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Current Biology : CB Jan 2017In most sexually reproducing organisms, crossover formation between homologous chromosomes is necessary for proper chromosome disjunction during meiosis I. During...
In most sexually reproducing organisms, crossover formation between homologous chromosomes is necessary for proper chromosome disjunction during meiosis I. During meiotic recombination, a subset of programmed DNA double-strand breaks (DSBs) are repaired as crossovers, with the remainder becoming noncrossovers [1]. Whether a repair intermediate is designated to become a crossover is a highly regulated decision that integrates several crossover patterning processes, both along chromosome arms (interference and the centromere effect) and between chromosomes (crossover assurance) [2]. Because the mechanisms that generate crossover patterning have remained elusive for over a century, it has been difficult to assess the relationship between crossover patterning and meiotic chromosome behavior. We show here that meiotic crossover patterning is lost in Drosophila melanogaster mutants that lack the Bloom syndrome helicase. In the absence of interference and the centromere effect, crossovers are distributed more uniformly along chromosomes. Crossovers even occur on the small chromosome 4, which normally never has meiotic crossovers [3]. Regulated distribution of crossovers between chromosome pairs is also lost, resulting in an elevated frequency of homologs that do not receive a crossover, which in turn leads to elevated nondisjunction.
Topics: Animals; DNA Helicases; Drosophila Proteins; Drosophila melanogaster; Female; Homologous Recombination; Male; Meiosis; Nondisjunction, Genetic
PubMed: 27989672
DOI: 10.1016/j.cub.2016.10.055 -
PloS One 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 BLM cause Bloom syndrome (BS), an autosomal recessive disorder that leads to myriad negative health impacts including a predisposition to cancer. BS-causing mutations in BLM often negatively impact BLM ATPase and helicase activity. While BLM mutations that cause BS have been well characterized both in vitro and in vivo, there are other less studied BLM 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 in vitro, we purified the BLM catalytic core (BLMcore, residues 636-1298) with either the P868L or G1120R substitution. We also purified a BLMcore K869A K870A mutant protein, which alters a lysine-rich loop proximal to the P868 residue. We found that BLMcore 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 BLMcore P868L and G1120R retain helicase function in vitro, it is likely that the increased genome instability is caused by specific impacts of the mutant proteins in vivo. Interestingly, we found that BLMcore K869A K870A has diminished ATPase activity, weakened binding to duplex DNA structures, and less robust helicase activity compared to wild-type BLMcore. Thus, the lysine-rich loop may have an important role in ATPase activity and specific binding and DNA unwinding functions in BLM.
Topics: Humans; Bloom Syndrome; Lysine; RecQ Helicases; DNA; Mutant Proteins
PubMed: 37267408
DOI: 10.1371/journal.pone.0281524 -
Mutation Research 2013Helicases have important roles in nucleic acid metabolism, and their prominence is marked by the discovery of genetic disorders arising from disease-causing mutations.... (Review)
Review
Helicases have important roles in nucleic acid metabolism, and their prominence is marked by the discovery of genetic disorders arising from disease-causing mutations. Missense mutations can yield unique insight to molecular functions and basis for disease pathology. XPB or XPD missense mutations lead to Xeroderma pigmentosum, Cockayne's syndrome, Trichothiodystrophy, or COFS syndrome, suggesting that DNA repair and transcription defects are responsible for clinical heterogeneity. Complex phenotypes are also observed for RECQL4 helicase mutations responsible for Rothmund-Thomson syndrome, Baller-Gerold syndrome, or RAPADILINO. Bloom's syndrome causing missense mutations are found in the conserved helicase and RecQ C-terminal domain of BLM that interfere with helicase function. Although rare, patient-derived missense mutations in the exonuclease or helicase domain of Werner syndrome protein exist. Characterization of WRN separation-of-function mutants may provide insight to catalytic requirements for suppression of phenotypes associated with the premature aging disorder. Characterized FANCJ missense mutations associated with breast cancer or Fanconi anemia interfere with FANCJ helicase activity required for DNA repair and the replication stress response. For example, a FA patient-derived mutation in the FANCJ Iron-Sulfur domain was shown to uncouple its ATPase and translocase activity from DNA unwinding. Mutations in DDX11 (ChlR1) are responsible for Warsaw Breakage syndrome, a recently discovered autosomal recessive cohesinopathy. Ongoing and future studies will address clinically relevant helicase mutations and polymorphisms, including those that interfere with key protein interactions or exert dominant negative phenotypes (e.g., certain mutant alleles of Twinkle mitochondrial DNA helicase). Chemical rescue may be an approach to restore helicase activity in loss-of-function helicase disorders. Genetic and biochemical analyses of disease-causing missense mutations in human helicase disorders have led to new insights to the molecular defects underlying aberrant cellular and clinical phenotypes.
