Publications by authors named "Izabela Sumara"

33 Publications

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

The NANOTUMOR consortium - Towards the Tumor Cell Atlas.

Biol Cell 2021 Jun 26;113(6):272-280. Epub 2021 Feb 26.

INSERM UMR_S1109, Tumor Biomechanics Lab, Université de Strasbourg, Fédération de Médecine Translationnelle de Strasbourg (FMTS), CNRS SNC5055, Strasbourg, France.

Cancer is a multi-step disease where an initial tumour progresses through critical steps shaping, in most cases, life-threatening secondary foci called metastases. The oncogenic cascade involves genetic, epigenetic, signalling pathways, intracellular trafficking and/or metabolic alterations within cancer cells. In addition, pre-malignant and malignant cells orchestrate complex and dynamic interactions with non-malignant cells and acellular matricial components or secreted factors within the tumour microenvironment that is instrumental in the progression of the disease. As our aptitude to effectively treat cancer mostly depends on our ability to decipher, properly diagnose and impede cancer progression and metastasis formation, full characterisation of molecular complexes and cellular processes at play along the metastasis cascade is crucial. For many years, the scientific community lacked adapted imaging and molecular technologies to accurately dissect, at the highest resolution possible, tumour and stromal cells behaviour within their natural microenvironment. In that context, the NANOTUMOR consortium is a French national multi-disciplinary workforce which aims at a providing a multi-scale characterisation of the oncogenic cascade, from the atomic level to the dynamic organisation of the cell in response to genetic mutations, environmental changes or epigenetic modifications. Ultimately, this program aims at identifying new therapeutic targets using innovative drug design.
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http://dx.doi.org/10.1111/boc.202000135DOI Listing
June 2021

Deubiquitylase UCHL3 regulates bi-orientation and segregation of chromosomes during mitosis.

FASEB J 2020 09 1;34(9):12751-12767. Epub 2020 Aug 1.

Institut de Génétique et de Biologie Moléculaire et Cellulaire (IGBMC), Department of development and stem cells, Illkirch, France.

Equal segregation of chromosomes during mitosis ensures euploidy of daughter cells. Defects in this process may result in an imbalance in the chromosomal composition and cellular transformation. Proteolytic and non-proteolytic ubiquitylation pathways ensure directionality and fidelity of mitotic progression but specific mitotic functions of deubiquitylating enzymes (DUBs) remain less studied. Here we describe the role of the DUB ubiquitin carboxyl-terminal hydrolase isozyme L3 (UCHL3) in the regulation of chromosome bi-orientation and segregation during mitosis. Downregulation or inhibition of UCHL3 leads to chromosome alignment defects during metaphase. Frequent segregation errors during anaphase are also observed upon inactivation of UCHL3. Mechanistically, UCHL3 interacts with and deubiquitylates Aurora B, the catalytic subunit of chromosome passenger complex (CPC), known to be critically involved in the regulation of chromosome alignment and segregation. UCHL3 does not regulate protein levels of Aurora B or the binding of Aurora B to other CPC subunits. Instead, UCHL3 promotes localization of Aurora B to kinetochores, suggesting its role in the error correction mechanism monitoring bi-orientation of chromosomes during metaphase. Thus, UCHL3 contributes to the regulation of faithful genome segregation and maintenance of euploidy in human cells.
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http://dx.doi.org/10.1096/fj.202000769RDOI Listing
September 2020

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

Intraflagellar Transport Complex B Proteins Regulate the Hippo Effector Yap1 during Cardiogenesis.

Cell Rep 2020 07;32(3):107932

Institut de Génétique et de Biologie Moléculaire et Cellulaire, Illkirch, France; Centre National de la Recherche Scientifique, UMR7104, Illkirch, France; Institut National de la Santé et de la Recherche Médicale, U964, Illkirch, France; Université de Strasbourg, Illkirch, France; Sorbonne Université, Collège Doctoral, F-75005, Paris, France; Department of Bioengineering, Imperial College London, London, UK. Electronic address:

