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Day HA, Pavlou P, Waller ZAE. i-Motif DNA: structure, stability and targeting with ligands. Bioorg Med Chem 2014; 22:4407-18. [PMID: 24957878 DOI: 10.1016/j.bmc.2014.05.047] [Citation(s) in RCA: 270] [Impact Index Per Article: 27.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2014] [Revised: 05/09/2014] [Accepted: 05/22/2014] [Indexed: 10/25/2022]
Abstract
i-Motifs are four-stranded DNA secondary structures which can form in sequences rich in cytosine. Stabilised by acidic conditions, they are comprised of two parallel-stranded DNA duplexes held together in an antiparallel orientation by intercalated, cytosine-cytosine(+) base pairs. By virtue of their pH dependent folding, i-motif forming DNA sequences have been used extensively as pH switches for applications in nanotechnology. Initially, i-motifs were thought to be unstable at physiological pH, which precluded substantial biological investigation. However, recent advances have shown that this is not always the case and that i-motif stability is highly dependent on factors such as sequence and environmental conditions. In this review, we discuss some of the different i-motif structures investigated to date and the factors which affect their topology, stability and dynamics. Ligands which can interact with these structures are necessary to aid investigations into the potential biological functions of i-motif DNA and herein we review the existing i-motif ligands and give our perspective on the associated challenges with targeting this structure.
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Affiliation(s)
- Henry A Day
- School of Pharmacy, University of East Anglia, Norwich Research Park, Norwich, Norfolk NR4 7TJ, UK
| | - Pavlos Pavlou
- School of Pharmacy, University of East Anglia, Norwich Research Park, Norwich, Norfolk NR4 7TJ, UK
| | - Zoë A E Waller
- School of Pharmacy, University of East Anglia, Norwich Research Park, Norwich, Norfolk NR4 7TJ, UK.
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52
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Modi S, Halder S, Nizak C, Krishnan Y. Recombinant antibody mediated delivery of organelle-specific DNA pH sensors along endocytic pathways. NANOSCALE 2014; 6:1144-1152. [PMID: 24297098 DOI: 10.1039/c3nr03769j] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
DNA has been used to build nanomachines with potential in cellulo and in vivo applications. However their different in cellulo applications are limited by the lack of generalizable strategies to deliver them to precise intracellular locations. Here we describe a new molecular design of DNA pH sensors with response times that are nearly 20 fold faster. Further, by changing the sequence of the pH sensitive domain of the DNA sensor, we have been able to tune their pH sensitive regimes and create a family of DNA sensors spanning ranges from pH 4 to 7.6. To enable a generalizable targeting methodology, this new sensor design also incorporates a 'handle' domain. We have identified, using a phage display screen, a set of three recombinant antibodies (scFv) that bind sequence specifically to the handle domain. Sequence analysis of these antibodies revealed several conserved residues that mediate specific interactions with the cognate DNA duplex. We also found that all three scFvs clustered into different branches indicating that their specificity arises from mutations in key residues. When one of these scFvs is fused to a membrane protein (furin) that traffics via the cell surface, the scFv-furin chimera binds the 'handle' and ferries a family of DNA pH sensors along the furin endocytic pathway. Post endocytosis, all DNA nanodevices retain their functionality in cellulo and provide spatiotemporal pH maps of retrogradely trafficking furin inside living cells. This new molecular technology of DNA-scFv-protein chimeras can be used to site-specifically complex DNA nanostructures for bioanalytical applications.
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Affiliation(s)
- Souvik Modi
- National Centre for Biological Sciences, TIFR, GKVK, Bellary Road, Bangalore 560 065, India.
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53
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Benabou S, Aviñó A, Eritja R, González C, Gargallo R. Fundamental aspects of the nucleic acid i-motif structures. RSC Adv 2014. [DOI: 10.1039/c4ra02129k] [Citation(s) in RCA: 129] [Impact Index Per Article: 12.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
The latest research on fundamental aspects of i-motif structures is reviewed with special attention to their hypothetical rolein vivo.
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Affiliation(s)
- S. Benabou
- Department of Analytical Chemistry
- University of Barcelona
- E-08028 Barcelona, Spain
| | - A. Aviñó
- Institute for Advanced Chemistry of Catalonia (IQAC-CSIC)
- CIBER-BBN Networking Centre on Bioengineering
- Biomaterials and Nanomedicine
- E-08034 Barcelona, Spain
| | - R. Eritja
- Institute for Advanced Chemistry of Catalonia (IQAC-CSIC)
- CIBER-BBN Networking Centre on Bioengineering
- Biomaterials and Nanomedicine
- E-08034 Barcelona, Spain
| | - C. González
- Institute of Physical Chemistry “Rocasolano”
- CSIC
- E-28006 Madrid, Spain
| | - R. Gargallo
- Department of Analytical Chemistry
- University of Barcelona
- E-08028 Barcelona, Spain
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54
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Cui J, Waltman P, Le VH, Lewis EA. The effect of molecular crowding on the stability of human c-MYC promoter sequence I-motif at neutral pH. Molecules 2013; 18:12751-67. [PMID: 24132198 PMCID: PMC6270392 DOI: 10.3390/molecules181012751] [Citation(s) in RCA: 81] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2013] [Revised: 09/26/2013] [Accepted: 10/10/2013] [Indexed: 12/20/2022] Open
Abstract
We have previously shown that c-MYC promoter sequences can form stable i-motifs in acidic solution (pH 4.5-5.5). In terms of drug targeting, the question is whether c-MYC promoter sequence i-motifs will exist in the nucleus at neutral pH. In this work, we have investigated the stability of a mutant c-MYC i-motif in solutions containing a molecular crowding agent. The crowded nuclear environment was modeled by the addition of up to 40% w/w polyethylene glycols having molecular weights up to 12,000 g/mol. CD and DSC were used to establish the presence and stability of c-MYC i-motifs in buffer solutions over the pH range 4 to 7. We have shown that the c-MYC i-motif can exist as a stable structure at pH values as high as 6.7 in crowded solutions. Generic dielectric constant effects, e.g., a shift in the pKa of cytosine by more than 2 units (e.g., 4.8 to 7.0), or the formation of non-specific PEG/DNA complexes appear to contribute insignificantly to i-motif stabilization. Molecular crowding, largely an excluded volume effect of added PEG, having a molecular weight in excess of 1,000 g/mol, appears to be responsible for stabilizing the more compact i-motif over the random coil at higher pH values.
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Affiliation(s)
- Jingjing Cui
- Department of Chemistry, Mississippi State University, Mississippi State, MS 39762, USA.
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55
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Ma DL, He HZ, Leung KH, Chan DSH, Leung CH. Bioactive Luminescent Transition-Metal Complexes for Biomedical Applications. Angew Chem Int Ed Engl 2013; 52:7666-7682. [DOI: 10.1002/anie.201208414] [Citation(s) in RCA: 293] [Impact Index Per Article: 26.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 08/30/2023]
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56
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Ma DL, He HZ, Leung KH, Chan DSH, Leung CH. Bioaktive lumineszierende Übergangsmetallkomplexe für biomedizinische Anwendungen. Angew Chem Int Ed Engl 2013. [DOI: 10.1002/ange.201208414] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
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57
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Dembska A, Rzepecka P, Juskowiak B. Spectroscopic characterization of i-motif forming c-myc derived sequences double-labeled with pyrene. J Fluoresc 2013; 23:807-12. [PMID: 23519528 PMCID: PMC3696180 DOI: 10.1007/s10895-013-1184-z] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2012] [Accepted: 02/24/2013] [Indexed: 11/25/2022]
Abstract
In current studies we use the oligonucleotides based on c-myc sequence: CCC CAC CCT CCC CAC CCT CCC C (cmyc22) and CCC CAC CCT CCC CAC CCT CCC CA (cmyc22A) functionalized by pyrene moieties at both termini. Results of the circular dichroism (CD), UV absorption melting experiments, and steady-state fluorescence measurements of pyrene-modified i-motifs as well as their unlabeled precursors are presented and discussed here. The pyrene labels have a remarkable influence on i-motif stability which was deduced from CD spectra and confirmed by UV melting experiments. Both probes emit fluorescence band of pyrene monomer with intensity decreasing upon pH lowering.
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Affiliation(s)
- Anna Dembska
- Laboratory of Bioanalytical Chemistry, Faculty of Chemistry, A. Mickiewicz University, Umultowska 89b, 61-614, Poznań, Poland.
