scholarly journals The Lamin B receptor is essential for cholesterol synthesis and perturbed by disease-causing mutations

eLife ◽  
2016 ◽  
Vol 5 ◽  
Author(s):  
Pei-Ling Tsai ◽  
Chenguang Zhao ◽  
Elizabeth Turner ◽  
Christian Schlieker
Keyword(s):  
Nuclear Membrane ◽  
Cholesterol Synthesis ◽  
Point Mutations ◽  
Nuclear Lamina ◽  
Human Cell Line ◽  
Loss Of Function ◽  
Lamin B ◽  
Inner Nuclear Membrane ◽  
Lamin B Receptor ◽  
Polytopic Membrane Protein

Lamin B receptor (LBR) is a polytopic membrane protein residing in the inner nuclear membrane in association with the nuclear lamina. We demonstrate that human LBR is essential for cholesterol synthesis. LBR mutant derivatives implicated in Greenberg skeletal dysplasia or Pelger-Huët anomaly fail to rescue the cholesterol auxotrophy of a LBR-deficient human cell line, consistent with a loss-of-function mechanism for these congenital disorders. These disease-causing variants fall into two classes: point mutations in the sterol reductase domain perturb enzymatic activity by reducing the affinity for the essential cofactor NADPH, while LBR truncations render the mutant protein metabolically unstable, leading to its rapid degradation at the inner nuclear membrane. Thus, metabolically unstable LBR variants may serve as long-sought-after model substrates enabling previously impossible investigations of poorly understood protein turnover mechanisms at the inner nuclear membrane of higher eukaryotes.

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 Fate of the Inner Nuclear Membrane Protein Lamin B Receptor and Nuclear Lamins in Herpes Simplex Virus Type 1 Infection

2001 ◽  
Vol 75 (18) ◽  
pp. 8818-8830 ◽  
Author(s):  
Emily S. Scott ◽  
Peter O'Hare
Keyword(s):  
Herpes Simplex ◽  
Nuclear Membrane ◽  
Nuclear Lamina ◽  
Lamin B ◽  
Inner Nuclear Membrane ◽  
Lamin B Receptor ◽  
Infected Cells ◽  
Simplex Virus ◽  
Inner Nuclear Membrane Protein

ABSTRACT During herpesvirus egress, capsids bud through the inner nuclear membrane. Underlying this membrane is the nuclear lamina, a meshwork of intermediate filaments with which it is tightly associated. Details of alterations to the lamina and the inner nuclear membrane during infection and the mechanisms involved in capsid transport across these structures remain unclear. Here we describe the fate of key protein components of the nuclear envelope and lamina during herpes simplex virus type 1 (HSV-1) infection. We followed the distribution of the inner nuclear membrane protein lamin B receptor (LBR) and lamins A and B2 tagged with green fluorescent protein (GFP) in live infected cells. Together with additional results from indirect immunofluorescence, our studies reveal major morphologic distortion of nuclear-rim LBR and lamins A/C, B1, and B2. By 8 h p.i., we also observed a significant redistribution of LBR-GFP to the endoplasmic reticulum, where it colocalized with a subpopulation of cytoplasmic glycoprotein B by immunofluorescence. In addition, analysis by fluorescence recovery after photobleaching reveals that LBR-GFP exhibited increased diffusional mobility within the nuclear membrane of infected cells. This is consistent with the disruption of interactions between LBR and the underlying lamina. In addition to studying stably expressed GFP-lamins by fluorescence microscopy, we studied endogenous A- and B-type lamins in infected cells by Western blotting. Both approaches reveal a loss of lamins associated with virus infection. These data indicate major disruption of the nuclear envelope and lamina of HSV-1-infected cells and are consistent with a virus-induced dismantling of the nuclear lamina, possibly in order to gain access to the inner nuclear membrane.

scholarly journals Temporal Association of Protamine 1 with the Inner Nuclear Membrane Protein Lamin B Receptor during Spermiogenesis

2003 ◽  
Vol 279 (12) ◽  
pp. 11626-11631 ◽  
Author(s):  
Ilias Mylonis ◽  
Victoria Drosou ◽  
Stefano Brancorsini ◽  
Eleni Nikolakaki ◽  
Paolo Sassone-Corsi ◽  
...  
Keyword(s):  
Membrane Protein ◽  
Nuclear Membrane ◽  
Temporal Association ◽  
Lamin B ◽  
Inner Nuclear Membrane ◽  
Lamin B Receptor ◽  
Inner Nuclear Membrane Protein ◽  
Protamine 1 ◽  
Nuclear Membrane Protein