Cilia and the intraflagellar transport (IFT) proteins involved in ciliogenesis are associated with congenital heart diseases (CHDs). However, the molecular links between cilia, IFT proteins, and cardiogenesis are yet to be established. Using a combination of biochemistry, genetics, and live-imaging methods, we show that IFT complex B proteins (Ift88, Ift54, and Ift20) modulate the Hippo pathway effector YAP1 in zebrafish and mouse. We demonstrate that this interaction is key to restrict the formation of the proepicardium and the myocardium. In cellulo experiments suggest that IFT88 and IFT20 interact with YAP1 in the cytoplasm and functionally modulate its activity, identifying a molecular link between cilia-related proteins and the Hippo pathway. Taken together, our results highlight a noncanonical role for IFT complex B proteins during cardiogenesis and shed light on a mechanism of action for ciliary proteins in YAP1 regulation.
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http://dx.doi.org/10.1016/j.celrep.2020.107932DOI Listing
July 2020

Cullin 3, a cellular scripter of the non-proteolytic ubiquitin code.

Semin Cell Dev Biol 2019 09 28;93:100-110. Epub 2018 Dec 28.

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:

Cullin-RING ubiquitin ligases (CRLs) represent the largest family of E3 ubiquitin ligases that control most if not all cellular processes. In CUL3-based CRLs, the substrate specificity is conferred by the interaction with one of around 183 existing BTB proteins, implying a broad spectrum of possible ubiquitylation signals and possible direct ubiquitylation substrates. Indeed, CUL3-based E3-ligases can catalyze various proteolytic and non-proteolytic ubiquitin signals regulating many physiological and pathophysiological states. Here, we discuss the recent studies focusing on the non-proteolytic CUL3-based signaling in mammalian cells, which emerge as important pathways during cell division, embryonic development as well as other biological processes. Mechanistically, non-proteolytic ubiquitin signals generated by CUL3 E3-ligases often regulate substrates' interactions with other downstream factors or their subcellular localization. Existing data also demonstrate an interplay with the proteolytic ubiquitylation catalyzed on the same substrates by different E3-ligases or by the same CUL3-BTB CRL3s on different substrates. In future, a deeper understanding of the upstream spatiotemporal regulatory mechanisms will help to dissect this fascinating CUL3 ubiquitin code.
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http://dx.doi.org/10.1016/j.semcdb.2018.12.007DOI Listing
September 2019

UBASH3B-mediated silencing of the mitotic checkpoint: Therapeutic perspectives in cancer.

Mol Cell Oncol 2018 30;5(2):e1271494. Epub 2017 Nov 30.

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, Illkirch, France.

Defects in mitosis can lead to aneuploidy, which is a common feature of human cancers. Spindle Assembly Checkpoint (SAC) controls fidelity of chromosome segregation in mitosis to prevent aneuploidy. The ubiquitin receptor protein Ubiquitin Associated and SH3 Domain Containing B (UBASH3B) was recently found to control SAC silencing and faithful chromosome segregation by relocalizing Aurora B kinase to the mitotic microtubules. Accordingly, loss and gain of function of UBASH3B have strong effects on mitotic progression. Downregulation of UBASH3B prevents SAC satisfaction leading to inhibition of chromosome segregation, mitotic arrest, and cell death. In contrast, increased cellular levels of UBASH3B trigger premature and uncontrolled chromosome segregation. Interestingly, elevated levels of UBASH3B were found in aggressive tumors. Therefore, we raised the question whether the oncogenic potential of UBASH3B is linked to its role in chromosome segregation. Here we show that in cancer cells expressing high levels of UBASH3B and SAC proteins, downregulation of UBASH3B, can further potentiate SAC response inducing mitotic arrest and cell death. Moreover, data mining approaches identified a correlation between mRNA levels of UBASH3B and SAC components in a set of primary patient tumors including kidney and liver carcinomas. Thus, inhibition of UBASH3B may offer an attractive therapeutic perspective for cancers.
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http://dx.doi.org/10.1080/23723556.2016.1271494DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5821415PMC
November 2017

The MTM1-UBQLN2-HSP complex mediates degradation of misfolded intermediate filaments in skeletal muscle.

Nat Cell Biol 2018 02 22;20(2):198-210. Epub 2018 Jan 22.

Department of Translational Medicine and Neurogenetics, IGBMC, Illkirch, France.