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58
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Brazier JA, Shah A, Brown GD. I-motif formation in gene promoters: unusually stable formation in sequences complementary to known G-quadruplexes. Chem Commun (Camb) 2013; 48:10739-41. [PMID: 23012694 DOI: 10.1039/c2cc30863k] [Citation(s) in RCA: 88] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
I-motif formation has been confirmed in a number of gene promoter sequences known to form G-quadruplex structures. I-motif formation can occur close to physiological temperature and pH for h-tert and PDGF-A. The i-motif structure formed by a HIF-1α promoter sequence shows unexpected stability near neutral pH.
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Affiliation(s)
- John A Brazier
- School of Pharmacy, University of Reading, Whiteknights, Reading, Berks, RG6 6AD.
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59
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Vummidi BR, Alzeer J, Luedtke NW. Fluorescent Probes for G-Quadruplex Structures. Chembiochem 2013; 14:540-58. [DOI: 10.1002/cbic.201200612] [Citation(s) in RCA: 197] [Impact Index Per Article: 17.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2012] [Indexed: 12/19/2022]
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Chen C, Li M, Xing Y, Li Y, Joedecke CC, Jin J, Yang Z, Liu D. Study of pH-induced folding and unfolding kinetics of the DNA i-motif by stopped-flow circular dichroism. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2012; 28:17743-17748. [PMID: 23148777 DOI: 10.1021/la303851a] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
Using the stopped-flow circular dichroism (SFCD) technique, we investigate the kinetics of the pH-induced folding and unfolding process of the DNA i-motif. The results show that the molecule can fold or unfold on a time scale of 100 ms when the solution pH is changed. It is also found that the folding and unfolding rates strongly depend on the solution pH. On the basis of quantitative data, we propose theoretical models to decipher the folding and unfolding kinetics. Our models suggest that the cooperativity of protons is crucial for both the folding and unfolding process. In the unfolding process, the cooperative neutralization of two protons (out of the total six protons in the i-motif molecule) is the only rate-limiting step. In the folding process, there exists a critical step in which three protons bind cooperatively to the DNA strand. These results offer an in-depth understanding of the folding and unfolding kinetics of the DNA i-motif and may give precise guidance for constructing novel nanodevices based on the DNA i-motif.
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Affiliation(s)
- Chun Chen
- Key Laboratory of Organic Optoelectronics & Molecular Engineering of the Ministry of Education, Department of Chemistry, Tsinghua University, Beijing 100084, China
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61
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Abstract
The physicochemical properties of small molecules as well as macromolecules are modulated by solution pH, and DNA is no exception. Special sequences of DNA can adopt unusual conformations e.g., triplex, i-motif and A-motif, depending on solution pH. The specific range of pH for these unusual structures is dictated by the pKa of protonation of the relevant nucleobase involved in the resultant non-canonical base pairing that is required to stabilise the structure. The biological significance of these pH-dependent structures is not yet clear. However, these non-B-DNA structures have been used to design different devices to direct chemical reactions, generate mechanical force, sense pH, etc. The performance of these devices can be monitored by a photonic signal. They are autonomous and their ‘waste free’ operation cycles makes them highly processive. Applications of these devices help to increase understanding of the structural polymorphism of the motifs themselves. The design of these devices has continuously evolved to improve their performance efficiency in different contexts. In some examples, these devices have been shown to perform inside complex living systems with similar efficiencies, to report on the chemical environment there. The robust performance of these devices opens up exciting possibilities for pH-sensitive DNA devices in the study of various pH-regulated biological events.
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Affiliation(s)
- Sonali Saha
- National Centre for Biological Sciences TIFR, GKVK, Bellary Road, Bangalore 560065 India
| | - Yamuna Krishnan*
- National Centre for Biological Sciences TIFR, GKVK, Bellary Road, Bangalore 560065 India
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62
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Wang SR, Zhang D, Luo FL, Liu L, Weng XC, Huang J, Li GR, Zhang XL, Zhou X. Some cationic porphyrins: synthesis, stabilization of G-quadruplexes, and down-regulation of c-myc in Hep G2 cells. J PORPHYR PHTHALOCYA 2012. [DOI: 10.1142/s1088424609001121] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
The stabilization of G-quadruplex DNA represents an attractive strategy for the design and development of novel antitumor drugs. In the present work, we have designed and synthesized nine cationic porphyrins, each with four side arms at their meso positions. The interactions of these porphyrins with both human telomeric DNA and NHE III1 G-quadruplexes were measured by various DNA binding assays, including polymerase stop assay, circular dichroism (CD) and CD melting assay. We then proceeded to investigate their effects on the expression of c-myc oncogene in the Hep G2 cell line. The experimental results indicate that these porphyrins are capable of effectively inducing or stabilizing both human telomeric and NHE III1 G-quadruplexes in the presence or absence of metal ions. Furthermore, we have discovered that porphyrins with a stronger stabilizing effect on c-myc G-quadruplexes lead to more pronounced down-regulation of the c-myc oncogene in the Hep G2 cell line.
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Affiliation(s)
- Shao R. Wang
- College of Chemistry and Molecular Sciences, Wuhan University, Hubei, Wuhan 430072, P.R. China
| | - Dan Zhang
- College of Chemistry and Molecular Sciences, Wuhan University, Hubei, Wuhan 430072, P.R. China
| | - Feng L. Luo
- State Key Laboratory of Virology, Department of Immunology, Hubei Province Key Laboratory of Allergy and Immunology, Wuhan University School of Medicine, Wuhan 430071, P.R. China
| | - Lin Liu
- College of Chemistry and Molecular Sciences, Wuhan University, Hubei, Wuhan 430072, P.R. China
| | - Xiao C. Weng
- College of Chemistry and Molecular Sciences, Wuhan University, Hubei, Wuhan 430072, P.R. China
| | - Jing Huang
- College of Chemistry and Molecular Sciences, Wuhan University, Hubei, Wuhan 430072, P.R. China
| | - Guo R. Li
- College of Chemistry and Molecular Sciences, Wuhan University, Hubei, Wuhan 430072, P.R. China
| | - Xiao L. Zhang
- State Key Laboratory of Virology, Department of Immunology, Hubei Province Key Laboratory of Allergy and Immunology, Wuhan University School of Medicine, Wuhan 430071, P.R. China
| | - Xiang Zhou
- College of Chemistry and Molecular Sciences, Wuhan University, Hubei, Wuhan 430072, P.R. China
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63
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Circular dichroism and guanine quadruplexes. Methods 2012; 57:64-75. [PMID: 22450044 DOI: 10.1016/j.ymeth.2012.03.011] [Citation(s) in RCA: 311] [Impact Index Per Article: 25.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2012] [Revised: 03/08/2012] [Accepted: 03/09/2012] [Indexed: 11/22/2022] Open
Abstract
Circular dichroism (CD) is remarkably sensitive to the conformational states of nucleic acids; therefore, CD spectroscopy has been used to study most features of DNA and RNA structures. Quadruplexes are among the significant noncanonical nucleic acids architectures that have received special attentions recently. This article presents examples on the contribution of CD spectroscopy to our knowledge of quadruplex structures and their polymorphism. The examples were selected to demonstrate the potential of this simple method in the quadruplex field. As CD spectroscopy detects only the global feature of a macromolecule, it should preferably be used in combination with other techniques. On the other hand, CD spectroscopy, often as a pioneering approach, can reveal the formation of particular structural arrangements, to search for the conditions stabilizing the structures, to follow the transitions between various structural states, to explore kinetics of their appearance, to determine thermodynamic parameters and also detect formation of higher order structures. This article aims to show that CD spectroscopy is an important complementary technique to NMR spectroscopy and X-ray diffraction in quadruplex studies.
