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Huang Y, Liu L, Fang F, Zhou H, Liu X. Identification of a novel heterozygous variant in the PEX26 gene in an infant: a case report. Transl Pediatr 2024; 13:192-199. [PMID: 38323187 PMCID: PMC10839275 DOI: 10.21037/tp-23-454] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/06/2023] [Accepted: 12/10/2023] [Indexed: 02/08/2024] Open
Abstract
Background The protein PEX26 is involved in the biogenesis and maintenance of peroxisomes, which are organelles within cells. Dysfunction of PEX26 results in peroxisome biogenesis disorders (PBDs) complementation group 8 (CG8), leading to Zellweger spectrum disorders (ZSDs). These disorders present as a syndrome with multiple congenital anomalies, varying in clinical severity. Case Description We present the case of a 7-month-old boy who exhibited hepatic impairment with hepatomegaly, sensorineural hearing loss, developmental delay, abnormal ossification, and mild craniofacial dysmorphology. Tandem mass spectrometry analysis of plasma isolated from whole blood revealed a significant increase in the levels of very long chain fatty acids (VLCFAs) C26:0, C26:0/C22:0, and C24:0/C22:0, consistent with peroxisomal fatty acid oxidation disorder. Exome sequencing identified two variants in the PEX26 gene (c.347T>C and c.616C>T), with the latter being a suspected pathogenic variation. The variant can lead to a defect in the PEX26 gene, resulting in impaired peroxisome biogenesis, β-oxidation of VLCFAs, and disruption of other biochemical pathways. Ultimately, this cascade of events manifests as ZSDs. Currently, symptomatic supportive treatment is the main approach for managing this condition and regular follow-up is being conducted for the patient. Conclusions The present study introduces a novel heterozygous variant comprising two previously unidentified variants in the PEX26 gene, thereby expanding the range of known genetic alterations and highlighting the effectiveness of highly efficient exome sequencing in patients with undetermined multiple system dysfunctions.
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Affiliation(s)
- Yuan Huang
- Department of Pediatrics, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China
| | - Lingling Liu
- Department of Pediatrics, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China
| | - Feng Fang
- Department of Pediatrics, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China
| | - Hua Zhou
- Department of Pediatrics, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China
| | - Xinglou Liu
- Department of Pediatrics, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China
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2
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Yan B, Cao L, Gao L, Wei S, Wang M, Tian Y, Yang J, Chen E. PEX26 Functions as a Metastasis Suppressor in Colorectal Cancer. Dig Dis Sci 2024; 69:112-122. [PMID: 37957408 DOI: 10.1007/s10620-023-08168-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/04/2023] [Accepted: 10/23/2023] [Indexed: 11/15/2023]
Abstract
BACKGROUND/AIMS Aberrant Peroxisomal Biogenesis Factor 26 (PEX26) occurs in multiple cell process. However, the role of PEX26 in colorectal cancer (CRC) development remains unknown. We aimed to study PEX26 expression, regulation, and function in CRC cells. METHODS Using the bioinformatic analysis, real-time quantitative PCR, and immunohistochemistry staining, we detected the expression of PEX26 in CRC and normal tissues. We performed functional experiments in vitro to elucidate the effect of PEX26 on CRC cells. We analyzed the RNA-seq data to reveal the downstream regulating network of PEX26. RESULTS PEX26 is significantly down-regulated in CRC and its low expression correlates with the poor overall survival of CRC patients. We further demonstrated that PEX26 over-expression inhibits the ability of CRC cell migration, invasion, and epithelial-mesenchymal transition (EMT), while PEX26 knockdown promotes the malignant phenotypes of migration, invasion, and EMT via activating the Wnt pathway. CONCLUSION Overall, our results showed that the loss of PEX26 contributes to the malignant phenotype of CRC. PEX26 may serve as a novel metastasis repressor for CRC.
