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Title: The regulation of actin cytoskeleton dynamics and membrane trafficking by ARHGAP44
Author: Curnock , Rachel Marie
ISNI:       0000 0004 5924 0738
Awarding Body: University of Bristol
Current Institution: University of Bristol
Date of Award: 2014
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Membrane shape is dynamic, and cellular membranes adopt different curvatures during fundamental vesicle trafficking events. This is exemplified by the concept of iterative, geometric based sorting. The BAR (Bin/Amphiphysin/Rvs) domain protein superfamily is the largest group of proteins responsible for generating membrane curvature. The work presented in this thesis has examined the cellular function of the BAR domain containing Rho GTPase-activating protein 44 (ARHGAP44; also known as RhoGAP interacting with CIP4 homologs 2 (RICH2)). Recent studies have strongly suggested that ARHGAP44 contributes to intracellular trafficking pathways. In support of this role, work presented here demonstrates that ARHGAP44 functions as a component of the endosomal recycling machinery. ARHGAP44 localises to the Rab4-, Rabll- tubulovesicular recycling compartment, where it facilitates the sorting of endocytic cargo, namely the transferrin receptor and CD317/tetherin, away from the degradation pathway promoting their redelivery to the plasma membrane. Based on its domain organisation, ARHGAP44 would be predicted to link the actin-based cytoskeleton with membrane curvature. I have shown that ARHGAP44 promotes membrane deformation in vitro and in cellulo, and further examination revealed that ARHGAP44-driven membrane tubulation is dependent on its amino-terminal amphipathic helix. Suppression of ARHGAP44 led to an extensive loss of F-actin and an intracellular accumulation of actin into short disorganised bundles, which were frequently found in close proximity to EEA1-positive early endosomes. Rescue experiments revealed that the domain organisation of ARHGAP44 is critical for its ability to regulate endocytic recycling of the transferrin receptor. The activity of ARHGAP44's RhoGAP domain and the hydrophobic composition of its amino-terminal amphipathic helix and conjoined BAR domain were indispensable for this function. In light of these findings, the function of ARHGAP44 was examined during the highly specialised developmental process of erythropoiesis. Data acquired using a model in vitro erythropoiesis culture system demonstrated that ARHGAP44 regulates the intracellular distribution and cell surface homeostasis of the transferrin receptor in maturing erythroblasts.
Supervisor: Not available Sponsor: Medical Research Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available