Publications by authors named "Stephane Schmucker"

14 Publications

  • Page 1 of 1

A PKD-MFF signaling axis couples mitochondrial fission to mitotic progression.

Cell Rep 2021 May;35(7):109129

Institut de Génétique et de Biologie Moléculaire et Cellulaire (IGBMC), Illkirch, France; Centre National de la Recherche Scientifique UMR 7104, Strasbourg, France; Institut National de la Santé et de la Recherche Médicale U964, Strasbourg, France; Université de Strasbourg, Strasbourg, France. Electronic address:

Mitochondria are highly dynamic organelles subjected to fission and fusion events. During mitosis, mitochondrial fission ensures equal distribution of mitochondria to daughter cells. If and how this process can actively drive mitotic progression remains largely unknown. Here, we discover a pathway linking mitochondrial fission to mitotic progression in mammalian cells. The mitochondrial fission factor (MFF), the main mitochondrial receptor for the Dynamin-related protein 1 (DRP1), is directly phosphorylated by Protein Kinase D (PKD) specifically during mitosis. PKD-dependent MFF phosphorylation is required and sufficient for mitochondrial fission in mitotic but not in interphasic cells. Phosphorylation of MFF is crucial for chromosome segregation and promotes cell survival by inhibiting adaptation of the mitotic checkpoint. Thus, PKD/MFF-dependent mitochondrial fission is critical for the maintenance of genome integrity during cell division.
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http://dx.doi.org/10.1016/j.celrep.2021.109129DOI Listing
May 2021

Spatial control of nucleoporin condensation by fragile X-related proteins.

EMBO J 2020 10 24;39(20):e104467. Epub 2020 Jul 24.

Institut de Génétique et de Biologie Moléculaire et Cellulaire (IGBMC), Illkirch, France.

Nucleoporins (Nups) build highly organized nuclear pore complexes (NPCs) at the nuclear envelope (NE). Several Nups assemble into a sieve-like hydrogel within the central channel of the NPCs. In the cytoplasm, the soluble Nups exist, but how their assembly is restricted to the NE is currently unknown. Here, we show that fragile X-related protein 1 (FXR1) can interact with several Nups and facilitate their localization to the NE during interphase through a microtubule-dependent mechanism. Downregulation of FXR1 or closely related orthologs FXR2 and fragile X mental retardation protein (FMRP) leads to the accumulation of cytoplasmic Nup condensates. Likewise, models of fragile X syndrome (FXS), characterized by a loss of FMRP, accumulate Nup granules. The Nup granule-containing cells show defects in protein export, nuclear morphology and cell cycle progression. Our results reveal an unexpected role for the FXR protein family in the spatial regulation of nucleoporin condensation.
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http://dx.doi.org/10.15252/embj.2020104467DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7560220PMC
October 2020

ISCA1 is essential for mitochondrial FeS biogenesis in vivo.

Nat Commun 2017 05 11;8:15124. Epub 2017 May 11.

IGBMC (Institut de Génétique et de Biologie Moléculaire et Cellulaire) Translational Medicine and Neurogenetics Department, 67404 Illkirch, France.

Mammalian A-type proteins, ISCA1 and ISCA2, are evolutionarily conserved proteins involved in iron-sulfur cluster (Fe-S) biogenesis. Recently, it was shown that ISCA1 and ISCA2 form a heterocomplex that is implicated in the maturation of mitochondrial FeS proteins. Here we report that mouse ISCA1 and ISCA2 are FeS-containing proteins that combine all features of Fe-S carrier proteins. We use biochemical, spectroscopic and in vivo approaches to demonstrate that despite forming a complex, ISCA1 and ISCA2 establish discrete interactions with components of the late Fe-S machinery. Surprisingly, knockdown experiments in mouse skeletal muscle and in primary cultures of neurons suggest that ISCA1, but not ISCA2, is required for mitochondrial FeS proteins biogenesis. Collectively, our data suggest that cellular processes with different requirements for ISCA1, ISCA2 and ISCA1-ISCA2 complex seem to exist.
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http://dx.doi.org/10.1038/ncomms15124DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5437272PMC
May 2017

Mutations in the HECT domain of NEDD4L lead to AKT-mTOR pathway deregulation and cause periventricular nodular heterotopia.