Sequential PKC- and Cdc2-mediated phosphorylation events elicit zebrafish nuclear envelope disassembly

1999 ◽  
Vol 112 (6) ◽  
pp. 977-987 ◽  
Author(s):  
P. Collas
Keyword(s):  
Nuclear Envelope ◽  
Nuclear Membrane ◽  
Nuclear Lamina ◽  
Cdc2 Kinase ◽  
Lamin B ◽  
Inner Nuclear Membrane ◽  
Nuclear Envelope Breakdown ◽  
Simultaneous Inhibition ◽  
Integral Proteins

Molecular markers of the zebrafish inner nuclear membrane (NEP55) and nuclear lamina (L68) were identified, partially characterized and used to demonstrate that disassembly of the zebrafish nuclear envelope requires sequential phosphorylation events by first PKC, then Cdc2 kinase. NEP55 and L68 are immunologically and functionally related to human LAP2beta and lamin B, respectively. Exposure of zebrafish nuclei to meiotic cytosol elicits rapid phosphorylation of NEP55 and L68, and disassembly of both proteins. L68 phosphorylation is completely inhibited by simultaneous inhibition of Cdc2 and PKC and only partially blocked by inhibition of either kinase. NEP55 phosphorylation is completely prevented by inhibition or immunodepletion of cytosolic Cdc2. Inhibition of cAMP-dependent kinase, MEK or CaM kinase II does not affect NEP55 or L68 phosphorylation. In vitro, nuclear envelope disassembly requires phosphorylation of NEP55 and L68 by both mammalian PKC and Cdc2. Inhibition of either kinase is sufficient to abolish NE disassembly. Furthermore, novel two-step phosphorylation assays in cytosol and in vitro indicate that PKC-mediated phosphorylation of L68 prior to Cdc2-mediated phosphorylation of L68 and NEP55 is essential to elicit nuclear envelope breakdown. Phosphorylation elicited by Cdc2 prior to PKC prevents nuclear envelope disassembly even though NEP55 is phosphorylated. The results indicate that sequential phosphorylation events elicited by PKC, followed by Cdc2, are required for zebrafish nuclear disassembly. They also argue that phosphorylation of inner nuclear membrane integral proteins is not sufficient to promote nuclear envelope breakdown, and suggest a multiple-level regulation of disassembly of nuclear envelope components during meiosis and at mitosis.

scholarly journals Stepwise reassembly of the nuclear envelope at the end of mitosis

1993 ◽  
Vol 122 (2) ◽  
pp. 295-306 ◽  
Author(s):  
N Chaudhary ◽  
JC Courvalin
Keyword(s):  
Nuclear Envelope ◽  
Nuclear Membrane ◽  
Nuclear Pore ◽  
Membrane Domains ◽  
Lamin B ◽  
Inner Nuclear Membrane ◽  
Domain Specific ◽  
Lamin B Receptor ◽  
Different Populations ◽  
Pore Complexes

The nuclear envelope consists of three distinct membrane domains: the outer membrane with the bound ribosomes, the inner membrane with the bound lamina, and the pore membrane with the bound pore complexes. Using biochemical and morphological methods, we observed that the nuclear membranes of HeLa cells undergoing mitosis are disassembled in a domain-specific manner, i.e., integral membrane proteins representing the inner nuclear membrane (the lamin B receptor) and the nuclear pore membrane (gp210) are segregated into different populations of mitotic vesicles. At the completion of mitosis, the inner nuclear membrane-derived vesicles associate with chromatin first, beginning in anaphase, whereas the pore membranes and the lamina assemble later, during telophase and cytokinesis. Our data suggest that the ordered reassembly of the nuclear envelope is triggered by the early attachment of inner nuclear membrane-derived vesicles to the chromatin.

