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Document Type



Doctor of Philosophy (PhD)



First Advisor's Name

Lou Kim

First Advisor's Committee Title

Committee Chair

Second Advisor's Name

Xiaotang Wang

Second Advisor's Committee Title

Committee Member

Third Advisor's Name

Lidia Kos

Third Advisor's Committee Title

Committee Member

Fourth Advisor's Name

Jessica Liberles

Fourth Advisor's Committee Title

Committee Member


Superoxide Dismutase C, Macropinocytosis, Phagocytosis, Dictyostelium Discoideum

Date of Defense



Macropinocytosis and phagocytosis, two actin-dependent and clathrin independent events of endocytosis, enable the cells such as macrophages and neutrophils to either internalize pathogens and initiates the human innate immune response or serve as a direct entry route for productive infection of pathogen. Dictyostelium discoideum, soil-living amoeba, a unicellular eukaryote that could professionally internalize fluid phase or particles several folds more than that of macrophages and neutrophils. Additionally, multiple key signaling pathways are conserved between Dictyostelium and mammalian cells, including pathways affecting small GTPases Ras and Rac and their downstream effectors, and F-Actin remodeling. All these traits makes Dictyostelium an excellent model organism to study the process pf macropinocytosis and phagocytosis.

Upon internalization of the prey, these macropinocytes and phagocytes are often in an environment of increased production of superoxide radicals in the prey-containing vesicles, which helps stimulates the downstream signaling pathways to digest the prey inside. However, the mechanism of how superoxide regulates the process of macropinocytosis and phagocytosis is not fully understood. We had previously reported that Dictyostelium cells lacking Superoxide dismutase C (SodC) exhibited aberrantly high level of active RasG, high basal level of Phosphatidylinositol-3,4,5-triphosphate (PIP3), and severe chemotaxis defects. Now we report that sodC- cells displayed aberrant endosomal vesicle trafficking, significantly compromised particle uptake and defective cell to substratum matrix adhesion compared to that of wild type cells. By using high resolution live imaging microscope we also show that sodC- cells have defects in F-Actin remodeling at the phagocytic rim extension and F-Actin depolymerization of the nascent phagosome. Interestingly, the introduction of overexpressing of cytoplasmic superoxide dismutase (SodA), redox insensitive RasG (C118A) or treatment of PI3K inhibitor LY294002 in sodC- cells significantly rescued the defects of endosomal vesicle trafficking, particle uptake and adhesion. This project suggests that superoxide dismutase C regulates the endosomal vesicle trafficking, phagocytosis and cell to substratum matrix adhesion through the RasG/PI3K signaling axis in Dictyostelium cells.





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