therefore propose that HtrA and its RGD-motif serve as recognition site for the host cell receptor integrin-b1. We generated C. jejuni strains expressing HtrA variants with point mutations in the RGD-motif or protease-inactive S197A, which will be further analysed using in vitro binding and cell invasion assays, quantitative immunoprecipitation combined with knockdown (QUICK), signaling methods, confocal microscopy and live cell imaging as well as short- and longterm mouse infections experiments. This approach will allow us to reconstruct the sequence of events occurring at the pathogen-host cell interface, and to identify novel key pathogenicity determinants. Further progress both in understanding of the biological significance of bacterial virulence factors and the nature of bacterial interactions with its host will lead to new strategies for detecting, controlling, and reducing Campylobacter infections. In a longterm perspective, this could help both to decrease the burden of Campylobacter-induced human illness and to reduce clinical expenses.