51
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Characterization of the mitochondrial localization of the nuclear receptor SHP and regulation of its subcellular distribution by interaction with Bcl2 and HNF4α. PLoS One 2013; 8:e68491. [PMID: 23874642 PMCID: PMC3706418 DOI: 10.1371/journal.pone.0068491] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2013] [Accepted: 05/29/2013] [Indexed: 12/20/2022] Open
Abstract
The nuclear receptor small heterodimer partner SHP was shown recently to translocate to the mitochondria, interact with Bcl2, and induce apoptosis in liver cancer cells. However, the exact mitochondrial localization of SHP remains to be determined. In addition, the detailed interaction domains between SHP and Bcl2 have not been characterized. Using biochemistry and molecular biology approaches, we demonstrate that SHP is localized to the mitochondrial outer membrane. Interestingly, compared with the full-length SHP, the N-terminal deleted protein exhibits increased expression in the mitochondria and decreased expression in the nucleus. GST pull-down assays demonstrate that the interaction domain of SHP shows the strongest interaction with Bcl2. Furthermore, the interaction of Bcl2 with SHP is completely abolished by deletion of the Bcl2 transmembrane domain (TM), whereas deletion of the Bcl2 BH1 domain enhances the interaction. As expected, AHPN, a synthetic SHP ligand, markedly augments the direct protein-protein interaction between Bcl2 and SHP. Ectopic expression of hepatocyte nuclear factor 4 alpha (HNF4α) results in exclusive nuclear translocation of SHP proteins that contain either the full-length or the N-terminal domain, but has a minimal effect on the subcellular distribution of SHP protein containing only the interaction domain or repression domain. These results indicate that the N-terminal domain of SHP is important for itsnuclear translocation via HNF4α. Overall, this study provides novel insights into the domains of SHP that are critical for its shutting between different subcellular compartments.
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52
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Saita S, Shirane M, Nakayama KI. Selective escape of proteins from the mitochondria during mitophagy. Nat Commun 2013; 4:1410. [PMID: 23361001 DOI: 10.1038/ncomms2400] [Citation(s) in RCA: 106] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2012] [Accepted: 12/17/2012] [Indexed: 12/22/2022] Open
Abstract
Mitophagy refers to the degradation of mitochondria by the autophagy system that is regulated by Parkin and PINK1, mutations in the genes for which have been linked to Parkinson's disease. Here we show that certain mitochondrial outer membrane proteins, including FKBP38 and Bcl-2, translocate from the mitochondria to the endoplasmic reticulum (ER) during mitophagy, thereby escaping degradation by autophagosomes. This translocation depends on the ubiquitylation activity of Parkin and on microtubule polymerization. Photoconversion analysis confirmed that FKBP38 detected at the ER during mitophagy indeed represents preexisting protein transported from the mitochondria. The escape of FKBP38 and Bcl-2 from the mitochondria is determined by the number of basic amino acids in their COOH-terminal signal sequences. Furthermore, the translocation of FKBP38 is essential for the suppression of apoptosis during mitophagy. Our results thus show that not all mitochondrial proteins are degraded during mitophagy, with some proteins being evacuated to the ER to prevent unwanted apoptosis.
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Affiliation(s)
- Shotaro Saita
- Department of Molecular and Cellular Biology, Medical Institute of Bioregulation, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka, Fukuoka 812-8582, Japan
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53
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Echeverry N, Bachmann D, Ke F, Strasser A, Simon HU, Kaufmann T. Intracellular localization of the BCL-2 family member BOK and functional implications. Cell Death Differ 2013; 20:785-99. [PMID: 23429263 PMCID: PMC3647236 DOI: 10.1038/cdd.2013.10] [Citation(s) in RCA: 96] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
The pro-apoptotic BCL-2 family member BOK is widely expressed and resembles the multi-BH domain proteins BAX and BAK based on its amino acid sequence. The genomic region encoding BOK was reported to be frequently deleted in human cancer and it has therefore been hypothesized that BOK functions as a tumor suppressor. However, little is known about the molecular functions of BOK. We show that enforced expression of BOK activates the intrinsic (mitochondrial) apoptotic pathway in BAX/BAK-proficient cells but fails to kill cells lacking both BAX and BAK or sensitize them to cytotoxic insults. Interestingly, major portions of endogenous BOK are localized to and partially inserted into the membranes of the Golgi apparatus as well as the endoplasmic reticulum (ER) and associated membranes. The C-terminal transmembrane domain of BOK thereby constitutes a 'tail-anchor' specific for targeting to the Golgi and ER. Overexpression of full-length BOK causes early fragmentation of ER and Golgi compartments. A role for BOK on the Golgi apparatus and the ER is supported by an abnormal response of Bok-deficient cells to the Golgi/ER stressor brefeldin A. Based on these results, we propose that major functions of BOK are exerted at the Golgi and ER membranes and that BOK induces apoptosis in a manner dependent on BAX and BAK.
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Affiliation(s)
- N Echeverry
- Institute of Pharmacology, University of Bern, Bern, Switzerland
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54
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Compartmentalized Ras signaling differentially contributes to phenotypic outputs. Cell Signal 2013; 25:1748-53. [PMID: 23707528 PMCID: PMC3776226 DOI: 10.1016/j.cellsig.2013.05.004] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2013] [Accepted: 05/07/2013] [Indexed: 12/30/2022]
Abstract
Ras isoforms are membrane bound proteins that differentially localize to the plasma membrane and subcellular compartments within the cell. Whilst the cell surface is the main site for Ras activity the extent to which intracellular pools contribute to Ras function is debated. We have generated Ras chimeras targeting Ras to the ER, Golgi, mitochondria and endosomes to compare the capacity of each of these locations to support activity equivalent to normal Ras function. We find that all locations are capable of regulating the MAP kinase and Akt pathways. Furthermore, whilst endomembranous Ras pools show location-specific competence to support proliferation and transformation, Golgi-Ras is as potent as N-Ras.
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55
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Uversky VN. The most important thing is the tail: multitudinous functionalities of intrinsically disordered protein termini. FEBS Lett 2013; 587:1891-901. [PMID: 23665034 DOI: 10.1016/j.febslet.2013.04.042] [Citation(s) in RCA: 105] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2013] [Revised: 04/24/2013] [Accepted: 04/29/2013] [Indexed: 01/29/2023]
Abstract
Many functional proteins do not have well-folded structures in their substantial parts, representing hybrids that possess both ordered and disordered regions. Disorder is unevenly distributed within these hybrid proteins and is typically more common at protein termini. Disordered tails are engaged in a wide range of functions, some of which are unique for termini and cannot be found in other disordered parts of a protein. This review covers some of the key functions of disordered protein termini and emphasizes that these tails are not simple flexible protrusions but are evolved to serve.
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Affiliation(s)
- Vladimir N Uversky
- Department of Molecular Medicine, USF Health Byrd Alzheimer's Research Institute, Morsani College of Medicine, University of South Florida, Tampa, FL 33612, USA.
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56
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Takagi C, Sakamaki K, Morita H, Hara Y, Suzuki M, Kinoshita N, Ueno N. Transgenic Xenopus laevis for live imaging in cell and developmental biology. Dev Growth Differ 2013; 55:422-33. [PMID: 23480392 DOI: 10.1111/dgd.12042] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2012] [Revised: 01/08/2013] [Accepted: 01/08/2013] [Indexed: 01/28/2023]
Abstract
The stable transgenesis of genes encoding functional or spatially localized proteins, fused to fluorescent proteins such as green fluorescent protein (GFP) or red fluorescent protein (RFP), is an extremely important research tool in cell and developmental biology. Transgenic organisms constructed with fluorescent labels for cell membranes, subcellular organelles, and functional proteins have been used to investigate cell cycles, lineages, shapes, and polarity, in live animals and in cells or tissues derived from these animals. Genes of interest have been integrated and maintained in generations of transgenic animals, which have become a valuable resource for the cell and developmental biology communities. Although the use of Xenopus laevis as a transgenic model organism has been hampered by its relatively long reproduction time (compared to Drosophila melanogaster and Caenorhabditis elegans), its large embryonic cells and the ease of manipulation in early embryos have made it a historically valuable preparation that continues to have tremendous research potential. Here, we report on the Xenopus laevis transgenic lines our lab has generated and discuss their potential use in biological imaging.
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Affiliation(s)
- Chiyo Takagi
- National Institute for Basic Biology, 38 Nishigonaka, Myodaiji, Okazaki, 444-8585, Japan
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57
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Yagita Y, Hiromasa T, Fujiki Y. Tail-anchored PEX26 targets peroxisomes via a PEX19-dependent and TRC40-independent class I pathway. ACTA ACUST UNITED AC 2013; 200:651-66. [PMID: 23460677 PMCID: PMC3587837 DOI: 10.1083/jcb.201211077] [Citation(s) in RCA: 75] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Tail-anchored (TA) proteins are anchored into cellular membranes by a single transmembrane domain (TMD) close to the C terminus. Although the targeting of TA proteins to peroxisomes is dependent on PEX19, the mechanistic details of PEX19-dependent targeting and the signal that directs TA proteins to peroxisomes have remained elusive, particularly in mammals. The present study shows that PEX19 formed a complex with the peroxisomal TA protein PEX26 in the cytosol and translocated it directly to peroxisomes by interacting with the peroxisomal membrane protein PEX3. Unlike in yeast, the adenosine triphosphatase TRC40, which delivers TA proteins to the endoplasmic reticulum, was dispensable for the peroxisomal targeting of PEX26. Moreover, the basic amino acids within the luminal domain of PEX26 were essential for binding to PEX19 and thereby for peroxisomal targeting. Finally, our results suggest that a TMD that escapes capture by TRC40 and is followed by a highly basic luminal domain directs TA proteins to peroxisomes via the PEX19-dependent route.
