scholarly journals The Inner Nuclear Membrane Takes On Lipid Metabolism

2018 ◽  
Vol 47 (4) ◽  
pp. 397-399
Author(s):  
Holly Merta ◽  
Shirin Bahmanyar
Keyword(s):  
Lipid Metabolism ◽  
Nuclear Membrane ◽  
Inner Nuclear Membrane

Lamin B receptor: role on chromatin structure, cellular senescence and possibly aging

2020 ◽  
Vol 477 (14) ◽  
pp. 2715-2720
Author(s):  
Susana Castro-Obregón
Keyword(s):  
Cellular Senescence ◽  
Nuclear Membrane ◽  
Chromatin Structure ◽  
Cholesterol Synthesis ◽  
Reductase Activity ◽  
Chimeric Protein ◽  
Nuclear Lamina ◽  
Lamin B ◽  
Inner Nuclear Membrane ◽  
Lamin B Receptor

The nuclear envelope is composed by an outer nuclear membrane and an inner nuclear membrane, which is underlain by the nuclear lamina that provides the nucleus with mechanical strength for maintaining structure and regulates chromatin organization for modulating gene expression and silencing. A layer of heterochromatin is beneath the nuclear lamina, attached by inner nuclear membrane integral proteins such as Lamin B receptor (LBR). LBR is a chimeric protein, having also a sterol reductase activity with which it contributes to cholesterol synthesis. Lukasova et al. showed that when DNA is damaged by ɣ-radiation in cancer cells, LBR is lost causing chromatin structure changes and promoting cellular senescence. Cellular senescence is characterized by terminal cell cycle arrest and the expression and secretion of various growth factors, cytokines, metalloproteinases, etc., collectively known as senescence-associated secretory phenotype (SASP) that cause chronic inflammation and tumor progression when they persist in the tissue. Therefore, it is fundamental to understand the molecular basis for senescence establishment, maintenance and the regulation of SASP. The work of Lukasova et al. contributed to our understanding of cellular senescence establishment and provided the basis that lead to the further discovery that chromatin changes caused by LBR reduction induce an up-regulated expression of SASP factors. LBR dysfunction has relevance in several diseases and possibly in physiological aging. The potential bifunctional role of LBR on cellular senescence establishment, namely its role in chromatin structure together with its enzymatic activity contributing to cholesterol synthesis, provide a new target to develop potential anti-aging therapies.

scholarly journals The CaaX motif is required for isoprenylation, carboxyl methylation, and nuclear membrane association of lamin B2.

1991 ◽  
Vol 113 (1) ◽  
pp. 13-23 ◽  
Author(s):  
G T Kitten ◽  
E A Nigg
Keyword(s):  
Nuclear Membrane ◽  
Stop Codon ◽  
Mevalonic Acid ◽  
Cysteine Residue ◽  
Inner Nuclear Membrane ◽  
Nuclear Lamins ◽  
Carboxyl Methylation ◽  
Reticulocyte Lysates ◽  
Caax Motif

Recent evidence suggests that the conserved COOH-terminal CaaX motif of nuclear lamins may play a role in targeting newly synthesized proteins to the nuclear envelope. We have shown previously that in rabbit reticulocyte lysates the cysteine residue of the CaaX motif of chicken lamin B2 is necessary for incorporation of a derivative of mevalonic acid, the precursor of isoprenoids. Here we have analyzed the properties of normal and mutated forms of chicken lamin B2 stably expressed in mouse L cells. Mutation of the cysteine residue of the CaaX motif to alanine or introduction of a stop codon immediately after the cysteine residue was found to abolish both isoprenylation and carboxyl methylation of transfected lamin B2. Concomitantly, although nuclear import of the mutant lamin B2 proteins was preserved, their association with the inner nuclear membrane was severely impaired. From these results we conclude that the COOH-terminal CaaX motif is required for isoprenylation and carboxyl methylation of lamins in vivo, and that these modifications are important for association of B-type lamins with the nucleoplasmic surface of the inner nuclear membrane.

scholarly journals Lysine 242 within Helix 10 of the Pseudorabies Virus Nuclear Egress Complex pUL31 Component Is Critical for Primary Envelopment of Nucleocapsids

