1
|
Rosenbusch KE, Oun A, Sanislav O, Lay ST, Keizer-Gunnink I, Annesley SJ, Fisher PR, Dolga AM, Kortholt A. A Conserved Role for LRRK2 and Roco Proteins in the Regulation of Mitochondrial Activity. Front Cell Dev Biol 2021; 9:734554. [PMID: 34568343 PMCID: PMC8455996 DOI: 10.3389/fcell.2021.734554] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2021] [Accepted: 08/16/2021] [Indexed: 01/02/2023] Open
Abstract
Parkinson's Disease (PD) is the second most common neurodegenerative disease world-wide. Mutations in the multidomain protein Leucine Rich Repeat Kinase 2 (LRRK2) are the most frequent cause of hereditary PD. Furthermore, recent data suggest that independent of mutations, increased kinase activity of LRRK2 plays an essential role in PD pathogenesis. Isolated mitochondria of tissue samples from PD patients carrying LRRK2 mutations display a significant impairment of mitochondrial function. However, due to the complexity of the mitochondrial signaling network, the role of LRRK2 in mitochondrial metabolism is still not well understood. Previously we have shown that D. discoideum Roco4 is a suitable model to study the activation mechanism of LRRK2 in vivo. To get more insight in the LRRK2 pathways regulating mitochondrial activity we used this Roco4 model system in combination with murine RAW macrophages. Here we show that both Dictyostelium roco4 knockout and cells expressing PD-mutants show behavioral and developmental phenotypes that are characteristic for mitochondrial impairment. Mitochondrial activity measured by Seahorse technology revealed that the basal respiration of D. discoideum roco4- cells is significantly increased compared to the WT strain, while the basal and maximal respiration values of cells overexpressing Roco4 are reduced compared to the WT strain. Consistently, LRRK2 KO RAW 264.7 cells exhibit higher maximal mitochondrial respiration activity compared to the LRRK2 parental RAW264.7 cells. Measurement on isolated mitochondria from LRRK2 KO and parental RAW 264.7 cells revealed no difference in activity compared to the parental cells. Furthermore, neither D. discoideum roco4- nor LRRK2 KO RAW 264.7 showed a difference in either the number or the morphology of mitochondria compared to their respective parental strains. This suggests that the observed effects on the mitochondrial respiratory in cells are indirect and that LRRK2/Roco proteins most likely require other cytosolic cofactors to elicit mitochondrial effects.
Collapse
Affiliation(s)
| | - Asmaa Oun
- Department of Cell Biochemistry, University of Groningen, Groningen, Netherlands.,Groningen Research Institute of Pharmacy (GRIP), Molecular Pharmacology XB10, Groningen, Netherlands.,Department of Biotechnology, Institute of Graduate Studies and Research, Alexandria University, Alexandria, Egypt
| | - Oana Sanislav
- Department of Physiology Anatomy and Microbiology, La Trobe University, Melbourne, VIC, Australia
| | - Sui T Lay
- Department of Physiology Anatomy and Microbiology, La Trobe University, Melbourne, VIC, Australia
| | - Ineke Keizer-Gunnink
- Department of Physiology Anatomy and Microbiology, La Trobe University, Melbourne, VIC, Australia
| | - Sarah J Annesley
- Department of Physiology Anatomy and Microbiology, La Trobe University, Melbourne, VIC, Australia
| | - Paul R Fisher
- Department of Physiology Anatomy and Microbiology, La Trobe University, Melbourne, VIC, Australia
| | - Amalia M Dolga
- Groningen Research Institute of Pharmacy (GRIP), Molecular Pharmacology XB10, Groningen, Netherlands
| | - Arjan Kortholt
- Department of Cell Biochemistry, University of Groningen, Groningen, Netherlands.,Department of Pharmacology, Faculty of Medicine, Suleyman Demirel University, Isparta, Turkey
| |
Collapse
|
2
|
Loesch DZ, Trost N, Bui MQ, Hammersley E, Lay ST, Annesley SJ, Sanislav O, Allan CY, Tassone F, Chen ZP, Ngoei KRW, Kemp BE, Francis D, Fisher PR, Storey E. The Spectrum of Neurological and White Matter Changes and Premutation Status Categories of Older Male Carriers of the FMR1 Alleles Are Linked to Genetic (CGG and FMR1 mRNA) and Cellular Stress (AMPK) Markers. Front Genet 2018; 9:531. [PMID: 30483310 PMCID: PMC6241173 DOI: 10.3389/fgene.2018.00531] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2018] [Accepted: 10/22/2018] [Indexed: 12/16/2022] Open
