SALT3SPH · The role of the pH inside the Salmonella-containing vacuole on type-III secretion triggering and on bacterial intracellular multiplication

Final Activity Report Summary - SALT3SPH (The role of the pH inside the Salmonella-containing vacuole on type-III secretion triggering and on bacterial intracellular multiplication)

A crucial strategy in the study of infectious diseases - one of the major causes of morbidity and mortality worldwide - is to develop fundamental research aimed at understanding the mechanisms by which the microbial pathogens manipulate host cells. This basic knowledge can then be translated into the development of appropriate vaccines and therapies. Infections caused by Salmonella enterica serovars are still an important public health concern worldwide. S. enterica has the capacity to replicate intracellularly in a membrane-bound vacuole, termed Salmonella-containing vacuole. The intracellular replication of Salmonella is modulated by a type III secretion system. Type III secretion is a wide-spread virulence mechanism that consists of a kind of syringe which injects a cocktail of bacterial proteins ("effectors") into the cytoplasm of host cells. This protein cocktail paralyses or enslaves the animal cell to the benefit of the bacterium. In the case of intracellular Salmonella, more than 20 effector proteins are delivered into the host cell across the vacuolar membrane that encloses the bacteria. Because intracellular Salmonella is enclosed by a vacuolar lipid membrane, replication of the bacteria within host cells is dependent on interactions with host cell membrane trafficking pathways. Membrane trafficking inside a eukaryotic cell consists in a very complex network of pathways that can be compared to the entire traffic network in a big metropolis. Its major role is to mediate specific protein transport in membrane vesicles while maintaining cellular homeostasis. This transport network can nevertheless be divided in two major pathways: the endocytic pathway, which generally mediates transport of material (e.g. proteins, nutrients, or microbes) from the outside of the cell, or from the plasma membrane; and the secretory pathway, which directs transport towards the outside of the cell, or to the plasma membrane. The intracellular replication of a vacuolated microbe, such as Salmonella, requires that the microbe has the capacity to acquire membrane and nutrients from the host cell membrane trafficking system while avoiding or resisting the degradation pathways by which cells normally destroy invading organisms. In this work, using up-to-date methodologies, such as small-interference RNA (siRNA) and different light microscopy techniques, we aimed to study the molecular and cellular mechanisms that mediate Salmonella virulence and, in particular, the interaction between intracellular Salmonella and the trafficking of lipid membranes within the host cell. In epithelial cells, Salmonella type III secretion effectors determine that bacterial vacuoles localise close to the Golgi network, a major cellular station of the secretory pathway. Nevertheless, while interaction between Salmonella type III secretion effectors and the endocytic pathway are well documented, little was known about a possible interaction with the secretory pathway. In this work, we performed a siRNA screen of Golgi-related proteins to identify host cell proteins that could be involved in positioning of Salmonella vacuoles within epithelial cells. This was followed by a detailed characterisation of the cellular function of some of the candidates that were found with respect to intracellular replication of Salmonella. As a major outcome of these studies, we unveiled a distinct interaction between intracellular Salmonella and its type III secretion effectors with the secretory pathway, specifically with post-Golgi trafficking. This indicates that Salmonella effectors have the capacity to manipulate not only the endocytic pathway but also the secretory pathway. The physiological implications of this finding will be addressed in the future, but potentially could also indicate a new mechanism by which Salmonella may interfere with host immune functions such as cytokine secretion or antigen presentation.

Текст от CORDIS, на английски · Данни: CORDIS, © Европейски съюз