scholarly journals Unrestrained ESCRT-III drives chromosome fragmentation and micronuclear catastrophe

2019 ◽  
Author(s):  
Marina Vietri ◽  
Sebastian W. Schultz ◽  
Aurélie Bellanger ◽  
Carl M. Jones ◽  
Camilla Raiborg ◽  
...  
Keyword(s):  
Nuclear Envelope ◽  
Nuclear Membrane ◽  
Genome Stability ◽  
Membrane Deformation ◽  
Chromosome Fragmentation ◽  
Inner Nuclear Membrane ◽  
Membrane Rupture ◽  
Membrane Fission ◽  
Stable Association ◽  
Inner Nuclear Membrane Protein

AbstractThe ESCRT-III membrane fission machinery1,2 restores nuclear envelope integrity during mitotic exit3,4 and interphase5,6. Whereas primary nuclei resealing takes minutes, micronuclear envelope ruptures appear irreversible and result in catastrophic collapse associated with chromosome fragmentation and rearrangements (chromothripsis), thought to be a major driving force in cancer development7-10. Despite its importance11-13, the mechanistic underpinnings of nuclear envelope sealing in primary nuclei and the defects observed in micronuclei remain largely unknown. Here we show that CHMP7, the nucleator of ESCRT-III filaments at the nuclear envelope3,14, and the inner nuclear membrane protein LEMD215 act as a compartmentalization sensor detecting the loss of nuclear integrity. In cells with intact nuclear envelope, CHMP7 is actively excluded from the nucleus to preclude its binding to LEMD2. Nuclear influx of CHMP7 results in stable association with LEMD2 at the inner nuclear membrane that licenses local polymerization of ESCRT-III. Tight control of nuclear CHMP7 levels is critical, as induction of nuclear CHMP7 mutants is sufficient to induce unrestrained growth of ESCRT-III foci at the nuclear envelope, causing dramatic membrane deformation, local DNA torsional stress, single-stranded DNA formation and fragmentation of the underlying chromosomes. At micronuclei, membrane rupture is not associated with repair despite timely recruitment of ESCRT-III. Instead, micronuclei inherently lack the capacity to restrict accumulation of CHMP7 and LEMD2. This drives unrestrained ESCRT-III recruitment, membrane deformation and DNA defects that strikingly resemble those at primary nuclei upon induction of nuclear CHMP7 mutants. Preventing ESCRT-III recruitment suppresses membrane deformation and DNA damage, without restoring nucleocytoplasmic compartmentalization. We propose that the ESCRT-III nuclear integrity surveillance machinery is a double-edged sword, as its exquisite sensitivity ensures rapid repair at primary nuclei while causing unrestrained polymerization at micronuclei, with catastrophic consequences for genome stability16-18.

Function and assembly of nuclear pore complex proteins

1999 ◽  
Vol 77 (4) ◽  
pp. 321-329 ◽  
Author(s):  
Khaldon Bodoor ◽  
Sarah Shaikh ◽  
Paul Enarson ◽  
Sharmin Chowdhury ◽  
Davide Salina ◽  
...  
Keyword(s):  
Membrane Protein ◽  
Nuclear Envelope ◽  
Nuclear Pore Complex ◽  
Nuclear Membrane ◽  
Current View ◽  
Nuclear Pore ◽  
Dynamic Component ◽  
Inner Nuclear Membrane ◽  
Inner Nuclear Membrane Protein ◽  
Nuclear Membrane Protein

