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Molecular and Cellular Biology Mar 2007Bloom's syndrome is a genetic disorder characterized by increased incidence of cancer and an immunodeficiency of unknown origin. The BLM gene mutated in Bloom's syndrome... (Comparative Study)
Comparative Study
Bloom's syndrome is a genetic disorder characterized by increased incidence of cancer and an immunodeficiency of unknown origin. The BLM gene mutated in Bloom's syndrome encodes a DNA helicase involved in the maintenance of genomic integrity. To explore the role of BLM in the immune system, we ablated murine Blm in the T-cell lineage. In the absence of Blm, thymocytes were severely reduced in numbers and displayed a developmental block at the beta-selection checkpoint that was partially p53 dependent. Blm-deficient thymocytes rearranged their T-cell receptor (TCR) beta genes normally yet failed to survive and proliferate in response to pre-TCR signaling. Furthermore, peripheral T cells were reduced in numbers, manifested defective homeostatic and TCR-induced proliferation, and produced extensive chromosomal damage. Finally, CD4(+) and CD8(+) T-cell responses were impaired upon antigen challenge. Thus, by ensuring genomic stability, Blm serves a vital role for development, maintenance, and function of T lymphocytes, suggesting a basis for the immune deficiency in Bloom's syndrome.
Topics: Adenosine Triphosphatases; Alleles; Animals; Cell Lineage; Cells, Cultured; Chromosome Aberrations; DNA Helicases; Mice; Mice, Knockout; Mice, Transgenic; RecQ Helicases; Receptors, Antigen, T-Cell, alpha-beta; T-Lymphocytes; Thymus Gland
PubMed: 17210642
DOI: 10.1128/MCB.01402-06 -
Biochemistry Aug 2011Cells cope with blockage of replication fork progression in a manner that allows DNA synthesis to be completed and genomic instability minimized. Models for resolution...
Cells cope with blockage of replication fork progression in a manner that allows DNA synthesis to be completed and genomic instability minimized. Models for resolution of blocked replication involve fork regression to form Holliday junction structures. The human RecQ helicases WRN and BLM (deficient in Werner and Bloom syndromes, respectively) are critical for maintaining genomic stability and thought to function in accurate resolution of replication blockage. Consistent with this notion, WRN and BLM localize to sites of blocked replication after certain DNA-damaging treatments and exhibit enhanced activity on replication and recombination intermediates. Here we examine the actions of WRN and BLM on a special Holliday junction substrate reflective of a regressed replication fork. Our results demonstrate that, in reactions requiring ATP hydrolysis, both WRN and BLM convert this Holliday junction substrate primarily to a four-stranded replication fork structure, suggesting they target the Holliday junction to initiate branch migration. In agreement, the Holliday junction binding protein RuvA inhibits the WRN- and BLM-mediated conversion reactions. Importantly, this conversion product is suitable for replication with its leading daughter strand readily extended by DNA polymerases. Furthermore, binding to and conversion of this Holliday junction are optimal at low MgCl(2) concentrations, suggesting that WRN and BLM preferentially act on the square planar (open) conformation of Holliday junctions. Our findings suggest that, subsequent to fork regression events, WRN and/or BLM could re-establish functional replication forks to help overcome fork blockage. Such a function is highly consistent with phenotypes associated with WRN- and BLM-deficient cells.
Topics: DNA; DNA Replication; Electrophoretic Mobility Shift Assay; Exodeoxyribonucleases; Humans; RecQ Helicases; Recombinant Proteins; Substrate Specificity; Werner Syndrome Helicase
PubMed: 21736299
DOI: 10.1021/bi2001054 -
Cellular and Molecular Life Sciences :... Nov 2013RecQ DNA helicases are critical for proper maintenance of genomic stability, and mutations in multiple human RecQ genes are linked with genetic disorders characterized... (Review)
Review
RecQ DNA helicases are critical for proper maintenance of genomic stability, and mutations in multiple human RecQ genes are linked with genetic disorders characterized by a predisposition to cancer. RecQ proteins are conserved from prokaryotes to humans and in all cases form higher-order complexes with other proteins to efficiently execute their cellular functions. The focus of this review is a conserved complex that is formed between RecQ helicases and type-I topoisomerases. In humans, this complex is referred to as the BLM dissolvasome or BTR complex, and is comprised of the RecQ helicase BLM, topoisomerase IIIα, and the RMI proteins. The BLM dissolvasome functions to resolve linked DNA intermediates without exchange of genetic material, which is critical in somatic cells. We will review the history of this complex and highlight its roles in DNA replication, recombination, and repair. Additionally, we will review recently established interactions between BLM dissolvasome and a second set of genome maintenance factors (the Fanconi anemia proteins) that appear to allow coordinated genome maintenance efforts between the two systems.