Nat Genet 2016 11 3;48(11):1349-1358. Epub 2016 Oct 3.

Institute of Molecular Pathology, Vienna, Austria.

Neurodevelopmental disorders with periventricular nodular heterotopia (PNH) are etiologically heterogeneous, and their genetic causes remain in many cases unknown. Here we show that missense mutations in NEDD4L mapping to the HECT domain of the encoded E3 ubiquitin ligase lead to PNH associated with toe syndactyly, cleft palate and neurodevelopmental delay. Cellular and expression data showed sensitivity of PNH-associated mutants to proteasome degradation. Moreover, an in utero electroporation approach showed that PNH-related mutants and excess wild-type NEDD4L affect neurogenesis, neuronal positioning and terminal translocation. Further investigations, including rapamycin-based experiments, found differential deregulation of pathways involved. Excess wild-type NEDD4L leads to disruption of Dab1 and mTORC1 pathways, while PNH-related mutations are associated with deregulation of mTORC1 and AKT activities. Altogether, these data provide insights into the critical role of NEDD4L in the regulation of mTOR pathways and their contributions in cortical development.
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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5086093PMC
http://dx.doi.org/10.1038/ng.3676DOI Listing
November 2016

Ubiquitin Receptor Protein UBASH3B Drives Aurora B Recruitment to Mitotic Microtubules.

Dev Cell 2016 Jan;36(1):63-78

Institut de Génétique et de Biologie Moléculaire et Cellulaire (IGBMC), Centre National de la Recherche Scientifique UMR 7104, Institut National de la Santé et de la Recherche Médicale U964, Université de Strasbourg, 67404 Illkirch, France. Electronic address:

Mitosis ensures equal segregation of the genome and is controlled by a variety of ubiquitylation signals on substrate proteins. However, it remains unexplored how the versatile ubiquitin code is read out during mitotic progression. Here, we identify the ubiquitin receptor protein UBASH3B as an important regulator of mitosis. UBASH3B interacts with ubiquitylated Aurora B, one of the main kinases regulating chromosome segregation, and controls its subcellular localization but not protein levels. UBASH3B is a limiting factor in this pathway and is sufficient to localize Aurora B to microtubules prior to anaphase. Importantly, targeting Aurora B to microtubules by UBASH3B is necessary for the timing and fidelity of chromosome segregation in human cells. Our findings uncover an important mechanism defining how ubiquitin attachment to a substrate protein is decoded during mitosis.
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http://dx.doi.org/10.1016/j.devcel.2015.12.017DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5400057PMC
January 2016

Iron regulatory protein 1 sustains mitochondrial iron loading and function in frataxin deficiency.

Cell Metab 2015 Feb;21(2):311-323

Translational Medecine and Neurogenetics, Institut de Génétique et de Biologie Moléculaire et Cellulaire (IGBMC), 67400 Illkirch, France; INSERM, U596, 67400 Illkirch, France; CNRS, UMR7104, 67400 Illkirch, France; Université de Strasbourg, 67000 Strasbourg, France; Collège de France, Chaire de génétique humaine, 67400 Illkirch, France. Electronic address:

Mitochondrial iron accumulation is a hallmark of diseases associated with impaired iron-sulfur cluster (Fe-S) biogenesis, such as Friedreich ataxia linked to frataxin (FXN) deficiency. The pathophysiological relevance of the mitochondrial iron loading and the underlying mechanisms are unknown. Using a mouse model of hepatic FXN deficiency in combination with mice deficient for iron regulatory protein 1 (IRP1), a key regulator of cellular iron metabolism, we show that IRP1 activation in conditions of Fe-S deficiency increases the available cytosolic labile iron pool. Surprisingly, our data indicate that IRP1 activation sustains mitochondrial iron supply and function rather than driving detrimental iron overload. Mitochondrial iron accumulation is shown to depend on mitochondrial dysfunction and heme-dependent upregulation of the mitochondrial iron importer mitoferrin-2. Our results uncover an unexpected protective role of IRP1 in pathological conditions associated with altered Fe-S metabolism.
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http://dx.doi.org/10.1016/j.cmet.2015.01.010DOI Listing
February 2015

Molecular dynamics of PLK1 during mitosis.

Mol Cell Oncol 2014 Apr-Jun;1(2):e954507. Epub 2014 Oct 29.

