101
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Hasper AA, Trindade LM, van der Veen D, van Ooyen AJJ, de Graaff LH. Functional analysis of the transcriptional activator XlnR from Aspergillus niger. MICROBIOLOGY-SGM 2004; 150:1367-1375. [PMID: 15133098 DOI: 10.1099/mic.0.26557-0] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
The transcriptional activator XlnR from Aspergillus niger is a zinc binuclear cluster transcription factor that belongs to the GAL4 superfamily. Several putative structural domains in XlnR were predicted using database and protein sequence analysis. Thus far, only the functionality of the N-terminal DNA-binding domain has been determined experimentally. Deletion mutants of the xlnR gene were constructed to localize the functional regions of the protein. The results showed that a putative C-terminal coiled-coil region is involved in nuclear import of XlnR. After deletion of the C-terminus, including the coiled-coil region, XlnR was found in the cytoplasm, while deletion of the C-terminus downstream of the coiled-coil region resulted in nuclear import of XlnR. The latter mutant also showed increased xylanase activity, indicating the presence of a region with an inhibitory function in XlnR-controlled transcription. Previous findings had already shown that a mutation in the XlnR C-terminal region resulted in transcription of the structural genes under non-inducing conditions. A regulatory model of XlnR is presented in which the C-terminus responds to repressing signals, resulting in an inactive state of the protein.
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Affiliation(s)
- Alinda A Hasper
- Fungal Genomics section, Laboratory of Microbiology, Wageningen University, Dreijenlaan 2, NL-6703 HA Wageningen, The Netherlands
| | - Luisa M Trindade
- Fungal Genomics section, Laboratory of Microbiology, Wageningen University, Dreijenlaan 2, NL-6703 HA Wageningen, The Netherlands
| | - Douwe van der Veen
- Fungal Genomics section, Laboratory of Microbiology, Wageningen University, Dreijenlaan 2, NL-6703 HA Wageningen, The Netherlands
| | - Albert J J van Ooyen
- Fungal Genomics section, Laboratory of Microbiology, Wageningen University, Dreijenlaan 2, NL-6703 HA Wageningen, The Netherlands
| | - Leo H de Graaff
- Fungal Genomics section, Laboratory of Microbiology, Wageningen University, Dreijenlaan 2, NL-6703 HA Wageningen, The Netherlands
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102
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Schubert P, Pfleiderer K, Hillen W. Tet repressor residues indirectly recognizing anhydrotetracycline. ACTA ACUST UNITED AC 2004; 271:2144-52. [PMID: 15153105 DOI: 10.1111/j.1432-1033.2004.04130.x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Two tetracycline repressor (TetR) sequence variants sharing 63% identical amino acids were investigated in terms of their recognition specificity for tetracycline and anhydrotetracycline. Thermodynamic complex stabilities determined by urea-dependent unfolding reveal that tetracycline stabilizes both variants to a similar extent but that anhydrotetracycline discriminates between them significantly. Isofunctional TetR hybrid proteins of these sequence variants were constructed and their denaturation profiles identified residues 57 and 61 as the complex stability determinant. Association kinetics reveal different recognition of these TetR variants by anhydrotetracycline, but the binding constants indicate similar stabilization. The identified residues connect to an internal water network, which suggests that the discrepancy in the observed thermodynamics may be caused by an entropy effect. Exchange of these interacting residues between the two TetR variants appears to influence the flexibility of this water organization, demonstrating the importance of buried, structural water molecules for ligand recognition and protein function. Therefore, this structural module seems to be a key requisite for the plasticity of the multiple ligand binding protein TetR.
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Affiliation(s)
- Peter Schubert
- Lehrstuhl für Mikrobiologie, Institut für Mikrobiologie, Biochemie und Genetik, Friedrich-Alexander-Universität Erlangen-Nurnberg, Staudtstrasse 5, 91058 Erlangen, Germany
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103
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Maertens G, Cherepanov P, Debyser Z, Engelborghs Y, Engelman A. Identification and characterization of a functional nuclear localization signal in the HIV-1 integrase interactor LEDGF/p75. J Biol Chem 2004; 279:33421-9. [PMID: 15163664 DOI: 10.1074/jbc.m404700200] [Citation(s) in RCA: 80] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Human lens epithelium-derived growth factor (LEDGF)/p75 protein forms a specific nuclear complex with human immunodeficiency virus type 1 (HIV-1) integrase and is essential for nuclear localization and chromosomal association of the viral protein. We now studied nuclear import of LEDGF/p75 in live and semipermeabilized cells. We show that nuclear import of LEDGF/p75 is GTP-, Ran-, importin-alpha/beta-, and energy-dependent and that the protein competes with the canonical SV40 large T antigen nuclear localization signal (NLS) for nuclear import receptors. We identified the NLS of LEDGF/p75 through deletion analysis and site-directed mutagenesis. The LEDGF/p75 NLS, 148GRKRKAEKQ156, belongs to the canonical SV40-like family. Fusion of this short peptide to the amino terminus of Escherichia coli beta-galactosidase rendered the fusion protein nuclear, confirming that the LEDGF/p75 NLS is transferable. Moreover, a single amino acid change in the NLS was sufficient to exclude the mutant LEDGF/p75 protein from the nucleus and abolish nuclear import of HIV-1 integrase.
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Affiliation(s)
- Goedele Maertens
- Department of Cancer Immunology and AIDS, Dana-Farber Cancer Institute, Boston, Massachusetts 02115, USA
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104
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Okeley NM, Gelb MH. A designed probe for acidic phospholipids reveals the unique enriched anionic character of the cytosolic face of the mammalian plasma membrane. J Biol Chem 2004; 279:21833-40. [PMID: 15007075 DOI: 10.1074/jbc.m313469200] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
It is generally accepted that the cytosolic face of the plasma membrane of mammalian cells is enriched in acidic phospholipids due to an asymmetric distribution of neutral and anionic phospholipids in the two bilayer leaflets. However, the phospholipid asymmetry across intracellular membranes is not known. Two models have been proposed for the selective targeting of K-Ras4B, which contains a C-terminal farnesyl cysteine methyl ester adjacent to a polybasic peptide segment, to the cytosolic face of the plasma membrane. One involves electrostatic interaction of the lipidated polybasic domain with anionic phospholipids in the plasma membrane, and the other involves binding of K-Ras4B to a specific protein receptor. To address this issue, we prepared by semi-synthesis a green fluorescent protein variant that is linked to a farnesylated, polybasic peptide corresponding to the K-Ras4B C terminus as well as a variant that contains an all-d amino acid version of the K-Ras4B peptide. As expected based on electrostatics, both constructs showed preferential in vitro binding to anionic phospholipid vesicles versus those composed only of zwitterionic phospholipid. Both constructs fully targeted to the plasma membrane when microinjected into live Chinese hamster ovary and Madin-Darby canine kidney cells. Because the all-d amino acid peptide should be devoid of binding affinity to a putative highly specific K-Ras membrane receptor, these results support an electrostatic basis for the targeting of K-Ras4B to the plasma membrane, and they support an intracellular landscape of phospholipids in which the cytosolic face of the plasma membrane is the most enriched in acidic phospholipids.
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Affiliation(s)
- Nicole M Okeley
- Departments of Chemistry and Biochemistry, University of Washington, Seattle, Washington 98195, USA
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105
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Vaysse L, Harbottle R, Bigger B, Bergau A, Tolmachov O, Coutelle C. Development of a Self-assembling Nuclear Targeting Vector System Based on the Tetracycline Repressor Protein. J Biol Chem 2004; 279:5555-64. [PMID: 14607832 DOI: 10.1074/jbc.m311894200] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The ultimate destination for most gene therapy vectors is the nucleus and nuclear import of potentially therapeutic DNA is one of the major barriers for nonviral vectors. We have developed a novel approach of attaching a nuclear localization sequence (NLS) peptide to DNA in a non-essential position, by generating a fusion between the tetracycline repressor protein TetR and the SV40-derived NLS peptide. The high affinity and specificity of TetR for the short DNA sequence tetO was used in these studies to bind the NLS to DNA as demonstrated by the reduced electrophoretic mobility of the TetR.tetO-DNA complexes. The protein TetR-NLS, but not control protein TetR, specifically enhances gene expression from lipofected tetO-containing DNA between 4- and 16-fold. The specific enhancement is observed in a variety of cell types, including primary and growth-arrested cells. Intracellular trafficking studies demonstrate an increased accumulation of fluorescence labeled DNA in the nucleus after TetR-NLS binding. In comparison, binding studies using the similar fusion of peptide nucleic acid (PNA) with NLS peptide, demonstrate specific binding of PNA to plasmid DNA. However, although we observed a 2-8.5-fold increase in plasmid-mediated luciferase activity with bis-PNA-NLS, control bis-PNA without an NLS sequence gave a similar increase, suggesting that the effect may not be because of a specific bis-PNA-NLS-mediated enhancement of nuclear transfer of the plasmid. Overall, we found TetRNLS-enhanced plasmid-mediated transgene expression at a similar level to that by bis-PNA-NLS or bis-PNA alone but specific to nuclear uptake and significantly more reliable and reproducible.
