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Datta S, Patel M, Sathyaseelan C, Ghosh C, Mudgal A, Patel D, Rathinavelan T, Singh U. G-quadruplex landscape and its regulation revealed by a new antibody capture method. Oncotarget 2024; 15:175-198. [PMID: 38484151 PMCID: PMC10939474 DOI: 10.18632/oncotarget.28564] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2023] [Accepted: 02/12/2024] [Indexed: 03/17/2024] Open
Abstract
Our understanding of DNA G-quadruplexes (G4s) from in vitro studies has been complemented by genome-wide G4 landscapes from cultured cells. Conventionally, the formation of G4s is accepted to depend on G-repeats such that they form tetrads. However, genome-wide G4s characterized through high-throughput sequencing suggest that these structures form at a large number of regions with no such canonical G4-forming signatures. Many G4-binding proteins have been described with no evidence for any protein that binds to and stabilizes G4s. It remains unknown what fraction of G4s formed in human cells are protein-bound. The G4-chromatin immunoprecipitation (G4-ChIP) method hitherto employed to describe G4 landscapes preferentially reports G4s that get crosslinked to proteins in their proximity. Our current understanding of the G4 landscape is biased against representation of G4s which escape crosslinking as they are not stabilized by protein-binding and presumably transient. We report a protocol that captures G4s from the cells efficiently without any bias as well as eliminates the detection of G4s formed artifactually on crosslinked sheared chromatin post-fixation. We discover that G4s form sparingly at SINEs. An application of this method shows that depletion of a repeat-binding protein CGGBP1 enhances net G4 capture at CGGBP1-dependent CTCF-binding sites and regions of sharp interstrand G/C-skew transitions. Thus, we present an improved method for G4 landscape determination and by applying it we show that sequence property-specific constraints of the nuclear environment mitigate G4 formation.
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Affiliation(s)
- Subhamoy Datta
- HoMeCell Lab, Discipline of Biological Engineering, Indian Institute of Technology Gandhinagar, Gandhinagar, Gujarat 382355, India
| | - Manthan Patel
- Centre for Genomics and Child Health, Blizard Institute, Barts and The London School of Medicine and Dentistry, Queen Mary University of London, London E1 2AT, UK
| | - Chakkarai Sathyaseelan
- Department of Biotechnology, Indian Institute of Technology Hyderabad, Kandi Campus, Telangana 502285, India
| | - Chandrama Ghosh
- Azrieli Faculty of Medicine, Bar-Ilan University, Henrietta Szold 8A, Safed 1311502, Israel
| | - Akanksha Mudgal
- Department of Biopharmacy, Medical University of Lublin, Lublin 20059, Poland
| | - Divyesh Patel
- Research Programs Unit, Applied Tumor Genomics Program, Faculty of Medicine, University of Helsinki, Biomedicum, Helsinki 00290, Finland
| | | | - Umashankar Singh
- HoMeCell Lab, Discipline of Biological Engineering, Indian Institute of Technology Gandhinagar, Gandhinagar, Gujarat 382355, India
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Patel M, Patel D, Datta S, Singh U. An immunochemistry-based screen for chemical inhibitors of DNA-protein interactions and its application to human CGGBP1. BMC Cancer 2020; 20:1016. [PMID: 33081720 PMCID: PMC7576722 DOI: 10.1186/s12885-020-07526-5] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2020] [Accepted: 10/14/2020] [Indexed: 12/14/2022] Open
Abstract
BACKGROUND Inhibition of DNA-binding of proteins by small-molecule chemicals holds immense potential in manipulating the activities of DNA-binding proteins. Such a chemical inhibition of DNA-binding of proteins can be used to modulate processes such as replication, transcription, DNA repair and maintenance of epigenetic states. This prospect is currently challenged with the absence of robust and generic protocols to identify DNA-protein interactions. Additionally, much of the current approaches to designing inhibitors requires structural information of the target proteins. METHODS We have developed a simple dot blot and immunodetection-based assay to screen chemical libraries for inhibitors of DNA-protein interactions. The assay has been applied to a library of 1685 FDA-approved chemicals to discover inhibitors of CGGBP1, a multifunctional DNA-binding protein with no known structure. Additional in vitro and in cellulo assays have been performed to verify and supplement the findings of the screen. RESULTS Our primary screen has identified multiple inhibitors of direct or indirect interactions between CGGBP1 and genomic DNA. Of these, one inhibitor, Givinostat, was found to inhibit direct DNA-binding of CGGBP1 in the secondary screen using purified recombinant protein as the target. DNA and chromatin immunoprecipitation assays reinforced the findings of the screen that Givinostat inhibits CGGBP1-DNA binding. CONCLUSIONS The assay we have described successfully identifies verifiable inhibitors of DNA-binding of protein; in this example, the human CGGBP1. This assay is customizable for a wide range of targets for which primary antibodies are available. It works with different sources of the target protein, cell lysates or purified recombinant preparations and does not require special equipment, DNA modifications or protein structural data. This assay is scalable and highly adaptable with the potential to discover inhibitors of transcription factors with implications in cancer biology.
