Investigating Cellular Nutrient Responses

Abstract

Cells require nutrients to support growth and survival. To adapt to fluctuations in nutrient availability, they have evolved mechanisms to sense these fluctuations and respond accordingly – either by promoting anabolic processes like growth and nutrient storage during nutrient surplus, or by activating catabolic responses and mobilising energy reserves during starvation. Central to coordinating these responses is the mechanistic/mammalian Target Of Rapamycin Complex 1 (mTORC1).
Although the core components of the mTORC1 pathway are well defined, many questions remain around its regulation, such as how the inhibitory TSC complex is recruited to and controls activity of the small GTPase Rheb. To uncover novel mTORC1 signalling modulators, I performed proteomic analyses to identify new interactors of the TSC-Rheb axis. I identified metabolic regulators such as CYB5R3, involved in cholesterol synthesis and fatty acid desaturation/elongation, and SLC7A11, a cysteine/glutamate antiporter.
I also investigated a protein that was identified previously as a potential novel TSC interactor. TMEM263 is an uncharacterised transmembrane protein genetically linked to proportional dwarfism and skeletal dysplasia. Based on its association with growth phenotypes and its presence in TSC-associated proteomic data, I initially hypothesised TMEM263 may act via mTORC1. However, this thesis reveals that TMEM263 does not influence mTORC1 signalling, but interestingly plays an important role in lipid droplet (LD) biology. Specifically, this thesis shows TMEM263 is necessary for LD accumulation. Furthermore, TMEM263 structural prediction reveals two transmembrane helical regions which I identified as necessary for its role in LD accumulation. Molecular Dynamics (MD) simulations revealed TMEM263 binding neutral lipids and aiding lipid lens formation, a key stage of LD biogenesis. I then showed lipid-binding residues identified in MD as necessary for TMEM263-driven LD accumulation.
Therefore, this thesis has identified several putative TSC-Rheb interacting proteins and characterised a new LD regulator which contributes to organismal growth.

Date of Award	9 Dec 2025
Original language	English
Awarding Institution	University of Bristol
Supervisor	Bernadette M Carroll (Supervisor), Mark P Dodding (Supervisor) & Jon D Lane (Supervisor)