PEX5, the Shuttling Import Receptor for Peroxisomal Matrix Proteins, Is a Redox-Sensitive Protein

Peroxisome maintenance depends on the import of nuclear-encoded proteins from the cytosol. The vast majority of these proteins is destined for the peroxisomal lumen and contains a C-terminal peroxisomal targeting signal, called PTS1. This targeting signal is recognized in the cytosol by the receptor PEX5. After docking at the peroxisomal membrane and release of the cargo into the organelle matrix, PEX5 is recycled to the cytosol through a process requiring monoubiquitination of an N-terminal, cytosolically exposed cysteine residue (Cys11 in the human protein). At present, the reason why a cysteine, and not a lysine residue, is the target of ubiquitination remains unclear. Here, we provide evidence that PTS1 protein import into human fibr oblasts is a redox-sensitive process. We also demonstrate that Cys11 in human PEX5 functions as a redox switch that regulates PEX5 activity in response to intracellular oxidative stress. Finally, we show that exposure of human PEX5 to oxidized glutathione results in a ubiquitination-deficient PEX5 molecule, and that substitution of Cys11 by a lysine can counteract this effect. In summary, these findings reveal that the activity of PEX5, and hence PTS1 import, is controlled by the redox state of the cytosol. The potential physiological implications of these findings are discussed.The authors are grateful to Dr. Ann Moser (Baltimore, USA) for the primary PEX5 null human fibroblasts. This work was supported bygrants from the ‘Fonds voor Wetenschappelijk Onderzoek-Vlaanderen (Onderzoeksproject G.0754.09)’ (to M. F. and P. P.V.V.), by the KU Leuven grants OT/09/045 (toM. F. and P. P. V. V.) and DBOF/10/059 (to P. P. V. V. and M. F.), and by FEDER funds through the Operational Competitiveness Programme – COMPETE and by National Funds through FCT – Fundac¸ão para a Ciência e a Tecnologia under the project FCOMP-01-0124-FEDER-019731 (PTDC/BIA-BCM/118577/2010) (to J. E. A.). M.N. is supported by a FLOF fellowship from the Department of Cellular and Molecular Medicine, KU Leuven. B.W. is a recipient of a DBOF fellowship (DBOF/10/059) from the KU Leuven. C. P. G. is supported by Fundac¸ão para a Ciência e a Tecnologia, Programa Operacional Potencial Humano do QREN, and Fundo Social Europeu

The life of the peroxisome: from birth to death

Peroxisomes are dynamic and metabolically plastic organelles. Their multiplicity of functions impacts on many aspects of plant development and survival. New functions for plant peroxisomes such as in the synthesis of biotin, ubiquinone and phylloquinone are being uncovered and their role in generating reactive oxygen species (ROS) and reactive nitrogen species (RNS) as signalling hubs in defence and development is becoming appreciated. Understanding of the biogenesis of peroxisomes, mechanisms of import and turnover of their protein complement, and the wholesale destruction of the organelle by specific autophagic processes is giving new insight into the ways that plants can adjust peroxisome function in response to changing needs

Interplay between peroxisome biogenesis and redox balance in mammalian cells.

Peroxisomes are multifunctional organelles with a wide spectrum of functions. Currently, there is growing evidence that alterations in peroxisome function can also be linked to cellular aging and age-related diseases. The molecular mechanisms underlying these phenomena are not yet known. During the past decades, many efforts have been done in order to get more insight on the contribution of this organelle to cellularredox metabolism and aging. To shed more light on these mechanisms, we aspired to develop first a suitable approach for the compartment-specific modulation and monitoring of the cellular redox state. Therefore, we designed and validated genetically-encoded probes suitable for the generation and detection of ROS in peroxisomes, mitochondria and the cytosol. A combined use of these tools allowed us to draw some interesting conclusions. We demonstrated that the intraperoxisomal redox state is influenced by cellular metabolism. We also showed that disturbances in the peroxisomal redox state may trigger the degradation of the organelle. In addition, we were able to confirm and extend previous observations that peroxisomes and mitochondria share a redox-sensitive relationship. For example, we found that the mitochondrial redox state is perturbed in cells lacking catalase or functional peroxisomes. Furthermore, we provided direct evidence that the import of PTS1 matrix proteins into peroxisomes is aredox-regulated process, and that this redox-sensitivity is mediated byPex5p. Briefly, we demonstrated that Cys11 of human Pex5p functions as a redox switch that modulates Pex5p activity in response to intracellular oxidative stress, most likely by modulating its monoubiquitination at the peroxisomal membrane. Finally, we found that Fis1, a protein displaying a peroxisomal/mitochondrial distribution pattern, can be exchanged between individual peroxisomes. Although the molecular mechanisms underlying the redox-sensitive relationship between peroxisomes and mitochondria are far from being understood, the results presented in this work contribute to our understanding of how peroxisomes may participate in the complex intracellular redox communication network. As such, the outcome ofthese studies sheds more light on how cellular oxidative stress may contribute to a demise of peroxisome function, a condition associated with cellular senescence, organismal aging and age-related diseases.justify;text-justify:inter-ideograph;text-indent:1.0cm;line-height:150%">mso-bidi-font-family:"Times New Roman";mso-bidi-theme-font:minor-bidi;color:black;mso-ansi-language:EN-US;mso-bidi-font-weight:bold" lang="EN-US">mso-bidi-font-family:"Times New Roman";mso-bidi-theme-font:minor-bidi;color:black;mso-ansi-language:EN-US" lang="EN-US"> 21 false falsefalse RU X-NONE X-NONE LatentStyleCount="267"> classid="clsid:38481807-CA0E-42D2-BF39-B33AF135CC4D" id=ieooui>st1\:*{behavior:url(#ieooui) } /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-parent:""; mso-padding-alt:0cm5.4pt 0cm 5.4pt; mso-para-margin-top:0cm; mso-para-margin-right:0cm; mso-para-margin-bottom:10.0pt; mso-para-margin-left:0cm; line-height:115%; mso-pagination:widow-orphan; font-size:11.0pt; font-family:"Calibri","sans-serif"; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin; mso-bidi-font-family:"Times New Roman"; mso-bidi-theme-font:minor-bidi;}nrpages: 129status: publishe