The ubiquitin proteasome system and autophagy are major protein turnover mechanisms in muscle cells, which ensure stemness and muscle fibre maintenance. Muscle cells contain a high proportion of cytoskeletal proteins, which are prone to misfolding and aggregation; pathological processes that are observed in several neuromuscular diseases called proteinopathies. Despite advances in deciphering the mechanisms underlying misfolding and aggregation, little is known about how muscle cells manage cytoskeletal degradation. Here, we describe a process by which muscle cells degrade the misfolded intermediate filament proteins desmin and vimentin by the proteasome. This relies on the MTM1-UBQLN2 complex to recognize and guide these misfolded proteins to the proteasome and occurs prior to aggregate formation. Thus, our data highlight a safeguarding function of the MTM1-UBQLN2 complex that ensures cytoskeletal integrity to avoid proteotoxic aggregate formation.
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http://dx.doi.org/10.1038/s41556-017-0024-9DOI Listing
February 2018

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

Liver ubiquitome uncovers nutrient-stress-mediated trafficking and secretion of complement C3.

Cell Death Dis 2016 10 13;7(10):e2411. Epub 2016 Oct 13.

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, Illkirch 67404, France.

Adaptation to changes in nutrient availability is crucial for cells and organisms. Posttranslational modifications of signaling proteins are very dynamic and are therefore key to promptly respond to nutrient deprivation or overload. Herein we screened for ubiquitylation of proteins in the livers of fasted and refed mice using a comprehensive systemic proteomic approach. Among 1641 identified proteins, 117 were differentially ubiquitylated upon fasting or refeeding. Endoplasmic reticulum (ER) and secretory proteins were enriched in the livers of refed mice in part owing to an ER-stress-mediated response engaging retro-translocation and ubiquitylation of proteins from the ER. Complement C3, an innate immune factor, emerged as the most prominent ER-related hit of our screen. Accordingly, we found that secretion of C3 from the liver and primary hepatocytes as well as its dynamic trafficking are nutrient dependent. Finally, obese mice with a chronic nutrient overload show constitutive trafficking of C3 in the livers despite acute changes in nutrition, which goes in line with increased C3 levels and low-grade inflammation reported for obese patients. Our study thus suggests that nutrient sensing in the liver is coupled to release of C3 and potentially its metabolic and inflammatory functions.
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http://dx.doi.org/10.1038/cddis.2016.312DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5133979PMC
October 2016

Cortical dynamics during cell motility are regulated by CRL3(KLHL21) E3 ubiquitin ligase.

Nat Commun 2016 09 19;7:12810. Epub 2016 Sep 19.

Institute of Biochemistry, Department of Biology, ETH Zurich, Otto-Stern-Weg 3, 8093 Zürich, Switzerland.

Directed cell movement involves spatial and temporal regulation of the cortical microtubule (Mt) and actin networks to allow focal adhesions (FAs) to assemble at the cell front and disassemble at the rear. Mts are known to associate with FAs, but the mechanisms coordinating their dynamic interactions remain unknown. Here we show that the CRL3(KLHL21) E3 ubiquitin ligase promotes cell migration by controlling Mt and FA dynamics at the cell cortex. Indeed, KLHL21 localizes to FA structures preferentially at the leading edge, and in complex with Cul3, ubiquitylates EB1 within its microtubule-interacting CH-domain. Cells lacking CRL3(KLHL21) activity or expressing a non-ubiquitylatable EB1 mutant protein are unable to migrate and exhibit strong defects in FA dynamics, lamellipodia formation and cortical plasticity. Our study thus reveals an important mechanism to regulate cortical dynamics during cell migration that involves ubiquitylation of EB1 at focal adhesions.
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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5031805PMC
http://dx.doi.org/10.1038/ncomms12810DOI Listing
September 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

Insulin granules. Insulin secretory granules control autophagy in pancreatic β cells.

Science 2015 Feb;347(6224):878-82

Institut de Génétique et de Biologie Moléculaire et Cellulaire (IGBMC), INSERM, CNRS, Université de Strasbourg, 67404 Illkirch, France. Nouvel Hôpital Civil, Laboratoire de Biochimie et de Biologie Moléculaire, Université de Strasbourg, 67091 Strasbourg, France.