Abstract
The fragile X premutation (PM) allele contains a CGG expansion of 55-200 repeats in the FMR1 gene's promoter. Male PM carriers have an elevated risk of developing neurological and psychiatric changes, including an approximately 50% risk of the fragile X-associated tremor/ataxia syndrome (FXTAS). The aim of this study was to assess the relationships of regional white matter hyperintensities (wmhs) semi-quantitative scores, clinical status, motor (UPDRS, ICARS, Tremor) scales, and cognitive impairments, with FMR1-specific genetic changes, in a sample of 32 unselected male PM carriers aged 39-81 years. Half of these individuals were affected with FXTAS, while the non-FXTAS group comprised subcategories of non-affected individuals and individuals affected with non-syndromic changes. The dynamics of pathological processes at the cellular level relevant to the clinical status of PM carriers was investigated using the enzyme AMP-activated protein kinase (AMPK), which is a highly sensitive cellular stress-sensing alarm protein. This enzyme, as well as genetic markers - CGG repeat number and the levels of the FMR1 mRNA - were assessed in blood lymphoblasts. The results showed that the repeat distribution for FXTAS individuals peaked at 85-90 CGGs; non-FXTAS carriers were distributed within the lowest end of the PM repeat range, and non-syndromic carriers assumed an intermediate position. The size of the CGG expansion was significantly correlated, across all three categories, with infratentorial and total wmhs and with all motor scores, and the FMR1 mRNA levels with all the wmh scores, whilst AMPK activity showed considerable elevation in the non-FXTAS combined group, decreasing in the FXTAS group, proportionally to increasing severity of the wmhs and tremor/ataxia. We conclude that the size of the CGG expansion relates to the risk for FXTAS, to severity of infratentorial wmhs lesions, and to all three motor scale scores. FMR1 mRNA shows a strong association with the extent of wmhs, which is the most sensitive marker of the pathological process. However, the AMPK activity findings - suggestive of a role of this enzyme in the risk of FXTAS - need to be verified and expanded in future studies using larger samples and longitudinal assessment.
Collapse
Affiliation(s)
- Danuta Z. Loesch
- Department of Psychology and Counselling, School of Psychology and Public Health, College of Science Health and Engineering, La Trobe University, Melbourne, VIC, Australia
| | - Nicholas Trost
- Medical Imaging Department, St Vincent’s Hospital, Melbourne, VIC, Australia
| | - Minh Q. Bui
- Centre for Epidemiology and Biostatistics, Melbourne School of Population and Global Health, University of Melbourne, Melbourne, VIC, Australia
| | - Eleanor Hammersley
- Department of Psychology and Counselling, School of Psychology and Public Health, College of Science Health and Engineering, La Trobe University, Melbourne, VIC, Australia
| | - Sui T. Lay
- Discipline of Microbiology, Department of Physiology Anatomy and Microbiology, School of Life Sciences, College of Science Health and Engineering, La Trobe University, Melbourne, VIC, Australia
| | - Sarah J. Annesley
- Discipline of Microbiology, Department of Physiology Anatomy and Microbiology, School of Life Sciences, College of Science Health and Engineering, La Trobe University, Melbourne, VIC, Australia
| | - Oana Sanislav
- Discipline of Microbiology, Department of Physiology Anatomy and Microbiology, School of Life Sciences, College of Science Health and Engineering, La Trobe University, Melbourne, VIC, Australia
| | - Claire Y. Allan
- Discipline of Microbiology, Department of Physiology Anatomy and Microbiology, School of Life Sciences, College of Science Health and Engineering, La Trobe University, Melbourne, VIC, Australia
| | - Flora Tassone
- UC Davis MIND Institute, Sacramento, CA, United States
| | - Zhi-Ping Chen