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Affiliation(s)
- Laurence Vaysse
- Gene Therapy Research Group, Division of Biomedical Science, Imperial College London, Sir Alexander Fleming Building, Exhibition Road, London SW7 2AZ, United Kingdom
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106
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Romanelli MG, Tato' L, Lorenzi P, Morandi C. Nuclear localization domains in human thyroid transcription factor 2. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2004; 1643:55-64. [PMID: 14654228 DOI: 10.1016/j.bbamcr.2003.09.002] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Thyroid transcription factor-2 (TTF2) is a nuclear protein involved in morphogenesis and gene expression in thyroid gland, belonging to the family of the forkhead/winged-helix transcription factors. In the present study we have investigated the sequence determinants for transport and accumulation into the nucleus of the TTF2 protein. By transient expression of fusion proteins constructed by joining different parts of TTF2 to the reporter gene of the jellyfish green fluorescent protein (GFP) and, in a separate set of deleted constructs, the glutathione S-transferase (GST) coding sequence, we have demonstrated that a basic amino acid stretch present at both ends of the DNA-binding domain is a bona fide nuclear localization signal (NLS). We have analyzed the subcellular localization of deleted GFP-GST-TTF2 fusion proteins and have shown that residues inside the forkhead domain (FHD) contributed to the complete nuclear TTF2 protein accumulation. Furthermore, by means of GST binding assays we have shown that distinct TTF2 fragments, containing the NLS, were able to bind the nuclear import receptor importin alpha. Taken together, our results provide the first documentation about nuclear targeting of a forkhead protein containing two identical NLS signal flanking the DNA-binding domain.
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Affiliation(s)
- Maria Grazia Romanelli
- Department of Mother and Child, Biology and Genetics, University of Verona, Strada le Grazie 8, 37134 Verona, Italy.
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107
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Martin IV, MacNeill SA. Functional analysis of subcellular localization and protein-protein interaction sequences in the essential DNA ligase I protein of fission yeast. Nucleic Acids Res 2004; 32:632-42. [PMID: 14752051 PMCID: PMC373326 DOI: 10.1093/nar/gkh199] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
DNA ligase I (Lig I) has key roles in chromosomal DNA replication and repair in the eukaryotic cell nucleus. In the budding yeast Saccharomyces cerevisiae the Lig I enzyme Cdc9p is also required for mitochondrial DNA replication and repair. In this report, dual nuclear-mitochondrial localization is demonstrated to be a property of the essential Lig I enzyme Cdc17 from the distantly related fission yeast Schizosaccharomyces pombe. Expression of nuclear and mitochondrial forms of Cdc17 from separate genes shows that, whereas expression of either protein alone is insufficient to restore viability to cells lacking endogenous Cdc17, co-expression restores full viability. In the nucleus, Lig I interacts with the sliding clamp proliferating cell nuclear antigen (PCNA) via a conserved PCNA interacting sequence motif known as a PIP box. Deletion of the PIP motif from the N-terminus of the nuclear form of Cdc17 fails to abolish Cdc17 function, indicating that PCNA binding by Cdc17 is not an absolute requirement for completion of S-phase.
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Affiliation(s)
- Ina V Martin
- Wellcome Trust Centre for Cell Biology, University of Edinburgh, Michael Swann Building, King's Buildings, Mayfield Road, Edinburgh EH9 3JR, UK
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108
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Williams CL. The polybasic region of Ras and Rho family small GTPases: a regulator of protein interactions and membrane association and a site of nuclear localization signal sequences. Cell Signal 2003; 15:1071-80. [PMID: 14575862 DOI: 10.1016/s0898-6568(03)00098-6] [Citation(s) in RCA: 161] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Many small GTPases in the Ras and Rho families have a C-terminal polybasic region (PBR) comprised of multiple lysines or arginines. The PBR controls diverse functions of these small GTPases, including their ability to associate with membranes, interact with specific proteins, and localize in subcellular compartments. Different signaling pathways mediated by Ras and Rho family members may converge when the small GTPases are directed by their PBRs to shared binding sites in specific proteins or at cell membranes. The PBR promotes the interactions of small GTPases with SmgGDS, which is a nucleocytoplasmic shuttling protein that stimulates guanine nucleotide exchange by small GTPases. The PBR of Rac1 was recently found to have a functional nuclear localization signal (NLS) sequence, which enhances the nuclear accumulation of protein complexes containing SmgGDS and Rac1. Sequence analysis demonstrates that canonical NLS sequences (K-K/R-x-K/R) are present in the PBRs of additional Ras and Rho family members, and are evolutionarily conserved across several phyla. These findings suggest that the PBR regulates the nucleocytoplasmic shuttling of some Ras and Rho family members when they are in protein complexes that are too large to diffuse through nuclear pores. These diverse functions of the PBR indicate its critical role in signaling by Ras and Rho family GTPases.
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Affiliation(s)
- Carol L Williams
- Molecular Pharmacology Laboratory, Guthrie Research Institute, One Guthrie Square, Sayre, PA 18840, USA.
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109
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Lee DK, Lança AJ, Cheng R, Nguyen T, Ji XD, Gobeil F, Chemtob S, George SR, O'Dowd BF. Agonist-independent nuclear localization of the Apelin, angiotensin AT1, and bradykinin B2 receptors. J Biol Chem 2003; 279:7901-8. [PMID: 14645236 DOI: 10.1074/jbc.m306377200] [Citation(s) in RCA: 151] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Signaling of the apelin, angiotensin, and bradykinin peptides is mediated by G protein-coupled receptors related through structure and similarities of physiological function. We report nuclear expression as a characteristic of these receptors, including a nuclear localization for the apelin receptor in brain and cerebellum-derived D283 Med cells and the AT(1) and bradykinin B(2) receptors in HEK-293T cells. Immunocytochemical analyses revealed the apelin receptor with localization in neuronal nuclei in cerebellum and hypothalamus, exhibiting expression in neuronal cytoplasm or in both nuclei and cytoplasm. Confocal microscopy of HEK-293T cells revealed the majority of transfected cells displayed constitutive nuclear localization of AT(1) and B(2) receptors, whereas apelin receptors did not show nuclear localization in these cells. The majority of apelin receptor-transfected cerebellum D283 Med cells showed receptor nuclear expression. Immunoblot analyses of subcellular-fractionated D283 Med cells demonstrated endogenous apelin receptor species in nuclear fractions. In addition, an identified nuclear localization signal motif in the third intracellular loop of the apelin receptor was disrupted by a substituted glutamine in place of lysine. This apelin receptor (K242Q) did not exhibit nuclear localization in D283 Med cells. These results demonstrate the following: (i) the apelin receptor exhibits nuclear localization in human brain; (ii) distinct cell-dependent mechanisms for the nuclear transport of apelin, AT(1), and B(2) receptors; and (iii) the disruption of a nuclear localization signal sequence disrupts the nuclear translocation of the apelin receptor. This discovery of apelin, AT(1), and B(2) receptors with agonist-independent nuclear translocation suggests major unanticipated roles for these receptors in cell signaling and function.
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MESH Headings
- Animals
- Apelin Receptors
- Brain/ultrastructure
- COS Cells
- Cell Fractionation
- Cell Line
- Cell Nucleus/chemistry
- Cerebellum/ultrastructure
- Chlorocebus aethiops
- Cytoplasm/chemistry
- Embryo, Mammalian
- Gene Expression
- Green Fluorescent Proteins
- Humans
- Hypothalamus/ultrastructure
- Immunohistochemistry
- Kidney
- Luminescent Proteins/genetics
- Microscopy, Confocal
- Neurons/ultrastructure
- Protein Sorting Signals
- Rats
- Receptor, Angiotensin, Type 1/analysis
- Receptor, Angiotensin, Type 1/genetics
- Receptor, Bradykinin B2/analysis
- Receptor, Bradykinin B2/genetics
- Receptors, G-Protein-Coupled/analysis
- Receptors, G-Protein-Coupled/genetics
- Recombinant Fusion Proteins
- Signal Transduction
- Transfection
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Affiliation(s)
- Dennis K Lee
- Department of Pharmacology, University of Toronto, Toronto, Ontario M5S 1A8, USA
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110
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Sfakianos JN, LaCasse RA, Hunter E. The M-PMV cytoplasmic targeting-retention signal directs nascent Gag polypeptides to a pericentriolar region of the cell. Traffic 2003; 4:660-70. [PMID: 12956869 DOI: 10.1034/j.1600-0854.2003.00125.x] [Citation(s) in RCA: 93] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Intracytoplasmic protein targeting in mammalian cells is critical for organelle function as well as virus assembly, but the signals that mediate it are poorly defined. We show here that Mason-Pfizer monkey virus specifically targets Gag precursor proteins to the pericentriolar region of the cytoplasm in a microtubule dependent process through interactions between a short peptide signal, known as the cytoplasmic targeting-retention signal, and the dynein/dynactin motor complex. The Gag molecules are concentrated in pericentriolar microdomains, where they assemble to form immature capsids. Depletion of Gag from this region by cycloheximide treatment, coupled with the presence of ribosomal clusters that are in close vicinity to the assembling capsids, suggests that the dominant N-terminal cytoplasmic targeting-retention signal functions in a cotranslational manner. Transport of the capsids out of the pericentriolar assembly site requires the env-gene product, and a functional vesicular transport system. A single point mutation that renders the cytoplasmic targeting-retention signal defective abrogates pericentriolar targeting of Gag molecules. Thus the previously defined cytoplasmic targeting-retention signal appears to act as a cotranslational intracellular targeting signal that concentrates Gag proteins at the centriole for assembly of capsids.
