Journal articles on the topic 'RecQ4 helicases'
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1
Thangavel, Saravanabhavan, Ramiro Mendoza-Maldonado, Erika Tissino, Julia M. Sidorova, Jinhu Yin, Weidong Wang, Raymond J. Monnat, Arturo Falaschi, and Alessandro Vindigni. "Human RECQ1 and RECQ4 Helicases Play Distinct Roles in DNA Replication Initiation." Molecular and Cellular Biology 30, no. 6 (January 11, 2010): 1382–96. http://dx.doi.org/10.1128/mcb.01290-09.
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ABSTRACT Cellular and biochemical studies support a role for all five human RecQ helicases in DNA replication; however, their specific functions during this process are unclear. Here we investigate the in vivo association of the five human RecQ helicases with three well-characterized human replication origins. We show that only RECQ1 (also called RECQL or RECQL1) and RECQ4 (also called RECQL4) associate with replication origins in a cell cycle-regulated fashion in unperturbed cells. RECQ4 is recruited to origins at late G1, after ORC and MCM complex assembly, while RECQ1 and additional RECQ4 are loaded at origins at the onset of S phase, when licensed origins begin firing. Both proteins are lost from origins after DNA replication initiation, indicating either disassembly or tracking with the newly formed replisome. Nascent-origin DNA synthesis and the frequency of origin firing are reduced after RECQ1 depletion and, to a greater extent, after RECQ4 depletion. Depletion of RECQ1, though not that of RECQ4, also suppresses replication fork rates in otherwise unperturbed cells. These results indicate that RECQ1 and RECQ4 are integral components of the human replication complex and play distinct roles in DNA replication initiation and replication fork progression in vivo.
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BACHRATI, Csanád Z., and Ian D. HICKSON. "RecQ helicases: suppressors of tumorigenesis and premature aging." Biochemical Journal 374, no. 3 (September 15, 2003): 577–606. http://dx.doi.org/10.1042/bj20030491.
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The RecQ helicases represent a subfamily of DNA helicases that are highly conserved in evolution. Loss of RecQ helicase function leads to a breakdown in the maintenance of genome integrity, in particular hyper-recombination. Germ-line defects in three of the five known human RecQ helicases give rise to defined genetic disorders associated with cancer predisposition and/or premature aging. These are Bloom's syndrome, Werner's syndrome and Rothmund–Thomson syndrome, which are caused by defects in the genes BLM, WRN and RECQ4 respectively. Here we review the properties of RecQ helicases in organisms from bacteria to humans, with an emphasis on the biochemical functions of these enzymes and the range of protein partners that they operate with. We will discuss models in which RecQ helicases are required to protect against replication fork demise, either through prevention of fork breakdown or restoration of productive DNA synthesis.
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Rogers, Cody M., Elsbeth Sanders, Phoebe A. Nguyen, Whitney Smith-Kinnaman, Amber L. Mosley, and Matthew L. Bochman. "The Genetic and Physical Interactomes of the Saccharomyces cerevisiae Hrq1 Helicase." G3: Genes|Genomes|Genetics 10, no. 12 (October 28, 2020): 4347–57. http://dx.doi.org/10.1534/g3.120.401864.
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The human genome encodes five RecQ helicases (RECQL1, BLM, WRN, RECQL4, and RECQL5) that participate in various processes underpinning genomic stability. Of these enzymes, the disease-associated RECQL4 is comparatively understudied due to a variety of technical challenges. However, Saccharomyces cerevisiae encodes a functional homolog of RECQL4 called Hrq1, which is more amenable to experimentation and has recently been shown to be involved in DNA inter-strand crosslink (ICL) repair and telomere maintenance. To expand our understanding of Hrq1 and the RecQ4 subfamily of helicases in general, we took a multi-omics approach to define the Hrq1 interactome in yeast. Using synthetic genetic array analysis, we found that mutations of genes involved in processes such as DNA repair, chromosome segregation, and transcription synthetically interact with deletion of HRQ1 and the catalytically inactive hrq1-K318A allele. Pull-down of tagged Hrq1 and mass spectrometry identification of interacting partners similarly underscored links to these processes and others. Focusing on transcription, we found that hrq1 mutant cells are sensitive to caffeine and that mutation of HRQ1 alters the expression levels of hundreds of genes. In the case of hrq1-K318A, several of the most highly upregulated genes encode proteins of unknown function whose expression levels are also increased by DNA ICL damage. Together, our results suggest a heretofore unrecognized role for Hrq1 in transcription, as well as novel members of the Hrq1 ICL repair pathway. These data expand our understanding of RecQ4 subfamily helicase biology and help to explain why mutations in human RECQL4 cause diseases of genomic instability.
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Rogers, Cody M., Chun-Ying Lee, Samuel Parkins, Nicholas J. Buehler, Sabine Wenzel, Francisco Martínez-Márquez, Yuichiro Takagi, Sua Myong, and Matthew L. Bochman. "The yeast Hrq1 helicase stimulates Pso2 translesion nuclease activity and thereby promotes DNA interstrand crosslink repair." Journal of Biological Chemistry 295, no. 27 (May 5, 2020): 8945–57. http://dx.doi.org/10.1074/jbc.ra120.013626.
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DNA interstrand crosslink (ICL) repair requires a complex network of DNA damage response pathways. Removal of the ICL lesions is vital, as they are physical barriers to essential DNA processes that require the separation of duplex DNA, such as replication and transcription. The Fanconi anemia (FA) pathway is the principal mechanism for ICL repair in metazoans and is coupled to DNA replication. In Saccharomyces cerevisiae, a vestigial FA pathway is present, but ICLs are predominantly repaired by a pathway involving the Pso2 nuclease, which is hypothesized to use its exonuclease activity to digest through the lesion to provide access for translesion polymerases. However, Pso2 lacks translesion nuclease activity in vitro, and mechanistic details of this pathway are lacking, especially relative to FA. We recently identified the Hrq1 helicase, a homolog of the disease-linked enzyme RecQ-like helicase 4 (RECQL4), as a component of Pso2-mediated ICL repair. Here, using genetic, biochemical, and biophysical approaches, including single-molecule FRET (smFRET)– and gel-based nuclease assays, we show that Hrq1 stimulates the Pso2 nuclease through a mechanism that requires Hrq1 catalytic activity. Importantly, Hrq1 also stimulated Pso2 translesion nuclease activity through a site-specific ICL in vitro. We noted that stimulation of Pso2 nuclease activity is specific to eukaryotic RecQ4 subfamily helicases, and genetic and biochemical data suggest that Hrq1 likely interacts with Pso2 through their N-terminal domains. These results advance our understanding of FA-independent ICL repair and establish a role for the RecQ4 helicases in the repair of these detrimental DNA lesions.
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Séguéla-Arnaud, Mathilde, Wayne Crismani, Cécile Larchevêque, Julien Mazel, Nicole Froger, Sandrine Choinard, Afef Lemhemdi, et al. "Multiple mechanisms limit meiotic crossovers: TOP3α and two BLM homologs antagonize crossovers in parallel to FANCM." Proceedings of the National Academy of Sciences 112, no. 15 (March 30, 2015): 4713–18. http://dx.doi.org/10.1073/pnas.1423107112.
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Meiotic crossovers (COs) have two important roles, shuffling genetic information and ensuring proper chromosome segregation. Despite their importance and a large excess of precursors (i.e., DNA double-strand breaks, DSBs), the number of COs is tightly regulated, typically one to three per chromosome pair. The mechanisms ensuring that most DSBs are repaired as non-COs and the evolutionary forces imposing this constraint are poorly understood. Here we identified Topoisomerase3α (TOP3α) and the RECQ4 helicases—the Arabidopsis slow growth suppressor 1 (Sgs1)/Bloom syndrome protein (BLM) homologs—as major barriers to meiotic CO formation. First, the characterization of a specific TOP3α mutant allele revealed that, in addition to its role in DNA repair, this topoisomerase antagonizes CO formation. Further, we found that RECQ4A and RECQ4B constitute the strongest meiotic anti-CO activity identified to date, their concomitant depletion leading to a sixfold increase in CO frequency. In both top3α and recq4ab mutants, DSB number is unaffected, and extra COs arise from a normally minor pathway. Finally, both TOP3α and RECQ4A/B act independently of the previously identified anti-CO Fanconi anemia of complementation group M (FANCM) helicase. This finding shows that several parallel pathways actively limit CO formation and suggests that the RECQA/B and FANCM helicases prevent COs by processing different substrates. Despite a ninefold increase in CO frequency, chromosome segregation was unaffected. This finding supports the idea that CO number is restricted not because of mechanical constraints but likely because of the long-term costs of recombination. Furthermore, this work demonstrates how manipulating a few genes holds great promise for increasing recombination frequency in plant-breeding programs.
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Park, Youngji, Guangbin Luo, and Stanton Gerson. "Repopulation Advantage of Blm−/− Cells in the Primary Recipients Can Be Reversed by Cisplatin Treatment." Blood 104, no. 11 (November 16, 2004): 2683. http://dx.doi.org/10.1182/blood.v104.11.2683.2683.