Topics: Anaphase; Animals; Bloom Syndrome; DNA; DNA Damage; DNA Repair; DNA Replication; Fanconi Anemia; Genomic Instability; Humans; Mutation; Protein Structure, Tertiary; RecQ Helicases
PubMed: 23543275
DOI: 10.1007/s00018-013-1325-1 -
American Journal of Human Genetics Nov 1995
Low-sister-chromatid-exchange Bloom syndrome cell lines: an important new tool for mapping the basic genetic defect in Bloom syndrome and for unraveling the biology of human tumor development.
Topics: Bloom Syndrome; Cell Line; Chromosome Mapping; Humans; Sister Chromatid Exchange
PubMed: 7485184
DOI: No ID Found -
Critical Reviews in Biochemistry and... 2013DNA helicases are ubiquitous enzymes that catalyze unwinding of duplex DNA and function in all metabolic processes in which access to single-stranded DNA is required,... (Review)
Review
DNA helicases are ubiquitous enzymes that catalyze unwinding of duplex DNA and function in all metabolic processes in which access to single-stranded DNA is required, including DNA replication, repair, recombination and RNA transcription. RecQ helicases are a conserved family of DNA helicases that display highly specialized and vital roles in the maintenance of genome stability. Mutations in three of the five human RecQ helicases, BLM, WRN and RECQL4 are associated with the genetic disorders Bloom syndrome, Werner syndrome and Rothmund-Thomson syndrome that are characterized by chromosomal instability, premature aging and predisposition to cancer. The biological role of human RECQL5 is only partially understood and RECQL5 has not yet been associated with any human disease. Illegitimate recombination and replication stress are hallmarks of human cancers and common instigators for genomic instability and cell death. Recql5 knockout mice are cancer prone and show increased chromosomal instability. Recql5-deficient mouse embryonic fibroblasts are sensitive to camptothecin and display elevated levels of sister chromatid exchanges. Unlike other human RecQ helicases, RECQL5 is recruited to single-stranded DNA breaks and is also proposed to play an essential role in RNA transcription. Here, we review the established roles of RECQL5 at the cross roads of DNA replication, recombination and transcription, and propose that human RECQL5 provides important backup functions in the absence of other DNA helicases.
Topics: Animals; DNA Repair; DNA Replication; Homologous Recombination; Humans; RecQ Helicases; Transcription, Genetic
PubMed: 23627586
DOI: 10.3109/10409238.2013.792770 -
The Journal of Investigative Dermatology Oct 2009Despite their rarity, diseases of premature aging, or "progeroid" syndromes, have provided important insights into basic mechanisms that may underlie cancer and normal... (Review)
Review
Despite their rarity, diseases of premature aging, or "progeroid" syndromes, have provided important insights into basic mechanisms that may underlie cancer and normal aging. In this review, we highlight these recent developments in Hutchinson-Gilford progeria syndrome (HGPS), Werner syndrome, Bloom syndrome, Cockayne syndrome, trichothiodystrophy, ataxia-telangiectasia, Rothmund-Thomson syndrome, and xeroderma pigmentosum. Though they are caused by different mutations in various genes and often result in quite disparate phenotypes, deciphering the molecular bases of these conditions has served to highlight their underlying basic similarities. Studies of progeroid syndromes, particularly HGPS, the most dramatic form of premature aging, have contributed to our knowledge of fundamental processes of importance to skin biology, including DNA transcription, replication, and repair, genome instability, cellular senescence, and stem-cell differentiation.
Topics: Aging, Premature; Cellular Senescence; DNA Damage; Genomic Instability; Humans; Mutation; Progeria; Skin Neoplasms; Syndrome
PubMed: 19387478
DOI: 10.1038/jid.2009.103 -
BioRxiv : the Preprint Server For... Jan 2023Bloom syndrome helicase (BLM) is a RecQ-family helicase implicated in a variety of cellular processes, including DNA replication, DNA repair, and telomere maintenance....
Bloom syndrome helicase (BLM) is a RecQ-family helicase implicated in a variety of cellular processes, including DNA replication, DNA repair, and telomere maintenance. Mutations in human cause Bloom syndrome (BS), an autosomal recessive disorder that leads to myriad negative health impacts including a predisposition to cancer. BS-causing mutations in often negatively impact BLM ATPase and helicase activity. While mutations that cause BS have been well characterized both and , there are other less studied mutations that exist in the human population that do not lead to BS. Two of these non-BS mutations, encoding BLM P868L and BLM G1120R, when homozygous, increase sister chromatid exchanges in human cells. To characterize these naturally occurring BLM mutant proteins , we purified the BLM catalytic core (BLM , residues 636-1298) with either the P868L or G1120R substitution. We also purified a BLM K869A K870A mutant protein, which alters a lysine-rich loop proximal to the P868 residue. We found that BLM P868L and G1120R proteins were both able to hydrolyze ATP, bind diverse DNA substrates, and unwind G-quadruplex and duplex DNA structures. Molecular dynamics simulations suggest that the P868L substitution weakens the DNA interaction with the winged-helix domain of BLM and alters the orientation of one lobe of the ATPase domain. Because BLM P868L and G1120R retain helicase function , it is likely that the increased genome instability is caused by specific impacts of the mutant proteins . Interestingly, we found that BLM K869A K870A has diminished ATPase activity, weakened binding to duplex DNA structures, and less robust helicase activity compared to wild-type BLM . Thus, the lysine-rich loop may have an important role in ATPase activity and specific binding and DNA unwinding functions in BLM.