Institut de Génétique et de Biologie Moléculaire et Cellulaire (IGBMC) ; Illkirch, France.

Polo-like kinase 1 (PLK1) is a key regulator of eukaryotic cell division. During mitosis, dynamic regulation of PLK1 is crucial for its roles in centrosome maturation, spindle assembly, microtubule-kinetochore attachment, and cytokinesis. Similar to other members of the PLK family, the molecular architecture of PLK1 protein is characterized by 2 domains-the kinase domain and the regulatory substrate-binding domain (polo-box domain)-that cooperate and control PLK1 function during mitosis. Mitotic cells employ many layers of regulation to activate and target PLK1 to different cellular structures in a timely manner. During the last decade, numerous studies have shed light on the precise molecular mechanisms orchestrating the mitotic activity of PLK1 in time and space. This review aims to discuss available data and concepts related to regulation of the molecular dynamics of human PLK1 during mitotic progression.
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http://dx.doi.org/10.1080/23723548.2014.954507DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4905186PMC
June 2016

Mammalian frataxin: an essential function for cellular viability through an interaction with a preformed ISCU/NFS1/ISD11 iron-sulfur assembly complex.

PLoS One 2011 Jan 26;6(1):e16199. Epub 2011 Jan 26.

Department of Translational Medicine and Neurogenetics, Institut de Génétique et de Biologie Moléculaire et Cellulaire, Illkirch, France.

Background: Frataxin, the mitochondrial protein deficient in Friedreich ataxia, a rare autosomal recessive neurodegenerative disorder, is thought to be involved in multiple iron-dependent mitochondrial pathways. In particular, frataxin plays an important role in the formation of iron-sulfur (Fe-S) clusters biogenesis.

Methodology/principal Findings: We present data providing new insights into the interactions of mammalian frataxin with the Fe-S assembly complex by combining in vitro and in vivo approaches. Through immunoprecipitation experiments, we show that the main endogenous interactors of a recombinant mature human frataxin are ISCU, NFS1 and ISD11, the components of the core Fe-S assembly complex. Furthermore, using a heterologous expression system, we demonstrate that mammalian frataxin interacts with the preformed core complex, rather than with the individual components. The quaternary complex can be isolated in a stable form and has a molecular mass of ≈190 kDa. Finally, we demonstrate that the mature human FXN(81-210) form of frataxin is the essential functional form in vivo.

Conclusions/significance: Our results suggest that the interaction of frataxin with the core ISCU/NFS1/ISD11 complex most likely defines the essential function of frataxin. Our results provide new elements important for further understanding the early steps of de novo Fe-S cluster biosynthesis.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0016199PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3027643PMC
January 2011

Understanding the molecular mechanisms of Friedreich's ataxia to develop therapeutic approaches.

Hum Mol Genet 2010 Apr 22;19(R1):R103-10. Epub 2010 Apr 22.

Institut de Genetique et de Biologie Moleculaire et Cellulaire, BP10142, IllkirchF-67400, France.

Friedreich's ataxia (FRDA) is a neurodegenerative disease caused by reduced expression of the mitochondrial protein frataxin. The physiopathological consequences of frataxin deficiency are a severe disruption of iron-sulfur cluster biosynthesis, mitochondrial iron overload coupled to cellular iron dysregulation and an increased sensitivity to oxidative stress. Frataxin is a highly conserved protein, which has been suggested to participate in a variety of different roles associated with cellular iron homeostasis. The present review discusses recent advances that have made crucial contributions in understanding the molecular mechanisms underlying FRDA and in advancements toward potential novel therapeutic approaches. Owing to space constraints, this review will focus on the most commonly accepted and solid molecular and biochemical studies concerning the function of frataxin and the physiopathology of the disease. We invite the reader to read the following reviews to have a more exhaustive overview of the field [Pandolfo, M. and Pastore, A. (2009) The pathogenesis of Friedreich ataxia and the structure and function of frataxin. J. Neurol., 256 (Suppl. 1), 9-17; Gottesfeld, J.M. (2007) Small molecules affecting transcription in Friedreich ataxia. Pharmacol. Ther., 116, 236-248; Pandolfo, M. (2008) Drug insight: antioxidant therapy in inherited ataxias. Nat. Clin. Pract. Neurol., 4, 86-96; Puccio, H. (2009) Multicellular models of Friedreich ataxia. J. Neurol., 256 (Suppl. 1), 18-24].
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http://dx.doi.org/10.1093/hmg/ddq165DOI Listing
April 2010

The first cellular models based on frataxin missense mutations that reproduce spontaneously the defects associated with Friedreich ataxia.

