DNA polymerase gamma mutations that impair holoenzyme stability cause catalytic subunit depletion

• Published in: Nucleic acids research 2021-05, Vol.49 (9), p.5230-5248
• Main Authors: Silva-Pinheiro, Pedro, Pardo-Hernández, Carlos, Reyes, Aurelio, Tilokani, Lisa, Mishra, Anup, Cerutti, Raffaele, Li, Shuaifeng, Rozsivalova, Dieu-Hien, Valenzuela, Sebastian, Dogan, Sukru A, Peter, Bradley, Fernández-Silva, Patricio, Trifunovic, Aleksandra, Prudent, Julien, Minczuk, Michal, Bindoff, Laurence, Macao, Bertil, Zeviani, Massimo, Falkenberg, Maria, Viscomi, Carlo
• Format: Article
• Language: English
• Subjects: accessory subunit; Animals; ATP-Dependent Proteases - metabolism; binding; Biochemistry & Molecular Biology; Cell Biology; Cellbiologi; Cells, Cultured; degradation; Dentistry; DNA Polymerase gamma - genetics; DNA Polymerase gamma - metabolism; DNA Replication; DNA, Mitochondrial - analysis; Enzyme Stability - genetics; HeLa Cells; Holoenzymes - metabolism; human mitochondrial-DNA; Humans; lon protease; loop strands; Mice; Mitochondrial Proteins - metabolism; mtdna-maintenance; Mutation; Nucleic Acid Enzymes; Odontologi; replication; transcription factor; twinkle
• ISSN: 0305-1048; 1362-4962
• DOI: 10.1093/nar/gkab282

Abstract Mutations in POLG, encoding POLγA, the catalytic subunit of the mitochondrial DNA polymerase, cause a spectrum of disorders characterized by mtDNA instability. However, the molecular pathogenesis of POLG-related diseases is poorly understood and efficient treatments are missing. Here, we generate the PolgA449T/A449T mouse model, which reproduces the A467T change, the most common human recessive mutation of POLG. We show that the mouse A449T mutation impairs DNA binding and mtDNA synthesis activities of POLγ, leading to a stalling phenotype. Most importantly, the A449T mutation also strongly impairs interactions with POLγB, the accessory subunit of the POLγ holoenzyme. This allows the free POLγA to become a substrate for LONP1 protease degradation, leading to dramatically reduced levels of POLγA in A449T mouse tissues. Therefore, in addition to its role as a processivity factor, POLγB acts to stabilize POLγA and to prevent LONP1-dependent degradation. Notably, we validated this mechanism for other disease-associated mutations affecting the interaction between the two POLγ subunits. We suggest that targeting POLγA turnover can be exploited as a target for the development of future therapies. Graphical Abstract Graphical Abstract The A449T mutation in mouse POLγA, corresponding to the common A467T in patients, impairs the interaction between POLγA and B subunits, making POLγA amenable to degradation by LONP1 protease.