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Luo X, Zhang J, Gao Y, Pan W, Yang Y, Li X, Chen L, Wang C, Wang Y. Emerging roles of i-motif in gene expression and disease treatment. Front Pharmacol 2023; 14:1136251. [PMID: 37021044 PMCID: PMC10067743 DOI: 10.3389/fphar.2023.1136251] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2023] [Accepted: 02/27/2023] [Indexed: 03/22/2023] Open
Abstract
As non-canonical nucleic acid secondary structures consisting of cytosine-rich nucleic acids, i-motifs can form under certain conditions. Several i-motif sequences have been identified in the human genome and play important roles in biological regulatory functions. Due to their physicochemical properties, these i-motif structures have attracted attention and are new targets for drug development. Herein, we reviewed the characteristics and mechanisms of i-motifs located in gene promoters (including c-myc, Bcl-2, VEGF, and telomeres), summarized various small molecule ligands that interact with them, and the possible binding modes between ligands and i-motifs, and described their effects on gene expression. Furthermore, we discussed diseases closely associated with i-motifs. Among these, cancer is closely associated with i-motifs since i-motifs can form in some regions of most oncogenes. Finally, we introduced recent advances in the applications of i-motifs in multiple areas.
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Affiliation(s)
| | | | | | | | | | | | | | - Chang Wang
- *Correspondence: Chang Wang, ; Yuqing Wang,
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2
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Fang J, Xie C, Tao Y, Wei D. An overview of single-molecule techniques and applications in the study of nucleic acid structure and function. Biochimie 2023; 206:1-11. [PMID: 36179939 DOI: 10.1016/j.biochi.2022.09.014] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2022] [Revised: 09/20/2022] [Accepted: 09/22/2022] [Indexed: 11/02/2022]
Abstract
Nucleic acids are an indispensable component in all known life forms. The biological processes are regulated by Nucleic acids, which associate to form special high-order structures. since the high-level structures of nucleic acids are related to gene expression in cancer cells or viruses, it is very likely to become a potential drug target. Traditional biochemical methods are limited to distinguish the conformational distribution and dynamic transition process of single nucleic acid structure. The ligands based on the intermediate and transition states between different conformations are not designed by traditional biochemical methods. The single-molecule techniques enable real-time observation of the individual nucleic acid behavior due to its high resolution. Here, we introduce the application of single-molecule techniques in the study of small molecules to recognize nucleic acid structures, such as single-molecule FRET, magnetic tweezers, optical tweezers and atomic force microscopy. At the same time, we also introduce the specific advantages of single-molecule technology compared with traditional biochemical methods and some problems arisen in current research.
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Affiliation(s)
- Junkang Fang
- State Key Laboratory of Agricultural Microbiology, College of Veterinary Medicine, Huazhong Agricultural University, Wuhan, Hubei 430070, China; Hubei Hongshan Laboratory, Huazhong Agricultural University, Wuhan 430070, China; Interdisciplinary Sciences Institute, Huazhong Agricultural University, Wuhan 430070, China; National Reference Laboratory of Veterinary Drug Residues (HZAU) and MAO Key Laboratory for Detection of Veterinary Drug Residues, Huazhong Agricultural University, Wuhan, Hubei 430070, China; Shenzhen Institute of Nutrition and Health, Huazhong Agricultural University, Shenzhen 518000, China; Shenzhen Branch, Huazhong Agricultural University, Genome Analysis Laboratory of the Ministry of Agriculture, Agricultural Genomics Institute at Shenzhen, Chinese Academy of Agricultural Sciences, Shenzhen 518000, China
| | - Congbao Xie
- State Key Laboratory of Agricultural Microbiology, College of Veterinary Medicine, Huazhong Agricultural University, Wuhan, Hubei 430070, China; Hubei Hongshan Laboratory, Huazhong Agricultural University, Wuhan 430070, China; Interdisciplinary Sciences Institute, Huazhong Agricultural University, Wuhan 430070, China; National Reference Laboratory of Veterinary Drug Residues (HZAU) and MAO Key Laboratory for Detection of Veterinary Drug Residues, Huazhong Agricultural University, Wuhan, Hubei 430070, China; Shenzhen Institute of Nutrition and Health, Huazhong Agricultural University, Shenzhen 518000, China; Shenzhen Branch, Huazhong Agricultural University, Genome Analysis Laboratory of the Ministry of Agriculture, Agricultural Genomics Institute at Shenzhen, Chinese Academy of Agricultural Sciences, Shenzhen 518000, China
| | - Yanfei Tao
- State Key Laboratory of Agricultural Microbiology, College of Veterinary Medicine, Huazhong Agricultural University, Wuhan, Hubei 430070, China; Hubei Hongshan Laboratory, Huazhong Agricultural University, Wuhan 430070, China; Interdisciplinary Sciences Institute, Huazhong Agricultural University, Wuhan 430070, China; National Reference Laboratory of Veterinary Drug Residues (HZAU) and MAO Key Laboratory for Detection of Veterinary Drug Residues, Huazhong Agricultural University, Wuhan, Hubei 430070, China; Shenzhen Institute of Nutrition and Health, Huazhong Agricultural University, Shenzhen 518000, China; Shenzhen Branch, Huazhong Agricultural University, Genome Analysis Laboratory of the Ministry of Agriculture, Agricultural Genomics Institute at Shenzhen, Chinese Academy of Agricultural Sciences, Shenzhen 518000, China.
| | - Dengguo Wei
- State Key Laboratory of Agricultural Microbiology, College of Veterinary Medicine, Huazhong Agricultural University, Wuhan, Hubei 430070, China; Hubei Hongshan Laboratory, Huazhong Agricultural University, Wuhan 430070, China; Interdisciplinary Sciences Institute, Huazhong Agricultural University, Wuhan 430070, China; National Reference Laboratory of Veterinary Drug Residues (HZAU) and MAO Key Laboratory for Detection of Veterinary Drug Residues, Huazhong Agricultural University, Wuhan, Hubei 430070, China; Shenzhen Institute of Nutrition and Health, Huazhong Agricultural University, Shenzhen 518000, China; Shenzhen Branch, Huazhong Agricultural University, Genome Analysis Laboratory of the Ministry of Agriculture, Agricultural Genomics Institute at Shenzhen, Chinese Academy of Agricultural Sciences, Shenzhen 518000, China.
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3
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Khatik SY, Srivatsan SG. Environment-Sensitive Nucleoside Probe Unravels the Complex Structural Dynamics of i-Motif DNAs. Bioconjug Chem 2022; 33:1515-1526. [PMID: 35819865 DOI: 10.1021/acs.bioconjchem.2c00237] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Although evidence for the existence and biological role of i-motif (iM) DNA structures in cells is emerging, probing their structural polymorphism and identifying physiologically active conformations using currently available tools remain a major challenge. Here, we describe the development of an innovative device to investigate the conformation equilibrium of different iMs formed by C-rich telomeric repeat and oncogenic B-raf promoter sequences using a new conformation-sensitive dual-purpose nucleoside probe. The nucleoside is composed of a trifluoromethyl-benzofuran-2-yl moiety at the C5 position of 2'-deoxyuridine, which functions as a responsive fluorescent and 19F NMR probe. While the fluorescent component is useful in monitoring and estimating the folding process, the 19F label provides spectral signatures for various iMs, thereby enabling a systematic analysis of their complex population equilibrium under different conditions (e.g., pH, temperature, metal ions, and cell lysate). Distinct 19F signals exhibited by the iMs formed by the human telomeric repeat helped in calculating their relative population. A battery of fluorescence and 19F NMR studies using native and mutated B-raf oligonucleotides gave valuable insights into the iM structure landscape and its dependence on environmental conditions and also helped in predicting the structure of the major iM conformation. Overall, our findings indicate that the probe is highly suitable for studying complex nucleic acid systems.