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Abstract Deficiencies in DNA repair-related genes such RecQ DNA helicases lead to human genetic disorders such as Bloom’s syndrome, Werner’s syndrome, and Rothmund-Thomson syndrome characterized by premature aging and cancer predisposition. We hypothesized that deficiency in RecQ DNA helicases may lead to drug hypersensitivity and/or stem cell failure after serial transplantation. Several genotoxic agents were tested on the bone marrow cells isolated from Bloom (Blm)−/− and RecQ4−/− knockout mice and compared to wildtype bone marrow cells. RecQ4−/− bone marrow showed mild sensitivity to γ-ray irradiation and very mild sensitivity to cisplatin. RecQ4−/− bone marrow did not show sensitivity to etoposide. However, Blm−/− bone marrow cells did not show hypersensitivity to either γ-ray irradiation or etoposide treatment, implying each RecQ DNA helicase may have different roles for DNA repair and/or proliferation in bone marrow cells. To assess how deficiency in RecQ DNA helicase affects hematopoietic stem cell function, serial transplantation capacity into lethally irradiated recipients was compared between bone marrow cells isolated from Blm−/− (Ly5.2) and wildtype (Ly5.1) mice. Competitive repopulating capacity was monitored by Ly5.1 / Ly5.2 marker analysis of peripheral blood every three weeks. There was no difference in early repopulating capacity between Blm−/− and wildtype in primary transplants at 3, 6 and 9 weeks post-transplantation (wt 46.6% ± 11.9% vs. Blm−/− 53.5% ± 11.9%, n=6, p=0.33 at 9 weeks post-transplantation). However, at 15 weeks post-transplantation, Blm−/− cells showed higher repopulation than wildtype bone marrow cells (wt 30.7 % ± 7.1 % vs. Blm−/− 69.3% ± 7.1%, n=3, p=0.003), implying Blm−/− cells might gradually accumulate a proliferative advantage over wildtype cells. To assess whether drug treatment may cause sensitivity in Blm−/− cells after transplantation, primary recipients of an equal mixture of Blm−/− and wildtype bone marrow were treated with 1 mg/kg cisplatin biweekly i.p. between 9 to 15 weeks post-transplantation and repopulation capacity was monitored. The repopulation advantage of Blm−/− cells in primary transplants was abolished by cisplatin treatment (wt 61.3 % ± 17.3 % vs. Blm−/− 38.7% ± 17.3%, n=3, p=0.19, in the cisplatin-treated cohort compared to wt 30.7 % ± 7.1 % vs. Blm−/− 69.3% ± 7.1%, n=3, p=0.003, in the control cohort). Thus, a proliferative advantage of progenitors is apparent in Blm−/− bone marrow, but lost after cisplatin-mediated DNA damage. This suggests that defective DNA repair of Blm−/− cell may promote deregulated proliferation of hematopoietic progenitors.
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Cheok, C. F., C. Z. Bachrati, K. L. Chan, C. Ralf, L. Wu, and I. D. Hickson. "Roles of the Bloom's syndrome helicase in the maintenance of genome stability." Biochemical Society Transactions 33, no. 6 (October 26, 2005): 1456–59. http://dx.doi.org/10.1042/bst0331456.
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The RecQ family of DNA helicases is highly conserved in evolution from bacteria to humans. Of the five known human RecQ family members, three (BLM, WRN and RECQ4, which cause Bloom's syndrome, Werner's syndrome and Rothmund–Thomson syndrome respectively) are mutated in distinct clinical disorders associated with cancer predisposition and/or premature aging. BLM forms part of a multienzyme complex including topoisomerase IIIα, replication protein A and a newly identified factor called BLAP75. Together, these proteins play a role in the resolution of DNA structures that arise during the process of homologous recombination repair. In the absence of BLM, cells show genomic instability and a high incidence of sister-chromatid exchanges. In addition to a DNA structure-specific helicase activity, BLM also catalyses Holliday-junction branch migration and the annealing of complementary single-stranded DNA molecules.
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Garige, Mamatha, and Sudha Sharma. "Cellular Deficiency of Werner Syndrome Protein or RECQ1 Promotes Genotoxic Potential of Hydroquinone and Benzo[a]pyrene Exposure." International Journal of Toxicology 33, no. 5 (September 2014): 373–81. http://dx.doi.org/10.1177/1091581814547422.
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The 5 known RecQ helicases in humans (RECQ1, BLM, WRN, RECQL4, and RECQ5) have demonstrated roles in diverse genome maintenance mechanisms but their functions in safeguarding the genome from environmental toxicants are poorly understood. Here, we have evaluated a potential role of WRN (mutated in Werner syndrome) and RECQ1 (the most abundant homolog of WRN) in hydroquinone (HQ)- and benzo[a]pyrene (BaP)-induced genotoxicity. Silencing of WRN or RECQ1 expression in HeLa cells increased their sensitivity to HQ and BaP but elicited distinct DNA damage response. The RECQ1-depleted cells exhibited increased replication protein A phosphorylation, Chk1 activation, and DNA double-strand breaks (DSBs) as compared to control or WRN-depleted cells following exposure to BaP treatment. The BaP-induced DSBs in RECQ1-depleted cells were dependent on DNA-dependent protein kinase activity. Notably, loss of WRN in RECQ1-depleted cells ameliorated BaP toxicity. Collectively, our results provide first indication of nonredundant participation of WRN and RECQ1 in protection from the potentially carcinogenic effects of BaP and HQ.
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Gupta, Sonia Vidushi, and Kristina Hildegard Schmidt. "Maintenance of Yeast Genome Integrity by RecQ Family DNA Helicases." Genes 11, no. 2 (February 18, 2020): 205. http://dx.doi.org/10.3390/genes11020205.
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With roles in DNA repair, recombination, replication and transcription, members of the RecQ DNA helicase family maintain genome integrity from bacteria to mammals. Mutations in human RecQ helicases BLM, WRN and RecQL4 cause incurable disorders characterized by genome instability, increased cancer predisposition and premature adult-onset aging. Yeast cells lacking the RecQ helicase Sgs1 share many of the cellular defects of human cells lacking BLM, including hypersensitivity to DNA damaging agents and replication stress, shortened lifespan, genome instability and mitotic hyper-recombination, making them invaluable model systems for elucidating eukaryotic RecQ helicase function. Yeast and human RecQ helicases have common DNA substrates and domain structures and share similar physical interaction partners. Here, we review the major cellular functions of the yeast RecQ helicases Sgs1 of Saccharomyces cerevisiae and Rqh1 of Schizosaccharomyces pombe and provide an outlook on some of the outstanding questions in the field.
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Pike, Ashley C. W., Shivasankari Gomathinayagam, Paolo Swuec, Matteo Berti, Ying Zhang, Christina Schnecke, Francesca Marino, et al. "Human RECQ1 helicase-driven DNA unwinding, annealing, and branch migration: Insights from DNA complex structures." Proceedings of the National Academy of Sciences 112, no. 14 (March 23, 2015): 4286–91. http://dx.doi.org/10.1073/pnas.1417594112.
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RecQ helicases are a widely conserved family of ATP-dependent motors with diverse roles in nearly every aspect of bacterial and eukaryotic genome maintenance. However, the physical mechanisms by which RecQ helicases recognize and process specific DNA replication and repair intermediates are largely unknown. Here, we solved crystal structures of the human RECQ1 helicase in complexes with tailed-duplex DNA and ssDNA. The structures map the interactions of the ssDNA tail and the branch point along the helicase and Zn-binding domains, which, together with reported structures of other helicases, define the catalytic stages of helicase action. We also identify a strand-separating pin, which (uniquely in RECQ1) is buttressed by the protein dimer interface. A duplex DNA-binding surface on the C-terminal domain is shown to play a role in DNA unwinding, strand annealing, and Holliday junction (HJ) branch migration. We have combined EM and analytical ultracentrifugation approaches to show that RECQ1 can form what appears to be a flat, homotetrameric complex and propose that RECQ1 tetramers are involved in HJ recognition. This tetrameric arrangement suggests a platform for coordinated activity at the advancing and receding duplexes of an HJ during branch migration.
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Debnath, Subrata, and Sudha Sharma. "RECQ1 Helicase in Genomic Stability and Cancer." Genes 11, no. 6 (June 5, 2020): 622. http://dx.doi.org/10.3390/genes11060622.
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RECQ1 (also known as RECQL or RECQL1) belongs to the RecQ family of DNA helicases, members of which are linked with rare genetic diseases of cancer predisposition in humans. RECQ1 is implicated in several cellular processes, including DNA repair, cell cycle and growth, telomere maintenance, and transcription. Earlier studies have demonstrated a unique requirement of RECQ1 in ensuring chromosomal stability and suggested its potential involvement in tumorigenesis. Recent reports have suggested that RECQ1 is a potential breast cancer susceptibility gene, and missense mutations in this gene contribute to familial breast cancer development. Here, we provide a framework for understanding how the genetic or functional loss of RECQ1 might contribute to genomic instability and cancer.
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Marino, Francesca, Alessandro Vindigni, and Silvia Onesti. "Bioinformatic analysis of RecQ4 helicases reveals the presence of a RQC domain and a Zn knuckle." Biophysical Chemistry 177-178 (July 2013): 34–39. http://dx.doi.org/10.1016/j.bpc.2013.02.009.
