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Galsky MD, Arija JÁA, Bamias A, Davis ID, De Santis M, Kikuchi E, Garcia-Del-Muro X, De Giorgi U, Mencinger M, Izumi K, Panni S, Gumus M, Özgüroğlu M, Kalebasty AR, Park SH, Alekseev B, Schutz FA, Li JR, Ye D, Vogelzang NJ, Bernhard S, Tayama D, Mariathasan S, Mecke A, Thåström A, Grande E. Atezolizumab with or without chemotherapy in metastatic urothelial cancer (IMvigor130): a multicentre, randomised, placebo-controlled phase 3 trial. Lancet 2020; 395:1547-1557. [PMID: 32416780 DOI: 10.1016/s0140-6736(20)30230-0] [Citation(s) in RCA: 477] [Impact Index Per Article: 119.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/04/2019] [Revised: 01/16/2020] [Accepted: 01/24/2020] [Indexed: 12/14/2022]
Abstract
BACKGROUND Atezolizumab can induce sustained responses in metastatic urothelial carcinoma. We report the results of IMvigor130, a phase 3 trial that compared atezolizumab with or without platinum-based chemotherapy versus placebo plus platinum-based chemotherapy in first-line metastatic urothelial carcinoma. METHODS In this multicentre, phase 3, randomised trial, untreated patients aged 18 years or older with locally advanced or metastatic urothelial carcinoma, from 221 sites in 35 countries, were randomly assigned to receive atezolizumab plus platinum-based chemotherapy (group A), atezolizumab monotherapy (group B), or placebo plus platinum-based chemotherapy (group C). Patients received 21-day cycles of gemcitabine (1000 mg/m2 body surface area, administered intravenously on days 1 and 8 of each cycle), plus either carboplatin (area under the curve of 4·5 mg/mL per min administered intravenously) or cisplatin (70 mg/m2 body surface area administered intravenously) on day 1 of each cycle with either atezolizumab (1200 mg administered intravenously on day 1 of each cycle) or placebo. Group B patients received 1200 mg atezolizumab, administered intravenously on day 1 of each 21-day cycle. The co-primary efficacy endpoints for the intention-to-treat population were investigator-assessed Response Evaluation Criteria in Solid Tumours 1.1 progression-free survival and overall survival (group A vs group C) and overall survival (group B vs group C), which was to be formally tested only if overall survival was positive for group A versus group C. The trial is registered with ClinicalTrials.gov, NCT02807636. FINDINGS Between July 15, 2016, and July 20, 2018, we enrolled 1213 patients. 451 (37%) were randomly assigned to group A, 362 (30%) to group B, and 400 (33%) to group C. Median follow-up for survival was 11·8 months (IQR 6·1-17·2) for all patients. At the time of final progression-free survival analysis and interim overall survival analysis (May 31, 2019), median progression-free survival in the intention-to-treat population was 8·2 months (95% CI 6·5-8·3) in group A and 6·3 months (6·2-7·0) in group C (stratified hazard ratio [HR] 0·82, 95% CI 0·70-0·96; one-sided p=0·007). Median overall survival was 16·0 months (13·9-18·9) in group A and 13·4 months (12·0-15·2) in group C (0·83, 0·69-1·00; one-sided p=0·027). Median overall survival was 15·7 months (13·1-17·8) for group B and 13·1 months (11·7-15·1) for group C (1·02, 0·83-1·24). Adverse events that led to withdrawal of any agent occurred in 156 (34%) patients in group A, 22 (6%) patients in group B, and 132 (34%) patients in group C. 50 (11%) patients in group A, 21 (6%) patients in group B, and 27 (7%) patients in group C had adverse events that led to discontinuation of atezolizumab or placebo. INTERPRETATION Addition of atezolizumab to platinum-based chemotherapy as first-line treatment prolonged progression-free survival in patients with metastatic urothelial carcinoma. The safety profile of the combination was consistent with that observed with the individual agents. These results support the use of atezolizumab plus platinum-based chemotherapy as a potential first-line treatment option for metastatic urothelial carcinoma. FUNDING F Hoffmann-La Roche and Genentech.
