1
|
Li X, Wei Q, Zhao K, Wang W, Liu B, Li W, Wang J. Monitoring Intracellular IP6 with a Genetically Encoded Fluorescence Biosensor. ACS Sens 2023; 8:4484-4493. [PMID: 38079595 DOI: 10.1021/acssensors.3c00268] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2023]
Abstract
Inositol hexakisphosphate (IP6), a naturally occurring metabolite of inositol with specific functions in different organelles or tissues, participates in numerous physiological processes and plays a key role in mammalian metabolic regulation. However, current IP6 detection methods, i.e., high-performance liquid chromatography and gel electrophoresis, require sample destruction and lack spatiotemporal resolution. Here, we construct and characterize a genetically encoded fluorescence biosensor named HIPSer that enables ratiometric quantitative IP6 detection in HEK293T cells and subcellular compartments. We demonstrate that HIPSer has a high sensitivity and relative selectivity for IP6 in vitro. We also provide proof-of-concept evidence that HIPSer can monitor IP6 levels in real time in HEK293T cells and can be targeted for IP6 detection in the nucleus of HEK293T cells. Moreover, HIPSer could also detect changes in IP6 content induced by chemical inhibition of IP6-metabolizing enzymes in HEK293T cells. Thus, HIPSer achieves spatiotemporally precise detection of fluctuations in endogenous IP6 in live cells and provides a versatile tool for mechanistic investigations of inositol phosphate functions in metabolism and signaling.
Collapse
Affiliation(s)
- Xi Li
- State Key Laboratory of Natural and Biomimetic Drugs and Department of Chemical Biology, School of Pharmaceutical Sciences, Peking University, Beijing 100191, China
| | - Qingpeng Wei
- State Key Laboratory of Natural and Biomimetic Drugs and Department of Chemical Biology, School of Pharmaceutical Sciences, Peking University, Beijing 100191, China
| | - Kaiyuan Zhao
- State Key Laboratory of Natural and Biomimetic Drugs and Department of Chemical Biology, School of Pharmaceutical Sciences, Peking University, Beijing 100191, China
| | - Weibo Wang
- State Key Laboratory of Natural and Biomimetic Drugs and Department of Chemical Biology, School of Pharmaceutical Sciences, Peking University, Beijing 100191, China
- Key Laboratory of Pesticide & Chemical Biology of Ministry of Education, International Joint Research Center for Intelligent Biosensor Technology and Health, College of Chemistry, Central China Normal University, Wuhan 430079, China
| | - Bingjie Liu
- State Key Laboratory of Natural and Biomimetic Drugs and Department of Chemical Biology, School of Pharmaceutical Sciences, Peking University, Beijing 100191, China
| | - Wenzhe Li
- State Key Laboratory of Natural and Biomimetic Drugs and Department of Chemical Biology, School of Pharmaceutical Sciences, Peking University, Beijing 100191, China
| | - Jing Wang
- State Key Laboratory of Natural and Biomimetic Drugs and Department of Chemical Biology, School of Pharmaceutical Sciences, Peking University, Beijing 100191, China
| |
Collapse
|
2
|
Maffucci T, Falasca M. Signalling Properties of Inositol Polyphosphates. Molecules 2020; 25:molecules25225281. [PMID: 33198256 PMCID: PMC7696153 DOI: 10.3390/molecules25225281] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2020] [Revised: 11/02/2020] [Accepted: 11/04/2020] [Indexed: 12/16/2022] Open
Abstract
Several studies have identified specific signalling functions for inositol polyphosphates (IPs) in different cell types and have led to the accumulation of new information regarding their cellular roles as well as new insights into their cellular production. These studies have revealed that interaction of IPs with several proteins is critical for stabilization of protein complexes and for modulation of enzymatic activity. This has not only revealed their importance in regulation of several cellular processes but it has also highlighted the possibility of new pharmacological interventions in multiple diseases, including cancer. In this review, we describe some of the intracellular roles of IPs and we discuss the pharmacological opportunities that modulation of IPs levels can provide.
Collapse
Affiliation(s)
- Tania Maffucci
- Centre for Cell Biology and Cutaneous Research, Blizard Institute, Barts and The London School of Medicine and Dentistry, Queen Mary University of London, London E1 2AT, UK
- Correspondence: (T.M.); (M.F.); Tel.: +61-08-92669712 (M.F.)
| | - Marco Falasca
- School of Pharmacy and Biomedical Sciences, CHIRI, Curtin University, Perth 6102, Australia
- Correspondence: (T.M.); (M.F.); Tel.: +61-08-92669712 (M.F.)
| |
Collapse
|
3
|
Structural analyses of inositol phosphate second messengers bound to signaling effector proteins. Adv Biol Regul 2019; 75:100667. [PMID: 31648945 DOI: 10.1016/j.jbior.2019.100667] [Citation(s) in RCA: 23] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2019] [Revised: 09/17/2019] [Accepted: 09/30/2019] [Indexed: 01/02/2023]
Abstract
The higher-order inositol phosphate second messengers inositol tetrakisphosphate (IP4), inositol pentakisphosphate (IP5) and inositol hexakisphosphate (IP6) are important signaling molecules that regulate DNA-damage repair, cohesin dynamics, RNA-editing, retroviral assembly, nuclear transport, phosphorylation, acetylation, crotonylation, and ubiquitination. This functional diversity has made understanding how inositol polyphosphates regulate cellular processes challenging to dissect. However, some inositol phosphates have been unexpectedly found in X-ray crystal structures, occasionally revealing structural and mechanistic details of effector protein regulation before functional consequences have been described. This review highlights a sampling of crystal structures describing the interaction between inositol phosphates and protein effectors. This list includes the RNA editing enzyme "adenosine deaminase that acts on RNA 2" (ADAR2), the Pds5B regulator of cohesin dynamics, the class 1 histone deacetylases (HDACs) HDAC1 and HDAC3, and the PH domain of Bruton's tyrosine kinase (Btk). One of the most important enzymes responsible for higher-order inositol phosphate synthesis is inositol polyphosphate multikinase (IPMK), which plays dual roles in both inositol and phosphoinositide signaling. Structures of phosphoinositide lipid binding proteins have also revealed new aspects of protein effector regulation, as mediated by the nuclear receptors Steroidogenic Factor-1 (SF-1, NR5A2) and Liver Receptor Homolog-1 (LRH-1, NR5A2). Together, these studies underscore the structural diversity in binding interactions between effector proteins and inositol phosphate small signaling molecules, and further support that detailed structural studies can lead to new biological discovery.
Collapse
|
4
|
Aryanpur PP, Regan CA, Collins JM, Mittelmeier TM, Renner DM, Vergara AM, Brown NP, Bolger TA. Gle1 Regulates RNA Binding of the DEAD-Box Helicase Ded1 in Its Complex Role in Translation Initiation. Mol Cell Biol 2017; 37:e00139-17. [PMID: 28784717 PMCID: PMC5640818 DOI: 10.1128/mcb.00139-17] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2017] [Revised: 05/05/2017] [Accepted: 07/21/2017] [Indexed: 02/07/2023] Open
Abstract
DEAD-box proteins (DBPs) are required in gene expression to facilitate changes to ribonucleoprotein complexes, but the cellular mechanisms and regulation of DBPs are not fully defined. Gle1 is a multifunctional regulator of DBPs with roles in mRNA export and translation. In translation, Gle1 modulates Ded1, a DBP required for initiation. However, DED1 overexpression causes defects, suggesting that Ded1 can promote or repress translation in different contexts. Here we show that GLE1 expression suppresses the repressive effects of DED1 in vivo and Gle1 counteracts Ded1 in translation assays in vitro Furthermore, both Ded1 and Gle1 affect the assembly of preinitiation complexes. Through mutation analysis and binding assays, we show that Gle1 inhibits Ded1 by reducing its affinity for RNA. Our results are consistent with a model wherein active Ded1 promotes translation but inactive or excess Ded1 leads to translation repression. Gle1 can inhibit either role of Ded1, positioning it as a gatekeeper to optimize Ded1 activity to the appropriate level for translation. This study suggests a paradigm for finely controlling the activity of DEAD-box proteins to optimize their function in RNA-based processes. It also positions the versatile regulator Gle1 as a potential node for the coordination of different steps of gene expression.
Collapse
Affiliation(s)
- Peyman P Aryanpur
- Department of Molecular and Cellular Biology, University of Arizona, Tucson, Arizona, USA
| | - Chelsea A Regan
- Department of Molecular and Cellular Biology, University of Arizona, Tucson, Arizona, USA
| | - John M Collins
- Department of Molecular and Cellular Biology, University of Arizona, Tucson, Arizona, USA
| | - Telsa M Mittelmeier
- Department of Molecular and Cellular Biology, University of Arizona, Tucson, Arizona, USA
| | - David M Renner
- Department of Molecular and Cellular Biology, University of Arizona, Tucson, Arizona, USA
| | - Ashley M Vergara
- Department of Molecular and Cellular Biology, University of Arizona, Tucson, Arizona, USA
| | - Nicolette P Brown
- Department of Molecular and Cellular Biology, University of Arizona, Tucson, Arizona, USA
| | - Timothy A Bolger
- Department of Molecular and Cellular Biology, University of Arizona, Tucson, Arizona, USA
| |
Collapse
|
5
|
Adams RL, Mason AC, Glass L, Aditi, Wente SR. Nup42 and IP 6 coordinate Gle1 stimulation of Dbp5/DDX19B for mRNA export in yeast and human cells. Traffic 2017; 18:776-790. [PMID: 28869701 DOI: 10.1111/tra.12526] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2017] [Revised: 08/30/2017] [Accepted: 08/30/2017] [Indexed: 11/30/2022]
Abstract
The mRNA lifecycle is driven through spatiotemporal changes in the protein composition of mRNA particles (mRNPs) that are triggered by RNA-dependent DEAD-box protein (Dbp) ATPases. As mRNPs exit the nuclear pore complex (NPC) in Saccharomyces cerevisiae, this remodeling occurs through activation of Dbp5 by inositol hexakisphosphate (IP6 )-bound Gle1. At the NPC, Gle1 also binds Nup42, but Nup42's molecular function is unclear. Here we employ the power of structure-function analysis in S. cerevisiae and human (h) cells, and find that the high-affinity Nup42-Gle1 interaction is integral to Dbp5 (hDDX19B) activation and efficient mRNA export. The Nup42 carboxy-terminal domain (CTD) binds Gle1/hGle1B at an interface distinct from the Gle1-Dbp5/hDDX19B interaction site. A nup42-CTD/gle1-CTD/Dbp5 trimeric complex forms in the presence of IP6 . Deletion of NUP42 abrogates Gle1-Dbp5 interaction, and disruption of the Nup42 or IP6 binding interfaces on Gle1/hGle1B leads to defective mRNA export in S. cerevisiae and human cells. In vitro, Nup42-CTD and IP6 stimulate Gle1/hGle1B activation of Dbp5 and DDX19B recombinant proteins in similar, nonadditive manners, demonstrating complete functional conservation between humans and S. cerevisiae. Together, a highly conserved mechanism governs spatial coordination of mRNP remodeling during export. This has implications for understanding human disease mutations that perturb the Nup42-hGle1B interaction.
