bims-mitdyn Biomed News
on Mitochondrial dynamics: mechanisms
Issue of 2022‒06‒05
nine papers selected by
Edmond Chan
Queen’s University, School of Medicine

  1. J Clin Invest. 2022 Jun 02. pii: e149906. [Epub ahead of print]
      Mitochondrial proteostasis, regulated by the mitochondrial unfolded protein response (UPRmt), is crucial for maintenance of cellular functions and survival. Elevated oxidative and proteotoxic stress in mitochondria must be attenuated by the activation of ubiquitous UPRmt to promote prostate cancer (PCa) growth. Here we show that the two key components of the UPRmt, heat shock protein 60 (HSP60, a mitochondrial chaperonin) and caseinolytic protease (ClpP, a mitochondrial protease) were required for the development of advanced PCa. HSP60 regulated ClpP expression via c-Myc and physically interacted with ClpP to restore mitochondrial functions promoting cancer cell survival. HSP60 maintained the ATP-producing functions of mitochondria, which activated β-catenin pathway leading to the upregulation of c-Myc. We identified an UPRmt inhibitor that blocked HSP60 interaction with ClpP and abrogated survival signaling without altering HSP60 chaperonin function. Disruption of HSP60-ClpP interaction by UPRmt inhibitor triggered metabolic stress and impeded PCa promoting signaling. Treatment with UPRmt inhibitor, or genetic ablation of Hsp60, inhibited PCa growth and progression. Together, our findings identify that HSP60-ClpP mediated UPRmt is essential for prostate tumorigenesis and HSP60-ClpP interaction represents a therapeutic vulnerability in PCa.
    Keywords:  Cell Biology; Cell stress; Mitochondria; Oncology; Prostate cancer
  2. Nat Commun. 2022 Jun 02. 13(1): 3084
      Mitochondrial protein import in the parasitic protozoan Trypanosoma brucei is mediated by the atypical outer membrane translocase, ATOM. It consists of seven subunits including ATOM69, the import receptor for hydrophobic proteins. Ablation of ATOM69, but not of any other subunit, triggers a unique quality control pathway resulting in the proteasomal degradation of non-imported mitochondrial proteins. The process requires a protein of unknown function, an E3 ubiquitin ligase and the ubiquitin-like protein (TbUbL1), which all are recruited to the mitochondrion upon ATOM69 depletion. TbUbL1 is a nuclear protein, a fraction of which is released to the cytosol upon triggering of the pathway. Nuclear release is essential as cytosolic TbUbL1 can bind mislocalised mitochondrial proteins and likely transfers them to the proteasome. Mitochondrial quality control has previously been studied in yeast and metazoans. Finding such a pathway in the highly diverged trypanosomes suggests such pathways are an obligate feature of all eukaryotes.
  3. Cell Rep. 2022 May 31. pii: S2211-1247(22)00645-3. [Epub ahead of print]39(9): 110870
      Overcoming resistance to chemotherapies remains a major unmet need for cancers, such as triple-negative breast cancer (TNBC). Therefore, mechanistic studies to provide insight for drug development are urgently needed to overcome TNBC therapy resistance. Recently, an important role of fatty acid β-oxidation (FAO) in chemoresistance has been shown. But how FAO might mitigate tumor cell apoptosis by chemotherapy is unclear. Here, we show that elevated FAO activates STAT3 by acetylation via elevated acetyl-coenzyme A (CoA). Acetylated STAT3 upregulates expression of long-chain acyl-CoA synthetase 4 (ACSL4), resulting in increased phospholipid synthesis. Elevating phospholipids in mitochondrial membranes leads to heightened mitochondrial integrity, which in turn overcomes chemotherapy-induced tumor cell apoptosis. Conversely, in both cultured tumor cells and xenograft tumors, enhanced cancer cell apoptosis by inhibiting ASCL4 or specifically targeting acetylated-STAT3 is associated with a reduction in phospholipids within mitochondrial membranes. This study demonstrates a critical mechanism underlying tumor cell chemoresistance.
