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Tornesello ML, Tornesello AL, Starita N, Cerasuolo A, Izzo F, Buonaguro L, Buonaguro FM. Telomerase: a good target in hepatocellular carcinoma? An overview of relevant preclinical data. Expert Opin Ther Targets 2022; 26:767-780. [PMID: 36369706 DOI: 10.1080/14728222.2022.2147062] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Affiliation(s)
- Maria Lina Tornesello
- Molecular Biology and Viral Oncology Unit, Istituto Nazionale Tumori IRCCS “Fondazione G. Pascale”, 80131 Napoli, Italy
| | - Anna Lucia Tornesello
- Molecular Biology and Viral Oncology Unit, Istituto Nazionale Tumori IRCCS “Fondazione G. Pascale”, 80131 Napoli, Italy
| | - Noemy Starita
- Molecular Biology and Viral Oncology Unit, Istituto Nazionale Tumori IRCCS “Fondazione G. Pascale”, 80131 Napoli, Italy
| | - Andrea Cerasuolo
- Molecular Biology and Viral Oncology Unit, Istituto Nazionale Tumori IRCCS “Fondazione G. Pascale”, 80131 Napoli, Italy
| | - Francesco Izzo
- Hepatobiliary Surgical Oncology Unit, Istituto Nazionale Tumori IRCCS Fondazione Pascale-IRCCS di Napoli, 80131 Naples, Italy
| | - Luigi Buonaguro
- Laboratory of Cancer Immunoregulation, Istituto Nazionale Tumori IRCCS “Fondazione G. Pascale”, 80131 Napoli, Italy
| | - Franco Maria Buonaguro
- Molecular Biology and Viral Oncology Unit, Istituto Nazionale Tumori IRCCS “Fondazione G. Pascale”, 80131 Napoli, Italy
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2
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Single-Run Catalysis and Kinetic Control of Human Telomerase Holoenzyme. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2021; 1371:109-129. [PMID: 34962637 DOI: 10.1007/5584_2021_676] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
Abstract
Genome stability in eukaryotic cells relies on proper maintenance of telomeres at the termini of linear chromosomes. Human telomerase holoenzyme is required for maintaining telomere stability in a majority of proliferative human cells, making it essential for control of cell division and aging, stem cell maintenance, and development and survival of tumor or cancer. A dividing human cell usually contains a limited number of active telomerase holoenzymes. Recently, we discovered that a human telomerase catalytic site undergoes catalysis-dependent shut-off and an inactive site can be reactivated by cellular fractions containing human intracellular telomerase-activating factors (hiTAFs). Such ON-OFF control of human telomerase activity suggests a dynamic switch between inactive and active pools of the holoenzymes. In this review, we will link the ON-OFF control to the thermodynamic and kinetic properties of human telomerase holoenzymes, and discuss its potential contributions to the maintenance of telomere length equilibrium. This treatment suggests probabilistic fluctuations in the number of active telomerase holoenzymes as well as the number of telomeres that are extended in a limited number of cell cycles, and may be an important component of a fully quantitative model for the dynamic control of telomerase activities and telomere lengths in different types of eukaryotic cells.
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Musgrove C, Jansson LI, Stone MD. New perspectives on telomerase RNA structure and function. WILEY INTERDISCIPLINARY REVIEWS-RNA 2017; 9. [PMID: 29124890 DOI: 10.1002/wrna.1456] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/29/2017] [Revised: 09/08/2017] [Accepted: 09/18/2017] [Indexed: 12/20/2022]
Abstract
Telomerase is an ancient ribonucleoprotein (RNP) that protects the ends of linear chromosomes from the loss of critical coding sequences through repetitive addition of short DNA sequences. These repeats comprise the telomere, which together with many accessory proteins, protect chromosomal ends from degradation and unwanted DNA repair. Telomerase is a unique reverse transcriptase (RT) that carries its own RNA to use as a template for repeat addition. Over decades of research, it has become clear that there are many diverse, crucial functions played by telomerase RNA beyond simply acting as a template. In this review, we highlight recent findings in three model systems: ciliates, yeast and vertebrates, that have shifted the way the field views the structural and mechanistic role(s) of RNA within the functional telomerase RNP complex. Viewed in this light, we hope to demonstrate that while telomerase RNA is just one example of the myriad functional RNA in the cell, insights into its structure and mechanism have wide-ranging impacts. WIREs RNA 2018, 9:e1456. doi: 10.1002/wrna.1456 This article is categorized under: RNA Structure and Dynamics > Influence of RNA Structure in Biological Systems RNA Structure and Dynamics > RNA Structure, Dynamics and Chemistry RNA Evolution and Genomics > RNA and Ribonucleoprotein Evolution.
