scholarly journals Selective clearance of the inner nuclear membrane protein emerin by vesicular transport during ER stress

2019 ◽  
Author(s):  
Abigail Buchwalter ◽  
Roberta Schulte ◽  
Hsiao Tsai ◽  
Juliana Capitanio ◽  
Martin Hetzer
Keyword(s):  
Er Stress ◽  
Nuclear Membrane ◽  
Mammalian Cells ◽  
Vesicular Transport ◽  
Vesicular Trafficking ◽  
Nuclear Pore ◽  
Inner Nuclear Membrane ◽  
Turn Over ◽  
Inner Nuclear Membrane Protein

AbstractThe inner nuclear membrane (INM) is a subdomain of the endoplasmic reticulum (ER) that is gated by the nuclear pore complex. It is unknown whether proteins of the INM and ER are degraded through shared or distinct pathways in mammalian cells. We applied dynamic proteomics to profile protein half-lives and report that INM and ER residents turn over at similar rates, indicating that the INM’s unique topology is not a barrier to turnover. Using a microscopy approach, we observed that the proteasome can degrade INM proteins in situ. However, we also uncovered evidence for selective, vesicular transport-mediated turnover of a single INM protein, emerin, that is potentiated by ER stress. Emerin is rapidly cleared from the INM by a mechanism that requires emerin’s LEM domain to mediate vesicular trafficking to lysosomes. This work demonstrates that the INM can be dynamically remodeled in response to environmental inputs.

scholarly journals Selective clearance of the inner nuclear membrane protein emerin by vesicular transport during ER stress

eLife ◽  
2019 ◽  
Vol 8 ◽  
Author(s):  
Abigail Buchwalter ◽  
Roberta Schulte ◽  
Hsiao Tsai ◽  
Juliana Capitanio ◽  
Martin Hetzer
Keyword(s):  
Er Stress ◽  
Nuclear Membrane ◽  
Mammalian Cells ◽  
Vesicular Transport ◽  
Vesicular Trafficking ◽  
Nuclear Pore ◽  
Inner Nuclear Membrane ◽  
Turn Over ◽  
Inner Nuclear Membrane Protein

The inner nuclear membrane (INM) is a subdomain of the endoplasmic reticulum (ER) that is gated by the nuclear pore complex. It is unknown whether proteins of the INM and ER are degraded through shared or distinct pathways in mammalian cells. We applied dynamic proteomics to profile protein half-lives and report that INM and ER residents turn over at similar rates, indicating that the INM’s unique topology is not a barrier to turnover. Using a microscopy approach, we observed that the proteasome can degrade INM proteins in situ. However, we also uncovered evidence for selective, vesicular transport-mediated turnover of a single INM protein, emerin, that is potentiated by ER stress. Emerin is rapidly cleared from the INM by a mechanism that requires emerin’s LEM domain to mediate vesicular trafficking to lysosomes. This work demonstrates that the INM can be dynamically remodeled in response to environmental inputs.

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 ESCRT recruitment by the S. cerevisiae inner nuclear membrane protein Heh1 is regulated by Hub1-mediated alternative splicing

2020 ◽  
Vol 133 (24) ◽  
pp. jcs250688 ◽  
Author(s):  
Matías Capella ◽  
Lucía Martín Caballero ◽  
Boris Pfander ◽  
Sigurd Braun ◽  
Stefan Jentsch
Keyword(s):  
Alternative Splicing ◽  
Membrane Protein ◽  
Nuclear Membrane ◽  
Nuclear Pore ◽  
Nuclear Pore Complexes ◽  
Inner Nuclear Membrane ◽  
Growth Defects ◽  
Pore Complexes ◽  
Inner Nuclear Membrane Protein ◽  
Nuclear Membrane Protein

ABSTRACTMisassembled nuclear pore complexes (NPCs) are removed by sealing off the surrounding nuclear envelope (NE), which is conducted by the endosomal sorting complexes required for transport (ESCRT) 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 in production of its shorter form Heh1-S, is critical for the integrity of the NE in Saccharomyces cerevisiae. 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, which is only present in the longer variant Heh1-L. Heh1 variants assemble into heterodimers, and we demonstrate that a unique splice segment in Heh1-S suppresses growth defects associated with the uncontrolled interaction between Heh1-L and Chm7. Together, our findings reveal that Hub1-mediated splicing generates Heh1-S to regulate ESCRT recruitment to the NE.This article has an associated First Person interview with the first author of the paper.

scholarly journals The inner nuclear membrane protein Src1 associates with subtelomeric genes and alters their regulated gene expression

2008 ◽  
Vol 182 (5) ◽  
pp. 897-910 ◽  
Author(s):  
Stefanie E. Grund ◽  
Tamás Fischer ◽  
Ghislain G. Cabal ◽  
Oreto Antúnez ◽  
José E. Pérez-Ortín ◽  
...  
Keyword(s):  
Gene Expression ◽  
Membrane Protein ◽  
Nuclear Membrane ◽  
Genetic Interaction ◽  
Nuclear Pore ◽  
Inner Nuclear Membrane ◽  
Regulated Gene Expression ◽  
Inner Nuclear Membrane Protein ◽  
Subtelomeric Regions ◽  
Nuclear Membrane Protein

Inner nuclear membrane proteins containing a LEM (LAP2, emerin, and MAN1) domain participate in different processes, including chromatin organization, gene expression, and nuclear envelope biogenesis. In this study, we identify a robust genetic interaction between transcription export (TREX) factors and yeast Src1, an integral inner nuclear membrane protein that is homologous to vertebrate LEM2. DNA macroarray analysis revealed that the expression of the phosphate-regulated genes PHO11, PHO12, and PHO84 is up-regulated in src1Δ cells. Notably, these PHO genes are located in subtelomeric regions of chromatin and exhibit a perinuclear location in vivo. Src1 spans the nuclear membrane twice and exposes its N and C domains with putative DNA-binding motifs to the nucleoplasm. Genome-wide chromatin immunoprecipitation–on-chip analyses indicated that Src1 is highly enriched at telomeres and subtelomeric regions of the yeast chromosomes. Our data show that the inner nuclear membrane protein Src1 functions at the interface between subtelomeric gene expression and TREX-dependent messenger RNA export through the nuclear pore complexes.

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.

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.

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