Graduation Date

Spring 5-7-2022

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Programs

Biochemistry & Molecular Biology

First Advisor

Steve Caplan

Abstract

Endocytic trafficking is a fundamental cellular process that regulates the transport of lipids and proteins. Our lab focuses on the intracellular trafficking of receptors involved in cellular processes such as cell division, migration, and proliferation. Accordingly, the regulation of these trafficking pathways is tightly controlled, involving a complex series of events, of which a key step is the endosomal fission. Perturbations in the endosomal network can eventually lead to impaired receptor recycling to the plasma membrane (PM) and, therefore, have pathological consequences like Alzheimer’s disease and multiple cancers. Upon internalization, cargo-laden vesicles released from the PM fuse with the sorting endosomes, an organelle where the cargo is sorted, in part by sorting nexin (SNX) proteins. Recent studies suggest the role of SNX17 in sorting cargo to the recycling pathway in a sequence-specific manner. However, the mechanisms by which SNX17- containing vesicles bud and undergo fission remain elusive. Recently, a dynamin homolog, Eps15 homology domain protein 1 (EHD1), has been implicated in endosomal fission and regulating the receptor recycling to the PM. Since EHD1 does not directly interact with the receptors whose recycling it regulates, I focused on elucidating a novel mechanism by which EHD1 connects with the receptors via its interaction with SNX17. Additionally, studies have pointed out the significance of fission machinery components other than EHD1, including the actin cytoskeleton and the ER, in facilitating endosomal fission. However, how these components coordinate fission remains unexplored. Herein, I describe for the first time a connection between EHD1 and the actin cytoskeleton in catalyzing endosomal fission and regulating receptor recycling. I propose a model in which the actin branching induces budding endosomes formation where SNX17 sorts the internalized receptor for recycling. The actin branching continues to cause constriction of the neck of the budding endosomes until the actin-binding protein, CORO2A, is recruited to inhibit further actin branching, thus, allowing access of EHD1 to the neck of the endosome, where it ultimately catalyzes fission and releases budding vesicles containing receptors bound for the PM.

Available for download on Friday, April 21, 2023

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