Collapse
Affiliation(s)
- Rebecca L Adams
- Department of Cell and Developmental Biology, Vanderbilt University School of Medicine, Nashville, Tennessee
| | - Aaron C Mason
- Department of Cell and Developmental Biology, Vanderbilt University School of Medicine, Nashville, Tennessee
| | - Laura Glass
- Department of Cell and Developmental Biology, Vanderbilt University School of Medicine, Nashville, Tennessee
| | - Aditi
- Department of Cell and Developmental Biology, Vanderbilt University School of Medicine, Nashville, Tennessee
| | - Susan R Wente
- Department of Cell and Developmental Biology, Vanderbilt University School of Medicine, Nashville, Tennessee
| |
Collapse
|
6
|
Jiao C, Summerlin M, Bruzik KS, Hanakahi L. Synthesis of Biotinylated Inositol Hexakisphosphate To Study DNA Double-Strand Break Repair and Affinity Capture of IP6-Binding Proteins. Biochemistry 2015; 54:6312-22. [PMID: 26397942 DOI: 10.1021/acs.biochem.5b00642] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Inositol hexakisphosphate (IP6) is a soluble inositol polyphosphate, which is abundant in mammalian cells. Despite the participation of IP6 in critical cellular functions, few IP6-binding proteins have been characterized. We report on the synthesis, characterization, and application of biotin-labeled IP6 (IP6-biotin), which has biotin attached at position 2 of the myo-inositol ring via an aminohexyl linker. Like natural IP6, IP6-biotin stimulated DNA ligation by nonhomologous end joining (NHEJ) in vitro. The Ku protein is a required NHEJ factor that has been shown to bind IP6. We found that IP6-biotin could affinity capture Ku and other required NHEJ factors from human cell extracts, including the DNA-dependent protein kinase catalytic subunit (DNA-PKcs), XRCC4, and XLF. Direct binding studies with recombinant proteins show that Ku is the only NHEJ factor with affinity for IP6-biotin. DNA-PKcs, XLF, and the XRCC4:ligase IV complex interact with Ku in cell extracts and likely interact indirectly with IP6-biotin. IP6-biotin was used to tether streptavidin to Ku, which inhibited NHEJ in vitro. These proof-of-concept experiments suggest that molecules like IP6-biotin might be used to molecularly target biologically important proteins that bind IP6. IP6-biotin affinity capture experiments show that numerous proteins specifically bind IP6-biotin, including casein kinase 2, which is known to bind IP6, and nucleolin. Protein binding to IP6-biotin is selective, as IP3, IP4, and IP5 did not compete for binding of proteins to IP6-biotin. Our results document IP6-biotin as a useful tool for investigating the role of IP6 in biological systems.
Collapse
Affiliation(s)
- Chensong Jiao
- Department of Medicinal Chemistry and Pharmacognosy, College of Pharmacy, University of Illinois, Chicago , 833 South Wood Street (M/C 781), Chicago, Illinois 60612, United States
| | - Matthew Summerlin
- Department of Medicinal Chemistry and Pharmacognosy, College of Pharmacy, University of Illinois, Chicago , Rockford Health Sciences Campus, 1601 Parkview Avenue, Rockford, Illinois 61107, United States
| | - Karol S Bruzik
- Department of Medicinal Chemistry and Pharmacognosy, College of Pharmacy, University of Illinois, Chicago , 833 South Wood Street (M/C 781), Chicago, Illinois 60612, United States
| | - Leslyn Hanakahi
- Department of Medicinal Chemistry and Pharmacognosy, College of Pharmacy, University of Illinois, Chicago , Rockford Health Sciences Campus, 1601 Parkview Avenue, Rockford, Illinois 61107, United States
| |
Collapse
|
7
|
Lee HS, Lee DH, Cho HK, Kim SH, Auh JH, Pai HS. InsP6-sensitive variants of the Gle1 mRNA export factor rescue growth and fertility defects of the ipk1 low-phytic-acid mutation in Arabidopsis. THE PLANT CELL 2015; 27:417-31. [PMID: 25670768 PMCID: PMC4456929 DOI: 10.1105/tpc.114.132134] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/12/2014] [Revised: 12/19/2014] [Accepted: 01/22/2015] [Indexed: 05/22/2023]
Abstract
Myo-inositol-1,2,3,4,5,6-hexakisphosphate (InsP(6)), also known as phytic acid, accumulates in large quantities in plant seeds, serving as a phosphorus reservoir, but is an animal antinutrient and an important source of water pollution. Here, we report that Gle1 (GLFG lethal 1) in conjunction with InsP(6) functions as an activator of the ATPase/RNA helicase LOS4 (low expression of osmotically responsive genes 4), which is involved in mRNA export in plants, supporting the Gle1-InsP(6)-Dbp5 (LOS4 homolog) paradigm proposed in yeast. Interestingly, plant Gle1 proteins have modifications in several key residues of the InsP(6) binding pocket, which reduce the basicity of the surface charge. Arabidopsis thaliana Gle1 variants containing mutations that increase the basic charge of the InsP(6) binding surface show increased sensitivity to InsP(6) concentrations for the stimulation of LOS4 ATPase activity in vitro. Expression of the Gle1 variants with enhanced InsP(6) sensitivity rescues the mRNA export defect of the ipk1 (inositol 1,3,4,5,6-pentakisphosphate 2-kinase) InsP(6)-deficient mutant and, furthermore, significantly improves vegetative growth, seed yield, and seed performance of the mutant. These results suggest that Gle1 is an important factor responsible for mediating InsP(6) functions in plant growth and reproduction and that Gle1 variants with increased InsP(6) sensitivity may be useful for engineering high-yielding low-phytate crops.
Collapse
Affiliation(s)
- Ho-Seok Lee
- Department of Systems Biology, Yonsei University, Seoul 120-749, Korea
| | - Du-Hwa Lee
- Department of Systems Biology, Yonsei University, Seoul 120-749, Korea
| | - Hui Kyung Cho
- Department of Systems Biology, Yonsei University, Seoul 120-749, Korea
| | - Song Hee Kim
- Division of Food Science and Technology, Chung-Ang University, Ansung, Kyunggi-do 456-756, Korea
| | - Joong Hyuck Auh
- Division of Food Science and Technology, Chung-Ang University, Ansung, Kyunggi-do 456-756, Korea
| | - Hyun-Sook Pai
- Department of Systems Biology, Yonsei University, Seoul 120-749, Korea
| |
Collapse
|
8
|
Erkizan HV, Schneider JA, Sajwan K, Graham GT, Griffin B, Chasovskikh S, Youbi SE, Kallarakal A, Chruszcz M, Padmanabhan R, Casey JL, Üren A, Toretsky JA. RNA helicase A activity is inhibited by oncogenic transcription factor EWS-FLI1. Nucleic Acids Res 2015; 43:1069-80. [PMID: 25564528 PMCID: PMC4333382 DOI: 10.1093/nar/gku1328] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
RNA helicases impact RNA structure and metabolism from transcription through translation, in part through protein interactions with transcription factors. However, there is limited knowledge on the role of transcription factor influence upon helicase activity. RNA helicase A (RHA) is a DExH-box RNA helicase that plays multiple roles in cellular biology, some functions requiring its activity as a helicase while others as a protein scaffold. The oncogenic transcription factor EWS-FLI1 requires RHA to enable Ewing sarcoma (ES) oncogenesis and growth; a small molecule, YK-4-279 disrupts this complex in cells. Our current study investigates the effect of EWS-FLI1 upon RHA helicase activity. We found that EWS-FLI1 reduces RHA helicase activity in a dose-dependent manner without affecting intrinsic ATPase activity; however, the RHA kinetics indicated a complex model. Using separated enantiomers, only (S)-YK-4-279 reverses the EWS-FLI1 inhibition of RHA helicase activity. We report a novel RNA binding property of EWS-FLI1 leading us to discover that YK-4-279 inhibition of RHA binding to EWS-FLI1 altered the RNA binding profile of both proteins. We conclude that EWS-FLI1 modulates RHA helicase activity causing changes in overall transcriptome processing. These findings could lead to both enhanced understanding of oncogenesis and provide targets for therapy.