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Affiliation(s)
- Bianbian Yan
- Key Laboratory of Resource Biology and Biotechnology in Western China, Ministry of Education, School of Life Sciences, Northwest University, Xi'an, China
- Institute of Preventive Genomic Medicine, School of Life Sciences, Northwest University, Xi'an, China
| | - Lichao Cao
- Key Laboratory of Resource Biology and Biotechnology in Western China, Ministry of Education, School of Life Sciences, Northwest University, Xi'an, China
- Institute of Preventive Genomic Medicine, School of Life Sciences, Northwest University, Xi'an, China
| | - Liyang Gao
- Key Laboratory of Resource Biology and Biotechnology in Western China, Ministry of Education, School of Life Sciences, Northwest University, Xi'an, China
- Institute of Preventive Genomic Medicine, School of Life Sciences, Northwest University, Xi'an, China
| | - Shangqing Wei
- Key Laboratory of Resource Biology and Biotechnology in Western China, Ministry of Education, School of Life Sciences, Northwest University, Xi'an, China
- Institute of Preventive Genomic Medicine, School of Life Sciences, Northwest University, Xi'an, China
| | - Mengwei Wang
- Key Laboratory of Resource Biology and Biotechnology in Western China, Ministry of Education, School of Life Sciences, Northwest University, Xi'an, China
- Institute of Preventive Genomic Medicine, School of Life Sciences, Northwest University, Xi'an, China
| | - Ye Tian
- Key Laboratory of Resource Biology and Biotechnology in Western China, Ministry of Education, School of Life Sciences, Northwest University, Xi'an, China
- Institute of Preventive Genomic Medicine, School of Life Sciences, Northwest University, Xi'an, China
| | - Jin Yang
- Key Laboratory of Resource Biology and Biotechnology in Western China, Ministry of Education, School of Life Sciences, Northwest University, Xi'an, China
- Institute of Preventive Genomic Medicine, School of Life Sciences, Northwest University, Xi'an, China
| | - Erfei Chen
- Key Laboratory of Resource Biology and Biotechnology in Western China, Ministry of Education, School of Life Sciences, Northwest University, Xi'an, China.
- Institute of Preventive Genomic Medicine, School of Life Sciences, Northwest University, Xi'an, China.
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Judy RM, Sheedy CJ, Gardner BM. Insights into the Structure and Function of the Pex1/Pex6 AAA-ATPase in Peroxisome Homeostasis. Cells 2022; 11. [PMID: 35805150 DOI: 10.3390/cells11132067] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2022] [Revised: 06/25/2022] [Accepted: 06/26/2022] [Indexed: 02/01/2023] Open
Abstract
The AAA-ATPases Pex1 and Pex6 are required for the formation and maintenance of peroxisomes, membrane-bound organelles that harbor enzymes for specialized metabolism. Together, Pex1 and Pex6 form a heterohexameric AAA-ATPase capable of unfolding substrate proteins via processive threading through a central pore. Here, we review the proposed roles for Pex1/Pex6 in peroxisome biogenesis and degradation, discussing how the unfolding of potential substrates contributes to peroxisome homeostasis. We also consider how advances in cryo-EM, computational structure prediction, and mechanisms of related ATPases are improving our understanding of how Pex1/Pex6 converts ATP hydrolysis into mechanical force. Since mutations in PEX1 and PEX6 cause the majority of known cases of peroxisome biogenesis disorders such as Zellweger syndrome, insights into Pex1/Pex6 structure and function are important for understanding peroxisomes in human health and disease.
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Lotz-Havla AS, Woidy M, Guder P, Schmiesing J, Erdmann R, Waterham HR, Muntau AC, Gersting SW. Edgetic Perturbations Contribute to Phenotypic Variability in PEX26 Deficiency. Front Genet 2021; 12:726174. [PMID: 34804114 PMCID: PMC8600046 DOI: 10.3389/fgene.2021.726174] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [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: 06/16/2021] [Accepted: 10/18/2021] [Indexed: 12/11/2022] Open
Abstract
Peroxisomes share metabolic pathways with other organelles and peroxisomes are embedded into key cellular processes. However, the specific function of many peroxisomal proteins remains unclear and restricted knowledge of the peroxisomal protein interaction network limits a precise mapping of this network into the cellular metabolism. Inborn peroxisomal disorders are autosomal or X-linked recessive diseases that affect peroxisomal biogenesis (PBD) and/or peroxisomal metabolism. Pathogenic variants in the PEX26 gene lead to peroxisomal disorders of the full Zellweger spectrum continuum. To investigate the phenotypic complexity of PEX26 deficiency, we performed a combined organelle protein interaction screen and network medicine approach and 1) analyzed whether PEX26 establishes interactions with other peroxisomal proteins, 2) deciphered the PEX26 interaction network, 3) determined how PEX26 is involved in further processes of peroxisomal biogenesis and metabolism, and 4) showed how variant-specific disruption of protein-protein interactions (edgetic perturbations) may contribute to phenotypic variability in PEX26 deficient patients. The discovery of 14 novel protein-protein interactions for PEX26 revealed a hub position of PEX26 inside the peroxisomal interactome. Analysis of edgetic perturbations of PEX26 variants revealed a strong correlation between the number of affected protein-protein interactions and the molecular phenotype of matrix protein import. The role of PEX26 in peroxisomal biogenesis was expanded encompassing matrix protein import, division and proliferation, and membrane assembly. Moreover, the PEX26 interaction network intersects with cellular lipid metabolism at different steps. The results of this study expand the knowledge about the function of PEX26 and refine genotype-phenotype correlations, which may contribute to our understanding of the underlying disease mechanism of PEX26 deficiency.