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64
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Sedoris KC, Thomas SD, Clarkson CR, Muench D, Islam A, Singh R, Miller DM. Genomic c-Myc quadruplex DNA selectively kills leukemia. Mol Cancer Ther 2011; 11:66-76. [PMID: 22084162 DOI: 10.1158/1535-7163.mct-11-0515] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
c-Myc, a key regulator of cell cycle and proliferation, is commonly overexpressed in leukemia and associated with poor prognosis. Conventional antisense oligonucleotides targeting c-myc may attenuate leukemic cell growth, however, are poorly taken into cells, rapidly degraded, and have unwanted effects on normal cells. The c-myc promoter contains a guanine-rich sequence (PU27) capable of forming quadruplex (four-stranded) DNA, which may negatively regulate c-myc transcription. However, its biological significance is unknown. We show that treatment of leukemia with an oligonucleotide encoding the genomic PU27 sequence induces cell-cycle arrest and death by oncotic necrosis due to PU27-mediated suppression of c-myc mRNA/protein expression. Furthermore, PU27 is abundantly taken into cells, localized in the cytoplasm/nucleus, inherently stable in serum and intracellularly, and has no effect on normal cells. Suppression of c-myc expression by PU27 caused significant DNA damage, cell and mitochondrial swelling, and membrane permeability characteristic of oncotic necrosis. Induction of oncosis caused mitochondrial dysfunction, depletion of cellular ATP levels, and enhanced oxidative stress. This novel antileukemic strategy addresses current concerns of oligonucleotide therapeutics including problems with uptake, stability, and unintentional effects on normal cells and is the first report of selective cancer cell killing by a genomic DNA sequence.
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Affiliation(s)
- Kara C Sedoris
- Department of Medicine, James Graham Brown Cancer Center, University of Louisville School of Medicine, Louisville, Kentucky 40202, USA
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65
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Influence of pH, temperature and the cationic porphyrin TMPyP4 on the stability of the i-motif formed by the 5′-(C3TA2)4-3′ sequence of the human telomere. Int J Biol Macromol 2011; 49:729-36. [DOI: 10.1016/j.ijbiomac.2011.07.004] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2011] [Revised: 07/04/2011] [Accepted: 07/05/2011] [Indexed: 12/11/2022]
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66
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Collie GW, Parkinson GN. The application of DNA and RNA G-quadruplexes to therapeutic medicines. Chem Soc Rev 2011; 40:5867-92. [PMID: 21789296 DOI: 10.1039/c1cs15067g] [Citation(s) in RCA: 461] [Impact Index Per Article: 35.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
The intriguing structural diversity in folded topologies available to guanine-rich nucleic acid repeat sequences have made four-stranded G-quadruplex structures the focus of both basic and applied research, from cancer biology and novel therapeutics through to nanoelectronics. Distributed widely in the human genome as targets for regulating gene expression and chromosomal maintenance, they offer unique avenues for future cancer drug development. In particular, the recent advances in chemical and structural biology have enabled the construction of bespoke selective DNA based aptamers to be used as novel therapeutic agents and access to detailed structural models for structure based drug discovery. In this critical review, we will explore the important underlying characteristics of G-quadruplexes that make them functional, stable, and predictable nanoscaffolds. We will review the current structural database of folding topologies, molecular interfaces and novel interaction surfaces, with a consideration to their future exploitation in drug discovery, molecular biology, supermolecular assembly and aptamer design. In recent years the number of potential applications for G-quadruplex motifs has rapidly grown, so in this review we aim to explore the many future challenges and highlight where possible successes may lie. We will highlight the similarities and differences between DNA and RNA folded G-quadruplexes in terms of stability, distribution, and exploitability as small molecule targets. Finally, we will provide a detailed review of basic G-quadruplex geometry, experimental tools used, and a critical evaluation of the application of high-resolution structural biology and its ability to provide meaningful and valid models for future applications (255 references).
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Affiliation(s)
- Gavin W Collie
- CRUK Biomolecular Structure Group, The School of Pharmacy, University of London, London, UK WC1N 1AX
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67
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Abstract
G-quadruplexes are four-stranded DNA structures that are over-represented in gene promoter regions and are viewed as emerging therapeutic targets in oncology, as transcriptional repression of oncogenes through stabilization of these structures could be a novel anticancer strategy. Many gene promoter G-quadruplexes have physicochemical properties and structural characteristics that might make them druggable, and their structural diversity suggests that a high degree of selectivity might be possible. Here, we describe the evidence for G-quadruplexes in gene promoters and discuss their potential as therapeutic targets, as well as progress in the development of strategies to harness this potential through intervention with small-molecule ligands.
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68
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Zikich D, Liu K, Sagiv L, Porath D, Kotlyar A. I-motif nanospheres: unusual self-assembly of long cytosine strands. SMALL (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2011; 7:1029-34. [PMID: 21381197 DOI: 10.1002/smll.201002213] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/04/2010] [Revised: 01/14/2011] [Indexed: 05/25/2023]
Abstract
The synthesis and characterization of novel DNA structures based on tetraplex cytosine (C) arrangements, known as i-motifs or i-tetraplexes, is reported. Atomic force microscopy (AFM) investigation shows that long C-strands in mild acidic conditions form compact spherically shaped nanostructures. The DNA nanospheres are characterized by a typical uniform shape and narrow height distribution. Electrostatic force microscopy (EFM) measurements performed on the i-motif spheres clearly show their electrical polarizability. Further investigations by scanning tunneling microscopy (STM) at ultrahigh vacuum reveals that the structures exhibit an average voltage gap of 1.9 eV, which is narrower than the voltage gap previously measured for poly(dG)-poly(dC) molecules in similar conditions.
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Affiliation(s)
- Dragoslav Zikich
- Department of Biochemistry George S. Wise Faculty of Life Sciences, Tel Aviv University Ramat Aviv 69978, Israel
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69
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Spectrometric study of the folding process of i-motif-forming DNA sequences upstream of the c-kit transcription initiation site. Anal Chim Acta 2010; 683:69-77. [DOI: 10.1016/j.aca.2010.10.008] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2010] [Revised: 10/04/2010] [Accepted: 10/06/2010] [Indexed: 12/30/2022]
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70
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Chemical equilibria studies using multivariate analysis methods. Anal Bioanal Chem 2010; 399:1983-97. [DOI: 10.1007/s00216-010-4310-7] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2010] [Revised: 10/02/2010] [Accepted: 10/06/2010] [Indexed: 12/30/2022]
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71
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Dettler JM, Buscaglia R, Cui J, Cashman D, Blynn M, Lewis EA. Biophysical characterization of an ensemble of intramolecular i-motifs formed by the human c-MYC NHE III1 P1 promoter mutant sequence. Biophys J 2010; 99:561-7. [PMID: 20643075 DOI: 10.1016/j.bpj.2010.04.042] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2009] [Revised: 03/16/2010] [Accepted: 04/05/2010] [Indexed: 10/19/2022] Open
Abstract
i-Motif-forming sequences are present in or near the regulatory regions of >40% of all genes, including known oncogenes. We report here the results of a biophysical characterization and computational study of an ensemble of intramolecular i-motifs that model the polypyrimidine sequence in the human c-MYC P1 promoter. Circular dichroism results demonstrate that the mutant sequence (5'-CTT TCC TAC CCTCCC TAC CCT AA-3') can adopt multiple "i-motif-like," classical i-motif, and single-stranded structures as a function of pH. The classical i-motif structures are predominant in the pH range 4.2-5.2. The "i-motif-like" and single-stranded structures are the most significant species in solution at pH higher and lower, respectively, than that range. Differential scanning calorimetry results demonstrate an equilibrium mixture of at least three i-motif folded conformations with Tm values of 38.1, 46.6, and 49.5 degrees C at pH 5.0. The proposed ensemble of three folded conformations includes the three lowest-energy conformations obtained by computational modeling and two folded conformers that were proposed in a previous NMR study. The NMR study did not report the most stable conformer found in this study.
