scholarly journals Divergent Mitochondrial and Endoplasmic Reticulum Association of DMPK Splice Isoforms Depends on Unique Sequence Arrangements in Tail Anchors

2005 ◽  
Vol 25 (4) ◽  
pp. 1402-1414 ◽  
Author(s):  
René E. M. A. van Herpen ◽  
Ralph J. A. Oude Ophuis ◽  
Mietske Wijers ◽  
Miranda B. Bennink ◽  
Fons A. J. van de Loo ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Protein Kinase ◽  
Myotonic Dystrophy ◽  
Mammalian Cells ◽  
Cell Types ◽  
Unique Sequence ◽  
Protein Isoforms ◽  
Mitochondrial Outer Membrane ◽  
Splice Isoforms ◽  
Triplet Repeat Expansion

ABSTRACT Myotonic dystrophy protein kinase (DMPK) is a Ser/Thr-type protein kinase with unknown function, originally identified as the product of the gene that is mutated by triplet repeat expansion in patients with myotonic dystrophy type 1 (DM1). Alternative splicing of DMPK transcripts results in multiple protein isoforms carrying distinct C termini. Here, we demonstrate by expressing individual DMPKs in various cell types, including C2C12 and DMPK −/− myoblast cells, that unique sequence arrangements in these tails control the specificity of anchoring into intracellular membranes. Mouse DMPK A and C were found to associate specifically with either the endoplasmic reticulum (ER) or the mitochondrial outer membrane, whereas the corresponding human DMPK A and C proteins both localized to mitochondria. Expression of mouse and human DMPK A—but not C—isoforms in mammalian cells caused clustering of ER or mitochondria. Membrane association of DMPK isoforms was resistant to alkaline conditions, and mutagenesis analysis showed that proper anchoring was differentially dependent on basic residues flanking putative transmembrane domains, demonstrating that DMPK tails form unique tail anchors. This work identifies DMPK as the first kinase in the class of tail-anchored proteins, with a possible role in organelle distribution and dynamics.

The LAMMER Protein Kinase Encoded by the Doa Locus of Drosophila Is Required in Both Somatic and Germline Cells and Is Expressed as Both Nuclear and Cytoplasmic Isoforms Throughout Development

Genetics ◽  
2000 ◽  
Vol 156 (2) ◽  
pp. 749-761 ◽  
Author(s):  
Bokyoung Yun ◽  
Kun Lee ◽  
Robert Farkaš ◽  
Christophe Hitte ◽  
Leonard Rabinow
Keyword(s):  
Protein Kinase ◽  
Sexual Differentiation ◽  
Signal Transduction Pathway ◽  
Cell Types ◽  
Protein Isoforms ◽  
Transduction Pathway ◽  
Pupal Development ◽  
Salivary Gland Cells ◽  
Mosaic Analysis ◽  
Embryonic Nervous System

Abstract Activity of the Darkener of apricot (Doa) locus of Drosophila melanogaster is required for development of the embryonic nervous system, segmentation, photoreceptor maintenance, normal transcription, and sexual differentiation. The gene encodes a protein kinase, with homologues throughout eukaryotes known as the LAMMER kinases. We show here that DOA is expressed as at least two different protein isoforms of 105 and 55 kD throughout development, which are primarily localized to the cytoplasm and nucleus, respectively. Doa transcripts and protein are expressed in all cell types both during embryogenesis and in imaginal discs. Although it was recently shown that DOA kinase is essential for normal sexual differentiation, levels of both kinase isoforms are equal between the sexes during early pupal development. The presence of the kinase on the cell membrane and in the nuclei of polytene salivary gland cells, as well as exclusion from the nuclei of specific cells, may be indicative of regulated kinase localization. Mosaic analysis in both the soma and germline demonstrates that Doa function is essential for cell viability. Finally, in contrast to results reported in other systems and despite some phenotypic similarities, genetic data demonstrate that the LAMMER kinases do not participate in the ras-MAP kinase signal transduction pathway.

scholarly journals Mitofusin 2 ablation increases endoplasmic reticulum–mitochondria coupling

2015 ◽  
Vol 112 (17) ◽  
pp. E2174-E2181 ◽  
Author(s):  
Riccardo Filadi ◽  
Elisa Greotti ◽  
Gabriele Turacchio ◽  
Alberto Luini ◽  
Tullio Pozzan ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Mammalian Cells ◽  
Morphological Analysis ◽  
Cell Types ◽  
Mitofusin 2 ◽  
Electron And Fluorescence Microscopy ◽  
Microscopy Data ◽  
Key Aspects ◽  
Different Cell Types ◽  
Close Contacts