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Affiliation(s)
- Saddam Y Khatik
- Department of Chemistry, Indian Institute of Science Education and Research (IISER), Pune, Dr. Homi Bhabha Road, Pune 411008, India
| | - Seergazhi G Srivatsan
- Department of Chemistry, Indian Institute of Science Education and Research (IISER), Pune, Dr. Homi Bhabha Road, Pune 411008, India
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4
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Long W, Zheng BX, Li Y, Huang XH, Lin DM, Chen CC, Hou JQ, Ou TM, Wong WL, Zhang K, Lu YJ. Rational design of small-molecules to recognize G-quadruplexes of c-MYC promoter and telomere and the evaluation of their in vivo antitumor activity against breast cancer. Nucleic Acids Res 2022; 50:1829-1848. [PMID: 35166828 PMCID: PMC8887543 DOI: 10.1093/nar/gkac090] [Citation(s) in RCA: 19] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2021] [Revised: 01/20/2022] [Accepted: 01/27/2022] [Indexed: 12/31/2022] Open
Abstract
DNA G4-structures from human c-MYC promoter and telomere are considered as important drug targets; however, the developing of small-molecule-based fluorescent binding ligands that are highly selective in targeting these G4-structures over other types of nucleic acids is challenging. We herein report a new approach of designing small molecules based on a non-selective thiazole orange scaffold to provide two-directional and multi-site interactions with flanking residues and loops of the G4-motif for better selectivity. The ligands are designed to establish multi-site interactions in the G4-binding pocket. This structural feature may render the molecules higher selectivity toward c-MYC G4s than other structures. The ligand–G4 interaction studied with 1H NMR may suggest a stacking interaction with the terminal G-tetrad. Moreover, the intracellular co-localization study with BG4 and cellular competition experiments with BRACO-19 may suggest that the binding targets of the ligands in cells are most probably G4-structures. Furthermore, the ligands that either preferentially bind to c-MYC promoter or telomeric G4s are able to downregulate markedly the c-MYC and hTERT gene expression in MCF-7 cells, and induce senescence and DNA damage to cancer cells. The in vivo antitumor activity of the ligands in MCF-7 tumor-bearing mice is also demonstrated.
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Affiliation(s)
- Wei Long
- School of Biomedical and Pharmaceutical Sciences, Guangdong University of Technology, Guangzhou 510006, PR China
| | - Bo-Xin Zheng
- School of Biomedical and Pharmaceutical Sciences, Guangdong University of Technology, Guangzhou 510006, PR China
| | - Ying Li
- School of Biomedical and Pharmaceutical Sciences, Guangdong University of Technology, Guangzhou 510006, PR China
| | - Xuan-He Huang
- School of Biomedical and Pharmaceutical Sciences, Guangdong University of Technology, Guangzhou 510006, PR China
| | - Dan-Min Lin
- School of Biomedical and Pharmaceutical Sciences, Guangdong University of Technology, Guangzhou 510006, PR China
| | - Cui-Cui Chen
- School of Biomedical and Pharmaceutical Sciences, Guangdong University of Technology, Guangzhou 510006, PR China
| | - Jin-Qiang Hou
- Department of Chemistry, Lakehead University, 955 Oliver Road, Thunder Bay, Ontario P7B 5E1, Canada.,Thunder Bay Regional Health Research Institute, 980 Oliver Road, Thunder Bay, Ontario P7B 6V4, Canada
| | - Tian-Miao Ou
- Guangdong Provincial Key Laboratory of New Drug Design and Evaluation, School of Pharmaceutical Sciences, Sun Yat-Sen University, Guangzhou 510006, China
| | - Wing-Leung Wong
- State Key Laboratory of Chemical Biology and Drug Discovery, Department of Applied Biology and Chemical Technology, The Hong Kong Polytechnic University, Hung Hom, Hong Kong SAR, China
| | - Kun Zhang
- School of Biomedical and Pharmaceutical Sciences, Guangdong University of Technology, Guangzhou 510006, PR China.,School of Biotechnology and Health Sciences, Wuyi University, Jiangmen, 529020, P.R. China; International Healthcare Innovation Institute (Jiangmen), Jiangmen, 529040, PR China
| | - Yu-Jing Lu
- School of Biomedical and Pharmaceutical Sciences, Guangdong University of Technology, Guangzhou 510006, PR China
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5
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Gao B, Zheng YT, Su AM, Sun B, Xi XG, Hou XM. Remodeling the conformational dynamics of I-motif DNA by helicases in ATP-independent mode at acidic environment. iScience 2022; 25:103575. [PMID: 34988409 PMCID: PMC8704484 DOI: 10.1016/j.isci.2021.103575] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2021] [Revised: 10/09/2021] [Accepted: 12/03/2021] [Indexed: 01/18/2023] Open
Abstract
I-motifs are noncanonical four-stranded DNA structures formed by C-rich sequences at acidic environment with critical biofunctions. The particular pH sensitivity has inspired the development of i-motifs as pH sensors and DNA motors in nanotechnology. However, the folding and regulation mechanisms of i-motifs remain elusive. Here, using single-molecule FRET, we first show that i-motifs are more dynamic than G4s. Impressively, i-motifs display a high diversity of six folding species with slow interconversion. Further results indicate that i-motifs can be linearized by Replication protein A. More importantly, we identified a number of helicases with high specificity to i-motifs at low pH. All these helicases directly act on and efficiently resolve i-motifs into intermediates independent of ATP, although they poorly unwind G4 or duplex at low pH. Owing to the extreme sensitivity to helicases and no need for ATP, i-motif may be applied as a probe for helicase sensing both in vitro and in vivo.
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Affiliation(s)
- Bo Gao
- State Key Laboratory of Crop Stress Biology for Arid Areas and College of Life Sciences, Northwest A&F University, Yangling 712100, China
| | - Ya-Ting Zheng
- State Key Laboratory of Crop Stress Biology for Arid Areas and College of Life Sciences, Northwest A&F University, Yangling 712100, China
| | - Ai-Min Su
- State Key Laboratory of Crop Stress Biology for Arid Areas and College of Life Sciences, Northwest A&F University, Yangling 712100, China
| | - Bo Sun
- School of Life Science and Technology, ShanghaiTech University, Shanghai 201210, China
| | - Xu-Guang Xi
- State Key Laboratory of Crop Stress Biology for Arid Areas and College of Life Sciences, Northwest A&F University, Yangling 712100, China
- LBPA, Ecole Normale Supérieure Paris-Saclay, CNRS, Gif-sur-Yvette, France
| | - Xi-Miao Hou
- State Key Laboratory of Crop Stress Biology for Arid Areas and College of Life Sciences, Northwest A&F University, Yangling 712100, China
- Corresponding author
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6
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Cheng Y, Zhang Y, You H. Characterization of G-Quadruplexes Folding/Unfolding Dynamics and Interactions with Proteins from Single-Molecule Force Spectroscopy. Biomolecules 2021; 11:1579. [PMID: 34827577 PMCID: PMC8615981 DOI: 10.3390/biom11111579] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2021] [Revised: 10/16/2021] [Accepted: 10/19/2021] [Indexed: 12/19/2022] Open
Abstract
G-quadruplexes (G4s) are stable secondary nucleic acid structures that play crucial roles in many fundamental biological processes. The folding/unfolding dynamics of G4 structures are associated with the replication and transcription regulation functions of G4s. However, many DNA G4 sequences can adopt a variety of topologies and have complex folding/unfolding dynamics. Determining the dynamics of G4s and their regulation by proteins remains challenging due to the coexistence of multiple structures in a heterogeneous sample. Here, in this mini-review, we introduce the application of single-molecule force-spectroscopy methods, such as magnetic tweezers, optical tweezers, and atomic force microscopy, to characterize the polymorphism and folding/unfolding dynamics of G4s. We also briefly introduce recent studies using single-molecule force spectroscopy to study the molecular mechanisms of G4-interacting proteins.
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Affiliation(s)
| | | | - Huijuan You
- Hubei Key Laboratory of Natural Medicinal Chemistry and Resource Evaluation, School of Pharmacy, Tongji Medical College, Huazhong University of Science and Technology, Wuhan 430030, China; (Y.C.); (Y.Z.)
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7
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Miglietta G, Russo M, Capranico G. G-quadruplex-R-loop interactions and the mechanism of anticancer G-quadruplex binders. Nucleic Acids Res 2020; 48:11942-11957. [PMID: 33137181 PMCID: PMC7708042 DOI: 10.1093/nar/gkaa944] [Citation(s) in RCA: 79] [Impact Index Per Article: 19.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2020] [Revised: 10/05/2020] [Accepted: 10/08/2020] [Indexed: 12/17/2022] Open
Abstract
Genomic DNA and cellular RNAs can form a variety of non-B secondary structures, including G-quadruplex (G4) and R-loops. G4s are constituted by stacked guanine tetrads held together by Hoogsteen hydrogen bonds and can form at key regulatory sites of eukaryote genomes and transcripts, including gene promoters, untranslated exon regions and telomeres. R-loops are 3-stranded structures wherein the two strands of a DNA duplex are melted and one of them is annealed to an RNA. Specific G4 binders are intensively investigated to discover new effective anticancer drugs based on a common rationale, i.e.: the selective inhibition of oncogene expression or specific impairment of telomere maintenance. However, despite the high number of known G4 binders, such a selective molecular activity has not been fully established and several published data point to a different mode of action. We will review published data that address the close structural interplay between G4s and R-loops in vitro and in vivo, and how these interactions can have functional consequences in relation to G4 binder activity. We propose that R-loops can play a previously-underestimated role in G4 binder action, in relation to DNA damage induction, telomere maintenance, genome and epigenome instability and alterations of gene expression programs.