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Affiliation(s)
- Yuichi Yagita
- Graduate School of Systems Life Sciences, Faculty of Sciences, Kyushu University, Higashi-ku, Fukuoka, Japan
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58
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Taguchi A, Takii M, Motoishi M, Orii H, Mochii M, Watanabe K. Analysis of localization and reorganization of germ plasm in Xenopus transgenic line with fluorescence-labeled mitochondria. Dev Growth Differ 2013; 54:767-76. [PMID: 23067138 DOI: 10.1111/dgd.12005] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Germ plasm is found in germ-line cells of Xenopus and thought to include the determinant of primordial germ cells (PGCs). As mitochondria is abundant in germ plasm, vital staining of mitochondria was used to analyze the movement and function of germ plasm; however, its application was limited in early cleavage embryos. We made transgenic Xenopus, harboring enhanced green fluorescent protein (EGFP) fused to the mitochondria transport signal (Dria-line). Germ plasm with EGFP-labeled mitochondria was clearly distinguishable from the other cytoplasm, and retained mostly during one generation of germ-line cells in Dria-line females. Using the Dria-line, we show that germ plasm is reorganized from near the cell membrane to the perinuclear space at St. 9, dependent on the microtubule system.
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Affiliation(s)
- Ayaka Taguchi
- Department of Life Science, Graduate School of Life Science, University of Hyogo, 3-2-1 Koto, Kamigori, Akou-gun, Hyogo, 678-1297, Japan
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59
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Terasaki K, Won S, Makino S. The C-terminal region of Rift Valley fever virus NSm protein targets the protein to the mitochondrial outer membrane and exerts antiapoptotic function. J Virol 2013; 87:676-82. [PMID: 23097454 PMCID: PMC3536385 DOI: 10.1128/jvi.02192-12] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2012] [Accepted: 10/18/2012] [Indexed: 11/20/2022] Open
Abstract
The NSm nonstructural protein of Rift Valley fever virus (family Bunyaviridae, genus Phlebovirus) has an antiapoptotic function and affects viral pathogenesis. We found that NSm integrates into the mitochondrial outer membrane and that the protein's N terminus is exposed to the cytoplasm. The C-terminal region of NSm, which contains a basic amino acid cluster and a putative transmembrane domain, targeted the protein to the mitochondrial outer membrane and exerted antiapoptotic function.
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Affiliation(s)
| | | | - Shinji Makino
- Department of Microbiology and Immunology
- Center for Biodefense and Emerging Infectious Diseases
- UTMB Center for Tropical Diseases
- Sealy Center for Vaccine Development, The University of Texas Medical Branch, Galveston, Texas, USA
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60
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Tada H, Mochii M, Orii H, Watanabe K. Ectopic formation of primordial germ cells by transplantation of the germ plasm: direct evidence for germ cell determinant in Xenopus. Dev Biol 2012; 371:86-93. [PMID: 23046626 DOI: 10.1016/j.ydbio.2012.08.014] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2012] [Revised: 08/13/2012] [Accepted: 08/19/2012] [Indexed: 11/24/2022]
Abstract
In many animals, the germ line is specified by a distinct cytoplasmic structure called germ plasm (GP). GP is necessary for primordial germ cell (PGC) formation in anuran amphibians including Xenopus. However, it is unclear whether GP is a direct germ cell determinant in vertebrates. Here we demonstrate that GP acts autonomously for germ cell formation in Xenopus. EGFP-labeled GP from the vegetal pole was transplanted into animal hemisphere of recipient embryos. Cells carrying transplanted GP (T-GP) at the ectopic position showed characteristics similar to the endogenous normal PGCs in subcellular distribution of GP and presence of germ plasm specific molecules. However, T-GP-carrying-cells in the ectopic tissue did not migrate towards the genital ridge. T-GP-carrying cells from gastrula or tailbud embryos were transferred into the endoderm of wild-type hosts. From there, they migrated into the developing gonad. To clarify whether ectopic T-GP-carrying cells can produce functional germ cells, they were identified by changing the recipients, from the wild-type Xenopus to transgenic Xenopus expressing DsRed2. After transferring T-GP carrying cells labeled genetically with DsRed2 into wild-type hosts, we could find chimeric gonads in mature hosts. Furthermore, the spermatozoa and eggs derived from T-GP-carrying cells were fertile. Thus, we have demonstrated that Xenopus germ plasm is sufficient for germ cell determination.
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Affiliation(s)
- Haru Tada
- Graduate School of Life Science, University of Hyogo, 3-2-1 Koto, Kamigori, Akou-gun, Hyogo 678-1297, Japan
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61
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Krumpe K, Frumkin I, Herzig Y, Rimon N, Özbalci C, Brügger B, Rapaport D, Schuldiner M. Ergosterol content specifies targeting of tail-anchored proteins to mitochondrial outer membranes. Mol Biol Cell 2012; 23:3927-35. [PMID: 22918956 PMCID: PMC3469509 DOI: 10.1091/mbc.e11-12-0994] [Citation(s) in RCA: 104] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Mitochondrial outer membrane tail-anchored proteins are a unique class of membrane proteins with unknown targeting mechanism. Using two high-throughput microscopy screens, we demonstrate that the inherent differences in membrane composition between organelle membranes is enough to determine membrane integration specificity in a living cell. Tail-anchored (TA) proteins have a single C-terminal transmembrane domain, making their biogenesis dependent on posttranslational translocation. Despite their importance, no dedicated insertion machinery has been uncovered for mitochondrial outer membrane (MOM) TA proteins. To decipher the molecular mechanisms guiding MOM TA protein insertion, we performed two independent systematic microscopic screens in which we visualized the localization of model MOM TA proteins on the background of mutants in all yeast genes. We could find no mutant in which insertion was completely blocked. However, both screens demonstrated that MOM TA proteins were partially localized to the endoplasmic reticulum (ER) in ∆spf1 cells. Spf1, an ER ATPase with unknown function, is the first protein shown to affect MOM TA protein insertion. We found that ER membranes in ∆spf1 cells become similar in their ergosterol content to mitochondrial membranes. Indeed, when we visualized MOM TA protein distribution in yeast strains with reduced ergosterol content, they phenocopied the loss of Spf1. We therefore suggest that the inherent differences in membrane composition between organelle membranes are sufficient to determine membrane integration specificity in a eukaryotic cell.
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Affiliation(s)
- Katrin Krumpe
- Interfaculty Institute of Biochemistry, University of Tübingen, 72076 Tübingen, Germany
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62
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Ferrer PE, Frederick P, Gulbis JM, Dewson G, Kluck RM. Translocation of a Bak C-terminus mutant from cytosol to mitochondria to mediate cytochrome C release: implications for Bak and Bax apoptotic function. PLoS One 2012; 7:e31510. [PMID: 22442658 PMCID: PMC3307716 DOI: 10.1371/journal.pone.0031510] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2011] [Accepted: 01/11/2012] [Indexed: 11/19/2022] Open
Abstract
BACKGROUND One of two proapoptotic Bcl-2 proteins, Bak or Bax, is required to permeabilize the mitochondrial outer membrane during apoptosis. While Bax is mostly cytosolic and translocates to mitochondria following an apoptotic stimulus, Bak is constitutively integrated within the outer membrane. Membrane anchorage occurs via a C-terminal transmembrane domain that has been studied in Bax but not in Bak, therefore what governs their distinct subcellular distribution is uncertain. In addition, whether the distinct subcellular distributions of Bak and Bax contributes to their differential regulation during apoptosis remains unclear. METHODOLOGY/PRINCIPAL FINDINGS To gain insight into Bak and Bax targeting to mitochondria, elements of the Bak C-terminus were mutated, or swapped with those of Bax. Truncation of the C-terminal six residues (C-segment) or substitution of three basic residues within the C-segment destabilized Bak. Replacing the Bak C-segment with that from Bax rescued stability and function, but unexpectedly resulted in a semi-cytosolic protein, termed Bak/BaxCS. When in the cytosol, both Bax and Bak/BaxCS sequestered their hydrophobic transmembrane domains in their hydrophobic surface groove. Upon apoptotic signalling, Bak/BaxCS translocated to the mitochondrial outer membrane, inserted its transmembrane domain, oligomerized, and released cytochrome c. Despite this Bax-like subcellular distribution, Bak/BaxCS retained Bak-like regulation following targeting of Mcl-1. CONCLUSIONS/SIGNIFICANCE Residues in the C-segment of Bak and of Bax contribute to their distinct subcellular localizations. That a semi-cytosolic form of Bak, Bak/BaxCS, could translocate to mitochondria and release cytochrome c indicates that Bak and Bax share a conserved mode of activation. In addition, the differential regulation of Bak and Bax by Mcl-1 is predominantly independent of the initial subcellular localizations of Bak and Bax.