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Affiliation(s)
- Amelie S Lotz-Havla
- Dr. von Hauner Children's Hospital, Ludwig-Maximilians-University, Munich, Germany
| | - Mathias Woidy
- University Children's Research, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
| | - Philipp Guder
- University Children's Research, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
| | - Jessica Schmiesing
- University Children's Research, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
| | - Ralf Erdmann
- Institut für Physiologische Chemie, Medizinische Fakultät der Ruhr-Universität Bochum, Bochum, Germany
| | - Hans R Waterham
- Laboratory Genetic Metabolic Diseases, Academic Medical Center, University of Amsterdam, Amsterdam, Netherlands
| | - Ania C Muntau
- Children's Hospital, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
| | - Søren W Gersting
- University Children's Research, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
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5
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He Y, Lin SB, Li WX, Yang L, Zhang R, Chen C, Yuan L. PEX26 gene genotype-phenotype correlation in neonates with Zellweger syndrome. Transl Pediatr 2021; 10:1825-1833. [PMID: 34430430 PMCID: PMC8349955 DOI: 10.21037/tp-21-103] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/17/2021] [Accepted: 05/25/2021] [Indexed: 12/20/2022] Open
Abstract
BACKGROUND Zellweger syndrome (ZS) is commonly manifested as facial deformities, hypotonia, and liver dysfunction. However, ZS caused by PEX26 gene mutation shows a broad and dispersed clinical pattern. In this study, the PEX26 gene in ZS was analyzed to enrich its clinical characteristics. Meanwhile, phenotypic and genotypic characteristics of Zellweger spectrum disorder (ZSD) induced by PEX26 mutation were evaluated. METHODS The clinical data of newborn with ZS in our hospital were analyzed retrospectively. We performed WES and found that the infant carried the PEX26 gene variant. We searched the biomedical literature databases (PubMed, Web of Science, and EMBASE) to compare clinical features and genotypes. RESULTS The neonate developed facial deformities, hypotonia, feeding difficulties, and seizures. Her homozygous variant was found in the PEX26 gene (NM_017929: exon2: c.34del) inherited from both parents. Electronic databases, including our case, reported 32 pathogenic variants in PEX26. We found that variation c.292C> T accounted for the largest proportion of PEX26 mutations (16/66, 24.24%). The proportion of deleterious mutations in ZS patients was significantly higher than that in NALD and IRD patients. CONCLUSIONS We identified pathogenic variations in the PEX26 gene and expanded the known mutant spectrum. By comparing patients with PEX26 mutations, the study determined that a significantly higher percentage of deleterious mutations in ZS was associated with severe clinical phenotypic characteristics.