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Affiliation(s)
- Jamie M Dettler
- Department of Chemistry, Mississippi State University, Mississippi State, Mississippi, USA
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72
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Wang P, Leung CH, Ma DL, Yan SC, Che CM. Structure-based design of platinum(II) complexes as c-myc oncogene down-regulators and luminescent probes for G-quadruplex DNA. Chemistry 2010; 16:6900-11. [PMID: 20437426 DOI: 10.1002/chem.201000167] [Citation(s) in RCA: 100] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
A series of platinum(II) complexes with tridentate ligands was synthesized and their interactions with G-quadruplex DNA within the c-myc gene promoter were evaluated. Complex 1, which has a flat planar 2,6-bis(benzimidazol-2-yl)pyridine (bzimpy) scaffold, was found to stabilize the c-myc G-quadruplex structure in a cell-free system. An in silico G-quadruplex DNA model has been constructed for structure-based virtual screening to develop new Pt(II)-based complexes with superior inhibitory activities. By using complex 1 as the initial structure for hit-to-lead optimization, bzimpy and related 2,6-bis(pyrazol-3-yl)pyridine (dPzPy) scaffolds containing amine side-chains emerge as the top candidates. Six of the top-scoring complexes were synthesized and their interactions with c-myc G-quadruplex DNA have been investigated. The results revealed that all of the complexes have the ability to stabilize the c-myc G-quadruplex. Complex 3 a ([Pt(II)L2R](+); L2=2,6-bis[1-(3-piperidinepropyl)-1H-enzo[d]imidazol-2-yl]pyridine, R=Cl) displayed the strongest inhibition in a cell-free system (IC(50)=2.2 microM) and was 3.3-fold more potent than that of 1. Complexes 3 a and 4 a ([Pt(II)L3R](+); L3=2,6-bis[1-(3-morpholinopropyl)-1H-pyrazol-3-yl]pyridine, R=Cl) were found to effectively inhibit c-myc gene expression in human hepatocarcinoma cells with IC(50) values of approximately 17 microM, whereas initial hit 1 displayed no significant effect on gene expression at concentrations up to 50 microM. Complexes 3 a and 4 a have a strong preference for G-quadruplex DNA over duplex DNA, as revealed by competition dialysis experiments and absorption titration; 3 a and 4 a bind G-quadruplex DNA with binding constants (K) of approximately 10(6)-10(7) dm(3) mol(-1), which are at least an order of magnitude higher than the K values for duplex DNA. NMR spectroscopic titration experiments and molecular modeling showed that 4 a binds c-myc G-quadruplex DNA through an external end-stacking mode at the 3'-terminal face of the G-quadruplex. Intriguingly, binding of c-myc G-quadruplex DNA by 3 b is accompanied by an increase of up to 38-fold in photoluminescence intensity at lambda(max)=622 nm.
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Affiliation(s)
- Ping Wang
- Department of Chemistry and Open Laboratory of Chemical Biology of the Institute of Molecular Technology for Drug Discovery and Synthesis, The University of Hong Kong, Pokfulam Road, Hong Kong, PR China
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73
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Stasik CJ, Nitta H, Zhang W, Mosher CH, Cook JR, Tubbs RR, Unger JM, Brooks TA, Persky DO, Wilkinson ST, Grogan TM, Rimsza LM. Increased MYC gene copy number correlates with increased mRNA levels in diffuse large B-cell lymphoma. Haematologica 2010; 95:597-603. [PMID: 20378577 DOI: 10.3324/haematol.2009.012864] [Citation(s) in RCA: 81] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
BACKGROUND Translocations involving the MYC gene and increased MYC mRNA levels are associated with poor outcome in diffuse large B-cell lymphoma. However, the presence of increased MYC gene copy number and/or polysomy of chromosome 8 have not been previously described. DESIGN AND METHODS Utilizing dual color chromogenic in situ hybridization, we investigated MYC gene copy and chromosome 8 centromere numbers in 52 cases of diffuse large B-cell lymphoma. Cases were divided into those with "increased" or "not increased" MYC gene copy number for comparison with MYC mRNA levels, Ki-67 values, and survival. RESULTS Increased MYC gene copy number was present in 38% of cases. Overall, the average MYC mRNA level was 2398 (range, 342 - 9783) and the percentage of nuclei positive for Ki-67 was 57.5% (range, 20-87%). Within the group with increased MYC copy number, the MYC mRNA values ranged from 816 to 5912 (average, 2843) and the Ki-67 values ranged from 23% to 83% (average, 57%). Within the group with not increased MYC copy number, MYC mRNA values ranged from 342 to 9783 (average, 2118) and the Ki-67 values ranged from 20% to 87% (average, 58%). There was a statistically significant relationship between increased MYC gene copy number and increased MYC mRNA (P=0.034) and a trend toward a relationship between increased mRNA and higher Ki-67 values. CONCLUSIONS This is the first report that low level copy number increases are common in diffuse large B-cell lymphoma and that these changes correlate with MYC mRNA in a statistically significant manner. MYC copy number changes are an additional possible molecular mechanism that may result in increased mRNA and, likely, high proliferation and poor outcome.
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Affiliation(s)
- Christopher J Stasik
- Department of Pathology, University of Arizona, 1501 N Campbell Avenue, PO Box 245043, Tucson, AZ 85724-5043, USA
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74
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Abstract
In this review, the authors describe a novel mechanism for control of MYC expression that involves a four-stranded DNA structure, termed a G-quadruplex, amenable to small molecule targeting. The DNA element involved in this mechanism, the nuclease hypersensitive element III(1) (NHE III(1)), is just upstream of the P1 promoter and is subjected to dynamic stress (negative superhelicity) resulting from transcription. This is sufficient to convert the duplex DNA to a G-quadruplex on the purine-rich strand and an i-motif of the pyrimidine-rich strand, which displaces the activating transcription factors to silence gene expression. Specific proteins have been identified, NM23-H2 and nucleolin, that resolve and fold the G-quadruplex to activate and silence MYC expression, respectively. Inhibition of the activity of NM23-H2 molecules that bind to the G-quadruplex silences gene expression, and redistribution of nucleolin from the nucleolus to the nucleoplasm is expected to inhibit MYC. The authors also describe the mechanism of action of Quarfloxin, a first-in-class G-quadruplex-interactive compound that involves the redistribution of nucleolin from the nucleolus to the nucleoplasm. G-quadruplexes have been best known as test-tube oddities for more than four decades. However, during the past decade, they have emerged as likely players in a number of important biological processes, including transcriptional control. Only time will tell if these odd DNA structures will assume the role of an established receptor class, but it is clear from the scientific literature that there is a dramatic increase in interest in this little-known area in the past few years.
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Affiliation(s)
- Tracy A Brooks
- College of Pharmacy, BIO5 Institute, and Arizona Cancer Center, University of Arizona, Tucson, AZ, USA
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75
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Agarwal T, Roy S, Chakraborty TK, Maiti S. Furan based cyclic homo-oligopeptides bind G-quadruplex selectively and repress c-MYC transcription. Bioorg Med Chem Lett 2010; 20:4346-9. [DOI: 10.1016/j.bmcl.2010.06.080] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2010] [Revised: 05/24/2010] [Accepted: 06/14/2010] [Indexed: 12/01/2022]
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76
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Dai J, Hatzakis E, Hurley LH, Yang D. I-motif structures formed in the human c-MYC promoter are highly dynamic--insights into sequence redundancy and I-motif stability. PLoS One 2010; 5:e11647. [PMID: 20657837 PMCID: PMC2906509 DOI: 10.1371/journal.pone.0011647] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2010] [Accepted: 06/22/2010] [Indexed: 11/24/2022] Open
Abstract
The GC-rich nuclease hypersensitivity element III1 (NHE III1) of the c-MYC promoter largely controls the transcriptional activity of the c-MYC oncogene. The C-rich strand in this region can form I-motif DNA secondary structures. We determined the folding pattern of the major I-motif formed in the NHE III1, which can be formed at near-neutral pH. While we find that the I-motif formed in the four 3′ consecutive runs of cytosines appears to be the most favored, our results demonstrate that the C-rich strand of the c-MYC NHE III1 exhibits a high degree of dynamic equilibration. Using a trisubstituted oligomer of this region, we determined the formation of two equilibrating loop isomers, one of which contains a flipped-out cytosine. Our results indicate that the intercalative cytosine+–cytosine base pairs are not always necessary for an intramolecular I-motif. The dynamic character of the c-MYC I-motif is intrinsic to the NHE III1 sequence and appears to provide stability to the c-MYC I-motif.
