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Niemi NM, Friedman JR. Coordinating BNIP3/NIX-mediated mitophagy in space and time. Biochem Soc Trans 2024:BST20221364. [PMID: 39377319 DOI: 10.1042/bst20221364] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2024] [Revised: 09/16/2024] [Accepted: 09/17/2024] [Indexed: 10/09/2024]
Abstract
Mitochondria maintain organellar homeostasis through multiple quality control pathways, including the clearance of defective or unwanted mitochondria by selective autophagy. This removal of mitochondria, mitophagy, is controlled in large part by the outer mitochondrial membrane mitophagy receptors BNIP3 and NIX. While it has long been appreciated that BNIP3 and NIX mediate mitophagy by controlling the recruitment of autophagic machinery to the mitochondrial surface, the requirement for the carefully controlled spatiotemporal regulation of receptor-mediated mitophagy has only recently come to light. Several new factors that regulate the BNIP3/NIX-mediated mitophagy pathway have emerged, and various loss-of-function cell and animal models have revealed the dire consequences of their dysregulation. In this mini-review, we discuss new insights into the mechanisms and roles of the regulation of BNIP3 and NIX and highlight questions that have emerged from the identification of these new regulators.
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Affiliation(s)
- Natalie M Niemi
- Washington University School of Medicine in St. Louis, St. Louis, MO 63110, U.S.A
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2
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Wei L, Gok MO, Svoboda JD, Kozul KL, Forny M, Friedman JR, Niemi NM. Dual-localized PPTC7 limits mitophagy through proximal and dynamic interactions with BNIP3 and NIX. Life Sci Alliance 2024; 7:e202402765. [PMID: 38991726 PMCID: PMC11239977 DOI: 10.26508/lsa.202402765] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2024] [Revised: 06/10/2024] [Accepted: 06/11/2024] [Indexed: 07/13/2024] Open
Abstract
PPTC7 is a mitochondrial-localized phosphatase that suppresses BNIP3- and NIX-mediated mitophagy, but the mechanisms underlying this regulation remain ill-defined. Here, we demonstrate that loss of PPTC7 upregulates BNIP3 and NIX post-transcriptionally and independent of HIF-1α stabilization. Loss of PPTC7 prolongs the half-life of BNIP3 and NIX while blunting their accumulation in response to proteasomal inhibition, suggesting that PPTC7 promotes the ubiquitin-mediated turnover of BNIP3 and NIX. Consistently, overexpression of PPTC7 limits the accumulation of BNIP3 and NIX protein levels, which requires an intact catalytic motif but is surprisingly independent of its targeting to mitochondria. Consistently, we find that PPTC7 is dual-localized to the outer mitochondrial membrane and the matrix. Importantly, anchoring PPTC7 to the outer mitochondrial membrane is sufficient to blunt BNIP3 and NIX accumulation, and proximity labeling and fluorescence co-localization experiments demonstrate that PPTC7 dynamically associates with BNIP3 and NIX within the native cellular environment. Collectively, these data reveal that a fraction of PPTC7 localizes to the outer mitochondrial membrane to promote the proteasomal turnover of BNIP3 and NIX, limiting basal mitophagy.