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Affiliation(s)
- Pedro Eitz Ferrer
- The Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria, Australia
| | - Paul Frederick
- The Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria, Australia
| | - Jacqueline M. Gulbis
- The Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria, Australia
- Department of Medical Biology, The University of Melbourne, Parkville, Victoria, Australia
| | - Grant Dewson
- The Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria, Australia
- Department of Medical Biology, The University of Melbourne, Parkville, Victoria, Australia
| | - Ruth M. Kluck
- The Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria, Australia
- Department of Medical Biology, The University of Melbourne, Parkville, Victoria, Australia
- * E-mail:
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63
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Wilfling F, Weber A, Potthoff S, Vögtle FN, Meisinger C, Paschen SA, Häcker G. BH3-only proteins are tail-anchored in the outer mitochondrial membrane and can initiate the activation of Bax. Cell Death Differ 2012; 19:1328-36. [PMID: 22343714 DOI: 10.1038/cdd.2012.9] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
During mitochondrial apoptosis, pro-apoptotic BH3-only proteins cause the translocation of cytosolic Bcl-2-associated X protein (Bax) to the outer mitochondrial membrane (OMM) where it is activated to release cytochrome c from the mitochondrial intermembrane space, but the mechanism is under dispute. We show that most BH3-only proteins are mitochondrial proteins that are imported into the OMM via a C-terminal tail-anchor domain in isolated yeast mitochondria, independently of binding to anti-apoptotic Bcl-2 proteins. This C-terminal domain acted as a classical mitochondrial targeting signal and was sufficient to direct green fluorescent protein to mitochondria in human cells. When expressed in mouse fibroblasts, these BH3-only proteins localised to mitochondria and were inserted in the OMM. The BH3-only proteins Bcl-2-interacting mediator of cell death (Bim), tBid and p53-upregulated modulator of apoptosis sensitised isolated mitochondria from Bax/Bcl-2 homologous antagonist/killer-deficient fibroblasts to cytochrome c-release by recombinant, extramitochondrial Bax. For Bim, this activity is shown to require the C-terminal-targeting signal and to be independent of binding capacity to and presence of anti-apoptotic Bcl-2 proteins. Bim further enhanced Bax-dependent killing in yeast. A model is proposed where OMM-tail-anchored BH3-only proteins permit passive 'recruitment' and catalysis-like activation of extra-mitochondrial Bax. The recognition of C-terminal membrane-insertion of BH3-only proteins will permit the development of a more detailed concept of the initiation of mitochondrial apoptosis.
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Affiliation(s)
- F Wilfling
- Institute of Medical Microbiology, Technische Universität München, Germany
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64
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Membrane integration of a mitochondrial signal-anchored protein does not require additional proteinaceous factors. Biochem J 2012; 442:381-9. [DOI: 10.1042/bj20111363] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
The MOM (mitochondrial outer membrane) contains SA (signal-anchored) proteins that bear at their N-terminus a single hydrophobic segment that serves as both a mitochondrial targeting signal and an anchor at the membrane. These proteins, like the vast majority of mitochondrial proteins, are encoded in the nucleus and have to be imported into the organelle. Currently, the mechanisms by which they are targeted to and inserted into the OM (outer membrane) are unclear. To shed light on these issues, we employed a recombinant version of the SA protein OM45 and a synthetic peptide corresponding to its signal-anchor segment. Both forms are associated with isolated mitochondria independently of cytosolic factors. Interaction with mitochondria was diminished when a mutated form of the signal-anchor was employed. We demonstrate that the signal-anchor peptide acquires an α-helical structure in a lipid environment and adopted a TM (transmembrane) topology within artificial lipid bilayers. Moreover, the peptide's affinity to artificial membranes with OM-like lipid composition was much higher than that of membranes with ER (endoplasmic reticulum)-like lipid composition. Collectively, our results suggest that SA proteins are specifically inserted into the MOM by a process that is not dependent on additional proteins, but is rather facilitated by the distinct lipid composition of this membrane.
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65
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Williamson CD, DeBiasi RL, Colberg-Poley AM. Viral product trafficking to mitochondria, mechanisms and roles in pathogenesis. Infect Disord Drug Targets 2012; 12:18-37. [PMID: 22034933 PMCID: PMC4435936 DOI: 10.2174/187152612798994948] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2011] [Revised: 04/21/2011] [Accepted: 05/02/2011] [Indexed: 05/31/2023]
Abstract
A wide variety of viruses cause significant morbidity and mortality in humans. However, targeted antiviral therapies have been developed for only a subset of these viruses, with the majority of currently licensed antiviral drugs targeting viral entry, replication or exit steps during the viral life cycle. Due to increasing emergence of antiviral drug resistant viruses, the isolation of multiple viral subtypes, and toxicities of existing therapies, there remains an urgent need for the timely development of novel antiviral agents, including those targeting host factors essential for viral replication. This review summarizes viral products that target mitochondria and their effects on common mitochondria regulated pathways. These viral products and the mitochondrial pathways affected by them provide potential novel targets for the rational design of antiviral drugs. Viral products alter oxidative balance, mitochondrial permeability transition pore, mitochondrial membrane potential, electron transport and energy production. Moreover, viruses may cause the Warburg Effect, in which metabolism is reprogrammed to aerobic glycolysis as the main source of energy. Finally, viral products affect proapoptotic and antiapoptotic signaling, as well as mitochondrial innate immune signaling. Because of their importance for the generation of metabolic intermediates and energy as well as cell survival, mitochondrial pathways are targeted by multiple independent viral products. Structural modifications of existing drugs targeted to mitochondrial pathways may lead to the development of novel antiviral drugs with improved efficacy and reduced toxicity.
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Affiliation(s)
- Chad D. Williamson
- Center for Cancer and Immunology Research, Children’s National Medical Center, 111 Michigan Avenue, NW, Washington, DC 20010
| | - Roberta L. DeBiasi
- Center for Cancer and Immunology Research, Children’s National Medical Center, 111 Michigan Avenue, NW, Washington, DC 20010
- Division of Pediatric Infectious Diseases, Children’s National Medical Center, 111 Michigan Avenue, NW, Washington, DC 20010
- Department of Pediatrics, George Washington University School of Medicine and Health Sciences, Washington DC 20037 Tel. 202-476-3984 FAX 202-476-3929
| | - Anamaris M. Colberg-Poley
- Center for Cancer and Immunology Research, Children’s National Medical Center, 111 Michigan Avenue, NW, Washington, DC 20010
- Department of Pediatrics, George Washington University School of Medicine and Health Sciences, Washington DC 20037 Tel. 202-476-3984 FAX 202-476-3929
- Department of Biochemistry and Molecular Biology, George Washington University School of Medicine and Health Sciences, Washington DC 20037 Tel. 202-476-3984 FAX 202-476-3929
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66
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Lackey SWK, Wideman JG, Kennedy EK, Go NE, Nargang FE. The Neurospora crassa TOB complex: analysis of the topology and function of Tob38 and Tob37. PLoS One 2011; 6:e25650. [PMID: 21980517 PMCID: PMC3182244 DOI: 10.1371/journal.pone.0025650] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2011] [Accepted: 09/07/2011] [Indexed: 11/18/2022] Open
Abstract
The TOB or SAM complex is responsible for assembling several proteins into the mitochondrial outer membrane, including all β-barrel proteins. We have identified several forms of the complex in Neurospora crassa. One form contains Tob55, Tob38, and Tob37; another contains these three subunits plus the Mdm10 protein; while additional complexes contain only Tob55. As previously shown for Tob55, both Tob37 and Tob38 are essential for viability of the organism. Mitochondria deficient in Tob37 or Tob38 have reduced ability to assemble β-barrel proteins. The function of two hydrophobic domains in the C-terminal region of the Tob37 protein was investigated. Mutant Tob37 proteins lacking either or both of these regions are able to restore viability to cells lacking the protein. One of the domains was found to anchor the protein to the outer mitochondrial membrane but was not necessary for targeting or association of the protein with mitochondria. Examination of the import properties of mitochondria containing Tob37 with deletions of the hydrophobic domains reveals that the topology of Tob37 may be important for interactions between specific classes of β-barrel precursors and the TOB complex.
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Affiliation(s)
| | - Jeremy G. Wideman
- Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada
| | - Erin K. Kennedy
- Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada
| | - Nancy E. Go
- Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada
| | - Frank E. Nargang
- Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada
- * E-mail:
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67
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Rada P, Doležal P, Jedelský PL, Bursac D, Perry AJ, Šedinová M, Smíšková K, Novotný M, Beltrán NC, Hrdý I, Lithgow T, Tachezy J. The core components of organelle biogenesis and membrane transport in the hydrogenosomes of Trichomonas vaginalis. PLoS One 2011; 6:e24428. [PMID: 21935410 PMCID: PMC3174187 DOI: 10.1371/journal.pone.0024428] [Citation(s) in RCA: 64] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2011] [Accepted: 08/09/2011] [Indexed: 12/02/2022] Open
Abstract
Trichomonas vaginalis is a parasitic protist of the Excavata group. It contains an anaerobic form of mitochondria called hydrogenosomes, which produce hydrogen and ATP; the majority of mitochondrial pathways and the organellar genome were lost during the mitochondrion-to-hydrogenosome transition. Consequently, all hydrogenosomal proteins are encoded in the nucleus and imported into the organelles. However, little is known about the membrane machineries required for biogenesis of the organelle and metabolite exchange. Using a combination of mass spectrometry, immunofluorescence microscopy, in vitro import assays and reverse genetics, we characterized the membrane proteins of the hydrogenosome. We identified components of the outer membrane (TOM) and inner membrane (TIM) protein translocases include multiple paralogs of the core Tom40-type porins and Tim17/22/23 channel proteins, respectively, and uniquely modified small Tim chaperones. The inner membrane proteins TvTim17/22/23-1 and Pam18 were shown to possess conserved information for targeting to mitochondrial inner membranes, but too divergent in sequence to support the growth of yeast strains lacking Tim17, Tim22, Tim23 or Pam18. Full complementation was seen only when the J-domain of hydrogenosomal Pam18 was fused with N-terminal region and transmembrane segment of the yeast homolog. Candidates for metabolite exchange across the outer membrane were identified including multiple isoforms of the β-barrel proteins, Hmp35 and Hmp36; inner membrane MCF-type metabolite carriers were limited to five homologs of the ATP/ADP carrier, Hmp31. Lastly, hydrogenosomes possess a pathway for the assembly of C-tail-anchored proteins into their outer membrane with several new tail-anchored proteins being identified. These results show that hydrogenosomes and mitochondria share common core membrane components required for protein import and metabolite exchange; however, they also reveal remarkable differences that reflect the functional adaptation of hydrogenosomes to anaerobic conditions and the peculiar evolutionary history of the Excavata group.
