Student Theses and Dissertations
Date of Award
2023
Document Type
Thesis
Degree Name
Doctor of Philosophy (PhD)
Abstract
Lipids, along with nucleic acids, carbohydrates, and proteins, are essential biomolecules.These diverse hydrophobic metabolites are composed of fatty acids and include sterols, phospholipids, and glycerides. Lipids can be broken down to fuel energy demands, form the structural basis of all membranes, and can both act as signaling molecules themselves and regulate signaling by impacting membrane fluidity and receptor stability. Given the diverse and essential functions of lipids for normal cell function, it is no surprise that cancer cells leverage lipid metabolic pathways to fuel uncontrolled growth and proliferation and evade cell death. Indeed, enhanced lipid availability has been implicated in tumor initiation, growth,and metastasis, and metabolic genes involved in lipid uptake and synthesis are downstream of oncogenic alterations.Though excess lipids are known to correlate with disease progression, the precise enzymatic players required for cancer cell survival under distinct stressors have not been systematically studied. In this body of work, we designed and implemented loss of function CRISPR-Cas9 genetic screens to identify lipid metabolic dependencies in cancer cells growing under lipid peroxidation or immune pressure. Cancer cells rewire their metabolism and rely on endogenous antioxidants to mitigate lethal oxidative damage to lipids. However, the metabolic processes which modulate the response to lipid peroxidation are poorly defined. Using genetic screens, we compared metabolic genes essential for proliferation upon inhibition of cystine uptake or glutathione peroxidase-4 (GPX4), two pathways reported to mitigate lipid reactive oxygen species (ROS). Interestingly, very few genes were commonly required under both conditions, suggesting that cystine limitation and GPX4 inhibition may impair proliferation via distinct mechanisms. Our screens also identified tetrahydrobiopterin (BH4) biosynthesis as an essential metabolic pathway upon GPX4 inhibition. Mechanistically, BH4 is a potent radical-trapping antioxidant that protects lipid membranes from autoxidation, alone and in synergy with Vitamin-E. Dihydrofolate reductase (DHFR) catalyzes the regeneration of BH4 and its inhibition by methotrexate synergizes with GPX4 inhibition. In sum, we identify the mechanism by which BH4 acts as an endogenous antioxidant and provides a compendium of metabolic modifiers of lipid peroxidation. This work is summarized in Chapter 2. Despite the critical functions of lipid metabolism in membrane physiology, signaling, and energy production, how specific lipids contribute to tumorigenesis is incompletely understood. Here, using functional genomics and lipidomic approaches, we identified de novo sphingolipid synthesis as an essential pathway for cancer immune evasion. Synthesis of sphingolipids is surprisingly dispensable for cancer proliferation in culture or in immunodeficient mice but required for tumor growth in multiple syngeneic models. Blocking sphingolipid production in cancer cells enhances the anti-proliferative effects of natural killer (NK) and CD8+T cells via interferon gamma (IFNγ) signaling. Mechanistically, glycosphingolipids impact IFNγ receptor subunit 1 (Ifngr1) localization, mediating IFNγ-induced growth arrest and proinflammatory signaling. Finally, high expression of sphingolipid synthesis genes correlates with poor survival in cancer patients and increasing tumor sphingolipids impairs immune surveillance. Altogether, we show that glycosphingolipids are both necessary and limiting metabolites for cancer immune evasion. This work is summarized in Chapter 3. Overall, this thesis defines metabolic pathways that are required for cell survival during ferroptotic stress and immune surveillance. Using a combination of in vitro and in vivo functional genetic screens in multiple cell lines, were port on a compendium of genes regulating cancer cell sensitivity to lipid ROS and immune pressure. Though we hone in on the GCH1-BH4-DHFR and glycosphingolipid-Ifngr1 axes, future work may unravel the molecular mechanisms underlying the many genetic dependencies identified by our screening strategies. Ultimately, we anticipate that the findings reported here will advance the understanding of how lipid metabolism in cancer cells impacts disease progression and hope it will contribute to the development and improvement of therapeutics.
Recommended Citation
Soula, Mariluz, "Dissecting the Roles of Cancer Cell Lipid Metabolism in Tumor Progression and Immune Evasion" (2023). Student Theses and Dissertations. 783.
https://digitalcommons.rockefeller.edu/student_theses_and_dissertations/783
Comments
A Thesis Presented to the Faculty of The Rockefeller University in Partial Fulfillment of the Requirements for the degree of Doctor of Philosophy