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Samp1 is functionally associated with the LINC complex and A-type lamina networks
Stockholm University, Faculty of Science, Department of Neurochemistry.
Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics. Stockholm University, Faculty of Science, Department of Neurochemistry.ORCID iD: 0000-0003-1476-6675
Stockholm University, Faculty of Science, Department of Neurochemistry. Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
Stockholm University, Faculty of Science, Department of Neurochemistry.
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2011 (English)In: Journal of Cell Science, ISSN 0021-9533, E-ISSN 1477-9137, Vol. 124, 2077-2085 p.Article in journal (Refereed) Published
Abstract [en]

The transmembrane inner nuclear membrane (INM) protein Samp1 is required for anchoring centrosomes near the nuclei. Using high-resolution fluorescence microscopy we show that Samp1 is distributed in a distinct and characteristic pattern in the nuclear envelope (NE), where it partially colocalizes with the LINC complex protein Sun1. By studying the localization of Samp1 deletion mutants and fusion proteins, we conclude that the cysteine-rich N-terminal half of Samp1 is nucleoplasmically exposed and is responsible for targeting to the INM. It contains four conserved CxxC motifs with the potential to form zinc fingers. The distribution of cysteine-to-alanine substitution mutants, designed to prevent zinc finger formation, showed that NE localization of Samp1 depends on intact CxxC motifs. Overexpression of Samp1 zinc finger mutants produced an abnormal dominant phenotype characterized by disrupted organization of a selective subset NE proteins, including emerin, Sun1, endogenous Samp1 and, in some cases, lamin A/C, but not lamin B, Sun2 or nucleoporins. Silencing of Samp1 expression showed that emerin depends on Samp1 for its correct localization in the NE. Our results demonstrate that Samp1 is functionally associated with the LINC complex protein Sun1 and proteins of the A-type lamina network.

Place, publisher, year, edition, pages
2011. Vol. 124, 2077-2085 p.
Keyword [en]
Cancer, Centrosome, Laminopathies, Nuclear membrane, Nuclear migration
National Category
Biological Sciences Chemical Sciences
Research subject
Biochemistry
Identifiers
URN: urn:nbn:se:su:diva-63558DOI: 10.1242/jcs.078923ISI: 000291048000014OAI: oai:DiVA.org:su-63558DiVA: diva2:450860
Available from: 2011-10-23 Created: 2011-10-23 Last updated: 2017-12-08Bibliographically approved
In thesis
1. The functional organization of nuclear membrane proteins and development of new technology for studies of cell signaling
Open this publication in new window or tab >>The functional organization of nuclear membrane proteins and development of new technology for studies of cell signaling
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The eukaryotic cell is defined by the nucleus, which is delimited by a double membrane structure termed the nuclear envelope (NE). The NE is implicated in a multitude of different processes, for example chromatin organization. During mitosis in higher eukaryotes the nucleus is disassembled to allow the formation of the mitotic spindle, which segregates the duplicated chromosomes between daughter cells. We have characterized a novel transmembrane protein of the inner nuclear membrane. Because of its distribution along spindle microtubule during mitosis, we termed the protein Samp1 (Spindle associated membrane protein 1). Samp1 is the founding member of transmembrane proteins that define a novel membrane domain that we have termed the SE (spindle endomembrane). Furthermore, we have shown that in interphase Samp1 specifically interacts with the centrosome and A-type lamina network proteins. Moreover, Samp1 contains an evolutionary highly conserved N-terminal tail containing two putative zinc fingers.

Recent studies indicate local caspase activity in dendrites or axons during development and in neurodegenerative disorders. Here I present the development of a novel and unique system to monitor protease activity at sub-cellular resolution in live cells. This system relies on a cleavable FRET sensor that is anchored to the cytoskeleton. Using this system we demonstrate local caspase activation of the soma in neuronaly differentiated cells. We also used the anchored FRET sensors to monitor caspase activation after treatment with the Alzheimer’s decease related amyloid-β peptide.