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Zhu, Longfei, Nadia Fernández-Jiménez, Maja Szymanska-Lejman, Alexandre Pelé, Charles J. Underwood, Heïdi Serra, Christophe Lambing, et al. "Natural variation identifies SNI1, the SMC5/6 component, as a modifier of meiotic crossover in Arabidopsis." Proceedings of the National Academy of Sciences 118, no. 33 (August 12, 2021): e2021970118. http://dx.doi.org/10.1073/pnas.2021970118.
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The frequency and distribution of meiotic crossovers are tightly controlled; however, variation in this process can be observed both within and between species. Using crosses of two natural Arabidopsis thaliana accessions, Col and Ler, we mapped a crossover modifier locus to semidominant polymorphisms in SUPPRESSOR OF NPR1-1 INDUCIBLE 1 (SNI1), which encodes a component of the SMC5/6 complex. The sni1 mutant exhibits a modified pattern of recombination across the genome with crossovers elevated in chromosome distal regions but reduced in pericentromeres. Mutations in SNI1 result in reduced crossover interference and can partially restore the fertility of a Class I crossover pathway mutant, which suggests that the protein affects noninterfering crossover repair. Therefore, we tested genetic interactions between SNI1 and both RECQ4 and FANCM DNA helicases, which showed that additional Class II crossovers observed in the sni1 mutant are FANCM independent. Furthermore, genetic analysis of other SMC5/6 mutants confirms the observations of crossover redistribution made for SNI1. The study reveals the importance of the SMC5/6 complex in ensuring the proper progress of meiotic recombination in plants.
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Sharma, Sudha, Deborah J. Stumpo, Adayabalam S. Balajee, Cheryl B. Bock, Peter M. Lansdorp, Robert M. Brosh, and Perry J. Blackshear. "RECQL, a Member of the RecQ Family of DNA Helicases, Suppresses Chromosomal Instability." Molecular and Cellular Biology 27, no. 5 (December 11, 2006): 1784–94. http://dx.doi.org/10.1128/mcb.01620-06.
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ABSTRACT The mouse gene Recql is a member of the RecQ subfamily of DEx-H-containing DNA helicases. Five members of this family have been identified in both humans and mice, and mutations in three of these, BLM, WRN, and RECQL4, are associated with human diseases and a cellular phenotype that includes genomic instability. To date, no human disease has been associated with mutations in RECQL and no cellular phenotype has been associated with its deficiency. To gain insight into the physiological function of RECQL, we disrupted Recql in mice. RECQL-deficient mice did not exhibit any apparent phenotypic differences compared to wild-type mice. Cytogenetic analyses of embryonic fibroblasts from the RECQL-deficient mice revealed aneuploidy, spontaneous chromosomal breakage, and frequent translocation events. In addition, the RECQL-deficient cells were hypersensitive to ionizing radiation, exhibited an increased load of DNA damage, and displayed elevated spontaneous sister chromatid exchanges. These results provide evidence that RECQL has a unique cellular role in the DNA repair processes required for genomic integrity. Genetic background, functional redundancy, and perhaps other factors may protect the unstressed mouse from the types of abnormalities that might be expected from the severe chromosomal aberrations detected at the cellular level.
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Chen, Sheng-Chia, Chi-Hung Huang, Chia Shin Yang, Tzong-Der Way, Ming-Chung Chang, and Yeh Chen. "Crystal Structure ofDeinococcus radioduransRecQ Helicase Catalytic Core Domain: The Interdomain Flexibility." BioMed Research International 2014 (2014): 1–8. http://dx.doi.org/10.1155/2014/342725.
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RecQ DNA helicases are key enzymes in the maintenance of genome integrity, and they have functions in DNA replication, recombination, and repair. In contrast to most RecQs, RecQ fromDeinococcus radiodurans(DrRecQ) possesses an unusual domain architecture that is crucial for its remarkable ability to repair DNA. Here, we determined the crystal structures of the DrRecQ helicase catalytic core and its ADP-bound form, revealing interdomain flexibility in its first RecA-like and winged-helix (WH) domains. Additionally, the WH domain of DrRecQ is positioned in a different orientation from that of theE. coliRecQ (EcRecQ). These results suggest that the orientation of the protein during DNA-binding is significantly different when comparing DrRecQ and EcRecQ.
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Luong, Thong T., Zheqi Li, Nolan Priedigkeit, Phoebe S. Parker, Stefanie Böhm, Kyle Rapchak, Adrian V. Lee, and Kara A. Bernstein. "Hrq1/RECQL4 regulation is critical for preventing aberrant recombination during DNA intrastrand crosslink repair and is upregulated in breast cancer." PLOS Genetics 18, no. 9 (September 20, 2022): e1010122. http://dx.doi.org/10.1371/journal.pgen.1010122.
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Human RECQL4 is a member of the RecQ family of DNA helicases and functions during DNA replication and repair. RECQL4 mutations are associated with developmental defects and cancer. Although RECQL4 mutations lead to disease, RECQL4 overexpression is also observed in cancer, including breast and prostate. Thus, tight regulation of RECQL4 protein levels is crucial for genome stability. Because mammalian RECQL4 is essential, how cells regulate RECQL4 protein levels is largely unknown. Utilizing budding yeast, we investigated the RECQL4 homolog, HRQ1, during DNA crosslink repair. We find that Hrq1 functions in the error-free template switching pathway to mediate DNA intrastrand crosslink repair. Although Hrq1 mediates repair of cisplatin-induced lesions, it is paradoxically degraded by the proteasome following cisplatin treatment. By identifying the targeted lysine residues, we show that preventing Hrq1 degradation results in increased recombination and mutagenesis. Like yeast, human RECQL4 is similarly degraded upon exposure to crosslinking agents. Furthermore, over-expression of RECQL4 results in increased RAD51 foci, which is dependent on its helicase activity. Using bioinformatic analysis, we observe that RECQL4 overexpression correlates with increased recombination and mutations. Overall, our study uncovers a role for Hrq1/RECQL4 in DNA intrastrand crosslink repair and provides further insight how misregulation of RECQL4 can promote genomic instability, a cancer hallmark.
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Estep, Katrina N., and Robert M. Brosh. "RecQ and Fe–S helicases have unique roles in DNA metabolism dictated by their unwinding directionality, substrate specificity, and protein interactions." Biochemical Society Transactions 46, no. 1 (December 22, 2017): 77–95. http://dx.doi.org/10.1042/bst20170044.
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Helicases are molecular motors that play central roles in nucleic acid metabolism. Mutations in genes encoding DNA helicases of the RecQ and iron–sulfur (Fe–S) helicase families are linked to hereditary disorders characterized by chromosomal instabilities, highlighting the importance of these enzymes. Moreover, mono-allelic RecQ and Fe–S helicase mutations are associated with a broad spectrum of cancers. This review will discuss and contrast the specialized molecular functions and biological roles of RecQ and Fe–S helicases in DNA repair, the replication stress response, and the regulation of gene expression, laying a foundation for continued research in these important areas of study.
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Choi, Seoyun, Seung-Won Lee, Hajin Kim, and Byungchan Ahn. "Molecular characteristics of reiterative DNA unwinding by the Caenorhabditis elegans RecQ helicase." Nucleic Acids Research 47, no. 18 (August 22, 2019): 9708–20. http://dx.doi.org/10.1093/nar/gkz708.
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Abstract The RecQ family of helicases is highly conserved both structurally and functionally from bacteria to humans. Defects in human RecQ helicases are associated with genetic diseases that are characterized by cancer predisposition and/or premature aging. RecQ proteins exhibit 3′-5′ helicase activity and play critical roles in genome maintenance. Recent advances in single-molecule techniques have revealed the reiterative unwinding behavior of RecQ helicases. However, the molecular mechanisms involved in this process remain unclear, with contradicting reports. Here, we characterized the unwinding dynamics of the Caenorhabditis elegans RecQ helicase HIM-6 using single-molecule fluorescence resonance energy transfer measurements. We found that HIM-6 exhibits reiterative DNA unwinding and the length of DNA unwound by the helicase is sharply defined at 25–31 bp. Experiments using various DNA substrates revealed that HIM-6 utilizes the mode of ‘sliding back’ on the translocated strand, without strand-switching for rewinding. Furthermore, we found that Caenorhabditis elegans replication protein A, a single-stranded DNA binding protein, suppresses the reiterative behavior of HIM-6 and induces unidirectional, processive unwinding, possibly through a direct interaction between the proteins. Our findings shed new light on the mechanism of DNA unwinding by RecQ family helicases and their co-operation with RPA in processing DNA.
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Król, Sylwia K., Agnieszka Kaczmarczyk, Kamil Wojnicki, Bartosz Wojtas, Bartłomiej Gielniewski, Wieslawa Grajkowska, Katarzyna Kotulska, et al. "Aberrantly Expressed RECQL4 Helicase Supports Proliferation and Drug Resistance of Human Glioma Cells and Glioma Stem Cells." Cancers 12, no. 10 (October 11, 2020): 2919. http://dx.doi.org/10.3390/cancers12102919.