The organization and mutual interactions between endoplasmic reticulum (ER) and mitochondria modulate key aspects of cell pathophysiology. Several proteins have been suggested to be involved in keeping ER and mitochondria at a correct distance. Among them, in mammalian cells, mitofusin 2 (Mfn2), located on both the outer mitochondrial membrane and the ER surface, has been proposed to be a physical tether between the two organelles, forming homotypic interactions and heterocomplexes with its homolog Mfn1. Recently, this widely accepted model has been challenged using quantitative EM analysis. Using a multiplicity of morphological, biochemical, functional, and genetic approaches, we demonstrate that Mfn2 ablation increases the structural and functional ER–mitochondria coupling. In particular, we show that in different cell types Mfn2 ablation or silencing increases the close contacts between the two organelles and strengthens the efficacy of inositol trisphosphate (IP3)-induced Ca2+ transfer from the ER to mitochondria, sensitizing cells to a mitochondrial Ca2+ overload-dependent death. We also show that the previously reported discrepancy between electron and fluorescence microscopy data on ER–mitochondria proximity in Mfn2-ablated cells is only apparent. By using a different type of morphological analysis of fluorescent images that takes into account (and corrects for) the gross modifications in mitochondrial shape resulting from Mfn2 ablation, we demonstrate that an increased proximity between the organelles is also observed by confocal microscopy when Mfn2 levels are reduced. Based on these results, we propose a new model for ER–mitochondria juxtaposition in which Mfn2 works as a tethering antagonist preventing an excessive, potentially toxic, proximity between the two organelles.

scholarly journals A novel physical and functional association between nucleoside diphosphate kinase A and AMP-activated protein kinase α1 in liver and lung

2005 ◽  
Vol 392 (1) ◽  
pp. 201-209 ◽  
Author(s):  
Russell M. Crawford ◽  
Kate J. Treharne ◽  
O. Giles Best ◽  
Richmond Muimo ◽  
Claudia E. Riemen ◽  
...  
Keyword(s):  
Protein Kinase ◽  
Mammalian Cells ◽  
Nucleoside Diphosphate Kinase ◽  
Cell Types ◽  
Acid Synthesis ◽  
Cellular Fatty Acid ◽  
Energy Status ◽  
Amp Activated Protein Kinase

Nucleoside diphosphate kinase (NDPK, NM23/awd) belongs to a multifunctional family of highly conserved proteins (∼16–20 kDa) containing two well-characterized isoforms (NM23-H1 and -H2; also known as NDPK A and B). NDPK catalyses the conversion of nucleoside diphosphates into nucleoside triphosphates, regulates a diverse array of cellular events and can act as a protein histidine kinase. AMPK (AMP-activated protein kinase) is a heterotrimeric protein complex that responds to cellular energy status by switching off ATP-consuming pathways and switching on ATP-generating pathways when ATP is limiting. AMPK was first discovered as an activity that inhibited preparations of ACC1 (acetyl-CoA carboxylase), a regulator of cellular fatty acid synthesis. We report that NM23-H1/NDPK A and AMPK α1 are associated in cytosol from two different tissue sources: rat liver and a human lung cell line (Calu-3). Co-immunoprecipitation and binding assay data from both cell types show that the H1/A (but not H2/B) isoform of NDPK is associated with AMPK complexes containing the α1 (but not α2) catalytic subunit. Manipulation of NM23-H1/NDPK A nucleotide transphosphorylation activity to generate ATP (but not GTP) enhances the activity of AMPK towards its specific peptide substrate in vitro and also regulates the phosphorylation of ACC1, an in vivo target for AMPK. Thus novel NM23-H1/NDPK A-dependent regulation of AMPK α1-mediated phosphorylation is present in mammalian cells.

scholarly journals The Major Sites of Cellular Phospholipid Synthesis and Molecular Determinants of Fatty Acid and Lipid Head Group Specificity

2002 ◽  
Vol 13 (9) ◽  
pp. 3148-3161 ◽  
Author(s):  
Annette L. Henneberry ◽  
Marcia M. Wright ◽  
Christopher R. McMaster
Keyword(s):  
Endoplasmic Reticulum ◽  
Mammalian Cells ◽  
De Novo ◽  
Brefeldin A ◽  
Cell Types ◽  
Subcellular Fractionation ◽  
Fatty Acyl ◽  
Head Group ◽  
Ctp:Phosphocholine Cytidylyltransferase ◽  
Lipid Head Group

