Abstract

Lipid Droplets (LDs) are lipid storage organelles that can be readily tapped to resupply cells with energy or lipid building blocks, and, therefore, play a central role in cellular metabolism. It has emerged that Double FYVE Domain Containing Protein 1 (DFCP1), which has routinely been used as a marker for early autophagy, is an LD-associated protein and is implicated in establishing contacts between the endoplasmic reticulum (ER) and LDs, but little is known about DFCP1’s function or how it influences either autophagy or LD metabolism. Here, we show that DFCP1 contains a novel NTPase domain that regulates its assembly onto LDs, as well as LD metabolism, in response to changes in nutrient availability. Specifically, we show that endogenous DFCP1 accumulates on LDs independently of its PI3P-binding tandem FYVE domains, and instead uses a combination of the ER-binding domain and a novel NTPase domain. This NTPase domain can dimerize, and possesses a low basal GTP turnover rate, as well as ATPase activity. Further, mutations in the DFCP1 NTPase domain that either impact NTP hydrolysis or dimerization result in changes in the accumulation of DFCP1 on LDs, where DFCP1 unable to bind LDs instead localizes to LC3-rich regions. The presence of DFCP1 on the LDs regulates lipid metabolism, inhibiting FA-dependent OCR and TAG hydrolysis when capable of binding LDs. This functionality is due to slight inhibition of lipophagy and significant inhibition of lipolysis, due to DFCP1’s interaction with ATGL. In fact, DFCP1 uses its FYVE domains to recruit ATGL to LDs but inhibits its lipase activity. This inhibition occurs despite DFCP1 also recruiting ATGL’s coactivator CGI-58 to the LDs. Collectively, our findings indicate that DFCP1 is an NTP-dependent metabolic sensor capable of modulating cellular storage of free fatty acid by modulating lipophagy, and lipolytic activity via recruitment and inhibition of ATGL.

Committee Chair

David Kast

Degree

Doctor of Philosophy (PhD)

Author's Department

Biology & Biomedical Sciences (Biochemistry)

Author's School

Graduate School of Arts and Sciences

Document Type

Dissertation

Date of Award

9-11-2023

Language

English (en)

Author's ORCID

https://orcid.org/0000-0002-6754-9941

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