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Affiliation(s)
- Petr Rada
- Department of Parasitology, Charles University in Prague, Faculty of Science, Prague, Czech Republic
| | - Pavel Doležal
- Department of Parasitology, Charles University in Prague, Faculty of Science, Prague, Czech Republic
| | - Petr L. Jedelský
- Department of Parasitology, Charles University in Prague, Faculty of Science, Prague, Czech Republic
- Laboratory of Mass Spectrometry, Charles University in Prague, Faculty of Science, Prague, Czech Republic
| | - Dejan Bursac
- Department of Biochemistry & Molecular Biology, Monash University, Melbourne, Australia
| | - Andrew J. Perry
- Department of Biochemistry & Molecular Biology, Monash University, Melbourne, Australia
| | - Miroslava Šedinová
- Department of Parasitology, Charles University in Prague, Faculty of Science, Prague, Czech Republic
| | - Kateřina Smíšková
- Department of Parasitology, Charles University in Prague, Faculty of Science, Prague, Czech Republic
| | - Marian Novotný
- Department of Parasitology, Charles University in Prague, Faculty of Science, Prague, Czech Republic
| | - Neritza Campo Beltrán
- Department of Parasitology, Charles University in Prague, Faculty of Science, Prague, Czech Republic
| | - Ivan Hrdý
- Department of Parasitology, Charles University in Prague, Faculty of Science, Prague, Czech Republic
| | - Trevor Lithgow
- Department of Biochemistry & Molecular Biology, Monash University, Melbourne, Australia
| | - Jan Tachezy
- Department of Parasitology, Charles University in Prague, Faculty of Science, Prague, Czech Republic
- * E-mail:
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68
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Hradsky J, Raghuram V, Reddy PP, Navarro G, Hupe M, Casado V, McCormick PJ, Sharma Y, Kreutz MR, Mikhaylova M. Post-translational membrane insertion of tail-anchored transmembrane EF-hand Ca2+ sensor calneurons requires the TRC40/Asna1 protein chaperone. J Biol Chem 2011; 286:36762-76. [PMID: 21878631 DOI: 10.1074/jbc.m111.280339] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Calneuron-1 and -2 are neuronal EF-hand-type calcium sensor proteins that are prominently targeted to trans-Golgi network membranes and impose a calcium threshold at the Golgi for phosphatidylinositol 4-OH kinase IIIβ activation and the regulated local synthesis of phospholipids that are crucial for TGN-to-plasma membrane trafficking. In this study, we show that calneurons are nonclassical type II tail-anchored proteins that are post-translationally inserted into the endoplasmic reticulum membrane via an association of a 23-amino acid-long transmembrane domain (TMD) with the TRC40/Asna1 chaperone complex. Following trafficking to the Golgi, calneurons are probably retained in the TGN because of the length of the TMD and phosphatidylinositol 4-phosphate lipid binding. Both calneurons rapidly self-associate in vitro and in vivo via their TMD and EF-hand containing the N terminus. Although dimerization and potentially multimerization precludes TRC40/Asna1 binding and thereby membrane insertion, we found no evidence for a cytosolic pool of calneurons and could demonstrate that self-association of calneurons is restricted to membrane-inserted protein. The dimerization properties and the fact that they, unlike every other EF-hand calmodulin-like Ca(2+) sensor, are always associated with membranes of the secretory pathway, including vesicles and plasma membrane, suggests a high degree of spatial segregation for physiological target interactions.
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Affiliation(s)
- Johannes Hradsky
- Research Group Neuroplasticity, Leibniz-Institute for Neurobiology, 39118 Magdeburg, Germany
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69
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Yoshii SR, Kishi C, Ishihara N, Mizushima N. Parkin mediates proteasome-dependent protein degradation and rupture of the outer mitochondrial membrane. J Biol Chem 2011; 286:19630-40. [PMID: 21454557 PMCID: PMC3103342 DOI: 10.1074/jbc.m110.209338] [Citation(s) in RCA: 481] [Impact Index Per Article: 37.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2010] [Revised: 03/15/2011] [Indexed: 01/15/2023] Open
Abstract
Upon mitochondrial depolarization, Parkin, a Parkinson disease-related E3 ubiquitin ligase, translocates from the cytosol to mitochondria and promotes their degradation by mitophagy, a selective type of autophagy. Here, we report that in addition to mitophagy, Parkin mediates proteasome-dependent degradation of outer membrane proteins such as Tom20, Tom40, Tom70, and Omp25 of depolarized mitochondria. By contrast, degradation of the inner membrane and matrix proteins largely depends on mitophagy. Furthermore, Parkin induces rupture of the outer membrane of depolarized mitochondria, which also depends on proteasomal activity. Upon induction of mitochondrial depolarization, proteasomes are recruited to mitochondria in the perinuclear region. Neither proteasome-dependent degradation of outer membrane proteins nor outer membrane rupture is required for mitophagy. These results suggest that Parkin regulates degradation of outer and inner mitochondrial membrane proteins differently through proteasome- and mitophagy-dependent pathways.
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Affiliation(s)
- Saori R. Yoshii
- From the Department of Physiology and Cell Biology, Tokyo Medical and Dental University, Tokyo 113-8519 and
| | - Chieko Kishi
- From the Department of Physiology and Cell Biology, Tokyo Medical and Dental University, Tokyo 113-8519 and
| | - Naotada Ishihara
- From the Department of Physiology and Cell Biology, Tokyo Medical and Dental University, Tokyo 113-8519 and
- the Department of Protein Biochemistry, Institute of Life Science, Kurume University, Kurume 839-0864, Japan
| | - Noboru Mizushima
- From the Department of Physiology and Cell Biology, Tokyo Medical and Dental University, Tokyo 113-8519 and
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70
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Dukanovic J, Rapaport D. Multiple pathways in the integration of proteins into the mitochondrial outer membrane. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2011; 1808:971-80. [DOI: 10.1016/j.bbamem.2010.06.021] [Citation(s) in RCA: 92] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/06/2010] [Revised: 06/22/2010] [Accepted: 06/23/2010] [Indexed: 11/25/2022]
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71
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Borgese N, Fasana E. Targeting pathways of C-tail-anchored proteins. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2011; 1808:937-46. [DOI: 10.1016/j.bbamem.2010.07.010] [Citation(s) in RCA: 145] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/11/2010] [Revised: 07/09/2010] [Accepted: 07/10/2010] [Indexed: 10/19/2022]
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72
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Rosivatz E, Woscholski R. Removal or masking of phosphatidylinositol(4,5)bisphosphate from the outer mitochondrial membrane causes mitochondrial fragmentation. Cell Signal 2011; 23:478-86. [PMID: 21044681 PMCID: PMC3032883 DOI: 10.1016/j.cellsig.2010.10.025] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2010] [Revised: 09/23/2010] [Accepted: 10/26/2010] [Indexed: 12/11/2022]
Abstract
Mitochondria are central players in programmed cell death and autophagy. While phosphoinositides are well established regulators of membrane traffic, cellular signalling and the destiny of certain organelles, their presence and role for mitochondria remain elusive. In this study we show that removal of PtdIns(4,5)P₂ by phosphatases or masking the lipid with PH domains leads to fission of mitochondria and increased autophagy. Induction of general autophagy by amino acid starvation also coincides with the loss of mitochondrial PtdIns(4,5)P₂, suggesting an important role for this lipid in the processes that govern mitophagy. Our findings reveal that PKCα can rescue the removal or masking of PtdIns(4,5)P₂, indicating that the inositol lipid is upstream of PKC.
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Key Words
- ptdins(4,5)p2, phosphatidylinositol(4,5)bisphosphate
- ptdins, phosphatidylinositol
- omm, outer mitochondrial membrane
- imm, inner mitochondrial membrane
- plc, phospholipase c
- pma, 12-o-tetradecanoylphorbol 13-acetate
- pkc, protein kinase c
- ins(1,4,5)p3, inositol 1,4,5-trisphosphate
- dag, 1,2-diacylglycerol
- n.d., not determined
- mitochondria
- autophagy
- phosphatidylinositol(4,5)bisphosphate
- protein kinase c
- ph domain
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Affiliation(s)
| | - Rudiger Woscholski
- The Division of Cell and Molecular Biology, Imperial College London, Exhibition Road, London SW7 2AZ, UK
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73
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Abstract
The L* protein encoded by Theiler's murine encephalomyelitis virus (TMEV) is a unique example of a picornaviral protein encoded by an alternative open reading frame. This protein is an important determinant of TMEV persistence in the mouse central nervous system. We showed that in infected cells, L* is partitioned between the cytosol and the mitochondria. In mitochondria, L* is anchored in the outer membrane and exposed to the cytosol. The targeting of L* to mitochondria is independent of other viral components and likely depends on a conformational signal. L* targeting to mitochondria might involve chaperones of the Hsp70 family, as these proteins are shown to interact.