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Affiliation(s)
- Cherie Musgrove
- Department of Microbiology and Environmental Toxicology, University of California, Santa Cruz, CA, USA
| | - Linnea I Jansson
- Department of Molecular, Cellular, and Developmental Biology, University of California, Santa Cruz, CA, USA
| | - Michael D Stone
- Department of Chemistry and Biochemistry, University of California, Santa Cruz, CA, USA.,Center for Molecular Biology of RNA, University of California, Santa Cruz, CA, USA
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Direct single-stranded DNA binding by Teb1 mediates the recruitment of Tetrahymena thermophila telomerase to telomeres. Mol Cell Biol 2014; 34:4200-12. [PMID: 25225329 DOI: 10.1128/mcb.01030-14] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The eukaryotic reverse transcriptase telomerase copies its internal RNA template to synthesize telomeric DNA repeats at chromosome ends in balance with sequence loss during cell proliferation. Previous work has established several factors involved in telomerase recruitment to telomeres in yeast and mammalian cells; however, it remains unclear what determines the association of telomerase with telomeres in other organisms. Here we investigate the cell cycle dependence of telomere binding by each of the seven Tetrahymena thermophila telomerase holoenzyme proteins TERT, p65, Teb1, p50, p75, p45, and p19. We observed coordinate cell cycle-regulated recruitment and release of all of the subunits, including the telomeric-repeat DNA-binding subunit Teb1. Using domain truncation and mutagenesis approaches, we investigated which subunits govern the interaction of telomerase holoenzyme with telomeres. Our results show that Teb1 is critical for telomere interaction of other holoenzyme subunits and demonstrate that high-affinity Teb1 DNA-binding activity is necessary and sufficient for cell cycle-regulated telomere association. Overall, these and additional findings indicate that in the ciliate Tetrahymena, telomerase recruitment to telomeres requires direct binding to single-stranded DNA, unlike the indirect DNA recognition through telomere-bound proteins essential in yeast and mammalian cells.
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Holmstrom ED, Nesbitt DJ. Single-molecule fluorescence resonance energy transfer studies of the human telomerase RNA pseudoknot: temperature-/urea-dependent folding kinetics and thermodynamics. J Phys Chem B 2014; 118:3853-63. [PMID: 24617561 PMCID: PMC4030807 DOI: 10.1021/jp501893c] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2014] [Indexed: 02/06/2023]
Abstract
The ribonucleoprotein telomerase is an RNA-dependent DNA polymerase that catalyzes the repetitive addition of a short, species-specific, DNA sequence to the ends of linear eukaryotic chromosomes. The single RNA component of telomerase contains both the template sequence for DNA synthesis and a functionally critical pseudoknot motif, which can also exist as a less stable hairpin. Here we use a minimal version of the human telomerase RNA pseudoknot to study this hairpin-pseudoknot structural equilibrium using temperature-controlled single-molecule fluorescence resonance energy transfer (smFRET) experiments. The urea dependence of these experiments aids in determination of the folding kinetics and thermodynamics. The wild-type pseudoknot behavior is compared and contrasted to a mutant pseudoknot sequence implicated in a genetic disorder-dyskeratosis congenita. These findings clearly identify that this 2nt noncomplementary mutation destabilizes the folding of the wild-type pseudoknot by substantially reducing the folding rate constant (≈ 400-fold) while only nominally increasing the unfolding rate constant (≈ 5-fold). Furthermore, the urea dependence of the equilibrium and rate constants is used to develop a free energy landscape for this unimolecular equilibrium and propose details about the structure of the transition state. Finally, the urea-dependent folding experiments provide valuable physical insights into the mechanism for destabilization of RNA pseudoknots by such chemical denaturants.
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Affiliation(s)
- Erik D. Holmstrom
- JILA, University of Colorado and National
Institute of Standards and Technology, and Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado 80309-0440, United States
| | - David J. Nesbitt
- JILA, University of Colorado and National
Institute of Standards and Technology, and Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado 80309-0440, United States
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Lin J, Kaur P, Countryman P, Opresko PL, Wang H. Unraveling secrets of telomeres: one molecule at a time. DNA Repair (Amst) 2014; 20:142-153. [PMID: 24569170 DOI: 10.1016/j.dnarep.2014.01.012] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2013] [Revised: 01/03/2014] [Accepted: 01/13/2014] [Indexed: 01/23/2023]
Abstract
Telomeres play important roles in maintaining the stability of linear chromosomes. Telomere maintenance involves dynamic actions of multiple proteins interacting with long repetitive sequences and complex dynamic DNA structures, such as G-quadruplexes, T-loops and t-circles. Given the heterogeneity and complexity of telomeres, single-molecule approaches are essential to fully understand the structure-function relationships that govern telomere maintenance. In this review, we present a brief overview of the principles of single-molecule imaging and manipulation techniques. We then highlight results obtained from applying these single-molecule techniques for studying structure, dynamics and functions of G-quadruplexes, telomerase, and shelterin proteins.