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Affiliation(s)
- Jeffrey N Sfakianos
- Department of Microbiology, University of Alabama at Birmingham, Birmingham, AL 35294, USA
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111
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Abstract
The regulators of G protein signaling (RGS) are an extraordinary class of diverse multifunctional signaling proteins best known for their potent capacity to down-regulate the activity of Galpha subunits at the plasma membrane. In certain circumstances, some RGS proteins undergo translocation to the nucleus or plasma membrane from the cytoplasm. Translocation demonstrates a potentially dynamic alternative mechanism for Galpha subunit or effector regulation. The nuclear localization of the regulators of G protein signaling proteins further suggests these proteins possess even greater functional heterogeneity than that envisioned previously, as regulators of transcription and cell cycle control.
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Affiliation(s)
- Scott A Burchett
- National Institutes of Health, National Institute of Child Health and Human Development, Laboratory of Neural Connectivity, Bethesda, Maryland 20892, USA.
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112
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Buchner DA, Trudeau M, Meisler MH. SCNM1, a putative RNA splicing factor that modifies disease severity in mice. Science 2003; 301:967-9. [PMID: 12920299 DOI: 10.1126/science.1086187] [Citation(s) in RCA: 105] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
The severity of many inherited disorders is influenced by genetic background. We describe a modifier interaction in C57BL/6Jmice that converts a chronic movement disorder into a lethal neurological disease. The primary mutation (medJ) changes a splice donor site of the sodium channel gene Scn8a (Nav1.6). The modifier mutation is characteristic of strain C57BL/6Jand introduces a nonsense codon into sodium channel modifier 1 (SCNM1), a zinc finger protein and a putative splice factor. An internally deleted SCNM1 protein is also predicted as a result of exon skipping associated with disruption of a consensus exonic splicing enhancer. The effect of the modifier mutation is to reduce the abundance of correctly spliced sodium channel transcripts below the threshold for survival. Our finding that genetic variation in a putative RNA splicing factor influences disease susceptibility in mice raises the possibility that a similar mechanism modifies the severity of human inherited disorders.
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Affiliation(s)
- David A Buchner
- Department of Human Genetics, University of Michigan School of Medicine, Ann Arbor, MI 48109-0618, USA
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113
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Tinkelenberg BA, Fazzone W, Lynch FJ, Ladner RD. Identification of sequence determinants of human nuclear dUTPase isoform localization. Exp Cell Res 2003; 287:39-46. [PMID: 12799180 DOI: 10.1016/s0014-4827(03)00048-x] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
dUTP nucleotidohydrolase (dUTPase) catalyzes the hydrolysis of dUTP to dUMP and pyrophosphate and is the central regulator of cellular dUTP pools. Nuclear (DUT-N) and mitochondrial (DUT-M) isoforms of the protein have been identified in humans and arise from the same gene by the alternative use of 5' exons. Recently, it has been shown that these isoforms are aberrantly expressed in some cancers and overexpression of dUTPase in the nucleus is associated with resistance to chemotherapeutic agents that target thymidylate biosynthesis. In this study, we have examined the signals necessary for dUTPase isoform localization using green fluorescent protein fusion constructs. We report that the N-terminal 23 amino acids of DUT-N are required but not sufficient for complete nuclear localization. Within this region, we identified a small cluster of basic residues (K(14)R(15)R(17)) that resemble a classic monopartite nuclear localization signal (NLS). Mutation of these residues completely abolishes nuclear localization. In addition, phosphorylation of Ser11 near the putative NLS has no affect on DUT-N nuclear localization. Through deletion analysis we show improved sorting of DUT-N to the nucleus when most of the protein sequence is present. Therefore, we conclude that DUT-N may contain a complex NLS that is located throughout the entire protein.
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Affiliation(s)
- Beverly A Tinkelenberg
- Department of Molecular Biology, School of Osteopathic Medicine, University of Medicine and Dentistry of New Jersey, 2 Medical Center Drive, Stratford, NJ 08084, USA
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114
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Michel K, Atkinson PW. Nuclear localization of the Hermes transposase depends on basic amino acid residues at the N-terminus of the protein. J Cell Biochem 2003; 89:778-90. [PMID: 12858343 DOI: 10.1002/jcb.10554] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
For the Hermes transposable element to be mobilized in its eukaryotic host, the transposase, encoded by the element, must make contact with its DNA. After synthesis in the cytoplasm, the transposase has to be actively imported into the nucleus because its size of 70.1 kDa prevents passive diffusion through the nuclear pore. Studies in vitro using transient expression of a Hermes-EGFP fusion protein in Drosophila melanogaster Schneider 2 cells showed the transposase was located predominantly in the nucleus. In silico sequence analysis, however, did not reveal any nuclear localization signal (NLS). To identify the sequence(s) responsible for localization of Hermes transposase in the nucleus, truncated or mutated forms of the transposase were examined for their influence on sub-cellular localization of marker proteins fused to the transposase. Using the same expression system and a GFP-GUS fusion double marker, residues 1-110 were recognized as sufficient, and residues 1-32 as necessary, for nuclear localization. Amino acid K25 greatly facilitated nuclear localization, indicating that at least this basic amino acid plays a significant role in this process. This sequence overlaps the proposed DNA binding region of the Hermes transposase and is not necessarily conserved in all members of the hAT transposable element family.
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Affiliation(s)
- K Michel
- Department of Entomology, University of California, Riverside, California 92521, USA
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115
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Köster M, Lykke-Andersen S, Elnakady YA, Gerth K, Washausen P, Höfle G, Sasse F, Kjems J, Hauser H. Ratjadones inhibit nuclear export by blocking CRM1/exportin 1. Exp Cell Res 2003; 286:321-31. [PMID: 12749860 DOI: 10.1016/s0014-4827(03)00100-9] [Citation(s) in RCA: 69] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
In addition to previously isolated ratjadone A we describe three new members of this family, ratjadones B, C, and D, from another strain of the myxobacterium Sorangium cellulosum. We have investigated the properties of these ratjadones with respect to their activity on mammalian cell lines. We found IC(50) values in the picomolar range and a significant increase in the size of nuclei. A further examination showed that they inhibit the export of the leucine-rich nuclear export signal (LR-NES) containing proteins in different cell lines. Ratjadones are able to inhibit the formation of the nuclear export complex composed of the CRM1, RanGTP, and the cargo protein, as shown by two different in vitro assays. Finally, the binding of ratjadone C to CRM1 was demonstrated. These ratjadone activities are in the same concentration range as described for the polyketide leptomycin B (LMB) from Streptomyces sp. Like LMB, it seems that the ratjadones covalently bind to CRM1, inhibit cargo protein binding via LR-NES, and thereby block nuclear export. Thus, the ratjadones represent a new class of natural compounds which inhibit proliferation in eukaryotes by blocking nuclear export.
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Affiliation(s)
- Mario Köster
- Department of Gene Regulation and Differentiation, GBF-German Research Centre for Biotechnology, Mascheroder Weg 1, D-38124 Braunschweig, Germany
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116
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Valgardsdottir R, Prydz H. Transport signals and transcription-dependent nuclear localization of the putative DEAD-box helicase MDDX28. J Biol Chem 2003; 278:21146-54. [PMID: 12663657 DOI: 10.1074/jbc.m300888200] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The human protein MDDX28 is a putative RNA helicase and a nucleocytoplasmic shuttling protein also localized to the mitochondria. Its localization is novel among RNA helicases. We have studied its intracellular targeting signals and show that the first 20 amino acids of MDDX28 are necessary and sufficient for both mitochondrial import and nuclear export of the protein. Mutation of the five leucines in the sequence to alanines abolished the mitochondrial targeting signal as well as greatly reducing the nuclear export signal, indicating that these signal sequences are highly overlapping. Two short stretches of basic amino acids separated by 44 residues were both necessary and sufficient for full nuclear localization. However, they were not absolutely essential, because the protein was present in 7% of the nuclei when both signals were mutated. This indicates that MDDX28 contains another unidentified weak nuclear localization signal(s). Three basic domains in the N-terminal half of the protein and its RNA binding ability were essential for nucleolar localization as well as transcription-inhibition-dependent localization to nuclear subcompartments. Two of these basic domains were the same as those constituting the nuclear localization signal, suggesting that they are responsible for bringing the protein into the nucleus to the sites of RNA binding. Our results indicate that MDDX28 nucleo-cytoplasmic shuttling is dependent on the availability of nascent RNA.
