Abstract 2400: PINK1 is a novel regulator of mitochondria and iron metabolism in colon cancer
Authors: Chen Brandon , Devenport Samantha , Lyssiotis Costas , Shah Yatrik 
Published: July 2021

Abstract
Mitophagy is a cargo-specific autophagic process that recycles damaged mitochondria to promote mitochondrial turnover and cellular health. In particular, PINK and Parkin mediate one of the canonical mitophagy pathways. The mechanisms behind PINK1-Parkin mediated mitophagy is well established, yet its role in cancer remains equivocal. Based on differential gene expression analyses on colon cancer patients, higher PINK1 expressions are correlated with worsened survival. To confirm increased mitophagy in colon cancer cells, we assessed lysosomal proteome under nutrient stress and observed an enrichment of mitochondrial peptides. Then, we generated inducible shRNA knockdown (KD) models for PINK1 in a panel of colon cancer cell lines. Preliminary data suggest loss of PINK1 hinders colon cancer cell growth and induces cell death.
We showed that PINK1 KD hinders mitophagy assessed by decreased phospho-ubiquitin, a marker of PINK1 activity. We observed high levels of basal mitophagy in colon cancer cells, and PINK1 KD can efficiently inhibit mitophagy using a fluorescent mitophagy reporter. Interestingly, we demonstrated PINK KD disrupts mitochondria dynamics by decreasing MFN2 protein level, suggesting mitochondrial fusion could be inhibited. In summary, we demonstrated colon cancer cells have high levels of mitophagy and PINK1 KD decreases mitophagy and disrupts mitochondria network.
Mitochondria are important organelles that integrates cellular metabolic pathways. With PINK1's role as an overall mitochondrial health sensor, we hypothesized disrupting PINK1 could affect mitochondria metabolism in colon cancer cells. We demonstrated alterations in mitochondrial metabolites as assessed by metabolomics, NAD/NADH imbalance, membrane hyperpolarization, and decreased oxygen consumption rate. It is known that TCA cycle and electron transport chain require iron sulfur clusters (ISC) to maintain proper function. Although the exact quantification of mitochondrial iron fraction is elusive, some studies suggested that mitochondria could harbor up to 20% of cellular iron. These evidences suggest mitochondria play pivotal roles in cellular iron homeostasis. Upon PINK1 KD, we saw an accumulation of cytosolic and mitochondrial iron storage protein, ferritin. Interestingly, we also observed a decrease in ISC-containing ETC proteins upon PINK1 KD. We believe PINK1 could have a non-canonical function in regulating mitochondria iron and play a profound role in regulating cellular iron balance.
Overall, these results indicate that PINK1 is essential for maintaining mitochondria metabolism and survival in colon cancers. Here, we showcased that PINK has a unique role in regulating mitochondrial metabolism. In conclusion, the growth and mitochondrial defects we observed from PINK1 KD cells suggest a potential oncogenic role of PINK1 in colorectal cancer that can be targeted for future therapeutic purposes.
Citation Format: Brandon Chen, Samantha Devenport, Costas Lyssiotis, Yatrik Shah. PINK1 is a novel regulator of mitochondria and iron metabolism in colon cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2400.