- St Vincent’s Institute of Medical Research, Melbourne, VIC, Australia
| | - Kevin R. W. Ngoei
- St Vincent’s Institute of Medical Research, Melbourne, VIC, Australia
| | - Bruce E. Kemp
- St Vincent’s Institute of Medical Research, Melbourne, VIC, Australia
| | - David Francis
- Cytomolecular Diagnostic Research, Victorian Clinical Genetics Services, Melbourne, VIC, Australia
| | - Paul R. Fisher
- Discipline of Microbiology, Department of Physiology Anatomy and Microbiology, School of Life Sciences, College of Science Health and Engineering, La Trobe University, Melbourne, VIC, Australia
| | - Elsdon Storey
- Department of Medicine (Neuroscience), Monash University, Melbourne, VIC, Australia
| |
Collapse
|
3
|
Shahul Hameed UF, Sanislav O, Lay ST, Annesley SJ, Jobichen C, Fisher PR, Swaminathan K, Arold ST. Proteobacterial Origin of Protein Arginine Methylation and Regulation of Complex I Assembly by MidA. Cell Rep 2018; 24:1996-2004. [DOI: 10.1016/j.celrep.2018.07.075] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2018] [Revised: 06/06/2018] [Accepted: 07/23/2018] [Indexed: 10/28/2022] Open
|
4
|
Annesley SJ, Lay ST, De Piazza SW, Sanislav O, Hammersley E, Allan CY, Francione LM, Bui MQ, Chen ZP, Ngoei KRW, Tassone F, Kemp BE, Storey E, Evans A, Loesch DZ, Fisher PR. Immortalized Parkinson's disease lymphocytes have enhanced mitochondrial respiratory activity. Dis Model Mech 2016; 9:1295-1305. [PMID: 27638668 PMCID: PMC5117226 DOI: 10.1242/dmm.025684] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2016] [Accepted: 09/13/2016] [Indexed: 12/14/2022] Open
Abstract
In combination with studies of post-mortem Parkinson's disease (PD) brains, pharmacological and genetic models of PD have suggested that two fundamental interacting cellular processes are impaired – proteostasis and mitochondrial respiration. We have re-examined the role of mitochondrial dysfunction in lymphoblasts isolated from individuals with idiopathic PD and an age-matched control group. As previously reported for various PD cell types, the production of reactive oxygen species (ROS) by PD lymphoblasts was significantly elevated. However, this was not due to an impairment of mitochondrial respiration, as is often assumed. Instead, basal mitochondrial respiration and ATP synthesis are dramatically elevated in PD lymphoblasts. The mitochondrial mass, genome copy number and membrane potential were unaltered, but the expression of indicative respiratory complex proteins was also elevated. This explains the increased oxygen consumption rates by each of the respiratory complexes in experimentally uncoupled mitochondria of iPD cells. However, it was not attributable to increased activity of the stress- and energy-sensing protein kinase AMPK, a regulator of mitochondrial biogenesis and activity. The respiratory differences between iPD and control cells were sufficiently dramatic as to provide a potentially sensitive and reliable biomarker of the disease state, unaffected by disease duration (time since diagnosis) or clinical severity. Lymphoblasts from control and PD individuals thus occupy two distinct, quasi-stable steady states; a ‘normal’ and a ‘hyperactive’ state characterized by two different metabolic rates. The apparent stability of the ‘hyperactive’ state in patient-derived lymphoblasts in the face of patient ageing, ongoing disease and mounting disease severity suggests an early, permanent switch to an alternative metabolic steady state. With its associated, elevated ROS production, the ‘hyperactive’ state might not cause pathology to cells that are rapidly turned over, but brain cells might accumulate long-term damage leading ultimately to neurodegeneration and the loss of mitochondrial function observed post-mortem. Whether the ‘hyperactive’ state in lymphoblasts is a biomarker specifically of PD or more generally of neurodegenerative disease remains to be determined. Editors' choice: Cultured Parkinson's disease lymphocytes are metabolically hyperactive, suggesting a new understanding of the underlying cytopathology and biomarkers for this and potentially other neurodegenerative diseases.