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Affiliation(s)
- Jixun Dai
- College of Pharmacy, The University of Arizona, Tucson, Arizona, United States of America
| | - Emmanuel Hatzakis
- College of Pharmacy, The University of Arizona, Tucson, Arizona, United States of America
| | - Laurence H. Hurley
- College of Pharmacy, The University of Arizona, Tucson, Arizona, United States of America
- BIO5 Institute, The University of Arizona, Tucson, Arizona, United States of America
- Arizona Cancer Center, The University of Arizona, Tucson, Arizona, United States of America
- Department of Chemistry, The University of Arizona, Tucson, Arizona, United States of America
| | - Danzhou Yang
- College of Pharmacy, The University of Arizona, Tucson, Arizona, United States of America
- BIO5 Institute, The University of Arizona, Tucson, Arizona, United States of America
- Arizona Cancer Center, The University of Arizona, Tucson, Arizona, United States of America
- Department of Chemistry, The University of Arizona, Tucson, Arizona, United States of America
- * E-mail:
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77
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Kendrick S, Hurley LH. The role of G-quadruplex/i-motif secondary structures as cis-acting regulatory elements. ACTA ACUST UNITED AC 2010; 82:1609-1621. [PMID: 21796223 DOI: 10.1351/pac-con-09-09-29] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
The nature of DNA has captivated scientists for more than fifty years. The discovery of the double-helix model of DNA by Watson and Crick in 1953 not only established the primary structure of DNA, but also provided the mechanism behind DNA function. Since then, researchers have continued to further the understanding of DNA structure and its pivotal role in transcription. The demonstration of DNA secondary structure formation has allowed for the proposal that the dynamics of DNA itself can function to modulate transcription. This review presents evidence that DNA can exist in a dynamic equilibrium between duplex and secondary conformations. In addition, data demonstrating that intracellular proteins as well as small molecules can shift this equilibrium in either direction to alter gene transcription will be discussed, with a focus on the modulation of proto-oncogene expression.
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78
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Abstract
c-MYC is an important regulator of a wide array of cellular processes necessary for normal cell growth and differentiation, and its dysregulation is one of the hallmarks of many cancers. Consequently, understanding c-MYC transcriptional activation is critical for understanding developmental and cancer biology, as well as for the development of new anticancer drugs. The nuclease hypersensitive element (NHE) III(1) region of the c-MYC promoter has been shown to be particularly important in regulating c-MYC expression. Specifically, the formation of a G-quadruplex structure appears to promote repression of c-MYC transcription. This review focuses on what is known about the formation of a G-quadruplex in the NHE III(1) region of the c-MYC promoter, as well as on those factors that are known to modulate its formation. Last, we discuss the development of small molecules that stabilize or induce the formation of G-quadruplex structures and could potentially be used as anticancer agents.
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79
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Kendrick S, Akiyama Y, Hecht SM, Hurley LH. The i-motif in the bcl-2 P1 promoter forms an unexpectedly stable structure with a unique 8:5:7 loop folding pattern. J Am Chem Soc 2010; 131:17667-76. [PMID: 19908860 DOI: 10.1021/ja9076292] [Citation(s) in RCA: 111] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Transcriptional regulation of the bcl-2 proto-oncogene is highly complex, with the majority of transcription driven by the P1 promoter site and the interaction of multiple regulatory proteins. A guanine- and cytosine-rich (GC-rich) region directly upstream of the P1 site has been shown to be integral to bcl-2 promoter activity, as deletion or mutation of this region significantly increases transcription. This GC-rich element consists of six contiguous runs of guanines and cytosines that have the potential to adopt DNA secondary structures, the G-quadruplex and i-motif, respectively. Our laboratory has previously demonstrated that the polypurine-rich strand of the bcl-2 promoter can form a mixture of three different G-quadruplex structures. In this current study, we demonstrate that the complementary polypyrimidine-rich strand is capable of forming one major intramolecular i-motif DNA secondary structure with a transition pH of 6.6. Characterization of the i-motif folding pattern using mutational studies coupled with circular dichroic spectra and thermal stability analyses revealed an 8:5:7 loop conformation as the predominant structure at pH 6.1. The folding pattern was further supported by chemical footprinting with bromine. In addition, a novel assay involving the sequential incorporation of a fluorescent thymine analog at each thymine position provided evidence of a capping structure within the top loop region of the i-motif. The potential of the GC-rich element within the bcl-2 promoter region to form DNA secondary structures suggests that the transition from the B-DNA to non-B-DNA conformation may play an important role in bcl-2 transcriptional regulation. Furthermore, the two adjacent large lateral loops in the i-motif structure provide an unexpected opportunity for protein and small molecule recognition.
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Affiliation(s)
- Samantha Kendrick
- Arizona Cancer Center, 1515 North Campbell Avenue, Tucson, Arizona 85724, USA
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80
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Kaushik M, Prasad M, Kaushik S, Singh A, Kukreti S. Structural transition from dimeric to tetrameric i-motif, caused by the presence of TAA at the 3â²-end of human telomeric C-rich sequence. Biopolymers 2010; 93:150-60. [DOI: 10.1002/bip.21313] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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81
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Wu P, Ma DL, Leung CH, Yan SC, Zhu N, Abagyan R, Che CM. Stabilization of G-quadruplex DNA with platinum(II) Schiff base complexes: luminescent probe and down-regulation of c-myc oncogene expression. Chemistry 2010; 15:13008-21. [PMID: 19876976 DOI: 10.1002/chem.200901943] [Citation(s) in RCA: 129] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
The interactions of a series of platinum(II) Schiff base complexes with c-myc G-quadruplex DNA were studied. Complex [PtL(1a)] (1 a; H(2)L(1a)=N,N'-bis(salicylidene)-4,5-methoxy-1,2-phenylenediamine) can moderately inhibit c-myc gene promoter activity in a cell-free system through stabilizing the G-quadruplex structure and can inhibit c-myc oncogene expression in cultured cells. The interaction between 1 a and G-quadruplex DNA has been examined by (1)H NMR spectroscopy. By using computer-aided structure-based drug design for hit-to-lead optimization, an in silico G-quadruplex DNA model has been constructed for docking-based virtual screening to develop new platinum(II) Schiff base complexes with improved inhibitory activities. Complex [PtL(3)] (3; H(2)L(3)=N,N'-bis{4-[1-(2-propylpiperidine)oxy]salicylidene}-4,5-methoxy-1,2-phenylenediamine) has been identified with a top score in the virtual screening. This complex was subsequently prepared and experimentally tested in vitro for its ability to stabilize or induce the formation of the c-myc G-quadruplex. The inhibitory activity of 3 (IC(50)=4.4 muM) is tenfold more than that of 1 a. The interaction between 1 a or 3 with c-myc G-quadruplex DNA has been examined by absorption titration, emission titration, molecular modeling, and NMR titration experiments, thus revealing that both 1 a and 3 bind c-myc G-quadruplex DNA through an external end-stacking mode at the 3' terminal face of the G-quadruplex. Such binding of G-quadruplex DNA with 3 is accompanied by up to an eightfold increase in the intensity of photoluminescence at lambda(max)=652 nm. Complex 3 also effectively down-regulated the expression of c-myc in human hepatocarcinoma cells.
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Affiliation(s)
- Peng Wu
- Department of Chemistry and Open Laboratory of Chemical Biology, Institute of Molecular Technology for Drug Discovery and Synthesis, The University of Hong Kong, Pokfulam Road, Hong Kong, China
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82
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Zhou J, Wei C, Jia G, Wang X, Feng Z, Li C. Formation of i-motif structure at neutral and slightly alkaline pH. MOLECULAR BIOSYSTEMS 2009; 6:580-6. [PMID: 20174686 DOI: 10.1039/b919600e] [Citation(s) in RCA: 84] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
It is well known that oligonucleotides containing tracts cytosines can form i-motif structures under acidic conditions (pH < 7). However, whether i-motif can be formed under normal physiological cellular conditions (pH 7.0-7.5) is yet no conclusive proof. In the present work, using circular dichroism (CD), UV absorption spectroscopies and native polyacrylamide gel electrophoresis (PAGE), we provided the compelling evidence for the formation of i-motif structures by four cytosine clusters, [C(3)TA(2)](3)C(3) (HT), [C(4)G](3)C(4)TA (RET), C(2)T(3)C(2)T(4)C(2)T(3)C(2) (CTC) and GC(2)GC(3)A(4)C(6)G (Rb), at neutral and slightly alkaline pH at 4 degrees C. Furthermore, for HT, we also supplied the evidence for the formation of i-motif structure by fluorescence resonance energy transfer (FRET) and investigated its folding kinetics. The formation time constants obtained by CD and fluorescence experiments are 214 and 493 s, respectively, indicating that HT can slowly form i-motif structure at pH 7.0 and 4 degrees C. This work implies that i-motif structures may possible form in vivo.