Pancreatic β cells lower insulin release in response to nutrient depletion. The question of whether starved β cells induce macroautophagy, a predominant mechanism maintaining energy homeostasis, remains poorly explored. We found that, in contrast to many mammalian cells, macroautophagy in pancreatic β cells was suppressed upon starvation. Instead, starved β cells induced lysosomal degradation of nascent secretory insulin granules, which was controlled by protein kinase D (PKD), a key player in secretory granule biogenesis. Starvation-induced nascent granule degradation triggered lysosomal recruitment and activation of mechanistic target of rapamycin that suppressed macroautophagy. Switching from macroautophagy to insulin granule degradation was important to keep insulin secretion low upon fasting. Thus, β cells use a PKD-dependent mechanism to adapt to nutrient availability and couple autophagy flux to secretory function.
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http://dx.doi.org/10.1126/science.aaa2628DOI 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

CUL3 and protein kinases: insights from PLK1/KLHL22 interaction.

Cell Cycle 2013 Jul;12(14):2291-6

Institute of Genetics and Molecular and Cellular Biology, Illkirch, France.

Posttranslational mechanisms drive fidelity of cellular processes. Phosphorylation and ubiquitination of substrates represent very common, covalent, posttranslational modifications and are often co-regulated. Phosphorylation may play a critical role both by directly regulating E3-ubiquitin ligases and/or by ensuring specificity of the ubiquitination substrate. Importantly, many kinases are not only critical regulatory components of these pathways but also represent themselves the direct ubiquitination substrates. Recent data suggest the role of CUL3-based ligases in both proteolytic and non-proteolytic regulation of protein kinases. Our own recent study identified the mitotic kinase PLK1 as a direct target of the CUL3 E3-ligase complex containing BTB-KELCH adaptor protein KLHL22. (1) In this study, we aim at gaining mechanistic insights into CUL3-mediated regulation of the substrates, in particular protein kinases, by analyzing mechanisms of interaction between KLHL22 and PLK1. We find that kinase activity of PLK1 is redundant for its targeting for CUL3-ubiquitination. Moreover, CUL3/KLHL22 may contact 2 distinct motifs within PLK1 protein, consistent with the bivalent mode of substrate targeting found in other CUL3-based complexes. We discuss these findings in the context of the existing knowledge on other protein kinases and substrates targeted by CUL3-based E3-ligases.
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http://dx.doi.org/10.4161/cc.25369DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3755079PMC
July 2013

The emerging family of CULLIN3-RING ubiquitin ligases (CRL3s): cellular functions and disease implications.

EMBO J 2013 Aug 2;32(17):2307-20. Epub 2013 Aug 2.

Unité Propre de Recherche 2357, Centre National de la Recherche Scientifique, Institut de Biologie Moléculaire des Plantes, Conventionné avec l'Université de Strasbourg, Strasbourg, France.

Protein ubiquitylation is a post-translational modification that controls all aspects of eukaryotic cell functionality, and its defective regulation is manifested in various human diseases. The ubiquitylation process requires a set of enzymes, of which the ubiquitin ligases (E3s) are the substrate recognition components. Modular CULLIN-RING ubiquitin ligases (CRLs) are the most prevalent class of E3s, comprising hundreds of distinct CRL complexes with the potential to recruit as many and even more protein substrates. Best understood at both structural and functional levels are CRL1 or SCF (SKP1/CUL1/F-box protein) complexes, representing the founding member of this class of multimeric E3s. Another CRL subfamily, called CRL3, is composed of the molecular scaffold CULLIN3 and the RING protein RBX1, in combination with one of numerous BTB domain proteins acting as substrate adaptors. Recent work has firmly established CRL3s as major regulators of different cellular and developmental processes as well as stress responses in both metazoans and higher plants. In humans, functional alterations of CRL3s have been associated with various pathologies, including metabolic disorders, muscle, and nerve degeneration, as well as cancer. In this review, we summarize recent discoveries on the function of CRL3s in both metazoans and plants, and discuss their mode of regulation and specificities.
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http://dx.doi.org/10.1038/emboj.2013.173DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3770339PMC
August 2013

Decoding ubiquitin for mitosis.