    Keywords:  ACSL; CP: Cancer; CP: Metabolism; STAT3 acetylation; anti-apoptosis; chemoresistance; fatty acid oxidation; mitochondrial membrane potential; phospholipids
  4. Nat Cell Biol. 2022 Jun 02.
      The distinct activities of organelles depend on the proper function of their membranes. Coordinated membrane biogenesis of different organelles necessitates lipid transport from their site of synthesis to their destination. Several factors have been proposed to participate in lipid distribution, but despite its basic importance, in vivo evidence linking the absence of putative transport pathways to specific transport defects remains scarce. A reason for this scarcity is the near absence of in vivo lipid trafficking assays. Here we introduce a versatile method named METALIC (Mass tagging-Enabled TrAcking of Lipids In Cells) to track interorganelle lipid flux inside cells. In this strategy, two enzymes, one directed to a 'donor' and the other to an 'acceptor' organelle, add two distinct mass tags to lipids. Mass-spectrometry-based detection of lipids bearing the two mass tags is then used to quantify exchange between the two organelles. By applying this approach, we show that the ERMES and Vps13-Mcp1 complexes have transport activity in vivo, and unravel their relative contributions to endoplasmic reticulum-mitochondria lipid exchange.
  5. Biochim Biophys Acta Mol Basis Dis. 2022 May 26. pii: S0925-4439(22)00123-5. [Epub ahead of print] 166453
      Fanconi anemia (FA) is the most common inherited bone marrow failure syndrome. The FA proteins have functions in genome maintenance and in the cytoplasmic process of selective autophagy, beyond their canonical roles of repairing DNA interstrand cross-links. FA core complex proteins FANCC, FANCF, FANCL, FANCA, FANCD2, BRCA1 and BRCA2, which previously had no known direct functions outside the nucleus, have recently been implicated in mitophagy. Although mutations in FANCL account for only a very small number of cases in FA families, it plays a key role in the FA pathophysiology and might drive carcinogenesis. Here, we demonstrate that FANCL protein is present in mitochondria in the control and Oligomycin and Antimycin (OA)-treated cells and its ubiquitin ligase activity is not required for its localization to mitochondria. CRISPR/Cas9-mediated knockout of FANCL in HeLa cells overexpressing parkin results in increased sensitivity to mitochondrial stress and defective clearing of damaged mitochondria upon OA treatment. This defect was reversed by the reintroduction of either wild-type FANCL or FANCL(C307A), a mutant lacking ubiquitin ligase activity. To summarize, FANCL protects from mitochondrial stress and supports Parkin-mediated mitophagy in a ubiquitin ligase-independent manner.
    Keywords:  FANCL; Fanconi anemia; Mitophagy; Parkin; Ubiquitin ligase
  6. Front Cell Dev Biol. 2022 ;10 868465
      Mitochondrial repair is essential to metabolic homeostasis. Outer mitochondrial membrane mitofusin (MFN) proteins orchestrate mitochondrial fusion that opposes mitochondrial degeneration caused by senescence. Depending upon physiological context, MFN2 can either mediate mitochondrial fusion or recruit cytosolic Parkin to initiate mitophagic elimination. Because it is not clear how these events are counter-regulated we engineered and expressed MFN2 mutants that mimic phosphorylated or non-phosphorylatable MFN2 at its PINK1 phosphorylation sites: T111, S378, and S442. By interrogating mitochondrial fusion, polarization status, and Parkin binding/mitophagy as a function of inferred MFN2 phosphorylation, we discovered that individual MFN2 phosphorylation events act as a biological "bar-code", directing mitochondrial fate based on phosphorylation site state. Experiments in Pink1 deficient cells supported a central role for PINK1 kinase as the pivotal regulator of MFN2 functionality. Contrary to popular wisdom that Parkin-mediated ubiquitination regulates MFN-mediated mitochondrial fusion, results in Prkn null cells demonstrated the dispensability of Parkin for MFN2 inactivation. These data demonstrate that PINK1-mediated phosphorylation is necessary and sufficient, and that Parkin is expendable, to switch MFN2 from fusion protein to mitophagy effector.