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Affiliation(s)
- Matthew D Galsky
- Icahn School of Medicine at Mount Sinai, Tisch Cancer Institute, New York, NY, USA.
| | | | | | - Ian D Davis
- Eastern Health, Monash University, Melbourne, VIC, Australia
| | - Maria De Santis
- Charité University Hospital, Berlin, Germany; Department of Urology, Medical University, Vienna, Austria
| | - Eiji Kikuchi
- Keio University School of Medicine, Tokyo, Japan
| | | | - Ugo De Giorgi
- Istituto Scientifico Romagnolo per lo Studio e la Cura dei Tumori (IRST), IRCCS, Meldola, Italy
| | | | - Kouji Izumi
- Kanazawa University Hospital, Kanazawa, Japan
| | | | - Mahmut Gumus
- Istanbul Medeniyet University, Goztepe Research Hospital, Istanbul, Turkey
| | - Mustafa Özgüroğlu
- Istanbul University-Cerrahpaşa, Cerrahpaşa School of Medicine, Istanbul, Turkey
| | | | - Se Hoon Park
- Sungkyunkwan University Samsung Medical Center, Seoul, Korea
| | | | | | - Jian-Ri Li
- Taichung Veterans General Hospital, HungKuang University, Taichung, Taiwan
| | - Dingwei Ye
- Fudan University Shanghai Cancer Center, Shanghai, China
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Vander Velde N, Guerin A, Ionescu-Ittu R, Shi S, Wu EQ, Lin SW, Hsu LI, Saum KU, de Ducla S, Wang J, Li S, Thåström A, Liu S, Shi L, Leppert JT. Comparative Effectiveness of Non-cisplatin First-line Therapies for Metastatic Urothelial Carcinoma: Phase 2 IMvigor210 Study Versus US Patients Treated in the Veterans Health Administration. Eur Urol Oncol 2019; 2:12-20. [DOI: 10.1016/j.euo.2018.07.003] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2018] [Revised: 06/25/2018] [Accepted: 07/10/2018] [Indexed: 10/28/2022]
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Galsky M, Banchereau R, Kadel E, Ramirez-Montagut T, Mariathasan S, Thåström A, Rosenberg J, Powles T, van der Heijden M, Necchi A. Biological features and clinical outcomes in atezolizumab (atezo)-treated patients (pts) with metastatic urothelial cancer (mUC) of the upper vs lower urinary tract (UTUC vs LTUC). Ann Oncol 2018. [DOI: 10.1093/annonc/mdy283.111] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
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Balar AV, Galsky MD, Rosenberg JE, Powles T, Petrylak DP, Bellmunt J, Loriot Y, Necchi A, Hoffman-Censits J, Perez-Gracia JL, Dawson NA, van der Heijden MS, Dreicer R, Srinivas S, Retz MM, Joseph RW, Drakaki A, Vaishampayan UN, Sridhar SS, Quinn DI, Durán I, Shaffer DR, Eigl BJ, Grivas PD, Yu EY, Li S, Kadel EE, Boyd Z, Bourgon R, Hegde PS, Mariathasan S, Thåström A, Abidoye OO, Fine GD, Bajorin DF. Atezolizumab as first-line treatment in cisplatin-ineligible patients with locally advanced and metastatic urothelial carcinoma: a single-arm, multicentre, phase 2 trial. Lancet 2017; 389:67-76. [PMID: 27939400 PMCID: PMC5568632 DOI: 10.1016/s0140-6736(16)32455-2] [Citation(s) in RCA: 1491] [Impact Index Per Article: 213.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/01/2016] [Revised: 11/15/2016] [Accepted: 11/15/2016] [Indexed: 12/16/2022]
Abstract