Topics: Bloom Syndrome; Cockayne Syndrome; DNA Helicases; Fanconi Anemia; Humans; Mutation, Missense; Xeroderma Pigmentosum
PubMed: 23276657
DOI: 10.1016/j.mrrev.2012.12.004 -
Frontiers in Genetics 2021DNA damage repair response is an important biological process involved in maintaining the fidelity of the genome in eukaryotes and prokaryotes. Several proteins that... (Review)
Review
DNA damage repair response is an important biological process involved in maintaining the fidelity of the genome in eukaryotes and prokaryotes. Several proteins that play a key role in this process have been identified. Alterations in these key proteins have been linked to different diseases including cancer. BLM is a 3'-5' ATP-dependent RecQ DNA helicase that is one of the most essential genome stabilizers involved in the regulation of DNA replication, recombination, and both homologous and non-homologous pathways of double-strand break repair. BLM structure and functions are known to be conserved across many species like yeast, , mouse, and human. Genetic mutations in the BLM gene cause a rare, autosomal recessive disorder, Bloom syndrome (BS). BS is a monogenic disease characterized by genomic instability, premature aging, predisposition to cancer, immunodeficiency, and pulmonary diseases. Hence, these characteristics point toward BLM being a tumor suppressor. However, in addition to mutations, gene undergoes various types of alterations including increase in the copy number, transcript, and protein levels in multiple types of cancers. These results, along with the fact that the lack of wild-type BLM in these cancers has been associated with increased sensitivity to chemotherapeutic drugs, indicate that BLM also has a pro-oncogenic function. While a plethora of studies have reported the effect of gene mutations in various model organisms, there is a dearth in the studies undertaken to investigate the effect of its oncogenic alterations. We propose to rationalize and integrate the dual functions of BLM both as a tumor suppressor and maybe as a proto-oncogene, and enlist the plausible mechanisms of its deregulation in cancers.
PubMed: 33777104
DOI: 10.3389/fgene.2021.634789 -
Biochimie Aug 2011The physiological and pharmacological role of nucleic acids structures folded into the non canonical G-quadruplex conformation have recently emerged. Their activities... (Review)
Review
The physiological and pharmacological role of nucleic acids structures folded into the non canonical G-quadruplex conformation have recently emerged. Their activities are targeted at vital cellular processes including telomere maintenance, regulation of transcription and processing of the pre-messenger or telomeric RNA. In addition, severe conditions like cancer, fragile X syndrome, Bloom syndrome, Werner syndrome and Fanconi anemia J are related to genomic defects that involve G-quadruplex forming sequences. In this connection G-quadruplex recognition and processing by nucleic acid directed proteins and enzymes represents a key event to activate or deactivate physiological or pathological pathways. In this review we examine protein-G-quadruplex recognition in physiologically significant conditions and discuss how to possibly exploit the interactions' selectivity for targeted therapeutic intervention.
Topics: Antibodies; Aptamers, Nucleotide; Base Sequence; DNA Helicases; Drug Design; G-Quadruplexes; Heterogeneous-Nuclear Ribonucleoproteins; Molecular Sequence Data; Peptides; Promoter Regions, Genetic; Protein Biosynthesis; Proteins; RNA Helicases; RNA, Untranslated; Shelterin Complex; Telomere; Telomere-Binding Proteins; Transcription, Genetic
PubMed: 21549174
DOI: 10.1016/j.biochi.2011.04.018 -
Frontiers in Genetics 2014The RecQ family DNA helicases Werner syndrome protein (WRN) and Bloom syndrome protein (BLM) play a key role in protecting the genome against deleterious changes. In... (Review)
Review
The RecQ family DNA helicases Werner syndrome protein (WRN) and Bloom syndrome protein (BLM) play a key role in protecting the genome against deleterious changes. In humans, mutations in these proteins lead to rare genetic diseases associated with cancer predisposition and accelerated aging. WRN and BLM are distinguished from other helicases by possessing signature tandem domains toward the C terminus, referred to as the RecQ C-terminal (RQC) and helicase-and-ribonuclease D-C-terminal (HRDC) domains. Although the precise function of the HRDC domain remains unclear, the previous crystal structure of a WRN RQC-DNA complex visualized a central role for the RQC domain in recognizing, binding and unwinding DNA at branch points. In particular, a prominent hairpin structure (the β-wing) within the RQC winged-helix motif acts as a scalpel to induce the unpairing of a Watson-Crick base pair at the DNA duplex terminus. A similar RQC-DNA interaction was also observed in the recent crystal structure of a BLM-DNA complex. I review the latest structures of WRN and BLM, and then provide a docking simulation of BLM with a Holliday junction. The model offers an explanation for the efficient branch migration activity of the RecQ family toward recombination and repair intermediates.
PubMed: 25400656
DOI: 10.3389/fgene.2014.00366 -
Molecular Syndromology Jun 2020Bloom syndrome is an autosomal recessive disorder characterized by prenatal and postnatal growth deficiency, photosensitive skin changes, immune deficiency, insulin...
