Investigating the Roles of Phospholipase A2s and Diacylglycerol Signaling in Ferroptosis

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PROJECT SUMMARY Despite rapid advances in cancer therapeutic development, acquired drug resistance continues to threaten the long-term efficacy of existing chemotherapeutic agents, necessitating the expansion of treatment options targeting novel mechanisms to induce tumor cell death. To that end, induction of ferroptosis, a non- apoptotic, regulated cell death modality, has been shown to be a promising anti-cancer strategy. To date, ferroptosis susceptibility has been demonstrated in many cancer cell types, including clear-cell renal carcinoma and hepatocellular carcinoma25. Ferroptosis has also been shown to be involved in the therapeutic mechanism of existing therapies including sorafenib, a multi-kinase inhibitor, and immune checkpoint blockade therapy26,27,30. Furthermore, multiple studies have reported that therapy-resistant cancer cells that persist after conventional first-line drug treatments or that have undergone epithelial-to-mesenchymal transition exhibit an increased dependency on a druggable phospholipid hydroperoxidase enzyme, namely glutathione peroxidase 4 (GPX4)22-24, the central component and major inhibitor of the ferroptotic cell death pathway. Therefore, defining the molecular mechanisms governing ferroptosis will likely reveal potential targets for the development of novel cancer therapeutics. Ferroptosis is characterized by extensive lipid peroxidative damage to biological membranes that overwhelms the ability of GPX4 to detoxify these lipid reactive oxygen species, eventually leading to cell death. While the central mechanisms of this regulated cell death pathway have been elucidated, the mediators of ferroptosis susceptibility are not fully characterized and the molecular signals and events that ultimately result in cellular demise remain unknown. Our lab and others have demonstrated that widespread changes in the cellular lipidome occur during ferroptosis, characterized by the significant upregulation of lysophospholipids and certain polyunsaturated fatty acid-containing diacylglycerols (PUFA-DAGs)2-7. The mechanisms that mediate these changes and the functions they play in ferroptosis are as yet unknown. In this study, I will use small molecule dose response, genetic modulation techniques, and lipidomic profiling to investigate the role of phospholipase A2s (PLA2s, lipid remodeling enzymes that generate lysophospholipids), and PUFA-DAG signaling pathways in ferroptosis. I propose that specific phospholipase A2 enzymes (specifically, ABHD12, PLA2G15, and PLA2G10) are active in the removal of key sensitizing lipid species from the membrane and potentially in the repair of oxidatively damaged membranes during ferroptosis (Aim 1). I further propose that specific PUFA-DAGs coordinate downstream signaling cascades through activation of certain protein kinase C subtypes, which have been implicated in oxidative stress pathways15, directing the cell toward cell death (Aim 2). A tipping of the balance between these opposing processes may determine cell fate.