ER-mitochondria contacts mediate lipid radical transfer via RMDN3/PTPIP51 phosphorylation to reduce mitochondrial oxidative stress
Isshin Shiiba, Naoki Ito, Hijiri Oshio, Yuto Ishikawa, Takahiro Nagao, Hiroki Shimura, Keon Bong Oh, Eiki Takasaki, Fuya Yamaguchi, Ryoan Konagaya, Hisae Kadowaki, Hideki Nishitoh, Takehito Tanzawa, Shun Nagashima, Ayumu Sugiura, Yuuta Fujikawa, Keitaro Umezawa, Yasushi Tamura, Byung Il Lee, Yusuke Hirabayashi, Yasushi Okazaki, Tomohiro Sawa, Ryoko Inatome, Shigeru Yanagi
Abstract
The proximal domains of mitochondria and the endoplasmic reticulum (ER) are linked by tethering factors on each membrane, allowing the efficient transport of substances, including lipids and calcium, between them. However, little is known about the regulation and function of mitochondria-ER contacts (MERCs) dynamics under mitochondrial damage. In this study, we apply NanoBiT technology to develop the MERBiT system, which enables the measurement of reversible MERCs formation in living cells. Analysis using this system suggests that induction of mitochondrial ROS increases MERCs formation via RMDN3 (also known as PTPIP51)-VAPB tethering driven by RMDN3 phosphorylation. Disruption of this tethering caused lipid radical accumulation in mitochondria, leading to cell death. The lipid radical transfer activity of the TPR domain in RMDN3, as revealed by an in vitro liposome assay, suggests that RMDN3 transfers lipid radicals from mitochondria to the ER. Our findings suggest a potential role for MERCs in cell survival strategy by facilitating the removal of mitochondrial lipid radicals under mitochondrial damage. Mitochondria-ER contacts are an organelle exchange site for lipids and ions, but their regulation is not well understood. Here, Isshin et al. find that RMDN3 transfers lipid radicals, generated by mtROS, from mitochondria to the ER at contact sites to reduce toxicity to the cell.