PLoS One 2009 Jul 24;4(7):e6379. Epub 2009 Jul 24.

Institut de Génétique et de Biologie Moléculaire et Cellulaire, Illkirch, France.

Background: Friedreich ataxia (FRDA), the most common form of recessive ataxia, is due to reduced levels of frataxin, a highly conserved mitochondrial iron-chaperone involved in iron-sulfur cluster (ISC) biogenesis. Most patients are homozygous for a (GAA)(n) expansion within the first intron of the frataxin gene. A few patients, either with typical or atypical clinical presentation, are compound heterozygous for the GAA expansion and a micromutation.

Methodology: We have developed a new strategy to generate murine cellular models for FRDA: cell lines carrying a frataxin conditional allele were used in combination with an EGFP-Cre recombinase to create murine cellular models depleted for endogenous frataxin and expressing missense-mutated human frataxin. We showed that complete absence of murine frataxin in fibroblasts inhibits cell division and leads to cell death. This lethal phenotype was rescued through transgenic expression of human wild type as well as mutant (hFXN(G130V) and hFXN(I154F)) frataxin. Interestingly, cells expressing the mutated frataxin presented a FRDA-like biochemical phenotype. Though both mutations affected mitochondrial ISC enzymes activities and mitochondria ultrastructure, the hFXN(I154F) mutant presented a more severe phenotype with affected cytosolic and nuclear ISC enzyme activities, mitochondrial iron accumulation and an increased sensitivity to oxidative stress. The differential phenotype correlates with disease severity observed in FRDA patients.

Conclusions: These new cellular models, which are the first to spontaneously reproduce all the biochemical phenotypes associated with FRDA, are important tools to gain new insights into the in vivo consequences of pathological missense mutations as well as for large-scale pharmacological screening aimed at compensating frataxin deficiency.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0006379PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2710521PMC
July 2009

Induction of heat shock response by curcumin in human leukemia cells.

Cancer Lett 2009 Jul 25;279(2):145-54. Epub 2009 Feb 25.

Laboratoire de Biologie Moléculaire et Cellulaire du Cancer, Hôpital Kirchberg, 9 rue Edward Steichen, L-2540 Luxembourg, Luxembourg.

Heat shock response is an adaptive response, which helps the cells to regulate their physiological homeostasis under stress. Here we show that the natural compound curcumin induces nuclear translocation of the heat shock transcription factor (HSF)-1, its binding to a heat shock regulatory element (HSE), and the subsequent activation of the hsp70 promoter through the extracellular regulated kinase (ERK)/mitogen activated protein (MAP) ERK (MEK) and c-jun N-terminal kinase (JNK) pathways, but not through p38. We observe that curcumin activates hsp70A and hsp70B mRNA transcription, increases HSP protein expression but decreases the expression of Bag-1, a Hsp70 co-chaperone in K562 cells. This induction Hsp70 protein expression goes in line with the anti-inflammatory and anti-proliferative properties of curcumin in chronic myelogenous leukemia.
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http://dx.doi.org/10.1016/j.canlet.2009.01.031DOI Listing
July 2009

Frataxin deficiency causes upregulation of mitochondrial Lon and ClpP proteases and severe loss of mitochondrial Fe-S proteins.

FEBS J 2009 Feb 12;276(4):1036-47. Epub 2008 Jan 12.

Institut de Chimie des Substances Naturelles, Centre National de la Recherche Scientifique, Gif-sur-Yvette, France.