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74
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Lindsay J, Esposti MD, Gilmore AP. Bcl-2 proteins and mitochondria--specificity in membrane targeting for death. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2010; 1813:532-9. [PMID: 21056595 DOI: 10.1016/j.bbamcr.2010.10.017] [Citation(s) in RCA: 215] [Impact Index Per Article: 15.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/20/2010] [Revised: 10/22/2010] [Accepted: 10/27/2010] [Indexed: 01/10/2023]
Abstract
The localization and control of Bcl-2 proteins on mitochondria is essential for the intrinsic pathway of apoptosis. Anti-apoptotic Bcl-2 proteins reside on the outer mitochondrial membrane (OMM) and prevent apoptosis by inhibiting the activation of the pro-apoptotic family members Bax and Bak. The Bcl-2 subfamily of BH3-only proteins can either inhibit the anti-apoptotic proteins or directly activate Bax or Bak. How these proteins interact with each other, the mitochondrial surface and within the OMM are complex processes we are only beginning to understand. However, these interactions are fundamental for the transduction of apoptotic signals to mitochondria and the subsequent release of caspase activating factors into the cytosol. In this review we will discuss our knowledge of how Bcl-2 proteins are directed to mitochondria in the first place, a crucial but poorly understood aspect of their regulation. This article is part of a Special Issue entitled Mitochondria: the deadly organelle.
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Affiliation(s)
- Jennefer Lindsay
- Wellcome Trust Centre for Cell Matrix Research, Faculty of Life Sciences The University of Manchester, UK.
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75
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Tanaka Y, Mori Y, Tani H, Abe T, Moriishi K, Kojima H, Nagano T, Okabe T, Suzuki T, Tatsumi M, Matsuura Y. Establishment of an indicator cell system for hepatitis C virus. Microbiol Immunol 2010; 54:206-20. [PMID: 20377749 DOI: 10.1111/j.1348-0421.2010.00209.x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Although a cell culture system for HCV JFH-1 strain has been developed, no robust cell culture system for serum-derived HCV is available. In this study, we have established systems capable of monitoring infection with JFH-1 virus based on specific reporter gene expression through proteolysis of chimeric transcription factors by HCV NS3/4A protease. We utilized a transcriptional factor Gal4-TBP that synergistically enhances transcription of the GAL4UAS and HIV-1 LTR tandem promoter with the Tat protein. We constructed chimeric Tat and Gal4-TBP transcription factors containing the HCV NS3/4A cleavage sequence of a mitochondria-resident IPS-1, but not those of the HCV polyprotein, and manipulated them to localize in the ER. Upon infection with JFH-1 virus, the transcription factors were efficiently cleaved by HCV protease, migrated into the nucleus and activated the reporter gene under the tandem promoter. Upon infection with JFH-1 virus, the Huh7OK1/TG-Luc cell line carrying the transcription factors and a luciferase gene under the promoter expressed luciferase in a dose-dependent manner in close correlation with HCV RNA replication. Huh7OK1/TG-LNGFR cells carrying the transcription factors and a cDNA of human low affinity nerve growth factor receptor under the promoter were selectively concentrated by immunomagnetic cell sorting upon infection with JFH-1 virus. These results indicate that the chimeric constructs bearing the ER-resident IPS-1 sequence are specifically recognized and efficiently cleaved by HCV protease and are harnessed for detection of HCV replication and for recovery of HCV-infected cells. This strategy may be applicable for the establishment of cell culture systems for the isolation of serum-derived HCV.
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Affiliation(s)
- Yoshinori Tanaka
- Department of Molecular Virology, Research Institute for Microbial Diseases, Osaka University, Osaka, Japan
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76
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Intracellular sorting signals for sequential trafficking of human cytomegalovirus UL37 proteins to the endoplasmic reticulum and mitochondria. J Virol 2010; 84:6400-9. [PMID: 20410282 DOI: 10.1128/jvi.00556-10] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
Human cytomegalovirus UL37 antiapoptotic proteins, including the predominant UL37 exon 1 protein (pUL37x1), traffic sequentially from the endoplasmic reticulum (ER) through the mitochondrion-associated membrane compartment to the mitochondrial outer membrane (OMM), where they inactivate the proapoptotic activity of Bax. We found that widespread mitochondrial distribution occurs within 1 h of pUL37x1 synthesis. The pUL37x1 mitochondrial targeting signal (MTS) spans its first antiapoptotic domain (residues 5 to 34) and consists of a weak hydrophobicity leader (MTSalpha) and proximal downstream residues (MTSbeta). This MTS arrangement of a hydrophobic leader and downstream proximal basic residues is similar to that of the translocase of the OMM 20, Tom20. We examined whether the UL37 MTS functions analogously to Tom20 leader. Surprisingly, lowered hydropathy of the UL37x1 MTSalpha, predicted to block ER translocation, still allowed dual targeting of mutant to the ER and OMM. However, increased hydropathy of the MTS leader caused exclusion of the UL37x1 high-hydropathy mutant from mitochondrial import. Conversely, UL37 MTSalpha replacement with the Tom20 leader did not retarget pUL37x1 exclusively to the OMM; rather, the UL37x1-Tom20 chimera retained dual trafficking. Moreover, replacement of the UL37 MTSbeta basic residues did not reduce OMM import. Ablation of the MTSalpha posttranslational modification site or of the downstream MTS proline-rich domain (PRD) increased mitochondrial import. Our results suggest that pUL37x1 sequential ER to mitochondrial trafficking requires a weakly hydrophobic leader and is regulated by MTSbeta sequences. Thus, HCMV pUL37x1 uses a mitochondrial importation pathway that is genetically distinguishable from that of known OMM proteins.
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77
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Two Modular Forms of the Mitochondrial Sorting and Assembly Machinery Are Involved in Biogenesis of α-Helical Outer Membrane Proteins. J Mol Biol 2010; 396:540-9. [DOI: 10.1016/j.jmb.2009.12.026] [Citation(s) in RCA: 80] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2009] [Revised: 12/11/2009] [Accepted: 12/13/2009] [Indexed: 11/19/2022]
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78
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Quintero OA, DiVito MM, Adikes RC, Kortan MB, Case LB, Lier AJ, Panaretos NS, Slater SQ, Rengarajan M, Feliu M, Cheney RE. Human Myo19 is a novel myosin that associates with mitochondria. Curr Biol 2009; 19:2008-13. [PMID: 19932026 DOI: 10.1016/j.cub.2009.10.026] [Citation(s) in RCA: 143] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2008] [Revised: 10/01/2009] [Accepted: 10/02/2009] [Indexed: 12/21/2022]
Abstract
Mitochondria are pleomorphic organelles that have central roles in cell physiology. Defects in their localization and dynamics lead to human disease. Myosins are actin-based motors that power processes such as muscle contraction, cytokinesis, and organelle transport. Here we report the initial characterization of myosin-XIX (Myo19), the founding member of a novel class of myosin that associates with mitochondria. The 970 aa heavy chain consists of a motor domain, three IQ motifs, and a short tail. Myo19 mRNA is expressed in multiple tissues, and antibodies to human Myo19 detect an approximately 109 kDa band in multiple cell lines. Both endogenous Myo19 and GFP-Myo19 exhibit striking localization to mitochondria. Deletion analysis reveals that the Myo19 tail is necessary and sufficient for mitochondrial localization. Expressing full-length GFP-Myo19 in A549 cells reveals a remarkable gain of function where the majority of the mitochondria move continuously. Moving mitochondria travel for many micrometers with an obvious leading end and distorted shape. The motility and shape change are sensitive to latrunculin B, indicating that both are actin dependent. Expressing the GFP-Myo19 tail in CAD cells resulted in decreased mitochondrial run lengths in neurites. These results suggest that this novel myosin functions as an actin-based motor for mitochondrial movement in vertebrate cells.
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Affiliation(s)
- Omar A Quintero
- Department of Cell and Molecular Physiology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA.
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79
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The Bax carboxy-terminal hydrophobic helix does not determine organelle-specific targeting but is essential for maintaining Bax in an inactive state and for stable mitochondrial membrane insertion. Apoptosis 2009; 15:14-27. [DOI: 10.1007/s10495-009-0410-2] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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80
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Abstract
PMD (Pelizaeus–Merzbacher disease), a CNS (central nervous system) disease characterized by shortened lifespan and severe neural dysfunction, is caused by mutations of the PLP1 (X-linked myelin proteolipid protein) gene. The majority of human PLP1 mutations are caused by duplications; almost all others are caused by missense mutations. The cellular events leading to the phenotype are unknown. The same mutations in non-humans make them ideal models to study the mechanisms that cause neurological sequelae. In the present study we show that mice with Plp1 duplications (Plp1tg) have major mitochondrial deficits with a 50% reduction in ATP, a drastically reduced mitochondrial membrane potential and increased numbers of mitochondria. In contrast, the jp (jimpy) mouse with a Plp1 missense mutation exhibits normal mitochondrial function. We show that PLP in the Plp1tg mice and in Plp1-transfected cells is targeted to mitochondria. PLP has motifs permissive for insertion into mitochondria and deletions near its N-terminus prevent its co-localization to mitochondria. These novel data show that Plp1 missense mutations and duplications of the native Plp1 gene initiate uniquely different cellular responses.
