Legionnaire's disease is a pneumonia that results from aerosolized water sources containing the bacterial pathogen Legionella pneumophila, which initiates disease by replicating within lung macrophages. Although the bacterium is capable of growing extracellularly, it is thought that in the environment it primarily replicates within amoebae. Once inside host cells, Legionella has the capacity to modulate host cell processes in order to form a compartment surrounded by endoplasmic reticulum, where the bacteria resides and replicates. Formation of this compartment, known as the Legionella Containing Vacuole (LCV), requires the presence of the bacterial Dot/Icm system, a Type IV Secretion System (T4SS). Numerous studies have highlighted the importance of the T4SS in modulating the host endocytic and secretory pathways to form the LCV, but little is known about host factors outside of the early secretory apparatus that could modulate intracellular growth. A large-scale RNAi screen demonstrated that depletion of host proteins involved in cell cycle control or initiation of protein synthesis resulted in enhanced intracellular growth of the bacterium, consistent with the model that disruption of the host cell cycle stimulates intracellula replication. The goal of this fellowship proposal is to understand how host factors involved in cel cycle control and translational initiation contribute to bacterial proliferation. Experiments will e performed to: 1) determine if L. pneumophila is able to control the host cell cycle to stimulate intracellular replication;and 2) determine if L. pneumophila translocated proteins play are role i stimulating bacteria growth by modulating host translation and cell cycle networks. The results acquired from the proposed experiments will allow the determination of why cell cycle disruption stimulates L. pneumophila intracellular growth, with the intention of determining if the microorganism replicates preferentially in terminally differentiated cells.
Pneumonia is one of the leading causes of death in the United States, with the elderly and immunocompromised individuals being particularly susceptible. Studies proposed in this application on the pneumonia-causing agent Legionella pneumophila will identify important host cell factors that allow this intracellular organism to gro in environmental sources prior to its spread to humans. Identification of these factors will uncover targets for intervention that will result in the elimination of Legionella from environmental sources, thus preventing epidemic outbreaks of Legionnaire's disease that have been seen with increasing regularity in recent years.
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