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Affiliation(s)
- Rut Valgardsdottir
- Biotechnology Centre of Oslo, University of Oslo, Gaustadalleen 21, N0349 Oslo, Norway
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117
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Nalaskowski MM, Bertsch U, Fanick W, Stockebrand MC, Schmale H, Mayr GW. Rat inositol 1,4,5-trisphosphate 3-kinase C is enzymatically specialized for basal cellular inositol trisphosphate phosphorylation and shuttles actively between nucleus and cytoplasm. J Biol Chem 2003; 278:19765-76. [PMID: 12649294 DOI: 10.1074/jbc.m211059200] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The calcium-liberating second messenger inositol 1,4,5-trisphosphate (Ins(1,4,5)P3) is converted to inositol 1,3,4,5-tetrakisphosphate (Ins(1,3,4,5)P4) by Ins(1,4,5)P3 3-kinases (IP3Ks) that add a fourth phosphate group to the 3-position of the inositol ring. Two isoforms of IP3Ks (named A and B) from different vertebrate species have been well studied. Recently the cloning and examination of a human full-length cDNA encoding a novel isoform, termed human IP3K-C (HsIP3K-C), has been reported. In the present study we report the cloning of a full-length cDNA encoding a rat homologue of HsIP3K-C with a unique mRNA expression pattern, which differs remarkably from the tissue distribution of HsIP3K-C. Of the rat tissues examined, rat IP3K-C (RnIP3K-C) is mainly present in heart, brain, and testis and shows the strongest expression in an epidermal tissue, namely tongue epithelium. RnIP3K-C has a calculated molecular mass of approximately 74.5 kDa and shows an overall identity of approximately 75% with HsIP3K-C. A bacterially expressed, enzymatically active and Ca2+-calmodulin-regulated fragment of this isoform displays remarkable enzymatic properties like a very low Km for Ins(1,4,5)P3 ( approximately 0.2 microm), substrate inhibition by high concentrations of Ins(1,4,5)P3, allosteric product activation by Ins(1,3,4,5)P4 in absence of Ca2+-calmodulin (Ka(app) 0.52 microm), and the ability to efficiently phosphorylate a second InsP3 substrate, inositol 2,4,5-trisphosphate, to inositol 2,4,5,6-tetrakisphosphate in the presence of Ins(1,3,4,5)P4. Furthermore, the RnIP3K-C fused with a fluorescent protein tag is actively transported into and out of the nucleus when transiently expressed in mammalian cells. A leucine-rich nuclear export signal and an uncharacterized nuclear import activity are localized in the N-terminal domain of the protein and determine its nucleocytoplasmic shuttling. These findings point to a particular role of RnIP3K-C in nuclear inositol trisphosphate phosphorylation and cellular growth.
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Affiliation(s)
- Marcus M Nalaskowski
- Institute for Cellular Signal Transduction, University Hospital Hamburg-Eppendorf, Martinistrasse 52, Germany
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118
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Qin J, Kang W, Leung B, McLeod M. Ste11p, a high-mobility-group box DNA-binding protein, undergoes pheromone- and nutrient-regulated nuclear-cytoplasmic shuttling. Mol Cell Biol 2003; 23:3253-64. [PMID: 12697825 PMCID: PMC153199 DOI: 10.1128/mcb.23.9.3253-3264.2003] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2002] [Revised: 12/12/2002] [Accepted: 02/03/2003] [Indexed: 11/20/2022] Open
Abstract
The high-mobility-group (HMG) box is a conserved DNA-binding domain found in a family of transcription factors that regulate growth and development. One family member, Ste11p, directs sexual differentiation of Schizosaccharomyces pombe by binding specific DNA sequences upstream of genes required for mating and meiosis. Here, we show that Ste11p is a shuttling protein. In growing cells, Ste11p is present in low levels and is pancellular. Mating pheromones and nutrient limitation trigger nuclear accumulation and increased expression of the transcription factor. Several mechanisms likely control Ste11p localization. First, the 14-3-3 protein, Rad24p, binds phosphorylated Ste11p and inhibits its nuclear accumulation. Second, the HMG domain of Ste11p contains a basic cluster nuclear localization signal. Finally, treatment of cells with leptomycin B, an exportin inhibitor, results in the nuclear accumulation of Ste11p. A Ste11p deletion mutation, DeltaC54, mimics the effects of leptomycin B. The C54 region contains no identifiable nuclear export signal but instead is required for biological activity and to stimulate Ste11p target gene expression. These results provide evidence that both nuclear import and export mechanisms operate to regulate cellular localization of an HMG box protein. In addition, they establish a paradigm for the potential role of pheromone/hormone-like polypeptides in cellular localization of this important class of developmental regulators.
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Affiliation(s)
- Jian Qin
- Department of Microbiology and Immunology, Morse Institute for Molecular Genetics, and Program in Molecular and Cellular Biology, State University of New York Downstate Medical Center, Brooklyn, New York 11203-2098, USA
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119
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Gupta S, Lee A, Hu C, Fanzo J, Goldberg I, Cattoretti G, Pernis AB. Molecular cloning of IBP, a SWAP-70 homologous GEF, which is highly expressed in the immune system. Hum Immunol 2003; 64:389-401. [PMID: 12651066 DOI: 10.1016/s0198-8859(03)00024-7] [Citation(s) in RCA: 69] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Rho GTPases play a fundamental role in a variety of biological processes ranging from the reorganization of the actin cytoskeleton to the regulation of cell proliferation. The activation of Rho GTPases is regulated by guanine nucleotide exchange factors (GEFs) belonging to the Dbl family of proteins. The hallmark of this large family of GEFs is the presence of a tandem DH-PH module in which a pleckstrin-homology (PH) domain is located at the C-terminus of a Dbl-homology (DH) domain. Recent studies have demonstrated that SWAP-70 constitutes a novel class of Rac-GEF, in which the PH domain is located at the N-terminus, rather than the C terminus, of the DH domain. Here we report the molecular cloning of human IBP (IRF-4 binding protein), a new member of this novel family of GEFs. The IBP gene maps to human chromosome 6p21.31 centromeric to the MHC locus. Isolation of the murine IBP cDNA reveals a very high degree of homology with the human IBP cDNA suggesting that IBP is evolutionarily conserved. The 5' portion of the murine IBP cDNA is furthermore identical to the Def-6 cDNA fragment, which was identified in the course of a search for genes differentially expressed in the murine hematopoietic system. IBP is broadly expressed in the immune system and can be detected in both T and B cell compartments in contrast to SWAP-70 whose expression is primarily restricted to B cells. Taken together these findings indicate that IBP is a novel type of GEF, which participates in the activation of Rho GTPases in lymphoid tissues.
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Affiliation(s)
- Sanjay Gupta
- Department of Pathology, Columbia University, New York, NY 10032, USA
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120
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Maiyar AC, Leong MLL, Firestone GL. Importin-alpha mediates the regulated nuclear targeting of serum- and glucocorticoid-inducible protein kinase (Sgk) by recognition of a nuclear localization signal in the kinase central domain. Mol Biol Cell 2003; 14:1221-39. [PMID: 12631736 PMCID: PMC151592 DOI: 10.1091/mbc.e02-03-0170] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2002] [Revised: 10/17/2002] [Accepted: 11/17/2002] [Indexed: 12/19/2022] Open
Abstract
The transcriptionally regulated serum and glucocorticoid inducible protein kinase (Sgk) is localized to the nucleus in a serum-dependent manner, and a yeast two-hybrid genetic screen uncovered a specific interaction between Sgk and the importin-alpha nuclear import receptor. In vitro GST pull down assays demonstrated a strong and direct association of importin-alpha with endogenous Sgk and exogenously expressed HA-tagged Sgk, whereas both components coimmunoprecipitate and colocalize to the nucleus after serum stimulation. Consistent with an active mechanism of nuclear localization, the nuclear import of HA-Sgk in permeabilized cells required ATP, cytoplasm, and a functional nuclear pore complex. Ectopic addition of a 107 amino acid carboxy-terminal fragment of importin-alpha, which contains the Sgk binding region, competitively inhibited the ability of endogenous importin-alpha to import Sgk into nuclei in vitro. Mutagenesis of lysines by alanine substitution defined a KKAILKKKEEK sequence within the central domain of Sgk between amino acids 131-141 that functions as a nuclear localization signal (NLS) required for the in vitro interaction with importin-alpha and for nuclear import of full-length Sgk in cultured cells. The serum-induced nuclear import of Sgk requires the NLS-dependent recognition of Sgk by importin-alpha as well as the PI3-kinase-dependent phosphorylation of Sgk. Our results define a new role importin-alpha in the stimulus-dependent control of signal transduction by nuclear localized protein kinases.