Collapse
Affiliation(s)
- Sarah J Annesley
- Discipline of Microbiology, Department of Physiology Anatomy and Microbiology, School of Life Sciences, College of Science Health and Engineering, La Trobe University, Melbourne, Victoria 3086, Australia
| | - Sui T Lay
- Discipline of Microbiology, Department of Physiology Anatomy and Microbiology, School of Life Sciences, College of Science Health and Engineering, La Trobe University, Melbourne, Victoria 3086, Australia
| | - Shawn W De Piazza
- Discipline of Microbiology, Department of Physiology Anatomy and Microbiology, School of Life Sciences, College of Science Health and Engineering, La Trobe University, Melbourne, Victoria 3086, Australia
| | - Oana Sanislav
- Discipline of Microbiology, Department of Physiology Anatomy and Microbiology, School of Life Sciences, College of Science Health and Engineering, La Trobe University, Melbourne, Victoria 3086, Australia
| | - Eleanor Hammersley
- Department of Psychology and Counselling, School of Psychology and Public Health, College of Science Health and Engineering, La Trobe University, Melbourne, Victoria 3986, Australia
| | - Claire Y Allan
- Discipline of Microbiology, Department of Physiology Anatomy and Microbiology, School of Life Sciences, College of Science Health and Engineering, La Trobe University, Melbourne, Victoria 3086, Australia
| | - Lisa M Francione
- Discipline of Microbiology, Department of Physiology Anatomy and Microbiology, School of Life Sciences, College of Science Health and Engineering, La Trobe University, Melbourne, Victoria 3086, Australia
| | - Minh Q Bui
- Centre for Epidemiology and Biostatistics, Melbourne School of Population and Global Health, University of Melbourne, Melbourne, Victoria 3010, Australia
| | - Zhi-Ping Chen
- Department of Medicine, University of Melbourne St. Vincent's Institute of Medical Research, Fitzroy, Victoria 3065, Australia
| | - Kevin R W Ngoei
- Department of Medicine, University of Melbourne St. Vincent's Institute of Medical Research, Fitzroy, Victoria 3065, Australia
| | | | - Bruce E Kemp
- Department of Medicine, University of Melbourne St. Vincent's Institute of Medical Research, Fitzroy, Victoria 3065, Australia
| | - Elsdon Storey
- Department of Medicine (Neuroscience), Monash University, (Alfred Hospital Campus), Commercial Road, Melbourne, Victoria 3004, Australia
| | - Andrew Evans
- Department of Neurology, Royal Melbourne Hospital, Parkville, Victoria 3052, Australia
| | - Danuta Z Loesch
- Department of Psychology and Counselling, School of Psychology and Public Health, College of Science Health and Engineering, La Trobe University, Melbourne, Victoria 3986, Australia
| | - Paul R Fisher
- Discipline of Microbiology, Department of Physiology Anatomy and Microbiology, School of Life Sciences, College of Science Health and Engineering, La Trobe University, Melbourne, Victoria 3086, Australia
| |
Collapse
|
5
|
Loesch DZ, Annesley SJ, Trost N, Bui MQ, Lay ST, Storey E, De Piazza SW, Sanislav O, Francione LM, Hammersley EM, Tassone F, Francis D, Fisher PR. Novel Blood Biomarkers Are Associated with White Matter Lesions in Fragile X- Associated Tremor/Ataxia Syndrome. NEURODEGENER DIS 2016; 17:22-30. [PMID: 27602566 PMCID: PMC10964908 DOI: 10.1159/000446803] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2016] [Accepted: 05/13/2016] [Indexed: 11/19/2022] Open
Abstract