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Anti-tumour therapies eliminate proliferating tumour cells by induction of DNA damage, but genomic aberrations or transcriptional deregulation may limit responses to therapy. Glioblastoma (GBM) is a malignant brain tumour, which recurs inevitably due to chemo- and radio-resistance. Human RecQ helicases participate in DNA repair, responses to DNA damage and replication stress. We explored if a helicase RECQL4 contributes to gliomagenesis and responses to chemotherapy. We found upregulated RECQL4 expression in GBMs associated with poor survival of GBM patients. Increased levels of nuclear and cytosolic RECQL4 proteins were detected in GBMs on tissue arrays and in six glioma cell lines. RECQL4 was detected both in cytoplasm and mitochondria by Western blotting and immunofluorescence. RECQL4 depletion in glioma cells with siRNAs and CRISPR/Cas9 did not affect basal cell viability, slightly impaired DNA replication, but induced profound transcriptomic changes and increased chemosensitivity of glioma cells. Sphere cultures originated from RECQL4-depleted cells had reduced sphere forming capacity, stronger responded to temozolomide upregulating cell cycle inhibitors and pro-apoptotic proteins. RECQL4 deficiency affected mitochondrial network and reduced mitochondrial membrane polarization in LN18 glioblastoma cells. We demonstrate that targeting RECQL4 overexpressed in glioblastoma could be a new strategy to sensitize glioma cells to chemotherapeutics.
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Mankouri, H. W., and I. D. Hickson. "Understanding the roles of RecQ helicases in the maintenance of genome integrity and suppression of tumorigenesis." Biochemical Society Transactions 32, no. 6 (October 26, 2004): 957–58. http://dx.doi.org/10.1042/bst0320957.
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RecQ helicases are evolutionarily conserved enzymes required for the maintenance of genome stability. Mutations in three of the five known human RecQ helicase genes cause distinct clinical disorders that are characterized by genome instability and cancer predisposition. Recent studies have begun to reveal the cellular roles of RecQ helicases and how these enzymes may prevent tumorigenesis at the molecular level.
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Maity, Jyotirindra, Sachi Horibata, Grant Zurcher, and Jung-Min Lee. "Targeting of RecQ Helicases as a Novel Therapeutic Strategy for Ovarian Cancer." Cancers 14, no. 5 (February 26, 2022): 1219. http://dx.doi.org/10.3390/cancers14051219.
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RecQ helicases are essential for DNA replication, recombination, DNA damage repair, and other nucleic acid metabolic pathways required for normal cell growth, survival, and genome stability. More recently, RecQ helicases have been shown to be important for replication fork stabilization, one of the major mechanisms of PARP inhibitor resistance. Cancer cells often have upregulated helicases and depend on these enzymes to repair rapid growth-promoted DNA lesions. Several studies are now evaluating the use of RecQ helicases as potential biomarkers of breast and gynecologic cancers. Furthermore, RecQ helicases have attracted interest as possible targets for cancer treatment. In this review, we discuss the characteristics of RecQ helicases and their interacting partners that may be utilized for effective treatment strategies (as cancers depend on helicases for survival). We also discuss how targeting helicase in combination with DNA repair inhibitors (i.e., PARP and ATR inhibitors) can be used as novel approaches for cancer treatment to increase sensitivity to current treatment to prevent rise of treatment resistance.
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Wu, Yuliang. "Unwinding and Rewinding: Double Faces of Helicase?" Journal of Nucleic Acids 2012 (2012): 1–14. http://dx.doi.org/10.1155/2012/140601.
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Helicases are enzymes that use ATP-driven motor force to unwind double-stranded DNA or RNA. Recently, increasing evidence demonstrates that some helicases also possess rewinding activity—in other words, they can anneal two complementary single-stranded nucleic acids. All five members of the human RecQ helicase family, helicase PIF1, mitochondrial helicase TWINKLE, and helicase/nuclease Dna2 have been shown to possess strand-annealing activity. Moreover, two recently identified helicases—HARP and AH2 have only ATP-dependent rewinding activity. These findings not only enhance our understanding of helicase enzymes but also establish the presence of a new type of protein: annealing helicases. This paper discusses what is known about these helicases, focusing on their biochemical activity to zip and unzip double-stranded DNA and/or RNA, their possible regulation mechanisms, and biological functions.
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Matsuno, Kumiko, Maya Kumano, Yumiko Kubota, Yoshitami Hashimoto, and Haruhiko Takisawa. "The N-Terminal Noncatalytic Region of Xenopus RecQ4 Is Required for Chromatin Binding of DNA Polymerase α in the Initiation of DNA Replication." Molecular and Cellular Biology 26, no. 13 (July 1, 2006): 4843–52. http://dx.doi.org/10.1128/mcb.02267-05.
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ABSTRACT Recruitment of DNA polymerases onto replication origins is a crucial step in the assembly of eukaryotic replication machinery. A previous study in budding yeast suggests that Dpb11 controls the recruitment of DNA polymerases α and ε onto the origins. Sld2 is an essential replication protein that interacts with Dpb11, but no metazoan homolog has yet been identified. We isolated Xenopus RecQ4 as a candidate Sld2 homolog. RecQ4 is a member of the metazoan RecQ helicase family, and its N-terminal region shows sequence similarity with Sld2. In Xenopus egg extracts, RecQ4 is essential for the initiation of DNA replication, in particular for chromatin binding of DNA polymerase α. An N-terminal fragment of RecQ4 devoid of the helicase domain could rescue the replication activity of RecQ4-depleted extracts, and antibody against the fragment inhibited DNA replication and chromatin binding of the polymerase. Further, N-terminal fragments of RecQ4 physically interacted with Cut5, a Xenopus homolog of Dpb11, and their ability to bind to Cut5 closely correlated with their ability to rescue the replication activity of the depleted extracts. Our data suggest that RecQ4 performs an essential role in the assembly of replication machinery through interaction with Cut5 in vertebrates.
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Teng, Fang-Yuan, Ting-Ting Wang, Hai-Lei Guo, Ben-Ge Xin, Bo Sun, Shuo-Xing Dou, Xu-Guang Xi, and Xi-Miao Hou. "The HRDC domain oppositely modulates the unwinding activity of E. coli RecQ helicase on duplex DNA and G-quadruplex." Journal of Biological Chemistry 295, no. 51 (October 14, 2020): 17646–58. http://dx.doi.org/10.1074/jbc.ra120.015492.
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RecQ family helicases are highly conserved from bacteria to humans and have essential roles in maintaining genome stability. Mutations in three human RecQ helicases cause severe diseases with the main features of premature aging and cancer predisposition. Most RecQ helicases shared a conserved domain arrangement which comprises a helicase core, an RecQ C-terminal domain, and an auxiliary element helicase and RNaseD C-terminal (HRDC) domain, the functions of which are poorly understood. In this study, we systematically characterized the roles of the HRDC domain in E. coli RecQ in various DNA transactions by single-molecule FRET. We found that RecQ repetitively unwinds the 3′-partial duplex and fork DNA with a moderate processivity and periodically patrols on the ssDNA in the 5′-partial duplex by translocation. The HRDC domain significantly suppresses RecQ activities in the above transactions. In sharp contrast, the HRDC domain is essential for the deep and long-time unfolding of the G4 DNA structure by RecQ. Based on the observations that the HRDC domain dynamically switches between RecA core- and ssDNA-binding modes after RecQ association with DNA, we proposed a model to explain the modulation mechanism of the HRDC domain. Our findings not only provide new insights into the activities of RecQ on different substrates but also highlight the novel functions of the HRDC domain in DNA metabolisms.
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Ren, Hua, Shuo-Xing Dou, Xing-Dong Zhang, Peng-Ye Wang, Radhakrishnan Kanagaraj, Jie-lin Liu, Pavel Janscak, Jin-Shan Hu, and Xu Guang Xi. "The zinc-binding motif of human RECQ5β suppresses the intrinsic strand-annealing activity of its DExH helicase domain and is essential for the helicase activity of the enzyme." Biochemical Journal 412, no. 3 (May 28, 2008): 425–33. http://dx.doi.org/10.1042/bj20071150.
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RecQ family helicases, functioning as caretakers of genomic integrity, contain a zinc-binding motif which is highly conserved among these helicases, but does not have a substantial structural similarity with any other known zinc-finger folds. In the present study, we show that a truncated variant of the human RECQ5β helicase comprised of the conserved helicase domain only, a splice variant named RECQ5α, possesses neither ATPase nor DNA-unwinding activities, but surprisingly displays a strong strand-annealing activity. In contrast, fragments of RECQ5β including the intact zinc-binding motif, which is located immediately downstream of the helicase domain, exhibit much reduced strand-annealing activity but are proficient in DNA unwinding. Quantitative measurements indicate that the regulatory role of the zinc-binding motif is achieved by enhancing the DNA-binding affinity of the enzyme. The novel intramolecular modulation of RECQ5β catalytic activity mediated by the zinc-binding motif may represent a universal regulation mode for all RecQ family helicases.
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Laursen, Louise V., Eleni Ampatzidou, Anni H. Andersen, and Johanne M. Murray. "Role for the Fission Yeast RecQ Helicase in DNA Repair in G2." Molecular and Cellular Biology 23, no. 10 (May 15, 2003): 3692–705. http://dx.doi.org/10.1128/mcb.23.10.3692-3705.2003.