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Affiliation(s)
- Anita C Maiyar
- Department of Molecular and Cell Biology and The Cancer Research Laboratory, University of California at Berkeley, 94720-3200, USA
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121
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Abstract
Macromolecular therapeutics provide numerous benefits for the delivery of cytotoxic or poorly soluble drugs in vivo. However, these constructs often encounter barriers for drug delivery on both the systemic and subcellular level. Many soluble polymer carriers have been designed to surmount specific physiological barriers individually, but less work has been dedicated to designing an all-encompassing construct that addresses multiple therapeutic barriers at once. Incorporation of multiple agents already individually known to increase effectiveness into one carrier could further improve current drug delivery technology. Recent developments in subcellular delivery of therapeutic agents in soluble macromolecular carriers are discussed in the context of the future possibility for the design of an all-encompassing soluble multi-functional drug delivery vehicle.
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Affiliation(s)
- R J Christie
- Department of Chemistry, Colorado State University, Fort Collins, CO 80523-1872, USA
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122
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Gobeil F, Vazquez-Tello A, Marrache AM, Bhattacharya M, Checchin D, Bkaily G, Lachapelle P, Ribeiro-Da-Silva A, Chemtob S. Nuclear prostaglandin signaling system: biogenesis and actions via heptahelical receptors. Can J Physiol Pharmacol 2003; 81:196-204. [PMID: 12710534 DOI: 10.1139/y02-163] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Prostaglandins are ubiquitous lipid mediators that play pivotal roles in cardiovascular homeostasis, reproduction, and inflammation, as well as in many important cellular processes including gene expression and cell proliferation. The mechanism of action of these lipid messengers is thought to be primarily dependent on their interaction with specific cell surface receptors that belong to the heptahelical transmembrane spanning G protein-coupled receptor superfamily. Accumulating evidence suggests that these receptors may co-localize at the cell nucleus where they can modulate gene expression through a series of biochemical events. In this context, we have recently demonstrated that prostaglandin E2-EP3 receptors display an atypical nuclear compartmentalization in cerebral microvascular endothelial cells. Stimulation of these nuclear EP3 receptors leads to an increase of eNOS RNA in a cell-free isolated nuclear system. This review will emphasize these findings and describe how nuclear prostaglandin receptors, notably EP3 receptors, may affect gene expression, specifically of eNOS, by identifying putative transducing elements located within this organelle. The potential sources of lipid ligand activators for these intracellular sites will also be addressed. The expressional control of G-protein-coupled receptors located at the perinuclear envelope constitutes a novel and distinctive mode of gene regulation.
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Affiliation(s)
- Fernand Gobeil
- Department of Pharmacology, Université de Sherbrooke, 3001, 12th North Avenue, Fleurimont, Sherbrooke, QC J1H 5N4, Canada.
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123
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Abstract
The integrase (Int) protein of coliphage HK022 catalyzes the site-specific integration and excision of the phage into and from its Escherichia coli host chromosome. Int expressed from a plasmid in COS1 monkey cells is localized in the nucleus, as is a fusion protein between Int and the green fluorescent protein (GFP). Mutation analysis of the GFP-Int fusion has revealed in Int two regions of positively charged amino acid residues that cooperate in the nuclear localization. One region harbors residues Arg90 and Arg93. The other, which spans residues 307-340 belongs to the catalytic domain of Int, is rich in basic residues and is strongly conserved within the Int protein family. Being localized in the nucleus renders Int of HK022 as a potential recombinase for site-specific gene manipulations in mammals.
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Affiliation(s)
- Mikhail Kolot
- Department of Biochemistry, Tel-Aviv University, Tel-Aviv 69978, Israel
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124
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Ma L, Liu Y, Ky B, Shughrue PJ, Austin CP, Morris JA. Cloning and characterization of Disc1, the mouse ortholog of DISC1 (Disrupted-in-Schizophrenia 1). Genomics 2002; 80:662-72. [PMID: 12504857 DOI: 10.1006/geno.2002.7012] [Citation(s) in RCA: 75] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We cloned the mouse ortholog of DISC1 (Disrupted-in-Schizophrenia 1), a candidate gene for schizophrenia. Disc1 is 3163 nucleotides long and has 60% identity with the human DISC1. Disc1 encodes 851 amino acids and has 56% identity with the human protein. Disc1 maps to the DISC1 syntenic region in the mouse, and genomic structure is conserved. A Disc1 splice variant deletes a portion of Disc1 beginning at amino acids orthologous to the human truncation. Bioinformatic analysis and cross-species comparisons revealed sequence conservation distributed across the genes and conservation of leucine zipper and coiled-coil domains in both orthologs. In situ hybridization in adult mouse brain revealed a restricted expression pattern, with highest levels in the dentate gyrus of the hippocampus and lower expression in CA1-CA3 of the hippocampus, cerebellum, cerebral cortex, and olfactory bulbs. Identification of Disc1 will facilitate the study of DISC1's function and creation of mouse models of DISC1 disruption.
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MESH Headings
- Alternative Splicing
- Amino Acid Sequence
- Animals
- Base Sequence
- Blotting, Northern
- Brain/metabolism
- Chromosome Mapping
- Chromosomes, Human, Pair 1/genetics
- Cloning, Molecular
- DNA, Complementary/chemistry
- DNA, Complementary/genetics
- Exons
- Gene Expression
- Genes/genetics
- Humans
- In Situ Hybridization
- Introns
- Male
- Mice
- Molecular Sequence Data
- Nerve Tissue Proteins/genetics
- RNA, Messenger/genetics
- RNA, Messenger/metabolism
- Rats
- Sequence Alignment
- Sequence Analysis, DNA
- Sequence Homology, Amino Acid
- Synteny
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Affiliation(s)
- Lei Ma
- Department of Neuroscience, West Point, Pennsylvania 19486, USA
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125
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Bäuerle M, Doenecke D, Albig W. The requirement of H1 histones for a heterodimeric nuclear import receptor. J Biol Chem 2002; 277:32480-9. [PMID: 12080050 DOI: 10.1074/jbc.m202765200] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
After synthesis in the cytoplasm, H1 histones are imported into the nucleus through an energy-dependent process that can be mediated by an importin beta-importin 7 (Impbeta-Imp7) heterodimer. H1 histones contain two structurally different types of nuclear localization signals (NLS). The first type of NLS resides within the unstructured C-terminal domain and is rich in basic amino acids. In contrast, the highly conserved central domain of the H1 histone contains comparatively few basic amino acids but also represents a functional NLS. The competence for the nuclear import of this globular domain seems to be based on its secondary structure. Here, we show that the Impbeta-Imp7 heterodimer is the only receptor for H1 import. Furthermore, we identified the import receptors mediating the in vitro transport of different NLS of the H1 histone. Using the digitonin-permeabilized cell import assay we show that Impbeta is the most efficient import receptor for the globular domain of H1 histones, whereas the heterodimer of Impbeta and Imp7 is the functional receptor for the entire C-terminal domain. However, short fragments of the C-terminal domain are imported in vitro by at least four different importins, which resembles the import pathway of ribosomal proteins and core histones. In addition, we show that heterodimerization of Impbeta with Imp7 is absolutely necessary for their proper function as an import receptor for H1 histones. These findings point to a chaperone-like function of the heterodimeric complex in addition to its function as an import receptor. It appears that the Impbeta-Imp7 heterodimer is specialized for NLS consisting of extended basic domains.