2017 ◽  
Vol 91 (22) ◽  
Author(s):  
Sebastian Rönfeldt ◽  
Barbara G. Klupp ◽  
Kati Franzke ◽  
Thomas C. Mettenleiter
Keyword(s):  
Lipid Bilayers ◽  
Nuclear Membrane ◽  
Pseudorabies Virus ◽  
Amino Acid Position ◽  
Distal Portion ◽  
Lysine Residue ◽  
Interaction Domain ◽  
Inner Nuclear Membrane ◽  
Nuclear Egress ◽  
Membrane Budding

ABSTRACT Newly assembled herpesvirus nucleocapsids are translocated from the nucleus to the cytosol by a vesicle-mediated process engaging the nuclear membranes. This transport is governed by the conserved nuclear egress complex (NEC), consisting of the alphaherpesviral pUL34 and pUL31 homologs. The NEC is not only required for efficient nuclear egress but also sufficient for vesicle formation from the inner nuclear membrane (INM), as well as from synthetic lipid bilayers. The recently solved crystal structures for the NECs from different herpesviruses revealed molecular details of this membrane deformation and scission machinery uncovering the interfaces involved in complex and coat formation. However, the interaction domain with the nucleocapsid remained undefined. Since the NEC assembles a curved hexagonal coat on the nucleoplasmic side of the INM consisting of tightly interwoven pUL31/pUL34 heterodimers arranged in hexamers, only the membrane-distal end of the NEC formed by pUL31 residues appears to be accessible for interaction with the nucleocapsid cargo. To identify the amino acids involved in capsid incorporation, we mutated the corresponding regions in the alphaherpesvirus pseudorabies virus (PrV). Site-specifically mutated pUL31 homologs were tested for localization, interaction with pUL34, and complementation of PrV-ΔUL31. We identified a conserved lysine residue at amino acid position 242 in PrV pUL31 located in the alpha-helical domain H10 exposed on the membrane-distal end of the NEC as a key residue for nucleocapsid incorporation into the nascent primary particle. IMPORTANCE Vesicular transport through the nuclear envelope is a focus of research but is still not well understood. Herpesviruses pioneered this mechanism for translocation of the newly assembled nucleocapsid from the nucleus into the cytosol via vesicles derived from the inner nuclear membrane which fuse in a well-tuned process with the outer nuclear membrane to release their content. The structure of the viral nuclear membrane budding and scission machinery has been solved recently, providing in-depth molecular details. However, how cargo is incorporated remained unclear. We identified a conserved lysine residue in the membrane-distal portion of the nuclear egress complex required for capsid uptake into inner nuclear membrane-derived vesicles.

Intranuclear membranous inclusions in oocytes of a viviparous teleost (Xiphophorus helleri)

1976 ◽  
Vol 22 (2) ◽  
pp. 325-334
Author(s):  
C. Azevedo
Keyword(s):  
Nuclear Membrane ◽  
Inclusion Bodies ◽  
Intranuclear Inclusions ◽  
Late Prophase ◽  
Xiphophorus Helleri ◽  
Inner Nuclear Membrane ◽  
Prophase I ◽  
Fixed Material ◽  
Metabolic Phenomena

Intranuclear inclusions were observed in oocytes of Xiphophorus helleri during prophase I. In osmium-fixed leptotene nuclei, the inclusions were made up of groups of membrane-limited vesicles or tubules with pale contents, situated near the inner nuclear membrane with which some of them exhibited apparent continuities. In zygotene nuclei, larger vesicles also appeared bounded by two or three membranes and containing tubules apparently invaginated from their walls. In pachytene-dictyate nuclei most vesicular bodies had a wall formed by stratified membranes, or were entirely made up of membranous whorls. In glutaraldehyde-osmium fixed material some of these myeline-like bodies showed a peculiar arrangement, consisting of concentric bands each containing thick inner dense lamellae 2-0-3-0 nm thick and a 5-0 nm outer lamella. It is suggested that these inclusion bodies arise from the inner nuclear membrane of oocytes when cells start to grow intensely during prophase I. The bodies seem to become more complex at late prophase, probably by association of individual vesicles and the occurrence of multiple membrane invaginations, which may be related to active metabolic phenomena taking place at this stage in oocytes.

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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