IPAH FUNCTIONS

Role and natural host targets of Shigella IpaH during infection

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 Obiettivo del progetto (Objective)

'Numerous pathogens grow inside host cells. During the intracellular stage of infection, pathogen proteins establish intricate interactions with host proteins to hijack their cellular machinery. The bacterium Shigella flexneri thrives in the cytoplasm of human intestinal epithelial cells. To do so this bacterium must inject proteins that are dubbed effectors before and after cell invasion. IpaH are an uncommonly large family of effectors, comprising 9 members, for example, in S. flexneri 5. These proteins are hypothesized to interfere with normal cellular function by deregulating their degradation by the ubiquitin-proteasome system. Although IpaH9.8 has been implicated in dampening the innate immune response, diversity in the putative substrate binding domain across the IpaH family indicates that there might be other targets. Thus, the primary objectives of this project are: 1) perform a spatio-temporal study of the transcription, injection and sub cellular localization of IpaH effectors inside infected cell; 2) track the host cell protein targeted to the proteasome by the IpaH. In the frame of this project, I will develop a multidisciplinary strategy to study host-pathogen interactions by combining proteomics and cell biology approaches, pathophysiologic models of Shigellosis and computer simulations.'

Introduzione (Teaser)

Shigellosis, the infection caused by the bacteria of the genus Shigella affects our intestine and causes dysentery. Understanding the mechanisms by which bacteria thrive within our cells could lead to the development of novel therapeutic targets.

Descrizione progetto (Article)

Shigella, like other gram-negative bacteria, possess a unique needle-like secretory system (type III secretion apparatus or T3SA) to facilitate inoculation of infective proteins. They contain invasion-plasmid antigen-H proteins (IpaH), which can subvert the host's normal cellular processes.

Scientists of the EU-funded ?Role and natural host targets of Shigella IpaH during infection? (IPAH FUNCTIONS) project set out to determine the dynamics of IpaH protein secretion and impact on the host machinery. They developed vector tools for expressing these proteins under their native promoter to identify IpaH protein substrates by looking at the changes impacted on the host cell.

Following optimisation of the reporter system used to express the IpaH genes, scientists were able to specify the spatiotemporal context of IpaH expression. Visualisation of the IpaH proteins within cells revealed that after initial entry, the T3SA system is inactivated and is only reactivated upon infection of other cells. Key to this spread was the pathogen protein IcsA, which causes microfilament remodelling to propel the bacteria.

Regarding subcellular localisation, the IpaH proteins seemed to associate with unknown structures. However, scientists were able to identify IpaH protein substrates using mass spectrometry.

The observed spatiotemporal restrained expression of the virulent IpaH proteins indicates the importance of such studies in determining the dynamics of pathogen infectivity. Project deliverables have the potential to provide effective therapeutic options with minimal risk for development of antibiotic resistance in bacteria.