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81
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Mateja A, Szlachcic A, Downing ME, Dobosz M, Mariappan M, Hegde RS, Keenan RJ. The structural basis of tail-anchored membrane protein recognition by Get3. Nature 2009; 461:361-6. [PMID: 19675567 DOI: 10.1038/nature08319] [Citation(s) in RCA: 139] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2009] [Accepted: 07/27/2009] [Indexed: 11/09/2022]
Abstract
Targeting of newly synthesized membrane proteins to the endoplasmic reticulum is an essential cellular process. Most membrane proteins are recognized and targeted co-translationally by the signal recognition particle. However, nearly 5% of membrane proteins are 'tail-anchored' by a single carboxy-terminal transmembrane domain that cannot access the co-translational pathway. Instead, tail-anchored proteins are targeted post-translationally by a conserved ATPase termed Get3. The mechanistic basis for tail-anchored protein recognition or targeting by Get3 is not known. Here we present crystal structures of yeast Get3 in 'open' (nucleotide-free) and 'closed' (ADP.AlF(4)(-)-bound) dimer states. In the closed state, the dimer interface of Get3 contains an enormous hydrophobic groove implicated by mutational analyses in tail-anchored protein binding. In the open state, Get3 undergoes a striking rearrangement that disrupts the groove and shields its hydrophobic surfaces. These data provide a molecular mechanism for nucleotide-regulated binding and release of tail-anchored proteins during their membrane targeting by Get3.
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Affiliation(s)
- Agnieszka Mateja
- Department of Biochemistry & Molecular Biology, The University of Chicago, Gordon Center for Integrative Science, Room W238, 929 East 57th Street, Chicago, Illinois 60637, USA
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82
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Byers JT, Guzzo RM, Salih M, Tuana BS. Hydrophobic profiles of the tail anchors in SLMAP dictate subcellular targeting. BMC Cell Biol 2009; 10:48. [PMID: 19538755 PMCID: PMC2712456 DOI: 10.1186/1471-2121-10-48] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2008] [Accepted: 06/19/2009] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Tail anchored (TA) membrane proteins target subcellular structures via a C-terminal transmembrane domain and serve prominent roles in membrane fusion and vesicle transport. Sarcolemmal Membrane Associated Protein (SLMAP) possesses two alternatively spliced tail anchors (TA1 or TA2) but their specificity of subcellular targeting remains unknown. RESULTS TA1 or TA2 can direct SLMAP to reticular structures including the endoplasmic reticulum (ER), whilst TA2 directs SLMAP additionally to the mitochondria. Despite the general structural similarity of SLMAP to other vesicle trafficking proteins, we found no evidence for its localization with the vesicle transport machinery or a role in vesicle transport. The predicted transmembrane region of TA2 is flanked on either side by a positively charged amino acid and is itself less hydrophobic than the transmembrane helix present in TA1. Substitution of the positively charged amino acids, in the regions flanking the transmembrane helix of TA2, with leucine did not alter its subcellular targeting. The targeting of SLMAP to the mitochondria was dependent on the hydrophobic nature of TA2 since targeting of SLMAP-TA2 was prevented by the substitution of leucine (L) for moderately hydrophobic amino acid residues within the transmembrane region. The SLMAP-TA2-4L mutant had a hydrophobic profile that was comparable to that of SLMAP-TA1 and had identical targeting properties to SLMAP-TA1. CONCLUSION Thus the overall hydrophobicity of the two alternatively spliced TAs in SLMAP determines its subcellular targeting and TA2 predominantly directs SLMAP to the mitochondira where it may serve roles in the function of this organelle.
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Affiliation(s)
- Joseph T Byers
- Department of Cellular and Molecular Medicine, 451 Smyth Road, University of Ottawa, Ottawa, Ontario K1H 8M5, Canada
| | - Rosa M Guzzo
- Department of Cellular and Molecular Medicine, 451 Smyth Road, University of Ottawa, Ottawa, Ontario K1H 8M5, Canada
| | - Maysoon Salih
- Department of Cellular and Molecular Medicine, 451 Smyth Road, University of Ottawa, Ottawa, Ontario K1H 8M5, Canada
| | - Balwant S Tuana
- Department of Cellular and Molecular Medicine, 451 Smyth Road, University of Ottawa, Ottawa, Ontario K1H 8M5, Canada
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83
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Lueder F, Lithgow T. The three domains of the mitochondrial outer membrane protein Mim1 have discrete functions in assembly of the TOM complex. FEBS Lett 2009; 583:1475-80. [PMID: 19345216 DOI: 10.1016/j.febslet.2009.03.064] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2009] [Revised: 03/18/2009] [Accepted: 03/27/2009] [Indexed: 11/28/2022]
Abstract
The assembly of mitochondrial outer membrane proteins is an essential process, mediated by the SAM complex and a set of additional protein modules. We show that one of these, Mim1, is anchored in the outer membrane with its N-terminus exposed to the cytosol and its C-terminus in the mitochondrial intermembrane space. Using an in vitro assay to measure the multi-step pathway for assembly of Tom40 into the TOM complex, we find that an "early reaction" mediated by the SAM complex is regulated by the N-terminal domain of Mim1. In addition, a "late reaction" catalysed by the Sam37 subunit of the SAM complex is also influenced by Mim1. Thus, Mim1 participates at multiple stages in the assembly of the TOM complex.
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Affiliation(s)
- Franziska Lueder
- Department of Biochemistry and Molecular Biology, Monash University, Clayton 3800, Australia
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84
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Coffman JA, Coluccio A, Planchart A, Robertson AJ. Oral-aboral axis specification in the sea urchin embryo III. Role of mitochondrial redox signaling via H2O2. Dev Biol 2009; 330:123-30. [PMID: 19328778 DOI: 10.1016/j.ydbio.2009.03.017] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2008] [Revised: 02/21/2009] [Accepted: 03/18/2009] [Indexed: 10/21/2022]
Abstract
In sea urchin embryos, specification of the secondary (oral-aboral) axis occurs via nodal, expression of which is entirely zygotic and localized to prospective oral ectoderm at blastula stage. The initial source of this spatial anisotropy is not known. Previous studies have shown that oral-aboral (OA) polarity correlates with a mitochondrial gradient, and that nodal activity is dependent both on mitochondrial respiration and p38 stress-activated protein kinase. Here we show that the spatial pattern of nodal activity also correlates with the mitochondrial gradient, and that the latter correlates with inhomogeneous levels of intracellular reactive oxygen species. To test whether mitochondrial H(2)O(2) functions as a redox signal to activate nodal, zygotes were injected with mRNA encoding either mitochondrially-targeted catalase, which quenches mitochondrial H(2)O(2) and down-regulates p38, or superoxide dismutase, which augments mitochondrial H(2)O(2) and up-regulates p38. Whereas the former treatment inhibits the initial activation of nodal and entrains OA polarity toward aboral when confined to half of the embryo via 2-cell stage blastomere injections, the latter does not produce the opposite effects. We conclude that mitochondrial H(2)O(2) is rate-limiting for the initial activation of nodal, but that additional rate-limiting factors, likely also involving mitochondria, contribute to the asymmetry in nodal expression.
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Affiliation(s)
- James A Coffman
- Mount Desert Island Biological Laboratory, Old Bar Harbor Road, Salisbury Cove, ME 04672, USA.
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85
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Sugiura T, Tazaki A, Ueno N, Watanabe K, Mochii M. Xenopus Wnt-5a induces an ectopic larval tail at injured site, suggesting a crucial role for noncanonical Wnt signal in tail regeneration. Mech Dev 2009; 126:56-67. [DOI: 10.1016/j.mod.2008.10.002] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2007] [Revised: 10/08/2008] [Accepted: 10/09/2008] [Indexed: 01/07/2023]
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86
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Abstract
The default pathway of cell-surface T-cell receptor (TCR) complex formation, and the subsequent transport to the membrane, is thought to entail endoplasmic reticulum (ER) localization followed by proteasome degradation of the unassembled chains. We show herein an alternative pathway: short, incomplete peptide versions of TCRbeta naturally occur in the thymus. Such peptides, which have minimally lost the leader sequence or have been massively truncated, leaving only the very C terminus intact, are sorted preferentially to the mitochondrion. As a consequence of the mitochondrial localization, apoptotic cell death is induced. Structure function analysis showed that both the specific localization and induction of apoptosis depend on the transmembrane domain (TMD) and associated residues at the COOH-terminus of TCR. Truncated forms of TCR, such as the short peptides that we detected in the thymus, may be products of protein degradation within thymocytes. Alternatively, they may occur through the translation of truncated mRNAs resulting from unfruitful rearrangement or from germline transcription. It is proposed that mitochondria serve as a subcellular sequestration site for incomplete TCR molecules.