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Affiliation(s)
- Yue He
- Department of Neonatology, Children's Hospital of Fudan University, Shanghai, China
| | - Sam Bill Lin
- Department of Neonatology, Children's Hospital of Fudan University, Shanghai, China
| | - Wen-Xuan Li
- Department of Neonatology, Children's Hospital of Fudan University, Shanghai, China
| | - Lin Yang
- Clinical Genetic Center, Children's Hospital of Fudan University, Shanghai, China
| | - Rong Zhang
- Department of Neonatology, Children's Hospital of Fudan University, Shanghai, China
| | - Chao Chen
- Department of Neonatology, Children's Hospital of Fudan University, Shanghai, China
| | - Lin Yuan
- Department of Neonatology, Children's Hospital of Fudan University, Shanghai, China
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Kim YJ, Abe Y, Kim YJ, Fujiki Y, Kim JW. Identification of a Homozygous PEX26 Mutation in a Heimler Syndrome Patient. Genes (Basel) 2021; 12:646. [PMID: 33926089 DOI: 10.3390/genes12050646] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2021] [Revised: 04/26/2021] [Accepted: 04/26/2021] [Indexed: 12/30/2022] Open
Abstract
This study aimed to identify the molecular genetic etiology of an 8-year-old boy with amelogenesis imperfecta in permanent dentition. Bilateral cochlear implants were placed due to sensorineural hearing loss, and there was no other family member with a similar phenotype. Peripheral blood samples were collected with the understanding and written consent of the participating family members. A constitutional chromosome study was performed for the proband. Genomic DNA was isolated, and whole exome sequencing was performed. A series of bioinformatic analyses were performed with the obtained paired-end sequencing reads, and the variants were filtered and annotated with dbSNP147. There was no abnormality in the constitutional chromosome study. Whole exome sequencing analysis with trio samples identified a homozygous mutation (c.506T>C, p. (Leu169Pro)) in the PEX26 gene. We verified “temperature sensitivity (ts)” of patient-derived Pex26-L169P by expression in pex26 CHO mutant ZP167 cells to determine the effect of the L169P mutation on Pex26 function. The L169P mutation causes a mild ts-cellular phenotype representing the decreased peroxisomal import of catalase. This study supports the finding that the recessive mutations in PEX26 are associated with Heimler syndrome and demonstrates the importance of an early and correct diagnosis.
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Guder P, Lotz-Havla AS, Woidy M, Reiß DD, Danecka MK, Schatz UA, Becker M, Ensenauer R, Pagel P, Büttner L, Muntau AC, Gersting SW. Isoform-specific domain organization determines conformation and function of the peroxisomal biogenesis factor PEX26. Biochim Biophys Acta Mol Cell Res 2018; 1866:518-531. [PMID: 30366024 DOI: 10.1016/j.bbamcr.2018.10.013] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/29/2018] [Revised: 10/11/2018] [Accepted: 10/18/2018] [Indexed: 10/28/2022]
Abstract
Peroxisomal biogenesis factor PEX26 is a membrane anchor for the multi-subunit PEX1-PEX6 protein complex that controls ubiquitination and dislocation of PEX5 cargo receptors for peroxisomal matrix protein import. PEX26 associates with the peroxisomal translocation pore via PEX14 and a splice variant (PEX26Δex5) of unknown function has been reported. Here, we demonstrate PEX26 homooligomerization mediated by two heptad repeat domains adjacent to the transmembrane domain. We show that isoform-specific domain organization determines PEX26 oligomerization and impacts peroxisomal β-oxidation and proliferation. PEX26 and PEX26Δex5 displayed different patterns of interaction with PEX2-PEX10 or PEX13-PEX14 complexes, which relate to distinct pre-peroxisomes in the de novo synthesis pathway. Our data support an alternative PEX14-dependent mechanism of peroxisomal membrane association for the splice variant, which lacks a transmembrane domain. Structure-function relationships of PEX26 isoforms explain an extended function in peroxisomal homeostasis and these findings may improve our understanding of the broad phenotype of PEX26-associated human disorders.