BACKGROUND The need for accessible cellular biomarkers of neurodegeneration in carriers of the fragile X mental retardation 1 (FMR1) premutation (PM) alleles. OBJECTIVE To assess the mitochondrial status and respiration in blood lymphoblasts from PM carriers manifesting the fragile X-associated tremor/ataxia syndrome (FXTAS) and non-FXTAS carriers, and their relationship with the brain white matter lesions. METHODS Oxygen consumption rates (OCR) and ATP synthesis using a Seahorse XFe24 Extracellular Flux Analyser, and steady-state parameters of mitochondrial function were assessed in cultured lymphoblasts from 16 PM males (including 11 FXTAS patients) and 9 matched controls. The regional white matter hyperintensity (WMH) scores were obtained from MRI. RESULTS Mitochondrial respiratory activity was significantly elevated in lymphoblasts from PM carriers compared with controls, with a 2- to 3-fold increase in basal and maximum OCR attributable to complex I activity, and ATP synthesis, accompanied by unaltered mitochondrial mass and membrane potential. The changes, which were more advanced in FXTAS patients, were significantly associated with the WMH scores in the supratentorial regions. CONCLUSION The dramatic increase in mitochondrial activity in lymphoblasts from PM carriers may represent either the early stages of disease (specific alterations in short-lived blood cells) or an activation of the lymphocytes under pathological situations. These changes may provide early, convenient blood biomarkers of clinical involvements.
Collapse
Affiliation(s)
- Danuta Z. Loesch
- Department of Psychology and Counselling, School of Psychology and Public Health, Melbourne, Vic., Australia
| | - Sarah J. Annesley
- Discipline of Microbiology, Department of Physiology Anatomy and Microbiology, School of Life Sciences, College of Science Health and Engineering, La Trobe University, Melbourne, Vic., Australia
| | - Nicholas Trost
- Medical Imaging Department, St Vincent's Hospital, Melbourne, Vic., Australia
| | - Minh Q. Bui
- Centre for Epidemiology and Biostatistics, Melbourne School of Population and Global Health, University of Melbourne, Melbourne, Vic., Australia
| | - Sui T. Lay
- Discipline of Microbiology, Department of Physiology Anatomy and Microbiology, School of Life Sciences, College of Science Health and Engineering, La Trobe University, Melbourne, Vic., Australia
| | - Elsdon Storey
- Department of Medicine (Neuroscience), Monash University (Alfred Hospital Campus), Melbourne, Vic., Australia
| | - Shawn W. De Piazza
- Discipline of Microbiology, Department of Physiology Anatomy and Microbiology, School of Life Sciences, College of Science Health and Engineering, La Trobe University, Melbourne, Vic., Australia
| | - Oana Sanislav
- Discipline of Microbiology, Department of Physiology Anatomy and Microbiology, School of Life Sciences, College of Science Health and Engineering, La Trobe University, Melbourne, Vic., Australia
| | - Lisa M. Francione
- Discipline of Microbiology, Department of Physiology Anatomy and Microbiology, School of Life Sciences, College of Science Health and Engineering, La Trobe University, Melbourne, Vic., Australia
| | - Eleanor M. Hammersley
- Department of Psychology and Counselling, School of Psychology and Public Health, Melbourne, Vic., Australia
| | | | - David Francis
- Cytomolecular Diagnostic Research, Victorian Clinical Genetic Services, Murdoch Institute, Royal Children's Hospital, Melbourne, Vic., Australia
| | - Paul R. Fisher
- Discipline of Microbiology, Department of Physiology Anatomy and Microbiology, School of Life Sciences, College of Science Health and Engineering, La Trobe University, Melbourne, Vic., Australia
| |
Collapse
|
6
|
Annesley SJ, Chen S, Francione LM, Sanislav O, Chavan AJ, Farah C, De Piazza SW, Storey CL, Ilievska J, Fernando SG, Smith PK, Lay ST, Fisher PR. Dictyostelium, a microbial model for brain disease. Biochim Biophys Acta Gen Subj 2013; 1840:1413-32. [PMID: 24161926 DOI: 10.1016/j.bbagen.2013.10.019] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2013] [Revised: 10/05/2013] [Accepted: 10/10/2013] [Indexed: 12/25/2022]