Bloom syndrome is an autosomal recessive disorder characterized by prenatal and postnatal growth deficiency, photosensitive skin changes, immune deficiency, insulin resistance, and a greatly increased risk of early-onset cancer and development of multiple malignancies. Loss-of-function variants of the gene, which codes for a RecQ helicase, cause Bloom syndrome. We report a consanguineous family, with 2 siblings showing clinical signs of suspected chromosome breakage disorder. One of them developed recurrent malignant lymphoma during lifetime. We performed next-generation sequencing analysis, focusing on cancer predisposition syndromes. We identified a homozygous pathogenic nonsense variant c.1642C>T (p.Gln548*) in the gene in the proband, associated with Bloom syndrome. Sanger sequencing validated the presence of a homozygous pathogenic variant in the proband and also in the brother with short stature. In this article, we will focus on the clinical presentation of the syndrome in this particular family as well as the characteristics of malignancies found in the proband.
PubMed: 32655338
DOI: 10.1159/000507006 -
Familial Cancer Jan 2022Bloom syndrome (BS) is a genomic and chromosomal instability disorder with prodigious cancer predisposition caused by pathogenic variants in BLM. We report the clinical...
Bloom syndrome (BS) is a genomic and chromosomal instability disorder with prodigious cancer predisposition caused by pathogenic variants in BLM. We report the clinical and genetic details of a boy who first presented with infantile fibrosarcoma (IFS) at the age of 6 months and subsequently was diagnosed with BS at the age of 9 years. Molecular analysis identified the pathogenic germline BLM sequence variants (c.1642C>T and c.2207_2212delinsTAGATTC). This is the first report of IFS related to BS, for which we show that both BLM alleles are maintained in the tumor and demonstrate a TPM3-NTKR1 fusion transcript in the IFS. Our communication emphasizes the importance of long-term follow up after treatment for pediatric neoplastic conditions, as clues to important genetic entities might manifest later, and the identification of a heritable tumor predisposition often leads to changes in patient surveillance and management.
Topics: Alleles; Bloom Syndrome; Child; Fibrosarcoma; Genetic Predisposition to Disease; Genotype; Humans; Infant; Male; RecQ Helicases; Tropomyosin
PubMed: 33219493
DOI: 10.1007/s10689-020-00221-1 -
SAGE Open Medical Case Reports 2019Bloom syndrome is a rare autosomal recessive disorder characterized by distinct physical features, such as short stature, genomic instability, and predisposition to...
Bloom syndrome is a rare autosomal recessive disorder characterized by distinct physical features, such as short stature, genomic instability, and predisposition to numerous cancers. The gene encodes for the RecQ helicase that plays an important role in genome editing, maintenance, and stability. Mutations in the gene cause genomic instability that exposes the carriers to a variety of cancers, and in particular hematological and gastrointestinal cancers. Herein, we report the first case of pancreatic cancer in a 32-year-old patient with bloom syndrome.
PubMed: 31210938
DOI: 10.1177/2050313X19855587 -
Molecular Cell Jul 2019Genetic recombination in all kingdoms of life initiates when helicases and nucleases process (resect) the free DNA ends to expose single-stranded DNA (ssDNA) overhangs....
Genetic recombination in all kingdoms of life initiates when helicases and nucleases process (resect) the free DNA ends to expose single-stranded DNA (ssDNA) overhangs. Resection regulation in bacteria is programmed by a DNA sequence, but a general mechanism limiting resection in eukaryotes has remained elusive. Using single-molecule imaging of reconstituted human DNA repair factors, we identify phosphorylated RPA (pRPA) as a negative resection regulator. Bloom's syndrome (BLM) helicase together with exonuclease 1 (EXO1) and DNA2 nucleases catalyze kilobase-length DNA resection on nucleosome-coated DNA. The resulting ssDNA is rapidly bound by RPA, which further stimulates DNA resection. RPA is phosphorylated during resection as part of the DNA damage response (DDR). Remarkably, pRPA inhibits DNA resection in cellular assays and in vitro via inhibition of BLM helicase. pRPA suppresses BLM initiation at DNA ends and promotes the intrinsic helicase strand-switching activity. These findings establish that pRPA provides a feedback loop between DNA resection and the DDR.
Topics: Binding Sites; DNA Helicases; DNA Repair Enzymes; DNA, Single-Stranded; Escherichia coli; Exodeoxyribonucleases; Feedback, Physiological; Gene Expression Regulation; Homologous Recombination; Humans; Microscopy, Fluorescence; Nucleosomes; Oligopeptides; Phosphorylation; Protein Binding; RecQ Helicases; Recombinant Fusion Proteins; Replication Protein A; Saccharomyces cerevisiae; Single Molecule Imaging
PubMed: 31153714
DOI: 10.1016/j.molcel.2019.05.005