Critical role of mitochondrial ubiquitination and the OPTN–ATG9A axis in mitophagy

• Published in: The Journal of cell biology Vol. 219; no. 9; p. 1
• Main Authors: Yamano, Koji, Kikuchi, Reika, Kojima, Waka, Hayashida, Ryota, Koyano, Fumika, Kawawaki, Junko, Shoda, Takuji, Demizu, Yosuke, Naito, Mikihiko, Tanaka, Keiji, Matsuda, Noriyuki
• Format: Journal Article
• Language: English
• Published: United States Rockefeller University Press 07.09.2020
• Subjects: Activation; Adapters; Adaptor proteins; Animals; Autophagy; Autophagy - physiology; Autophagy-Related Proteins - metabolism; Binding; Biochemistry; Carrier Proteins - metabolism; Cell Cycle Proteins - metabolism; Cell Line, Tumor; Cells, Cultured; Fluorescence; HCT116 Cells; HEK293 Cells; HeLa Cells; Humans; Mammals - metabolism; Mammals - physiology; Membrane Proteins - metabolism; Membrane Transport Proteins - metabolism; Mitochondria; Mitochondria - metabolism; Mitochondria - physiology; Mitophagy; Mitophagy - physiology; Movement disorders; Neurodegenerative diseases; Organelles; Parkin protein; Parkinson's disease; Phagocytosis; Protein Kinases - metabolism; Proteins; PTEN-induced putative kinase; Ubiquitin; Ubiquitin - metabolism; Ubiquitin-Protein Ligases - metabolism; Ubiquitination; Ubiquitination - physiology; Vesicular Transport Proteins - metabolism
• ISSN: 0021-9525; 1540-8140; 1540-8140
• DOI: 10.1083/jcb.201912144

Damaged mitochondria are selectively eliminated in a process called mitophagy. Parkin and PINK1, proteins mutated in Parkinson’s disease, amplify ubiquitin signals on damaged mitochondria with the subsequent activation of autophagic machinery. Autophagy adaptors are thought to link ubiquitinated mitochondria and autophagy through ATG8 protein binding. Here, we establish methods for inducing mitophagy by mitochondria-targeted ubiquitin chains and chemical-induced mitochondrial ubiquitination. Using these tools, we reveal that the ubiquitin signal is sufficient for mitophagy and that PINK1 and Parkin are unnecessary for autophagy activation per se. Furthermore, using phase-separated fluorescent foci, we show that the critical autophagy adaptor OPTN forms a complex with ATG9A vesicles. Disruption of OPTN–ATG9A interactions does not induce mitophagy. Therefore, in addition to binding ATG8 proteins, the critical autophagy adaptors also bind the autophagy core units that contribute to the formation of multivalent interactions in the de novo synthesis of autophagosomal membranes near ubiquitinated mitochondria.