Phosphatidylcholine and phosphatidylethanolamine are the two main phospholipids in eukaryotic cells comprising ∼50 and 25% of phospholipid mass, respectively. Phosphatidylcholine is synthesized almost exclusively through the CDP-choline pathway in essentially all mammalian cells. Phosphatidylethanolamine is synthesized through either the CDP-ethanolamine pathway or by the decarboxylation of phosphatidylserine, with the contribution of each pathway being cell type dependent. Two human genes, CEPT1 and CPT1, code for the total compliment of activities that directly synthesize phosphatidylcholine and phosphatidylethanolamine through the CDP-alcohol pathways. CEPT1 transfers a phosphobase from either CDP-choline or CDP-ethanolamine to diacylglycerol to synthesize both phosphatidylcholine and phosphatidylethanolamine, whereas CPT1 synthesizes phosphatidylcholine exclusively. We show through immunofluorescence that brefeldin A treatment relocalizes CPT1, but not CEPT1, implying CPT1 is found in the Golgi. A combination of coimmunofluorescence and subcellular fractionation experiments with various endoplasmic reticulum, Golgi, and nuclear markers confirmed that CPT1 was found in the Golgi and CEPT1 was found in both the endoplasmic reticulum and nuclear membranes. The rate-limiting step for phosphatidylcholine synthesis is catalyzed by the amphitropic CTP:phosphocholine cytidylyltransferase α, which is found in the nucleus in most cell types. CTP:phosphocholine cytidylyltransferase α is found immediately upstream cholinephosphotransferase, and it translocates from a soluble nuclear location to the nuclear membrane in response to activators of the CDP-choline pathway. Thus, substrate channeling of the CDP-choline produced by CTP:phosphocholine cytidylyltransferase α to nuclear located CEPT1 is the mechanism by which upregulation of the CDP-choline pathway increases de novo phosphatidylcholine biosynthesis. In addition, a series of CEPT1 site-directed mutants was generated that allowed for the assignment of specific amino acid residues as structural requirements that directly alter either phospholipid head group or fatty acyl composition. This pinpointed glycine 156 within the catalytic motif as being responsible for the dual CDP-alcohol specificity of CEPT1, whereas mutations within helix 214–228 allowed for the orientation of transmembrane helices surrounding the catalytic site to be definitively positioned.

scholarly journals Coiled-coil interactions modulate multimerization, mitochondrial binding and kinase activity of myotonic dystrophy protein kinase splice isoforms

FEBS Journal ◽  
2006 ◽  
Vol 273 (6) ◽  
pp. 1124-1136 ◽  
Author(s):  
Rene E. M. A. Herpen ◽  
Jorrit V. Tjeertes ◽  
Susan A. M. Mulders ◽  
Ralph J. A. Oude Ophuis ◽  
Be Wieringa ◽  
...  
Keyword(s):  
Protein Kinase ◽  
Myotonic Dystrophy ◽  
Kinase Activity ◽  
Coiled Coil ◽  
Splice Isoforms ◽  
Myotonic Dystrophy Protein Kinase

scholarly journals Intracellular transport of a variant surface glycoprotein in Trypanosoma brucei.

1988 ◽  
Vol 106 (1) ◽  
pp. 77-86 ◽  
Author(s):  
M Duszenko ◽  
I E Ivanov ◽  
M A Ferguson ◽  
H Plesken ◽  
G A Cross
Keyword(s):  
Endoplasmic Reticulum ◽  
Cell Surface ◽  
Mammalian Cells ◽  
Intracellular Transport ◽  
Cell Types ◽  
Surface Glycoprotein ◽  
Surface Coat ◽  
Golgi Region ◽  
Golgi Network ◽  
Variant Surface Glycoproteins

Trypanosome variant surface glycoproteins (VSGs) have a novel glycan-phosphatidylinositol membrane anchor, which is cleavable by a phosphatidylinositol-specific phospholipase C. A similar structure serves to anchor some membrane proteins in mammalian cells. Using kinetic and ultrastructural approaches, we have addressed the question of whether this structure directs the protein to the cell surface by a different pathway from the classical one described in other cell types for plasma membrane and secreted glycoproteins. By immunogold labeling on thin cryosections we were able to show that, intracellularly, VSG is associated with the rough endoplasmic reticulum, all Golgi cisternae, and tubulovesicular elements and flattened cisternae, which form a network in the area adjacent to the trans side of the Golgi apparatus. Our data suggest that, although the glycan-phosphatidylinositol anchor is added in the endoplasmic reticulum, VSG is nevertheless subsequently transported along the classical intracellular route for glycoproteins, and is delivered to the flagellar pocket, where it is integrated into the surface coat. Treatment of trypanosomes with 1 microM monensin had no effect on VSG transport, although dilation of the trans-Golgi stacks and lysosomes occurred immediately. Incubation of trypanosomes at 20 degrees C, a treatment that arrests intracellular transport from the trans-Golgi region to the cell surface in mammalian cells, caused the accumulation of VSG molecules in structures of the trans-Golgi network, and retarded the incorporation of newly synthesized VSG into the surface coat.