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Affiliation(s)
- Giulia Miglietta
- Department of Pharmacy and Biotechnology, Alma Mater Studiorum University of Bologna, via Selmi 3, 40126 Bologna, Italy
| | - Marco Russo
- Department of Pharmacy and Biotechnology, Alma Mater Studiorum University of Bologna, via Selmi 3, 40126 Bologna, Italy
| | - Giovanni Capranico
- Department of Pharmacy and Biotechnology, Alma Mater Studiorum University of Bologna, via Selmi 3, 40126 Bologna, Italy
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8
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Školáková P, Badri Z, Foldynová-Trantírková S, Ryneš J, Šponer J, Fojtová M, Fajkus J, Marek R, Vorlíčková M, Mergny JL, Trantírek L. Composite 5-methylations of cytosines modulate i-motif stability in a sequence-specific manner: Implications for DNA nanotechnology and epigenetic regulation of plant telomeric DNA. Biochim Biophys Acta Gen Subj 2020; 1864:129651. [DOI: 10.1016/j.bbagen.2020.129651] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2020] [Revised: 05/23/2020] [Accepted: 05/28/2020] [Indexed: 12/14/2022]
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9
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Jonchhe S, Pandey S, Karna D, Pokhrel P, Cui Y, Mishra S, Sugiyama H, Endo M, Mao H. Duplex DNA Is Weakened in Nanoconfinement. J Am Chem Soc 2020; 142:10042-10049. [PMID: 32383870 PMCID: PMC7295077 DOI: 10.1021/jacs.0c01978] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
For proteins and DNA secondary structures such as G-quadruplexes and i-motifs, nanoconfinement can facilitate their folding and increase structural stabilities. However, the properties of the physiologically prevalent B-DNA duplex have not been elucidated inside the nanocavity. Using a 17-bp DNA duplex in the form of a hairpin stem, here, we probed folding and unfolding transitions of the hairpin DNA duplex inside a DNA origami nanocavity. Compared to the free solution, the DNA hairpin inside the nanocage with a 15 × 15 nm cross section showed a drastic decrease in mechanical (20 → 9 pN) and thermodynamic (25 → 6 kcal/mol) stabilities. Free energy profiles revealed that the activation energy of unzipping the hairpin DNA duplex decreased dramatically (28 → 8 kcal/mol), whereas the transition state moved closer to the unfolded state inside the nanocage. All of these indicate that nanoconfinement weakens the stability of the hairpin DNA duplex to an unexpected extent. In a DNA hairpin made of a stem that contains complementary telomeric G-quadruplex (GQ) and i-motif (iM) forming sequences, formation of the Hoogsteen base pairs underlining the GQ or iM is preferred over the Watson-Crick base pairs in the DNA hairpin. These results shed light on the behavior of DNA in nanochannels, nanopores, or nanopockets of various natural or synthetic machineries. It also elucidates an alternative pathway to populate noncanonical DNA over B-DNA in the cellular environment where the nanocavity is abundant.
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Affiliation(s)
- Sagun Jonchhe
- Department of Chemistry & Biochemistry, Kent State University, Kent, OH 44242, USA
| | - Shankar Pandey
- Department of Chemistry & Biochemistry, Kent State University, Kent, OH 44242, USA
| | - Deepak Karna
- Department of Chemistry & Biochemistry, Kent State University, Kent, OH 44242, USA
| | - Pravin Pokhrel
- Department of Chemistry & Biochemistry, Kent State University, Kent, OH 44242, USA
| | - Yunxi Cui
- Department of Chemistry & Biochemistry, Kent State University, Kent, OH 44242, USA
| | - Shubham Mishra
- Department of Chemistry, Graduate School of Science, Kyoto University, Sakyo, Kyoto 606-8502, Japan
- Institute for Integrated Cell–Material Sciences, Kyoto University, Sakyo, Kyoto 606-8501, Japan
| | - Hiroshi Sugiyama
- Department of Chemistry, Graduate School of Science, Kyoto University, Sakyo, Kyoto 606-8502, Japan
- Institute for Integrated Cell–Material Sciences, Kyoto University, Sakyo, Kyoto 606-8501, Japan
| | - Masayuki Endo
- Department of Chemistry, Graduate School of Science, Kyoto University, Sakyo, Kyoto 606-8502, Japan
- Institute for Integrated Cell–Material Sciences, Kyoto University, Sakyo, Kyoto 606-8501, Japan
| | - Hanbin Mao
- Department of Chemistry & Biochemistry, Kent State University, Kent, OH 44242, USA
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10
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Školáková P, Renčiuk D, Palacký J, Krafčík D, Dvořáková Z, Kejnovská I, Bednářová K, Vorlíčková M. Systematic investigation of sequence requirements for DNA i-motif formation. Nucleic Acids Res 2019; 47:2177-2189. [PMID: 30715498 PMCID: PMC6412112 DOI: 10.1093/nar/gkz046] [Citation(s) in RCA: 44] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2018] [Revised: 01/16/2019] [Accepted: 01/18/2019] [Indexed: 12/13/2022] Open
Abstract
The formation of intercalated motifs (iMs) - secondary DNA structures based on hemiprotonated C.C+ pairs in suitable cytosine-rich DNA sequences, is reflected by typical changes in CD and UV absorption spectra. By means of spectroscopic methods, electrophoresis, chemical modifications and other procedures, we characterized iM formation and stability in sequences with different cytosine block lengths interrupted by various numbers and types of nucleotides. Particular attention was paid to the formation of iMs at pH conditions close to neutral. We identified the optimal conditions and minimal requirements for iM formation in DNA sequences, and addressed gaps and inaccurate data interpretations in existing studies to specify principles of iM formation and modes of their folding.
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Affiliation(s)
- Petra Školáková
- Institute of Biophysics of the Czech Academy of Sciences, v.v.i., Královopolská 135, 612 65 Brno, Czech Republic
| | - Daniel Renčiuk
- Institute of Biophysics of the Czech Academy of Sciences, v.v.i., Královopolská 135, 612 65 Brno, Czech Republic
| | - Jan Palacký
- Institute of Biophysics of the Czech Academy of Sciences, v.v.i., Královopolská 135, 612 65 Brno, Czech Republic
| | - Daniel Krafčík
- CEITEC-Central European Institute of Technology, Masaryk University, Kamenice 735/5, 625 00 Brno, Czech Republic
| | - Zuzana Dvořáková
- Institute of Biophysics of the Czech Academy of Sciences, v.v.i., Královopolská 135, 612 65 Brno, Czech Republic
| | - Iva Kejnovská
- Institute of Biophysics of the Czech Academy of Sciences, v.v.i., Královopolská 135, 612 65 Brno, Czech Republic
| | - Klára Bednářová
- Institute of Biophysics of the Czech Academy of Sciences, v.v.i., Královopolská 135, 612 65 Brno, Czech Republic
| | - Michaela Vorlíčková
- Institute of Biophysics of the Czech Academy of Sciences, v.v.i., Královopolská 135, 612 65 Brno, Czech Republic
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11
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Cheng Y, Tang Q, Li Y, Zhang Y, Zhao C, Yan J, You H. Folding/unfolding kinetics of G-quadruplexes upstream of the P1 promoter of the human BCL-2 oncogene. J Biol Chem 2019; 294:5890-5895. [PMID: 30787104 DOI: 10.1074/jbc.ra119.007516] [Citation(s) in RCA: 38] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2019] [Revised: 02/14/2019] [Indexed: 12/29/2022] Open
Abstract
The G-rich Pu39 region of the P1 promoter of the oncogene BCL-2, an apoptosis regulator, can fold into multiple G-quadruplex (G4) structures. Bcl2-2345 and Bcl2-1245 are two major G4 species forming with high thermal stability and distinct topologies in the Pu39 region, but their folding/unfolding kinetics have not yet been investigated. Here, we used magnetic tweezers to measure the mechanical stability and the folding/unfolding kinetics of the Bcl2-2345 and Bcl2-1245 G4 structures. We report that the hybrid-stranded Bcl2-2345 G4 had a lower mechanical stability than the parallel-stranded Bcl2-1245 G4. We observed that the Bcl2-2345 G4 is a kinetically favored structure, whereas the Bcl2-1245 G4, with a slow unfolding rate, may function as a kinetic barrier for transcription. We also determined that in addition to the Bcl2-2345 and Bcl2-1245 G4s, other stable DNA secondary structures, such as a hybrid-stranded Bcl2-1234 G4, can also form in the Pu39 sequence. The characterization of the folding/unfolding kinetics of specific G4s reported here sheds light on the participation of G4s during gene transcription and provides information for designing G4-targeting small molecules that could modulate BCL-2 gene expression.