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Affiliation(s)
- Jun Zhou
- State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China
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83
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Brooks TA, Hurley LH. The role of supercoiling in transcriptional control of MYC and its importance in molecular therapeutics. Nat Rev Cancer 2009; 9:849-61. [PMID: 19907434 DOI: 10.1038/nrc2733] [Citation(s) in RCA: 228] [Impact Index Per Article: 15.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
MYC is deregulated in most tumour types, but an effective means to selectively target its aberrant expression is not yet available. Supercoiling that is induced by transcription has been demonstrated to have dynamic effects on DNA in the MYC promoter element: it converts duplex DNA to non-duplex DNA structures, even at considerable distances from the transcriptional start site. These non-duplex DNA structures, which control both turning on and off of transcription and the rate of transcription firing, are amenable to small-molecule targeting. This dynamic system provides a unique opportunity for the treatment of tumours in which MYC is an important oncogene.
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Affiliation(s)
- Tracy A Brooks
- College of Pharmacy, University of Arizona, Tucson, Arizona 85721, USA
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84
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Bucek P, Jaumot J, Aviñó A, Eritja R, Gargallo R. pH-Modulated WatsonâCrick DuplexâQuadruplex Equilibria of Guanine-Rich and Cytosine-Rich DNA Sequences 140 Base Pairs Upstream of thec-kitTranscription Initiation Site. Chemistry 2009; 15:12663-71. [DOI: 10.1002/chem.200901631] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
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85
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Dai J, Ambrus A, Hurley LH, Yang D. A direct and nondestructive approach to determine the folding structure of the I-motif DNA secondary structure by NMR. J Am Chem Soc 2009; 131:6102-4. [PMID: 19400591 DOI: 10.1021/ja900967r] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
I-motifs are four-stranded DNA secondary structures formed in C-rich DNA sequences and consist of parallel-stranded DNA duplexes zipped together in an antiparallel orientation by intercalated, hemiprotonated cytosine(+)-cytosine base pairs. I-motif structures have been indicated to form in various regions of the human genome as well as in nanotechnological applications. While NMR is a major tool for structural studies of I-motifs, the determination of the folding topologies of unimolecular I-motifs has been a challenging and arduous task using conventional NMR spectral assignment strategies, due to the inherent sequence redundancy of the C-rich strands in the formation of unimolecular I-motif structures. We report here a direct and nondestructive method that can be utilized to unambiguously determine the hemiprotonated C(+)-C base pairs and thus the folding topology of unimolecular I-motif structures formed from native C-rich DNA sequences. The reported approach uses affordable low-enrichment site-specific labeling. More significantly, the reported method can directly and unambiguously determine the equilibrating multiple conformations coexisting in a single DNA sequence, which would be a very difficult task using conventional assignment strategies. Additionally, this method can be applied to the direct detection of the base-paired thymines that are involved in the capping structures.
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Affiliation(s)
- Jixun Dai
- College of Pharmacy, The University of Arizona, Tucson, Arizona 85721, USA
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86
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Sun D, Hurley LH. The importance of negative superhelicity in inducing the formation of G-quadruplex and i-motif structures in the c-Myc promoter: implications for drug targeting and control of gene expression. J Med Chem 2009; 52:2863-74. [PMID: 19385599 DOI: 10.1021/jm900055s] [Citation(s) in RCA: 288] [Impact Index Per Article: 19.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
The importance of DNA supercoiling in transcriptional regulation has been known for many years, and more recently, transcription itself has been shown to be a source of this superhelicity. To mimic the effect of transcriptionally induced negative superhelicity, the G-quadruplex/i-motif-forming region in the c-Myc promoter was incorporated into a supercoiled plasmid. We show, using enzymatic and chemical footprinting, that negative superhelicity facilitates the formation of secondary DNA structures under physiological conditions. Significantly, these structures are not the same as those formed in single-stranded DNA templates. Together with the recently demonstrated role of transcriptionally induced superhelicity in maintaining a mechanosensor mechanism for controlling the firing rate of the c-Myc promoter, we provide a more complete picture of how c-Myc transcription is likely controlled. Last, these physiologically relevant G-quadruplex and i-motif structures, along with the mechanosensor mechanism for control of gene expression, are proposed as novel mechanisms for small molecule targeting of transcriptional control of c-Myc.
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Affiliation(s)
- Daekyu Sun
- College of Pharmacy, University of Arizona, Tucson, Arizona 85721, USA.
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87
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Arora A, Nair DR, Maiti S. Effect of flanking bases on quadruplex stability and Watson-Crick duplex competition. FEBS J 2009; 276:3628-40. [PMID: 19490117 DOI: 10.1111/j.1742-4658.2009.07082.x] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
Abstract
Guanine-rich DNA sequences have the ability to fold into four-stranded structures called G-quadruplexes, and are considered as promising anticancer targets. Although the G-quadruplex structure is composed of quartets and interspersed loops, in the genome it is also flanked on each side by numerous bases. The effect of loop length and composition on quadruplex conformation and stability has been well investigated in the past, but the effect of flanking bases on quadruplex stability and Watson-Crick duplex competition has not been addressed. We have studied in detail the effect of flanking bases on quadruplex stability and on duplex formation by the G-quadruplex in the presence of complementary strands using the quadruplex-forming sequence located in the promoter region of the c-kit oncogene. The results obtained from CD, thermal difference spectrum and UV melting demonstrated the effect of flanking bases on quadruplex structure and stability. With the increase in flank length, the increase in the more favorable DeltaH(vH) is accompanied by a striking increase in the unfavorable DeltaS(vH), which resulted in a decrease in the overall DeltaG(vH) of quadruplex formation. Furthermore, CD, fluorescence and isothermal titration calorimetry studies demonstrated that the propensity to attain quadruplex structure decreases with increasing flank length.
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Affiliation(s)
- Amit Arora
- Proteomics and Structural Biology Unit, Institute of Genomics and Integrative Biology, Council for Scientific and Industrial Research, Delhi, India
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88
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Dexheimer TS, Carey SS, Zuohe S, Gokhale VM, Hu X, Murata LB, Maes EM, Weichsel A, Sun D, Meuillet EJ, Montfort WR, Hurley LH. NM23-H2 may play an indirect role in transcriptional activation of c-myc gene expression but does not cleave the nuclease hypersensitive element III(1). Mol Cancer Ther 2009; 8:1363-77. [PMID: 19435876 DOI: 10.1158/1535-7163.mct-08-1093] [Citation(s) in RCA: 85] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The formation of G-quadruplex structures within the nuclease hypersensitive element (NHE) III(1) region of the c-myc promoter and the ability of these structures to repress c-myc transcription have been well established. However, just how these extremely stable DNA secondary structures are transformed to activate c-myc transcription is still unknown. NM23-H2/nucleoside diphosphate kinase B has been recognized as an activator of c-myc transcription via interactions with the NHE III(1) region of the c-myc gene promoter. Through the use of RNA interference, we confirmed the transcriptional regulatory role of NM23-H2. In addition, we find that further purification of NM23-H2 results in loss of the previously identified DNA strand cleavage activity, but retention of its DNA binding activity. NM23-H2 binds to both single-stranded guanine- and cytosine-rich strands of the c-myc NHE III(1) and, to a lesser extent, to a random single-stranded DNA template. However, it does not bind to or cleave the NHE III(1) in duplex form. Significantly, potassium ions and compounds that stabilize the G-quadruplex and i-motif structures have an inhibitory effect on NM23-H2 DNA-binding activity. Mutation of Arg(88) to Ala(88) (R88A) reduced both DNA and nucleotide binding but had minimal effect on the NM23-H2 crystal structure. On the basis of these data and molecular modeling studies, we have proposed a stepwise trapping-out of the NHE III(1) region in a single-stranded form, thus allowing single-stranded transcription factors to bind and activate c-myc transcription. Furthermore, this model provides a rationale for how the stabilization of the G-quadruplex or i-motif structures formed within the c-myc gene promoter region can inhibit NM23-H2 from activating c-myc gene expression.
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89
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Abstract
Using spectroscopic techniques, we demonstrate the effect of LNA (locked nucleic acid) nucleotides in modulating the formation and stability of the i-motif structure formed by the c-MYC sequence.
