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- Eriksson, Ida, 1985-
(författare)
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Dealing with damaged lysosomes : Impact of lysosomal membrane stability in health and disease
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The lysosome is the main unit for degradation and plays important roles in various cellular processes, such as nutrient sensing, cholesterol regulation and cell death. Consequently, altered lysosomal function contributes to, or even causes, several diseases. Lysosomal membrane permeabilization (LMP) and release of lysosomal content to the cytosol can induce cell death, and is implicated in inflammation and neuronal decline in several neurodegenerative diseases. It has also emerged as a potential target in cancer therapy. Due to the detrimental effects of LMP, cells harbor several mechanisms to protect and prevent lysosomal membrane damage. The aim of this thesis was to elucidate how lysosomal membrane stability and repair mechanisms affect cell death and survival. We find that lysosomal cholesterol is upregulated in response to an increased load of reactive oxygen species in a Parkinson’s disease cell model, and that augmented cholesterol protects from LMP. However, cholesterol also induces accumulation of α-synuclein and inhibits lysosome-mediated degradation, which can destabilize the lysosomal membrane and accelerate the course of disease. Further, we demonstrate that lysosomal membrane damage is counteracted by a calcium-dependent repair mechanism to prevent LMP. Lysosomes damaged beyond repair are instead sequestered in an autophagosome and degraded by intact lysosomes in a process called lysophagy. As a result, small vesicles containing lysosomal membrane proteins are generated, which we believe are used to restore lysosomal function. We show that malignant cells are more sensitive to LMP, and that they differ in their activation of damage-response mechanisms compared to normal cells. Moreover, in malignant cells, the intracellular position of the lysosomes determines the susceptibility to lysosomal damage. Peripherally located lysosomes are less sensitive, and by relocating lysosomes to the perinuclear area in the cell, we can sensitize lysosomes to LMP induction. In summary, this thesis demonstrates the importance of damage-response mechanisms to protect from lysosomal membrane damage and maintain cellular function. It also indicates that targeting of lysosomal stability and repair is a potential therapeutic strategy in both neurodegenerative diseases and in cancer.
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| 2. |
- Gubat, Johannes, 1986-, et al.
(författare)
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Comprehensive Target Screening and Cellular Profiling of the Cancer-Active Compound b-AP15 Indicate Abrogation of Protein Homeostasis and Organelle Dysfunction as the Primary Mechanism of Action
- 2022
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Ingår i: Frontiers in Oncology. - : Frontiers Media SA. - 2234-943X. ; 12
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Tidskriftsartikel (refereegranskat)abstract
- Dienone compounds have been demonstrated to display tumor-selective anti-cancer activity independently of the mutational status of TP53. Previous studies have shown that cell death elicited by this class of compounds is associated with inhibition of the ubiquitin-proteasome system (UPS). Here we extend previous findings by showing that the dienone compound b-AP15 inhibits proteasomal degradation of long-lived proteins. We show that exposure to b-AP15 results in increased association of the chaperones VCP/p97/Cdc48 and BAG6 with proteasomes. Comparisons between the gene expression profile generated by b-AP15 to those elicited by siRNA showed that knock-down of the proteasome-associated deubiquitinase (DUB) USP14 is the closest related to drug response. USP14 is a validated target for b-AP15 and we show that b-AP15 binds covalently to two cysteines, Cys203 and Cys257, in the ubiquitin-binding pocket of the enzyme. Consistent with this, deletion of USP14 resulted in decreased sensitivity to b-AP15. Targeting of USP14 was, however, found to not fully account for the observed proteasome inhibition. In search for additional targets, we utilized genome-wide CRISPR/Cas9 library screening and Proteome Integral Solubility Alteration (PISA) to identify mechanistically essential genes and b-AP15 interacting proteins respectively. Deletion of genes encoding mitochondrial proteins decreased the sensitivity to b-AP15, suggesting that mitochondrial dysfunction is coupled to cell death induced by b-AP15. Enzymes known to be involved in Phase II detoxification such as aldo-ketoreductases and glutathione-S-transferases were identified as b-AP15-targets using PISA. The finding that different exploratory approaches yielded different results may be explained in terms of a “target” not necessarily connected to the “mechanism of action” thus highlighting the importance of a holistic approach in the identification of drug targets. We conclude that b-AP15, and likely also other dienone compounds of the same class, affect protein degradation and proteasome function at more than one level.
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