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Xin N, Durieux J, Yang C, Wolff S, Kim HE, Dillin A. The UPRmt preserves mitochondrial import to extend lifespan. J Cell Biol 2022; 221:e202201071. [PMID: 35608535 PMCID: PMC9134095 DOI: 10.1083/jcb.202201071] [Citation(s) in RCA: 23] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2022] [Revised: 04/14/2022] [Accepted: 04/26/2022] [Indexed: 01/07/2023] Open
Abstract
The mitochondrial unfolded protein response (UPRmt) is dedicated to promoting mitochondrial proteostasis and is linked to extreme longevity. The key regulator of this process is the transcription factor ATFS-1, which, upon UPRmt activation, is excluded from the mitochondria and enters the nucleus to regulate UPRmt genes. However, the repair proteins synthesized as a direct result of UPRmt activation must be transported into damaged mitochondria that had previously excluded ATFS-1 owing to reduced import efficiency. To address this conundrum, we analyzed the role of the import machinery when the UPRmt was induced. Using in vitro and in vivo analysis of mitochondrial proteins, we surprisingly find that mitochondrial import increases when the UPRmt is activated in an ATFS-1-dependent manner, despite reduced mitochondrial membrane potential. The import machinery is upregulated, and an intact import machinery is essential for UPRmt-mediated lifespan extension. ATFS-1 has a weak mitochondrial targeting sequence (MTS), allowing for dynamic subcellular localization during the initial stages of UPRmt activation.
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Affiliation(s)
- Nan Xin
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA
- Department of Integrated Biology and Pharmacology, University of Texas, Health Science Center, Houston, TX
| | - Jenni Durieux
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA
| | - Chunxia Yang
- Department of Integrated Biology and Pharmacology, University of Texas, Health Science Center, Houston, TX
| | - Suzanne Wolff
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA
| | - Hyun-Eui Kim
- Department of Integrated Biology and Pharmacology, University of Texas, Health Science Center, Houston, TX
| | - Andrew Dillin
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA
- Howard Hughes Medical Institute, Chevy Chase, MD
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Anderson JM, Box JM, Stuart RA. The mitospecific domain of Mrp7 (bL27) supports mitochondrial translation during fermentation and is required for effective adaptation to respiration. Mol Biol Cell 2021; 33:ar7. [PMID: 34731012 PMCID: PMC8886811 DOI: 10.1091/mbc.e21-07-0370] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
We demonstrate here that mitoribosomal protein synthesis, responsible for the synthesis of oxidative phosphorylation (OXPHOS) subunits encoded by mitochondrial genome, occurs at high levels during glycolysis fermentation and in a manner uncoupled from OXPHOS complex assembly regulation. Furthermore, we provide evidence that the mitospecific domain of Mrp7 (bL27), a mitoribosomal component, is required to maintain mitochondrial protein synthesis during fermentation, but is not required under respiration growth conditions. Maintaining mitotranslation under high glucose fermentation conditions also involves Mam33 (p32/gC1qR homolog), a binding partner of Mrp7's mitospecific domain, and together they confer a competitive advantage for a cell's ability to adapt to respiration-based metabolism when glucose becomes limiting. Furthermore, our findings support that the mitoribosome, and specifically the central protuberance (CP) region, may be differentially regulated and/or assembled, under the different metabolic conditions of fermentation and respiration. Based on our findings, we propose the purpose of mitotranslation is not limited to the assembly of OXPHOS complexes, but also plays a role in mitochondrial signaling critical for switching cellular metabolism from a glycolysis- to a respiratory-based state.
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Affiliation(s)
| | - Jodie M Box
- Dept. of Biological Sciences, Marquette University, Milwaukee, WI, USA
| | - Rosemary A Stuart
- Dept. of Biological Sciences, Marquette University, Milwaukee, WI, USA
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Abstract
Isolated mitochondria are useful to study fundamental processes including mitochondrial respiration, metabolic activity, protein import, membrane fusion, protein complex assembly, as well as interactions of mitochondria with the cytoskeleton, nuclear encoded mRNAs, and other organelles. In addition, studies of the mitochondrial proteome, phosphoproteome, and lipidome are dependent on preparation of highly purified mitochondria (Boldogh, Vojtov, Karmon, & Pon, 1998; Cui, Conte, Fox, Zara, & Winge, 2014; Marc et al., 2002; Meeusen, McCaffery, & Nunnari, 2004; Reinders et al., 2007; Schneiter et al., 1999; Stuart & Koehler, 2007). Most methods to isolate mitochondria rely on differential centrifugation, a two-step centrifugation carried out at low speed to remove intact cells, cell and tissue debris, and nuclei from whole cell extracts followed by high speed centrifugation to concentrate mitochondria and separate them from other organelles. However, methods to disrupt cells and tissue vary. Moreover, density gradient centrifugation or affinity purification of the organelle are used to further purify mitochondria or to separate different populations of the organelle. Here, we describe protocols to isolate mitochondria from different cells and tissues as well as approaches to assess the purity and integrity of isolated organelles.