Interaction between the inner nuclear membrane lamin B receptor and the heterochromatic methyl binding protein, MeCP2

2009 ◽  
Vol 315 (11) ◽  
pp. 1895-1903 ◽  
Author(s):  
Alessia Guarda ◽  
Fabrizio Bolognese ◽  
Ian Marc Bonapace ◽  
Gianfranco Badaracco
Keyword(s):  
Nuclear Membrane ◽  
Binding Protein ◽  
Lamin B ◽  
Inner Nuclear Membrane ◽  
Lamin B Receptor ◽  
Protein Mecp2

Subcellular distribution of the Xenopus p58/lamin B receptor in oocytes and eggs

1999 ◽  
Vol 112 (15) ◽  
pp. 2583-2596 ◽  
Author(s):  
A. Gajewski ◽  
G. Krohne
Keyword(s):  
Nuclear Membrane ◽  
Xenopus Oocytes ◽  
Immunofluorescence Microscopy ◽  
Significant Proportion ◽  
Sperm Chromatin ◽  
Lamin B ◽  
Inner Nuclear Membrane ◽  
Amino Terminal ◽  
Lamin B Receptor

The p58/lamin B receptor of vertebrates is localized in the inner nuclear membrane. Antibodies raised against the bacterially expressed amino-terminal half of Xenopus p58 (Xp58) revealed that in Xenopus oocytes the vast majority of this membrane protein is localized in cytoplasmic membranes. Only very small amounts of p58 not detectable by immunofluorescence microscopy were contained in the oocyte nuclear envelope. In contrast, nuclear membranes of 2-cell stage embryos were successfully stained with p58 antibodies, nuclei reconstituted in vitro in Xenopus egg extracts contained p58, and the nucleoplasmic domain of Xp58 could be specifically bound to sperm chromatin in vitro. One major difference between oocytes and early embryonic cells is that no chromatin is associated with the oocyte inner nuclear membrane whereas the complement of lamins is identical in both cell types. To gain insight into the properties of oocyte p58 we microinjected isolated nuclei of cultured rat cells into the cytoplasm of Xenopus oocytes. The oocyte p58 was detectable by immunofluorescence microscopy within 16–20 hours in the nuclear membrane of rat nuclei. Our data indicate that the peripheral chromatin but not lamins are required for the retention of p58 in the inner nuclear membrane. Sucrose step gradient centrifugation of total oocyte membranes revealed that the oocyte p58 was predominantly recovered in membrane fractions that did not contain lamins whereas membrane associated lamins and p58 of unfertilized eggs were found in the same fractions. By electron microscopical immunolocalizations one major population of meiotic p58 vesicles was identified that contained exclusively p58 and a second minor population (ca. 11% of p58 vesicles) contained in addition to p58 membrane bound B-type lamins. Egg vesicles containing pore membrane proteins were predominantly recovered in gradient fractions that did not contain p58 and B-type lamins. Our data indicate that the targeting of p58 to chromatin at the end of mitosis in the early Xenopus embryo is a process independent from that of lamin targeting. Comparable to the situation in oocytes and eggs, a significant proportion of p58 of interphase cells could be recovered in fractions that did not contain lamins. This population of p58 molecules could be extracted from A6-cells with buffers containing 1% Triton X-100/0.15 M NaCl and could be pelleted by a 50,000 g centrifugation. A- and B-type lamins were not detectable in the p58 containing pellet.

scholarly journals The first membrane spanning region of the lamin B receptor is sufficient for sorting to the inner nuclear membrane.

1993 ◽  
Vol 120 (3) ◽  
pp. 631-637 ◽  
Author(s):  
S Smith ◽  
G Blobel
Keyword(s):  
Nuclear Membrane ◽  
Mammalian Cells ◽  
Specific Interaction ◽  
Integral Membrane Protein ◽  
Transmembrane Segment ◽  
Hydrophobic Domain ◽  
Lamin B ◽  
Inner Nuclear Membrane ◽  
Amino Terminal ◽  
Lamin B Receptor

The lamin B receptor (LBR) is a polytopic integral membrane protein localized exclusively in the inner nuclear membrane domain of the nuclear envelope. Its cDNA deduced primary structure consists of a highly charged amino-terminal domain of 205 residues that faces the nucleoplasm followed by a hydrophobic domain with eight potential transmembrane segments. To identify determinants that sort LBR from its site of integration (RER and outer nuclear membrane) to the inner nuclear membrane, we prepared full-length, truncated, and chimeric cDNA constructs of chick LBR, transfected these into mammalian cells and detected the expressed protein by immunofluorescence microscopy using appropriate antibodies. Surprisingly, we found that the determinants for sorting of LBR to the inner nuclear membrane reside in a region comprising its first transmembrane sequence plus flanking residues on either side. The other transmembrane regions as well as the nucleoplasmic domain are not required for sorting. We propose that the first transmembrane segment of LBR interacts specifically with another transmembrane segment and consider several mechanisms by which such specific interaction could result in sorting to the inner nuclear membrane.

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