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Affiliation(s)
- Lianjie Wei
- https://ror.org/04cf69335 Department of Biochemistry & Molecular Biophysics, Washington University School of Medicine in St. Louis, St. Louis, MO, USA
| | - Mehmet Oguz Gok
- Department of Cell Biology, University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Jordyn D Svoboda
- https://ror.org/04cf69335 Department of Biochemistry & Molecular Biophysics, Washington University School of Medicine in St. Louis, St. Louis, MO, USA
| | - Keri-Lyn Kozul
- https://ror.org/04cf69335 Department of Biochemistry & Molecular Biophysics, Washington University School of Medicine in St. Louis, St. Louis, MO, USA
| | - Merima Forny
- https://ror.org/04cf69335 Department of Biochemistry & Molecular Biophysics, Washington University School of Medicine in St. Louis, St. Louis, MO, USA
| | - Jonathan R Friedman
- Department of Cell Biology, University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Natalie M Niemi
- https://ror.org/04cf69335 Department of Biochemistry & Molecular Biophysics, Washington University School of Medicine in St. Louis, St. Louis, MO, USA
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3
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Adriaenssens E, Schaar S, Cook ASI, Stuke JFM, Sawa-Makarska J, Nguyen TN, Ren X, Schuschnig M, Romanov J, Khuu G, Lazarou M, Hummer G, Hurley JH, Martens S. Reconstitution of BNIP3/NIX-mediated autophagy reveals two pathways and hierarchical flexibility of the initiation machinery. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.08.28.609967. [PMID: 39253418 PMCID: PMC11383309 DOI: 10.1101/2024.08.28.609967] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 09/11/2024]
Abstract
Selective autophagy is a lysosomal degradation pathway that is critical for maintaining cellular homeostasis by disposing of harmful cellular material. While the mechanisms by which soluble cargo receptors recruit the autophagy machinery are becoming increasingly clear, the principles governing how organelle-localized transmembrane cargo receptors initiate selective autophagy remain poorly understood. Here, we demonstrate that transmembrane cargo receptors can initiate autophagosome biogenesis not only by recruiting the upstream FIP200/ULK1 complex but also via a WIPI-ATG13 complex. This latter pathway is employed by the BNIP3/NIX receptors to trigger mitophagy. Additionally, other transmembrane mitophagy receptors, including FUNDC1 and BCL2L13, exclusively use the FIP200/ULK1 complex, while FKBP8 and the ER-phagy receptor TEX264 are capable of utilizing both pathways to initiate autophagy. Our study defines the molecular rules for initiation by transmembrane cargo receptors, revealing remarkable flexibility in the assembly and activation of the autophagy machinery, with significant implications for therapeutic interventions.
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Ahola S, Pazurek LA, Mayer F, Lampe P, Hermans S, Becker L, Amarie OV, Fuchs H, Gailus-Durner V, de Angelis MH, Riedel D, Nolte H, Langer T. Opa1 processing is dispensable in mouse development but is protective in mitochondrial cardiomyopathy. SCIENCE ADVANCES 2024; 10:eadp0443. [PMID: 39093974 PMCID: PMC11296347 DOI: 10.1126/sciadv.adp0443] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/04/2024] [Accepted: 06/28/2024] [Indexed: 08/04/2024]
Abstract
Mitochondrial fusion and fission accompany adaptive responses to stress and altered metabolic demands. Inner membrane fusion and cristae morphogenesis depends on optic atrophy 1 (Opa1), which is expressed in different isoforms and is cleaved from a membrane-bound, long to a soluble, short form. Here, we have analyzed the physiological role of Opa1 isoforms and Opa1 processing by generating mouse lines expressing only one cleavable Opa1 isoform or a non-cleavable variant thereof. Our results show that expression of a single cleavable or non-cleavable Opa1 isoform preserves embryonic development and the health of adult mice. Opa1 processing is dispensable under metabolic and thermal stress but prolongs life span and protects against mitochondrial cardiomyopathy in OXPHOS-deficient Cox10-/- mice. Mechanistically, loss of Opa1 processing disturbs the balance between mitochondrial biogenesis and mitophagy, suppressing cardiac hypertrophic growth in Cox10-/- hearts. Our results highlight the critical regulatory role of Opa1 processing, mitochondrial dynamics, and metabolism for cardiac hypertrophy.