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ABSTRACT Members of the RecQ helicase subfamily are mutated in several human genomic instability syndromes, such as Bloom, Werner, and Rothmund-Thomson syndromes. We show that Rqh1, the single Schizosaccharomyces pombe homologue, is a 3′-to-5′ helicase and exists with Top3 in a high-molecular-weight complex. top3 deletion is inviable, and this is suppressed by concomitant loss of rqh1 helicase activity or loss of recombination functions. This is consistent with RecQ helicases in other systems. By using epistasis analysis of the UV radiation sensitivity and by analyzing the kinetics of Rhp51 (Rad51 homologue), Rqh1, and Top3 focus formation in response to UV in synchronized cells, we identify the first evidence of a function for Rqh1 and Top3 in the repair of UV-induced DNA damage in G2. Our data provide evidence that Rqh1 functions after Rad51 focus formation during DNA repair. We also identify a function for Rqh1 upstream of recombination in an Rhp18-dependent (Rad18 homologue) pathway. The model that these data allow us to propose helps to reconcile different interpretations of RecQ family helicase function that have arisen between work based on the S. pombe system and models based on studies of Saccharomyces cerevisiae SGS1 suggesting that RecQ helicases act before Rad51.
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Andrs, Martin, Zdenka Hasanova, Anna Oravetzova, Jana Dobrovolna, and Pavel Janscak. "RECQ5: A Mysterious Helicase at the Interface of DNA Replication and Transcription." Genes 11, no. 2 (February 21, 2020): 232. http://dx.doi.org/10.3390/genes11020232.
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RECQ5 belongs to the RecQ family of DNA helicases. It is conserved from Drosophila to humans and its deficiency results in genomic instability and cancer susceptibility in mice. Human RECQ5 is known for its ability to regulate homologous recombination by disrupting RAD51 nucleoprotein filaments. It also binds to RNA polymerase II (RNAPII) and negatively regulates transcript elongation by RNAPII. Here, we summarize recent studies implicating RECQ5 in the prevention and resolution of transcription-replication conflicts, a major intrinsic source of genomic instability during cancer development.
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Gupta, Pooja, Ananda Guha Majumdar, and Birija Sankar Patro. "Enigmatic role of WRN-RECQL helicase in DNA repair and its implications in cancer." Journal of Translational Genetics and Genomics 6 (2022): 147–56. http://dx.doi.org/10.20517/jtgg.2021.60.
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Werner (WRN) helicase belongs to the RECQL class of DNA helicases. Mutation in Werner (WRN) RECQL helicase leads to premature aging syndrome, Werner syndrome (WS), and predisposition to multiple cancers. WS patients exhibit heightened incidence of neoplasia, e.g., soft tissue sarcoma, osteosarcoma, malignant melanoma, meningioma, thyroid cancer, breast cancer, and leukemias. Extensive research on WRN helicase has revealed its important and diverse roles in DNA repair pathways, especially in double-strand break repair. Consequently, WRN deficiency is causally associated with genomic instability and cancer predispositions. In this review, we summarize recent studies unraveling the fundamental roles WRN helicase plays in DNA repair and genome stability and its implications in cancer therapy and resistance.
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Luong, Thong T., and Kara A. Bernstein. "Role and Regulation of the RECQL4 Family during Genomic Integrity Maintenance." Genes 12, no. 12 (November 29, 2021): 1919. http://dx.doi.org/10.3390/genes12121919.
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RECQL4 is a member of the evolutionarily conserved RecQ family of 3’ to 5’ DNA helicases. RECQL4 is critical for maintaining genomic stability through its functions in DNA repair, recombination, and replication. Unlike many DNA repair proteins, RECQL4 has unique functions in many of the central DNA repair pathways such as replication, telomere, double-strand break repair, base excision repair, mitochondrial maintenance, nucleotide excision repair, and crosslink repair. Consistent with these diverse roles, mutations in RECQL4 are associated with three distinct genetic diseases, which are characterized by developmental defects and/or cancer predisposition. In this review, we provide an overview of the roles and regulation of RECQL4 during maintenance of genome homeostasis.
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Duan, Yangmiao, and Hongbo Fang. "RecQL4 regulates autophagy and apoptosis in U2OS cells." Biochemistry and Cell Biology 94, no. 6 (December 2016): 551–59. http://dx.doi.org/10.1139/bcb-2016-0005.
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RecQL4, one of the 5 human RecQ helicases, is a key mediator of genomic stability and its deficiency can cause premature aging phenotypes. Here, by using CRISPR/Cas and RNAi technology, we demonstrated that autophagy level was elevated in both RecQL4 knockdown and knockout cells compared with those of the control cells. Surprisingly, mitochondrial content was increased and LC3 co-localization with mitochondria was partially lost in RecQL4 knockout cells compared with the control cells, suggesting that RecQL4 deficiency impaired mitophagic processes in U2OS cells. Furthermore, we found that knockout of RecQL4 destabilized PINK1. In addition, RecQL4 knockout cells were more susceptible to apoptosis under mitochondrial stress than the control cells. In conclusion, our findings indicated a novel role of RecQL4 in the regulation of autophagy/mitophagy in U2OS cells.
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Shadrick, William R., Jean Ndjomou, Rajesh Kolli, Sourav Mukherjee, Alicia M. Hanson, and David N. Frick. "Discovering New Medicines Targeting Helicases." Journal of Biomolecular Screening 18, no. 7 (March 27, 2013): 761–81. http://dx.doi.org/10.1177/1087057113482586.
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Helicases are ubiquitous motor proteins that separate and/or rearrange nucleic acid duplexes in reactions fueled by adenosine triphosphate (ATP) hydrolysis. Helicases encoded by bacteria, viruses, and human cells are widely studied targets for new antiviral, antibiotic, and anticancer drugs. This review summarizes the biochemistry of frequently targeted helicases. These proteins include viral enzymes from herpes simplex virus, papillomaviruses, polyomaviruses, coronaviruses, the hepatitis C virus, and various flaviviruses. Bacterial targets examined include DnaB-like and RecBCD-like helicases. The human DEAD-box protein DDX3 is the cellular antiviral target discussed, and cellular anticancer drug targets discussed are the human RecQ-like helicases and eIF4A. We also review assays used for helicase inhibitor discovery and the most promising and common helicase inhibitor chemotypes, such as nucleotide analogues, polyphenyls, metal ion chelators, flavones, polycyclic aromatic polymers, coumarins, and various DNA binding pharmacophores. Also discussed are common complications encountered while searching for potent helicase inhibitors and possible solutions for these problems.
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Serra, Heïdi, Christophe Lambing, Catherine H. Griffin, Stephanie D. Topp, Divyashree C. Nageswaran, Charles J. Underwood, Piotr A. Ziolkowski, et al. "Massive crossover elevation via combination of HEI10 and recq4a recq4b during Arabidopsis meiosis." Proceedings of the National Academy of Sciences 115, no. 10 (February 20, 2018): 2437–42. http://dx.doi.org/10.1073/pnas.1713071115.
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During meiosis, homologous chromosomes undergo reciprocal crossovers, which generate genetic diversity and underpin classical crop improvement. Meiotic recombination initiates from DNA double-strand breaks (DSBs), which are processed into single-stranded DNA that can invade a homologous chromosome. The resulting joint molecules can ultimately be resolved as crossovers. In Arabidopsis, competing pathways balance the repair of ∼100–200 meiotic DSBs into ∼10 crossovers per meiosis, with the excess DSBs repaired as noncrossovers. To bias DSB repair toward crossovers, we simultaneously increased dosage of the procrossover E3 ligase gene HEI10 and introduced mutations in the anticrossovers helicase genes RECQ4A and RECQ4B. As HEI10 and recq4a recq4b increase interfering and noninterfering crossover pathways, respectively, they combine additively to yield a massive meiotic recombination increase. Interestingly, we also show that increased HEI10 dosage increases crossover coincidence, which indicates an effect on interference. We also show that patterns of interhomolog polymorphism and heterochromatin drive recombination increases distally towards the subtelomeres in both HEI10 and recq4a recq4b backgrounds, while the centromeres remain crossover suppressed. These results provide a genetic framework for engineering meiotic recombination landscapes in plant genomes.
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Kusano, Kohji, Mark E. Berres, and William R. Engels. "Evolution of the RECQ Family of Helicases: A Drosophila Homolog, Dmblm, Is Similar to the Human Bloom Syndrome Gene." Genetics 151, no. 3 (March 1, 1999): 1027–39. http://dx.doi.org/10.1093/genetics/151.3.1027.
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Abstract Several eukaryotic homologs of the Escherichia coli RecQ DNA helicase have been found. These include the human BLM gene, whose mutation results in Bloom syndrome, and the human WRN gene, whose mutation leads to Werner syndrome resembling premature aging. We cloned a Drosophila melanogaster homolog of the RECQ helicase family, Dmblm (Drosophila melanogaster Bloom), which encodes a putative 1487-amino-acid protein. Phylogenetic and dot plot analyses for the RECQ family, including 10 eukaryotic and 3 prokaryotic genes, indicate Dmblm is most closely related to the Homo sapiens BLM gene, suggesting functional similarity. Also, we found that Dmblm cDNA partially rescued the sensitivity to methyl methanesulfonate of Saccharomyces cerevisiae sgs1 mutant, demonstrating the presence of a functional similarity between Dmblm and SGS1. Our analyses identify four possible subfamilies in the RECQ family: (1) the BLM subgroup (H. sapiens Bloom, D. melanogaster Dmblm, and Caenorhabditis elegans T04A11.6); (2) the yeast RECQ subgroup (S. cerevisiae SGS1 and Schizosaccharomyces pombe rqh1/rad12); (3) the RECQL/Q1 subgroup (H. sapiens RECQL/Q1 and C. elegans K02F3.1); and (4) the WRN subgroup (H. sapiens Werner and C. elegans F18C5.2). This result may indicate that metazoans hold at least three RECQ genes, each of which may have a different function, and that multiple RECQ genes diverged with the generation of multicellular organisms. We propose that invertebrates such as nematodes and insects are useful as model systems of human genetic diseases.