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Affiliation(s)
- Yuanlei Cheng
- From the School of Pharmacy, Tongji Medical College, Huazhong University of Science and Technology, 430030 Wuhan, China
| | - Qingnan Tang
- the Department of Physics, National University of Singapore, Singapore 117542, Singapore
| | - Yutong Li
- From the School of Pharmacy, Tongji Medical College, Huazhong University of Science and Technology, 430030 Wuhan, China
| | - Yashuo Zhang
- From the School of Pharmacy, Tongji Medical College, Huazhong University of Science and Technology, 430030 Wuhan, China
| | - Chuyuan Zhao
- the Department of Physics, National University of Singapore, Singapore 117542, Singapore
| | - Jie Yan
- the Department of Physics, National University of Singapore, Singapore 117542, Singapore; the Mechanobiology Institute, National University of Singapore, Singapore 117411, Singapore
| | - Huijuan You
- From the School of Pharmacy, Tongji Medical College, Huazhong University of Science and Technology, 430030 Wuhan, China.
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12
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Shi J, Zhou M. Probing the conformational switch of I-motif DNA using tunable resistive pulse sensing. Biochim Biophys Acta Gen Subj 2018; 1862:2564-2569. [PMID: 30048743 DOI: 10.1016/j.bbagen.2018.07.016] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2018] [Revised: 07/08/2018] [Accepted: 07/11/2018] [Indexed: 02/04/2023]
Abstract
I-motif DNA, which can fold and unfold reversibly in various environments, plays a significant role in DNA nanotechnology and biological functions. Thus, it is of fundamental importance to identify the different conformations of i-motif DNA. Here, we demonstrate that distinct structures of i-motif DNA conjugated to polystyrene spheres can be distinguished through tunable resistive pulse sensing technique. When dispersed in acidic buffer, i-motif DNA coating on polystyrene spheres would fold into quadruplex structure and subsequently induce an apparent increase in the translocation duration time upon passing through a nanopore due to the shielding effect of the surface charge of the nanospheres. However, if the DNA strands don't have conformational changes in acidic buffer, little shift can be observed in the translocation duration time of the DNA functionalized polystyrene spheres. A before-and-after assay was also performed to illustrate the fast speed of i-motif DNA folding using this technique. The successful implementation of tunable resistive pulse sensing to monitor the conformational transition of i-motif DNA provides a potential tool to detect the structural changes of DNA and an alternative approach to study the function of DNA structures.
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Affiliation(s)
- Jing Shi
- State Key Laboratory of Tribology, Tsinghua University, Beijing 100084, People's Republic of China
| | - Ming Zhou
- State Key Laboratory of Tribology, Tsinghua University, Beijing 100084, People's Republic of China.
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13
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Manna S, Srivatsan SG. Fluorescence-based tools to probe G-quadruplexes in cell-free and cellular environments. RSC Adv 2018; 8:25673-25694. [PMID: 30210793 PMCID: PMC6130854 DOI: 10.1039/c8ra03708f] [Citation(s) in RCA: 31] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2018] [Accepted: 07/08/2018] [Indexed: 12/26/2022] Open
Abstract
Biophysical and biochemical investigations provide compelling evidence connecting the four-stranded G-quadruplex (GQ) structure with its role in regulating multiple cellular processes. Hence, modulating the function of GQs by using small molecule binders is being actively pursued as a strategy to develop new chemotherapeutic agents. However, sequence diversity and structural polymorphism of GQs have posed immense challenges in terms of understanding what conformation a G-rich sequence adopts inside the cell and how to specifically target a GQ motif amidst several other GQ-forming sequences. In this context, here we review recent developments in the applications of biophysical tools that use fluorescence readout to probe the GQ structure and recognition in cell-free and cellular environments. First, we provide a detailed discussion on the utility of covalently labeled environment-sensitive fluorescent nucleoside analogs in assessing the subtle difference in GQ structures and their ligand binding abilities. Furthermore, a detailed discussion on structure-specific antibodies and small molecule probes used to visualize and confirm the existence of DNA and RNA GQs in cells is provided. We also highlight the open challenges in the study of tetraplexes (GQ and i-motif structures) and how addressing these challenges by developing new tools and techniques will have a profound impact on tetraplex-directed therapeutic strategies.
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Affiliation(s)
- Sudeshna Manna
- Department of Chemistry, Indian Institute of Science Education and Research (IISER), PuneDr. Homi Bhabha RoadPune 411008India
| | - Seergazhi G. Srivatsan
- Department of Chemistry, Indian Institute of Science Education and Research (IISER), PuneDr. Homi Bhabha RoadPune 411008India
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14
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Jagdeo JM, Dufour A, Klein T, Solis N, Kleifeld O, Kizhakkedathu J, Luo H, Overall CM, Jan E. N-Terminomics TAILS Identifies Host Cell Substrates of Poliovirus and Coxsackievirus B3 3C Proteinases That Modulate Virus Infection. J Virol 2018; 92:e02211-17. [PMID: 29437971 PMCID: PMC5874412 DOI: 10.1128/jvi.02211-17] [Citation(s) in RCA: 52] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2017] [Accepted: 01/26/2018] [Indexed: 12/19/2022] Open
Abstract
Enteroviruses encode proteinases that are essential for processing of the translated viral polyprotein. In addition, viral proteinases also target host proteins to manipulate cellular processes and evade innate antiviral responses to promote replication and infection. Although some host protein substrates of enterovirus proteinases have been identified, the full repertoire of targets remains unknown. We used a novel quantitative in vitro proteomics-based approach, termed terminal amine isotopic labeling of substrates (TAILS), to identify with high confidence 72 and 34 new host protein targets of poliovirus and coxsackievirus B3 (CVB3) 3C proteinases (3Cpros) in HeLa cell and cardiomyocyte HL-1 cell lysates, respectively. We validated a subset of candidate substrates that are targets of poliovirus 3Cproin vitro including three common protein targets, phosphoribosylformylglycinamidine synthetase (PFAS), hnRNP K, and hnRNP M, of both proteinases. 3Cpro-targeted substrates were also cleaved in virus-infected cells but not noncleavable mutant proteins designed from the TAILS-identified cleavage sites. Knockdown of TAILS-identified target proteins modulated infection both negatively and positively, suggesting that cleavage by 3Cpro promotes infection. Indeed, expression of a cleavage-resistant mutant form of the endoplasmic reticulum (ER)-Golgi vesicle-tethering protein p115 decreased viral replication and yield. As the first comprehensive study to identify and validate functional enterovirus 3Cpro substrates in vivo, we conclude that N-terminomics by TAILS is an effective strategy to identify host targets of viral proteinases in a nonbiased manner.IMPORTANCE Enteroviruses are positive-strand RNA viruses that encode proteases that cleave the viral polyprotein into the individual mature viral proteins. In addition, viral proteases target host proteins in order to modulate cellular pathways and block antiviral responses in order to facilitate virus infection. Although several host protein targets have been identified, the entire list of proteins that are targeted is not known. In this study, we used a novel unbiased proteomics approach to identify ∼100 novel host targets of the enterovirus 3C protease, thus providing further insights into the network of cellular pathways that are modulated to promote virus infection.