Collapse
Affiliation(s)
- Hayriye Verda Erkizan
- Department of Oncology, Lombardi Comprehensive Cancer Center, Georgetown University, 3970 Reservoir Road NW, New Research Building E316, Washington, DC 20007, USA
| | - Jeffrey A Schneider
- Department of Oncology, Lombardi Comprehensive Cancer Center, Georgetown University, 3970 Reservoir Road NW, New Research Building E316, Washington, DC 20007, USA
| | - Kamal Sajwan
- Department of Oncology, Lombardi Comprehensive Cancer Center, Georgetown University, 3970 Reservoir Road NW, New Research Building E316, Washington, DC 20007, USA
| | - Garrett T Graham
- Department of Oncology, Lombardi Comprehensive Cancer Center, Georgetown University, 3970 Reservoir Road NW, New Research Building E316, Washington, DC 20007, USA
| | - Brittany Griffin
- Department of Microbiology and Immunology, Georgetown University Medical Center, SW 309 Med-Dent, Washington, DC 20007, USA
| | - Sergey Chasovskikh
- Department of Radiation Medicine, Georgetown University Medical Center, 3970 Reservoir Road NW, New Research Building E220, Washington, DC 20007, USA
| | - Sarah E Youbi
- Department of Oncology, Lombardi Comprehensive Cancer Center, Georgetown University, 3970 Reservoir Road NW, New Research Building E316, Washington, DC 20007, USA
| | - Abraham Kallarakal
- Department of Oncology, Lombardi Comprehensive Cancer Center, Georgetown University, 3970 Reservoir Road NW, New Research Building E316, Washington, DC 20007, USA
| | - Maksymilian Chruszcz
- Department of Chemistry and Biochemistry, University of South Carolina, 631 Sumter Street, Columbia, SC 29208, USA
| | - Radhakrishnan Padmanabhan
- Department of Microbiology and Immunology, Georgetown University Medical Center, SW 309 Med-Dent, Washington, DC 20007, USA
| | - John L Casey
- Department of Microbiology and Immunology, Georgetown University Medical Center, SW 309 Med-Dent, Washington, DC 20007, USA
| | - Aykut Üren
- Department of Oncology, Lombardi Comprehensive Cancer Center, Georgetown University, 3970 Reservoir Road NW, New Research Building E316, Washington, DC 20007, USA
| | - Jeffrey A Toretsky
- Department of Oncology, Lombardi Comprehensive Cancer Center, Georgetown University, 3970 Reservoir Road NW, New Research Building E316, Washington, DC 20007, USA
| |
Collapse
|
9
|
Nucleoporin FG domains facilitate mRNP remodeling at the cytoplasmic face of the nuclear pore complex. Genetics 2014; 197:1213-24. [PMID: 24931410 DOI: 10.1534/genetics.114.164012] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Directional export of messenger RNA (mRNA) protein particles (mRNPs) through nuclear pore complexes (NPCs) requires multiple factors. In Saccharomyces cerevisiae, the NPC proteins Nup159 and Nup42 are asymmetrically localized to the cytoplasmic face and have distinct functional domains: a phenylalanine-glycine (FG) repeat domain that docks mRNP transport receptors and domains that bind the DEAD-box ATPase Dbp5 and its activating cofactor Gle1, respectively. We speculated that the Nup42 and Nup159 FG domains play a role in positioning mRNPs for the terminal mRNP-remodeling steps carried out by Dbp5. Here we find that deletion (Δ) of both the Nup42 and Nup159 FG domains results in a cold-sensitive poly(A)+ mRNA export defect. The nup42ΔFG nup159ΔFG mutant also has synthetic lethal genetic interactions with dbp5 and gle1 mutants. RNA cross-linking experiments further indicate that the nup42ΔFG nup159ΔFG mutant has a reduced capacity for mRNP remodeling during export. To further analyze the role of these FG domains, we replaced the Nup159 or Nup42 FG domains with FG domains from other Nups. These FG "swaps" demonstrate that only certain FG domains are functional at the NPC cytoplasmic face. Strikingly, fusing the Nup42 FG domain to the carboxy-terminus of Gle1 bypasses the need for the endogenous Nup42 FG domain, highlighting the importance of proximal positioning for these factors. We conclude that the Nup42 and Nup159 FG domains target the mRNP to Gle1 and Dbp5 for mRNP remodeling at the NPC. Moreover, these results provide key evidence that character and context play a direct role in FG domain function and mRNA export.
Collapse
|
10
|
Braud C, Zheng W, Xiao W. Identification and analysis of LNO1-like and AtGLE1-like nucleoporins in plants. PLANT SIGNALING & BEHAVIOR 2013; 8:e27376. [PMID: 24384931 PMCID: PMC4091346 DOI: 10.4161/psb.27376] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/22/2013] [Revised: 11/28/2013] [Accepted: 11/28/2013] [Indexed: 06/03/2023]
Abstract
Nucleoporins (Nups) are building blocks of the nuclear pore complex (NPC) that mediate cargo trafficking between the nucleus and the cytoplasm. Although the physical structure of the NPC is well studied in yeast and vertebrates, little is known about the structure of NPCs or the function of most Nups in plants. Recently we demonstrated two Nups in Arabidopsis: LONO1 (LNO1), homolog of human NUP214 and yeast Nup159, and AtGLE1, homolog of yeast Gle1, are required for early embryogenesis and seed development. To identify LNO1 and AtGLE1 homologs in other plant species, we searched the protein databases and identified 30 LNO1-like and 35 AtGLE1-like proteins from lower plant species to higher plants. Furthermore, phylogenetic analyses indicate that the evolutionary trees of these proteins follow expected plant phylogenies. High sequence homology and conserved domain structure of these nucleoporins suggest important functions of these proteins in nucleocytoplasmic transport, growth and development in plants.
Collapse
|
11
|
Insights into mRNA export-linked molecular mechanisms of human disease through a Gle1 structure-function analysis. Adv Biol Regul 2013; 54:74-91. [PMID: 24275432 DOI: 10.1016/j.jbior.2013.10.002] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2013] [Revised: 10/23/2013] [Accepted: 10/28/2013] [Indexed: 02/02/2023]
Abstract
A critical step during gene expression is the directional export of nuclear messenger (m)RNA through nuclear pore complexes (NPCs) to the cytoplasm. During export, Gle1 in conjunction with inositol hexakisphosphate (IP6) spatially regulates the activity of the DEAD-box protein Dbp5 at the NPC cytoplasmic face. GLE1 mutations are causally linked to the human diseases lethal congenital contracture syndrome 1 (LCCS-1) and lethal arthrogryposis with anterior horn cell disease (LAAHD). Here, structure prediction and functional analysis provide strong evidence to suggest that the LCCS-1 and LAAHD disease mutations disrupt the function of Gle1 in mRNA export. Strikingly, direct fluorescence microscopy in living cells reveals a dramatic loss of steady-state NPC localization for GFP-gle1 proteins expressed from human gle1 genes harboring LAAHD and LCCS-1 mutations. The potential significance of these residues is further clarified by analyses of sequence and predicted structural conservation. This work offers insights into the perturbed mechanisms underlying human LCCS-1 and LAAHD disease states and emphasizes the potential impact of altered mRNA transport and gene expression in human disease.
Collapse
|
12
|
Tumour cells can employ extracellular Ins(1,2,3,4,5,6)P6 and multiple inositol-polyphosphate phosphatase 1 (MINPP1) dephosphorylation to improve their proliferation. Biochem J 2013. [DOI: 10.1042/bj20121524] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
InsP6 [Ins(1,2,3,4,5,6)P6; phytate] is the most abundant inositol phosphate in mammalian cells with cytosolic/nuclear concentrations of up to 50 μM. We noticed that InsP6 in culture medium at a concentration of ≤50 μM significantly stimulates H1299 tumour cell growth, whereas larger concentrations of InsP6 inhibit growth. A detailed study of the fate of 30 μM InsP6 added to H199 cells revealed a major fraction of InsP6 initially precipitates as cell-surface metal complexes, but becomes slowly re-solubilized by extracellular dephosphorylation first to InsP3 isomers and subsequently to free myo-inositol. The precipitated metal–InsP6 complex is endocytosed in a receptor-independent but intact-glycocalyx-dependent manner and appears in lysosomes, where it is immediately dephosphorylated to Ins(1,2,4,5,6)P5 and very slowly to free inositol. By RNA knockdown, we identified secreted and lysosome targeted MINPP1 (multiple inositol-polyphosphate phosphatase 1), the mammalian 3-phytase, to be essentially involved both in extracellular and in lysosomal InsP6 dephosphorylation. The results of the present study indicate that tumour cells employ this enzyme to utilize the micronutrients myo-inositol and metal-phosphate when encountering extracellular InsP6 and thus to enhance their growth potential.
Collapse
|
13
|
Tieg B, Krebber H. Dbp5 - from nuclear export to translation. BIOCHIMICA ET BIOPHYSICA ACTA-GENE REGULATORY MECHANISMS 2012; 1829:791-8. [PMID: 23128325 DOI: 10.1016/j.bbagrm.2012.10.010] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/30/2012] [Revised: 10/17/2012] [Accepted: 10/26/2012] [Indexed: 12/17/2022]
Abstract
The DEAD-box RNA helicase Dbp5 is an essential and conserved mRNA export factor which functions in the ATP dependent remodeling of RNA/protein complexes. As such it displaces mRNA bound proteins at the cytoplasmic site of the nuclear pore complex. For the regulation of its RNA-dependent ATPase activity during late steps of nuclear transport, Dbp5 requires the nucleoporin Nup159 and its cofactors Gle1 and IP6. In addition to its role in mRNA export, a second important function of Dbp5 was identified in translation termination, where it acts together with eRF1 once the translation machinery has reached the stop codon. Similar to mRNA export, this function also requires Gle1-IP6, however, the counterpart of Nup159 is still missing. Potential other functions of the nucleo-cytoplasmic protein Dbp5 are discussed as well as its substrate specificity and details in its regulatory cycle that are based on recent biochemical and structural characterization. This article is part of a Special Issue entitled: The Biology of RNA helicases - Modulation for life.