Moreover we have improved a NF-ĸB decoy delivery system. The system consists of a cell penetrating peptide, transportan-10, covalently linked to a peptide nucleic acid sequence that hybridizes with a nonanucleotide sequence in the decoy. We show that this system effectively delivered the decoy and inhibited an inflammatory response in primary rat glial cells.

Place, publisher, year, edition, pages
Stockholm: Department of Biochemistry and Biophysics, Stockholm University, 2011. 54 p.
National Category
Biochemistry and Molecular Biology Cell Biology
Research subject
Biochemistry
Identifiers
urn:nbn:se:su:diva-63559 (URN)978-91-7447-386-5 (ISBN)
Public defence
2011-11-25, Magnélisalen, Kemiska övningslaboratoriet, Svante Arrhenius väg 16 B, Stockholm, 10:00 (English)
Opponent
Supervisors
Available from: 2011-11-02 Created: 2011-10-23 Last updated: 2015-03-06Bibliographically approved
2. The roles of inner nuclear membrane proteins during interphase and mitosis
Open this publication in new window or tab >>The roles of inner nuclear membrane proteins during interphase and mitosis
2014 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

The nuclear envelope (NE) consists of two concentric membranes, the outer nuclear membrane (ONM) and the inner nuclear membrane (INM). The LINC (linker of nucleoskeleton and cytoskeleton) complex spans both the ONM and the INM connecting the cytoskeleton to the nucleoskeleton and chromatin. Only a few of the known INM proteins have been functionally characterized and shown to have important roles in chromatin organisation. Defects in the genes coding for proteins in the INM and the nuclear lamina give rise to serious human diseases, called envelopathies.

In 2009 (Buch et al. 2009) our group made two major discoveries. We showed for the first time, that an integral INM protein distributed along the microtubules of the mitotic spindle. This protein was therefore named Samp1, Spindle Associated Membrane Protein 1. The second discovery was that depletion of Samp1 caused detachment of the centrosome from the NE, suggesting that Samp1 is associated with the microtubule cytoskeleton both in interphase and mitosis.

In this thesis we continued to investigate Samp1´s role during interphase. We also wanted to investigate the localisation of Samp1 in the mitotic spindle and possible function during mitosis. We show that the expression of Samp1 mutants and depletion of Samp1 affects the distribution and organisation of A-type lamins, the LINC complex protein Sun1 and the LINC complex associated protein emerin. Thus, in interphase Samp1 is functionally connected to the LINC complex and the A-type lamina network. The LINC complex can help explain how the centrosomes detach from the NE in Samp1 depleted cells. In mitotic cells, we found that depletion of Samp1 caused prolonged metaphase and aberrant mitotic phenotypes such as bi-nucleation, enlarged nuclei and micronuclei. We also showed that Samp1 interacts with RanGTPase and importin-β, which are key players in assembling the mitotic spindle. Samp1 also modulates the levels of importin-β and NuMA in the mitotic spindle, which could explain the mitotic phenotypes that we se in Samp1 depleted cells. Here we present evidence showing, for the first time, that an INM protein is present on kinetochore microtubules and have an essential role for correct chromosome segregation and spindle assembly.

Place, publisher, year, edition, pages
Stockholm: Department of Neurochemistry, Stockholm University, 2014. 50 p.
Keyword
Samp1, mitotic spindle, centrosome, LINC complex, Lamina, Sun1, mitosis
National Category
Medical Biotechnology (with a focus on Cell Biology (including Stem Cell Biology), Molecular Biology, Microbiology, Biochemistry or Biopharmacy)
Research subject
Neurochemistry with Molecular Neurobiology
Identifiers
urn:nbn:se:su:diva-102827 (URN)978-91-7447-910-2 (ISBN)
Presentation
2014-05-13, Heilbronnsalen, C 458, Svante Arrheniusv. 16 B, Stockholm, 12:15 (English)
Opponent
Supervisors
Available from: 2014-04-25 Created: 2014-04-22 Last updated: 2015-03-05Bibliographically approved

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Gudise, SanthoshFigueroa, Ricardo A.Larsson, VeronicaHallberg, Einar
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