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Affiliation(s)
- Julienne M Jagdeo
- Department of Biochemistry and Molecular Biology, University of British Columbia, Vancouver, British Columbia, Canada
- Life Sciences Institute, University of British Columbia, Vancouver, British Columbia, Canada
| | - Antoine Dufour
- Life Sciences Institute, University of British Columbia, Vancouver, British Columbia, Canada
- Centre for Blood Research, Faculty of Dentistry, Department of Oral Biological and Medical Sciences, University of British Columbia, Vancouver, British Columbia, Canada
| | - Theo Klein
- Life Sciences Institute, University of British Columbia, Vancouver, British Columbia, Canada
- Centre for Blood Research, Faculty of Dentistry, Department of Oral Biological and Medical Sciences, University of British Columbia, Vancouver, British Columbia, Canada
| | - Nestor Solis
- Life Sciences Institute, University of British Columbia, Vancouver, British Columbia, Canada
- Centre for Blood Research, Faculty of Dentistry, Department of Oral Biological and Medical Sciences, University of British Columbia, Vancouver, British Columbia, Canada
| | - Oded Kleifeld
- School of Biomedical Sciences, Monash University, Victoria, Australia
| | - Jayachandran Kizhakkedathu
- Department of Pathology and Laboratory Medicine, University of British Columbia, Vancouver, British Columbia, Canada
| | - Honglin Luo
- Department of Pathology and Laboratory Medicine, University of British Columbia, Vancouver, British Columbia, Canada
| | - Christopher M Overall
- Department of Biochemistry and Molecular Biology, University of British Columbia, Vancouver, British Columbia, Canada
- Life Sciences Institute, University of British Columbia, Vancouver, British Columbia, Canada
- Centre for Blood Research, Faculty of Dentistry, Department of Oral Biological and Medical Sciences, University of British Columbia, Vancouver, British Columbia, Canada
| | - Eric Jan
- Department of Biochemistry and Molecular Biology, University of British Columbia, Vancouver, British Columbia, Canada
- Life Sciences Institute, University of British Columbia, Vancouver, British Columbia, Canada
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15
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Singh A, Kukreti S. Homoduplex to i-motif structural switch exhibited by a cytosine rich strand of the MYH7 heavy chain β gene promoter at physiological pH. RSC Adv 2018; 8:34202-34214. [PMID: 35548637 PMCID: PMC9087296 DOI: 10.1039/c8ra05179h] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2018] [Accepted: 09/09/2018] [Indexed: 11/21/2022] Open
Abstract
Genomic locations such as promoter, exon, intron, telomeric and non-telomeric regions are rich in GC-rich sequences with the potential to form G- and C-tetraplexes on both strands independently. Herein, we employed biophysical and biochemical methods to study a 34-mer C-rich DNA sequence of the myosin heavy chain β gene (MYH7β) promoter, namely HM34C for humans and the rabbit counterpart, RM34C, which differs from HM34C at three positions (three bases). Circular dichroism (CD), UV-thermal denaturation and native gel electrophoresis studies demonstrated that both the C-rich promoter segments form C-tetraplex (i-motif) structures. The CD studies revealed that HM34C forms the i-motif structure at acidic pH (5.2) in the presence of 0.1 M NaCl but remains unstructured at physiological pH. Interestingly, RM34C can form the stable i-motif structure in acidic as well as physiological pH. A shift in the positive peak from 280 nm to 275 nm with the increase in temperature from 4 °C to 30 °C was observed in temperature-dependent CD studies. UV-melting studies showed a biphasic transition for RM34C, indicating the existence of two structural species at neutral pH. In view of these findings we suggest that at physiological pH, the RM34C sequence exists in equilibrium between two structural motifs, i.e. the i-motif and homoduplex structure. This study may add to the understanding of the i-motif/homoduplex in equilibrium in physiological environments. Genomic locations such as promoter, exon, intron, telomeric and non-telomeric regions are rich in GC-rich sequences with the potential to form G- and C-tetraplexes on both strands independently.![]()
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Affiliation(s)
- Anju Singh
- Nucleic Acids Research Lab
- Department of Chemistry
- University of Delhi
- Delhi-110007
- India
| | - Shrikant Kukreti
- Nucleic Acids Research Lab
- Department of Chemistry
- University of Delhi
- Delhi-110007
- India
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16
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Debnath M, Ghosh S, Chauhan A, Paul R, Bhattacharyya K, Dash J. Preferential targeting of i-motifs and G-quadruplexes by small molecules. Chem Sci 2017; 8:7448-7456. [PMID: 29163897 PMCID: PMC5674183 DOI: 10.1039/c7sc02693e] [Citation(s) in RCA: 60] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2017] [Accepted: 09/07/2017] [Indexed: 01/01/2023] Open
Abstract
i-Motifs and G-quadruplexes are dynamic nucleic acid secondary structures, which are believed to play key roles in gene expression. We herein report two peptidomimetic ligands (PBP1 and PBP2) that selectively target i-motifs and G-quadruplexes over double-stranded DNA. These peptidomimetics, regioisomeric with respect to the position of triazole/prolinamide motifs, have been synthesized using a modular method involving Cu(i)-catalyzed azide and alkyne cycloaddition. The para-isomer, PBP1 exhibits high selectivity for i-motifs while the meta-isomer PBP2 binds selectively to G-quadruplex structures. Interestingly, these ligands have the ability to induce G-quadruplex or i-motif structures from the unstructured single-stranded DNA conformations, as observed using single molecule Förster resonance energy transfer (smFRET) studies. The quantitative real-time polymerase chain reaction (qRT-PCR), western blot, and dual-luciferase assays indicate that PBP1 upregulates and PBP2 downregulates BCL-2 gene expression in cancer cells.
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Affiliation(s)
- Manish Debnath
- Department of Organic Chemistry , Indian Association for the Cultivation of Science , Jadavpur , Kolkata-700032 , India .
| | - Shirsendu Ghosh
- Department of Physical Chemistry , Indian Association for the Cultivation of Science , Jadavpur , Kolkata-700032 , India
| | - Ajay Chauhan
- Department of Organic Chemistry , Indian Association for the Cultivation of Science , Jadavpur , Kolkata-700032 , India .
| | - Rakesh Paul
- Department of Organic Chemistry , Indian Association for the Cultivation of Science , Jadavpur , Kolkata-700032 , India .
| | - Kankan Bhattacharyya
- Department of Physical Chemistry , Indian Association for the Cultivation of Science , Jadavpur , Kolkata-700032 , India
| | - Jyotirmayee Dash
- Department of Organic Chemistry , Indian Association for the Cultivation of Science , Jadavpur , Kolkata-700032 , India .
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17
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Lannes L, Young P, Richter C, Morgner N, Schwalbe H. Interaction of the N-Terminal Tandem Domains of hnRNP LL with the BCL2 Promoter i-Motif DNA Sequence. Chembiochem 2017; 18:2033-2044. [PMID: 28805284 DOI: 10.1002/cbic.201700390] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2017] [Indexed: 01/26/2023]
Abstract
The human genome contains GC-rich sequences able to form tetraplex secondary structures known as the G-quadruplex and i-motif. Such sequences are notably present in the promoter region of oncogenes and are proposed to function as regulatory elements of gene expression. The P1 promoter of BCL2 contains a 39-mer C-rich sequence (Py39wt) that can fold into a hairpin or an i-motif in a pH-dependent manner in vitro. The protein hnRNP LL was identified to recognise the i-motif over the hairpin conformation and act as an activating transcription factor. Thus, the Py39wt sequence would act as an ON/OFF switch, according to the secondary structure adopted. Herein, a structural study of the interaction between hnRNP LL and Py39wt is reported. Both N-terminal RNA recognition motifs (RRM12) cooperatively recognise one Py39wt DNA sequence and engage their β-sheet to form a large binding platform. In contrast, the C-terminal RRMs show no binding capacity. It is observed that RRM12 binds to Py39wt regardless of the DNA conformation. We propose that RRM12 recognises a single-stranded CTCCC element present in loop 1 of the i-motif and in the apical loop of the hairpin conformation.
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Affiliation(s)
- Laurie Lannes
- Institute for Organic Chemistry and Chemical Biology, Center for Biomolecular Magnetic Resonance (BMRZ), Johann Wolfgang Goethe University Frankfurt, Max-von-Laue-Strasse 7, 60438, Frankfurt/Main, Germany
| | - Phoebe Young
- Institute for Physical and Theoretical Chemistry, Johann Wolfgang Goethe University Frankfurt, Max-von-Laue-Strasse 7, 60438, Frankfurt/Main, Germany
| | - Christian Richter
- Institute for Organic Chemistry and Chemical Biology, Center for Biomolecular Magnetic Resonance (BMRZ), Johann Wolfgang Goethe University Frankfurt, Max-von-Laue-Strasse 7, 60438, Frankfurt/Main, Germany
| | - Nina Morgner
- Institute for Physical and Theoretical Chemistry, Johann Wolfgang Goethe University Frankfurt, Max-von-Laue-Strasse 7, 60438, Frankfurt/Main, Germany
| | - Harald Schwalbe
- Institute for Organic Chemistry and Chemical Biology, Center for Biomolecular Magnetic Resonance (BMRZ), Johann Wolfgang Goethe University Frankfurt, Max-von-Laue-Strasse 7, 60438, Frankfurt/Main, Germany
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18
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Selvam S, Mandal S, Mao H. Quantification of Chemical and Mechanical Effects on the Formation of the G-Quadruplex and i-Motif in Duplex DNA. Biochemistry 2017; 56:4616-4625. [PMID: 28738141 DOI: 10.1021/acs.biochem.7b00279] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
The formation of biologically significant tetraplex DNA species, such as G-quadruplexes and i-motifs, is affected by chemical (ions and pH) and mechanical [superhelicity (σ) and molecular crowding] factors. Because of the extremely challenging experimental conditions, the relative importance of these factors on tetraplex folding is unknown. In this work, we quantitatively evaluated the chemical and mechanical effects on the population dynamics of DNA tetraplexes in the insulin-linked polymorphic region using magneto-optical tweezers. By mechanically unfolding individual tetraplexes, we found that ions and pH have the largest effects on the formation of the G-quadruplex and i-motif, respectively. Interestingly, superhelicity has the second largest effect followed by molecular crowding conditions. While chemical effects are specific to tetraplex species, mechanical factors have generic influences. The predominant effect of chemical factors can be attributed to the fact that they directly change the stability of a specific tetraplex, whereas the mechanical factors, superhelicity in particular, reduce the stability of the competing species by changing the kinetics of the melting and annealing of the duplex DNA template in a nonspecific manner. The substantial dependence of tetraplexes on superhelicity provides strong support that DNA tetraplexes can serve as topological sensors to modulate fundamental cellular processes such as transcription.