All three splice variants of the human sarco/endoplasmic reticulum Ca2+-ATPase 3 gene are translated to proteins: a study of their co-expression in platelets and lymphoid cells

2001 ◽  
Vol 358 (3) ◽  
pp. 559-568 ◽  
Author(s):  
Tünde KOVÁCS ◽  
Ferenc FELFÖLDI ◽  
Béla PAPP ◽  
Katalin PÁSZTY ◽  
Raymonde BREDOUX ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Splice Variants ◽  
Cell Types ◽  
Apparent Size ◽  
Lymphoid Cells ◽  
Jurkat Cells ◽  
Protein Isoforms ◽  
Published Data ◽  
Hek 293 ◽  
Tryptic Fragment

The molecular cloning of two previously unknown human sarco/endoplasmic reticulum Ca2+-ATPase 3 (SERCA3) 3′-end transcripts, 3b and 3c, has been recently published. Data were lacking, however, for the presence of these SERCA3 variants in different tissue or cell types at the protein level. Here we report the co-expression of three human SERCA3 protein isoforms in platelets and T lymphoid Jurkat cells. Isoform-specific polyclonal anti-peptide antibodies have been generated that recognize specifically the SERCA3a, 3b or 3c splice variants at their C-termini, and this has been confirmed by peptide-competition experiments as well. None of these antibodies cross-reacted with the housekeeping SERCA2b isoform co-expressed endogenously with SERCA3 proteins in non-muscle cells. Although all three SERCA3 isoforms could be detected in platelets, the 3a form was the most abundantly expressed species. Its size matched the apparent size of SERCA3a over-expressed in HEK-293 cells. Immunoprecipitation of the SERCA3 variants from platelet membranes using a PL/IM 430-affinity matrix provided evidence that the putative pan-anti-SERCA3 antibody, PL/IM 430, recognizes all SERCA3 protein isoforms. The epitope for the PL/IM 430 antibody could be localized in a 40kDa N-terminal tryptic fragment common to all three SERCA3 variants. Comparative Western-blot analysis showed that the expression level of the SERCA3a, 3b and 3c isoforms was more than 10 times lower in Jurkat cells than in platelets, whereas expression of the ubiquitous SERCA2b was nearly identical. This work highlights new Ca2+-transporting proteins of haematopoietic cells and provides specific antibodies for their detection.

scholarly journals STUDIES ON MICROPEROXISOMES V. ARE MICROPEROXISOMES UBIQUITOUS IN MAMMALIAN CELLS?

1973 ◽  
Vol 21 (8) ◽  
pp. 737-755 ◽  
Author(s):  
ALEX B. NOVIKOFF ◽  
PHYLLIS M. NOVIKOFF ◽  
CLEVELAND DAVIS ◽  
NELSON QUINTANA
Keyword(s):  
Electron Microscopy ◽  
Endoplasmic Reticulum ◽  
Mammalian Cells ◽  
Lipid Droplets ◽  
Cell Types ◽  
Malignant Cell ◽  
Zymogen Granules ◽  
Novikoff Hepatoma ◽  
A Cell ◽  
Different Cell Types

A variety of mammalian cell types has been studied by electron microscopy following incubation in a 3,3'-diaminobenzidine medium at pH 9.7 and containing a high H2O2 concentration. This medium visualizes the recently described anucleoid microperoxisomes as well as the nucleoid-containing peroxisomes. All 24 cell types contain 3,3'-diaminobenzidine-positive microperoxisomes but none shows nucleoid-containing peroxisomes. The number of microperoxisomes within a cell varies greatly among different cell types. There are huge numbers in some cell types; in others microperoxisomes are common, few or rare. Such differences imply varying functional significance of these organelles in the metabolism of different cell types. Whether the endoplasmic reticulum (ER) is abundant or scarce or whether its membrane is studded with numerous ribosomes or not, ribosomes are lacking where the ER is connected to the microperoxisomes by slender channels. It may be presumed that molecular interchange occurs between these two organelles. Such interchange may occur between microperoxisomes, ER and lipid droplets, as previously suggested, and between zymogen granules of guinea pig pancreas and ER and microperoxisomes. Two rapidly growing malignant cell types were studied (HeLa and Novikoff hepatoma) and both show moderate numbers of microperoxisomes.

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