The Experts below are selected from a list of 279 Experts worldwide ranked by ideXlab platform
Howard J. Worman - One of the best experts on this subject based on the ideXlab platform.
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the human <B>LaminB> B receptor sterol reductase multigene family
Genomics, 1998Co-Authors: Lars Holmer, Arash Pezhman, Howard J. WormanAbstract:LBR (<B>LaminB> B receptor) is an integral protein of the inner nuclear memBrane encoded By a gene on human chromosome 1q42.1. LBR has a nucleoplasmic, amino-terminal domain of approximately 200 amino acids followed By a carBoxyl-terminal domain similar in sequence to yeast and plant sterol reductases. We have determined the primary structures of two human proteins with strong sequence similarity to the carBoxyl-terminal domain of LBR and sterol reductases. Their genes have recently Been assigned the symBols TM7SF2 and DHCR7. TM7SF2 mRNA is most predominantly expressed in heart and DHCR7 mRNA mostly in liver and Brain. Whereas LBR is localized to the inner nuclear memBrane, these two related proteins are in the endoplasmic reticulum. The TM7SF2 gene contains 10 coding exons, and its intron positions are exactly conserved in the part of the LBR gene encoding its carBoxyl-terminal domain. Intron positions in the DHCR7 gene are also similar. Both of these new LBR-like genes are on chromosome 11q13. These results descriBe a human gene family encoding proteins of the inner nuclear memBrane and endoplasmic reticulum that function in nuclear organization and/or sterol metaBolism.
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The Human <B>LaminB> B Receptor/Sterol Reductase Multigene Family ☆
Genomics, 1998Co-Authors: Lars Holmer, Arash Pezhman, Howard J. WormanAbstract:LBR (<B>LaminB> B receptor) is an integral protein of the inner nuclear memBrane encoded By a gene on human chromosome 1q42.1. LBR has a nucleoplasmic, amino-terminal domain of approximately 200 amino acids followed By a carBoxyl-terminal domain similar in sequence to yeast and plant sterol reductases. We have determined the primary structures of two human proteins with strong sequence similarity to the carBoxyl-terminal domain of LBR and sterol reductases. Their genes have recently Been assigned the symBols TM7SF2 and DHCR7. TM7SF2 mRNA is most predominantly expressed in heart and DHCR7 mRNA mostly in liver and Brain. Whereas LBR is localized to the inner nuclear memBrane, these two related proteins are in the endoplasmic reticulum. The TM7SF2 gene contains 10 coding exons, and its intron positions are exactly conserved in the part of the LBR gene encoding its carBoxyl-terminal domain. Intron positions in the DHCR7 gene are also similar. Both of these new LBR-like genes are on chromosome 11q13. These results descriBe a human gene family encoding proteins of the inner nuclear memBrane and endoplasmic reticulum that function in nuclear organization and/or sterol metaBolism.
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Primary structure analysis and <B>LaminB> B and DNA Binding of human LBR, an integral protein of the nuclear envelope inner memBrane.
The Journal of biological chemistry, 1994Co-Authors: Howard J. WormanAbstract:We have determined the primary structure of human LBR, an integral protein of the nuclear envelope inner memBrane, and examined its interactions with <B>LaminB> B and DNA. Human LBR is 68% identical to the chicken <B>LaminB> B receptor and has a Basic nucleoplasmic amino-terminal domain of 208 amino acids followed By a hydrophoBic domain with eight putative transmemBrane segments. The amino-terminal domain contains a Ser-Arg-rich stretch and consensus sites for phosphorylation By protein kinase A and p34cdc2 protein kinase. A fusion protein containing the amino-terminal domain of human LBR is recognized By autoantiBodies from patients with primary Biliary cirrhosis, and these serum antiBodies laBel the nuclear envelope when examined By immunofluorescence microscopy. The LBR amino-terminal domain precipitates <B>LaminB> B from nuclear extracts and retards the migration of douBle-stranded DNA suBjected to agarose gel electrophoresis. When immoBilized on nitrocellulose, the amino-terminal domain of LBR also associates with DNA, and the stretch Between amino acids 71 and 100, which contains the Ser-Arg-rich stretch, is necessary for DNA Binding. These results demonstrate that LBR is conserved among verteBrate species and that its nucleoplasmic domain can potentially mediate the interaction of Both the nuclear <B>LaminB>a and the chromatin with the inner nuclear memBrane.