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Affiliation(s)
- Marc Bäuerle
- Institut für Biochemie und Molekulare Zellbiologie, Abteilung für Molekularbiologie, Universität Göttingen, D-37073 Göttingen, Germany
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126
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Nürnberger J, Bacallao RL, Phillips CL. Inversin forms a complex with catenins and N-cadherin in polarized epithelial cells. Mol Biol Cell 2002; 13:3096-106. [PMID: 12221118 PMCID: PMC124145 DOI: 10.1091/mbc.e02-04-0195] [Citation(s) in RCA: 90] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Nephrogenesis starts with the reciprocal induction of two embryonically distinct analages, metanephric mesenchyme and ureteric bud. This complex process requires the refined and coordinated expression of numerous developmental genes, such as inv. Mice that are homozygous for a mutation in the inv gene (inv/inv) develop renal cysts resembling autosomal-recessive polycystic kidney disease. The gene locus containing inv has been proposed to serve as a common modifier for some human and rodent polycystic kidney disease phenotypes. We generated polyclonal antibodies to inversin to study its subcellular distribution, potential binding partners, and functional aspects in cultured murine proximal tubule cells. A 125-kDa inversin protein isoform was found at cell-cell junctions. Two inversin isoforms, 140- and 90-kDa, were identified in the nuclear and perinuclear compartments. Plasma membrane allocation of inversin is dependent upon cell-cell contacts and was redistributed when cell adhesion was disrupted after incubation of the cell monolayer with low-calcium/EGTA medium. We further show that the membrane-associated 125-kDa inversin forms a complex with N-cadherin and the catenins. The 90-kDa nuclear inversin complexes with beta-catenin. These findings indicate that the inv gene product functions in several cellular compartments, including the nucleus and cell-cell adhesion sites.
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Affiliation(s)
- Jens Nürnberger
- Indiana University School of Medicine Department of Medicine, Division of Nephrology, Indianapolis 46202-5116, USA
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127
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Nalaskowski MM, Deschermeier C, Fanick W, Mayr GW. The human homologue of yeast ArgRIII protein is an inositol phosphate multikinase with predominantly nuclear localization. Biochem J 2002; 366:549-56. [PMID: 12027805 PMCID: PMC1222796 DOI: 10.1042/bj20020327] [Citation(s) in RCA: 76] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2002] [Revised: 05/23/2002] [Accepted: 05/23/2002] [Indexed: 11/17/2022]
Abstract
The function of the transcription regulator ArgRIII in the expression of several genes involved in the metabolism of arginine in yeast has been well studied. It was previously reported that it is also an inositol phosphate multikinase and an important factor of the mRNA export pathway [reviewed by Shears (2000) Bioessays 22, 786-789]. In the present study we report the cloning of a full-length 1248-bp cDNA encoding a human inositol phosphate multikinase (IPMK). This protein has a calculated molecular mass of 47.219 kDa. Functionally important motifs [inositol phosphate-binding site, ATP-binding site, catalytically important SSLL (Ser-Ser-Leu-Leu) domain] are conserved between the human IPMK and yeast ArgRIII. Bacterially expressed protein demonstrated an inositol phosphate multikinase activity similar to that of yeast ArgRIII. Ins(1,4,5)P3 is phosphorylated at positions 3 and 6 up to Ins(1,3,4,5,6)P5. The human IPMK fused with a fluorescent protein tag is localized predominantly in the nucleus when transiently expressed in mammalian cells. A basic cluster in the protein's C-terminus is positively involved in nuclear targeting. These findings are consistent with the concept of a nuclear inositol phosphate signalling and phosphorylation pathway in mammalian cells.
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Affiliation(s)
- Marcus M Nalaskowski
- Universitaetsklinikum Hamburg-Eppendorf, Institut für Medizinische Biochemie und Molekularbiologie, Abteilung für Zellulaere Signaltransduktion, Martinistrasse 52, 20246 Hamburg, Germany
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128
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Huang F, Wagner M, Siddiqui MAQ. Structure, expression, and functional characterization of the mouse CLP-1 gene. Gene 2002; 292:245-59. [PMID: 12119119 DOI: 10.1016/s0378-1119(02)00596-6] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Mouse CLP-1, a potential cardiac transcriptional regulatory factor, is encoded by a single copy gene lacking introns that is expressed into two mRNAs via alternative polyadenylation. Both mRNAs encode the same 41 kDa protein, a novel protein that is 85.3% homologous with a human homologue called HIS1. Mouse CLP-1 is widely expressed in a number of tissues as well as in early development and is localized to the nucleus. The CLP-1 gene promoter is active in different cell types and sequence analysis shows a number of potential binding sites for cardiogenic transcription factors such as Nkx2.5 and GATA-4, indicating a potential role in development. CLP-1 appears to "squelch" the cardiac MLC-2v promoter in a concentration-dependent manner in cardiac but not other cell types, suggesting that CLP-1 may be interacting with a cardiac-specific factor to regulate cardiac MLC-2v expression. The overall expression pattern of CLP-1 is similar to that of LCR-F1 and Oct-1, two widely expressed transcription factors that also play specific roles in the transcription of cell-specific genes. CLP-1 may be a transcriptional mediator capable of interacting with and potentiating cell-specific transcription factors.
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MESH Headings
- Acetamides/pharmacology
- Amino Acid Sequence
- Animals
- Bacteria/genetics
- Base Sequence
- Blotting, Northern
- Blotting, Southern
- Cell Line
- Cells, Cultured
- DNA/chemistry
- DNA/genetics
- DNA, Complementary/chemistry
- DNA, Complementary/genetics
- Embryo, Mammalian/metabolism
- Gene Expression
- Gene Expression Regulation, Developmental
- Genes/genetics
- Luciferases/genetics
- Luciferases/metabolism
- Mice
- Mice, Inbred Strains
- Molecular Sequence Data
- Muscle, Smooth, Vascular/cytology
- Muscle, Smooth, Vascular/drug effects
- Muscle, Smooth, Vascular/metabolism
- Myosin Light Chains/genetics
- Promoter Regions, Genetic/genetics
- RNA, Messenger/genetics
- RNA, Messenger/metabolism
- RNA-Binding Proteins
- Rats
- Recombinant Fusion Proteins/genetics
- Recombinant Fusion Proteins/isolation & purification
- Recombinant Fusion Proteins/metabolism
- Sequence Alignment
- Sequence Analysis, DNA
- Sequence Homology, Amino Acid
- Transcription Factors/genetics
- Transcription Factors/metabolism
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Affiliation(s)
- Facan Huang
- Department of Anatomy and Cell Biology, Center for Cardiovascular and Muscle Research, Box 5, State University of New York, Health Science Center at Brooklyn, 450 Clarkson Avenue, Brooklyn, NY 11203, USA
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129
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Pandya K, Townes TM. Basic residues within the Kruppel zinc finger DNA binding domains are the critical nuclear localization determinants of EKLF/KLF-1. J Biol Chem 2002; 277:16304-12. [PMID: 11844803 DOI: 10.1074/jbc.m200866200] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
EKLF/KLF-1 is an erythroid-restricted transcription factor essential for expression of the adult beta-globin gene. EKLF/KLF-1 is a 358-amino acid nuclear protein with an amino-terminal proline-rich domain and a carboxyl-terminal DNA binding domain. The nuclear localization signal (NLS) of EKLF/KLF-1 has not been empirically determined. We generated a series of epitope-tagged deletion and point mutants and assessed their subcellular localization. Our results delimit the NLS to the 83-amino acid (amino acids 276-358) DNA binding domain that consists of three Kruppel zinc fingers. All three zinc fingers are necessary for efficient nuclear localization; deletion of any individual finger results in cytoplasmic accumulation. Fusion of the three zinc fingers to green fluorescent protein (GFP) targeted GFP to the nucleus, demonstrating that the zinc finger domain is sufficient for nuclear localization. EKLF/KLF-1 containing histidine to alanine mutations that disrupt the structure of all three fingers retains appropriate nuclear localization, indicating that neither the tertiary structure of the zinc fingers nor specific DNA binding are necessary for nuclear localization. We demonstrate that basic residues within the fingers are the critical determinants for nuclear localization; mutations of these basic residues to alanine resulted in cytoplasmic mislocalization. The basic residues of all mammalian Kruppel zinc fingers are highly conserved; therefore we propose that these basic residues are a common NLS shared by all Kruppel family members.
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Affiliation(s)
- Kumar Pandya
- Department of Biochemistry and Molecular Genetics, School of Medicine, University of Alabama at Birmingham, Birmingham, Alabama 35294, USA
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130
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Fattori D, Kinzel O, Ingallinella P, Bianchi E, Pessi A. A practical approach to the synthesis of hairpin polyamide-peptide conjugates through the use of a safety-catch linker. Bioorg Med Chem Lett 2002; 12:1143-7. [PMID: 11934575 DOI: 10.1016/s0960-894x(02)00122-1] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Hairpin polyamides are high-affinity, sequence selective DNA binders. The use of a safety-catch linker for the solid phase synthesis of hairpin polyamides allows for easy preparation of derivatives ready for chemoselective ligation with unprotected peptides. Examples of ligations reported include thioether bond formation and thioester-mediated amide bond formation ('Native Chemical Ligation').