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Affiliation(s)
- Sangeetha Selvam
- Department of Chemistry and Biochemistry, Kent State University , Kent, Ohio 44242, United States
| | - Shankar Mandal
- Department of Chemistry and Biochemistry, Kent State University , Kent, Ohio 44242, United States
| | - Hanbin Mao
- Department of Chemistry and Biochemistry, Kent State University , Kent, Ohio 44242, United States
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19
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Wright EP, Huppert JL, Waller ZAE. Identification of multiple genomic DNA sequences which form i-motif structures at neutral pH. Nucleic Acids Res 2017; 45:2951-2959. [PMID: 28180276 PMCID: PMC5605235 DOI: 10.1093/nar/gkx090] [Citation(s) in RCA: 148] [Impact Index Per Article: 21.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2017] [Accepted: 02/06/2017] [Indexed: 01/15/2023] Open
Abstract
i-Motifs are alternative DNA secondary structures formed in cytosine-rich sequences. Particular examples of these structures, traditionally assumed to be stable only at acidic pH, have been found to form under near-physiological conditions. To determine the potential impact of these structures on physiological processes, investigation of sequences with the capacity to fold under physiological conditions is required. Here we describe a systematic study of cytosine-rich DNA sequences, with varying numbers of consecutive cytosines, to gain insights into i-motif DNA sequence and structure stability. i-Motif formation was assessed using ultraviolet spectroscopy, circular dichroism and native gel electrophoresis. We found that increasing cytosine tract lengths resulted in increased thermal stability; sequences with at least five cytosines per tract folded into i-motif at room temperature and neutral pH. Using these results, we postulated a folding rule for i-motif formation, analogous to (but different from) that for G-quadruplexes. This indicated that thousands of cytosine-rich sequences in the human genome may fold into i-motif structures under physiological conditions. Many of these were found in locations where structure formation is likely to influence gene expression. Characterization of a selection of these identified i-motif forming sequences uncovered 17 genomic i-motif forming sequence examples which were stable at neutral pH.
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Affiliation(s)
- Elisé P Wright
- School of Pharmacy, University of East Anglia, Norwich Research Park, Norwich NR4 7TJ, UK
| | - Julian L Huppert
- Intellectual Forum, Jesus College, University of Cambridge, Cambridge CB5 8BL, UK
| | - Zoë A E Waller
- School of Pharmacy, University of East Anglia, Norwich Research Park, Norwich NR4 7TJ, UK.,Centre for Molecular and Structural Biochemistry, University of East Anglia, Norwich Research Park, Norwich NR4 7TJ, UK
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20
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Kaiser CE, Van Ert NA, Agrawal P, Chawla R, Yang D, Hurley LH. Insight into the Complexity of the i-Motif and G-Quadruplex DNA Structures Formed in the KRAS Promoter and Subsequent Drug-Induced Gene Repression. J Am Chem Soc 2017; 139:8522-8536. [PMID: 28570076 PMCID: PMC5978000 DOI: 10.1021/jacs.7b02046] [Citation(s) in RCA: 127] [Impact Index Per Article: 18.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Activating KRAS mutations frequently occur in pancreatic, colorectal, and lung adenocarcinomas. While many attempts have been made to target oncogenic KRAS, no clinically useful therapies currently exist. Most efforts to target KRAS have focused on inhibiting the mutant protein; a less explored approach involves targeting KRAS at the transcriptional level. The promoter element of the KRAS gene contains a GC-rich nuclease hypersensitive site with three potential DNA secondary structure-forming regions. These are referred to as the Near-, Mid-, and Far-regions, on the basis of their proximity to the transcription start site. As a result of transcription-induced negative superhelicity, these regions can open up to form unique DNA secondary structures: G-quadruplexes on the G-rich strand and i-motifs on the C-rich strand. While the G-quadruplexes have been well characterized, the i-motifs have not been investigated as thoroughly. Here we show that the i-motif that forms in the C-rich Mid-region is the most stable and exists in a dynamic equilibrium with a hybrid i-motif/hairpin species and an unfolded hairpin species. The transcription factor heterogeneous nuclear ribonucleoprotein K (hnRNP K) was found to bind selectively to the i-motif species and to positively modulate KRAS transcription. Additionally, we identified a benzophenanthridine alkaloid that dissipates the hairpin species and destabilizes the interaction of hnRNP K with the Mid-region i-motif. This same compound stabilizes the three existing KRAS G-quadruplexes. The combined effect of the compound on the Mid-region i-motif and the G-quadruplexes leads to downregulation of KRAS gene expression. This dual i-motif/G-quadruplex-interactive compound presents a new mechanism to modulate gene expression.
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Affiliation(s)
- Christine E. Kaiser
- College of Pharmacy, University of Arizona, Tucson, Arizona 85721, United States
| | - Natalie A. Van Ert
- College of Pharmacy, University of Arizona, Tucson, Arizona 85721, United States
| | - Prashansa Agrawal
- College of Pharmacy, University of Arizona, Tucson, Arizona 85721, United States
| | - Reena Chawla
- BIO5 Institute, University of Arizona, Tucson, Arizona 85721, United States
| | - Danzhou Yang
- College of Pharmacy, University of Arizona, Tucson, Arizona 85721, United States
- University of Arizona Cancer Center, University of Arizona, Tucson, Arizona 85724, United States
- BIO5 Institute, University of Arizona, Tucson, Arizona 85721, United States
| | - Laurence H. Hurley
- College of Pharmacy, University of Arizona, Tucson, Arizona 85721, United States
- University of Arizona Cancer Center, University of Arizona, Tucson, Arizona 85724, United States
- BIO5 Institute, University of Arizona, Tucson, Arizona 85721, United States
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21
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Dolinnaya NG, Ogloblina AM, Yakubovskaya MG. Structure, Properties, and Biological Relevance of the DNA and RNA G-Quadruplexes: Overview 50 Years after Their Discovery. BIOCHEMISTRY (MOSCOW) 2017; 81:1602-1649. [PMID: 28260487 PMCID: PMC7087716 DOI: 10.1134/s0006297916130034] [Citation(s) in RCA: 47] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
G-quadruplexes (G4s), which are known to have important roles in regulation of key biological processes in both normal and pathological cells, are the most actively studied non-canonical structures of nucleic acids. In this review, we summarize the results of studies published in recent years that change significantly scientific views on various aspects of our understanding of quadruplexes. Modern notions on the polymorphism of DNA quadruplexes, on factors affecting thermodynamics and kinetics of G4 folding–unfolding, on structural organization of multiquadruplex systems, and on conformational features of RNA G4s and hybrid DNA–RNA G4s are discussed. Here we report the data on location of G4 sequence motifs in the genomes of eukaryotes, bacteria, and viruses, characterize G4-specific small-molecule ligands and proteins, as well as the mechanisms of their interactions with quadruplexes. New information on the structure and stability of G4s in telomeric DNA and oncogene promoters is discussed as well as proof being provided on the occurrence of G-quadruplexes in cells. Prominence is given to novel experimental techniques (single molecule manipulations, optical and magnetic tweezers, original chemical approaches, G4 detection in situ, in-cell NMR spectroscopy) that facilitate breakthroughs in the investigation of the structure and functions of G-quadruplexes.
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Affiliation(s)
- N G Dolinnaya
- Lomonosov Moscow State University, Department of Chemistry, Moscow, 119991, Russia.
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22
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Roux M, Dosseto A. From direct to indirect lithium targets: a comprehensive review of omics data. Metallomics 2017; 9:1326-1351. [DOI: 10.1039/c7mt00203c] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Metal ions are critical to a wide range of biological processes.