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Isolation of mitochondria from Saccharomyces cerevisiae using magnetic bead affinity purification. PLoS One 2018; 13:e0196632. [PMID: 29698455 PMCID: PMC5919621 DOI: 10.1371/journal.pone.0196632] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2018] [Accepted: 04/16/2018] [Indexed: 11/30/2022] Open
Abstract
Isolated mitochondria are widely used to study the function of the organelle. Typically, mitochondria are prepared using differential centrifugation alone or in conjunction with density gradient ultracentrifugation. However, mitochondria isolated using differential centrifugation contain membrane or organelle contaminants, and further purification of crude mitochondria by density gradient ultracentrifugation requires large amounts of starting material, and is time-consuming. Mitochondria have also been isolated by irreversible binding to antibody-coated magnetic beads. We developed a method to prepare mitochondria from budding yeast that overcomes many of the limitations of other methods. Mitochondria are tagged by insertion of 6 histidines (6xHis) into the TOM70 (Translocase of outer membrane 70) gene at its chromosomal locus, isolated using Ni-NTA (nickel (II) nitrilotriacetic acid) paramagnetic beads and released from the magnetic beads by washing with imidazole. Mitochondria prepared using this method contain fewer contaminants, and are similar in ultrastructure as well as protein import and cytochrome c oxidase complex activity compared to mitochondria isolated by differential centrifugation. Moreover, this isolation method is amenable to small samples, faster than purification by differential and density gradient centrifugation, and more cost-effective than purification using antibody-coated magnetic beads. Importantly, this method can be applied to any cell type where the genetic modification can be introduced by CRISPR or other methods.
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Darshi M, Trinh KN, Murphy AN, Taylor SS. Targeting and import mechanism of coiled-coil helix coiled-coil helix domain-containing protein 3 (ChChd3) into the mitochondrial intermembrane space. J Biol Chem 2012; 287:39480-91. [PMID: 23019327 PMCID: PMC3501047 DOI: 10.1074/jbc.m112.387696] [Citation(s) in RCA: 55] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/02/2022] Open
Abstract
Coiled-coil helix coiled-coil helix domain-containing protein 3 (ChChd3) is a mitochondrial inner membrane (IM) protein facing toward the intermembrane space (IMS). In the IMS, ChChd3 complexes with multiple proteins at the crista junctions and contact sites and plays a key role in maintaining crista integrity. ChChd3 is myristoylated at the N terminus and has a CHCH domain with twin CX9C motifs at its C terminus. The CHCH domain proteins are traditionally imported and trapped in the IMS by using a disulfide relay system mediated by Mia40 and Erv1. In this study, we systematically analyzed the role of the myristoylation and the CHCH domain in the import and mitochondrial localization of ChChd3. Based on our results, we predict that myristoylation promotes binding of ChChd3 to the outer membrane and that the CHCH domain translocates the protein across the outer membrane. By analysis of the CHCH domain cysteine mutants, we further show that they have distinct roles in binding to Mia40 in the IMS and proper folding of the protein. The transient disulfide-bonded intermediate with Mia40 is formed preferentially between the second cysteine in helix 1, Cys193, and the active site cysteine in Mia40, Cys55. Although each of the four cysteines is essential for folding of the protein and binding to mitofilin and Sam50, they are not involved in import. Together our results indicate that both the myristoylation and the CHCH domain are essential for the import and mitochondrial localization of ChChd3. Once imported, ChChd3 binds to Mia40 for further folding and assembly into macromolecular complexes.