Genes Cancer 2012 Nov;3(11-12):697-711

Institute of Genetics and Molecular and Cellular Biology (IGBMC), Illkirch, France.

Conjugation of ubiquitin (ubiquitination) to substrate proteins is a widespread modification that ensures fidelity of many cellular processes. During mitosis, different dynamic morphological transitions have to be coordinated in a temporal and spatial manner to allow for precise partitioning of the genetic material into two daughter cells, and ubiquitination of key mitotic factors is believed to provide both directionality and fidelity to this process. While directionality can be achieved by a proteolytic type of ubiquitination signal, the fidelity is often determined by various types of ubiquitin conjugation that does not target substrates for proteolysis by the proteasome. An additional level of complexity is provided by various ubiquitin-interacting proteins that act downstream of the ubiquitinated substrate and can serve as "decoders" for the ubiquitin signal. They may, specifically reverse ubiquitin attachment (deubiquitinating enzymes, DUBs) or, act as a receptor for transfer of the ubiquitinated substrate toward downstream signaling components and/or subcellular compartments (ubiquitin-binding proteins, UBPs). In this review, we aim at summarizing the knowledge and emerging concepts about the role of ubiquitin decoders, DUBs, and UBPs that contribute to faithful regulation of mitotic division.
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http://dx.doi.org/10.1177/1947601912473477DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3636754PMC
November 2012

Ubiquitylation-dependent localization of PLK1 in mitosis.

Nat Cell Biol 2013 Apr 3;15(4):430-9. Epub 2013 Mar 3.

Institute of Biochemistry, ETH Zurich, Schafmattstrasse 18, 8093 Zurich, Switzerland.

Polo-like kinase 1 (PLK1) critically regulates mitosis through its dynamic localization to kinetochores, centrosomes and the midzone. The polo-box domain (PBD) and activity of PLK1 mediate its recruitment to mitotic structures, but the mechanisms regulating PLK1 dynamics remain poorly understood. Here, we identify PLK1 as a target of the cullin 3 (CUL3)-based E3 ubiquitin ligase, containing the BTB adaptor KLHL22, which regulates chromosome alignment and PLK1 kinetochore localization but not PLK1 stability. In the absence of KLHL22, PLK1 accumulates on kinetochores, resulting in activation of the spindle assembly checkpoint (SAC). CUL3-KLHL22 ubiquitylates Lys 492, located within the PBD, leading to PLK1 dissociation from kinetochore phosphoreceptors. Expression of a non-ubiquitylatable PLK1-K492R mutant phenocopies inactivation of CUL3-KLHL22. KLHL22 associates with the mitotic spindle and its interaction with PLK1 increases on chromosome bi-orientation. Our data suggest that CUL3-KLHL22-mediated ubiquitylation signals degradation-independent removal of PLK1 from kinetochores and SAC satisfaction, which are required for faithful mitosis.
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http://dx.doi.org/10.1038/ncb2695DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7116173PMC
April 2013

The Cul3-KLHL21 E3 ubiquitin ligase targets aurora B to midzone microtubules in anaphase and is required for cytokinesis.

J Cell Biol 2009 Dec;187(6):791-800

Institute of Biochemistry, Swiss Federal Institute of Technology Zurich, CH-8093 Zurich, Switzerland.

Cul3 (Cullin3)-based E3 ubiquitin ligases recently emerged as critical regulators of mitosis. In this study, we identify two mammalian BTB (Bric-a-brac-Tramtrack-Broad complex)-Kelch proteins, KLHL21 and KLHL22, that interact with Cul3 and are required for efficient chromosome alignment. Interestingly, KLHL21 but not KLHL22 is necessary for cytokinesis and regulates translocation of the chromosomal passenger complex (CPC) from chromosomes to the spindle midzone in anaphase, similar to the previously described BTB-Kelch proteins KLHL9 and KLHL13. KLHL21 directly binds to aurora B and mediates ubiquitination of aurora B in vitro. In contrast to KLHL9 and KLHL13, KLHL21 localizes to midzone microtubules in anaphase and recruits aurora B and Cul3 to this region. Together, our results suggest that different Cul3 adaptors nonredundantly regulate aurora B during mitosis, possibly by ubiquitinating different pools of aurora B at distinct subcellular localizations.
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http://dx.doi.org/10.1083/jcb.200906117DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2806313PMC
December 2009

The human Dcn1-like protein DCNL3 promotes Cul3 neddylation at membranes.