PubMed: 36747637
DOI: 10.1101/2023.01.26.525669 -
Methods in Molecular Biology (Clifton,... 2019DNA double-strand breaks (DSBs) are a potentially lethal DNA lesions that disrupt both the physical and genetic continuity of the DNA duplex. Homologous recombination...
DNA double-strand breaks (DSBs) are a potentially lethal DNA lesions that disrupt both the physical and genetic continuity of the DNA duplex. Homologous recombination (HR) is a universally conserved genome maintenance pathway that initiates via nucleolytic processing of the broken DNA ends (resection). Eukaryotic DNA resection is catalyzed by the resectosome-a multicomponent molecular machine consisting of the nucleases DNA2 or Exonuclease 1 (EXO1), Bloom's helicase (BLM), the MRE11-RAD50-NBS1 (MRN) complex, and additional regulatory factors. Here, we describe methods for purification and single-molecule imaging and analysis of EXO1, DNA2, and BLM. We also describe how to adapt resection assays to the high-throughput single-molecule DNA curtain assay. By organizing hundreds of individual molecules on the surface of a microfluidic flowcell, DNA curtains visualize protein complexes with the required spatial and temporal resolution to resolve the molecular choreography during critical DNA-processing reactions.
Topics: DNA Breaks, Double-Stranded; DNA Helicases; DNA Repair Enzymes; Exodeoxyribonucleases; Microfluidic Analytical Techniques; Microscopy, Fluorescence; Quantum Dots; RecQ Helicases; Recombinant Proteins; Recombinational DNA Repair; Single Molecule Imaging
PubMed: 31127580
DOI: 10.1007/978-1-4939-9500-4_14 -
Journal of Medical Case Reports Dec 2013Bloom syndrome is a rare, autosomal recessive, chromosomal instability disorder caused by mutations in the BLM gene that increase the risk of developing neoplasias,...
INTRODUCTION
Bloom syndrome is a rare, autosomal recessive, chromosomal instability disorder caused by mutations in the BLM gene that increase the risk of developing neoplasias, particularly lymphomas and leukemias, at an early age.
CASE PRESENTATION
Case 1 was a 10-year-old Brazilian girl, the third child of a non-consanguineous non-Jewish family, who was born at 36 weeks of gestation and presented with severe intrauterine growth restriction. She had Bloom syndrome and was diagnosed with a unilateral Wilms' tumor at the age of 3.5 years. She responded well to oncological treatment and has remained disease-free for the last 17 years. Case 2 was a 2-year-old Brazilian girl born to non-Jewish first-degree cousins. Her gestation was marked by intrauterine growth restriction. She had Bloom syndrome; a unilateral stage II Wilms' tumor was diagnosed at the age of 4 years after the evaluation of a sudden onset abdominal mass. Surgical removal, neoadjuvant chemotherapy and radiotherapy were not sufficient to control the neoplasia. The tumor recurred after 8 months and she died from clinical complications.
CONCLUSION
Our study reports the importance of rapid diagnostics and clinical follow-up of these patients.
PubMed: 24377487
DOI: 10.1186/1752-1947-7-284 -
Cellular and Molecular Life Sciences :... Sep 2007The RecQ helicases belong to the Superfamily II group of DNA helicases, and are defined by amino acid motifs that show sequence similarity to the catalytic domain of... (Review)
Review
The RecQ helicases belong to the Superfamily II group of DNA helicases, and are defined by amino acid motifs that show sequence similarity to the catalytic domain of Escherichia coli RecQ. RecQ helicases have crucial roles in the maintenance of genome stability. In humans, there are five RecQ helicases and deficiencies in three of them cause genetic disorders characterised by cancer predisposition, premature aging and/or developmental abnormalities. RecQ helicase-deficient cells exhibit aberrant genetic recombination and/or DNA replication, which result in chromosomal instability and a decreased potential for proliferation. Here, we review the current knowledge of the molecular genetics of RecQ helicases, focusing on the human RecQ helicase disorders and mouse models of these conditions.
Topics: Adenosine Triphosphatases; Animals; Bloom Syndrome; Cellular Senescence; DNA Damage; DNA Helicases; DNA Repair-Deficiency Disorders; Disease Models, Animal; Humans; Mice; Phenotype; RecQ Helicases; Recombination, Genetic; Syndrome; Werner Syndrome
PubMed: 17571213
DOI: 10.1007/s00018-007-7121-z