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Affiliation(s)
- Manthan Patel
- HoMeCell Lab, Biological Engineering, Indian Institute of Technology Gandhinagar, Gandhinagar, Gujarat, 382355, India
| | - Divyesh Patel
- HoMeCell Lab, Biological Engineering, Indian Institute of Technology Gandhinagar, Gandhinagar, Gujarat, 382355, India
| | - Subhamoy Datta
- HoMeCell Lab, Biological Engineering, Indian Institute of Technology Gandhinagar, Gandhinagar, Gujarat, 382355, India
| | - Umashankar Singh
- HoMeCell Lab, Biological Engineering, Indian Institute of Technology Gandhinagar, Gandhinagar, Gujarat, 382355, India.
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Patel M, Patel D, Datta S, Singh U. CGGBP1-regulated cytosine methylation at CTCF-binding motifs resists stochasticity. BMC Genet 2020; 21:84. [PMID: 32727353 PMCID: PMC7392725 DOI: 10.1186/s12863-020-00894-8] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2020] [Accepted: 07/23/2020] [Indexed: 12/03/2022] Open
Abstract
Background The human CGGBP1 binds to GC-rich regions and interspersed repeats, maintains homeostasis of stochastic cytosine methylation and determines DNA-binding of CTCF. Interdependence between regulation of cytosine methylation and CTCF occupancy by CGGBP1 remains unknown. Results By analyzing methylated DNA-sequencing data obtained from CGGBP1-depleted cells, we report that some transcription factor-binding sites, including CTCF, resist stochastic changes in cytosine methylation. By analysing CTCF-binding sites we show that cytosine methylation changes at CTCF motifs caused by CGGBP1 depletion resist stochastic changes. These CTCF-binding sites are positioned at locations where the spread of cytosine methylation in cis depends on the levels of CGGBP1. Conclusion Our findings suggest that CTCF occupancy and functions are determined by CGGBP1-regulated cytosine methylation patterns.
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Affiliation(s)
- Manthan Patel
- HoMeCell Lab, Biological Engineering, Indian Institute of Technology Gandhinagar, Palaj, Gandhinagar, 382355, Gujarat, India
| | - Divyesh Patel
- HoMeCell Lab, Biological Engineering, Indian Institute of Technology Gandhinagar, Palaj, Gandhinagar, 382355, Gujarat, India
| | - Subhamoy Datta
- HoMeCell Lab, Biological Engineering, Indian Institute of Technology Gandhinagar, Palaj, Gandhinagar, 382355, Gujarat, India
| | - Umashankar Singh
- HoMeCell Lab, Biological Engineering, Indian Institute of Technology Gandhinagar, Palaj, Gandhinagar, 382355, Gujarat, India.