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Affiliation(s)
- Philipp Guder
- University Children's Research@Kinder-UKE, University Medical Center Hamburg-Eppendorf, 20246 Hamburg, Germany; Children's Hospital, University Medical Center Hamburg-Eppendorf, 20246 Hamburg, Germany
| | - Amelie S Lotz-Havla
- Dr. von Hauner Children's Hospital, Ludwig-Maximilians-University, 80337 Munich, Germany
| | - Mathias Woidy
- University Children's Research@Kinder-UKE, University Medical Center Hamburg-Eppendorf, 20246 Hamburg, Germany; Children's Hospital, University Medical Center Hamburg-Eppendorf, 20246 Hamburg, Germany
| | - Dunja D Reiß
- Dr. von Hauner Children's Hospital, Ludwig-Maximilians-University, 80337 Munich, Germany
| | - Marta K Danecka
- University Children's Research@Kinder-UKE, University Medical Center Hamburg-Eppendorf, 20246 Hamburg, Germany
| | - Ulrich A Schatz
- Department for Medical Genetics, Molecular and Clinical Pharmacology, Medical University Innsbruck, 6020 Innsbruck, Austria
| | - Marc Becker
- Dr. von Hauner Children's Hospital, Ludwig-Maximilians-University, 80337 Munich, Germany; Labor Becker Olgemöller und Kollegen, 81671 Munich, Germany
| | - Regina Ensenauer
- Dr. von Hauner Children's Hospital, Ludwig-Maximilians-University, 80337 Munich, Germany; Experimental Pediatrics, Department of General Pediatrics, Neonatology and Pediatric Cardiology, University Children's Hospital, Heinrich Heine University Düsseldorf, 40225 Düsseldorf, Germany
| | - Philipp Pagel
- Lehrstuhl für Genomorientierte Bioinformatik, Technische Universität, 85350 Freising, Germany; numares GmbH, Josef-Engert-Str. 9, 93053 Regensburg, Germany
| | - Lars Büttner
- Dr. von Hauner Children's Hospital, Ludwig-Maximilians-University, 80337 Munich, Germany
| | - Ania C Muntau
- Children's Hospital, University Medical Center Hamburg-Eppendorf, 20246 Hamburg, Germany
| | - Søren W Gersting
- University Children's Research@Kinder-UKE, University Medical Center Hamburg-Eppendorf, 20246 Hamburg, Germany; Children's Hospital, University Medical Center Hamburg-Eppendorf, 20246 Hamburg, Germany.
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Law KB, Bronte-Tinkew D, Di Pietro E, Snowden A, Jones RO, Moser A, Brumell JH, Braverman N, Kim PK. The peroxisomal AAA ATPase complex prevents pexophagy and development of peroxisome biogenesis disorders. Autophagy 2018; 13:868-884. [PMID: 28521612 PMCID: PMC5446072 DOI: 10.1080/15548627.2017.1291470] [Citation(s) in RCA: 70] [Impact Index Per Article: 11.7] [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] [Indexed: 02/01/2023] Open
Abstract
Peroxisome biogenesis disorders (PBDs) are metabolic disorders caused by the loss of peroxisomes. The majority of PBDs result from mutation in one of 3 genes that encode for the peroxisomal AAA ATPase complex (AAA-complex) required for cycling PEX5 for peroxisomal matrix protein import. Mutations in these genes are thought to result in a defect in peroxisome assembly by preventing the import of matrix proteins. However, we show here that loss of the AAA-complex does not prevent matrix protein import, but instead causes an upregulation of peroxisome degradation by macroautophagy, or pexophagy. The loss of AAA-complex function in cells results in the accumulation of ubiquitinated PEX5 on the peroxisomal membrane that signals pexophagy. Inhibiting autophagy by genetic or pharmacological approaches rescues peroxisome number, protein import and function. Our findings suggest that the peroxisomal AAA-complex is required for peroxisome quality control, whereas its absence results in the selective degradation of the peroxisome. Thus the loss of peroxisomes in PBD patients with mutations in their peroxisomal AAA-complex is a result of increased pexophagy. Our study also provides a framework for the development of novel therapeutic treatments for PBDs.
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Affiliation(s)
- Kelsey B Law
- a Cell Biology Program , Hospital for Sick Children, Peter Gilgan Centre for Research and Learning , Toronto , ON , Canada.,b Department of Biochemistry , University of Toronto , Toronto , ON , Canada
| | - Dana Bronte-Tinkew
- a Cell Biology Program , Hospital for Sick Children, Peter Gilgan Centre for Research and Learning , Toronto , ON , Canada
| | - Erminia Di Pietro
- c Research Institute of the MUHC and McGill University , Montreal , QC , Canada
| | - Ann Snowden
- d Kennedy Krieger Institute , Baltimore , MD , USA
| | | | - Ann Moser
- d Kennedy Krieger Institute , Baltimore , MD , USA
| | - John H Brumell
- a Cell Biology Program , Hospital for Sick Children, Peter Gilgan Centre for Research and Learning , Toronto , ON , Canada.,e Department of Molecular Genetics , University of Toronto , Toronto , ON , Canada.,f Institute of Medical Science, University of Toronto , Toronto , ON , Canada.,g SickKids IBD Centre , Hospital for Sick Children , Toronto , ON , Canada
