Graduation Date

Spring 5-7-2022

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Programs

Biochemistry & Molecular Biology

First Advisor

Steve Caplan

Second Advisor

Naava Naslavsky

Abstract

Endocytic membrane trafficking is a key cellular process that is critical for regulating the transport of internalized cargoes such as lipids and receptors. Our lab focuses on understanding the mechanisms and cellular functions of the proteins that regulate this pathway. One family of proteins that has seen significant interest over recent years is the C-terminal Eps15 Homology Domain (EHD) family of proteins. Mammalians have four EHD paralogs (EHD1-4) that are expressed ubiquitously in tissues. These proteins have distinct yet overlapping functions in regulating endocytic pathways. EHD1 has been shown to induce constriction and is recruited to induce fission of tubular recycling endosomes (TREs) through its interaction with Molecules Interacting with CAsL-Like 1 (MICAL-L1). EHD2 remains the most functionally distinct of the EHD proteins, regulating caveolae at the plasma membrane. EHD3 has been implicated in biogenesis and stabilization of TREs, whereas EHD4 remains the least characterized. Previous studies from our lab have put forth evidence that EHD4 influences endosomal fission in a manner similar to EHD1, though this remains poorly understood. Herein, I describe a role for EHD4 in the recruitment of EHD1 to endosomal structures through their hetero-dimerization and subsequent interaction with resident endosomal proteins such as MICAL-L1.

Furthermore, recent studies have also implicated EHD1 and EHD3 in the generation of the primary cilium, a key signaling organelle that emanates from the centrosome when the cell is in a non-mitotic state. EHD1 was shown to facilitate fusion of the ciliary vesicle and removal of CP110 from the mother centriole, a critical step in primary ciliogenesis. EHD3, the closest paralog to EHD1, has a similar regulatory role in retinal pigmented epithelium (RPE) cells, whereas EHD2 and EHD4 are dispensable for ciliogenesis. Given that EHD1 and EHD4 are significantly intertwined in the context of endosomal fission, it was surprising that EHD4 was as equally dispensable as EHD2 in ciliogenesis. Herein, I identified a novel role for EHD4, but not EHD2, in regulating primary ciliogenesis.

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