Collapse
Affiliation(s)
- Bettina Tieg
- Georg-August Universität Göttingen, Göttingen, Germany
| | | |
Collapse
|
14
|
Romes EM, Tripathy A, Slep KC. Structure of a yeast Dyn2-Nup159 complex and molecular basis for dynein light chain-nuclear pore interaction. J Biol Chem 2012; 287:15862-73. [PMID: 22411995 DOI: 10.1074/jbc.m111.336172] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The nuclear pore complex gates nucleocytoplasmic transport through a massive, eight-fold symmetric channel capped by a nucleoplasmic basket and structurally unique, cytoplasmic fibrils whose tentacles bind and regulate asymmetric traffic. The conserved Nup82 complex, composed of Nsp1, Nup82, and Nup159, forms the unique cytoplasmic fibrils that regulate mRNA nuclear export. Although the nuclear pore complex plays a fundamental, conserved role in nuclear trafficking, structural information about the cytoplasmic fibrils is limited. Here, we investigate the structural and biochemical interactions between Saccharomyces cerevisiae Nup159 and the nucleoporin, Dyn2. We find that Dyn2 is predominantly a homodimer and binds arrayed sites on Nup159, promoting the Nup159 parallel homodimerization. We present the first structure of Dyn2, determined at 1.85 Å resolution, complexed with a Nup159 target peptide. Dyn2 resembles homologous metazoan dynein light chains, forming homodimeric composite substrate binding sites that engage two independent 10-residue target motifs, imparting a β-strand structure to each peptide via antiparallel extension of the Dyn2 core β-sandwich. Dyn2 recognizes a highly conserved QT motif while allowing sequence plasticity in the flanking residues of the peptide. Isothermal titration calorimetric analysis of the comparative binding of Dyn2 to two Nup159 target sites shows similar affinities (18 and 13 μM), but divergent thermal binding modes. Dyn2 homodimers are arrayed in the crystal lattice, likely mimicking the arrayed architecture of Dyn2 on the Nup159 multivalent binding sites. Crystallographic interdimer interactions potentially reflect a cooperative basis for Dyn2-Nup159 complex formation. Our data highlight the determinants that mediate oligomerization of the Nup82 complex and promote a directed, elongated cytoplasmic fibril architecture.
Collapse
Affiliation(s)
- Erin M Romes
- Department of Biochemistry and Biophysics, University of North Carolina, Chapel Hill, North Carolina 27599, USA
| | | | | |
Collapse
|
15
|
Schlatter ID, Meira M, Ueberschlag V, Hoepfner D, Movva R, Hynes NE. MHO1, an evolutionarily conserved gene, is synthetic lethal with PLC1; Mho1p has a role in invasive growth. PLoS One 2012; 7:e32501. [PMID: 22412880 PMCID: PMC3296727 DOI: 10.1371/journal.pone.0032501] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2011] [Accepted: 01/27/2012] [Indexed: 01/10/2023] Open
Abstract
The novel protein Memo (Mediator of ErbB2 driven cell motility) was identified in a screen for ErbB2 interacting proteins and found to have an essential function in cell motility. Memo is evolutionarily conserved with homologs found in all branches of life; the human and yeast proteins have a similarity of >50%. In the present study we used the model organism S. cerevisiae to characterize the Memo-homologue Mho1 (Yjr008wp) and to investigate its function in yeast. In a synthetic lethal screen we found MHO1 as a novel synthetic lethal partner of PLC1, which encodes the single phospholipase C in yeast. Double-deleted cells lacking MHO1 and PLC1, proliferate for up to ten generations. Introduction of human Memo into the memoΔplc1Δ strain rescued the synthetic lethal phenotype suggesting that yeast and human proteins have similar functions. Mho1 is present in the cytoplasm and the nucleus of yeast cells; the same distribution of Memo was found in mammalian cells. None of the Memo homologues have a characteristic nuclear localization sequence, however, a conserved nuclear export sequence is found in all. In mammalian cells, blocking nuclear export with Leptomycin B led to nuclear Memo accumulation, suggesting that it is actively exported from the nucleus. In yeast MHO1 expression is induced by stress conditions. Since invasive growth in S. cerevisiea is also stress-induced, we tested Mho1's role in this response. MHO1 deletion had no effect on invasion induced by nutrient deprivation, however, Mho1 overexpression blocked the invasive ability of yeast cells, suggesting that Mho1 might be acting in a dominant negative manner. Taken together, our results show that MHO1 is a novel synthetic lethal interactor with PLC1, and that both gene products are required for proliferation. Moreover, a role for Memo in cell motility/invasion appears to be conserved across species.
Collapse
Affiliation(s)
- Ivan D. Schlatter
- Friedrich Miescher Institute for Biomedical Research, Basel, Switzerland
| | - Maria Meira
- Friedrich Miescher Institute for Biomedical Research, Basel, Switzerland
| | | | | | - Rao Movva
- Novartis Institutes for Biomedical Research, Basel, Switzerland
| | - Nancy E. Hynes
- Friedrich Miescher Institute for Biomedical Research, Basel, Switzerland
- * E-mail:
| |
Collapse
|
16
|
Valkov E, Dean JC, Jani D, Kuhlmann SI, Stewart M. Structural basis for the assembly and disassembly of mRNA nuclear export complexes. BIOCHIMICA ET BIOPHYSICA ACTA-GENE REGULATORY MECHANISMS 2012; 1819:578-92. [PMID: 22406340 DOI: 10.1016/j.bbagrm.2012.02.017] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/22/2011] [Revised: 01/26/2012] [Accepted: 02/17/2012] [Indexed: 12/17/2022]
Abstract
Most of the individual components of the nuclear elements of the gene expression pathway have been identified and high-resolution structural information is becoming available for many of them. Information is also starting to become available on the larger complexes they form and is beginning to give clues about how the dynamics of their interactions generate function. Although the translocation of export-competent messenger ribonucleoprotein particles (mRNPs) through the nuclear pore transport channel that is mediated by interactions with nuclear pore proteins (nucleoporins) is relatively well understood, the precise molecular mechanisms underlying the assembly of export-competent mRNPs in the nucleus and their Dbp5-mediated disassembly in the cytoplasm is less well defined. Considerable information has been obtained on the structure of Dbp5 in its different nucleotide-bound states and in complex with Gle1 or Nup159/NUP214. Although the precise manner by which the Dbp5 ATPase cycle is coupled to mRNP remodelling remains to be established, current models capture many key details of this process. The formation of export-competent mRNPs in the nucleus remains an elusive component of this pathway and the precise nature of the remodelling that generates these mRNPs as well as detailed understanding of the molecular mechanisms by which this step is integrated with the transcriptional, splicing and polyadenylation machinery by the TREX and TREX-2 complexes remain obscure. This article is part of a Special Issue entitled: Nuclear Transport and RNA Processing.
Collapse
Affiliation(s)
- Eugene Valkov
- MRC Laboratory of Molecular Biology, Hills Road, Cambridge, UK
| | | | | | | | | |
Collapse
|
17
|
Bolger TA, Wente SR. Gle1 is a multifunctional DEAD-box protein regulator that modulates Ded1 in translation initiation. J Biol Chem 2011; 286:39750-9. [PMID: 21949122 DOI: 10.1074/jbc.m111.299321] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
DEAD-box protein (Dbp) family members are essential for gene expression; however, their precise roles and regulation are not fully defined. During messenger (m)RNA export, Gle1 bound to inositol hexakisphosphate (IP(6)) acts via Dbp5 to facilitate remodeling of mRNA-protein complexes. In contrast, here we define a novel Gle1 role in translation initiation through regulation of a different DEAD-box protein, the initiation factor Ded1. We find that Gle1 physically and genetically interacts with Ded1. Surprisingly, whereas Gle1 stimulates Dbp5, it inhibits Ded1 ATPase activity in vitro, and IP(6) does not affect this inhibition. Functionally, a gle1-4 mutant specifically suppresses initiation defects in a ded1-120 mutant, and ded1 and gle1 mutants have complementary perturbations in AUG start site recognition. Consistent with this role in initiation, Gle1 inhibits translation in vitro in competent extracts. These results indicate that Gle1 has a direct role in initiation and negatively regulates Ded1. Together, the differential regulation of two distinct DEAD-box proteins by a common factor (Gle1) establishes a new paradigm for controlling gene expression and coupling translation with mRNA export.
Collapse
Affiliation(s)
- Timothy A Bolger
- Department of Cell & Developmental Biology, Vanderbilt University School of Medicine, Nashville, Tennessee 37232, USA
| | | |
Collapse
|
18
|
Hanakahi L. Effect of the Inositol Polyphosphate InsP6 on DNA-PK–Dependent Phosphorylation. Mol Cancer Res 2011; 9:1366-76. [DOI: 10.1158/1541-7786.mcr-11-0230] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
|
19
|
Noble KN, Tran EJ, Alcázar-Román AR, Hodge CA, Cole CN, Wente SR. The Dbp5 cycle at the nuclear pore complex during mRNA export II: nucleotide cycling and mRNP remodeling by Dbp5 are controlled by Nup159 and Gle1. Genes Dev 2011; 25:1065-77. [PMID: 21576266 DOI: 10.1101/gad.2040611] [Citation(s) in RCA: 87] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Essential messenger RNA (mRNA) export factors execute critical steps to mediate directional transport through nuclear pore complexes (NPCs). At cytoplasmic NPC filaments, the ATPase activity of DEAD-box protein Dbp5 is activated by inositol hexakisphosphate (IP(6))-bound Gle1 to mediate remodeling of mRNA-protein (mRNP) complexes. Whether a single Dbp5 executes multiple remodeling events and how Dbp5 is recycled are unknown. Evidence suggests that Dbp5 binding to Nup159 is required for controlling interactions with Gle1 and the mRNP. Using in vitro reconstitution assays, we found here that Nup159 is specifically required for ADP release from Dbp5. Moreover, Gle1-IP(6) stimulates ATP binding, thus priming Dbp5 for RNA loading. In vivo, a dbp5-R256D/R259D mutant with reduced ADP binding bypasses the need for Nup159 interaction. However, NPC spatial control is important, as a dbp5-R256D/R259D nup42Δ double mutant is temperature-sensitive for mRNA export. Further analysis reveals that remodeling requires a conformational shift to the Dbp5-ADP form. ADP release factors for DEAD-box proteins have not been reported previously and reflect a new paradigm for regulation. We propose a model wherein Nup159 and Gle1-IP(6) regulate Dbp5 cycles by controlling its nucleotide-bound state, allowing multiple cycles of mRNP remodeling by a single Dbp5 at the NPC.
