Lipid signaling and the role of COPI in Fc[gamma] receptor-mediated phagocytosis and phagosome maturation.
Published: 2004
Language: eng
Number of pages: 281
Description: During FcgammaR-mediated phagocytosis, antibody-coated pathogens and particles are eliminated from the body by their inclusion into a plasma membrane-derived vacuole, or phagosome. Phagosomes then embark on a maturation process by fusing with endosomes and lysosomes, which endows phagosomes with an acidic and hydrolytic milieu that digests the pathogen. FcgammaR engagement emanates a complex signal cascade that employs lipid signaling to coordinately modulate the underlying actin cytoskeleton and membrane. In this thesis, the dynamics and role of phosphatidylinositol-4,5-bisphosphate [PI(4,5)P2] in phagocytosis were examined. During the early stages of phagocytosis, generation of PI(4,5)P 2 appeared to occur while at the later stages depletion of PI(4,5)P 2 was observed. PI(4,5)P2 consumption was in part due to phospholipase C (PLC)-mediated hydrolysis, which released diacylglycerol (DAG) and was essential for phagocytosis. Evidence is provided that DAG recruits RasGRP3, a guanine nucleotide exchange factor for Ras, and activates Ras. While Ras was dispensable for phagocytosis, we postulate that a DAG-RasGRP3-Ras pathway regulates inflammatory gene expression through ERK. The role of phosphatidylinositol-3-phosphate [PI(3)P], an important endosomal modulator, in phagosome maturation was also investigated. We found that PI(3)P was synthesized on phagosomes  de novo through the Class III PI 3-kinase, VPS34, and that it was indispensable for phagosome-lysosome fusion. Finally, we demonstrate that protein recycling from the phagosome is partially dependent on the fission complex, COPI. In conclusion, we have revealed roles for phosphoinositide-dependent signaling in phagocytosis and phagosome maturation and provided a foundation for further work to explore the effectors of PI(4,5)P2 and PI(3)P in these processes.
Notes: Adviser:  Sergio Grinstein.

Thesis (Ph.D.)--University of Toronto, 2004.

Electronic version licensed for access by U. of T. users.

Source: Dissertation Abstracts International, Volume: 65-10, Section: B, page: 4937.