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Affiliation(s)
- Daniela Fattori
- Istituto di Ricerche di Biologia Molecolare P. Angeletti (IRBM), Via Pontina Km 30.600, 00040 Pomezia, Rome, Italy
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131
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Wolff T, Unterstab G, Heins G, Richt JA, Kann M. Characterization of an unusual importin alpha binding motif in the borna disease virus p10 protein that directs nuclear import. J Biol Chem 2002; 277:12151-7. [PMID: 11796712 DOI: 10.1074/jbc.m109103200] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Nuclear import of many cellular and viral proteins is mediated by short nuclear localization signals (NLS) that are recognized by intracellular receptor proteins belonging to the importin/karyopherin alpha and beta families. The primary structure of NLS is not well defined, but most contain at least three basic amino acids and harbor the relative consensus sequence K(K/R)X(K/R). We have studied the nuclear import of the Borna disease virus p10 protein that lacks a canonical oligobasic NLS. It is shown that the p10 protein exhibits all characteristics of an actively transported molecule in digitonin-permeabilized cells. Import activity was found to reside in the 20 N-terminal p10 amino acids that are devoid of an NLS consensus motif. Unexpectedly, p10-dependent import was blocked by a peptide inhibitor of importin alpha-dependent nuclear translocation, and the transport activity of the p10 N-terminal domain was shown to correlate with the ability to bind to importin alpha. These findings suggest that nuclear import of the Borna disease virus p10 protein occurs through a nonconventional karyophilic signal and highlight that the cellular importin alpha NLS receptor proteins can recognize nuclear targeting signals that substantially deviate from the consensus sequence.
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Affiliation(s)
- Thorsten Wolff
- Robert-Koch-Institut, Nordufer 20, 13353 Berlin, Germany.
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132
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Scheifele LZ, Garbitt RA, Rhoads JD, Parent LJ. Nuclear entry and CRM1-dependent nuclear export of the Rous sarcoma virus Gag polyprotein. Proc Natl Acad Sci U S A 2002; 99:3944-9. [PMID: 11891341 PMCID: PMC122628 DOI: 10.1073/pnas.062652199] [Citation(s) in RCA: 95] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2001] [Indexed: 01/26/2023] Open
Abstract
The retroviral Gag polyprotein directs budding from the plasma membrane of infected cells. Until now, it was believed that Gag proteins of type C retroviruses, including the prototypic oncoretrovirus Rous sarcoma virus, were synthesized on cytosolic ribosomes and targeted directly to the plasma membrane. Here we reveal a previously unknown step in the subcellular trafficking of the Gag protein, that of transient nuclear localization. We have identified a targeting signal within the N-terminal matrix domain that facilitates active nuclear import of the Gag polyprotein. We also found that Gag is transported out of the nucleus through the CRM1 nuclear export pathway, based on observations that treatment of virus-expressing cells with leptomycin B resulted in the redistribution of Gag proteins from the cytoplasm to the nucleus. Internal deletion of the C-terminal portion of the Gag p10 region resulted in the nuclear sequestration of Gag and markedly diminished budding, suggesting that the nuclear export signal might reside within p10. Finally, we observed that a previously described matrix mutant, Myr1E, was insensitive to the effects of leptomycin B, apparently bypassing the nuclear compartment during virus assembly. Myr1E has a defect in genomic RNA packaging, implying that nuclear localization of Gag might be involved in viral RNA interactions. Taken together, these findings provide evidence that nuclear entry and egress of the Gag polyprotein are intrinsic components of the Rous sarcoma virus assembly pathway.
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Affiliation(s)
- Lisa Z Scheifele
- Cell and Molecular Biology Program and Department of Microbiology and Immunology, Pennsylvania State University College of Medicine, 500 University Drive, Hershey, PA 17033, USA
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133
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Watano K, Iwabuchi K, Fujii S, Ishimori N, Mitsuhashi S, Ato M, Kitabatake A, Onoé K. Allograft inflammatory factor-1 augments production of interleukin-6, -10 and -12 by a mouse macrophage line. Immunology 2001; 104:307-16. [PMID: 11722645 PMCID: PMC1783316 DOI: 10.1046/j.1365-2567.2001.01301.x] [Citation(s) in RCA: 74] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Mouse allograft inflammatory factor-1 (AIF-1) cDNA was cloned and the AIF-1-specific monoclonal antibodies were established to examine its tissue distribution. The mouse AIF-1 was highly conserved among all reported AIF-1 from a variety of species, from invertebrates to mammals, and the cloned cDNA was in good accordance with putative expressed regions of genomic sequences in the mouse major histocompatibility complex (MHC) class III region. The messages of mouse AIF-1 were abundantly expressed in the testis, moderately in the spleen and lymph nodes and slightly in the liver and thymus of normal BALB/c mice. Immunohistological examination revealed that differentiating germ cells in the testis and presumably macrophages in the red pulp of the spleen were positive for AIF-1. To analyse the function of the AIF-1, a macrophage cell line, RAW 264.7, was transfected with mouse AIF-1 cDNA. Upon stimulation with bacterial lipopolysaccharide, the transfectants that overexpressed AIF-1 showed marked morphological changes and produced significantly large amounts of interleukin (IL)-6, IL-10 and IL-12p40 but not IL-12p70 compared with control cells. No difference was noted in production of tumour necrosis factor-alpha, transforming growth factor-beta1 and IL-1alpha. These results suggest that AIF-1 plays an important role in cells of a monocyte/macrophage lineage upon stimulation with inflammatory stimuli by augmenting particular cytokine production.
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Affiliation(s)
- K Watano
- Division of Immunobiology, Research Section of Pathophysiology, Institute for Genetic Medicine, Hokkaido University, Sapporo, Japan
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134
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Baake M, Bäuerle M, Doenecke D, Albig W. Core histones and linker histones are imported into the nucleus by different pathways. Eur J Cell Biol 2001; 80:669-77. [PMID: 11824786 DOI: 10.1078/0171-9335-00208] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Histones are the major structural proteins in eukaryotic chromosomes. This group of small very basic proteins consists of the H1 linker histones and the core histones H2A, H2B, H3 and H4. Despite their small size, the nuclear import of histones occurs by an active transport mechanism and not simply by diffusion. Histones contain several nuclear localisation signals (NLS) that can be subdivided into two different types of signal structures. We have previously shown that H1 histones are transported by a heterodimeric import receptor complex consisting of importin beta and importin 7, and we now describe the receptors required for the import of the core histones. Competition experiments using the in vitro transport assay indicate that the import pathway of the core histones differs from that of the linker histones and of nuclear proteins with classical NLS. In vitro binding assays show that each of the import receptors importin beta, importin 5, importin 7 and transportin, has the capacity to bind to any of the four core histones. Reconstitution experiments with recombinant factors indicate that each of these factors can independently serve as an import receptor for each of the core histones.
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Affiliation(s)
- M Baake
- Institut für Biochemie und Molekulare Zellbiologie, Abteilung für Molekularbiologie, Universität Göttingen, Germany
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135
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Andreeva AV, Kutuzov MA. Nuclear localization of the plant protein Ser/Thr phosphatase PP7. MOLECULAR CELL BIOLOGY RESEARCH COMMUNICATIONS : MCBRC 2001; 4:345-52. [PMID: 11703093 DOI: 10.1006/mcbr.2001.0302] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Recently we identified novel plant Ser/Thr phosphatases, termed PP7, which belong to the PPP family and have no known close homologs in other kingdoms. We now addressed the intracellular location of Arabidopsis thaliana PP7 using GFP fusions and confocal laser scanning microscopy. PP7. GFP fusion was expressed transiently or stably in Nicotiana benthamiana. PP7. GFP was found to be a predominantly nuclear protein. Effects of cytoskeleton-disrupting drugs indicate that cytoskeleton may be required for efficient PP7. GFP delivery to the nucleus. Deletion of a potential nuclear localization signal in the first insert in the catalytic domain, as well as exposure to the dark, cold, high salinity and abscisic acid failed to prevent nuclear localization of PP7. GFP. Deletion of the 44 C-terminal amino acids resulted in a fusion protein located exclusively in the cytoplasm. The results suggest a possible similarity of the nuclear targeting signals in PP7 and the PP5/PPT subfamily.
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Affiliation(s)
- A V Andreeva
- Research School of Biological and Molecular Sciences, Oxford Brookes University, Gipsy Lane Campus, Headington, Oxford, OX3 0BP, United Kingdom.
