Matthias Neddermann


B10 Molecular functions and signal transduction of the serine protease htrA, a novel secreted effector protein of bacterial pathogens

Principal investigator
Steffen Backert


Functional analysis of H. pylori virulence factors in host cell interaction

Gastric cancer is one of the leading death-causing cancers worldwide. One way gastric cancer can occur is by an infection with highly virulent Helicobacter pylori strains. H. pylori is a Gram-negative, spiral-shaped and flagellated bacterium that colonizes the stomach of over 50% of the human population. Infection with H. pylori can lead to chronic gastric inflammations and peptic ulcer disease.  Although every second person on the planet is infected with H. pylori most of them remain asympromatic. About 10-15 % of the patients infected with H. pylori develop peptic ulcer disease and in only 1-2 % of these cases the infection could lead to gastric cancer. Nevertheless, H. pylori is investigated by research groups all over the world and one of their aims is to elucidate how the different virulence factors of H. pylori interact with the host cell and trigger disease-associated processes.
H. pylori uses a type IV secretion system (T4SS) to infect host cells. A T4SS is a needle like structure that is used to transport proteins or DNA into a target cell or the surrounding medium. One of the proteins associated with the T4SS is CagL, which is located at the surface of the T4SS pilus. It is assumed that CagL functions as a specialized T4SS adhesin that binds to the integrin receptor followed by the delivery of the CagA effector protein into host cells (1).
Another important factor for the interaction between H. pylori and the host cell is HtrA (High temperature requirement A). HtrA and its homologues are well known serine proteases and chaperones expressed both in prokaryotes and eukaryotes. HtrA helps H. pylori to enter the mucus layer in the stomach and escape the harsh environment in the stomach. To achieve this, HtrA is secreted into the extracellular space, where it disrupts the host’s gastric epithelial barrier. By cleaving the tumor suppressor and adherens junctional protein E-cadherin H. pylori opens up the epithelial cells and allows H. pylori to pass the layer (2). The complete mechanism how this is done still needs to be elucidated.

The aim of this PhD work is to investigate how these virulence factors interact with the host cells and how they help H. pylori to establish persistent infections and trigger disease-associated processes. Unpublished data show that H. pylori is able to specifically bind to the host cell junctions by a yet unknown mechanism. This data hypothesizes  that a receptor might be involved in this H.pylori host interaction. Identifying this receptor and downstream signaling is another goal of this work.

[1] Helicobacter exploits integrin for type IV secretion and kinase activation.
Kwok T, Zabler D, Urman S, Rohde M, Hartig R, Wessler S, Misselwitz R, Berger J, Sewald N, König W, Backert S.Nature. 2007 Oct 18;449(7164):862-6.

[2] Helicobacter pylori HtrA is a new secreted virulence factor that cleaves E-cadherin to disrupt intercellular adhesion.Hoy B, Löwer M, Weydig C, Carra G, Tegtmeyer N, Geppert T, Schröder P, Sewald N, Backert S, Schneider G, Wessler S. EMBO Rep. 2010 Oct;11(10):798-804


Figure: Working model and specific aims of the project for investigating the role of H. pylori HtrA in pathogenesis. (A) Scanning electron microscopy of MDCK cells infected with H. pylori for 8 hours. Note that the bacetria bind to the cell-to-cell junctions highlighted with yellow lines. (B) We propose that the pathogen uses the paracellular transmigration route to reach their T4SS host cell receptor, integrin-b1, at basolateral surfaces as indicated. For this purpose, the bacteria bind apically to a yet unknown receptor and HtrA targets specific host cell factors which hijack host cell signaling. The model is simplified and various specific aims in this project are highlighted.





October 2016 8th Annual Retreat, Erlangen School of Molecular Communication, Schloss Schney, Lichtenfels, Germany
“Quantification of secreted Serin Protease HtrA by H. pylori