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Affiliation(s)
- Niti Kumar
- Structural Biology Unit, Institute of Genomics and Integrative Biology, CSIR, Mall Road, New Delhi 110 007, India
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90
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Kypr J, Kejnovská I, Renciuk D, Vorlícková M. Circular dichroism and conformational polymorphism of DNA. Nucleic Acids Res 2009; 37:1713-25. [PMID: 19190094 PMCID: PMC2665218 DOI: 10.1093/nar/gkp026] [Citation(s) in RCA: 1259] [Impact Index Per Article: 83.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Here we review studies that provided important information about conformational properties of DNA using circular dichroic (CD) spectroscopy. The conformational properties include the B-family of structures, A-form, Z-form, guanine quadruplexes, cytosine quadruplexes, triplexes and other less characterized structures. CD spectroscopy is extremely sensitive and relatively inexpensive. This fast and simple method can be used at low- as well as high-DNA concentrations and with short- as well as long-DNA molecules. The samples can easily be titrated with various agents to cause conformational isomerizations of DNA. The course of detected CD spectral changes makes possible to distinguish between gradual changes within a single DNA conformation and cooperative isomerizations between discrete structural states. It enables measuring kinetics of the appearance of particular conformers and determination of their thermodynamic parameters. In careful hands, CD spectroscopy is a valuable tool for mapping conformational properties of particular DNA molecules. Due to its numerous advantages, CD spectroscopy significantly participated in all basic conformational findings on DNA.
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Affiliation(s)
- Jaroslav Kypr
- Institute of Biophysics, vvi Academy of Sciences of the Czech Republic, Brno, Czech Republic.
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91
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Olsen CM, Lee HT, Marky LA. Unfolding Thermodynamics of Intramolecular G-Quadruplexes: Base Sequence Contributions of the Loops. J Phys Chem B 2008; 113:2587-95. [DOI: 10.1021/jp806853n] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Chris M. Olsen
- Department of Pharmaceutical Sciences, Department of Biochemistry and Molecular Biology, and Eppley Institute for Cancer Research, University of Nebraska Medical Center, Omaha, Nebraska 68198-6025
| | - Hui-Ting Lee
- Department of Pharmaceutical Sciences, Department of Biochemistry and Molecular Biology, and Eppley Institute for Cancer Research, University of Nebraska Medical Center, Omaha, Nebraska 68198-6025
| | - Luis A. Marky
- Department of Pharmaceutical Sciences, Department of Biochemistry and Molecular Biology, and Eppley Institute for Cancer Research, University of Nebraska Medical Center, Omaha, Nebraska 68198-6025
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92
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Kumar N, Maiti S. A thermodynamic overview of naturally occurring intramolecular DNA quadruplexes. Nucleic Acids Res 2008; 36:5610-22. [PMID: 18757890 PMCID: PMC2553590 DOI: 10.1093/nar/gkn543] [Citation(s) in RCA: 70] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
Loop length and its composition are important for the structural and functional versatility of quadruplexes. To date studies on the loops have mainly concerned model sequences compared with naturally occurring quadruplex sequences which have diverse loop lengths and compositions. Herein, we have characterized 36 quadruplex-forming sequences from the promoter regions of various proto-oncogenes using CD, UV and native gel electrophoresis. We examined folding topologies and determined the thermodynamic profile for quadruplexes varying in total loop length (5–18 bases) and composition. We found that naturally occurring quadruplexes have variable thermodynamic stabilities (ΔG37) ranging from −1.7 to −15.6 kcal/mol. Overall, our results suggest that both loop length and its composition affect quadruplex structure and thermodynamics, thus making it difficult to draw generalized correlations between loop length and thermodynamic stability. Additionally, we compared the thermodynamic stability of quadruplexes and their respective duplexes to understand quadruplex–duplex competition. Our findings invoke a discussion on whether biological function is associated with quadruplexes with lower thermodynamic stability which undergo facile formation and disruption, or by quadruplexes with high thermodynamic stability.
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Affiliation(s)
- Niti Kumar
- Proteomics and Structural Biology Unit, Institute of Genomics and Integrative Biology, CSIR, Mall Road, Delhi 110 007, India
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93
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Guo K, Gokhale V, Hurley LH, Sun D. Intramolecularly folded G-quadruplex and i-motif structures in the proximal promoter of the vascular endothelial growth factor gene. Nucleic Acids Res 2008; 36:4598-608. [PMID: 18614607 PMCID: PMC2504309 DOI: 10.1093/nar/gkn380] [Citation(s) in RCA: 133] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
A polyguanine/polycytosine (polyG/polyC) tract in the proximal promoter of the vascular endothelial growth factor (VEGF) gene is essential for transcriptional activation. The guanine-rich (G-rich) and cytosine-rich (C-rich) strands on this tract are shown to form specific secondary structures, characterized as G-quadruplexes and i-motifs, respectively. Mutational analysis of the G-rich strand combined with dimethyl sulfate (DMS) footprinting, a polymerase stop assay, and circular dichroism (CD) spectroscopy revealed that the G-quadruplex containing a 1:4:1 double-chain reversal loop is the most thermodynamically stable conformation that this strand readily adopts. These studies provide strong evidence that the size of loop regions plays a critical role in determining the most favored folding pattern of a G-quadruplex. The secondary structure formed on the complementary C-rich strand was also determined by mutational analysis combined with Br(2) footprinting and CD spectroscopy. Our results reveal that at a pH of 5.9 this strand is able to form an intramolecular i-motif structure that involves six C-C(+) base pairs and a 2:3:2 loop configuration. Taken together, our results demonstrate that the G-quadruplex and i-motif structures are able to form on the G- and C-rich strands, respectively, of the polyG/polyC tract in the VEGF proximal promoter under conditions that favor the transition from B-DNA to non-B-DNA conformations.
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Affiliation(s)
- Kexiao Guo
- Department of Biochemistry and Molecular Biophysics, University of Arizona, Tucson, AZ 85721, USA
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94
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Qin Y, Hurley LH. Structures, folding patterns, and functions of intramolecular DNA G-quadruplexes found in eukaryotic promoter regions. Biochimie 2008; 90:1149-71. [PMID: 18355457 DOI: 10.1016/j.biochi.2008.02.020] [Citation(s) in RCA: 373] [Impact Index Per Article: 23.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2008] [Accepted: 02/22/2008] [Indexed: 12/16/2022]
Abstract
In its simplest form, a DNA G-quadruplex is a four-stranded DNA structure that is composed of stacked guanine tetrads. G-quadruplex-forming sequences have been identified in eukaryotic telomeres, as well as in non-telomeric genomic regions, such as gene promoters, recombination sites, and DNA tandem repeats. Of particular interest are the G-quadruplex structures that form in gene promoter regions, which have emerged as potential targets for anticancer drug development. Evidence for the formation of G-quadruplex structures in living cells continues to grow. In this review, we examine recent studies on intramolecular G-quadruplex structures that form in the promoter regions of some human genes in living cells and discuss the biological implications of these structures. The identification of G-quadruplex structures in promoter regions provides us with new insights into the fundamental aspects of G-quadruplex topology and DNA sequence-structure relationships. Progress in G-quadruplex structural studies and the validation of the biological role of these structures in cells will further encourage the development of small molecules that target these structures to specifically modulate gene transcription.
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Affiliation(s)
- Yong Qin
- College of Pharmacy, 1703 E. Mabel, University of Arizona, Tucson, AZ 85721, USA
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95
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Saxena S, Bansal A, Kukreti S. Structural polymorphism exhibited by a homopurine.homopyrimidine sequence found at the right end of human c-jun protooncogene. Arch Biochem Biophys 2008; 471:95-108. [PMID: 18262488 DOI: 10.1016/j.abb.2008.01.015] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2007] [Revised: 01/15/2008] [Accepted: 01/19/2008] [Indexed: 11/17/2022]
Abstract
Homopurine.homopyrimidine (Pu.Py) tracts are likely to play important biological role in eukaryotes. Using circular dichroism, UV-thermal denaturation and gel electrophoresis, we have analyzed the structural polymorphism of a 21-bp Pu.Py DNA segment within human c-jun protooncogene 3'-region, a potential target for triplex formation. Results show that below physiological pH and in the presence of Na+/K+ with Mg2+ the duplex is destabilized/disproportionated, resulting in strand mediated structural transitions to the self-associated structures of G- and C-rich strands separately, identified as G-quadruplex and i-motif species. A significant differential behavior of the monovalent cations was observed, accordingly the presence of Na+ in acidic as well as neutral pH facilitated the duplex formation, while K+ favored the formation of self-associated structures. In Na+ and Mg2+, under acidic and neutral pH conditions, the duplex displayed triphasic and biphasic melting profiles, respectively. This self-association property of oligonucleotides might limit their use as duplex targets in triplex formation. Study is also relevant for understanding structural and biological properties of DNA sequence containing homopurine tracts.