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87
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Tamai S, Iida H, Yokota S, Sayano T, Kiguchiya S, Ishihara N, Hayashi JI, Mihara K, Oka T. Characterization of the mitochondrial protein LETM1, which maintains the mitochondrial tubular shapes and interacts with the AAA-ATPase BCS1L. J Cell Sci 2008; 121:2588-600. [PMID: 18628306 DOI: 10.1242/jcs.026625] [Citation(s) in RCA: 97] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
LETM1 is located in the chromosomal region that is deleted in patients suffering Wolf-Hirschhorn syndrome; it encodes a homolog of the yeast protein Mdm38 that is involved in mitochondrial morphology. Here, we describe the LETM1-mediated regulation of the mitochondrial volume and its interaction with the mitochondrial AAA-ATPase BCS1L that is responsible for three different human disorders. LETM1 is a mitochondrial inner-membrane protein with a large domain extruding to the matrix. The LETM1 homolog LETM2 is a mitochondrial protein that is expressed preferentially in testis and sperm. LETM1 downregulation caused mitochondrial swelling and cristae disorganization, but seemed to have little effect on membrane fusion and fission. Formation of the respiratory-chain complex was impaired by LETM1 knockdown. Cells lacking mitochondrial DNA lost active respiratory chains but maintained mitochondrial tubular networks, indicating that mitochondrial swelling caused by LETM1 knockdown is not caused by the disassembly of the respiratory chains. LETM1 was co-precipitated with BCS1L and formation of the LETM1 complex depended on BCS1L levels, suggesting that BCS1L stimulates the assembly of the LETM1 complex. BCS1L knockdown caused disassembly of the respiratory chains as well as LETM1 downregulation and induced distinct changes in mitochondrial morphology.
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Affiliation(s)
- Shoko Tamai
- Department of Molecular Biology, Graduate School of Medical Science, Kyushu University, Fukuoka, Japan
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88
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Mokranjac D, Neupert W. Thirty years of protein translocation into mitochondria: unexpectedly complex and still puzzling. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2008; 1793:33-41. [PMID: 18672008 DOI: 10.1016/j.bbamcr.2008.06.021] [Citation(s) in RCA: 88] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/03/2008] [Revised: 06/16/2008] [Accepted: 06/26/2008] [Indexed: 11/26/2022]
Abstract
Mitochondria are essential organelles of the eukaryotic cells that are made by expansion and division of pre-existing mitochondria. The majority of their protein constituents are synthesized in the cytosol. They are transported into and put together within the organelle. This complex process is facilitated by several protein translocases. Here we summarize current knowledge on these sophisticated molecular machines that mediate recognition, transport across membranes and intramitochondrial sorting of many hundreds of mitochondrial proteins.
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Affiliation(s)
- Dejana Mokranjac
- Institute for Physiological Chemistry, Ludwig-Maximilians University, Butenandtstr. 5, 81377 Munich, Germany
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89
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Oka T, Sayano T, Tamai S, Yokota S, Kato H, Fujii G, Mihara K. Identification of a novel protein MICS1 that is involved in maintenance of mitochondrial morphology and apoptotic release of cytochrome c. Mol Biol Cell 2008; 19:2597-608. [PMID: 18417609 PMCID: PMC2397309 DOI: 10.1091/mbc.e07-12-1205] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2007] [Revised: 03/26/2008] [Accepted: 04/03/2008] [Indexed: 11/11/2022] Open
Abstract
Mitochondrial morphology dynamically changes in a balance of membrane fusion and fission in response to the environment, cell cycle, and apoptotic stimuli. Here, we report that a novel mitochondrial protein, MICS1, is involved in mitochondrial morphology in specific cristae structures and the apoptotic release of cytochrome c from the mitochondria. MICS1 is an inner membrane protein with a cleavable presequence and multiple transmembrane segments and belongs to the Bi-1 super family. MICS1 down-regulation causes mitochondrial fragmentation and cristae disorganization and stimulates the release of proapoptotic proteins. Expression of the anti-apoptotic protein Bcl-XL does not prevent morphological changes of mitochondria caused by MICS1 down-regulation, indicating that MICS1 plays a role in maintaining mitochondrial morphology separately from the function in apoptotic pathways. MICS1 overproduction induces mitochondrial aggregation and partially inhibits cytochrome c release during apoptosis, regardless of the occurrence of Bax targeting. MICS1 is cross-linked to cytochrome c without disrupting membrane integrity. Thus, MICS1 facilitates the tight association of cytochrome c with the inner membrane. Furthermore, under low-serum condition, the delay in apoptotic release of cytochrome c correlates with MICS1 up-regulation without significant changes in mitochondrial morphology, suggesting that MICS1 individually functions in mitochondrial morphology and cytochrome c release.
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Affiliation(s)
- Toshihiko Oka
- *Department of Molecular Biology, Graduate School of Medical Science, Kyushu University, Fukuoka 812-8582, Japan
| | - Tomoko Sayano
- *Department of Molecular Biology, Graduate School of Medical Science, Kyushu University, Fukuoka 812-8582, Japan
| | - Shoko Tamai
- *Department of Molecular Biology, Graduate School of Medical Science, Kyushu University, Fukuoka 812-8582, Japan
| | - Sadaki Yokota
- Section of Functional Morphology, Faculty of Pharmaceutical Science, Nagasaki International University, 859-3298 Nagasaki, Japan; and
| | - Hiroki Kato
- *Department of Molecular Biology, Graduate School of Medical Science, Kyushu University, Fukuoka 812-8582, Japan
| | - Gen Fujii
- Pathology Division, National Cancer Center Research Institute, 104-0045 Tokyo, Japan
| | - Katsuyoshi Mihara
- *Department of Molecular Biology, Graduate School of Medical Science, Kyushu University, Fukuoka 812-8582, Japan
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90
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Walther DM, Rapaport D. Biogenesis of mitochondrial outer membrane proteins. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2008; 1793:42-51. [PMID: 18501716 DOI: 10.1016/j.bbamcr.2008.04.013] [Citation(s) in RCA: 94] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/29/2008] [Revised: 04/15/2008] [Accepted: 04/25/2008] [Indexed: 11/29/2022]
Abstract
Mitochondria are surrounded by two distinct membranes: the outer and the inner membrane. The mitochondrial outer membrane mediates numerous interactions between the mitochondrial metabolic and genetic systems and the rest of the eukaryotic cell. Proteins of this membrane are nuclear-encoded and synthesized as precursor proteins in the cytosol. They are targeted to the mitochondria and inserted into their target membrane via various pathways. This review summarizes our current knowledge of the sorting signals for this specific targeting and describes the mechanisms by which the mitochondrial import machineries recognize precursor proteins, mediate their membrane integration and facilitate assembly into functional complexes.
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Affiliation(s)
- Dirk M Walther
- Interfakultäres Institut für Biochemie, Hoppe-Seyler-Str. 4, University of Tübingen, 72076 Tübingen, Germany
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91
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Tsuchida M, Emi Y, Kida Y, Sakaguchi M. Human ABC transporter isoform B6 (ABCB6) localizes primarily in the Golgi apparatus. Biochem Biophys Res Commun 2008; 369:369-75. [DOI: 10.1016/j.bbrc.2008.02.027] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2008] [Accepted: 02/06/2008] [Indexed: 01/13/2023]
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92
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Valentijn AJ, Upton JP, Bates N, Gilmore AP. Bax targeting to mitochondria occurs via both tail anchor-dependent and -independent mechanisms. Cell Death Differ 2008; 15:1243-54. [PMID: 18437166 DOI: 10.1038/cdd.2008.39] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
Abstract
Bax is a member of the Bcl-2 family that, together with Bak, is required for permeabilisation of the outer mitochondrial membrane (OMM). Bax differs from Bak in that it is predominantly cytosolic in healthy cells and only associates with the OMM after an apoptotic signal. How Bax is targeted to the OMM is still a matter of debate, with both a C-terminal tail anchor and an N-terminal pre-sequence being implicated. We now show definitively that Bax does not contain an N-terminal import sequence, but does have a C-terminal anchor. The isolated N terminus of Bax cannot target a heterologous protein to the OMM, whereas the C terminus can. Furthermore, if the C terminus is blocked, Bax fails to target to mitochondria upon receipt of an apoptotic stimulus. Zebra fish Bax, which shows a high degree of amino-acid homology with mammalian Bax within the C terminus, but not in the N terminus, can rescue the defective cell-death phenotype of Bax/Bak-deficient cells. Interestingly, we find that Bax mutants, which themselves cannot target mitochondria or induce apoptosis, are recruited to clusters of activated wild-type Bax on the OMM of apoptotic cells. This appears to be an amplification of Bax activation during cell death that is independent of the normal tail anchor-mediated targeting.
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Affiliation(s)
- A J Valentijn
- Wellcome Trust Centre for Cell Matrix Research, Faculty of Life Sciences, The University of Manchester, Manchester, UK
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93
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Becker T, Vögtle FN, Stojanovski D, Meisinger C. Sorting and assembly of mitochondrial outer membrane proteins. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2008; 1777:557-63. [PMID: 18423394 DOI: 10.1016/j.bbabio.2008.03.017] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/31/2008] [Revised: 03/05/2008] [Accepted: 03/19/2008] [Indexed: 10/22/2022]
Abstract
In the last years the picture of protein import into the mitochondria has become much more complicated in terms of new components and new sorting pathways. These novel findings have also changed views concerning the biogenesis pathway of mitochondrial outer membrane proteins. In addition to proteins anchored with transmembrane alpha-helices, the endosymbiotic origin of the mitochondria has resulted in the presence of transmembrane beta-barrels in this compartment. The sorting and assembly pathway of outer membrane proteins involves three machineries: the translocase of the outer membrane (TOM complex) the sorting and assembly machinery (SAM complex) and the MDM complex (mitochondrial distribution and morphology). Here we review recent developments on the biogenesis pathways of outer membrane proteins with a focus on Tom proteins, the most intensively studied class of these precursor proteins.