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Patel D, Patel M, Westermark B, Singh U. Dynamic bimodal changes in CpG and non-CpG methylation genome-wide upon CGGBP1 loss-of-function. BMC Res Notes 2018; 11:419. [PMID: 29966527 PMCID: PMC6027561 DOI: 10.1186/s13104-018-3516-1] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2018] [Accepted: 06/19/2018] [Indexed: 12/13/2022] Open
Abstract
OBJECTIVES Although CpG methylation is well studied, mechanisms of non-CpG methylation in mammals remains elusive. Studying proteins with non-CpG cytosine methylation-sensitive DNA-binding, such as human CGGBP1, can unveil cytosine methylation regulatory mechanisms. Here we have resequenced a published genome-wide bisulfite sequencing library and analyzed it at base level resolution. CpG, CHG and CHH (where H is any nucleotide other than G) methylation states in non-targeting or CGGBP1-targeting shmiR lentivirus-transduced cells have been analyzed to identify how CGGBP1 regulates CpG and non-CpG methylation. RESULTS We report that CGGBP1 acts as a dynamic bimodal balancer of methylation. Both gain and loss of methylation observed upon CGGBP1 depletion were spatially overlapping at annotated functional regions and not identifiable with any sequence motifs but clearly associated with GC-skew. CGGBP1 depletion caused clustered methylation changes in cis, upstream of R-loop forming promoters. This was complemented by clustered occurrences of methylation changes in proximity of transcription start sites of known cytosine methylation regulatory genes, altered expression of which can regulate cytosine methylation in trans. Despite low coverage, our data provide reliable estimates of the spectrum of methylation changes regulated by CGGBP1 in all cytosine contexts genome-wide through a combination of cis and trans-acting mechanisms.
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Affiliation(s)
- Divyesh Patel
- HoMeCell Laboratory, Biological Sciences and Engineering, Indian Institute of Technology Gandhinagar, Gujarat, 382355, India
| | - Manthan Patel
- HoMeCell Laboratory, Biological Sciences and Engineering, Indian Institute of Technology Gandhinagar, Gujarat, 382355, India
| | - Bengt Westermark
- Department of Immunology, Genetics and Pathology, and Science for Life Laboratory, Uppsala University, 75185, Uppsala, Sweden
| | - Umashankar Singh
- HoMeCell Laboratory, Biological Sciences and Engineering, Indian Institute of Technology Gandhinagar, Gujarat, 382355, India.
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Affiliation(s)
- Kenji Ichiyanagi
- a Division of Epigenomics and Development; Medical Institute of Bioregulation ; Kyushu University ; Higashiku , Fukuoka , Japan
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Affiliation(s)
- Joseph F Cardiello
- a University of Colorado ; Department of Chemistry and Biochemistry ; Boulder , CO USA
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Abstract
The shelterin proteins are required for telomere integrity. Shelterin dysfunction can lead to initiation of unwarranted DNA damage and repair pathways at chromosomal termini. Interestingly, many shelterin accessory proteins are involved in DNA damage signaling and repair. We demonstrate here that in normal human fibroblasts, telomeric ends are protected by phosphorylation of CGG triplet repeat-binding protein 1 (CGGBP1) at serine 164 (S164). We show that serine 164 is a major phosphorylation site on CGGBP1 with important functions. We provide evidence that one of the kinases that can phosphorylate S164 CGGBP1 is ATR. Overexpression of S164A phospho-deficient CGGBP1 exerted a dominant-negative effect, causing telomeric dysfunction, accelerated telomere shortening, enhanced fusion of telomeres, and crisis. However, overexpression of wild-type or phospho-mimicking S164E CGGBP1 did not cause these effects. This telomere damage was associated with reduced binding of the shelterin protein POT1 to telomeric DNA. Our results suggest that CGGBP1 phosphorylation at S164 is a novel telomere protection signal, which can affect telomere-protective function of the shelterin complex.
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Affiliation(s)
- Umashankar Singh
- Department of Immunology, Genetics, and Pathology; Uppsala University; Tumor Biology; Rudbeck Laboratory; Uppsala, Sweden
| | - Varun Maturi
- Department of Immunology, Genetics, and Pathology; Uppsala University; Tumor Biology; Rudbeck Laboratory; Uppsala, Sweden; Ludwig Institute for Cancer Research; Science for Life Laboratory; Uppsala University; Biomedical Center; Uppsala, Sweden
| | - Rhiannon E Jones
- Department of Pathology; School of Medicine; Cardiff University; Cardiff, UK
| | - Ylva Paulsson
- Department of Immunology, Genetics, and Pathology; Uppsala University; Tumor Biology; Rudbeck Laboratory; Uppsala, Sweden
| | - Duncan M Baird
- Department of Pathology; School of Medicine; Cardiff University; Cardiff, UK
| | - Bengt Westermark
- Department of Immunology, Genetics, and Pathology; Uppsala University; Tumor Biology; Rudbeck Laboratory; Uppsala, Sweden
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