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Affiliation(s)
- Sofia Ahola
- Max Planck Institute for Biology of Ageing, Cologne, Germany
| | | | - Fiona Mayer
- Max Planck Institute for Biology of Ageing, Cologne, Germany
| | - Philipp Lampe
- Max Planck Institute for Biology of Ageing, Cologne, Germany
| | - Steffen Hermans
- Max Planck Institute for Biology of Ageing, Cologne, Germany
| | - Lore Becker
- Institute of Experimental Genetics, German Mouse Clinic, Helmholtz Zentrum München, German Research Center for Environmental Health (GmbH), Neuherberg, Germany
| | - Oana V Amarie
- Institute of Experimental Genetics, German Mouse Clinic, Helmholtz Zentrum München, German Research Center for Environmental Health (GmbH), Neuherberg, Germany
| | - Helmut Fuchs
- Institute of Experimental Genetics, German Mouse Clinic, Helmholtz Zentrum München, German Research Center for Environmental Health (GmbH), Neuherberg, Germany
| | - Valerie Gailus-Durner
- Institute of Experimental Genetics, German Mouse Clinic, Helmholtz Zentrum München, German Research Center for Environmental Health (GmbH), Neuherberg, Germany
| | - Martin Hrabe de Angelis
- Institute of Experimental Genetics, German Mouse Clinic, Helmholtz Zentrum München, German Research Center for Environmental Health (GmbH), Neuherberg, Germany
- Experimental Genetics, TUM School of Life Sciences, Technische Universität München, Freising, Germany
- German Center for Diabetes Research (DZD), 85764 Neuherberg
| | - Dietmar Riedel
- Max Planck Institute for Multidisciplinary Sciences, Göttingen, Germany
| | - Hendrik Nolte
- Max Planck Institute for Biology of Ageing, Cologne, Germany
| | - Thomas Langer
- Max Planck Institute for Biology of Ageing, Cologne, Germany
- Cologne Excellence Cluster on Cellular Stress Responses in Aging-Associated Diseases (CECAD), University of Cologne, Cologne, Germany
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5
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Nguyen-Dien GT, Townsend B, Kulkarni PG, Kozul KL, Ooi SS, Eldershaw DN, Weeratunga S, Liu M, Jones MJ, Millard SS, Ng DC, Pagano M, Bonfim-Melo A, Schneider T, Komander D, Lazarou M, Collins BM, Pagan JK. PPTC7 antagonizes mitophagy by promoting BNIP3 and NIX degradation via SCF FBXL4. EMBO Rep 2024; 25:3324-3347. [PMID: 38992176 PMCID: PMC11316107 DOI: 10.1038/s44319-024-00181-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2024] [Revised: 05/30/2024] [Accepted: 06/04/2024] [Indexed: 07/13/2024] Open
Abstract
Mitophagy must be carefully regulated to ensure that cells maintain appropriate numbers of functional mitochondria. The SCFFBXL4 ubiquitin ligase complex suppresses mitophagy by controlling the degradation of BNIP3 and NIX mitophagy receptors, and FBXL4 mutations result in mitochondrial disease as a consequence of elevated mitophagy. Here, we reveal that the mitochondrial phosphatase PPTC7 is an essential cofactor for SCFFBXL4-mediated destruction of BNIP3 and NIX, suppressing both steady-state and induced mitophagy. Disruption of the phosphatase activity of PPTC7 does not influence BNIP3 and NIX turnover. Rather, a pool of PPTC7 on the mitochondrial outer membrane acts as an adaptor linking BNIP3 and NIX to FBXL4, facilitating the turnover of these mitophagy receptors. PPTC7 accumulates on the outer mitochondrial membrane in response to mitophagy induction or the absence of FBXL4, suggesting a homoeostatic feedback mechanism that attenuates high levels of mitophagy. We mapped critical residues required for PPTC7-BNIP3/NIX and PPTC7-FBXL4 interactions and their disruption interferes with both BNIP3/NIX degradation and mitophagy suppression. Collectively, these findings delineate a complex regulatory mechanism that restricts BNIP3/NIX-induced mitophagy.
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Affiliation(s)
- Giang Thanh Nguyen-Dien
- Faculty of Medicine, School of Biomedical Sciences, University of Queensland, Brisbane, QLD, Australia
- Department of Biotechnology, School of Biotechnology, Viet Nam National University-International University, Ho Chi Minh City, Vietnam
| | - Brendan Townsend
- Faculty of Medicine, School of Biomedical Sciences, University of Queensland, Brisbane, QLD, Australia
| | - Prajakta Gosavi Kulkarni
- Faculty of Medicine, School of Biomedical Sciences, University of Queensland, Brisbane, QLD, Australia
| | - Keri-Lyn Kozul
- Faculty of Medicine, School of Biomedical Sciences, University of Queensland, Brisbane, QLD, Australia
