Control of Lysosome Cystine Release in the Regulation of Cellular Stress

Date of Award

Fall 1-1-2025

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Cell Biology

First Advisor

Ferguson, Shawn

Abstract

Lysosomes are degradative organelles that are also well-characterized as central hubsof nutrient sensing, cellular stress responses, and metabolic regulation. Cystine, the disulfide-linked dimer of the amino acid cysteine, is among the diverse metabolites handled by lysosomes. Cysteine is a highly reactive amino acid that serves as a precursor for protein synthesis and glutathione production, thereby supporting a variety of cellular functions including redox homeostasis. Due to its chemical reactivity, free cysteine is not stably stored in the cell but rather incorporated into other molecules; simultaneously, lysosomes accumulate cystine more than other amino acid. However, less clear is whether regulatory mechanisms dynamically control lysosomes to promote cystine efflux. Such evidence would open the possibility that lysosomes act as a cystine reservoir that can be mobilized under times of stress. In this dissertation, I reveal such regulation and further investigate theconsequences of this regulation to lysosomal cystine metabolism and cellular stress responses. Specifically, I identify a novel pathway centered on the scaffold protein JIP4, which acts as a stabilizer of the lysosomal cystine transporter cystinosin (CTNS). CTNS mutations are the root cause of cystinosis, a severe lysosomal storage disorder characterized by cystine accumulation leading to tissue damage within several organ systems. My work reveals that JIP4 maintains CTNS stability by suppressing TMEM55B-dependent ubiquitylation events that otherwise target CTNS for degradation. In the absence of JIP4, CTNS turnover is accelerated, leading to impaired lysosomalcystine export, increased cellular cystine accumulation, and phenotypes reminiscent of lysosomal storage disorders like cystinosis. Using JIP4-deficient mice, I demonstrate that disruption of JIP4 function produces renal abnormalities that mirror key aspects of cystinosis, including lysosomal storage pathology and tissue dysfunction. These findings establish a new paradigm in which scaffold-mediated regulation fine-tunes lysosomal amino acid transport to ensure appropriate cysteine availability under conditions of stress. More broadly, they underscore the principle that lysosomes are not passive depots of catabolic byproducts but actively adjust metabolite release in ways that sustain cellular homeostasis. These studies reveal a fundamental mechanism by which lysosomes regulate aminoacid metabolism to preserve cellular homeostasis. By identifying JIP4 as a scaffold that stabilizes CTNS and prevents its aberrant degradation, I define a new axis of control over lysosomal cystine efflux. The discovery that lysosomes finely control levels of cystine release has implications for ferroptosis, redox stress, and neurodegenerative disease. This work has broad implications for lysosomal biology, redox regulation, and rare disease, and they open new avenues for exploring therapeutic strategies that target lysosome-based metabolic control.

This document is currently not available here.

Share

COinS