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Alblihy, Adel, and Ahmed Shoqafi. "Abstract P6-01-28: Tangling the clinicopathological significance of MRE11-RAD50-NBS1 complex in sporadic breast cancers." Cancer Research 83, no. 5_Supplement (March 1, 2023): P6–01–28—P6–01–28. http://dx.doi.org/10.1158/1538-7445.sabcs22-p6-01-28.
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Abstract The MRE11–RAD50–NBS1 (MRN) complex is critical for genomic stability. Although germline mutations in MRN may increase breast cancer susceptibility, such mutations are extremely rare. Here, we have conducted a comprehensive clinicopathological study of MRN in sporadic breast cancers. We have protein expression profiled for MRN and a panel of DNA repair factors involved in double-strand break repair (BRCA1, BRCA2, ATM, CHK2, ATR, Chk1, pChk1, RAD51, γH2AX, RPA1, RPA2, DNA-PKcs), RECQ DNA helicases (BLM, WRN, RECQ1, RECQL4, RECQ5), nucleotide excision repair (ERCC1) and base excision repair (SMUG1, APE1, FEN1, PARP1, XRCC1, Pol β) in 1650 clinical breast cancers. The prognostic significance of MRE11, RAD50 and NBS1 transcripts and their microRNA regulators (hsa-miR-494 and hsa-miR-99b) were evaluated in large clinical datasets. Expression of MRN components was analysed in The Cancer Genome Atlas breast cancer cohort. We show that low nuclear MRN is linked to aggressive histopathological phenotypes such as high tumour grade, high mitotic index, oestrogen receptor- and high-risk Nottingham Prognostic Index. In univariate analysis, low nuclear MRE11 and low nuclear RAD50 were associated with poor survival. In multivariate analysis, low nuclear RAD50 remained independently linked with adverse clinical outcomes. Low RAD50 transcripts were also linked with reduced survival. In contrast, overexpression of hsa-miR-494 and hsa-miR-99b microRNAs was associated with poor survival. We observed large-scale genome-wide alterations in MRN-deficient tumours contributing to aggressive behaviour. We conclude that MRN status may be a useful tool to stratify tumours for precision medicine strategies. Citation Format: Ahmed Shoqafi. Tangling the clinicopathological significance of MRE11-RAD50-NBS1 complex in sporadic breast cancers [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P6-01-28.
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Brown, Adam D., Alison B. Claybon, and Alexander J. R. Bishop. "Mouse WRN Helicase Domain Is Not Required for Spontaneous Homologous Recombination-Mediated DNA Deletion." Journal of Nucleic Acids 2010 (2010): 1–6. http://dx.doi.org/10.4061/2010/356917.
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Werner syndrome is a rare disorder that manifests as premature aging and age-related diseases.WRNis the gene mutated in WS, and is one of five human RecQ helicase family members. WS cells exhibit genomic instability and altered proliferation, andin vitrostudies suggest that WRN has a role in suppressing homologous recombination. However, more recent studies propose that other RecQ helicases (including WRN) promote early events of homologous recombination. To study the role of WRN helicase on spontaneous homologous recombination, we obtained a mouse with a deleted WRN helicase domain and combined it with thein vivopink-eyed unstable homologous recombination system. In this paper, we demonstrate that WRN helicase is not necessary for suppressing homologous recombinationin vivocontrary to previous reports using a similar mouse model.
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Mukhopadhyay, Swagata, Tulika Das, Madhuparna Bose, Chetan Kumar Jain, Mayukh Chakraborty, Sunandan Mukherjee, Kumari Shikha, Amit K. Das, and Agneyo Ganguly. "Residues at the interface between zinc binding and winged helix domains of human RECQ1 play a significant role in DNA strand annealing activity." Nucleic Acids Research 49, no. 20 (November 9, 2021): 11834–54. http://dx.doi.org/10.1093/nar/gkab968.
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Abstract RECQ1 is the shortest among the five human RecQ helicases comprising of two RecA like domains, a zinc-binding domain and a RecQ C-terminal domain containing the winged-helix (WH). Mutations or deletions on the tip of a β-hairpin located in the WH domain are known to abolish the unwinding activity. Interestingly, the same mutations on the β-hairpin of annealing incompetent RECQ1 mutant (RECQ1T1) have been reported to restore its annealing activity. In an attempt to unravel the strand annealing mechanism, we have crystallized a fragment of RECQ1 encompassing D2–Zn–WH domains harbouring mutations on the β-hairpin. From our crystal structure data and interface analysis, we have demonstrated that an α-helix located in zinc-binding domain potentially interacts with residues of WH domain, which plays a significant role in strand annealing activity. We have shown that deletion of the α-helix or mutation of specific residues on it restores strand annealing activity of annealing deficient constructs of RECQ1. Our results also demonstrate that mutations on the α-helix induce conformational changes and affects DNA stimulated ATP hydrolysis and unwinding activity of RECQ1. Our study, for the first time, provides insight into the conformational requirements of the WH domain for efficient strand annealing by human RECQ1.
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Tadokoro, Takashi, Mahesh Ramamoorthy, Venkateswarlu Popuri, Alfred May, Jingyan Tian, Peter Sykora, Ivana Rybanska, David M. Wilson, Deborah L. Croteau, and Vilhelm A. Bohr. "Human RECQL5 participates in the removal of endogenous DNA damage." Molecular Biology of the Cell 23, no. 21 (November 2012): 4273–85. http://dx.doi.org/10.1091/mbc.e12-02-0110.
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Human RECQL5 is a member of the RecQ helicase family, which maintains genome stability via participation in many DNA metabolic processes, including DNA repair. Human cells lacking RECQL5 display chromosomal instability. We find that cells depleted of RECQL5 are sensitive to oxidative stress, accumulate endogenous DNA damage, and increase the cellular poly(ADP-ribosyl)ate response. In contrast to the RECQ helicase family members WRN, BLM, and RECQL4, RECQL5 accumulates at laser-induced single-strand breaks in normal human cells. RECQL5 depletion affects the levels of PARP-1 and XRCC1, and our collective results suggest that RECQL5 modulates and/or directly participates in base excision repair of endogenous DNA damage, thereby promoting chromosome stability in normal human cells.
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Lo, Yi-Chen, Kimberly S. Paffett, Or Amit, Jennifer A. Clikeman, Rosa Sterk, Mark A. Brenneman, and Jac A. Nickoloff. "Sgs1 Regulates Gene Conversion Tract Lengths and Crossovers Independently of Its Helicase Activity." Molecular and Cellular Biology 26, no. 11 (June 1, 2006): 4086–94. http://dx.doi.org/10.1128/mcb.00136-06.
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ABSTRACT RecQ helicases maintain genome stability and suppress tumors in higher eukaryotes through roles in replication and DNA repair. The yeast RecQ homolog Sgs1 interacts with Top3 topoisomerase and Rmi1. In vitro, Sgs1 binds to and branch migrates Holliday junctions (HJs) and the human RecQ homolog BLM, with Top3α, resolves synthetic double HJs in a noncrossover sense. Sgs1 suppresses crossovers during the homologous recombination (HR) repair of DNA double-strand breaks (DSBs). Crossovers are associated with long gene conversion tracts, suggesting a model in which Sgs1 helicase catalyzes reverse branch migration and convergence of double HJs for noncrossover resolution by Top3. Consistent with this model, we show that allelic crossovers and gene conversion tract lengths are increased in sgs1Δ. However, crossover and tract length suppression was independent of Sgs1 helicase activity, which argues against helicase-dependent HJ convergence. HJs may converge passively by a “random walk,” and Sgs1 may play a structural role in stimulating Top3-dependent resolution. In addition to the new helicase-independent functions for Sgs1 in crossover and tract length control, we define three new helicase-dependent functions, including the suppression of chromosome loss, chromosome missegregation, and synthetic lethality in srs2Δ. We propose that Sgs1 has helicase-dependent functions in replication and helicase-independent functions in DSB repair by HR.
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Rad, Behzad, Anthony L. Forget, Ronald J. Baskin, and Stephen C. Kowalczykowski. "Single-molecule visualization of RecQ helicase reveals DNA melting, nucleation, and assembly are required for processive DNA unwinding." Proceedings of the National Academy of Sciences 112, no. 50 (November 4, 2015): E6852—E6861. http://dx.doi.org/10.1073/pnas.1518028112.