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, MO, 63110, St Louis, USA
| | - Soo Siang Ooi
- Faculty of Medicine, School of Biomedical Sciences, University of Queensland, Brisbane, QLD, Australia
| | - Denaye N Eldershaw
- The University of Queensland, Institute for Molecular Bioscience, Brisbane, QLD, 4072, Australia
| | - Saroja Weeratunga
- The University of Queensland, Institute for Molecular Bioscience, Brisbane, QLD, 4072, Australia
| | - Meihan Liu
- The University of Queensland, Institute for Molecular Bioscience, Brisbane, QLD, 4072, Australia
| | - Mathew Jk Jones
- The University of Queensland Frazer Institute, Faculty of Medicine, The University of Queensland, Brisbane, QLD, 4102, Australia
- School of Chemistry & Molecular Biosciences, University of Queensland, Brisbane, QLD, 4072, Australia
| | - S Sean Millard
- Faculty of Medicine, School of Biomedical Sciences, University of Queensland, Brisbane, QLD, Australia
| | - Dominic Ch Ng
- Faculty of Medicine, School of Biomedical Sciences, University of Queensland, Brisbane, QLD, Australia
| | - Michele Pagano
- Department of Biochemistry and Molecular Pharmacology, New York University Grossman School of Medicine, New York, NY, 10016, USA
- Perlmutter Cancer Center, New York University Grossman School of Medicine, New York, NY, 10016, USA
- Howard Hughes Medical Institute, New York University Grossman School of Medicine, New York, NY, 10065, USA
| | - Alexis Bonfim-Melo
- The University of Queensland Frazer Institute, Faculty of Medicine, The University of Queensland, Brisbane, QLD, 4102, Australia
| | - Tobias Schneider
- Walter and Eliza Hall Institute of Medical Research, Parkville, VIC, Australia
- Department of Medical Biology, University of Melbourne, Melbourne, VIC, 3068, Australia
| | - David Komander
- Walter and Eliza Hall Institute of Medical Research, Parkville, VIC, Australia
- Department of Medical Biology, University of Melbourne, Melbourne, VIC, 3068, Australia
| | - Michael Lazarou
- Department of Biochemistry and Molecular Biology, Biomedicine Discovery Institute, Monash University, Melbourne, VIC, 3068, Australia
- Department of Medical Biology, University of Melbourne, Melbourne, VIC, 3068, Australia
- Walter and Eliza Hall Institute of Medical Research, Parkville, VIC, Australia
| | - Brett M Collins
- The University of Queensland, Institute for Molecular Bioscience, Brisbane, QLD, 4072, Australia.
| | - Julia K Pagan
- Faculty of Medicine, School of Biomedical Sciences, University of Queensland, Brisbane, QLD, Australia.
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Yamashita SI, Sugiura Y, Matsuoka Y, Maeda R, Inoue K, Furukawa K, Fukuda T, Chan DC, Kanki T. Mitophagy mediated by BNIP3 and NIX protects against ferroptosis by downregulating mitochondrial reactive oxygen species. Cell Death Differ 2024; 31:651-661. [PMID: 38519771 PMCID: PMC11094013 DOI: 10.1038/s41418-024-01280-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2023] [Revised: 03/12/2024] [Accepted: 03/12/2024] [Indexed: 03/25/2024] Open
Abstract
Mitophagy plays an important role in the maintenance of mitochondrial homeostasis and can be categorized into two types: ubiquitin-mediated and receptor-mediated pathways. During receptor-mediated mitophagy, mitophagy receptors facilitate mitophagy by tethering the isolation membrane to mitochondria. Although at least five outer mitochondrial membrane proteins have been identified as mitophagy receptors, their individual contribution and interrelationship remain unclear. Here, we show that HeLa cells lacking BNIP3 and NIX, two of the five receptors, exhibit a complete loss of mitophagy in various conditions. Conversely, cells deficient in the other three receptors show normal mitophagy. Using BNIP3/NIX double knockout (DKO) cells as a model, we reveal that mitophagy deficiency elevates mitochondrial reactive oxygen species (mtROS), which leads to activation of the Nrf2 antioxidant pathway. Notably, BNIP3/NIX DKO cells are highly sensitive to ferroptosis when Nrf2-driven antioxidant enzymes are compromised. Moreover, the sensitivity of BNIP3/NIX DKO cells is fully rescued upon the introduction of wild-type BNIP3 and NIX, but not the mutant forms incapable of facilitating mitophagy. Consequently, our results demonstrate that BNIP3 and NIX-mediated mitophagy plays a role in regulating mtROS levels and protects cells from ferroptosis.