Collapse
Affiliation(s)
- Kristen N Noble
- Department of Cell and Developmental Biology, Vanderbilt University School of Medicine, Nashville, Tennessee 37232, USA
| | | | | | | | | | | |
Collapse
|
20
|
Alcázar-Román AR, Bolger TA, Wente SR. Control of mRNA export and translation termination by inositol hexakisphosphate requires specific interaction with Gle1. J Biol Chem 2010; 285:16683-92. [PMID: 20371601 DOI: 10.1074/jbc.m109.082370] [Citation(s) in RCA: 66] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The unidirectional translocation of messenger RNA (mRNA) through the aqueous channel of the nuclear pore complex (NPC) is mediated by interactions between soluble mRNA export factors and distinct binding sites on the NPC. At the cytoplasmic side of the NPC, the conserved mRNA export factors Gle1 and inositol hexakisphosphate (IP(6)) play an essential role in mRNA export by activating the ATPase activity of the DEAD-box protein Dbp5, promoting localized messenger ribonucleoprotein complex remodeling, and ensuring the directionality of the export process. In addition, Dbp5, Gle1, and IP(6) are also required for proper translation termination. However, the specificity of the IP(6)-Gle1 interaction in vivo is unknown. Here, we characterize the biochemical interaction between Gle1 and IP(6) and the relationship to Dbp5 binding and stimulation. We identify Gle1 residues required for IP(6) binding and show that these residues are needed for IP(6)-dependent Dbp5 stimulation in vitro. Furthermore, we demonstrate that Gle1 is the primary target of IP(6) for both mRNA export and translation termination in vivo. In Saccharomyces cerevisiae cells, the IP(6)-binding mutants recapitulate all of the mRNA export and translation termination defects found in mutants depleted of IP(6). We conclude that Gle1 specifically binds IP(6) and that this interaction is required for the full potentiation of Dbp5 ATPase activity during both mRNA export and translation termination.
Collapse
Affiliation(s)
- Abel R Alcázar-Román
- Department of Cell and Developmental Biology, Vanderbilt University School of Medicine, Nashville, Tennessee 37232-8240, USA
| | | | | |
Collapse
|
21
|
Structure of the C-terminus of the mRNA export factor Dbp5 reveals the interaction surface for the ATPase activator Gle1. Proc Natl Acad Sci U S A 2009; 106:16251-6. [PMID: 19805289 DOI: 10.1073/pnas.0902251106] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
The DExD/H-box RNA-dependent ATPase Dbp5 plays an essential role in the nuclear export of mRNA. Dbp5 localizes to the nuclear pore complex, where its ATPase activity is stimulated by Gle1 and its coactivator inositol hexakisphosphate. Here, we present the crystal structure of the C-terminal domain of Dbp5, refined to 1.8 A. The structure reveals a RecA-like fold that contains two defining characteristics not present in other structurally characterized DExD/H-box proteins: a C-terminal alpha-helix and a loop connecting beta5 and alpha4, both of which are composed of conserved and unique elements in the Dbp5 primary sequence. Using structure-guided mutagenesis, we have identified several charged surface residues that, when mutated, weaken the binding of Gle1 and inhibit the ability of Gle1 to stimulate Dbp5's ATPase activity. In vivo analysis of the same mutations reveals that those mutants displaying the weakest ATPase stimulation in vitro are also unable to support yeast growth. Analysis of the correlation between the in vitro and in vivo data indicates that a threshold level of Dbp5 ATPase activity is required for cellular mRNA export that is not met by the unstimulated enzyme, suggesting a possible mechanism by which Dbp5's activity can be modulated to regulate mRNA export.
Collapse
|
22
|
The behaviour of inositol 1,3,4,5,6-pentakisphosphate in the presence of the major biological metal cations. J Biol Inorg Chem 2009; 14:1001-13. [PMID: 19415348 PMCID: PMC2745655 DOI: 10.1007/s00775-009-0510-z] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2009] [Accepted: 04/20/2009] [Indexed: 01/07/2023]
Abstract
The inositol phosphates are ubiquitous metabolites in eukaryotes, of which the most abundant are inositol hexakisphosphate (InsP 6) and inositol 1,3,4,5,6-pentakisphosphate [Ins(1,3,4,5,6)P5)]. These two compounds, poorly understood functionally, have complicated complexation and solid formation behaviours with multivalent cations. For InsP 6, we have previously described this chemistry and its biological implications (Veiga et al. in J Inorg Biochem 100:1800, 2006; Torres et al. in J Inorg Biochem 99:828, 2005). We now cover similar ground for Ins(1,3,4,5,6)P5, describing its interactions in solution with Na+, K+, Mg2+, Ca2+, Cu2+, Fe2+ and Fe3+, and its solid-formation equilibria with Ca2+ and Mg2+. Ins(1,3,4,5,6)P5 forms soluble complexes of 1:1 stoichiometry with all multivalent cations studied. The affinity for Fe3+ is similar to that of InsP6 and inositol 1,2,3-trisphosphate, indicating that the 1,2,3-trisphosphate motif, which Ins(1,3,4,5,6)P5 lacks, is not absolutely necessary for high-affinity Fe3+ complexation by inositol phosphates, even if it is necessary for their prevention of the Fenton reaction. With excess Ca2+ and Mg2+, Ins(1,3,4,5,6)P5 also forms the polymetallic complexes [M4(H2L)] [where L is fully deprotonated Ins(1,3,4,5,6)P5]. However, unlike InsP6, Ins(1,3,4,5,6)P5 is predicted not to be fully associated with Mg2+ under simulated cytosolic/nuclear conditions. The neutral Mg2+ and Ca2+ complexes have significant windows of solubility, but they precipitate as [Mg4(H2L)] x 23H2O or [Ca4(H2L)] x 16H2O whenever they exceed 135 and 56 microM in concentration, respectively. Nonetheless, the low stability of the [M4(H2L)] complexes means that the 1:1 species contribute to the overall solubility of Ins(1,3,4,5,6)P 5 even under significant Mg2+ or Ca2+ excesses. We summarize the solubility behaviour of Ins(1,3,4,5,6)P5 in straightforward plots.
Collapse
|
23
|
The mRNA export protein DBP5 binds RNA and the cytoplasmic nucleoporin NUP214 in a mutually exclusive manner. Nat Struct Mol Biol 2009; 16:247-54. [PMID: 19219046 DOI: 10.1038/nsmb.1561] [Citation(s) in RCA: 136] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2008] [Accepted: 01/16/2009] [Indexed: 11/08/2022]
Abstract
The DEAD-box protein DBP5 is essential for mRNA export in both yeast and humans. It binds RNA and is concentrated and locally activated at the cytoplasmic side of the nuclear pore complex. We have determined the crystal structures of human DBP5 bound to RNA and AMPPNP, and bound to the cytoplasmic nucleoporin NUP214. The structures reveal that binding of DBP5 to nucleic acid and to NUP214 is mutually exclusive. Using in vitro assays, we demonstrate that NUP214 decreases both the RNA binding and ATPase activities of DBP5. The interactions are mediated by conserved residues, implying a conserved recognition mechanism. These results suggest a framework for the consecutive steps leading to the release of mRNA at the final stages of nuclear export. More generally, they provide a paradigm for how binding of regulators can specifically inhibit DEAD-box proteins.
Collapse
|
24
|
Dual functions for the Schizosaccharomyces pombe inositol kinase Ipk1 in nuclear mRNA export and polarized cell growth. EUKARYOTIC CELL 2008; 8:134-46. [PMID: 19047361 DOI: 10.1128/ec.00279-08] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
The inositol 1,3,4,5,6-pentakisphosphate (IP(5)) 2-kinase (Ipk1) catalyzes the production of inositol hexakisphosphate (IP(6)) in eukaryotic cells. Previous studies have shown that IP(6) is required for efficient nuclear mRNA export in the budding yeast Saccharomyces cerevisiae. Here, we report the first functional analysis of ipk1(+) in Schizosaccharomyces pombe. S. pombe Ipk1 (SpIpk1) is unique among Ipk1 orthologues in that it harbors a novel amino (N)-terminal domain with coiled-coil structural motifs similar to those of BAR (Bin-amphiphysin-Rvs) domain proteins. Mutants with ipk1(+) deleted (ipk1Delta) had mRNA export defects as well as pleiotropic defects in polarized growth, cell morphology, endocytosis, and cell separation. The SpIpk1 catalytic carboxy-terminal domain was required to rescue these defects, and the mRNA export block was genetically linked to SpDbp5 function and, likely, IP(6) production. However, the overexpression of the N-terminal domain alone also inhibited these functions in wild-type cells. This revealed a distinct noncatalytic function for the N-terminal domain. To test for connections with other inositol polyphosphates, we also analyzed whether the loss of asp1(+) function, encoding an IP(6) kinase downstream of Ipk1, had an effect on ipk1Delta cells. The asp1Delta mutant alone did not block mRNA export, and its cell morphology, polarized growth, and endocytosis defects were less severe than those of ipk1Delta cells. Moreover, ipk1Delta asp1Delta double mutants had altered inositol polyphosphate levels distinct from those of the ipk1Delta mutant. This suggested novel roles for asp1(+) upstream of ipk1(+). We propose that IP(6) production is a key signaling linchpin for regulating multiple essential cellular processes.
Collapse
|
25
|
Synthetic genetic array analysis in Saccharomyces cerevisiae provides evidence for an interaction between RAT8/DBP5 and genes encoding P-body components. Genetics 2008; 179:1945-55. [PMID: 18689878 DOI: 10.1534/genetics.108.091256] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Coordination of the multiple steps of mRNA biogenesis helps to ensure proper regulation of gene expression. The Saccharomyces cerevisiae DEAD-box protein Rat8p/Dbp5p is an essential mRNA export factor that functions at the nuclear pore complex (NPC) where it is thought to remodel mRNA/protein complexes during mRNA export. Rat8p also functions in translation termination and has been implicated in functioning during early transcription. We conducted a synthetic genetic array analysis (SGA) using a strain harboring the temperature-sensitive rat8-2 allele. Although RAT8 had been shown to interact genetically with >15 other genes, we identified >40 additional genes whose disruption in a rat8-2 background causes synthetic lethality or dramatically reduced growth. Included were five that encode components of P-bodies, sites of cytoplasmic mRNA turnover and storage. Wild-type Rat8p localizes to NPCs and diffusely throughout the cell but rat8-2p localized to cytoplasmic granules at nonpermissive temperature that are distinct from P-bodies. In some genetic backgrounds, these granules also contain poly(A)-binding protein, Pab1p, and additional mRNA export factors. Although these foci are distinct from P-bodies, the two merge under heat-stress conditions. We suggest that these granules reflect defective mRNP remodeling during mRNA export and during cytoplasmic mRNA metabolism.