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136
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Catimel B, Teh T, Fontes MR, Jennings IG, Jans DA, Howlett GJ, Nice EC, Kobe B. Biophysical characterization of interactions involving importin-alpha during nuclear import. J Biol Chem 2001; 276:34189-98. [PMID: 11448961 DOI: 10.1074/jbc.m103531200] [Citation(s) in RCA: 134] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Proteins containing the classical nuclear localization sequences (NLSs) are imported into the nucleus by the importin-alpha/beta heterodimer. Importin-alpha contains the NLS binding site, whereas importin-beta mediates the translocation through the nuclear pore. We characterized the interactions involving importin-alpha during nuclear import using a combination of biophysical techniques (biosensor, crystallography, sedimentation equilibrium, electrophoresis, and circular dichroism). Importin-alpha is shown to exist in a monomeric autoinhibited state (association with NLSs undetectable by biosensor). Association with importin-beta (stoichiometry, 1:1; K(D) = 1.1 x 10(-8) m) increases the affinity for NLSs; the importin-alpha/beta complex binds representative monopartite NLS (simian virus 40 large T-antigen) and bipartite NLS (nucleoplasmin) with affinities (K(D) = 3.5 x 10(-8) m and 4.8 x 10(-8) m, respectively) comparable with those of a truncated importin-alpha lacking the autoinhibitory domain (T-antigen NLS, K(D) = 1.7 x 10(-8) m; nucleoplasmin NLS, K(D) = 1.4 x 10(-8) m). The autoinhibitory domain (as a separate peptide) binds the truncated importin-alpha, and the crystal structure of the complex resembles the structure of full-length importin-alpha. Our results support the model of regulation of nuclear import mediated by the intrasteric autoregulatory sequence of importin-alpha and provide a quantitative description of the binding and regulatory steps during nuclear import.
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Affiliation(s)
- B Catimel
- Ludwig Institute for Cancer Research, Royal Melbourne Hospital, Victoria 3050, Australia
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137
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Spizz G, Blackshear PJ. Overexpression of the myristoylated alanine-rich C-kinase substrate inhibits cell adhesion to extracellular matrix components. J Biol Chem 2001; 276:32264-73. [PMID: 11413143 DOI: 10.1074/jbc.m103960200] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Mice lacking the myristoylated alanine-rich C-kinase substrate, or MARCKS protein, exhibit abnormalities consistent with a defect in the ability of neurons to migrate appropriately during forebrain development. To investigate the possibility that this phenotype could be due to disruption of normal cellular adhesion to extracellular matrix, an assay was developed in which 293 cells co-expressing MARCKS and green fluorescent protein were tested for their adhesion competence on various substrates. Fluorescence-activated cell sorting of adherent and non-adherent green fluorescent protein-expressing cells demonstrated that wild-type MARCKS inhibited adhesion of cells to fibronectin, whereas a non-myristoylated mutant did not inhibit adhesion of cells to a variety of substrates. The fibronectin competitive inhibitor RGD peptide inhibited adhesion of cells expressing all MARCKS variants equally. Cytochalasin D inhibited the adhesion of cells expressing non-myristoylated MARCKS, but did not further decrease the adhesion of cells expressing adhesion-inhibitory proteins. Confocal microscopy demonstrated the presence of inhibitory, myristoylated MARCKS at the plasma membrane, suggesting that localization at this region might be important for MARCKS to inhibit cellular adhesion. These data suggest a possible myristoylation-dependent function of MARCKS to inhibit cellular adhesion to extracellular matrix proteins, indicating a potential mechanism for the cell migration defects seen in the MARCKS-deficient mice.
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Affiliation(s)
- G Spizz
- Office of Clinical Research and Laboratory of Signal Transduction, NIEHS, National Institutes of Health, Research Triangle Park, North Carolina, 27709, USA
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138
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Huber LJ, Yang TW, Sarkisian CJ, Master SR, Deng CX, Chodosh LA. Impaired DNA damage response in cells expressing an exon 11-deleted murine Brca1 variant that localizes to nuclear foci. Mol Cell Biol 2001; 21:4005-15. [PMID: 11359908 PMCID: PMC87063 DOI: 10.1128/mcb.21.12.4005-4015.2001] [Citation(s) in RCA: 88] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023] Open
Abstract
Both human and mouse cells express an alternatively spliced variant of BRCA1, BRCA1-Delta11, which lacks exon 11 in its entirety, including putative nuclear localization signals. Consistent with this, BRCA1-Delta11 has been reported to reside in the cytoplasm, a localization that would ostensibly preclude it from playing a role in the nuclear processes in which its full-length counterpart has been implicated. Nevertheless, the finding that murine embryos bearing homozygous deletions of exon 11 survive longer than embryos that are homozygous for Brca1 null alleles suggests that exon 11-deleted isoforms may perform at least some of the functions of Brca1. We have analyzed both the full-length and the exon 11-deleted isoforms of the murine Brca1 protein. Our results demonstrate that full-length murine Brca1 is identical to human BRCA1 with respect to its cell cycle regulation, DNA damage-induced phosphorylation, nuclear localization, and association with Rad51. Surprisingly, we show that endogenous Brca1-Delta11 localizes to discrete nuclear foci indistinguishable from those found in wild-type cells, despite the fact that Brca1-Delta11 lacks previously defined nuclear localization signals. However, we further show that DNA damage-induced phosphorylation of Brca1-Delta11 is significantly reduced compared to full-length Brca1, and that gamma irradiation-induced Rad51 focus formation is impaired in cells in which only Brca1-Delta11 is expressed. Our results suggest that the increased viability of embryos bearing homozygous deletions of exon 11 may be due to expression of Brca1-Delta11 and suggest an explanation for the genomic instability that accompanies the loss of full-length Brca1.
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Affiliation(s)
- L J Huber
- Department of Molecular & Cellular Engineering, Diabetes and Metabolism, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104-6160, USA
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139
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140
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Santagati F, Botta E, Stefanini M, Pedrini AM. Different dynamics in nuclear entry of subunits of the repair/transcription factor TFIIH. Nucleic Acids Res 2001; 29:1574-81. [PMID: 11266560 PMCID: PMC31283 DOI: 10.1093/nar/29.7.1574] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
We report here the different ways in which four subunits of the basal transcription/repair factor TFIIH (XPB, XPD, p62 and p44) and the damage recognition XPC repair protein can enter the nucleus. We examined their nuclear localization by transiently expressing the gene products tagged with the enhanced green fluorescent protein (EGFP) in transfected 3T3 cells. In agreement with the identification of more than one putative nuclear localization signal (NLS) in their protein sequences, XPB, XPC, p62 and p44 chimeras were rapidly sorted to the nucleus. In contrast, the XPD-EGFP chimeras appeared mainly localized in the cytoplasm, with a minor fraction of transfectants showing the EGFP-based fluorescence also in the nucleus. The ability of the XPD chimeras to enter the nucleus was confirmed by western blotting on fractionated cell extracts and by functional complementation of the repair defect in the UV5 rodent cells, mutated in the XPD homologous gene. By deletion mutagenesis, we were unable to identify any sequence specific for nuclear localization. In particular, deletion of the putative NLS failed to affect subcellular localization and, conversely, the C-terminal part of XPD containing the putative NLS showed no specific nuclear accumulation. These findings suggest that the nuclear entry of XPD depends on its complexation with other proteins in the cytoplasm, possibly other components of the TFIIH complex.
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Affiliation(s)
- F Santagati
- Istituto di Genetica Biochimica ed Evoluzionistica del CNR, Via Abbiategrasso 207, 27100 Pavia, Italy
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141
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142
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Kim JE, Chen J. Cytoplasmic-nuclear shuttling of FKBP12-rapamycin-associated protein is involved in rapamycin-sensitive signaling and translation initiation. Proc Natl Acad Sci U S A 2000; 97:14340-5. [PMID: 11114166 PMCID: PMC18920 DOI: 10.1073/pnas.011511898] [Citation(s) in RCA: 160] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Translation initiation is one of the key events regulated in response to mitogenic stimulation and nutrient availability, tightly coupled to mammalian cell cycle progression and growth. FKBP12-rapamycin-associated protein (FRAP; also named mTOR or RAFT1), a member of the ataxia telangiectasia mutated (ATM)-related kinase family, governs a rapamycin-sensitive membrane-to-cytoplasm signaling cascade that modulates translation initiation via p70 S6 kinase (p70(s6k)) and eIF-4E binding protein 1 (4E-BP1). Our studies reported here reveal a surprising regulatory mechanism of this signaling, which involves cytoplasmic-nuclear shuttling of FRAP. By using leptomycin B (LMB), a specific inhibitor of nuclear export receptor Crm1, we show that FRAP is a cytoplasmic-nuclear shuttling protein. Inhibition of FRAP nuclear export by LMB coincides with diminished p70(s6k) activation and 4E-BP1 phosphorylation. Further investigation by altering FRAP's nuclear shuttling activity with exogenous nuclear import and export signals has yielded results that are consistent with a direct link between nuclear shuttling of FRAP and mitogenic stimulation of p70(s6k) activation and 4E-BP1 phosphorylation. Furthermore, by using a reporter system, we provide evidence suggesting that nuclear shuttling of FRAP regulates mitogen-stimulated rapamycin-sensitive translation initiation. These findings uncover a function for the nucleus in the direct regulation of the protein synthesis machinery via extracellular signals.
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Affiliation(s)
- J E Kim
- Department of Cell and Structural Biology, University of Illinois at Urbana-Champaign, 601 South Goodwin Avenue, B107, Urbana, IL 61801, USA
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