Proc Natl Acad Sci U S A 2009 Jul 14;106(30):12365-70. Epub 2009 Jul 14.

Institute of Biochemistry, Eidgenössiche Technische Hochschule, 8093 Zurich, Switzerland.

Cullin (Cul)-based E3 ubiquitin ligases are activated through the attachment of Nedd8 to the Cul protein. In yeast, Dcn1 (defective in Cul neddylation 1 protein) functions as a scaffold-like Nedd8 E3-ligase by interacting with its Cul substrates and the Nedd8 E2 Ubc12. Human cells express 5 Dcn1-like (DCNL) proteins each containing a C-terminal potentiating neddylation domain but distinct amino-terminal extensions. Although the UBA-containing DCNL1 and DCNL2 are likely functional homologues of yeast Dcn1, DCNL3 also interacts with human Culs and is able to complement the neddylation defect of yeast dcn1Delta cells. DCNL3 down-regulation by RNAi decreases Cul neddylation, and overexpression of a Cul3 mutant deficient in DCNL3 binding interferes with Cul3 function in vivo. Interestingly, DCNL3 accumulates at the plasma membrane through a conserved, lipid-modified motif at the N terminus. Membrane-bound DCNL3 is able to recruit Cul3 to membranes and is functionally important for Cul3 neddylation in vivo. We conclude that DCNL proteins function as nonredundant Cul Nedd8-E3 ligases. Moreover, the diversification of the N termini in mammalian Dcn1 homologues may contribute to substrate specificity by regulating their subcellular localization.
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http://dx.doi.org/10.1073/pnas.0812528106DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2718329PMC
July 2009

An interaction network of the mammalian COP9 signalosome identifies Dda1 as a core subunit of multiple Cul4-based E3 ligases.

J Cell Sci 2009 Apr;122(Pt 7):1035-44

Swiss Federal Institute of Technology Zürich (ETH), Institute of Biochemistry, 8093 Zürich, Switzerland.

The COP9 signalosome (CSN) is an evolutionarily conserved macromolecular complex that interacts with cullin-RING E3 ligases (CRLs) and regulates their activity by hydrolyzing cullin-Nedd8 conjugates. The CSN sequesters inactive CRL4(Ddb2), which rapidly dissociates from the CSN upon DNA damage. Here we systematically define the protein interaction network of the mammalian CSN through mass spectrometric interrogation of the CSN subunits Csn1, Csn3, Csn4, Csn5, Csn6 and Csn7a. Notably, we identified a subset of CRL complexes that stably interact with the CSN and thus might similarly be activated by dissociation from the CSN in response to specific cues. In addition, we detected several new proteins in the CRL-CSN interactome, including Dda1, which we characterized as a chromatin-associated core subunit of multiple CRL4 proteins. Cells depleted of Dda1 spontaneously accumulated double-stranded DNA breaks in a similar way to Cul4A-, Cul4B- or Wdr23-depleted cells, indicating that Dda1 interacts physically and functionally with CRL4 complexes. This analysis identifies new components of the CRL family of E3 ligases and elaborates new connections between the CRL and CSN complexes.
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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2720933PMC
http://dx.doi.org/10.1242/jcs.043539DOI Listing
April 2009

Regulation of PKD by the MAPK p38delta in insulin secretion and glucose homeostasis.

Cell 2009 Jan 8;136(2):235-48. Epub 2009 Jan 8.

Institute of Cell Biology, ETH Zurich, CH-8093 Zurich, Switzerland.