Collapse
|
26
|
The DEAD-box protein Dbp5 controls mRNA export by triggering specific RNA:protein remodeling events. Mol Cell 2008; 28:850-9. [PMID: 18082609 DOI: 10.1016/j.molcel.2007.09.019] [Citation(s) in RCA: 174] [Impact Index Per Article: 10.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2007] [Revised: 09/11/2007] [Accepted: 09/25/2007] [Indexed: 01/16/2023]
Abstract
Messenger RNA (mRNA) export involves the unidirectional passage of ribonucleoprotein particles (RNPs) through nuclear pore complexes (NPCs), presumably driven by the ATP-dependent activity of the DEAD-box protein Dbp5. Here we report that Dbp5 functions as an RNP remodeling protein to displace the RNA-binding protein Nab2 from RNA. Strikingly, the ADP-bound form of Dbp5 and not ATP hydrolysis is required for RNP remodeling. In vivo studies with nab2 and dbp5 mutants show that a Nab2-bound mRNP is a physiological Dbp5 target. We propose that Dbp5 functions as a nucleotide-dependent switch to control mRNA export efficiency and release the mRNP from the NPC.
Collapse
|
27
|
Determining the architectures of macromolecular assemblies. Nature 2008; 450:683-94. [PMID: 18046405 DOI: 10.1038/nature06404] [Citation(s) in RCA: 419] [Impact Index Per Article: 26.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2007] [Accepted: 10/22/2007] [Indexed: 11/08/2022]
Abstract
To understand the workings of a living cell, we need to know the architectures of its macromolecular assemblies. Here we show how proteomic data can be used to determine such structures. The process involves the collection of sufficient and diverse high-quality data, translation of these data into spatial restraints, and an optimization that uses the restraints to generate an ensemble of structures consistent with the data. Analysis of the ensemble produces a detailed architectural map of the assembly. We developed our approach on a challenging model system, the nuclear pore complex (NPC). The NPC acts as a dynamic barrier, controlling access to and from the nucleus, and in yeast is a 50 MDa assembly of 456 proteins. The resulting structure, presented in an accompanying paper, reveals the configuration of the proteins in the NPC, providing insights into its evolution and architectural principles. The present approach should be applicable to many other macromolecular assemblies.
Collapse
|
28
|
A class II histone deacetylase acts on newly synthesized histones in Tetrahymena. EUKARYOTIC CELL 2008; 7:471-82. [PMID: 18178773 DOI: 10.1128/ec.00409-07] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Newly synthesized histones are acetylated prior to their deposition into nucleosomes. Following nucleosome formation and positioning, they are rapidly deacetylated, an event that coincides with further maturation of the chromatin fiber. The histone deacetylases (HDACs) used for histone deposition and de novo chromatin formation are poorly understood. In the ciliate Tetrahymena thermophila, transcription-related deacetylation in the macronucleus is physically separated from deposition-related deacetylation in the micronucleus. This feature was utilized to identify an HDAC named Thd2, a class II HDAC that acts on newly synthesized histones to remove deposition-related acetyl moieties. The THD2 transcript is alternatively spliced, and the major form contains a putative inositol polyphosphate kinase (IPK) domain similar to Ipk2, an enzyme that promotes chromatin remodeling by SWI/SNF remodeling complexes. Cells lacking Thd2, which retain deposition-related acetyl moieties on new histones, exhibit chromatin and cytological phenotypes indicative of a role for Thd2 in chromatin maturation, including the proteolytic processing of histone H3.
Collapse
|
29
|
Mitsuhashi N, Kondo M, Nakaune S, Ohnishi M, Hayashi M, Hara-Nishimura I, Richardson A, Fukaki H, Nishimura M, Mimura T. Localization of myo-inositol-1-phosphate synthase to the endosperm in developing seeds of Arabidopsis. JOURNAL OF EXPERIMENTAL BOTANY 2008; 59:3069-76. [PMID: 18603618 PMCID: PMC2504351 DOI: 10.1093/jxb/ern161] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/15/2008] [Revised: 05/07/2008] [Accepted: 05/12/2008] [Indexed: 05/19/2023]
Abstract
Expression and localization of myo-inositol-1-phosphate synthase (MIPS) in developing seeds of Arabidopsis thaliana was investigated. MIPS is an essential enzyme for production of inositol and inositol phosphates via its circularization of glucose-6-phosphate as the initial step. myo-inositol-6-phosphate (InsP(6) or phytic acid) is the predominant form of phosphorus found in seeds and accumulates as a consequence of MIPS action. Three MIPS genes have been identified in Arabidopsis, all of which were expressed not only in siliques but in both leaves and roots. Immunoelectron microscopy using a MIPS antibody showed that MIPS localizes to the cytosol primarily in the endosperm during seed development and not in the embryo. This is consistent with results obtained using fluorescent microscopy and western blot analysis that showed a similar pattern of localization. However, InsP(6), which is the final product of inositol phosphate metabolism, was present mainly in the embryo. This suggests that a complex interaction between the endosperm and embryo occurs during the synthesis and subsequent accumulation of InsP(6) in developing seeds of Arabidopsis.
Collapse
Affiliation(s)
- Naoto Mitsuhashi
- Department of Biology, Graduate School of Science, Kobe University, Rokkodai 1-1, Nada-ku, Kobe, 657-8501 Japan
| | | | | | | | | | | | | | | | | | | |
Collapse
|
30
|
Brehm M, Schenk T, Zhou X, Fanick W, Lin H, Windhorst S, Nalaskowski M, Kobras M, Shears S, Mayr G. Intracellular localization of human Ins(1,3,4,5,6)P5 2-kinase. Biochem J 2007; 408:335-45. [PMID: 17705785 PMCID: PMC2267366 DOI: 10.1042/bj20070382] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2007] [Revised: 07/18/2007] [Accepted: 08/17/2007] [Indexed: 01/05/2023]
Abstract
InsP6 is an intracellular signal with several proposed functions that is synthesized by IP5K [Ins(1,3,4,5,6)P5 2-kinase]. In the present study, we overexpressed EGFP (enhanced green fluorescent protein)-IP5K fusion proteins in NRK (normal rat kidney), COS7 and H1299 cells. The results indicate that there is spatial microheterogeneity in the intracellular localization of IP5K that could also be confirmed for the endogenous enzyme. This may facilitate changes in InsP6 levels at its sites of action. For example, overexpressed IP5K showed a structured organization within the nucleus. The kinase was preferentially localized in euchromatin and nucleoli, and co-localized with mRNA. In the cytoplasm, the overexpressed IP5K showed locally high concentrations in discrete foci. The latter were attributed to stress granules by using mRNA, PABP [poly(A)-binding protein] and TIAR (TIA-1-related protein) as markers. The incidence of stress granules, in which IP5K remained highly concentrated, was further increased by puromycin treatment. Using FRAP (fluorescence recovery after photobleaching) we established that IP5K was actively transported into the nucleus. By site-directed mutagenesis we identified a nuclear import signal and a peptide segment mediating the nuclear export of IP5K.