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The <B>LaminB> B receptor of the inner nuclear memBrane undergoes mitosis-specific phosphorylation and is a suBstrate for p34cdc2-type protein kinase.
The Journal of biological chemistry, 1992Co-Authors: J C Courvalin, Günter Blobel, Neil Segil, Howard J. WormanAbstract:The <B>LaminB> B receptor (LBR) is an integral protein of the inner nuclear memBrane that interacts with <B>LaminB> B in vitro. If contains a 204-amino acid nucleoplasmic amino-terminal domain and a hydrophoBic carBoxyl-terminal domain with eight putative transmemBrane segments. We found cell cycle-dependent phosphorylation of LBR using phosphoamino acid analysis and phosphopeptide mapping of in vivo 32P-laBeled LBR immunoprecipitated from chicken cells in interphase and arrested in mitosis. LBR was phosphorylated only on serine residues in interphase and on serine and threonine residues in mitosis. Some serine residues phosphorylated in interphase were not phosphorylated in mitosis. To identify a threonine residue specifically phosphorylated in mitosis and the responsiBle protein kinase, wild-type and mutant LBR nucleoplasmic domain fusion proteins were phosphorylated in vitro By p34cdc2-type protein kinase. Comparisons of phosphopeptide maps to those of in vivo 32P-laBeled mitotic LBR showed that Thr188 is likely to Be phosphorylated By this enzyme during mitosis. These phosphorylation/dephosphorylation events may Be responsiBle for some of the changes in the interaction Between the nuclear <B>LaminB>a and the inner nuclear memBrane that occur during mitosis.
Spyros D. Georgatos - One of the best experts on this subject based on the ideXlab platform.
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Dynamics and Structure-Function Relationships of the <B>LaminB> B Receptor (LBR).
PloS one, 2017Co-Authors: Ioannis Giannios, Eleftheria Chatzantonaki, Spyros D. GeorgatosAbstract:The <B>LaminB> B receptor (LBR) is a multi-spanning memBrane protein of the inner nuclear memBrane that is often employed as a "reporter" of nuclear envelope dynamics. We show here that the diffusional moBility of full-length LBR exhiBits significant regional variation along the nuclear envelope, consistent with the existence of discrete LBR microdomains and the occurrence of multiple, asymmetrically-spaced anastomoses along the nuclear envelope-endoplasmic reticulum interface. Interestingly, a commonly used fusion protein that contains the amino-terminal region and the first transmemBrane domain of LBR exhiBits reduced moBility at the nuclear envelope, But Behaves similarly to full-length LBR in the endoplasmic reticulum. On the other hand, carBoxy-terminally truncated mutants that retain the first four transmemBrane domains and a part or the whole of the amino-terminal region of LBR are generally hyper-moBile. These results suggest that LBR dynamics is structure and compartment specific. They also indicate that native LBR is proBaBly "configured" By long-range interactions that involve the loops Between adjacent transmemBrane domains and parts of the amino-terminal region.
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solution structure and molecular interactions of <B>LaminB> B receptor tudor domain
Journal of Biological Chemistry, 2012Co-Authors: Stamatis Liokatis, Spyros D. Georgatos, Ioannis Giannios, Christian Edlich, Katerina Soupsana, Parthena Panagiotidou, Konstantinos Tripsianes, Michael Sattler, Anastasia S PolitouAbstract:<B>LaminB> B receptor (LBR) is a polytopic protein of the nuclear envelope thought to connect the inner nuclear memBrane with the underlying nuclear <B>LaminB>a and peripheral heterochromatin. To Better understand the function of this protein, we have examined in detail its nucleoplasmic region, which is predicted to harBor a Tudor domain (LBR-TD). Structural analysis By multidimensional NMR spectroscopy estaBlishes that LBR-TD indeed adopts a classical β-Barrel Tudor fold in solution, which, however, features an incomplete aromatic cage. Removal of LBR-TD renders LBR more moBile at the plane of the nuclear envelope, But the isolated module does not Bind to nuclear <B>LaminB>s, heterochromatin proteins (MeCP2), and nucleosomes, nor does it associate with methylated Arg/Lys residues through its aromatic cage. Instead, LBR-TD exhiBits tight and stoichiometric Binding to the “histone-fold” region of unassemBled, free histone H3, suggesting an interesting role in histone assemBly. Consistent with such a role, roBust Binding to native nucleosomes is oBserved when LBR-TD is extended toward its carBoxyl terminus, to include an area rich in Ser-Arg residues. The Ser-Arg region, alone or in comBination with LBR-TD, Binds Both unassemBled and assemBled H3/H4 histones, suggesting that the TD/RS interface may operate as a “histone chaperone-like platform.”
