Department of Molecular and Integrative Physiology, University of Michigan, Ann Arbor, Michigan, USA.
Division of Radiation and Genome Stability, Department of Radiation Oncology, Dana-Farber Cancer Institute, Harvard Medical School, Boston, Massachusetts, USA.
J Biol Chem. 2023 May;299(5):104691. doi: 10.1016/j.jbc.2023.104691. Epub 2023 Apr 8.
Mitophagy is a cargo-specific autophagic process that recycles damaged mitochondria to promote mitochondrial turnover. PTEN-induced putative kinase 1 (PINK1) mediates the canonical mitophagic pathway. However, the role of PINK1 in diseases where mitophagy has been purported to play a role, such as colorectal cancer, is unclear. Our results here demonstrate that higher PINK1 expression is positively correlated with decreased colon cancer survival, and mitophagy is required for colon cancer growth. We show that doxycycline-inducible knockdown (KD) of PINK1 in a panel of colon cancer cell lines inhibited proliferation, whereas disruption of other mitophagy receptors did not impact cell growth. We observed that PINK KD led to a decrease in mitochondrial respiration, membrane hyperpolarization, accumulation of mitochondrial DNA, and depletion of antioxidant glutathione. In addition, mitochondria are important hubs for the utilization of iron and synthesizing iron-dependent cofactors such as heme and iron sulfur clusters. We observed an increase in the iron storage protein ferritin and a decreased labile iron pool in the PINK1 KD cells, but total cellular iron or markers of iron starvation/overload were not affected. Finally, cellular iron storage and the labile iron pool are maintained via autophagic degradation of ferritin (ferritinophagy). We found overexpressing nuclear receptor coactivator 4, a key adaptor for ferritinophagy, rescued cell growth and the labile iron pool in PINK1 KD cells. These results indicate that PINK1 integrates mitophagy and ferritinophagy to regulate intracellular iron availability and is essential for maintaining intracellular iron homeostasis to support survival and growth in colorectal cancer cells.
自噬是一种针对特定货物的自噬过程，可回收受损的线粒体以促进线粒体更新。PTEN 诱导的假定激酶 1（PINK1）介导经典的自噬途径。然而，PINK1 在自噬被认为起作用的疾病（如结直肠癌）中的作用尚不清楚。我们的研究结果表明，较高的 PINK1 表达与结直肠癌患者生存率降低呈正相关，并且自噬是结直肠癌细胞生长所必需的。我们发现，在一系列结直肠癌细胞系中，用强力霉素诱导的 PINK1 敲低（KD）抑制了增殖，而其他自噬受体的破坏则不影响细胞生长。我们观察到 PINK1 KD 导致线粒体呼吸减少、膜超极化、线粒体 DNA 积累和抗氧化谷胱甘肽耗竭。此外，线粒体是利用铁和合成铁依赖性辅因子（如血红素和铁硫簇）的重要枢纽。我们观察到 PINK1 KD 细胞中铁储存蛋白 ferritin 增加和不稳定铁池减少，但总细胞铁或铁饥饿/过载标志物没有受到影响。最后，通过 ferritin（铁蛋白自噬）的自噬降解来维持细胞内铁储存和不稳定铁池。我们发现，过表达核受体共激活因子 4（ferritinophagy 的关键衔接子）可挽救 PINK1 KD 细胞中的细胞生长和不稳定铁池。这些结果表明，PINK1 整合了自噬和 ferritinophagy 来调节细胞内铁的可用性，对于维持细胞内铁稳态以支持结直肠癌细胞的存活和生长是必不可少的。