Nuclear pore complexes (NPCs) are extremely elaborate structures that mediate the bidirectional movement of macromolecules between the nucleus and cytoplasm. The current view of NPC organization features a massive symmetrical framework that is embedded in the double membranes of the nuclear envelope. It embraces a central channel of as yet ill-defined structure but which may accommodate particles with diameters up to 26 nm provided that they bear specific import/export signals. Attached to both faces of the central framework are peripheral structures, short cytoplasmic filaments, and a nuclear basket assembly, which interact with molecules transiting the NPC. The mechanisms of assembly and the nature of NPC structural intermediates are still poorly understood. However, mutagenesis and expression studies have revealed discrete sequences within certain NPC proteins that are necessary and sufficient for their appropriate targeting. In addition, some details are emerging from observations on cells undergoing mitosis where the nuclear envelope is disassembled and its components, including NPC subunits, are dispersed throughout the mitotic cytoplasm. At the end of mitosis, all of these components are reutilized to form nuclear envelopes in the two daughter cells. To date, it has been possible to define a time course of postmitotic assembly for a group of NPC components (CAN/Nup214, Nup153, POM121, p62 and Tpr) relative to the integral inner nuclear membrane protein LAP2 and the NPC membrane glycoprotein gp210. Nup153, a dynamic component of the nuclear basket, associates with chromatin towards the end of anaphase coincident with, although independent of, the inner nuclear membrane protein, LAP2. Assembly of the remaining proteins follows that of the nuclear membranes and occurs in the sequence POM121, p62, CAN/Nup214 and gp210/Tpr. Since p62 remains as a complex with three other NPC proteins (p58, p54, p45) during mitosis, and CAN/Nup214 maintains a similar interaction with its partner, Nup84, the relative timing of assembly of these additional four proteins may also be inferred. These observations suggest that there is a sequential association of NPC proteins with chromosomes during nuclear envelope reformation and the recruitment of at least eight of these precedes that of gp210. These findings support a model in which it is POM121 rather than gp210 that defines initial membrane-associated NPC assembly intermediates and which may therefore represent an essential component of the central framework of the NPC. Key words: nuclear pore complex, nucleoporin, mitosis, nuclear transport

scholarly journals SUN-1 and ZYG-12, Mediators of Centrosome–Nucleus Attachment, Are a Functional SUN/KASH Pair in Caenorhabditis elegans

2009 ◽  
Vol 20 (21) ◽  
pp. 4586-4595 ◽  
Author(s):  
IL Minn ◽  
Melissa M. Rolls ◽  
Wendy Hanna-Rose ◽  
Christian J. Malone
Keyword(s):  
Caenorhabditis Elegans ◽  
Nuclear Envelope ◽  
Nuclear Membrane ◽  
Coiled Coil ◽  
Physical Interaction ◽  
Type Ii ◽  
Inner Nuclear Membrane ◽  
Sequence Elements ◽  
Inner Nuclear Membrane Protein ◽  
Sun Domain

Klarsicht/ANC-1/Syne/homology (KASH)/Sad-1/UNC-84 (SUN) protein pairs can act as connectors between cytoplasmic organelles and the nucleoskeleton. Caenorhabditis elegans ZYG-12 and SUN-1 are essential for centrosome–nucleus attachment. Although SUN-1 has a canonical SUN domain, ZYG-12 has a divergent KASH domain. Here, we establish that the ZYG-12 mini KASH domain is functional and, in combination with a portion of coiled-coil domain, is sufficient for nuclear envelope localization. ZYG-12 and SUN-1 are hypothesized to be outer and inner nuclear membrane proteins, respectively, and to interact, but neither their topologies nor their physical interaction has been directly investigated. We show that ZYG-12 is a type II outer nuclear membrane (ONM) protein and that SUN-1 is a type II inner nuclear membrane protein. The proteins interact in the luminal space of the nuclear envelope via the ZYG-12 mini KASH domain and a region of SUN-1 that does not include the SUN domain. SUN-1 is hypothesized to restrict ZYG-12 to the ONM, preventing diffusion through the endoplasmic reticulum. We establish that ZYG-12 is indeed immobile at the ONM by using fluorescence recovery after photobleaching and show that SUN-1 is sufficient to localize ZYG-12 in cells. This work supports current models of KASH/SUN pairs and highlights the diversity in sequence elements defining KASH domains.