Dysfunction and loss of insulin-producing pancreatic beta cells represent hallmarks of diabetes mellitus. Here, we show that mice lacking the mitogen-activated protein kinase (MAPK) p38delta display improved glucose tolerance due to enhanced insulin secretion from pancreatic beta cells. Deletion of p38delta results in pronounced activation of protein kinase D (PKD), the latter of which we have identified as a pivotal regulator of stimulated insulin exocytosis. p38delta catalyzes an inhibitory phosphorylation of PKD1, thereby attenuating stimulated insulin secretion. In addition, p38delta null mice are protected against high-fat-feeding-induced insulin resistance and oxidative stress-mediated beta cell failure. Inhibition of PKD1 reverses enhanced insulin secretion from p38delta-deficient islets and glucose tolerance in p38delta null mice as well as their susceptibility to oxidative stress. In conclusion, the p38delta-PKD pathway integrates regulation of the insulin secretory capacity and survival of pancreatic beta cells, pointing to a pivotal role for this pathway in the development of overt diabetes mellitus.
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http://dx.doi.org/10.1016/j.cell.2008.11.018DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2638021PMC
January 2009

E3 ubiquitin ligases and mitosis: embracing the complexity.

Trends Cell Biol 2008 Feb 22;18(2):84-94. Epub 2008 Jan 22.

Institute of Biochemistry, HPM G 8, ETH Hönggerberg, Schafmattstrasse 18, 8093 Zurich, Switzerland.

Faithful division of eukaryotic cells requires temporal and spatial coordination of morphological transitions, which ensures that the newly replicated copies of the genome are equally distributed into the two daughter cells during mitosis. One of the mechanisms ensuring the fidelity of mitotic progression is targeted, ubiquitin-dependent proteolysis of key regulators. E3-ubiquitin ligase complexes are crucial components in this pathway because they specifically select the relevant ubiquitination substrates. Cullin-based E3-ligases, such as Cul3, have recently emerged as crucial regulators of mitosis.
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http://dx.doi.org/10.1016/j.tcb.2007.12.001DOI Listing
February 2008

A Cul3-based E3 ligase regulates mitosis and is required to maintain the spindle assembly checkpoint in human cells.

Cell Cycle 2007 Dec 10;6(24):3004-10. Epub 2007 Sep 10.

Institute of Biochemistry, ETH Zurich, Zurich, Switzerland.

The spindle assembly checkpoint (SAC) is a mechanism that prevents premature chromosome segregation in anaphase before all chromosomes are correctly attached to the mitotic spindle. Errors in chromosome segregation lead to aneuploidy, which may be causally involved in tumorgenesis. Kinetochore complexes are the structural components of the SAC, which are tightly regulated by various mechanisms including phosphorylation and ubiquitin-dependent proteolysis. Recent studies shed new light on the regulatory pathways of the ubiquitin proteasome system involved in SAC signaling. Here we present evidence that a Cul3-based E3 ubiquitin-ligase is required to maintain SAC signaling in human cells. Inactivation of the Cul3/KLHL9/KLHL13 ligase leads to premature degradation of Cyclin B and exit from the mitotic state in the presence of microtubule poisons. We discuss possible mechanisms how Cul3 may be required to maintain SAC activity by ubiquitination of the chromosomal passenger protein Aurora B.
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http://dx.doi.org/10.4161/cc.6.24.5068DOI Listing
December 2007

A Cul3-based E3 ligase removes Aurora B from mitotic chromosomes, regulating mitotic progression and completion of cytokinesis in human cells.

Dev Cell 2007 Jun;12(6):887-900

Institute of Biochemistry, ETH Zurich, 8093 Zurich, Switzerland.

Faithful cell-cycle progression is tightly controlled by the ubiquitin-proteasome system. Here we identify a human Cullin 3-based E3 ligase (Cul3) which is essential for mitotic division. In a complex with the substrate-specific adaptors KLHL9 and KLHL13, Cul3 is required for correct chromosome alignment in metaphase, proper midzone and midbody formation, and completion of cytokinesis. This Cul3-based E3 ligase removes components of the chromosomal passenger complex from mitotic chromosomes and allows their accumulation on the central spindle during anaphase. Aurora B directly binds to the substrate-recognition domain of KLHL9 and KLHL13 in vitro, and coimmunoprecipitates with the Cul3 complex during mitosis. Moreover, Aurora B is ubiquitylated in a Cul3-dependent manner in vivo, and by reconstituted Cul3/KLHL9/KLHL13 ligase in vitro. We thus propose that the Cul3/KLHL9/KLHL13 E3 ligase controls the dynamic behavior of Aurora B on mitotic chromosomes, and thereby coordinates faithful mitotic progression and completion of cytokinesis.
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http://dx.doi.org/10.1016/j.devcel.2007.03.019DOI Listing
June 2007

c-Jun/AP-1 controls liver regeneration by repressing p53/p21 and p38 MAPK activity.