Collapse
Key Words
- euchromatin
- ins(1,3,4,5,6)p5 2-kinase (ip5k)
- in situ hybridization
- nuclear localization
- stress granule
- dapi, 4′,6-diamidino-2-phenylindole
- dtt, dithiothreitol
- egfp, enhanced green fluorescent protein
- fish, fluorescence in situ hybridization
- frap, fluorescence recover after photobleaching
- ipmk, inositol phosphate multikinase
- ipk, inositol phosphate kinase
- ip3k, ins(1,4,5)p3 3-kinase
- ip5k, ins(1,3,4,5,6)p5 2-kinase
- lmb, leptomycin b
- mdd-hplc, metal-dye-detection-hplc
- mrnp, messenger ribonucleoprotein
- nls, nuclear localization sequence
- nrk, normal rat kidney
- orf, open reading frame
- pabp, poly(a)-binding protein
- rnai, rna interference
- roi, region of interest
- sg, stress granule
- sirna, small-interfering rna
- tiar, tia-1-related protein
Collapse
Affiliation(s)
- Maria A. Brehm
- *NIEHS/NIH, 111 T.W. Alexander Drive, Research Triangle Park, NC 27709, U.S.A
| | - Tobias M. H. Schenk
- †Universitätsklinikum Hamburg-Eppendorf, Institut für Medizinische Biochemie und Molekularbiologie I: Zelluläre Signaltransduktion, Martinistraße 52, 20246 Hamburg, Germany
| | - Xuefei Zhou
- †Universitätsklinikum Hamburg-Eppendorf, Institut für Medizinische Biochemie und Molekularbiologie I: Zelluläre Signaltransduktion, Martinistraße 52, 20246 Hamburg, Germany
| | - Werner Fanick
- †Universitätsklinikum Hamburg-Eppendorf, Institut für Medizinische Biochemie und Molekularbiologie I: Zelluläre Signaltransduktion, Martinistraße 52, 20246 Hamburg, Germany
| | - Hongying Lin
- †Universitätsklinikum Hamburg-Eppendorf, Institut für Medizinische Biochemie und Molekularbiologie I: Zelluläre Signaltransduktion, Martinistraße 52, 20246 Hamburg, Germany
| | - Sabine Windhorst
- †Universitätsklinikum Hamburg-Eppendorf, Institut für Medizinische Biochemie und Molekularbiologie I: Zelluläre Signaltransduktion, Martinistraße 52, 20246 Hamburg, Germany
| | - Marcus M. Nalaskowski
- †Universitätsklinikum Hamburg-Eppendorf, Institut für Medizinische Biochemie und Molekularbiologie I: Zelluläre Signaltransduktion, Martinistraße 52, 20246 Hamburg, Germany
| | - Mario Kobras
- †Universitätsklinikum Hamburg-Eppendorf, Institut für Medizinische Biochemie und Molekularbiologie I: Zelluläre Signaltransduktion, Martinistraße 52, 20246 Hamburg, Germany
| | - Stephen B. Shears
- *NIEHS/NIH, 111 T.W. Alexander Drive, Research Triangle Park, NC 27709, U.S.A
| | - Georg W. Mayr
- †Universitätsklinikum Hamburg-Eppendorf, Institut für Medizinische Biochemie und Molekularbiologie I: Zelluläre Signaltransduktion, Martinistraße 52, 20246 Hamburg, Germany
| |
Collapse
|
31
|
Alcázar-Román AR, Wente SR. Inositol polyphosphates: a new frontier for regulating gene expression. Chromosoma 2007; 117:1-13. [DOI: 10.1007/s00412-007-0126-4] [Citation(s) in RCA: 74] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2007] [Revised: 09/12/2007] [Accepted: 09/13/2007] [Indexed: 10/22/2022]
|
32
|
Caddick S, Harrison C, Stavridou I, Johnson S, Brearley C. A lysine accumulation phenotype of ScIpk2Delta mutant yeast is rescued by Solanum tuberosum inositol phosphate multikinase. Biochem J 2007; 403:381-9. [PMID: 17274762 PMCID: PMC1876367 DOI: 10.1042/bj20061772] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Inositol phosphates and the enzymes that interconvert them are key regulators of diverse cellular processes including the transcriptional machinery of arginine synthesis [York (2006) Biochim. Biophys. Acta 1761, 552-559]. Despite considerable interest and debate surrounding the role of Saccharomyces cerevisiae inositol polyphosphate kinase (ScIPK2, ARG82, ARGRIII) and its inositol polyphosphate products in these processes, there is an absence of data describing how the transcripts of the arginine synthetic pathway, and the amino acid content of ScIpk2Delta, are altered under different nutrient regimes. We have cloned an IPMK (inositol phosphate multikinase) from Solanum tuberosum, StIPMK (GenBank(R) accession number EF362785), that despite considerable sequence divergence from ScIPK2, restores the arginine biosynthesis pathway transcripts ARG8, acetylornithine aminotransferase, and ARG3, ornithine carbamoyltransferase of ScIpk2Delta yeast to wild-type profiles. StIPMK also restores the amino acid profiles of mutant yeast to wild-type, and does so with ornithine or arginine as the sole nitrogen sources. Our data reveal a lysine accumulation phenotype in ScIpk2Delta yeast that is restored to a wild-type profile by expression of StIPMK, including restoration of the transcript profiles of lysine biosynthetic genes. The StIPMK protein shows only 18.6% identity with ScIPK2p which probably indicates that the rescue of transcript and diverse amino acid phenotypes is not mediated through a direct interaction of StIPMK with the ArgR-Mcm1 transcription factor complex that is a molecular partner of ScIPK2p.
Collapse
Affiliation(s)
- Samuel E. K. Caddick
- School of Biological Sciences, University of East Anglia, Norwich, Norfolk, NR4 7TJ, U.K
| | | | - Ioanna Stavridou
- School of Biological Sciences, University of East Anglia, Norwich, Norfolk, NR4 7TJ, U.K
| | - Sue Johnson
- School of Biological Sciences, University of East Anglia, Norwich, Norfolk, NR4 7TJ, U.K
| | - Charles A. Brearley
- School of Biological Sciences, University of East Anglia, Norwich, Norfolk, NR4 7TJ, U.K
- To whom correspondence should be addressed (email )
| |
Collapse
|
33
|
Seeds AM, Frederick JP, Tsui MMK, York JD. Roles for inositol polyphosphate kinases in the regulation of nuclear processes and developmental biology. ACTA ACUST UNITED AC 2007; 47:10-25. [PMID: 17467778 PMCID: PMC3258027 DOI: 10.1016/j.advenzreg.2006.12.019] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Affiliation(s)
| | | | | | - John D. York
- To whom correspondence should be addressed: Department of Pharmacology and Cancer Biology, Howard Hughes Medical Institute, Duke University Medical Center, DUMC 3813, Durham, NC 27710, Tel: 919-681-6414, Fax: 919-668-0991, E-mail:
| |
Collapse
|
34
|
Veiga N, Torres J, Domínguez S, Mederos A, Irvine RF, Díaz A, Kremer C. The behaviour of myo-inositol hexakisphosphate in the presence of magnesium(II) and calcium(II): protein-free soluble InsP6 is limited to 49 microM under cytosolic/nuclear conditions. J Inorg Biochem 2006; 100:1800-10. [PMID: 16920196 PMCID: PMC1874250 DOI: 10.1016/j.jinorgbio.2006.06.016] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2006] [Revised: 06/21/2006] [Accepted: 06/25/2006] [Indexed: 11/30/2022]
Abstract
Progress in the biology of myo-inositol hexakisphosphate (InsP(6)) has been delayed by the lack of a quantitative description of its multiple interactions with divalent cations. Our recent initial description of these [J. Torres, S. Dominguez, M.F. Cerda, G. Obal, A. Mederos, R.F. Irvine, A. Diaz, C. Kremer, J. Inorg. Biochem. 99 (2005) 828-840] predicted that under cytosolic/nuclear conditions, protein-free soluble InsP(6) occurs as Mg(5)(H(2)L), a neutral complex that exists thanks to a significant, but undefined, window of solubility displayed by solid Mg(5)(H(2)L).22H(2)O (L is fully deprotonated InsP(6)). Here we complete the description of the InsP(6)-Mg(2+)-Ca(2+) system, defining the solubilities of the Mg(2+) and Ca(2+) (Ca(5)(H(2)L).16H(2)O) solids in terms of K(s0)=[M(2+)](5)[H(2)L(10-)], with pK(s0)=32.93 for M=Mg and pK(s0)=39.3 for M=Ca. The concentration of soluble Mg(5)(H(2)L) at 37 degrees C and I=0.15M NaClO(4) is limited to 49muM, yet InsP(6) in mammalian cells may reach 100muM. Any cytosolic/nuclear InsP(6) in excess of 49muM must be protein- or membrane-bound, or as solid Mg(5)(H(2)L).22H(2)O, and any extracellular InsP(6) (e.g. in plasma) is surely protein-bound.
Collapse
Affiliation(s)
- Nicolás Veiga
- Cátedra de Química Inorgánica, Departamento Estrella Campos, Facultad de Química, Universidad de la República, Montevideo, Uruguay
| | - Julia Torres
- Cátedra de Química Inorgánica, Departamento Estrella Campos, Facultad de Química, Universidad de la República, Montevideo, Uruguay
| | - Sixto Domínguez
- Departamento de Química Inorgánica, Universidad de La Laguna, Tenerife, Canary Islands, Spain
| | - Alfredo Mederos
- Departamento de Química Inorgánica, Universidad de La Laguna, Tenerife, Canary Islands, Spain
| | - Robin F. Irvine
- Department of Pharmacology, University of Cambridge, Cambridge, UK
| | - Alvaro Díaz
- Cátedra de Inmunología, Facultad de Química/Ciencias, Universidad de la República, Montevideo, Uruguay
- Corresponding authors. Fax: +598 2 4874320 (A. Díaz), +598 2 9241906 (C. Kremer).
| | - Carlos Kremer
- Cátedra de Química Inorgánica, Departamento Estrella Campos, Facultad de Química, Universidad de la República, Montevideo, Uruguay
- Corresponding authors. Fax: +598 2 4874320 (A. Díaz), +598 2 9241906 (C. Kremer).
| |
Collapse
|
35
|
Alcázar-Román AR, Tran EJ, Guo S, Wente SR. Inositol hexakisphosphate and Gle1 activate the DEAD-box protein Dbp5 for nuclear mRNA export. Nat Cell Biol 2006; 8:711-6. [PMID: 16783363 DOI: 10.1038/ncb1427] [Citation(s) in RCA: 222] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2006] [Accepted: 04/21/2006] [Indexed: 01/08/2023]
Abstract
Regulation of nuclear mRNA export is critical for proper eukaryotic gene expression. A key step in this process is the directional translocation of mRNA-ribonucleoprotein particles (mRNPs) through nuclear pore complexes (NPCs) that are embedded in the nuclear envelope. Our previous studies in Saccharomyces cerevisiae defined an in vivo role for inositol hexakisphosphate (InsP6) and NPC-associated Gle1 in mRNA export. Here, we show that Gle1 and InsP6 act together to stimulate the RNA-dependent ATPase activity of the essential DEAD-box protein Dbp5. Overexpression of DBP5 specifically suppressed mRNA export and growth defects of an ipk1 nup42 mutant defective in InsP6 production and Gle1 localization. In vitro kinetic analysis showed that InsP6 significantly increased Dbp5 ATPase activity in a Gle1-dependent manner and lowered the effective RNA concentration for half-maximal ATPase activity. Gle1 alone had minimal effects. Maximal InsP6 binding required both Dbp5 and Gle1. It has been suggested that Dbp5 requires unidentified cofactors. We now propose that Dbp5 activation at NPCs requires Gle1 and InsP6. This would facilitate spatial control of the remodelling of mRNP protein composition during directional transport and provide energy to power transport cycles.
