School of Biological Sciences, Seoul National University, Seoul, Korea.
Department of Cellular Physiology, Niigata University Graduate School of Medical and Dental Sciences, Niigata, Japan.
FASEB J. 2020 Feb;34(2):2944-2957. doi: 10.1096/fj.201901735R. Epub 2019 Dec 26.
Mitochondrial quality control maintains mitochondrial function by regulating mitochondrial dynamics and mitophagy. Despite the identification of mitochondrial quality control factors, little is known about the crucial regulators coordinating both mitochondrial fission and mitophagy. Through a cell-based functional screening assay, FK506 binding protein 8 (FKBP8) was identified to target microtubule-associated protein 1 light chain 3 (LC3) to the mitochondria and to change mitochondrial morphology. Microscopy analysis revealed that the formation of tubular and enlarged mitochondria was observed in FKBP8 knockdown HeLa cells and the cortex of Fkbp8 heterozygote-knockout mouse embryos. Under iron depletion-induced stress, FKBP8 was recruited to the site of mitochondrial division through budding and colocalized with LC3. FKBP8 was also found to be required for mitochondrial fragmentation and mitophagy under hypoxic stress. Conversely, FKBP8 overexpression induced mitochondrial fragmentation in HeLa cells, human fibroblasts and mouse embryo fibroblasts (MEFs), and this fragmentation occurred in Drp1 knockout MEF cells, FIP200 knockout HeLa cells and BNIP3/NIX double knockout HeLa cells, but not in Opa1 knockout MEFs. Interestingly, we found an LIR motif-like sequence (LIRL), as well as an LIR motif, at the N-terminus of FKBP8 and LIRL was essential for both inducing mitochondrial fragmentation and binding of FKBP8 to OPA1. Together, we suggest that FKBP8 plays an essential role in mitochondrial fragmentation through LIRL during mitophagy and this activity of FKBP8 together with LIR is required for mitophagy under stress conditions.
线粒体质量控制通过调节线粒体动力学和线粒体自噬来维持线粒体功能。尽管已经鉴定出了线粒体质量控制因子，但对于协调线粒体裂变和线粒体自噬的关键调节因子知之甚少。通过基于细胞的功能筛选实验，发现 FK506 结合蛋白 8（FKBP8）将微管相关蛋白 1 轻链 3（LC3）靶向到线粒体，并改变线粒体形态。显微镜分析显示，在 FKBP8 敲低的 HeLa 细胞和 Fkbp8 杂合敲除小鼠胚胎皮质中观察到管状和扩大的线粒体形成。在铁耗竭诱导的应激下，FKBP8 通过出芽被募集到线粒体分裂部位，并与 LC3 共定位。还发现 FKBP8 在缺氧应激下对于线粒体片段化和线粒体自噬是必需的。相反，FKBP8 过表达诱导 HeLa 细胞、人成纤维细胞和小鼠胚胎成纤维细胞（MEF）中的线粒体片段化，这种片段化发生在 Drp1 敲除 MEF 细胞、FIP200 敲除 HeLa 细胞和 BNIP3/NIX 双敲除 HeLa 细胞中，但不在 Opa1 敲除 MEF 细胞中。有趣的是，我们在 FKBP8 的 N 端发现了一个 LIR 基序样序列（LIRL）和一个 LIR 基序，LIRL 对于诱导线粒体片段化和 FKBP8 与 OPA1 的结合都是必需的。总之，我们认为 FKBP8 通过 LIRL 在自噬过程中在线粒体片段化中发挥重要作用，这种 FKBP8 的活性和 LIR 是应激条件下线粒体自噬所必需的。