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Affiliation(s)
- Sarika Saxena
- Nucleic Acids Research Laboratory, Department of Chemistry, University of Delhi (North Campus), Delhi 110007, India
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96
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97
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Molecular modeling and biophysical analysis of the c-MYC NHE-III1 silencer element. J Mol Model 2007; 14:93-101. [PMID: 18087730 DOI: 10.1007/s00894-007-0254-z] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2007] [Accepted: 11/07/2007] [Indexed: 12/31/2022]
Abstract
G-Quadruplex and i-Motif-forming sequences in the promoter regions of several oncogenes show promise as targets for the regulation of oncogenes. In this study, molecular models were created for the c-MYC NHE-III(1) (nuclease hypersensitivity element III(1)) from two 39-base complementary sequences. The NHE modeled here consists of single folded conformers of the polypurine intramolecular G-Quadruplex and the polypyrimidine intramolecular i-Motif structures, flanked by short duplex DNA sequences. The G-Quadruplex was based on published NMR structural data for the c-MYC 1:2:1 loop isomer. The i-Motif structure is theoretical (with five cytosine-cytosine pairs), where the central intercalated cytosine core interactions are based on NMR structural data obtained for a tetramolecular [d(A(2)C(4))(4)] model i-Motif. The loop structures are in silico predictions of the c-MYC i-motif loops. The porphyrin meso-tetra(N-methyl-4-pyridyl)porphine (TMPyP4), as well as the ortho and meta analogs TMPyP2 and TMPyP3, were docked to six different locations in the complete c-MYC NHE. Comparisons are made for drug binding to the NHE and the isolated G-Quadruplex and i-Motif structures. NHE models both with and without bound cationic porphyrin were simulated for 100 ps using molecular dynamics techniques, and the non-bonded interaction energies between the DNA and porphyrins calculated for all of the docking interactions.
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98
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Khan N, Aviñó A, Tauler R, González C, Eritja R, Gargallo R. Solution equilibria of the i-motif-forming region upstream of the B-cell lymphoma-2 P1 promoter. Biochimie 2007; 89:1562-72. [PMID: 17850948 DOI: 10.1016/j.biochi.2007.07.026] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2007] [Accepted: 07/30/2007] [Indexed: 11/19/2022]
Abstract
The 5'-end of the P1 promoter of the B-cell lymphoma-2 (bcl-2) gene contains a highly guaninecytosine-rich region, which has a role in the regulation of bcl-2 transcription. Whereas the guanine-rich region has been the focus of recent studies, little attention has been paid to the cytosine-rich strand. Here we examine the structural transitions of the cytosine-rich sequence by means of acid-base, mole-ratio and melting experiments monitored by molecular absorption, circular dichroism, and NMR spectroscopies. Two intramolecular i-motif structures have been detected in the pH range 2-7, with maximal formation at pH 4 and 6, respectively. At pH 7.6 the majority species has been associated with a hairpin involving Watson-Crick base pairs. Upon addition of the quadruplex-interacting ligand TmPyP4, bcl-2c structures at pH 6.1 and 7.6 yield identical interaction species with stoichiometries 1:2 (DNA:ligand) and logarithms of formation constant 12.4+/-0.2 and 11.7+/-0.1, respectively. The initial i-motif structure at pH 6.1 is lost upon interaction with TmPyP4.
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Affiliation(s)
- Nasiruddin Khan
- Department of Analytical Chemistry, University of Barcelona, Diagonal 647, E-08028 Barcelona, Spain
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99
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Vorlícková M, Bednárová K, Kejnovská I, Kypr J. Intramolecular and intermolecular guanine quadruplexes of DNA in aqueous salt and ethanol solutions. Biopolymers 2007; 86:1-10. [PMID: 17211886 DOI: 10.1002/bip.20672] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
DNA guanine quadruplexes are all based on stacks of guanine tetrads, but they can be of many types differing by mutual strand orientation, topology, position and structure of loops, and the number of DNA molecules constituting their structure. Here we have studied a series of nine DNA fragments (G(3)Xn)(3)G(3), where X = A, C or T, and n = 1, 2 or 3, to find how the particular bases and their numbers enable folding of the molecule into quadruplex and what type of quadruplex is formed. We show that any single base between G(3) blocks gives rise to only four-molecular parallel-stranded quadruplexes in water solutions. In contrast to previous models, even two Ts in potential loops lead to tetramolecular parallel quadruplexes and only three consecutive Ts lead to an intramolecular quadruplex, which is antiparallel. Adenines make the DNA less prone to quadruplex formation. (G(3)A(2))(3)G(3) folds into an intramolecular antiparallel quadruplex. The same is true with (G(3)A(3))(3)G(3) but only in KCl. In NaCl or LiCl, (G(3)A(3))(3)G(3) prefers to generate homoduplexes. Cytosine still more interferes with the quadruplex, which only is generated by (G(3)C)(3)G(3), whereas (G(3)C(2))(3)G(3) and (G(3)C(3))(3)G(3) generate hairpins and/or homoduplexes. Ethanol is a more potent DNA guanine quadruplex inducer than are ions in water solutions. It promotes intramolecular folding and parallel orientation of quadruplex strands, which rather corresponds to quadruplex structures observed in crystals.
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Affiliation(s)
- Michaela Vorlícková
- Institute of Biophysics, Academy of Sciences of the Czech Republic, Královopolská 135, CZ-61265 Brno, Czech Republic.
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100
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Guo K, Pourpak A, Beetz-Rogers K, Gokhale V, Sun D, Hurley LH. Formation of pseudosymmetrical G-quadruplex and i-motif structures in the proximal promoter region of the RET oncogene. J Am Chem Soc 2007; 129:10220-8. [PMID: 17672459 PMCID: PMC2566970 DOI: 10.1021/ja072185g] [Citation(s) in RCA: 214] [Impact Index Per Article: 12.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
A polypurine (guanine)/polypyrimidine (cytosine)-rich sequence within the proximal promoter region of the human RET oncogene has been shown to be essential for RET basal transcription. Specifically, the G-rich strand within this region consists of five consecutive runs of guanines, which is consistent with the general motif capable of forming intramolecular G-quadruplexes. Here we demonstrate that, in the presence of 100 mM K+, this G-rich strand has the ability to adopt two intramolecular G-quadruplex structures in vitro. Moreover, comparative circular dichroism (CD) and DMS footprinting studies have revealed that the 3'-G-quadruplex structure is a parallel-type intramolecular structure containing three G-tetrads. The G-quadruplex-interactive agents TMPyP4 and telomestatin further stabilize this G-quadruplex structure. In addition, we demonstrate that the complementary C-rich strand forms an i-motif structure in vitro, as shown by CD spectroscopy and chemical footprinting. This 19-mer duplex sequence is predicted to form stable intramolecular G-quadruplex and i-motif species having minimum symmetrical loop sizes of 1:3:1 and 2:3:2, respectively. Together, our results indicate that stable G-quadruplex and i-motif structures can form within the proximal promoter region of the human RET oncogene, suggesting that these secondary structures play an important role in transcriptional regulation of this gene.
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Affiliation(s)
- Kexiao Guo
- Department of Biochemistry and Molecular Biophysics, University of Arizona, Tucson, Arizona 85721
| | - Alan Pourpak
- Department of Pharmacology, College of Medicine, University of Arizona, Tucson, Arizona 85724
| | - Kara Beetz-Rogers
- Department of Pharmacology, College of Medicine, University of Arizona, Tucson, Arizona 85724
| | - Vijay Gokhale
- Department of Pharmacology and Toxicology, College of Pharmacy, University of Arizona 85721
| | - Daekyu Sun
- Department of Pharmacology and Toxicology, College of Pharmacy, University of Arizona 85721
- Address correspondence to either author, Telephone: (520) 626-5622, FAX: (520) 626-5623, ,
| | - Laurence H. Hurley
- Department of Pharmacology and Toxicology, College of Pharmacy, University of Arizona 85721
- Arizona Cancer Center, 1515 N. Campbell Ave., Tucson, Arizona 85724
- BIO5 Collaborative Research Institute, 1657 E. Helen Street, Tucson, Arizona 85719
- Address correspondence to either author, Telephone: (520) 626-5622, FAX: (520) 626-5623, ,
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