Membrane remodelling and signal transduction during phagosome formation and maturation.
Published: 2006
Language: eng
Number of pages: 198
ISBN-13: 9780494219768
Description: Phagocytosis of IgG-opsonized pathogens begins when plasmalemmal Fcgamma receptors bind to the microbe, triggering clustering of receptors and receptor-activation. This in turn promotes remodelling of the actin cytoskeleton and plasma membrane leading to protrusion of membrane pseudopods (the phagocytic cup) that surround and engulf the pathogen. The internalized microbe is contained within a distinct organelle called the phagosome, which undergoes a maturation process consisting of sequential fusion and fission reactions with endosomes, culminating in fusion of the phagosome with lysosomes. The resultant phagolysosome is where most pathogens are degraded due to its highly proteolytic and acidic environment. However some microbes, notably M. tuberculosis, survive inside phagocytes by subverting phagosome maturation.In this thesis, we have examined different stages of phagocytosis. Firstly, because the membrane at the phagocytic cup undergoes focal exocytosis, pinocytosis, and other remodelling events, we performed a quantitative assessment of membrane remodelling at the phagocytic cup using multiple fluorescent membrane markers. In addition, we analyzed membrane remodelling during internalization of different-sized particles and demonstrate how, for large particles, focal exocytosis separates the Fc receptor from its effectors. Secondly, while activation of Fc receptors triggers actin polymerization necessary for formation of the phagocytic cup, the signalling events linking receptor activation to actin polymerization are poorly understood. We describe a novel role for the adaptor protein CrkII and the guanine nucleotide exchange factor Dock180 during Fc-mediated phagocytosis. These data establish a link between early Fc-receptor-mediated signalling events and Rac activation, which is necessary for actin dynamics during phagocytosis. Thirdly, although the phagosome undergoes fusion events with endosomes during maturation, it remains a constant size. This implies that fission from the evolving phagosome must occur, although little is known about how this is regulated. We describe a role for ubiquitin and the proteasome in this process, and establish that fusion and fission from the phagosome are regulated separately. Lastly, while it is known that the mycobacterial phagosome avoids fusion with lysosomes, the basis of this evasion remains unclear. We outline preliminary data on the nature of the mycobacterial phagosome inside macrophages, demonstrating that it is not enriched in Rab5 or Rab7.
Notes: Source: Dissertation Abstracts International, Volume: 68-01, Section: B, page: 0195.

Thesis (Ph.D.)--University of Toronto, 2006.

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