Abstract
BACKGROUND Most neurodegenerative diseases are associated with mitochondrial dysfunction. In humans, mutations in mitochondrial genes result in a range of phenotypic outcomes which do not correlate well with the underlying genetic cause. Other neurodegenerative diseases are caused by mutations that affect the function and trafficking of lysosomes, endosomes and autophagosomes. Many of the complexities of these human diseases can be avoided by studying them in the simple eukaryotic model Dictyostelium discoideum. SCOPE OF REVIEW This review describes research using Dictyostelium to study cytopathological pathways underlying a variety of neurodegenerative diseases including mitochondrial, lysosomal and vesicle trafficking disorders. MAJOR CONCLUSIONS Generalised mitochondrial respiratory deficiencies in Dictyostelium produce a consistent pattern of defective phenotypes that are caused by chronic activation of a cellular energy sensor AMPK (AMP-activated protein kinase) and not ATP deficiency per se. Surprisingly, when individual subunits of Complex I are knocked out, both AMPK-dependent and AMPK-independent, subunit-specific phenotypes are observed. Many nonmitochondrial proteins associated with neurological disorders have homologues in Dictyostelium and are associated with the function and trafficking of lysosomes and endosomes. Conversely, some genes associated with neurodegenerative disorders do not have homologues in Dictyostelium and this provides a unique avenue for studying these mutated proteins in the absence of endogeneous protein. GENERAL SIGNIFICANCE Using the Dictyostelium model we have gained insights into the sublethal cytopathological pathways whose dysregulation contributes to phenotypic outcomes in neurodegenerative disease. This work is beginning to distinguish correlation, cause and effect in the complex network of cross talk between the various organelles involved. This article is part of a Special Issue entitled Frontiers of Mitochondrial Research.
Collapse
Affiliation(s)
- S J Annesley
- Department of Microbiology, La Trobe University, Plenty Rd., Bundoora, VIC, Australia, 3086
| | - S Chen
- Department of Microbiology, La Trobe University, Plenty Rd., Bundoora, VIC, Australia, 3086
| | - L M Francione
- Department of Microbiology, La Trobe University, Plenty Rd., Bundoora, VIC, Australia, 3086
| | - O Sanislav
- Department of Microbiology, La Trobe University, Plenty Rd., Bundoora, VIC, Australia, 3086
| | - A J Chavan
- Department of Microbiology, La Trobe University, Plenty Rd., Bundoora, VIC, Australia, 3086
| | - C Farah
- Department of Microbiology, La Trobe University, Plenty Rd., Bundoora, VIC, Australia, 3086
| | - S W De Piazza
- Department of Microbiology, La Trobe University, Plenty Rd., Bundoora, VIC, Australia, 3086
| | - C L Storey
- Department of Microbiology, La Trobe University, Plenty Rd., Bundoora, VIC, Australia, 3086
| | - J Ilievska
- Department of Microbiology, La Trobe University, Plenty Rd., Bundoora, VIC, Australia, 3086
| | - S G Fernando
- Department of Microbiology, La Trobe University, Plenty Rd., Bundoora, VIC, Australia, 3086
| | - P K Smith
- Department of Microbiology, La Trobe University, Plenty Rd., Bundoora, VIC, Australia, 3086
| | - S T Lay
- Department of Microbiology, La Trobe University, Plenty Rd., Bundoora, VIC, Australia, 3086
| | - P R Fisher
- Department of Microbiology, La Trobe University, Plenty Rd., Bundoora, VIC, Australia, 3086.