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Affiliation(s)
- Jiangguo Lin
- Physics Department, North Carolina State University, Raleigh, NC 27695, USA
| | - Parminder Kaur
- Physics Department, North Carolina State University, Raleigh, NC 27695, USA
| | - Preston Countryman
- Physics Department, North Carolina State University, Raleigh, NC 27695, USA
| | - Patricia L Opresko
- Department of Environmental and Occupational Health, University of Pittsburgh Graduate School of Public Health, Pittsburgh, PA 15219, USA
| | - Hong Wang
- Physics Department, North Carolina State University, Raleigh, NC 27695, USA.
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Lin J, Countryman P, Buncher N, Kaur P, E L, Zhang Y, Gibson G, You C, Watkins SC, Piehler J, Opresko PL, Kad NM, Wang H. TRF1 and TRF2 use different mechanisms to find telomeric DNA but share a novel mechanism to search for protein partners at telomeres. Nucleic Acids Res 2013; 42:2493-504. [PMID: 24271387 PMCID: PMC3936710 DOI: 10.1093/nar/gkt1132] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
Human telomeres are maintained by the shelterin protein complex in which TRF1 and TRF2 bind directly to duplex telomeric DNA. How these proteins find telomeric sequences among a genome of billions of base pairs and how they find protein partners to form the shelterin complex remains uncertain. Using single-molecule fluorescence imaging of quantum dot-labeled TRF1 and TRF2, we study how these proteins locate TTAGGG repeats on DNA tightropes. By virtue of its basic domain TRF2 performs an extensive 1D search on nontelomeric DNA, whereas TRF1’s 1D search is limited. Unlike the stable and static associations observed for other proteins at specific binding sites, TRF proteins possess reduced binding stability marked by transient binding (∼9–17 s) and slow 1D diffusion on specific telomeric regions. These slow diffusion constants yield activation energy barriers to sliding ∼2.8–3.6 κBT greater than those for nontelomeric DNA. We propose that the TRF proteins use 1D sliding to find protein partners and assemble the shelterin complex, which in turn stabilizes the interaction with specific telomeric DNA. This ‘tag-team proofreading’ represents a more general mechanism to ensure a specific set of proteins interact with each other on long repetitive specific DNA sequences without requiring external energy sources.
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Affiliation(s)
- Jiangguo Lin
- Physics Department, North Carolina State University, Raleigh, NC 27695, USA, Department of Environmental and Occupational Health, University of Pittsburgh Graduate School of Public Health, Pittsburgh, PA 15219, USA, Electric and Computer Engineering Department, University of North Carolina at Charlotte, Charlotte, NC 28223, USA, Department of Industrial and System Engineering, North Carolina State University, Raleigh, NC 27695, USA, Department of Cell Biology, Center for Biologic Imaging, University of Pittsburgh Graduate School of Public Health, Pittsburgh, PA 15219, USA, Division of Biophysics, Universität Osnabrück, Barbarstrasse 11, 49076, Osnabrück, Germany and School of Biological Sciences, University of Essex, Colchester, Essex CO4 3SQ UK
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Hong K, Upton H, Miracco EJ, Jiang J, Zhou ZH, Feigon J, Collins K. Tetrahymena telomerase holoenzyme assembly, activation, and inhibition by domains of the p50 central hub. Mol Cell Biol 2013; 33:3962-71. [PMID: 23918804 PMCID: PMC3811867 DOI: 10.1128/mcb.00792-13] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2013] [Accepted: 07/29/2013] [Indexed: 01/10/2023] Open
Abstract
The eukaryotic reverse transcriptase, telomerase, adds tandem telomeric repeats to chromosome ends to promote genome stability. The fully assembled telomerase holoenzyme contains a ribonucleoprotein (RNP) catalytic core and additional proteins that modulate the ability of the RNP catalytic core to elongate telomeres. Electron microscopy (EM) structures of Tetrahymena telomerase holoenzyme revealed a central location of the relatively uncharacterized p50 subunit. Here we have investigated the biochemical and structural basis for p50 function. We have shown that the p50-bound RNP catalytic core has a relatively low rate of tandem repeat synthesis but high processivity of repeat addition, indicative of high stability of enzyme-product interaction. The rate of tandem repeat synthesis is enhanced by p50-dependent recruitment of the holoenzyme single-stranded DNA binding subunit, Teb1. An N-terminal p50 domain is sufficient to stimulate tandem repeat synthesis and bridge the RNP catalytic core, Teb1, and the p75 subunit of the holoenzyme subcomplex p75/p19/p45. In cells, the N-terminal p50 domain assembles a complete holoenzyme that is functional for telomere maintenance, albeit at shortened telomere lengths. Also, in EM structures of holoenzymes, only the N-terminal domain of p50 is visible. Our findings provide new insights about subunit and domain interactions and functions within the Tetrahymena telomerase holoenzyme.