Peroxisome degradation in mammals: mechanisms of action, recent advances, and perspectives

Peroxisomes are remarkably dynamic organelles that participate in a diverse array of cellular processes, including the metabolism of lipids and reactive oxygen species. In order to regulate peroxisome function in response to changing nutritional and environmental stimuli, new organelles need to be formed and superfluous and dysfunctional organelles have to be selectively removed. Disturbances in any of these processes have been associated with the etiology and progression of various congenital neurodegenerative and age-related human disorders. The aim of this review is to critically explore our current knowledge of how peroxisomes are degraded in mammalian cells and how defects in this process may contribute to human disease. Some of the key issues highlighted include the current concepts of peroxisome removal, the peroxisome quality control mechanisms, the initial triggers for peroxisome degradation, the factors for dysfunctional peroxisome recognition, and the regulation of peroxisome homeostasis. We also dissect the functional and mechanistic relationship between different forms of selective organelle degradation and consider how lysosomal dysfunction may lead to defects in peroxisome turnover. In addition, we draw lessons from studies on other organisms and extrapolate this knowledge to mammals. Finally, we discuss the potential pathological implications of dysfunctional peroxisome degradation for human health.status: publishe

Role of peroxisomes in ROS/RNS-metabolism: Implications for human disease

Peroxisomes are cell organelles that play a central role in lipid metabolism. At the same time, these organelles generate reactive oxygen and nitrogen species as byproducts. Peroxisomes also possess intricate protective mechanisms to counteract oxidative stress and maintain redox balance. An imbalance between peroxisomal reactive oxygen species/reactive nitrogen species production and removal may possibly damage biomolecules, perturb cellular thiol levels, and deregulate cellular signaling pathways implicated in a variety of human diseases. Somewhat surprisingly, the potential role of peroxisomes in cellular redox metabolism has been underestimated for a long time. However, in recent years, peroxisomal reactive oxygen species/reactive nitrogen species metabolism and signaling have become the focus of a rapidly evolving and multidisciplinary research field with great prospects. This review is mainly devoted to discuss evidence supporting the notion that peroxisomal metabolism and oxidative stress are intimately interconnected and associated with age-related diseases. We focus on several key aspects of how peroxisomes contribute to cellular reactive oxygen species/reactive nitrogen species levels in mammalian cells and how these cells cope with peroxisome-derived oxidative stress. We also provide a brief overview of recent strategies that have been successfully employed to detect and modulate the peroxisomal redox status. Finally, we highlight some gaps in our knowledge and propose potential avenues for further research. This article is part of a Special Issue entitled: Metabolic Functions and Biogenesis of peroxisomes in Health and Disease.status: publishe

The peroxisomal import receptor PEX5 functions as a stress sensor, retaining catalase in the cytosol in times of oxidative stress

Accumulating evidence indicates that peroxisome functioning, catalase localization, and cellular oxidative balance are intimately interconnected. Nevertheless, it remains largely unclear why modest increases in the cellular redox state especially interfere with the subcellular localization of catalase, the most abundant peroxisomal antioxidant enzyme. This study aimed at gaining more insight into this phenomenon. Therefore, we first established a simple and powerful approach to study peroxisomal protein import and protein-protein interactions in living cells in response to changes in redox state. By employing this approach, we confirm and extend previous observations that Cys-11 of human PEX5, the shuttling import receptor for peroxisomal matrix proteins containing a C-terminal peroxisomal targeting signal (PTS1), functions as a redox switch that modulates the protein's activity in response to intracellular oxidative stress. In addition, we show that oxidative stress affects the import of catalase, a non-canonical PTS1-containing protein, more than the import of a reporter protein containing a canonical PTS1. Furthermore, we demonstrate that changes in the local redox state do not affect PEX5-substrate binding and that human PEX5 does not oligomerize in cellulo, not even when the cells are exposed to oxidative stress. Finally, we present evidence that catalase retained in the cytosol can protect against H2O2-mediated redox changes in a manner that peroxisomally targeted catalase does not. Together, these findings lend credit to the idea that inefficient catalase import, when coupled with the role of PEX5 as a redox-regulated import receptor, constitutes a cellular defense mechanism to combat oxidative insults of extra-peroxisomal origin.status: publishe