| | - Nancy Braverman
- c Research Institute of the MUHC and McGill University , Montreal , QC , Canada
| | - Peter K Kim
- a Cell Biology Program , Hospital for Sick Children, Peter Gilgan Centre for Research and Learning , Toronto , ON , Canada.,b Department of Biochemistry , University of Toronto , Toronto , ON , Canada
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Gonzalez KL, Fleming WA, Kao YT, Wright ZJ, Venkova SV, Ventura MJ, Bartel B. Disparate peroxisome-related defects in Arabidopsis pex6 and pex26 mutants link peroxisomal retrotranslocation and oil body utilization. Plant J 2017; 92:110-128. [PMID: 28742939 PMCID: PMC5605450 DOI: 10.1111/tpj.13641] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/07/2017] [Revised: 06/22/2017] [Accepted: 07/18/2017] [Indexed: 05/29/2023]
Abstract
Catabolism of fatty acids stored in oil bodies is essential for seed germination and seedling development in Arabidopsis. This fatty acid breakdown occurs in peroxisomes, organelles that sequester oxidative reactions. Import of peroxisomal enzymes is facilitated by peroxins including PEX5, a receptor that delivers cargo proteins from the cytosol to the peroxisomal matrix. After cargo delivery, a complex of the PEX1 and PEX6 ATPases and the PEX26 tail-anchored membrane protein removes ubiquitinated PEX5 from the peroxisomal membrane. We identified Arabidopsis pex6 and pex26 mutants by screening for inefficient seedling β-oxidation phenotypes. The mutants displayed distinct defects in growth, response to a peroxisomally metabolized auxin precursor, and peroxisomal protein import. The low PEX5 levels in these mutants were increased by treatment with a proteasome inhibitor or by combining pex26 with peroxisome-associated ubiquitination machinery mutants, suggesting that ubiquitinated PEX5 is degraded by the proteasome when the function of PEX6 or PEX26 is reduced. Combining pex26 with mutations that increase PEX5 levels either worsened or improved pex26 physiological and molecular defects, depending on the introduced lesion. Moreover, elevating PEX5 levels via a 35S:PEX5 transgene exacerbated pex26 defects and ameliorated the defects of only a subset of pex6 alleles, implying that decreased PEX5 is not the sole molecular deficiency in these mutants. We found peroxisomes clustered around persisting oil bodies in pex6 and pex26 seedlings, suggesting a role for peroxisomal retrotranslocation machinery in oil body utilization. The disparate phenotypes of these pex alleles may reflect unanticipated functions of the peroxisomal ATPase complex.
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Affiliation(s)
| | | | | | | | | | | | - Bonnie Bartel
- Corresponding author: Bonnie Bartel, Department of Biosciences, MS-140, Rice University, 6100 Main St., Houston TX, USA. Phone: 713-348-5602, Fax: 713-348-5154;
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10
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Abstract
Peroxisome biogenesis disorders (PBDs) is a group of diseases caused by mutations in one of the peroxins, proteins responsible for biogenesis of the peroxisomes. In recent years, it became clear that many peroxins (e.g., PEX3 and PEX14) play additional roles in peroxisome homeostasis (such as promoting autophagic degradation of peroxisomes or pexophagy), which are often opposite to their originally established functions in peroxisome formation and maintenance. Even more interesting, the peroxins that make up the peroxisomal AAA ATPase complex (AAA-complex) in yeast (Pex1, Pex6 and Pex15) or mammals (PEX1, PEX6, PEX26) are responsible for the downregulation of pexophagy. Moreover, this might be even their primary role in human: to prevent pexophagy by removing from the peroxisomal membrane the ubiquitinated peroxisomal matrix protein import receptor, Ub-PEX5, which is also a signal for the Ub-binding pexophagy receptor, NBR1. Remarkably, the peroxisomes rescued from pexophagy by autophagic inhibitors in PEX1G843D (the most common PBD mutation) cells are able to import matrix proteins and improve their biochemical function suggesting that the AAA-complex per se is not essential for the protein import function in human. This paradigm-shifting discovery published in the current issue of Autophagy has raised hope for up to 65% of all PBD patients with various deficiencies in the AAA-complex. Recognizing PEX1, PEX6 and PEX26 as pexophagy suppressors will allow treating these patients with a new range of tools designed to target mammalian pexophagy.
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Affiliation(s)
- Taras Y Nazarko
- a Section of Molecular Biology , Division of Biological Sciences, UC San Diego , La Jolla , CA , USA
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