BACKGROUND First-line chemotherapy for patients with cisplatin-ineligible locally advanced or metastatic urothelial carcinoma is associated with short response duration, poor survival, and high toxicity. This study assessed atezolizumab (anti-programmed death-ligand 1 [PD-L1]) as treatment for metastatic urothelial cancer in cisplatin-ineligible patients. METHODS For this single-arm, multicentre, phase 2 study, in 47 academic medical centres and community oncology practices in seven countries in North America and Europe, we recruited previously untreated patients with locally advanced or metastatic urothelial cancer who were cisplatin ineligible. Patients were given 1200 mg intravenous atezolizumab every 21 days until progression. The primary endpoint was independently confirmed objective response rate per Response Evaluation Criteria in Solid Tumors version 1.1 (central review), assessed in prespecified subgroups based on PD-L1 expression and in all patients. All participants who received one or more doses of atezolizumab were included in the primary and safety analyses. This study was registered with ClinicalTrials.gov, number NCT02108652. FINDINGS Between June 9, 2014, and March 30, 2015, we enrolled 123 patients, of whom 119 received one or more doses of atezolizumab. At 17·2 months' median follow-up, the objective response rate was 23% (95% CI 16 to 31), the complete response rate was 9% (n=11), and 19 of 27 responses were ongoing. Median response duration was not reached. Responses occurred across all PD-L1 and poor prognostic factor subgroups. Median progression-free survival was 2·7 months (2·1 to 4·2). Median overall survival was 15·9 months (10·4 to not estimable). Tumour mutation load was associated with response. Treatment-related adverse events that occurred in 10% or more of patients were fatigue (36 [30%] patients), diarrhoea (14 [12%] patients), and pruritus (13 [11%] patients). One treatment-related death (sepsis) occurred. Nine (8%) patients had an adverse event leading to treatment discontinuation. Immune-mediated events occurred in 14 (12%) patients. INTERPRETATION Atezolizumab showed encouraging durable response rates, survival, and tolerability, supporting its therapeutic use in untreated metastatic urothelial cancer. FUNDING F Hoffmann-La Roche, Genentech.
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MESH Headings
- Aged
- Aged, 80 and over
- Antibodies, Monoclonal/administration & dosage
- Antibodies, Monoclonal/adverse effects
- Antibodies, Monoclonal/therapeutic use
- Antibodies, Monoclonal, Humanized
- Antineoplastic Agents/administration & dosage
- Antineoplastic Agents/adverse effects
- Antineoplastic Agents/therapeutic use
- B7-H1 Antigen/blood
- Biomarkers, Tumor/blood
- Carcinoma, Transitional Cell/blood
- Carcinoma, Transitional Cell/drug therapy
- Carcinoma, Transitional Cell/secondary
- Cisplatin
- Contraindications
- Female
- Humans
- Infusions, Intravenous
- Kaplan-Meier Estimate
- Lymphatic Metastasis
- Male
- Middle Aged
- Response Evaluation Criteria in Solid Tumors
- Urologic Neoplasms/blood
- Urologic Neoplasms/drug therapy
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Affiliation(s)
- Arjun V Balar
- Genitourinary Cancers Program, Perlmutter Cancer Center, New York University Langone Medical Center, New York, NY, USA.