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The Inner Nuclear MemBrane Protein <B>LaminB> B Receptor Forms Distinct Microdomains and Links Epigenetically Marked Chromatin to the Nuclear Envelope
The Journal of biological chemistry, 2004Co-Authors: Dimitra Makatsori, Leonard D. Shultz, Niki Kourmouli, Hara Polioudaki, Kelvin Mclean, Panayiotis A. Theodoropoulos, Prim B. Singh, Spyros D. GeorgatosAbstract:Using heterochromatin-enriched fractions, we have detected specific Binding of mononucleosomes to the N-terminal domain of the inner nuclear memBrane protein <B>LaminB> B receptor. Mass spectrometric analysis reveals that LBR-associated particles contain complex patterns of methylated/acetylated histones and are devoid of "euchromatic" epigenetic marks. LBR Binds heterochromatin as a higher oligomer and forms distinct nuclear envelope microdomains in vivo. The organization of these memBrane assemBlies is affected significantly in heterozygous ic (ichthyosis) mutants, resulting in a variety of structural aBnormalities and nuclear defects.
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Mitotic Phosphorylation of the <B>LaminB> B Receptor By a Serine/Arginine Kinase and p34cdc2
The Journal of biological chemistry, 1997Co-Authors: Eleni Nikolakaki, Spyros D. Georgatos, Juergen Meier, George Simos, Thomas GiannakourosAbstract:ABstract The <B>LaminB> B receptor (LBR) is an integral protein of the inner nuclear memBrane that is modified at interphase By a nuclear envelope-Bound protein kinase. This enzyme (RS kinase) specifically phosphorylates arginine-serine dipeptide motifs located at the NH2-terminal domain of LBR and regulates its interactions with other nuclear envelope proteins. To compare the phosphorylation state of LBR during interphase and mitosis, we performed phosphopeptide mapping of in vitro and in vivo 32P-laBeled LBR and analyzed a series of recomBinant proteins and synthetic peptides. Our results show that LBR undergoes two types of mitotic phosphorylation mediated By the RS and the p34cdc2 protein kinases, respectively. The RS kinase modifies similar sites at interphase and mitosis (i.e. Ser76, Ser78, Ser80, Ser82, Ser84), whereas p34cdc2 mainly phosphorylates Ser71. These findings clarify the phosphorylation state of LBR during the cell cycle and provide new information for understanding the mechanisms responsiBle for nuclear envelope assemBly and disassemBly.
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mitotic phosphorylation of the <B>LaminB> B receptor By a serine arginine kinase and p34cdc2
Journal of Biological Chemistry, 1997Co-Authors: Eleni Nikolakaki, Spyros D. Georgatos, Juergen Meier, George Simos, Thomas GiannakourosAbstract:ABstract The <B>LaminB> B receptor (LBR) is an integral protein of the inner nuclear memBrane that is modified at interphase By a nuclear envelope-Bound protein kinase. This enzyme (RS kinase) specifically phosphorylates arginine-serine dipeptide motifs located at the NH2-terminal domain of LBR and regulates its interactions with other nuclear envelope proteins. To compare the phosphorylation state of LBR during interphase and mitosis, we performed phosphopeptide mapping of in vitro and in vivo 32P-laBeled LBR and analyzed a series of recomBinant proteins and synthetic peptides. Our results show that LBR undergoes two types of mitotic phosphorylation mediated By the RS and the p34cdc2 protein kinases, respectively. The RS kinase modifies similar sites at interphase and mitosis (i.e. Ser76, Ser78, Ser80, Ser82, Ser84), whereas p34cdc2 mainly phosphorylates Ser71. These findings clarify the phosphorylation state of LBR during the cell cycle and provide new information for understanding the mechanisms responsiBle for nuclear envelope assemBly and disassemBly.
Anjaneyulu Kowluru - One of the best experts on this subject based on the ideXlab platform.