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Affiliation(s)
| | - Anthony Dosseto
- Wollongong Isotope Geochronology Laboratory
- School of Earth & Environmental Sciences
- University of Wollongong
- Wollongong
- Australia
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23
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Sutherland C, Cui Y, Mao H, Hurley LH. A Mechanosensor Mechanism Controls the G-Quadruplex/i-Motif Molecular Switch in the MYC Promoter NHE III1. J Am Chem Soc 2016; 138:14138-14151. [DOI: 10.1021/jacs.6b09196] [Citation(s) in RCA: 77] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Affiliation(s)
- Caleb Sutherland
- University of Arizona Cancer Center, 1515 North Campbell Avenue, Tucson, Arizona 85724, United States
| | - Yunxi Cui
- Department
of Chemistry and Biochemistry and School of Biomedical Sciences, Kent State University, Kent, Ohio 44242, United States
| | - Hanbin Mao
- Department
of Chemistry and Biochemistry and School of Biomedical Sciences, Kent State University, Kent, Ohio 44242, United States
| | - Laurence H. Hurley
- University of Arizona Cancer Center, 1515 North Campbell Avenue, Tucson, Arizona 85724, United States
- University of Arizona, College of Pharmacy, 1703 East Mabel Street, Tucson, Arizona 85721, United States
- BIO5 Institute, 1657 East
Helen Street, Tucson, Arizona 85721, United States
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24
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Kang HJ, Cui Y, Yin H, Scheid A, Hendricks WPD, Schmidt J, Sekulic A, Kong D, Trent JM, Gokhale V, Mao H, Hurley LH. A Pharmacological Chaperone Molecule Induces Cancer Cell Death by Restoring Tertiary DNA Structures in Mutant hTERT Promoters. J Am Chem Soc 2016; 138:13673-13692. [PMID: 27643954 DOI: 10.1021/jacs.6b07598] [Citation(s) in RCA: 76] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Activation of human telomerase reverse transcriptase (hTERT) is necessary for limitless replication in tumorigenesis. Whereas hTERT is transcriptionally silenced in normal cells, most tumor cells reactivate hTERT expression by alleviating transcriptional repression through diverse genetic and epigenetic mechanisms. Transcription-activating hTERT promoter mutations have been found to occur at high frequencies in multiple cancer types. These mutations have been shown to form new transcription factor binding sites that drive hTERT expression, but this model cannot fully account for differences in wild-type (WT) and mutant promoter activation and has not yet enabled a selective therapeutic strategy. Here, we demonstrate a novel mechanism by which promoter mutations activate hTERT transcription, which also sheds light on a unique therapeutic opportunity. Promoter mutations occur in a core promoter region that forms tertiary structures consisting of a pair of G-quadruplexes involved in transcriptional silencing. We show that promoter mutations exert a detrimental effect on the folding of one of these G-quadruplexes, resulting in a nonfunctional silencer element that alleviates transcriptional repression. We have also identified a small drug-like pharmacological chaperone (pharmacoperone) molecule, GTC365, that acts at an early step in the G-quadruplex folding pathway to redirect mutant promoter G-quadruplex misfolding, partially reinstate the correct folding pathway, and reduce hTERT activity through transcriptional repression. This transcription-mediated repression produces cancer cell death through multiple routes including both induction of apoptosis through inhibition of hTERT's role in regulating apoptosis-related proteins and induction of senescence by decreasing telomerase activity and telomere length. We demonstrate the selective therapeutic potential of this strategy in melanoma cells that overexpress hTERT.
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Affiliation(s)
- Hyun-Jin Kang
- University of Arizona , College of Pharmacy, 1703 East Mabel Street, Tucson, Arizona 85721, United States
| | - Yunxi Cui
- Department of Chemistry and Biochemistry and School of Biomedical Sciences, Kent State University , Kent, Ohio 44242, United States
| | - Holly Yin
- Translational Genomics Research Institute , 445 North Fifth Street, Phoenix, Arizona 85004, United States
| | - Amy Scheid
- College of Science, University of Arizona , 1040 East Fourth Street, Tucson, Arizona 85721, United States
| | - William P D Hendricks
- Translational Genomics Research Institute , 445 North Fifth Street, Phoenix, Arizona 85004, United States
| | - Jessica Schmidt
- Department of Dermatology, Mayo Clinic , 13400 East Shea Boulevard, Scottsdale, Arizona 85259, United States
| | - Aleksandar Sekulic
- Department of Dermatology, Mayo Clinic , 13400 East Shea Boulevard, Scottsdale, Arizona 85259, United States
| | - Deming Kong
- State Key Laboratory of Medicinal Chemical Biology, College of Chemistry, Nankai University , Tianjin 300071, People's Republic of China
| | - Jeffrey M Trent
- Translational Genomics Research Institute , 445 North Fifth Street, Phoenix, Arizona 85004, United States
| | - Vijay Gokhale
- BIO5 Institute , 1657 East Helen Street, Tucson, Arizona 85721, United States
| | - Hanbin Mao
- Department of Chemistry and Biochemistry and School of Biomedical Sciences, Kent State University , Kent, Ohio 44242, United States
| | - Laurence H Hurley
- University of Arizona , College of Pharmacy, 1703 East Mabel Street, Tucson, Arizona 85721, United States.,BIO5 Institute , 1657 East Helen Street, Tucson, Arizona 85721, United States.,Arizona Cancer Center , 1515 North Campbell Avenue, Tucson, Arizona 85724, United States
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25
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Cui Y, Kong D, Ghimire C, Xu C, Mao H. Mutually Exclusive Formation of G-Quadruplex and i-Motif Is a General Phenomenon Governed by Steric Hindrance in Duplex DNA. Biochemistry 2016; 55:2291-9. [DOI: 10.1021/acs.biochem.6b00016] [Citation(s) in RCA: 72] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Yunxi Cui
- Department
of Chemistry and Biochemistry and School of Biomedical Sciences, Kent State University, Kent, Ohio 44242, United States
| | - Deming Kong
- Key
Laboratory of Functional Polymer Materials, Ministry of Education, Nankai University, Tianjin 300071, China
| | - Chiran Ghimire
- Department
of Chemistry and Biochemistry and School of Biomedical Sciences, Kent State University, Kent, Ohio 44242, United States
| | - Cuixia Xu
- Department
of Chemistry and Biochemistry and School of Biomedical Sciences, Kent State University, Kent, Ohio 44242, United States
- MOE
Key Laboratory of Bioinorganic and Synthetic Chemistry, School of
Chemistry and Chemical Engineering, Sun Yat-Sen University, Guangzhou 510275, China
| | - Hanbin Mao
- Department
of Chemistry and Biochemistry and School of Biomedical Sciences, Kent State University, Kent, Ohio 44242, United States
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26
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Fujii T, Sugimoto N. Loop nucleotides impact the stability of intrastrand i-motif structures at neutral pH. Phys Chem Chem Phys 2016; 17:16719-22. [PMID: 26058487 DOI: 10.1039/c5cp02794b] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
The stability of i-motif structures at neutral pH is of interest due to the potential of these structures to impact gene expression. A systematic investigation of loop sequence and length revealed that certain loop nucleobases stabilize i-motif quadruplexes.
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Affiliation(s)
- Taiga Fujii
- Frontier Institute for Biomolecular Engineering Research (FIBER), Konan University, 8-9-1 Minatojima-minamimachi, Chuo-ku, Kobe 650-0047, Japan.
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27
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GC-elements controlling HRAS transcription form i-motif structures unfolded by heterogeneous ribonucleoprotein particle A1. Sci Rep 2015; 5:18097. [PMID: 26674223 PMCID: PMC4682182 DOI: 10.1038/srep18097] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2015] [Accepted: 11/11/2015] [Indexed: 02/07/2023] Open
Abstract
HRAS is regulated by two neighbouring quadruplex-forming GC-elements (hras-1 and hras-2), located upstream of the major transcription start sites (doi: 10.1093/nar/gku 5784). In this study we demonstrate that the C-rich strands of hras-1 and hras-2 fold into i-motif conformations (iMs) characterized under crowding conditions (PEG-300, 40% w/v) by semi-transitions at pH 6.3 and 6.7, respectively. Nondenaturing PAGE shows that the HRAS C-rich sequences migrate at both pH 5 and 7 as folded intramolecular structures. Chromatin immunoprecipitation shows that hnRNP A1 is associated under in vivo conditions to the GC-elements, while EMSA proves that hnRNP A1 binds tightly to the iMs. FRET and CD show that hnRNP A1 unfolds the iM structures upon binding. Furthermore, when hnRNP A1 is knocked out in T24 bladder cancer cells by a specific shRNA, the HRAS transcript level drops to 44 ± 5% of the control, suggesting that hnRNP A1 is necessary for gene activation. The sequestration by decoy oligonucleotides of the proteins (hnRNP A1 and others) binding to the HRAS iMs causes a significant inhibition of HRAS transcription. All these outcomes suggest that HRAS is regulated by a G-quadruplex/i-motif switch interacting with proteins that recognize non B-DNA conformations.