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Affiliation(s)
- Manjula Darshi
- Howard Hughes Medical Institute, University of California, San Diego, La Jolla, California 92093-0654, USA
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Sharma NK, Reyes A, Green P, Caron MJ, Bonini MG, Gordon DM, Holt IJ, Santos JH. Human telomerase acts as a hTR-independent reverse transcriptase in mitochondria. Nucleic Acids Res 2011; 40:712-25. [PMID: 21937513 PMCID: PMC3258147 DOI: 10.1093/nar/gkr758] [Citation(s) in RCA: 123] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Human telomerase reverse transcriptase (hTERT) is localized to mitochondria, as well as the nucleus, but details about its biology and function in the organelle remain largely unknown. Here we show, using multiple approaches, that mammalian TERT is mitochondrial, co-purifying with mitochondrial nucleoids and tRNAs. We demonstrate the canonical nuclear RNA [human telomerase RNA (hTR)] is not present in human mitochondria and not required for the mitochondrial effects of telomerase, which nevertheless rely on reverse transcriptase (RT) activity. Using RNA immunoprecipitations from whole cell and in organello, we show that hTERT binds various mitochondrial RNAs, suggesting that RT activity in the organelle is reconstituted with mitochondrial RNAs. In support of this conclusion, TERT drives first strand cDNA synthesis in vitro in the absence of hTR. Finally, we demonstrate that absence of hTERT specifically in mitochondria with maintenance of its nuclear function negatively impacts the organelle. Our data indicate that mitochondrial hTERT works as a hTR-independent reverse transcriptase, and highlight that nuclear and mitochondrial telomerases have different cellular functions. The implications of these findings to both the mitochondrial and telomerase fields are discussed.
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Affiliation(s)
- Nilesh K Sharma
- Department of Pharmacology and Physiology, New Jersey Medical School of UMDNJ, 185 South Orange Avenue, Medical Sciences Building, Newark, NJ 07103, USA
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Mitochondrial Unselective Channels throughout the eukaryotic domain. Mitochondrion 2011; 11:382-90. [DOI: 10.1016/j.mito.2011.02.004] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2010] [Revised: 02/16/2011] [Accepted: 02/25/2011] [Indexed: 02/03/2023]
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Wang G, Chen HW, Oktay Y, Zhang J, Allen EL, Smith GM, Fan KC, Hong JS, French SW, McCaffery JM, Lightowlers RN, Morse HC, Koehler CM, Teitell MA. PNPASE regulates RNA import into mitochondria. Cell 2010; 142:456-67. [PMID: 20691904 DOI: 10.1016/j.cell.2010.06.035] [Citation(s) in RCA: 260] [Impact Index Per Article: 18.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2009] [Revised: 03/20/2010] [Accepted: 05/13/2010] [Indexed: 02/04/2023]
Abstract
RNA import into mammalian mitochondria is considered essential for replication, transcription, and translation of the mitochondrial genome but the pathway(s) and factors that control this import are poorly understood. Previously, we localized polynucleotide phosphorylase (PNPASE), a 3' --> 5' exoribonuclease and poly-A polymerase, in the mitochondrial intermembrane space, a location lacking resident RNAs. Here, we show a new role for PNPASE in regulating the import of nuclear-encoded RNAs into the mitochondrial matrix. PNPASE reduction impaired mitochondrial RNA processing and polycistronic transcripts accumulated. Augmented import of RNase P, 5S rRNA, and MRP RNAs depended on PNPASE expression and PNPASE-imported RNA interactions were identified. PNPASE RNA processing and import activities were separable and a mitochondrial RNA targeting signal was isolated that enabled RNA import in a PNPASE-dependent manner. Combined, these data strongly support an unanticipated role for PNPASE in mediating the translocation of RNAs into mitochondria.
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Affiliation(s)
- Geng Wang
- Department of Chemistry and Biochemistry, University of California at Los Angeles, Los Angeles, CA 90095, USA
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Mitochondrion-enriched anionic phospholipids facilitate flock house virus RNA polymerase membrane association. J Virol 2009; 83:4498-507. [PMID: 19244330 DOI: 10.1128/jvi.00040-09] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
One characteristic of all positive-strand RNA viruses is the necessity to assemble viral RNA replication complexes on host intracellular membranes, a process whose molecular details are poorly understood. To study viral replication complex assembly we use the established model system of Flock House virus (FHV), which assembles its replication complexes on the mitochondrial outer membrane. The FHV RNA-dependent RNA polymerase, protein A, is the only viral protein necessary for genome replication in the budding yeast Saccharomyces cerevisiae. To examine the host components involved in protein A-membrane interactions, an initial step of FHV RNA replication complex assembly, we established an in vitro protein A membrane association assay. Protein A translated in vitro rapidly and specifically associated with mitochondria isolated from yeast, insect, and mammalian cells. This process was temperature dependent but independent of protease-sensitive mitochondrial outer membrane components or the host mitochondrial import machinery. Furthermore, lipid-binding studies revealed that protein A preferentially bound to specific anionic phospholipids, in particular the mitochondrion-specific phospholipid cardiolipin. These studies implicate membrane phospholipids as important host determinants for FHV RNA polymerase membrane association and provide evidence for the involvement of host phospholipids in positive-strand RNA virus membrane-specific targeting.
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