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Affiliation(s)
- Thomas Becker
- Institut für Biochemie und Molekularbiologie, Zentrum für Biochemie und Molekulare Zellforschung, Universität Freiburg, D-79104 Freiburg, Germany
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94
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Sierra AY, Gratacós E, Carrasco P, Clotet J, Ureña J, Serra D, Asins G, Hegardt FG, Casals N. CPT1c Is Localized in Endoplasmic Reticulum of Neurons and Has Carnitine Palmitoyltransferase Activity. J Biol Chem 2008; 283:6878-85. [DOI: 10.1074/jbc.m707965200] [Citation(s) in RCA: 120] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
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95
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Ma Y, Taylor SS. A molecular switch for targeting between endoplasmic reticulum (ER) and mitochondria: conversion of a mitochondria-targeting element into an ER-targeting signal in DAKAP1. J Biol Chem 2008; 283:11743-51. [PMID: 18287098 DOI: 10.1074/jbc.m710494200] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
dAKAP1 (AKAP121, S-AKAP84), a dual specificity PKA scaffold protein, exists in several forms designated as a, b, c, and d. Whether dAKAP1 targets to endoplasmic reticulum (ER) or mitochondria depends on the presence of the N-terminal 33 amino acids (N1), and these N-terminal variants are generated by either alternative splicing and/or differential initiation of translation. The mitochondrial targeting motif, which is localized between residues 49 and 63, is comprised of a hydrophobic helix followed by positive charges ( Ma, Y., and Taylor, S. (2002) J. Biol. Chem. 277, 27328-27336 ). dAKAP1 is located on the cytosolic surface of mitochondria outer membrane and both smooth and rough ER membrane. A single residue, Asp(31), within the first 33 residues of dAKAP1b is required for ER targeting. Asp(31), which functions as a separate motif from the mitochondrial targeting signal, converts the mitochondrial-targeting signal into a bipartite ER-targeting signal, without destroying the mitochondria-targeting signal. Therefore dAKAP1 possesses a single targeting element capable of targeting to both mitochondria and ER, with the ER signal overlapping the mitochondria signal. The specificity of ER or mitochondria targeting is determined and switched by the availability of the negatively charged residue, Asp(31).
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Affiliation(s)
- Yuliang Ma
- Howard Hughes Medical Institute and the Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, California 92093, USA
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96
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Cho GW, Shin SM, Kim HK, Ha SA, Kim S, Yoon JH, Hur SY, Kim TE, Kim JW. HCCR-1, a novel oncogene, encodes a mitochondrial outer membrane protein and suppresses the UVC-induced apoptosis. BMC Cell Biol 2007; 8:50. [PMID: 18045496 PMCID: PMC2222240 DOI: 10.1186/1471-2121-8-50] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2007] [Accepted: 11/28/2007] [Indexed: 11/24/2022] Open
Abstract
Background The Human cervical cancer oncogene (HCCR-1) has been isolated as a human oncoprotein, and has shown strong tumorigenic features. Its potential role in tumorigenesis may result from a negative regulation of the p53 tumor suppressor gene. Results To investigate the biological function of HCCR-1 in the cell, we predicted biological features using bioinformatic tools, and have identified a LETM1 homologous domain at position 75 to 346 of HCCR-1. This domain contains proteins identified from diverse species predicted to be mitochondrial proteins. Fluorescence microscopy and fractionation experiments showed that HCCR-1 is located in mitochondria in the COS-7, MCF-7 and HEK/293 cell lines, and subcompartamentally at the outer membrane in the HEK/293 cell line. The topological structure was revealed as the NH2-terminus of HCCR-1 oriented toward the cytoplasm. We also observed that the D1-2 region, at position 1 to 110 of HCCR-1, was required and sufficient for posttranslational mitochondrial import. The function of HCCR-1 on mitochondrial membrane is to retard the intrinsic apoptosis induced by UVC and staurosporine, respectively. Conclusion Our experiments show the biological features of HCCR-1 in the cell, and suggest that uncontrolled expression of HCCR-1 may cause mitochondrial dysfunction that can result in resisting the UVC or staurosporine-induced apoptosis and progressing in the tumor formation.
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Affiliation(s)
- Goang-Won Cho
- Molecular Genetic Laboratory, College of Medicine, The Catholic University of Korea, Seoul 137-040, Korea.
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97
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Wattenberg BW, Clark D, Brock S. An artificial mitochondrial tail signal/anchor sequence confirms a requirement for moderate hydrophobicity for targeting. Biosci Rep 2007; 27:385-401. [PMID: 17968654 DOI: 10.1007/s10540-007-9061-0] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2007] [Accepted: 09/06/2007] [Indexed: 10/22/2022] Open
Abstract
Tail-anchored proteins are a group of membrane proteins oriented with their amino terminus in the cytoplasm and their carboxy terminus embedded in intracellular membranes. This group includes the apoptosis-mediating proteins of the Bcl-2 family as well as the vesicle targeting proteins of the SNARE group, among others. A stretch of hydrophobic amino acids at the extreme carboxy terminus of these proteins serves both as a membrane anchor and as a targeting signal. Tail-anchored proteins are differentially targeted to either the endoplasmic reticulum or the mitochondrial outer membrane and the mechanism which accomplishes this selective targeting is poorly understood. Here we define important characteristics of the signal/anchor region which directs proteins to the mitochondrial outer membrane. We have created an artificial sequence consisting of a stretch of 16 leucines bounded by positively charged amino acids. Using this template we demonstrate that moderate hydrophobicity distinguishes the mitochondrial tail-anchor sequence from that of the endoplasmic reticulum tail-anchor sequence. A change as small as introduction of a single polar residue into a sequence that otherwise targets to the endoplasmic reticulum can substantially switch targeting to the mitochondrial outer membrane. Further we show that a mitochondrially targeted tail-anchor has a higher propensity for the formation of alpha-helical structure than a sequence directing tail-anchored proteins to the endoplasmic reticulum.
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Affiliation(s)
- Binks W Wattenberg
- Department of Medicine, University of Louisville School of Medicine, Louisville, KY 40202, USA.
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98
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Kalbfleisch T, Cambon A, Wattenberg BW. A bioinformatics approach to identifying tail-anchored proteins in the human genome. Traffic 2007; 8:1687-1694. [PMID: 17892534 DOI: 10.1111/j.1600-0854.2007.00661.x] [Citation(s) in RCA: 105] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Intracellular proteins with a carboxy-terminal transmembrane domain and the amino-terminus oriented toward the cytosol are known as 'tail-anchored' proteins. Tail-anchored proteins have been of considerable interest because several important classes of proteins, including the vesicle-targeting/fusion proteins known as SNAREs and the apoptosis-related proteins of the Bcl-2 family, among others, utilize this unique membrane-anchoring motif. Here, we use a bioinformatic technique to develop a comprehensive list of potentially tail-anchored proteins in the human genome. Our final list contains 411 entries derived from 325 unique genes. We also analyzed both known and predicted tail-anchored proteins with respect to the amino acid composition of the transmembrane segments. This analysis revealed a distinctive composition of the membrane anchor in SNARE proteins.
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Affiliation(s)
- Ted Kalbfleisch
- Department of Biochemistry and Molecular Biology, University of Louisville School of Medicine, Louisville, KY 40202, USA
- Center for Genetics and Molecular Medicine, University of Louisville School of Medicine, Louisville, KY 40202, USA
| | - Alex Cambon
- Department of Bioinformatics and Biostatistics, School of Public Health and Information Sciences, University of Louisville, Louisville, KY 40202, USA
| | - Binks W Wattenberg
- Department of Biochemistry and Molecular Biology, University of Louisville School of Medicine, Louisville, KY 40202, USA
- Department of Medicine, University of Louisville School of Medicine, Louisville, KY 40202, USA
- Department of Pharmacology and Toxicology, University of Louisville School of Medicine, Louisville, KY 40202, USA
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99
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Abstract
About 10% to 15% of the nuclear genes of eukaryotic organisms encode mitochondrial proteins. These proteins are synthesized in the cytosol and recognized by receptors on the surface of mitochondria. Translocases in the outer and inner membrane of mitochondria mediate the import and intramitochondrial sorting of these proteins; ATP and the membrane potential are used as energy sources. Chaperones and auxiliary factors assist in the folding and assembly of mitochondrial proteins into their native, three-dimensional structures. This review summarizes the present knowledge on the import and sorting of mitochondrial precursor proteins, with a special emphasis on unresolved questions and topics of current research.
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Affiliation(s)
- Walter Neupert
- Institut für Physiologische Chemie, Universität München, 81377 München, Germany.
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100
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Borgese N, Brambillasca S, Colombo S. How tails guide tail-anchored proteins to their destinations. Curr Opin Cell Biol 2007; 19:368-75. [PMID: 17629691 DOI: 10.1016/j.ceb.2007.04.019] [Citation(s) in RCA: 146] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2007] [Accepted: 04/18/2007] [Indexed: 11/28/2022]
Abstract
A large group of diverse, functionally important, and differently localized transmembrane proteins shares a particular membrane topology, consisting of a cytosolic N-terminal region, followed by a transmembrane domain close to the C-terminus. Because of their structure, these C-tail-anchored (TA) proteins must insert into all their target membranes by post-translational pathways. Recent work, based on the development of stringent and sensitive biochemical assays, has demonstrated that novel unexplored mechanisms underlie these post-translational targeting and membrane insertion pathways. Unravelling these pathways will shed light on the biosynthesis and regulation of an important group of membrane proteins and is likely to lead to new concepts in the field of membrane biogenesis.
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Affiliation(s)
- Nica Borgese
- National Research Council Institute for Neuroscience and Department of Medical Pharmacology, University of Milan, via Vanvitelli 32, 20129 Milano, Italy
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