    Keywords:  MFN2; PINK1 kinase; Parkin; fusion; mitochondrial quality control; mitofusin regulation; phosphorylation
  7. Cell Mol Life Sci. 2022 May 30. 79(6): 327
      The architecture of mitochondria adapts to physiological contexts: while mitochondrial fragmentation is usually associated to quality control and cell death, mitochondrial elongation often enhances cell survival during stress. Understanding how these events are regulated is important to elucidate how mitochondrial dynamics control cell fate. Here, we show that the tyrosine kinase Src regulates mitochondrial morphology. Deletion of Src increased mitochondrial size and reduced cellular respiration independently of mitochondrial mass, mitochondrial membrane potential or ATP levels. Re-expression of Src targeted to the mitochondrial matrix, but not of Src targeted to the plasma membrane, rescued mitochondrial morphology in a kinase activity-dependent manner. These findings highlight a novel function for Src in the control of mitochondrial dynamics.
    Keywords:  Cellular respiration; Mitochondria-shaping protein; Mitochondrial dynamics; Oxidative phosphorylation
  8. IUBMB Life. 2022 May 30.
      Mitochondrial E3 ubiquitin ligase (MUL1) is a mitochondrial outer membrane-anchored protein-containing transmembrane domains in both its N- and C-terminal regions, where both are exposed to the cytosol. Interestingly the C-terminal region has a RING finger domain responsible for its E3 ligase activity, as ubiquitin or in SUMOylation, interacting with proteins related to mitochondrial fusion and fission, cell survival, and tumor suppressor proteins, such as Akt. Therefore, MUL1 is involved in various cellular processes, such as mitochondrial dynamics, inter-organelle communication, proliferation, mitophagy, immune response, inflammation and cell apoptosis. MUL1 is expressed at a higher basal level in the heart, immune system organs, and blood. Here, we discuss the role of MUL1 in mitochondrial dynamics and its function in various pathological models, both in vitro and in vivo. In this context, we describe the role of MUL1 in: (1) the inflammatory response, by regulating NF-κB activity, (2) cancer, by promoting cell death and regulating exonuclear function of proteins, such as p53 (3) neurological diseases, by maintaining communication with other organelles and interacting with proteins to eliminate damaged organelles and (4) cardiovascular diseases, by maintaining mitochondrial fusion/fission homeostasis. In this review, we summarize the latest advances in the physiological and pathological functions of MUL1. We also describe the different substrates of MUL1, acting as a positive or negative regulator in various pathologies associated with mitochondrial dysfunction. In conclusion, MUL1 could be a potential key target for the development of therapies that focus on ensuring the functionality of the mitochondrial network and, furthermore, the quality control of intracellular components by synchronously modulating the activity of different cellular mechanisms involved in the aforementioned pathologies. This, in turn, will guide the development of targeted therapies. This article is protected by copyright. All rights reserved.
    Keywords:  Akt; C1orf166; FLJ12875; GIDE; MAPL; MULAN; Mitochondrial E3 ubiquitin ligase 1; RNF218; cell death; inflammation; mitochondria morphology
  9. STAR Protoc. 2022 Jun 17. 3(2): 101359
      Many aspects of mitochondrial gene expression are still unknown, which can be attributed to limitations in molecular tools. Here, we present a protocol to introduce reporter genes into the mitochondrial genome of budding yeast, Saccharomyces cerevisiae. Mitochondrially encoded reporter constructs can be used to interrogate various aspects of mitochondrial gene expression. The power of this technique is exemplified by a mitochondrially encoded nanoluciferase, which allows to monitor levels of mitochondrial translation under a variety of growth conditions.
    Keywords:  Cell Biology; Genetics; Model Organisms; Molecular Biology