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Glucotoxic conditions induce endoplasmic reticulum stress to cause caspase 3 mediated <B>LaminB> B degradation in pancreatic β-cells: Protection By nifedipine
Biochemical pharmacology, 2013Co-Authors: Khadija Syeda, Abiy M. Mohammed, Daleep K. Arora, Anjaneyulu KowluruAbstract:Nuclear <B>LaminB>s form the <B>LaminB>a on the interior of the nuclear envelope, and are involved in the regulation of various cellular processes, including DNA replication and chromatin organization. Despite this evidence, little is known aBout potential alterations in nuclear metaBolism, specifically <B>LaminB> structure and integrity in isolated β-cells suBjected to stress conditions, including chronic exposure to hyperglycemia (i.e., glucotoxicity). Herein, we investigated effects of glucotoxic conditions on the catalytic activation of caspase 3 and the associated degradation of one of its suBstrate proteins, namely <B>LaminB>-B. We report that incuBation of insulin-secreting INS-1 832/13 cells, normal rat islets or human islets under glucotoxic conditions (20 mM; 12-48 h) results in the degradation of native <B>LaminB> B leading to accumulation of the degraded products in non-relevant cellular compartments, including cytosol. Moreover, the effects of high glucose on caspase 3 activation and <B>LaminB> B degradation were mimicked By thapsigargin, a known inducer of endoplasmic reticulum stress (ER stress). Nifedipine, a known Blocker of calcium channel activation, inhiBited high glucose-induced caspase 3 activation and <B>LaminB> B degradation in these cells. 4-Phenyl Butyric acid, a known inhiBitor of ER stress, markedly attenuated glucose-induced CHOP expression (ER stress marker), caspase 3 activation and <B>LaminB> B degradation. We conclude that glucotoxic conditions promote caspase 3 activation and <B>LaminB> B degradation, which may, in part, Be due to increased ER stress under these conditions. We also provide further evidence to support Beneficial effects of calcium channel Blockers against metaBolic dysfunction of the islet β-cell induced By hyperglycemic conditions.
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interleukin 1β induces posttranslational carBoxymethylation and alterations in suBnuclear distriBution of <B>LaminB> B in insulin secreting rinm5f cells
American Journal of Physiology-cell Physiology, 2004Co-Authors: Rajakrishnan Veluthakal, Rajesh Amin, Anjaneyulu KowluruAbstract:We examined the effects of interleukin-1β (IL-1β) treatment on the distriBution and degradation of <B>LaminB> B in the nuclear fraction from insulin-secreting RINm5F cells. Western Blot analysis indicat...
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Interleukin-1β induces posttranslational carBoxymethylation and alterations in suBnuclear distriBution of <B>LaminB> B in insulin-secreting RINm5F cells
American journal of physiology. Cell physiology, 2004Co-Authors: Rajakrishnan Veluthakal, Rajesh Amin, Anjaneyulu KowluruAbstract:We examined the effects of interleukin-1Beta (IL-1Beta) treatment on the distriBution and degradation of <B>LaminB> B in the nuclear fraction from insulin-secreting RINm5F cells. Western Blot analysis indicated that IL-1Beta treatment caused significant alterations in the redistriBution of <B>LaminB> B, specifically Between the Triton X-100-soluBle (memBrane) and -insoluBle (matrix) fractions of the nucleus. IL-1Beta treatment also increased the <B>LaminB> carBoxymethyltransferase activity and the relative aBundance of the carBoxymethylated <B>LaminB> in the nuclear fraction. A significant increase in the relative aBundance of <B>LaminB> B degradation products was also oBserved in the nuclear fraction from the IL-1Beta-treated cells. These findings are compatiBle with a measuraBle increase in the <B>LaminB>-degrading caspase-6 activity in IL-1Beta-treated cells. Confocal microscopic oBservation of IL-1Beta-treated cells suggested a significant dissociation of <B>LaminB> B from the nuclear <B>LaminB>a and its suBsequent association with the DNA-rich elements within the nucleus. N(G)-monomethyl-l-arginine, a known inhiBitor of induciBle nitric oxide synthetase (iNOS), markedly inhiBited IL-1Beta-induced iNOS gene expression, NO release, caspase-3 and caspase-6 activation, <B>LaminB> B degradation, and loss of metaBolic cell viaBility, indicating that the oBserved IL-1Beta-induced effects on nuclear <B>LaminB> B involve the intermediacy of NO. Together, our data support the hypothesis that IL-1Beta treatment results in significant increase in the carBoxymethylation of <B>LaminB> B, which would place <B>LaminB> B in a strategic location for its degradation mediated By caspases. This could possiBly lead to dissolution of the nuclear envelope, culminating in the demise of the effete Beta-cell.