| |
Collapse
|
7
|
Ahmed AU, Beech PL, Lay ST, Gilson PR, Fisher PR. Import-associated translational inhibition: novel in vivo evidence for cotranslational protein import into Dictyostelium discoideum mitochondria. Eukaryot Cell 2006; 5:1314-27. [PMID: 16896215 PMCID: PMC1539133 DOI: 10.1128/ec.00386-05] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/27/2005] [Accepted: 05/29/2006] [Indexed: 11/20/2022]
Abstract
To investigate protein import into the mitochondria of Dictyostelium discoideum, green fluorescent protein (GFP) was fused as a reporter protein either to variable lengths of the N-terminal region of chaperonin 60 (the first 23, 40, 80, 97, and 150 amino acids) or to the mitochondrial targeting sequence of DNA topoisomerase II. The fusion proteins were expressed in AX2 cells under the actin-15 promoter. Fluorescence images of GFP transformants confirmed that Dictyostelium chaperonin 60 is a mitochondrial protein. The level of the mitochondrially targeted GFP fusion proteins was unexpectedly much lower than the nontargeted (cytoplasmic) forms. The distinction between targeted and nontargeted protein activities was investigated at both the transcriptional and translational levels in vivo. We found that targeting GFP to the mitochondria results in reduced levels of the fusion protein even though transcription of the fusion gene and the stability of the protein are unaffected. [(35)S]methionine labeling and GFP immunoprecipitation confirmed that mitochondrially targeted GFP is translated at much slower rates than nontargeted GFP. The results indicate a novel phenomenon, import-associated translational inhibition, whereby protein import into the mitochondria limits the rate of translation. The simplest explanation for this is that import of the GFP fusion proteins occurs cotranslationally, i.e., protein synthesis and import into mitochondria are coupled events. Consistent with cotranslational import, Northern analysis showed that the GFP mRNA is associated with isolated mitochondria. This association occurred regardless of whether the GFP was fused to a mitochondrial leader peptide. However, the presence of an import-competent leader peptide stabilized the mRNA-mitochondria association, rendering it more resistant to extensive EDTA washing. In contrast with GFP, the mRNA of another test protein, aequorin, did not associate with the mitochondria, and its translation was unaffected by import of the encoded polypeptide into the mitochondria.
Collapse
Affiliation(s)
- Afsar U Ahmed
- Department of Microbiology, La Trobe University, Bundoora, Victoria 3086, Australia
| | | | | | | | | |
Collapse
|
8
|
Abstract
The single Dictyostelium chaperonin 60 gene, hspA, was cloned, sequenced and characterized. Sequence comparisons and a three-dimensional model for the structure of the encoded protein showed that it exhibits the conserved sequence and structural features expected for its role as the Dictyostelium mitochondrial chaperonin 60. Dictyostelium hspA contains two introns and, unusually for a member of this major heat shock gene family, is not stress-inducible in response to heat, cold or cadmium ions. Although transcription of hspA is down regulated during early Dictyostelium development in response to starvation, the levels of the chaperonin 60 protein remain constant throughout the life cycle. Consistent with the essential role of chaperonin 60 in mitochondrial biogenesis, we were unable to isolate mutants in which the hspA gene had been disrupted. However, transformants were isolated that exhibited differing levels of antisense inhibition of chaperonin 60 expression, depending upon the number of copies of the antisense-expressing plasmid in the genome. Orientation in phototaxis (and thermotaxis) was severely impaired in all antisense transformants, while growth and morphogenesis were markedly defective only in transformants with higher levels of antisense inhibition. This pattern of phenotypes is similar to that reported previously to result from targeted disruption of the mitochondrial large subunit rRNA gene in a subpopulation of mitochondria. This suggests that, regardless of the nature of the underlying genetic defect, mitochondrial deficiency impairs signal transduction more sensitively than other cellular activities.
Collapse
Affiliation(s)
- Martha Kotsifas
- Department of Microbiology, La Trobe University, Victoria 3086, Australia
| | | | | | | | | |
Collapse
|
9
|
Cheng KK, Leong KH, Yu TJ, Lay ST, Lin YL, Kuo SM, Chiang BN, Laura Meng CC, Wang B. [Ventricular septal defect with aortic incompetence]. Taiwan Yi Xue Hui Za Zhi 1983; 82:1288-92. [PMID: 6585475] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
|