Therapeutic Targeting of Autophagy-Dependent Cancer

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PROJECT SUMMARY Mitochondria are key organelles in the cell and regulate many processes including energy production and cell signaling. Many cancer cells are dependent on functional mitochondria for cell survival. Mitochondrial homeostasis is therefore critical and is tightly regulated. Damaged mitochondria are turned over by a select form of autophagy, known as mitophagy, where an intact mitochondrion is engulfed by an autophagosome which then fuses with a lysosome to facilitate degradation. It has been previously shown that cancer cells are dependent on core autophagy regulators like ATG7 and FIP200 for survival, but rare cells from these populations can survive loss of this core pathway. The ATG7 KO cells that were derived from highly autophagy dependent cells switched to become autophagy independent. Despite a lack of canonical mitophagy, the autophagy deficient cells can still degrade mitochondria and maintain mitochondrial function. It was recently published that cells that survive loss of autophagy can instead form small mitochondrial derived vesicles (MDVs) that can directly fuse with lysosomes to maintain mitochondrial homeostasis. Cells with more MDVs are dependent on them for mitochondrial function and overall survival. MDVs are highly understudied, but this work suggests they could be a potential new target in cancer cells. The work proposed here will include more mechanistic studies to understand how MDVs are regulated. The only known regulator of these vesicles is the endocytosis-regulating sorting nexin, SNX9, but how it regulates MDV formation is unknown. These studies will include structure-function analysis to dissect the specific roles of each domain within SNX9 to determine how it regulates MDV formation and trafficking as well as its role in mitochondrial homeostasis and overall cell survival. SNX18 is homologous to SNX9 and can compensate for its role in endocytosis. These studies will test the hypothesis that SNX18 is also important in MDVs. A significant goal of this project is also to train and mentor Sienna. During these studies she will learn new techniques including molecular cloning, flow cytometry, and mitochondrial function assays among others. She will also learn how to develop her own hypotheses and design experiments with critical controls to drive her own project forward. Her next career goal is to get a PhD in cancer biology with a focus on cancer disparities. This project will provide her with the necessary tools and techniques as well additional course work to help prepare her for PhD programs. She will also attend national meetings like ABRCMS. This project is designed to help her make the successful transition into graduate programs in the Fall of 2023.