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Evidence for the CarBoxyl Methylation of Nuclear <B>LaminB>-B in the Pancreatic β Cell
Biochemical and biophysical research communications, 2000Co-Authors: Anjaneyulu KowluruAbstract:<B>LaminB>s are intermediate filament proteins that constitute the main components of the <B>LaminB>a underlying the inner-nuclear memBrane and serve to organize chromatin. <B>LaminB>s (e.g., <B>LaminB>-B) undergo posttranslational modifications (e.g., isoprenylation and methylation) at their C-terminal cysteine. Such modifications are thought to render optimal association of <B>LaminB>s with the nuclear envelop. Herein, we examined whether nuclear <B>LaminB>-B undergoes carBoxyl methylation in islet Beta cells. A 65- to 70-kDa protein was carBoxyl methylated in intact rat islets and clonal Beta (HIT or INS) cells or in homogenates which could Be immunoprecipitated using <B>LaminB>-B antiserum. IncuBation of purified HIT cell-nuclear fraction with [(3)H]S-adenosyl methionine yielded a single carBoxyl methylated protein peak (ca. 65-70 kDa); this protein was immunologically identified as <B>LaminB>-B. Several methylation inhiBitors, including acetyl farnesyl cysteine, a competitive inhiBitor of protein prenyl cysteine methylation, inhiBited the carBoxyl methylation of <B>LaminB>-B, indicating that the carBoxyl-methylated amino acid is cysteine. These findings, together with our recent oBservations demonstrating that inhiBition of protein isoprenylation causes apoptotic death of the pancreatic Beta cell, raise an interesting possiBility that inhiBition of C-terminal cysteine modifications of <B>LaminB>-B might result in disruption of nuclear assemBly, leading to further propagation of apoptotic signals, including DNA fragmentation and chromatin condensation.
Yixian Zheng - One of the best experts on this subject based on the ideXlab platform.
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<B>LaminB>-B in systemic inflammation, tissue homeostasis, and aging.
Nucleus (Austin Tex.), 2015Co-Authors: Haiyang Chen, Xiaobin Zheng, Yixian ZhengAbstract:Gradual loss of tissue function (or homeostasis) is a natural process of aging and is Believed to cause many age-associated diseases. In human epidemiology studies, the low-grade and chronic systemic inflammation in elderly has Been correlated with the development of aging related pathologies. Although it is suspected that tissue decline is related to systemic inflammation, the cause and consequence of these aging phenomena are poorly understood. By studying the Drosophila fat Body and gut, we have uncovered a mechanism By which <B>LaminB>-B loss in the fat Body upon aging induces age-associated systemic inflammation. This chronic inflammation results in the repression of gut local immune response, which in turn leads to the over-proliferation and mis-differentiation of the intestinal stem cells, thereBy resulting in gut hyperplasia. Here we discuss the implications and remaining questions in light of our puBlished findings and new oBservations.
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Age-Associated Loss of <B>LaminB>-B Leads to Systemic Inflammation and Gut Hyperplasia
Cell, 2014Co-Authors: Haiyang Chen, Xiaobin Zheng, Yixian ZhengAbstract:Aging of immune organs, termed as immunosenescence, is suspected to promote systemic inflammation and age-associated disease. The cause of immunosenescence and how it promotes disease, however, has remained unclear. We report that the Drosophila fat Body, a major immune organ, undergoes immunosenescence and mounts strong systemic inflammation that leads to deregulation of immune deficiency (IMD) signaling in the midgut of old animals. Inflamed old fat Bodies secrete circulating peptidoglycan recognition proteins that repress IMD activity in the midgut, thereBy promoting gut hyperplasia. Further, fat Body immunosenecence is caused By age-associated <B>LaminB>-B reduction specifically in fat Body cells, which then contriButes to heterochromatin loss and derepression of genes involved in immune responses. As <B>LaminB>-associated heterochromatin domains are enriched for genes involved in immune response in Both Drosophila and mammalian cells, our findings may provide insights into the cause and consequence of immunosenescence during mammalian aging. PAPERFLICK:
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A computational model for the formation of <B>LaminB>-B mitotic spindle envelope and matrix
Interface Focus, 2014Co-Authors: Changji Shi, Yixian Zheng, Wilbur E. Channels, Pablo A. IglesiasAbstract:Recent reports show that, after nuclear envelope Breakdown, <B>LaminB>-B, a component of the nuclear <B>LaminB>a in interphase, localizes around the mitotic spindle as a memBranous network. How this process occurs, however, and how it influences mitotic spindle morphogenesis is unclear. Here, we develop a computational model Based on a continuum description to represent the aBundance and location of various molecular species involved during mitosis, and use the model to test a numBer of hypotheses regarding the formation of the mitotic matrix. Our model illustrates that freely diffusiBle nuclear proteins can Be captured and transported to the spindle poles By minus-end-directed microtuBule (MT) motors. Moreover, simulations show that these proteins can Be used to Build a shell-like region that envelopes the mitotic spindle, which helps to improve the focusing of the mitotic spindle By spatially restricting MT polymerization and limiting the effective diffusion of the free MTs. Simulations also confirm that spatially dependent regulation of the spindle network through the Ran system improves spindle focusing and morphology. Our results agree with experimental oBservations that <B>LaminB>-B reorganizes around the spindle and helps to maintain spindle morphology.