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DNA helicases are motor proteins that unwind double-stranded DNA (dsDNA) to reveal single-stranded DNA (ssDNA) needed for many biological processes. The RecQ helicase is involved in repairing damage caused by DNA breaks and stalled replication forks via homologous recombination. Here, the helicase activity of RecQ was visualized on single molecules of DNA using a fluorescent sensor that directly detects ssDNA. By monitoring the formation and progression of individual unwinding forks, we observed that both the frequency of initiation and the rate of unwinding are highly dependent on RecQ concentration. We establish that unwinding forks can initiate internally by melting dsDNA and can proceed in both directions at up to 40–60 bp/s. The findings suggest that initiation requires a RecQ dimer, and that continued processive unwinding of several kilobases involves multiple monomers at the DNA unwinding fork. We propose a distinctive model wherein RecQ melts dsDNA internally to initiate unwinding and subsequently assembles at the fork into a distribution of multimeric species, each encompassing a broad distribution of rates, to unwind DNA. These studies define the species that promote resection of DNA, proofreading of homologous pairing, and migration of Holliday junctions, and they suggest that various functional forms of RecQ can be assembled that unwind at rates tailored to the diverse biological functions of RecQ helicase.
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Sanders, Elsbeth, Phoebe A. Nguyen, Cody M. Rogers, and Matthew L. Bochman. "Comprehensive Synthetic Genetic Array Analysis of Alleles That Interact with Mutation of the Saccharomyces cerevisiae RecQ Helicases Hrq1 and Sgs1." G3: Genes|Genomes|Genetics 10, no. 12 (October 28, 2020): 4359–68. http://dx.doi.org/10.1534/g3.120.401709.
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Most eukaryotic genomes encode multiple RecQ family helicases, including five such enzymes in humans. For many years, the yeast Saccharomyces cerevisiae was considered unusual in that it only contained a single RecQ helicase, named Sgs1. However, it has recently been discovered that a second RecQ helicase, called Hrq1, resides in yeast. Both Hrq1 and Sgs1 are involved in genome integrity, functioning in processes such as DNA inter-strand crosslink repair, double-strand break repair, and telomere maintenance. However, it is unknown if these enzymes interact at a genetic, physical, or functional level as demonstrated for their human homologs. Thus, we performed synthetic genetic array (SGA) analyses of hrq1Δ and sgs1Δ mutants. As inactive alleles of helicases can demonstrate dominant phenotypes, we also performed SGA analyses on the hrq1-K318A and sgs1-K706A ATPase/helicase-null mutants, as well as all combinations of deletion and inactive double mutants. We crossed these eight query strains (hrq1Δ, sgs1Δ, hrq1-K318A, sgs1-K706A, hrq1Δ sgs1Δ, hrq1Δ sgs1-K706A, hrq1-K318A sgs1Δ, and hrq1-K318A sgs1-K706A) to the S. cerevisiae single gene deletion and temperature-sensitive allele collections to generate double and triple mutants and scored them for synthetic positive and negative genetic effects based on colony growth. These screens identified hundreds of synthetic interactions, supporting the known roles of Hrq1 and Sgs1 in DNA repair, as well as suggesting novel connections to rRNA processing, mitochondrial DNA maintenance, transcription, and lagging strand synthesis during DNA replication.
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Venø, Susanne T., Tomasz Kulikowicz, Cezar Pestana, Piotr P. Stepien, Tinna Stevnsner, and Vilhelm A. Bohr. "The human Suv3 helicase interacts with replication protein A and flap endonuclease 1 in the nucleus." Biochemical Journal 440, no. 2 (November 14, 2011): 293–300. http://dx.doi.org/10.1042/bj20100991.
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The hSuv3 (human Suv3) helicase has been shown to be a major player in mitochondrial RNA surveillance and decay, but its physiological role might go beyond this functional niche. hSuv3 has been found to interact with BLM (Bloom's syndrome protein) and WRN (Werner's syndrome protein), members of the RecQ helicase family involved in multiple DNA metabolic processes, and in protection and stabilization of the genome. In the present study, we have addressed the possible role of hSuv3 in genome maintenance by examining its potential association with key interaction partners of the RecQ helicases. By analysis of hSuv3 co-IP (co-immunoprecipitation) complexes, we identify two new interaction partners of hSuv3: the RPA (replication protein A) and FEN1 (flap endonuclease 1). Utilizing an in vitro biochemical assay we find that low amounts of RPA inhibit helicase activity of hSuv3 on a forked substrate. Another single-strand-binding protein, mtSSB (mitochondrial single-strand-binding protein), fails to affect hSuv3 activity, indicating that the functional interaction is specific for hSuv3 and RPA. Further in vitro studies demonstrate that the flap endonuclease activity of FEN1 is stimulated by hSuv3 independently of flap length. hSuv3 is generally thought to be a mitochondrial helicase, but the physical and functional interactions between hSuv3 and known RecQ helicase-associated proteins strengthen the hypothesis that hSuv3 may play a significant role in nuclear DNA metabolism as well.
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Sánchez-Alonso, Patricia, and Plinio Guzmán. "Organization of Chromosome Ends in Ustilago maydis. RecQ-like Helicase Motifs at Telomeric Regions." Genetics 148, no. 3 (March 1, 1998): 1043–54. http://dx.doi.org/10.1093/genetics/148.3.1043.
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Abstract In this study we have established the structure of chromosome ends in the basidiomycete fungus Ustilago maydis. We isolated and characterized several clones containing telomeric regions and found that as in other organisms, they consist of middle repeated DNA sequences. Two principal types of sequence were found: UTASa was highly conserved in nucleotide sequence and located almost exclusively at the chromosome ends, and UTASb was less conserved in nucleotide sequence than UTASa and found not just at the ends but highly interspersed throughout the genome. Sequence analysis revealed that UTASa encodes an open reading frame containing helicase motifs with the strongest homology to RecQ helicases; these are DNA helicases whose function involves the maintenance of genome stability in Saccharomyces cerevisiae and in humans, and the suppression of illegitimate recombination in Escherichia coli. Both UTASa and UTASb contain a common region of about 300 bp located immediately adjacent to the telomere repeats that are also found interspersed in the genome. The analysis of the chromosome ends of U. maydis provides information on the general structure of chromosome ends in eukaryotes, and the putative RecQ helicase at UTASa may reveal a novel mechanism for the maintenance of chromosome stability.
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Mazina, Olga M., Matthew J. Rossi, Julianna S. Deakyne, Fei Huang, and Alexander V. Mazin. "Polarity and Bypass of DNA Heterology during Branch Migration of Holliday Junctions by Human RAD54, BLM, and RECQ1 Proteins." Journal of Biological Chemistry 287, no. 15 (February 22, 2012): 11820–32. http://dx.doi.org/10.1074/jbc.m112.341347.
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Several proteins have been shown to catalyze branch migration (BM) of the Holliday junction, a key intermediate in DNA repair and recombination. Here, using joint molecules made by human RAD51 or Escherichia coli RecA, we find that the polarity of the displaced ssDNA strand of the joint molecules defines the polarity of BM of RAD54, BLM, RECQ1, and RuvAB. Our results demonstrate that RAD54, BLM, and RECQ1 promote BM preferentially in the 3′→5′ direction, whereas RuvAB drives it in the 5′→3′ direction relative to the displaced ssDNA strand. Our data indicate that the helicase activity of BM proteins does not play a role in the heterology bypass. Thus, RAD54 that lacks helicase activity is more efficient in DNA heterology bypass than BLM or REQ1 helicases. Furthermore, we demonstrate that the BLM helicase and BM activities require different protein stoichiometries, indicating that different complexes, monomers and multimers, respectively, are responsible for these two activities. These results define BM as a mechanistically distinct activity of DNA translocating proteins, which may serve an important function in DNA repair and recombination.
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Liu, Yongqing, Shahenda El-Naggar, Brian Clem, Jason Chesney, and Douglas C. Dean. "The Rb/E2F pathway and Ras activation regulate RecQ helicase gene expression." Biochemical Journal 412, no. 2 (May 14, 2008): 299–306. http://dx.doi.org/10.1042/bj20070975.
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Disruption of the Rb (retinoblastoma protein)/E2F cell-cycle pathway and Ras activation are two of the most frequent events in cancer, and both of these mutations place oncogenic stress on cells to increase DNA replication. In the present study, we demonstrate that these mutations have an additive effect on induction of members of the RecQ DNA helicase family. RecQ activity is important for genomic stability, initiation of DNA replication and telomere maintenance, and mutation of the BLM (Bloom's syndrome gene), WRN (Werner's syndrome gene) or RECQL4 (Rothmund–Thomson syndrome gene) family members leads to premature aging syndromes characterized by genetic instability and telomere loss. RecQ family members are frequently overexpressed in cancers, and overexpression of BLM has been shown to cause telomere elongation. Concomitant with induction of RecQ genes in response to Rb family mutation and Ras activation, we show an increase in the number of telomeric repeats. We suggest that this induction of RecQ genes in response to common oncogenic mutations may explain the up-regulation of the genes seen in cancers, and it may provide a means for transformed cells to respond to an increased demand for DNA replication.
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DeLuca, Elisabetta, Monique Smeets, Meaghan Wall, Julie Quach, Andrew Deans, Jorg Heierhorst, Louise E. Purton, David Izon, and Carl R. Walkley. "A Mouse Model Of Rothmund-Thomson Syndrome Reveals An Essential Role For Recql4 In Maintenance Of Hematopoiesis." Blood 122, no. 21 (November 15, 2013): 591. http://dx.doi.org/10.1182/blood.v122.21.591.591.