Dissecting Peroxisome-Mediated Signaling Pathways: a New and Exciting Research Field

© 2014 Springer-Verlag Wien. All rights reserved. Peroxisomes are multifunctional organelles that play an important role in the metabolism of lipids and reactive oxygen species. As many cellular signaling functions are regulated via lipids, lipid second messengers, and oxidative stress-related factors, it is not surprising to see that these organelles are increasingly recognized as critical regulators of cellular signaling events. To fulfill these signaling functions, peroxisomes physically and functionally interact with other cell organelles, including mitochondria. Recent progress in the development of tools to visualize and modulate molecular processes at the subcellular level has made it possible to gain a better insight into the potential mechanisms governing peroxisomal signaling. This chapter is intended to provide a comprehensive overview of the tools and strategies that are currently available to study peroxisome-mediated signaling pathways in living cells. To provide the reader with relevant background information, we also highlight key studies that have contributed to our understanding of how peroxisomes may function as important sites of redox-, lipid-, inflammatory-, and viral-mediated signal transduction.status: publishe

Aging, age-related diseases and peroxisomes

pages: 45-65edition: 1ststatus: publishe

PEX5, the Shuttling Import Receptor for Peroxisomal Matrix Proteins, Is a Redox-Sensitive Protein

Peroxisome maintenance depends on the import of nuclear-encoded proteins from the cytosol. The vast majority of these proteins is destined for the peroxisomal lumen and contains a C-terminal peroxisomal targeting signal, called PTS1. This targeting signal is recognized in the cytosol by the receptor PEX5. After docking at the peroxisomal membrane and release of the cargo into the organelle matrix, PEX5 is recycled to the cytosol through a process requiring monoubiquitination of an N-terminal, cytosolically exposed cysteine residue (Cys11 in the human protein). At present, the reason why a cysteine, and not a lysine residue, is the target of ubiquitination remains unclear. Here, we provide evidence that PTS1 protein import into human fibroblasts is a redox-sensitive process. We also demonstrate that Cys11 in human PEX5 functions as a redox switch that regulates PEX5 activity in response to intracellular oxidative stress. Finally, we show that exposure of human PEX5 to oxidized glutathione results in a ubiquitination-deficient PEX5 molecule, and that substitution of Cys11 by a lysine can counteract this effect. In summary, these findings reveal that the activity of PEX5, and hence PTS1 import, is controlled by the redox state of the cytosol. The potential physiological implications of these findings are discussed.status: publishe

Mitochondria are targets for peroxisome-derived oxidative stress in cultured mammalian cells

Many cellular processes are driven by spatially and temporally regulated redox-dependent signaling events. Although mounting evidence indicates that organelles such as the endoplasmic reticulum and mitochondria can function as signaling platforms for oxidative stress-regulated pathways, little is known about the role of peroxisomes in these processes. In this study, we employ targeted variants of the genetically encoded photosensitizer KillerRed to gain a better insight into the interplay between peroxisomes and cellular oxidative stress. We show that the phototoxic effects of peroxisomal KillerRed induce mitochondria-mediated cell death and that this process can be counteracted by targeted overexpression of a select set of antioxidant enzymes, including peroxisomal glutathione S-transferase kappa 1, superoxide dismutase 1, and mitochondrial catalase. We also present evidence that peroxisomal disease cell lines deficient in plasmalogen biosynthesis or peroxisome assembly are more sensitive to KillerRed-induced oxidative stress than control cells. Collectively, these findings confirm and extend previous observations suggesting that disturbances in peroxisomal redox control and metabolism can sensitize cells to oxidative stress. In addition, they lend strong support to the ideas that peroxisomes and mitochondria share a redox-sensitive relationship and that the redox communication between these organelles is not only mediated by diffusion of reactive oxygen species from one compartment to the other. Finally, these findings indicate that mitochondria may act as dynamic receivers, integrators, and transmitters of peroxisome-derived mediators of oxidative stress, and this may have profound implications for our views on cellular aging and age-related diseases.publisher: Elsevier articletitle: Mitochondria are targets for peroxisome-derived oxidative stress in cultured mammalian cells journaltitle: Free Radical Biology and Medicine articlelink: http://dx.doi.org/10.1016/j.freeradbiomed.2013.08.173 content_type: article copyright: Copyright © 2013 Elsevier Inc. All rights reserved.status: publishe