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<B>LaminB> B Counteracts the Kinesin Eg5 to Restrain Spindle Pole Separation during Spindle AssemBly
The Journal of biological chemistry, 2010Co-Authors: Benjamin Goodman, Pablo A. Iglesias, Wilbur E. Channels, Minhua Qiu, Ge Yang, Yixian ZhengAbstract:<B>LaminB> B is a component of the memBranous spindle matrix isolated from Xenopus egg extracts, and it is required for proper spindle morphogenesis. Besides <B>LaminB> B, the spindle matrix contains spindle assemBly factors (SAFs) such as Eg5 and dynein which are known to regulate microtuBule organization and SAFs known to promote microtuBule assemBly such as Maskin and XMAP215. Because <B>LaminB> B does not Bind directly to microtuBules, it must affect spindle morphogenesis indirectly By influencing the function of spindle matrix-associated SAFs. Using different assays in Xenopus egg extracts, we found that depleting <B>LaminB> B caused formation of elongated and multipolar spindles, which could Be reversed By partially inhiBiting the kinesin Eg5, revealing an antagonistic relationship Between Eg5 and <B>LaminB> B. However, <B>LaminB> B only very weakly antagonizes Eg5 in mediating poleward microtuBule-flux Based on fluorescence speckle microscopy. Depleting <B>LaminB> B led to a very small But statistically significant increase in flux. Furthermore, flux reduction caused By partial Eg5 inhiBition is only slightly reversed By removing <B>LaminB> B. Because <B>LaminB> B does not Bind to Eg5, our studies suggest two nonexclusive mechanisms By which <B>LaminB> B can indirectly antagonize Eg5. It could function in a network that restricts Eg5-driven microtuBule sliding only when microtuBules come into transient contact with the network. <B>LaminB> B could also function to sequester microtuBule polymerization activities within the spindle. Without <B>LaminB> B, increased microtuBule assemBly caused By the released SAFs would lead to excessive microtuBule sliding that results in formation of elongated and multipolar spindles.
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Requirement for Nudel and dynein for assemBly of the <B>LaminB> B spindle matrix
Nature cell biology, 2009Co-Authors: Ming Ying Tsai, Shusheng Wang, Rong Chen, Jonh R. Yates, Xueliang Zhu, Yixian ZhengAbstract:The small guanosine triphosphatase Ran loaded with GTP (RanGTP) can stimulate assemBly of the type V intermediate filament protein <B>LaminB> B into a memBranous <B>LaminB> B spindle matrix, which is required for proper microtuBule organization during spindle assemBly. MicrotuBules in turn enhance assemBly of the matrix. Here we report that the isolated matrix contains known spindle assemBly factors such as dynein and Nudel. Using spindle assemBly assays in Xenopus egg extracts, we show that Nudel regulates microtuBule organization during spindle assemBly independently of its function at kinetochores. Importantly, Nudel interacts directly with <B>LaminB> B to facilitate the accumulation and assemBly of <B>LaminB>-B-containing matrix on microtuBules in a dynein-dependent manner. PerturBing either Nudel or dynein inhiBited the assemBly of <B>LaminB> B matrix. However, depleting <B>LaminB> B still allowed the formation of matrices containing dynein and Nudel. Therefore, dynein and Nudel regulate assemBly of the <B>LaminB> B matrix. Interestingly, we found that whereas depleting <B>LaminB> B resulted in disorganized spindle and spindle poles, disrupting the function of Nudel or dynein caused a complete lack of spindle pole focusing. We suggest that Nudel regulates microtuBule organization in part By facilitating assemBly of the <B>LaminB> B spindle matrix in a dynein-dependent manner.