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Affiliation(s)
- Kyungah Hong
- Department of Molecular and Cell Biology, University of California, Berkeley, California, USA
| | - Heather Upton
- Department of Molecular and Cell Biology, University of California, Berkeley, California, USA
| | - Edward J. Miracco
- Department of Chemistry and Biochemistry, University of California, Los Angeles, California, USA
| | - Jiansen Jiang
- Department of Chemistry and Biochemistry, University of California, Los Angeles, California, USA
- Department of Microbiology, Immunology and Molecular Genetics, University of California, Los Angeles, California, USA
| | - Z. Hong Zhou
- Department of Microbiology, Immunology and Molecular Genetics, University of California, Los Angeles, California, USA
| | - Juli Feigon
- Department of Chemistry and Biochemistry, University of California, Los Angeles, California, USA
| | - Kathleen Collins
- Department of Molecular and Cell Biology, University of California, Berkeley, California, USA
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9
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Li PTX. Analysis of diffuse K+ and Mg2+ ion binding to a two-base-pair kissing complex by single-molecule mechanical unfolding. Biochemistry 2013; 52:4991-5001. [PMID: 23842027 DOI: 10.1021/bi400646x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
The folding and stability of RNA tertiary interactions depend critically on cationic conditions. It is usually difficult, however, to isolate such effects on tertiary interactions from those on the entire RNA. By manipulating conformations of single RNA molecules using optical tweezers, we distinguished individual steps of breaking and forming of a two-base-pair kissing interaction from those of secondary folding. The binding of metal ions to the small tertiary structure appeared to be saturable with an apparent Kd of 160 mM for K(+) and 1.5 mM for Mg(2+). The kissing formation was estimated to be associated with binding of ~2-3 diffuse K(+) or Mg(2+) ions. At their saturated binding, Mg(2+) provided ~3 kcal/mol more stabilizing energy to the structure than K(+). Furthermore, the cations change the unkissing forces significantly more than the kissing ones. For example, the presence of Mg(2+) ions increased the average unkissing force from 21 pN to 44 pN, surprisingly high for breaking merely two base pairs; in contrast, the mean kissing force was changed by only 4.5 pN. Interestingly, the differential salt effects on the transition forces were not caused by different changes in the height of the kinetic barriers but were instead attributed to how different molecular structures respond to the applied force. Our results showed the importance of diffuse cation binding to the stability of tertiary interaction and demonstrated the utility of mechanical unfolding in studying tertiary interactions.
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Affiliation(s)
- Pan T X Li
- Department of Biological Sciences and The RNA Institute, University at Albany, SUNY , Albany, New York 12222, United States
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Akiyama BM, Gomez A, Stone MD. A conserved motif in Tetrahymena thermophila telomerase reverse transcriptase is proximal to the RNA template and is essential for boundary definition. J Biol Chem 2013; 288:22141-9. [PMID: 23760279 DOI: 10.1074/jbc.m113.452425] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
The ends of linear chromosomes are extended by telomerase, a ribonucleoprotein complex minimally consisting of a protein subunit called telomerase reverse transcriptase (TERT) and the telomerase RNA (TER). TERT functions by reverse transcribing a short template region of TER into telomeric DNA. Proper assembly of TERT and TER is essential for telomerase activity; however, a detailed understanding of how TERT interacts with TER is lacking. Previous studies have identified an RNA binding domain (RBD) within TERT, which includes three evolutionarily conserved sequence motifs: CP2, CP, and T. Here, we used site-directed hydroxyl radical probing to directly identify sites of interaction between the TERT RBD and TER, revealing that the CP2 motif is in close proximity to a conserved region of TER known as the template boundary element (TBE). Gel shift assays on CP2 mutants confirmed that the CP2 motif is an RNA binding determinant. Our results explain previous work that established that mutations to the CP2 motif of TERT and to the TBE of TER both permit misincorporation of nucleotides into the growing DNA strand beyond the canonical template. Taken together, these results suggest a model in which the CP2 motif binds the TBE to strictly define which TER nucleotides can be reverse transcribed.
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Affiliation(s)
- Benjamin M Akiyama
- Department of Molecular, Cell, and Developmental Biology, University of California, Santa Cruz, California 95064, USA
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