This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Entamoeba histolytica, the enteric protozoan parasite that causes amebic dysentery and liver abscess, infects an estimated 50 million people annually. The ability of E. histolytica to kill and phagocytose host cells correlates with parasite virulence. In fact, phagocytosis of host erythrocytes is the only feature on light microscopy that distinguishes E. histolytica from the non-pathogenic intestinal ameba Entamoeba dixpar. a feature used for clinical diagnosis. Despite the importance of cell killing and phagocytosis in invasive amebiasis, very little is known about the molecular mechanisms underlying these processes and their precise contribution to pathogenesis remains unknown. Our preliminary studies have shown that E. histolytica kills cells by inducing apoptosis, and ingests apoptotic cells more efficiently than healthy or necrotic cells. In addition, we have identified phosphatidylserine as a potential host cell ligand for an amebic phagocytosis receptor and the serine-rich E. histolytica protein as a potential receptor.
Specific aim 1 will define the nature and mechanism of surface :hanges on apoptotic host cells that trigger amebic ingestion. These studies will not only tell us the specificity of the amebic phagocytosis receptor, thereby helping to identify it; defining the host cell events that result in ligand exposure during amebic cell killing, will be an important step in understanding the still unclear mechanism of amebic cytotoxicity.
Aim 2 will use both biochemical and genetic approaches to characterize the function of the serine-rich protein and of the related asparagine-rich proteins, and will provide important data on the role of these proteins in virulence. A major innovation for the Entumoeha research community will be development of RNA-mediated interference as a method to silence expression of these proteins. If the function of the serine-rich and/or the asparagine-rich proteins in phagocytosis is confirmed, furthermore, these experiments will provide E. histolytica with a defined phagocytosis defect for future in vivo studies of the contribution of phagocytosis to pathogenesis.
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