Genes Dev 2006 Aug;20(16):2306-14

Research Institute of Molecular Pathology (IMP), A-1030 Vienna, Austria.

The AP-1 transcription factor c-Jun is a key regulator of hepatocyte proliferation. Mice lacking c-Jun in the liver (c-jun (Deltali*)) display impaired liver regeneration after partial hepatectomy (PH). This phenotype correlates with increased protein levels of the cdk-inhibitor p21 in the liver. We performed PH experiments in several double-knockout mouse models to genetically identify the signaling events regulated by c-Jun. Inactivation of p53 in c-jun (Deltali*) mice abrogated both hepatocyte cell cycle block and increased p21 protein expression. Consistently, liver regeneration was rescued in c-jun (Deltali*) p21 (-/-) double-mutant mice. This indicated that c-Jun controls hepatocyte proliferation by a p53/p21-dependent mechanism. Analyses of p21 mRNA and protein expression in livers of c-jun (Deltali*) mice after PH revealed that the accumulation of p21 protein is due to a post-transcriptional/post-translational mechanism. We have investigated several candidate pathways implicated in the regulation of p21 expression, and observed increased activity of the stress kinase p38 in regenerating livers of c-jun (Deltali*) mice. Importantly, conditional deletion of p38alpha in livers of c-jun (Deltali*) mice fully restored hepatocyte proliferation and attenuated increased p21 protein levels after PH. These data demonstrate that c-Jun/AP-1 regulates liver regeneration through a novel molecular pathway that involves p53, p21, and the stress kinase p38alpha.
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http://dx.doi.org/10.1101/gad.390506DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1553212PMC
August 2006

Distinct functions of junD in cardiac hypertrophy and heart failure.

Genes Dev 2005 Jan;19(2):208-13

Institute of Molecular Pathology, A-1030 Vienna, Austria.

Cardiac hypertrophic stimuli induce both adaptive and maladaptive growth response pathways in heart. Here we show that mice lacking junD develop less adaptive hypertrophy in heart after mechanical pressure overload, while cardiomyocyte-specific expression of junD in mice results in spontaneous ventricular dilation and decreased contractility. In contrast, fra-1 conditional knock-out mice have a normal hypertrophic response, whereas hearts from fra-1 transgenic mice decompensate prematurely. Moreover, fra-1 transgenic mice simultaneously lacking junD reveal a spontaneous dilated cardiomyopathy associated with increased cardiomyocyte apoptosis and a primary mitochondrial defect. These data suggest that junD promotes both adaptive-protective and maladaptive hypertrophy in heart, depending on its expression levels.
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http://dx.doi.org/10.1101/gad.327005DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC545879PMC
January 2005

Requirement of JNK2 for scavenger receptor A-mediated foam cell formation in atherogenesis.

Science 2004 Nov;306(5701):1558-61

Cardiovascular Research, Institute of Physiology, and Division of Cardiology, University Hospital Zurich, CH-8057 Zurich, Switzerland.

In vitro studies suggest a role for c-Jun N-terminal kinases (JNKs) in proatherogenic cellular processes. We show that atherosclerosis-prone ApoE-/- mice simultaneously lacking JNK2 (ApoE-/- JNK2-/- mice), but not ApoE-/- JNK1-/- mice, developed less atherosclerosis than do ApoE-/- mice. Pharmacological inhibition of JNK activity efficiently reduced plaque formation. Macrophages lacking JNK2 displayed suppressed foam cell formation caused by defective uptake and degradation of modified lipoproteins and showed increased amounts of the modified lipoprotein-binding and -internalizing scavenger receptor A (SR-A), whose phosphorylation was markedly decreased. Macrophage-restricted deletion of JNK2 was sufficient to decrease atherogenesis. Thus, JNK2-dependent phosphorylation of SR-A promotes uptake of lipids in macrophages, thereby regulating foam cell formation, a critical step in atherogenesis.
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http://dx.doi.org/10.1126/science.1101909DOI Listing
November 2004