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Affiliation(s)
- Shun-Ichi Yamashita
- Department of Cellular Physiology, Niigata University Graduate School of Medical and Dental Sciences, Niigata, 950-8510, Japan.
| | - Yuki Sugiura
- Center for Cancer Immunotherapy and Immunobiology, Kyoto University Graduate School of Medicine, Kyoto, 606-8501, Japan
| | - Yuta Matsuoka
- Center for Cancer Immunotherapy and Immunobiology, Kyoto University Graduate School of Medicine, Kyoto, 606-8501, Japan
| | - Rae Maeda
- Center for Cancer Immunotherapy and Immunobiology, Kyoto University Graduate School of Medicine, Kyoto, 606-8501, Japan
| | - Keiichi Inoue
- Department of Cellular Physiology, Niigata University Graduate School of Medical and Dental Sciences, Niigata, 950-8510, Japan
| | - Kentaro Furukawa
- Department of Cellular Physiology, Niigata University Graduate School of Medical and Dental Sciences, Niigata, 950-8510, Japan
| | - Tomoyuki Fukuda
- Department of Cellular Physiology, Niigata University Graduate School of Medical and Dental Sciences, Niigata, 950-8510, Japan
| | - David C Chan
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA, 91125, USA
| | - Tomotake Kanki
- Department of Cellular Physiology, Niigata University Graduate School of Medical and Dental Sciences, Niigata, 950-8510, Japan.
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7
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Cao M, Tang Y, Luo Y, Gu F, Zhu Y, Liu X, Yan C, Hu W, Wang S, Chao X, Xu H, Chen HB, Wang L. Natural compounds modulating mitophagy: Implications for cancer therapy. Cancer Lett 2024; 582:216590. [PMID: 38097131 DOI: 10.1016/j.canlet.2023.216590] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2023] [Revised: 11/27/2023] [Accepted: 12/05/2023] [Indexed: 01/04/2024]
Abstract
Cancer is considered as the second leading cause of mortality, and cancer incidence is still growing rapidly worldwide, which poses an increasing global health burden. Although chemotherapy is the most widely used treatment for cancer, its effectiveness is limited by drug resistance and severe side effects. Mitophagy is the principal mechanism that degrades damaged mitochondria via the autophagy/lysosome pathway to maintain mitochondrial homeostasis. Emerging evidence indicates that mitophagy plays crucial roles in tumorigenesis, particularly in cancer therapy. Mitophagy can exhibit dual effects in cancer, with both cancer-inhibiting or cancer-promoting function in a context-dependent manner. A variety of natural compounds have been found to affect cancer cell death and display anticancer properties by modulating mitophagy. In this review, we provide a systematic overview of mitophagy signaling pathways, and examine recent advances in the utilization of natural compounds for cancer therapy through the modulation of mitophagy. Furthermore, we address the inquiries and challenges associated with ongoing investigations concerning the application of natural compounds in cancer therapy based on mitophagy. Overcoming these limitations will provide opportunities to develop novel interventional strategies for cancer treatment.
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Affiliation(s)
- Min Cao
- School of Biomedical Sciences, Hunan University, Changsha, 410082, China; Hunan Key Laboratory of Animal Models and Molecular Medicine, School of Biomedical Sciences, Hunan University, Changsha, 410082, Hunan Province, China
| | - Yancheng Tang
- School of Biomedical Sciences, Hunan University, Changsha, 410082, China; Hunan Key Laboratory of Animal Models and Molecular Medicine, School of Biomedical Sciences, Hunan University, Changsha, 410082, Hunan Province, China; School of Chinese Medicine, Hong Kong Baptist University, Hong Kong SAR, China
| | - Yufei Luo
- School of Biomedical Sciences, Hunan University, Changsha, 410082, China; Hunan Key Laboratory of Animal Models and Molecular Medicine, School of Biomedical Sciences, Hunan University, Changsha, 410082, Hunan Province, China
| | - Fen Gu
- Department of Infection, Hunan Children's Hospital, Changsha, 410007, China
| | - Yuyuan Zhu
- School of Biomedical Sciences, Hunan University, Changsha, 410082, China; Hunan Key Laboratory of Animal Models and Molecular Medicine, School of Biomedical Sciences, Hunan University, Changsha, 410082, Hunan Province, China
| | - Xu Liu
- School of Biomedical Sciences, Hunan University, Changsha, 410082, China; Hunan Key Laboratory of Animal Models and Molecular Medicine, School of Biomedical Sciences, Hunan University, Changsha, 410082, Hunan Province, China
| | - Chenghao Yan
- School of Biomedical Sciences, Hunan University, Changsha, 410082, China; Hunan Key Laboratory of Animal Models and Molecular Medicine, School of Biomedical Sciences, Hunan University, Changsha, 410082, Hunan Province, China
| | - Wei Hu
- Department of Integrated Traditional Chinese and Western Medicine, Xiangya Boai Rehabilitation Hospital, Changsha, 410082, China
| | - Shaogui Wang
- School of Pharmaceutical Sciences, Guangzhou University of Chinese Medicine, Guangzhou, 510006, China
| | - Xiaojuan Chao
- Institute of Precision Medicine, The First Affiliated Hospital, Sun Yat-sen University, Guangzhou, 510080, China
| | - Haodong Xu
- Department of Orthopaedics, The Second Xiangya Hospital, Central South University, Changsha, Hunan, 410011, China
| | - Hu-Biao Chen
- School of Chinese Medicine, Hong Kong Baptist University, Hong Kong SAR, China
| | - Liming Wang
- School of Biomedical Sciences, Hunan University, Changsha, 410082, China; Hunan Key Laboratory of Animal Models and Molecular Medicine, School of Biomedical Sciences, Hunan University, Changsha, 410082, Hunan Province, China; Shenzhen Research Institute, Hunan University, Shenzhen, 518000, China.