The inner nuclear membrane protein Lem2 is critical for normal nuclear envelope morphology

FEBS Letters ◽  
2006 ◽  
Vol 580 (27) ◽  
pp. 6435-6441 ◽  
Author(s):  
Sebastian Ulbert ◽  
Wolfram Antonin ◽  
Melpomeni Platani ◽  
Iain W. Mattaj
Keyword(s):  
Membrane Protein ◽  
Nuclear Envelope ◽  
Nuclear Membrane ◽  
Inner Nuclear Membrane ◽  
Inner Nuclear Membrane Protein ◽  
Nuclear Membrane Protein

scholarly journals Opposing roles for distinct LINC complexes in regulation of the small GTPase RhoA

2017 ◽  
Vol 28 (1) ◽  
pp. 182-191 ◽  
Author(s):  
Ketan Thakar ◽  
Christopher K. May ◽  
Anna Rogers ◽  
Christopher W. Carroll
Keyword(s):  
Membrane Protein ◽  
Actin Cytoskeleton ◽  
Nuclear Envelope ◽  
Focal Adhesion ◽  
Nuclear Membrane ◽  
Active Form ◽  
Small Gtpase ◽  
Inner Nuclear Membrane ◽  
Inner Nuclear Membrane Protein ◽  
Nuclear Membrane Protein

Linker of Nucleoskeleton and Cytoskeleton (LINC) complexes span the nuclear envelope and transduce force from dynamic cytoskeletal networks to the nuclear lamina. Here we show that LINC complexes also signal from the nuclear envelope to critical regulators of the actin cytoskeleton. Specifically, we find that LINC complexes that contain the inner nuclear membrane protein Sun2 promote focal adhesion assembly by activating the small GTPase RhoA. A key effector in this process is the transcription factor/coactivator complex composed of SRF/Mkl1. A constitutively active form of SRF/Mkl1 was not sufficient to induce focal adhesion assembly in cells lacking Sun2, however, suggesting that LINC complexes support RhoA activity through a transcription-independent mechanism. Strikingly, we also find that the inner nuclear membrane protein Sun1 antagonizes Sun2 LINC complexes and inhibits RhoA activation and focal adhesion assembly. Thus different LINC complexes have opposing roles in the transcription-independent control of the actin cytoskeleton through the small GTPase RhoA.

scholarly journals ESCRT recruitment by the inner nuclear membrane protein Heh1 is regulated by Hub1-mediated alternative splicing

2020 ◽  
Author(s):  
Matías Capella ◽  
Lucía Martín Caballero ◽  
Boris Pfander ◽  
Sigurd Braun ◽  
Stefan Jentsch
Keyword(s):  
Alternative Splicing ◽  
Membrane Protein ◽  
Nuclear Envelope ◽  
Nuclear Membrane ◽  
Nuclear Pore ◽  
Nuclear Pore Complexes ◽  
Inner Nuclear Membrane ◽  
Growth Defects ◽  
Inner Nuclear Membrane Protein ◽  
Nuclear Membrane Protein

AbstractMisassembled nuclear pore complexes (NPCs) are removed by sealing off the surrounding nuclear envelope (NE), which is mediated by members of the ESCRT (endosomal sorting complexes required for transport) machinery. Recruitment of ESCRT proteins to the NE is mediated by the interaction between the ESCRT member Chm7 and the inner nuclear membrane protein Heh1, which belongs to the conserved LEM family. Increased ESCRT recruitment results in excessive membrane scission at damage sites but its regulation remains poorly understood. Here, we show that Hub1-mediated alternative splicing of HEH1 pre-mRNA, resulting into its shorter form Heh1-S, is critical for the integrity of the NE. ESCRT-III mutants lacking Hub1 or Heh1-S display severe growth defects and accumulate improperly assembled NPCs. This depends on the interaction of Chm7 with the conserved MSC domain only present in the longer spliced variant Heh1-L. Heh1 variants assemble into heterodimers and we demonstrate that a unique splice segment in Heh1-S suppresses growth defects associated with uncontrolled interaction between Heh1-L and Chm7. Together, our findings reveal that Hub1-mediated splicing generates Heh1-S to regulate ESCRT recruitment to the nuclear envelope.Summary statementHeh1-S, the Hub1-mediated spliced version of HEH1 pre-mRNA, contributes to nuclear envelope maintenance by preventing excessive recruitment of Chm7.

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