This proposal is focused on understanding the molecular basis for the ability of Legionella pneumophila toinfect, survive within, replicate within, and eventually kill human macrophages. We propose to study a group ofnovel proteins that are made by L. pneumophila and translocated to host cells by the Icm/Dot translocationsystem. We will test the hypothesis that the translocated proteins interact with organelle trafficking pathways inthe host and contribute to Legionella intracellular multiplication. One of the translocated proteins, VipA, wasfound to bind actin and promote polymerization of actin subunits. We will also focus on three proteins (LegC2,LegC3, LegC7) that contain coiled coil domains. VipA and the LegC proteins all cause organelle traffickingdefects when expressed in the model host, Saccharomyces cerevisiae.
The specific aims of this proposal areto : 1. Determine the molecular basis for the activity of VipA, an actin-binding, translocated effector thatinterferes with endosomal trafficking; 2. Test the hypothesis that components of the Vps/ESCRT complex arerelated to events during intracellular multiplication of Legionella; 3. Dominant-negative interfering alleles ofeffector genes and the role of effectors during intracellular multiplication; 4. Identify host cell tyrosine kinasesthat control the initial interactions between Legionella and host cells required for effector translocation; 5.Identify interaction partners of LegC2, LegC3 and LegC7. In order to carry out these Aims we will takeadvantage of a variety of cell biological tools such as depleting cells of specific organelle traffickingcomponents by siRNA and examining the effect on Legionella infection, co-localization of known organellemarkers with the Legionella -containing vacuole and ectopic expression of Legionella genes is humanmacrophage cell lines. We will also examine the effects of specifically targeting host tyrosine kinases and aphosphatase on Legionella intracellular multiplication and organelle trafficking. We will use bacterial geneticsto isolate dominant-negative alleles of the genes encoding the translocated proteins to better understand theirrole during Legionella infection. All of these approaches should clarify the mechanisms that Legionella uses toavoid killing by macrophages and produce a successful infection.
The proposed research will increase understanding about how bacterial pathogens subvert macrophages, a primary defense against infection. Legionella, the agent of Legionnaires'disease is able to grow inside macrophages. During infection, specialized Legionella proteins are delivered to the host macrophages by the bacteria where they wreak havoc with the antimicrobial system of the white cells.
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