Document Type
Dissertation
Degree
Doctor of Philosophy (PhD)
Major/Program
Biochemistry
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
Keywords
Superoxide Dismutase C, Macropinocytosis, Phagocytosis, Dictyostelium Discoideum
Date of Defense
11-9-2018
Abstract
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.
Identifier
FIDC007020
Recommended Citation
Gu, Cong, "Superoxide Dismutase C Modulates Macropinocytosis and Phagocytosis in Dictyostelium Discoideum" (2018). FIU Electronic Theses and Dissertations. 3887.
https://digitalcommons.fiu.edu/etd/3887
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