| | - Matthew D Galsky
- The Tisch Cancer Institute, Icahn School of Medicine at Mount Sinai, New York, NY, USA
| | - Jonathan E Rosenberg
- Genitourinary Oncology Service, Department of Medicine, Memorial Sloan Kettering Cancer Center, New York, NY, USA
| | - Thomas Powles
- Barts Cancer Institute ECMC, Barts Health and the Royal Free NHS Trust, Queen Mary University of London, London, UK
| | | | - Joaquim Bellmunt
- Lank Center for Genitourinary Oncology, Dana-Farber Cancer Institute, Harvard Medical School, Boston, MA, USA
| | - Yohann Loriot
- Département de médecine oncologique, Université Paris-Saclay and Gustave Roussy, Villejuif, France
| | - Andrea Necchi
- Department of Medical Oncology, Fondazione IRCCS Istituto Nazionale dei Tumori, Milan, Italy
| | | | - Jose Luis Perez-Gracia
- Department of Oncology, Clínica Universidad de Navarra, University of Navarra, Pamplona, Navarre, Spain
| | - Nancy A Dawson
- Medstar Georgetown University Hospital, Lombardi Comprehensive Cancer Center, Washington, DC, USA
| | | | - Robert Dreicer
- Division of Hematology/Oncology, University of Virginia School of Medicine, Charlottesville, VA, USA
| | - Sandy Srinivas
- Division of Oncology/Department of Medicine, Stanford University School of Medicine, Stanford, CA, USA
| | - Margitta M Retz
- Department of Urology, Klinikum rechts der Isar, Technical University Munich, Munich, Germany
| | - Richard W Joseph
- Department of Hematology/Oncology, Mayo Clinic, Jacksonville, FL, USA
| | - Alexandra Drakaki
- Department of Medicine, Division of Hematology and Oncology and Institute of Urologic Oncology, David Geffen School of Medicine, University of California, Los Angeles, CA, USA
| | | | - Srikala S Sridhar
- Department of Medical Oncology and Hematology, Princess Margaret Cancer Center, Toronto, ON, Canada
| | - David I Quinn
- University of Southern California Norris Comprehensive Cancer Center, Los Angeles, CA, USA
| | - Ignacio Durán
- Department of Medical Oncology, Hospital Universitario Virgen del Rocío and Institute of Biomedicine of Seville, Seville, Spain
| | | | - Bernhard J Eigl
- British Columbia Cancer Agency, British Columbia, Vancouver, Canada
| | - Petros D Grivas
- Department of Hematology and Medical Oncology, Taussig Cancer Institute, Cleveland Clinic, Cleveland, OH, USA
| | - Evan Y Yu
- Division of Oncology, Department of Medicine, University of Washington and Clinical Research Division, Fred Hutchinson Cancer Research Center, Seattle, WA, USA
| | - Shi Li
- Genentech, South San Francisco, CA, USA
| | | | | | | | | | | | | | | | | | - Dean F Bajorin
- Genitourinary Oncology Service, Department of Medicine, Memorial Sloan Kettering Cancer Center, New York, NY, USA
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Loriot Y, Rosenberg J, Powles T, Necchi A, Hussain S, Morales R, Retz M, Niegisch G, Duran I, Theodore C, Perez-Gracia J, Grande Pulido E, Thåström A, Danner B, Mariathasan S, Abidoye O, van der Heijden M. Atezolizumab (atezo) in platinum (plat)-treated locally advanced/metastatic urothelial carcinoma (mUC): Updated OS, safety and biomarkers from the Ph II IMvigor210 study. Ann Oncol 2016. [DOI: 10.1093/annonc/mdw373.11] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
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Segal E, Fondufe-Mittendorf Y, Chen L, Thåström A, Field Y, Moore IK, Wang JPZ, Widom J. A genomic code for nucleosome positioning. Nature 2006; 442:772-8. [PMID: 16862119 PMCID: PMC2623244 DOI: 10.1038/nature04979] [Citation(s) in RCA: 1097] [Impact Index Per Article: 60.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2006] [Accepted: 06/14/2006] [Indexed: 11/08/2022]
Abstract
Eukaryotic genomes are packaged into nucleosome particles that occlude the DNA from interacting with most DNA binding proteins. Nucleosomes have higher affinity for particular DNA sequences, reflecting the ability of the sequence to bend sharply, as required by the nucleosome structure. However, it is not known whether these sequence preferences have a significant influence on nucleosome position in vivo, and thus regulate the access of other proteins to DNA. Here we isolated nucleosome-bound sequences at high resolution from yeast and used these sequences in a new computational approach to construct and validate experimentally a nucleosome-DNA interaction model, and to predict the genome-wide organization of nucleosomes. Our results demonstrate that genomes encode an intrinsic nucleosome organization and that this intrinsic organization can explain approximately 50% of the in vivo nucleosome positions. This nucleosome positioning code may facilitate specific chromosome functions including transcription factor binding, transcription initiation, and even remodelling of the nucleosomes themselves.
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Affiliation(s)
- Eran Segal
- Department of Computer Science and Applied Mathematics, Weizmann Institute of Science, Rehovot 76100, Israel.