Collapse
Affiliation(s)
- Abel R Alcázar-Román
- Department of Cell and Developmental Biology, Vanderbilt University Medical Center, U-3209 MRBIII, 465 21st Avenue South, Nashville, TN 37232-8240, USA
| | | | | | | |
Collapse
|
36
|
Weirich CS, Erzberger JP, Flick JS, Berger JM, Thorner J, Weis K. Activation of the DExD/H-box protein Dbp5 by the nuclear-pore protein Gle1 and its coactivator InsP6 is required for mRNA export. Nat Cell Biol 2006; 8:668-76. [PMID: 16783364 DOI: 10.1038/ncb1424] [Citation(s) in RCA: 205] [Impact Index Per Article: 11.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2006] [Accepted: 05/19/2006] [Indexed: 02/07/2023]
Abstract
The DExD/H-box ATPase Dbp5 is essential for nuclear mRNA export, although its precise role in this process remains poorly understood. Here, we identify the nuclear pore protein Gle1 as a cellular activator of Dbp5. Dbp5 alone is unable to stably bind RNA or effectively hydrolyse ATP under physiological conditions, but addition of Gle1 dramatically stimulates these activities. A gle1 point mutant deficient for Dbp5 stimulation in vitro displays an mRNA export defect in vivo, indicating that activation of Dbp5 is an essential function of Gle1. Interestingly, Gle1 binds directly to inositol hexakisphosphate (InsP6) and InsP6 potentiates the Gle1-mediated stimulation of Dbp5. Dominant mutations in DBP5 and GLE1 that rescue mRNA export phenotypes associated with the lack of InsP6 mimic the InsP6 effects in vitro. Our results define specific functions for Gle1 and InsP6 in mRNA export and suggest that local activation of Dbp5 at the nuclear pore is critical for mRNA export.
Collapse
Affiliation(s)
- Christine S Weirich
- Division of Cell and Developmental Biology, University of California, Berkeley, Berkeley, CA 94720-3200, USA
| | | | | | | | | | | |
Collapse
|
37
|
Cole CN, Scarcelli JJ. Transport of messenger RNA from the nucleus to the cytoplasm. Curr Opin Cell Biol 2006; 18:299-306. [PMID: 16682182 DOI: 10.1016/j.ceb.2006.04.006] [Citation(s) in RCA: 87] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2006] [Accepted: 04/10/2006] [Indexed: 10/24/2022]
Abstract
All movement of molecules and macromolecules between the cytoplasm and the nucleus takes place through nuclear pore complexes (NPCs), very large macromolecular complexes that are the only channels connecting these compartments. mRNA export is mediated by multiple, highly conserved protein factors that couple steps of nuclear pre-mRNA biogenesis to mRNA transport. Mature messenger ribonucleoproteins (mRNPs) diffuse from sites of transcription to NPCs, although some active genes are positioned at the nuclear periphery where they interact physically with components of NPCs. As properly processed mRNPs translocate through the pore, certain mRNP proteins are removed, probably through the enzymatic action of the DEAD-box helicase Dbp5, which binds to Nup159 and Gle1, components of the cytoplasmic filaments of the NPC. Gle1 and the phosphoinositide IP6 activate Dbp5's ATPase activity in vitro and this could provide critical spatial regulation of Dbp5 activity in vivo.
Collapse
Affiliation(s)
- Charles N Cole
- Department of Biochemistry, Dartmouth Medical School Hanover, NH 03755, USA.
| | | |
Collapse
|
38
|
York JD. Regulation of nuclear processes by inositol polyphosphates. Biochim Biophys Acta Mol Cell Biol Lipids 2006; 1761:552-9. [PMID: 16781889 DOI: 10.1016/j.bbalip.2006.04.014] [Citation(s) in RCA: 119] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2006] [Accepted: 04/18/2006] [Indexed: 11/18/2022]
Abstract
Inositide signaling pathways represent a multifaceted ensemble of cellular switches capable of regulating a number of processes, for example, intracellular calcium release, membrane trafficking, chemotaxis, ion channel activity and several nuclear functions. Over 30 inositide messengers are found in eukaryotic cells that may be grouped into two classes: (1) inositol lipids, phosphatidylinositols or phosphoinositides (PIPs) and (2) water-soluble inositol polyphosphates (IPs). This review will focus on inositol polyphosphate kinases (IPK) and inositol pyrophosphate synthases (IPS) responsible for the cellular production of IP(4), IP(5) IP(6) and PP-IPs. Of interest, IPK and IPS proteins localize, in part, within the nucleus and their activities are necessary for proper regulation of gene expression, mRNA export, DNA repair and telomere maintenance. The breadth of nuclear processes regulated and the evolutionary conservation of the genes involved in their synthesis have sparked renewed interest in inositide messengers derived from sequential phosphorylation of inositol 1,4,5-trisphosphate.
Collapse
Affiliation(s)
- John D York
- Departments of Pharmacology and Cancer Biology and of Biochemistry, Howard Hughes Medical Institute, Duke University Medical Center, Box 3813, Durham, NC 27710, USA.
| |
Collapse
|
39
|
Affiliation(s)
- Lucy F Pemberton
- Department of Microbiology, Center for Cell Signaling, University of Virginia, Charlottesville, VA 22908, USA.
| | | |
Collapse
|
40
|
Strahl T, Hama H, DeWald DB, Thorner J. Yeast phosphatidylinositol 4-kinase, Pik1, has essential roles at the Golgi and in the nucleus. J Cell Biol 2005; 171:967-79. [PMID: 16365163 PMCID: PMC1382337 DOI: 10.1083/jcb.200504104] [Citation(s) in RCA: 104] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2005] [Accepted: 11/17/2005] [Indexed: 11/26/2022] Open
Abstract
Phosphatidylinositol 4-kinase, Pik1, is essential for viability. GFP-Pik1 localized to cytoplasmic puncta and the nucleus. The puncta colocalized with Sec7-DsRed, a marker of trans-Golgi cisternae. Kap95 (importin-beta) was necessary for nuclear entry, but not Kap60 (importin-alpha), and exportin Msn5 was required for nuclear exit. Frq1 (frequenin orthologue) also is essential for viability and binds near the NH2 terminus of Pik1. Frq1-GFP localized to Golgi puncta, and Pik1 lacking its Frq1-binding site (or Pik1 overexpressed in frq1Delta cells) did not decorate the Golgi, but nuclear localization was unperturbed. Pik1(Delta10-192), which lacks its nuclear export sequence, displayed prominent nuclear accumulation and did not rescue inviability of pik1Delta cells. A Pik1-CCAAX chimera was excluded from the nucleus and also did not rescue inviability of pik1Delta cells. However, coexpression of Pik1(Delta10-192) and Pik1-CCAAX in pik1Delta cells restored viability. Catalytically inactive derivatives of these compartment-restricted Pik1 constructs indicated that PtdIns4P must be generated both in the nucleus and at the Golgi for normal cell function.
Collapse
Affiliation(s)
- Thomas Strahl
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720, USA
| | | | | | | |
Collapse
|
41
|
Kendirgi F, Rexer DJ, Alcázar-Román AR, Onishko HM, Wente SR. Interaction between the shuttling mRNA export factor Gle1 and the nucleoporin hCG1: a conserved mechanism in the export of Hsp70 mRNA. Mol Biol Cell 2005; 16:4304-15. [PMID: 16000379 PMCID: PMC1196339 DOI: 10.1091/mbc.e04-11-0998] [Citation(s) in RCA: 68] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Translocation of messenger RNAs through the nuclear pore complex (NPC) requires coordinated physical interactions between stable NPC components, shuttling transport factors, and mRNA-binding proteins. In budding yeast (y) and human (h) cells, Gle1 is an essential mRNA export factor. Nucleocytoplasmic shuttling of hGle1 is required for mRNA export; however, the mechanism by which hGle1 associates with the NPC is unknown. We have previously shown that the interaction of hGle1 with the nucleoporin hNup155 is necessary but not sufficient for targeting hGle1 to NPCs. Here, we report that the unique C-terminal 43 amino acid region of the hGle1B isoform mediates binding to the C-terminal non-FG region of the nucleoporin hCG1/NPL1. Moreover, hNup155, hGle1B, and hCG1 formed a heterotrimeric complex in vitro. This suggested that these two nucleoporins were required for the NPC localization of hGle1. Using an siRNA-based approach, decreased levels of hCG1 resulted in hGle1 accumulation in cytoplasmic foci. This was coincident with inhibition of heat shock-induced production of Hsp70 protein and export of the Hsp70 mRNA in HeLa cells. Because this closely parallels the role of the hCG1 orthologue yNup42/Rip1, we speculate that hGle1-hCG1 function in the mRNA export mechanism is highly conserved.
Collapse
Affiliation(s)
- Frederic Kendirgi
- Department of Cell and Developmental Biology, Vanderbilt University Medical Center, Nashville, TN 37232-8240, USA
| | | | | | | | | |
Collapse
|
42
|
Mitsuhashi N, Ohnishi M, Sekiguchi Y, Kwon YU, Chang YT, Chung SK, Inoue Y, Reid RJ, Yagisawa H, Mimura T. Phytic acid synthesis and vacuolar accumulation in suspension-cultured cells of Catharanthus roseus induced by high concentration of inorganic phosphate and cations. PLANT PHYSIOLOGY 2005; 138:1607-14. [PMID: 15965017 PMCID: PMC1176430 DOI: 10.1104/pp.105.060269] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
We have established a new system for studying phytic acid, myo-inositol hexakisphosphate (InsP(6)) synthesis in suspension-cultured cells of Catharanthus. InsP(6) and other intermediates of myo-inositol (Ins) phosphate metabolism were measured using an ion chromatography method. The detection limit for InsP(6) was less than 50 nM, which was sufficient to analyze Ins phosphates in living cells. Synthesis of Ins phosphates was induced by incubation in high inorganic phosphate medium. InsP(6) was mainly accumulated in vacuoles and was enhanced when cells were grown in high concentration of inorganic phosphates with the cations K(+), Ca(2+), or Zn(2+). However, there was a strong tendency for InsP(6) to accumulate in the vacuole in the presence of Ca(2+) and in nonvacuolar compartments when supplied with Zn(2+), possibly due to precipitation of InsP(6) with Zn(2+) in the cytosol. A vesicle transport inhibitor, brefeldin A, stimulated InsP(6) accumulation. The amounts of both Ins(3)P(1) myo-inositol monophosphate synthase, a key enzyme for InsP(6) synthesis, and Ins(1,4,5)P(3) kinase were unrelated to the level of accumulation of InsP(6). The mechanisms for InsP(6) synthesis and localization into vacuoles in plant cells are discussed.
Collapse
Affiliation(s)
- Naoto Mitsuhashi
- Japan Society for the Promotion of Science, Tokyo 102-8471, Japan
| | | | | | | | | | | | | | | | | | | |
Collapse
|