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28
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Nesterova IV, Briscoe JR, Nesterov EE. Rational Control of Folding Cooperativity in DNA Quadruplexes. J Am Chem Soc 2015; 137:11234-7. [PMID: 26305404 DOI: 10.1021/jacs.5b06645] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Availability of basic tools for engineering molecular systems with precisely defined properties is crucial toward progress in development of new responsive materials. Among such materials are systems capable of generating an ultrasensitive response (i.e., large relative changes in output in response to small changes in input). Herein, we focus on a rational design of DNA quadruplex based structures as ultrasensitive response elements. In particular, we demonstrate how addition of allosteric guiding elements can be engineered into H(+)-responsive i-motif structure to yield maximized response sensitivity.
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Affiliation(s)
- Irina V Nesterova
- Department of Chemistry, Louisiana State University , Baton Rouge, Louisiana 70803, United States
| | - James R Briscoe
- Department of Chemistry, Louisiana State University , Baton Rouge, Louisiana 70803, United States
| | - Evgueni E Nesterov
- Department of Chemistry, Louisiana State University , Baton Rouge, Louisiana 70803, United States
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29
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Mata G, Luedtke NW. Fluorescent Probe for Proton-Coupled DNA Folding Revealing Slow Exchange of i-Motif and Duplex Structures. J Am Chem Soc 2015; 137:699-707. [DOI: 10.1021/ja508741u] [Citation(s) in RCA: 54] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Affiliation(s)
- Guillaume Mata
- Department of Chemistry, University of Zürich, Winterthurerstrasse
190, CH-8057 Zürich, Switzerland
| | - Nathan W. Luedtke
- Department of Chemistry, University of Zürich, Winterthurerstrasse
190, CH-8057 Zürich, Switzerland
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30
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Shrestha P, Xiao S, Dhakal S, Tan Z, Mao H. Nascent RNA transcripts facilitate the formation of G-quadruplexes. Nucleic Acids Res 2014; 42:7236-46. [PMID: 24829453 PMCID: PMC4066803 DOI: 10.1093/nar/gku416] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
Recent discovery of the RNA/DNA hybrid G-quadruplexes (HQs) and their potential wide-spread occurrence in human genome during transcription have suggested a new and generic transcriptional control mechanism. The G-rich sequence in which HQ may form can coincide with that for DNA G-quadruplexes (GQs), which are well known to modulate transcriptions. Understanding the molecular interaction between HQ and GQ is, therefore, of pivotal importance to dissect the new mechanism for transcriptional regulation. Using a T7 transcription model, herein we found that GQ and HQ form in a natural sequence, (GGGGA)4, downstream of many transcription start sites. Using a newly-developed single-molecular stalled-transcription assay, we revealed that RNA transcripts helped to populate quadruplexes at the expense of duplexes. Among quadruplexes, HQ predominates GQ in population and mechanical stabilities, suggesting HQ may serve as a better mechanical block during transcription. The fact that HQ and GQ folded within tens of milliseconds in the presence of RNA transcripts provided justification for the co-transcriptional folding of these species. The catalytic role of RNA transcripts in the GQ formation was strongly suggested as the GQ folded >7 times slower without transcription. These results shed light on the possible synergistic effect of GQs and HQs on transcriptional controls.
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Affiliation(s)
- Prakash Shrestha
- Department of Chemistry and Biochemistry and School of Biomedical Sciences, Kent State University, Kent, OH 44242, USA
| | - Shan Xiao
- State Key Laboratory of Biomembrane and Membrane Biotechnology, Institute of Zoology, Chinese Academy of Sciences, Beijing 100101, P.R. China
| | - Soma Dhakal
- Department of Chemistry and Biochemistry and School of Biomedical Sciences, Kent State University, Kent, OH 44242, USA
| | - Zheng Tan
- State Key Laboratory of Biomembrane and Membrane Biotechnology, Institute of Zoology, Chinese Academy of Sciences, Beijing 100101, P.R. China
| | - Hanbin Mao
- Department of Chemistry and Biochemistry and School of Biomedical Sciences, Kent State University, Kent, OH 44242, USA
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31
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Kim SE, Lee IB, Hyeon C, Hong SC. Destabilization of i-Motif by Submolar Concentrations of a Monovalent Cation. J Phys Chem B 2014; 118:4753-60. [DOI: 10.1021/jp500120d] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Affiliation(s)
- Sung Eun Kim
- Department
of Physics, Korea University, 145 Anam-ro, Seongbuk-gu, Seoul 136-713, Republic of Korea
| | - Il-Buem Lee
- Department
of Physics, Korea University, 145 Anam-ro, Seongbuk-gu, Seoul 136-713, Republic of Korea
| | - Changbong Hyeon
- School
of Computational Sciences, Korea Institute for Advanced Study, 85
Hoegi-ro Dongdaemun-gu, Seoul 130-722, Republic of Korea
| | - Seok-Cheol Hong
- Department
of Physics, Korea University, 145 Anam-ro, Seongbuk-gu, Seoul 136-713, Republic of Korea
- School
of Computational Sciences, Korea Institute for Advanced Study, 85
Hoegi-ro Dongdaemun-gu, Seoul 130-722, Republic of Korea
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32
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Kendrick S, Kang HJ, Alam MP, Madathil MM, Agrawal P, Gokhale V, Yang D, Hecht SM, Hurley LH. The dynamic character of the BCL2 promoter i-motif provides a mechanism for modulation of gene expression by compounds that bind selectively to the alternative DNA hairpin structure. J Am Chem Soc 2014; 136:4161-71. [PMID: 24559410 PMCID: PMC3985915 DOI: 10.1021/ja410934b] [Citation(s) in RCA: 193] [Impact Index Per Article: 19.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
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It
is generally accepted that DNA predominantly exists in duplex
form in cells. However, under torsional stress imposed by active transcription,
DNA can assume nonduplex structures. The BCL2 promoter
region forms two different secondary DNA structures on opposite strands
called the G-quadruplex and the i-motif. The i-motif is a highly dynamic
structure that exists in equilibrium with a flexible hairpin species.
Here we identify a pregnanol derivative and a class of piperidine
derivatives that differentially modulate gene expression by stabilizing
either the i-motif or the flexible hairpin species. Stabilization
of the i-motif structure results in significant upregulation of the BCL2 gene and associated protein expression; in contrast,
stabilization of the flexible hairpin species lowers BCL2 levels. The BCL2 levels reduced by the hairpin-binding
compound led to chemosensitization to etoposide in both in vitro and
in vivo models. Furthermore, we show antagonism between the two classes
of compounds in solution and in cells. For the first time, our results
demonstrate the principle of small molecule targeting of i-motif structures
in vitro and in vivo to modulate gene expression.
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Affiliation(s)
- Samantha Kendrick
- Arizona Cancer Center, University of Arizona , Tucson, Arizona 85724, United States
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33
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Kang HJ, Kendrick S, Hecht SM, Hurley LH. The transcriptional complex between the BCL2 i-motif and hnRNP LL is a molecular switch for control of gene expression that can be modulated by small molecules. J Am Chem Soc 2014; 136:4172-85. [PMID: 24559432 PMCID: PMC3985447 DOI: 10.1021/ja4109352] [Citation(s) in RCA: 188] [Impact Index Per Article: 18.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
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In a companion paper (DOI: 10.021/ja410934b) we demonstrate that the C-rich
strand of the cis-regulatory element in the BCL2 promoter element
is highly dynamic in nature and can form either an i-motif or a flexible
hairpin. Under physiological conditions these two secondary DNA structures
are found in an equilibrium mixture, which can be shifted by the addition
of small molecules that trap out either the i-motif (IMC-48) or the
flexible hairpin (IMC-76). In cellular experiments we demonstrate
that the addition of these molecules has opposite effects on BCL2 gene expression and furthermore that these effects
are antagonistic. In this contribution we have identified a transcriptional
factor that recognizes and binds to the BCL2 i-motif
to activate transcription. The molecular basis for the recognition
of the i-motif by hnRNP LL is determined, and we demonstrate that
the protein unfolds the i-motif structure to form a stable single-stranded
complex. In subsequent experiments we show that IMC-48 and IMC-76
have opposite, antagonistic effects on the formation of the hnRNP
LL–i-motif complex as well as on the transcription factor occupancy
at the BCL2 promoter. For the first time we propose
that the i-motif acts as a molecular switch that controls gene expression
and that small molecules that target the dynamic equilibrium of the
i-motif and the flexible hairpin can differentially modulate gene
expression.
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Affiliation(s)
- Hyun-Jin Kang
- College of Pharmacy and §BIO5 Institute, University of Arizona , Tucson, Arizona 85721, United States
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