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7
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Abstract
Nucleosome positioning DNA sequences are of increasing interest because of their proposed roles in gene regulation and other chromosome functions in vivo, and because they have revealed new insights into the sequence-dependent structures and mechanics of DNA itself. Here, we describe methods to quantify the relative affinities of histone-DNA interactions in nucleosomes, i.e., the nucleosome positioning power of differing DNA sequences. We review methods developed by others and then discuss in detail our own approach to measurement of histone-DNA interaction free energies. Compared to earlier methods, our dialysis-based approach reduces the possibility that non-equilibrium or irreproducible results could be obtained. It facilitates a direct comparison of free energies for many sequences at the same time and it allows analysis of DNAs having a wide range of relative affinities.
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Affiliation(s)
- A Thåström
- Department of Biochemistry, Molecular Biology, and Cell Biology, Northwestern University, 2153 Sheridan Road, Evanston, IL 60208-3500, USA
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8
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Thåström A, Bingham LM, Widom J. Nucleosomal locations of dominant DNA sequence motifs for histone-DNA interactions and nucleosome positioning. J Mol Biol 2004; 338:695-709. [PMID: 15099738 DOI: 10.1016/j.jmb.2004.03.032] [Citation(s) in RCA: 156] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2004] [Revised: 03/15/2004] [Accepted: 03/15/2004] [Indexed: 10/26/2022]
Abstract
DNA sequence is an important determinant of the positioning, stability, and activity of nucleosomes, yet the molecular basis of these effects remains elusive. A "consensus DNA sequence" for nucleosome positioning has not been reported and, while certain DNA sequence preferences or motifs for nucleosome positioning have been discovered, how they function is not known. Here, we report that an unexpected observation concerning the reassembly of nucleosomes during salt gradient dialysis has allowed a breakthrough in our efforts to identify the nucleosomal locations of the DNA sequence motifs that dominate histone-DNA interactions and nucleosome positioning. We conclude that a previous selection experiment for high-affinity, nucleosome-forming DNA sequences exerted selective pressure chiefly on the central stretch of the nucleosomal DNA. This observation implies that algorithms for aligning the selected DNA sequences should seek to optimize the alignment over much less than the full 147 bp of nucleosomal DNA. A new alignment calculation implemented these ideas and successfully aligned 19 of the 41 sequences in a non-redundant database of selected high-affinity, nucleosome-positioning sequences. The resulting alignment reveals strong conservation of several stretches within a central 71 bp of the nucleosomal DNA. The alignment further reveals an inherent palindromic symmetry in the selected DNAs; it makes testable predictions of nucleosome positioning on the aligned sequences and for the creation of new positioning sequences, both of which are upheld experimentally; and it suggests new signals that may be important in translational nucleosome positioning.
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Affiliation(s)
- A Thåström
- Department of Biochemistry, Molecular Biology, and Cell Biology, Northwestern University, 2153 Sheridan Road, Evanston, IL 60208-3500, USA
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9
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Abstract
Despite decades of study on nucleosomes, there has been no experimental determination of the free energy of association between histones and DNA. Instead, only the relative free energy of association of the histone octamer for differing DNA sequences has been available. Recently, a method was developed based on quantitative analysis of nucleosome dissociation in dilution experiments that provides a simple practical measure of nucleosome stability. Solution conditions were found in which nucleosome dissociation driven by dilution fit well to a simple model involving a noncooperative nucleosome assembly/disassembly equilibrium, suggesting that this approach might allow absolute equilibrium affinity of the histone octamer for DNA to be measured. Here, we show that the nucleosome assembly/disassembly process is not strictly reversible in these solution conditions, implying that equilibrium affinities cannot be obtained from these measurements. Increases in [NaCl] or temperature, commonly employed to suppress kinetic bottlenecks in nucleosome assembly, lead to cooperative behavior that cannot be interpreted with the simple assembly/disassembly equilibrium model. We conclude that the dilution experiments provide useful measures of kinetic but not equilibrium stability. Kinetic stability is of practical importance: it may govern nucleosome function in vivo, and it may (but need not) parallel absolute thermodynamic stability.