Friedreich ataxia (FRDA) is a rare hereditary neurodegenerative disease characterized by progressive ataxia and cardiomyopathy. The cause of the disease is a defect in mitochondrial frataxin, an iron chaperone involved in the maturation of Fe-S cluster proteins. Several human diseases, including cardiomyopathies, have been found to result from deficiencies in the activity of specific proteases, which have important roles in protein turnover and in the removal of damaged or unneeded protein. In this study, using the muscle creatine kinase mouse heart model for FRDA, we show a clear progressive increase in protein levels of two important mitochondrial ATP-dependent proteases, Lon and ClpP, in the hearts of muscle creatine kinase mutants. These proteases have been shown to degrade unfolded and damaged proteins in the matrix of mitochondria. Their upregulation, which was triggered at a mid-stage of the disease through separate pathways, was accompanied by an increase in proteolytic activity. We also demonstrate a simultaneous and significant progressive loss of mitochondrial Fe-S proteins with no substantial change in their mRNA level. The correlative effect of Lon and ClpP upregulation on loss of mitochondrial Fe-S proteins during the progression of the disease may suggest that Fe-S proteins are potential targets of Lon and ClpP proteases in FRDA.
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http://dx.doi.org/10.1111/j.1742-4658.2008.06847.xDOI Listing
February 2009

The in vivo mitochondrial two-step maturation of human frataxin.

Hum Mol Genet 2008 Nov 25;17(22):3521-31. Epub 2008 Aug 25.

IGBMC Institut de Génétique et de Biologie Moléculaire et Cellulaire, Illkirch, France.

Deficiency in the nuclear-encoded mitochondrial protein frataxin causes Friedreich ataxia (FRDA), a progressive neurodegenerative disorder associating spinocerebellar ataxia and cardiomyopathy. Although the exact function of frataxin is still a matter of debate, it is widely accepted that frataxin is a mitochondrial iron chaperone involved in iron-sulfur cluster and heme biosynthesis. Frataxin is synthesized as a precursor polypeptide, directed to the mitochondrial matrix where it is proteolytically cleaved by the mitochondrial processing peptidase to the mature form via a processing intermediate. The mature form was initially reported to be encoded by amino acids 56-210 (m(56)-FXN). However, two independent reports have challenged these studies describing two different forms encoded by amino acids 78-210 (m(78)-FXN) and 81-210 (m(81)-FXN). Here, we provide evidence that mature human frataxin corresponds to m(81)-FXN, and can rescue the lethal phenotype of fibroblasts completely deleted for frataxin. Furthermore, our data demonstrate that the migration profile of frataxin depends on the experimental conditions, a behavior which most likely contributed to the confusion concerning the endogenous mature frataxin. Interestingly, we show that m(56)-FXN and m(78)-FXN can be generated when the normal maturation process of frataxin is impaired, although the physiological relevance is not clear. Furthermore, we determine that the d-FXN form, previously reported to be a degradation product, corresponds to m(78)-FXN. Finally, we demonstrate that all frataxin isoforms are generated and localized within the mitochondria. The clear identification of the N-terminus of mature FXN is an important step for designing therapeutic approaches for FRDA based on frataxin replacement.
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http://dx.doi.org/10.1093/hmg/ddn244DOI Listing
November 2008

Frataxin is essential for extramitochondrial Fe-S cluster proteins in mammalian tissues.

Hum Mol Genet 2007 Nov 27;16(22):2651-8. Epub 2007 Jun 27.

Institut de Génétique et de Biologie Moléculaire et Cellulaire, 1 rue Laurent Fries BP 10142, Illkirch F-67400, France.

Friedreich ataxia, the most common recessive ataxia, is caused by the deficiency of the mitochondrial protein frataxin (Fxn), an iron chaperone involved in the assembly of Fe-S clusters (ISC). In yeast, mitochondria play a central role for all Fe-S proteins, independently of their subcellular localization. In mammalian cells, this central role of mitochondria remains controversial as an independent cytosolic ISC assembly machinery has been suggested. In the present work, we show that three extramitochondrial Fe-S proteins (xanthine oxido-reductase, glutamine phosphoribosylpyrophosphate amidotransferase and Nth1) are affected in Fxn-deleted mouse tissues. Furthermore, we show that Fxn is strictly localized to the mitochondria, excluding the presence of a cytosolic pool of Fxn in normal adult tissues. Together, these results demonstrate that in mammals, Fxn and mitochondria play a cardinal role in the maturation of extramitochondrial Fe-S proteins. The Fe-S scaffold protein IscU progressively decreases in Fxn-deleted tissues, further contributing to the impairment of Fe-S proteins. These results thus provide new cellular pathways that may contribute to molecular mechanisms of the disease.
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http://dx.doi.org/10.1093/hmg/ddm163DOI Listing
November 2007
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