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8
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Wei L, Oguz Gok M, Svoboda JD, Forny M, Friedman JR, Niemi NM. PPTC7 limits mitophagy through proximal and dynamic interactions with BNIP3 and NIX. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.01.24.576953. [PMID: 38328188 PMCID: PMC10849627 DOI: 10.1101/2024.01.24.576953] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/09/2024]
Abstract
PPTC7 is a mitochondrial-localized PP2C phosphatase that maintains mitochondrial protein content and metabolic homeostasis. We previously demonstrated that knockout of Pptc7 elevates mitophagy in a BNIP3- and NIX-dependent manner, but the mechanisms by which PPTC7 influences receptor-mediated mitophagy remain ill-defined. Here, we demonstrate that loss of PPTC7 upregulates BNIP3 and NIX post-transcriptionally and independent of HIF-1α stabilization. On a molecular level, loss of PPTC7 prolongs the half-life of BNIP3 and NIX while blunting their accumulation in response to proteasomal inhibition, suggesting that PPTC7 promotes the ubiquitin-mediated turnover of BNIP3 and NIX. Consistently, overexpression of PPTC7 limits the accumulation of BNIP3 and NIX protein levels in response to pseudohypoxia, a well-known inducer of mitophagy. This PPTC7-mediated suppression of BNIP3 and NIX protein expression requires an intact PP2C catalytic motif but is surprisingly independent of its mitochondrial targeting, indicating that PPTC7 influences mitophagy outside of the mitochondrial matrix. We find that PPTC7 exists in at least two distinct states in cells: a longer isoform, which likely represents full length protein, and a shorter isoform, which likely represents an imported, matrix-localized phosphatase pool. Importantly, anchoring PPTC7 to the outer mitochondrial membrane is sufficient to blunt BNIP3 and NIX accumulation, and proximity labeling and fluorescence co-localization experiments suggest that PPTC7 associates with BNIP3 and NIX within the native cellular environment. Importantly, these associations are enhanced in cellular conditions that promote BNIP3 and NIX turnover, demonstrating that PPTC7 is dynamically recruited to BNIP3 and NIX to facilitate their degradation. Collectively, these data reveal that a fraction of PPTC7 dynamically localizes to the outer mitochondrial membrane to promote the proteasomal turnover of BNIP3 and NIX.
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Affiliation(s)
- Lianjie Wei
- Department of Biochemistry & Molecular Biophysics, Washington University School of Medicine in St. Louis, St. Louis, MO, 63110, USA
| | - Mehmet Oguz Gok
- Department of Cell Biology, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA
| | - Jordyn D. Svoboda
- Department of Biochemistry & Molecular Biophysics, Washington University School of Medicine in St. Louis, St. Louis, MO, 63110, USA
| | - Merima Forny
- Department of Biochemistry & Molecular Biophysics, Washington University School of Medicine in St. Louis, St. Louis, MO, 63110, USA
| | - Jonathan R. Friedman
- Department of Cell Biology, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA
| | - Natalie M. Niemi
- Department of Biochemistry & Molecular Biophysics, Washington University School of Medicine in St. Louis, St. Louis, MO, 63110, USA
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