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Affiliation(s)
- A Thåström
- Department of Biochemistry, Molecular Biology, and Cell Biology, Northwestern University, Evanston, Illinois 60208-3500, USA
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10
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Anderson JD, Thåström A, Widom J. Spontaneous access of proteins to buried nucleosomal DNA target sites occurs via a mechanism that is distinct from nucleosome translocation. Mol Cell Biol 2002; 22:7147-57. [PMID: 12242292 PMCID: PMC139820 DOI: 10.1128/mcb.22.20.7147-7157.2002] [Citation(s) in RCA: 97] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Intrinsic nucleosome dynamics termed "site exposure" provides spontaneous and cooperative access to buried regions of nucleosomal DNA in vitro. Two different mechanisms for site exposure have been proposed, one based on nucleosome translocation, the other on dynamic nucleosome conformational changes in which a stretch of the nucleosomal DNA is transiently released off the histone surface. Here we report on three experiments that distinguish between these mechanisms. One experiment investigates the effects on the accessibilities of restriction enzyme target sites inside nucleosomes when extra DNA (onto which the nucleosome may move at low energetic cost) is appended onto one end. The other two experiments test directly for nucleosome mobility under the conditions used to probe accessibility to restriction enzymes: one on a selected nonnatural nucleosome positioning sequence, the other on the well-studied 5S rRNA gene nucleosome positioning sequence. We find from all three assays that restriction enzymes gain access to sites throughout the entire length of the nucleosomal DNA without contribution from nucleosome translocation. We conclude that site exposure in nucleosomes in vitro occurs via a nucleosome conformational change that leads to transient release of a stretch of DNA from the histone surface, most likely involving progressive uncoiling from an end. Recapture at a distal site along DNA that has partially uncoiled would result in looped structures which are believed to contribute to RNA polymerase elongation and may contribute to spontaneous or ATP-driven nucleosome mobility. Transient open states may facilitate the initial entry of transcription factors and enzymes in vivo.
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Affiliation(s)
- J D Anderson
- Department of Biochemistry, Molecular Biology, and Cell Biology and Department of Chemistry, Northwestern University, Evanston, Illinois 60208-3500, USA
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11
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Thåström A, Lowary PT, Widlund HR, Cao H, Kubista M, Widom J. Sequence motifs and free energies of selected natural and non-natural nucleosome positioning DNA sequences. J Mol Biol 1999; 288:213-29. [PMID: 10329138 DOI: 10.1006/jmbi.1999.2686] [Citation(s) in RCA: 299] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Our laboratories recently completed SELEX experiments to isolate DNA sequences that most-strongly favor or disfavor nucleosome formation and positioning, from the entire mouse genome or from even more diverse pools of chemically synthetic random sequence DNA. Here we directly compare these selected natural and non-natural sequences. We find that the strongest natural positioning sequences have affinities for histone binding and nucleosome formation that are sixfold or more lower than those possessed by many of the selected non-natural sequences. We conclude that even the highest-affinity sequence regions of eukaryotic genomes are not evolved for the highest affinity or nucleosome positioning power. Fourier transform calculations on the selected natural sequences reveal a special significance for nucleosome positioning of a motif consisting of approximately 10 bp periodic placement of TA dinucleotide steps. Contributions to histone binding and nucleosome formation from periodic TA steps are more significant than those from other periodic steps such as AA (=TT), CC (=GG) and more important than those from the other YR steps (CA (=TG) and CG), which are reported to have greater conformational flexibility in protein-DNA complexes even than TA. We report the development of improved procedures for measuring the free energies of even stronger positioning sequences that may be isolated in the future, and show that when the favorable free energy of histone-DNA interactions becomes sufficiently large, measurements based on the widely used exchange method become unreliable.
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Affiliation(s)
- A Thåström
- Department of Biochemistry Molecular Biology, and Cell Biology, Northwestern University, Evanston, IL 60208-3500, USA
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