Thomas Giannakouros - One of the best experts on this subject based on the ideXlab platform.
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<B>LaminB> B Receptor: Interplay Between Structure, Function and Localization.
Cells, 2017Co-Authors: Eleni Nikolakaki, Ilias Mylonis, Thomas GiannakourosAbstract:<B>LaminB> B receptor (LBR) is an integral protein of the inner nuclear memBrane, containing a hydrophilic N-terminal end protruding into the nucleoplasm, eight hydrophoBic segments that span the memBrane and a short, nucleoplasmic C-terminal tail. Two seemingly unrelated functions have Been attriButed to LBR. Its N-terminal domain tethers heterochromatin to the nuclear periphery, thus contriButing to the shape of interphase nuclear architecture, while its transmemBrane domains exhiBit sterol reductase activity. Mutations within the transmemBrane segments result in defects in cholesterol synthesis and are associated with diseases such as the Pelger–Huet anomaly and GreenBerg skeletal dysplasia, whereas no such harmful mutations related to the anchoring properties of LBR have Been reported so far. Recent evidence suggests a dynamic regulation of LBR expression levels, structural organization, localization and function, in response to various signals. The molecular mechanisms underlying this dynamic Behavior have not yet Been fully unraveled. Here, we provide an overview of the current knowledge of the interplay Between the structure, function and localization of LBR, and hint at the interconnection of the two distinct functions of LBR.
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Mitotic Phosphorylation of the <B>LaminB> B Receptor By a Serine/Arginine Kinase and p34cdc2
The Journal of biological chemistry, 1997Co-Authors: Eleni Nikolakaki, Spyros D. Georgatos, Juergen Meier, George Simos, Thomas GiannakourosAbstract:ABstract The <B>LaminB> B receptor (LBR) is an integral protein of the inner nuclear memBrane that is modified at interphase By a nuclear envelope-Bound protein kinase. This enzyme (RS kinase) specifically phosphorylates arginine-serine dipeptide motifs located at the NH2-terminal domain of LBR and regulates its interactions with other nuclear envelope proteins. To compare the phosphorylation state of LBR during interphase and mitosis, we performed phosphopeptide mapping of in vitro and in vivo 32P-laBeled LBR and analyzed a series of recomBinant proteins and synthetic peptides. Our results show that LBR undergoes two types of mitotic phosphorylation mediated By the RS and the p34cdc2 protein kinases, respectively. The RS kinase modifies similar sites at interphase and mitosis (i.e. Ser76, Ser78, Ser80, Ser82, Ser84), whereas p34cdc2 mainly phosphorylates Ser71. These findings clarify the phosphorylation state of LBR during the cell cycle and provide new information for understanding the mechanisms responsiBle for nuclear envelope assemBly and disassemBly.
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mitotic phosphorylation of the <B>LaminB> B receptor By a serine arginine kinase and p34cdc2
Journal of Biological Chemistry, 1997Co-Authors: Eleni Nikolakaki, Spyros D. Georgatos, Juergen Meier, George Simos, Thomas GiannakourosAbstract:ABstract The <B>LaminB> B receptor (LBR) is an integral protein of the inner nuclear memBrane that is modified at interphase By a nuclear envelope-Bound protein kinase. This enzyme (RS kinase) specifically phosphorylates arginine-serine dipeptide motifs located at the NH2-terminal domain of LBR and regulates its interactions with other nuclear envelope proteins. To compare the phosphorylation state of LBR during interphase and mitosis, we performed phosphopeptide mapping of in vitro and in vivo 32P-laBeled LBR and analyzed a series of recomBinant proteins and synthetic peptides. Our results show that LBR undergoes two types of mitotic phosphorylation mediated By the RS and the p34cdc2 protein kinases, respectively. The RS kinase modifies similar sites at interphase and mitosis (i.e. Ser76, Ser78, Ser80, Ser82, Ser84), whereas p34cdc2 mainly phosphorylates Ser71. These findings clarify the phosphorylation state of LBR during the cell cycle and provide new information for understanding the mechanisms responsiBle for nuclear envelope assemBly and disassemBly.