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Abstract Rothmund-Thomson Syndrome (RTS) is a rare autosomal recessive disorder that presents with congenital skeletal malformations, premature ageing and an increased incidence of malignant disease including osteosarcoma and hematologic malignancy. The majority of RTS patients have deleterious germ-line mutations in the RECQL4 helicase. RECQL4 is a member of a family of DNA helicases including Bloom (BLM) and Werner (WRN) syndrome helicases and is thought to play an important role in maintaining chromosome stability. Recql4 deficiency is associated with karyotypic abnormalities and increased rates of aneuploidy. To enable lineage-restricted deletion of Recql4 we generated a mouse Recql4fl/fl line where exon 9 and 10 are flanked by loxP sites. This region encodes the start of the ATP dependent helicase domain and corresponds to human exons 8 and 9, mutations of which are commonly associated with cancers in RTS patients. Germ-line deletion of Recql4 led to embryonic lethality before E10.5. To understand the role of Recql4 in adult hematopoiesis, Rosa26-CreERT2 Recql4+/+, Recql4fl/+ and Recql4fl/fl mice were fed a tamoxifen containing diet (which activates Cre) for up to 4 weeks from 7 weeks of age to somatically delete Recql4. The most striking phenotype observed in these mice was that all R26-CreERT2 Recql4fl/fl animals became anaemic and developed white extremities, which in nearly all cases necessitated euthanasia by 30 days after starting tamoxifen. No differences were observed between R26-CreERT2Recql4+/+ and R26-CreERT2Recql4fl/+. Hematopoietic analyses revealed a severe multi-lineage cytopenia including profound red cell aplasia in the peripheral blood, spleen and bone marrow of Recql4 deficient animals. Effects were observed across all lineages with myeloid, B-lymphoid and T-lymphoid cell numbers severely reduced with a phenotype consistent with acute bone marrow failure. Loss of Recql4 led to a block in B-lymphoid development in the BM at the PrePro-B to Pro-B cell stage. T-lymphoid development was severely interrupted and most populations in the thymus were impacted. Within the stem and progenitor fractions, phenotypic HSCs were preserved in the absence of Recql4 but we found that the erythroid progenitors were nearly completely lost and only CMP/GMP remained. Colony formation was reduced by ∼70% in the deleted bone marrow. Bone marrow transplantation was used to assess the functionality of the Recql4 deleted HSCs. Strikingly, and consistently observed using both R26-CreERT2 and an additional hScl-CreER model, there was a strong selection against deficient cells and a recovery of hematopoiesis by cells with incomplete deletion of Recql4. This result demonstrates an essential role for Recql4 in the maintenance of hematopoiesis. In vitro B and T cell cultures recapitulated the developmental defects observed in the R26-CreERT2 Recql4fl/fl demonstrating a cell intrinsic requirement for Recql4. Loss of Recql4 lead to an accumulation of cells in S-phase and increased levels of DNA damage as measured by gH2Ax staining. Interestingly, the failure in B cell, T cell development and LKS+ CFC formation could be rescued by overexpression of a either WT or a helicase-dead Recql4-K508A mutant. Collectively these data demonstrate that Recql4 is essential for the maintenance of hematopoiesis and acts to maintain the committed progenitor pool. Loss of Recql4 leads to bone marrow failure, demonstrating a unique requirement for Recql4 in the regulation of hematopoiesis. Disclosures: No relevant conflicts of interest to declare.
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Viziteu, Elena, Bernard Klein, Angelique Bruyer, Dirk Hose, Hartmut Goldschmidt, Camille Grandmougin, Jihane Basbous, Angelos Constantinou, and Jerome Moreaux. "Role Of RECQ1 Helicase In Multiple Myeloma Biology and Drug Resistance." Blood 122, no. 21 (November 15, 2013): 1889. http://dx.doi.org/10.1182/blood.v122.21.1889.1889.
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Abstract Multiple Myeloma (MM) is a still lethal disease in 2013 characterized by the accumulation in the bone marrow of a clone of malignant plasma cells. Recent studies have shown that epigenetic modifications play a role by silencing various cancer-related genes in MM. We initiated a microarray-based genome-wide screen for genes responding to DNMT inhibition in MM cells and built a “DNA methylation gene score” that makes it possible identification of myeloma patients that will be sensitive to DNMT inhibitors. Among the genes regulated by DNMT inhibitor and associated with the worst prognostic value in patients, RECQ1 was identified. RECQ helicase are DNA unwinding enzymes involved in the maintenance of chromosome stability. RECQ1 is highly expressed in various types of solid tumors. RECQ1 silencing in cancer cells results in mitotic catastrophe and prevents tumor growth in murine models. In glioblastoma cells, depletion of RECQ1 induces reduction in cellular proliferation, spontaneous γ-H2AX foci formation and hypersensitivity to drugs. Furthermore, it was described that RECQ1 protein could interact with MSH proteins, RAD51 and PARP1 involved in DNA repair pathways. RECQ1 protein is expressed in human myeloma cell lines (HMCLs) and primary myeloma cells of patients. In four HMCLs (XG2, XG7, XG19 and LP1), RECQ1 was downregulated by conditional shRNA expression through lentiviral delivery. RECQ1 knock down inhibits growth of myeloma cells, induces 53BP1 foci formation and apoptosis. RECQ1 depletion sensitizes myeloma cells to DNA alkylating agent (melphalan) but not to corticosteroid (dexamethasone) or proteasome inhibitor (bortezomib). Using immunoprecipitation of myeloma cell nuclear proteins with anti-RECQ1 antibody, RECQ1 was shown to interact with PARP1 but not RAD51 or MSH2. An increased association of the two proteins was found upon DNA damages induced by melphalan. In agreement, RECQ1 depletion sensitizes myeloma cell lines to the PJ34 hydrochloride hydrate PARP inhibitor. In conclusion, RECQ1 could represent a biomarker of drug resistance in MM, which is targeted by DNMT inhibitor. This suggests association of alkylating agents and/or PARP inhibitors with DNMT inhibitor may represent a promising therapeutic approach. Disclosures: Goldschmidt: Celgene and Janssen: Membership on an entity’s Board of Directors or advisory committees.
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Yokoyama, Hideki, Daniel Moreno-Andres, Susanne A. Astrinidis, Yuqing Hao, Marion Weberruss, Anna K. Schellhaus, Hongqi Lue, Yoshikazu Haramoto, Oliver J. Gruss, and Wolfram Antonin. "Chromosome alignment maintenance requires the MAP RECQL4, mutated in the Rothmund–Thomson syndrome." Life Science Alliance 2, no. 1 (February 2019): e201800120. http://dx.doi.org/10.26508/lsa.201800120.
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RecQ-like helicase 4 (RECQL4) is mutated in patients suffering from the Rothmund–Thomson syndrome, a genetic disease characterized by premature aging, skeletal malformations, and high cancer susceptibility. Known roles of RECQL4 in DNA replication and repair provide a possible explanation of chromosome instability observed in patient cells. Here, we demonstrate that RECQL4 is a microtubule-associated protein (MAP) localizing to the mitotic spindle. RECQL4 depletion in M-phase–arrested frog egg extracts does not affect spindle assembly per se, but interferes with maintaining chromosome alignment at the metaphase plate. Low doses of nocodazole depolymerize RECQL4-depleted spindles more easily, suggesting abnormal microtubule–kinetochore interaction. Surprisingly, inter-kinetochore distance of sister chromatids is larger in depleted extracts and patient fibroblasts. Consistent with a role to maintain stable chromosome alignment, RECQL4 down-regulation in HeLa cells causes chromosome misalignment and delays mitotic progression. Importantly, these chromosome alignment defects are independent from RECQL4’s reported roles in DNA replication and damage repair. Our data elucidate a novel function of RECQL4 in mitosis, and defects in mitotic chromosome alignment might be a contributing factor for the Rothmund–Thomson syndrome.
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Delagoutte, Emmanuelle, and Peter H. von Hippel. "Helicase mechanisms and the coupling of helicases within macromolecular machines Part II: Integration of helicases into cellular processes." Quarterly Reviews of Biophysics 36, no. 1 (January 27, 2003): 1–69. http://dx.doi.org/10.1017/s0033583502003864.
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1. Helicases as components of macromolecular machines 32. Helicases in replication 72.1 The loading of replicative helicases 72.1.1 Loading Rep helicase at the replication origin of bacteriophage ϕX174 72.1.2 How is a ssDNA strand passed through (and bound in?) the central channel of the hexameric replicative helicases? 82.1.3 Loading of E. coli DnaB helicase in the absence of an auxiliary protein-loading factor 82.1.4 The T7 gp4 primase-helicase is loaded by means of a facilitated ring-opening mechanism 102.1.5 Bacteriophage T4 gp61 primase can be viewed as a loading factor for the homologous gp41 helicase 112.1.6 DnaC serves as the loading factor for E. coli DnaB helicase 112.1.7 The role of bacteriophage T4 gp59 in loading the T4 gp41 helicase 122.1.8 Loading of helicases onto ssDNA covered by ssDNA-binding proteins (SSBPs) 152.2 DNA polymerase and ssDNA-binding proteins can serve as reporters for replicative helicases in their elongation mode 172.2.1 The DNA polymerase, the sliding clamp, and the clamp loader 172.2.2 The role of ssDNA-binding protein 182.2.3 Coupling is achieved by the DNA polymerase and the ssDNA-binding protein 182.3 Arrest of replicative helicases 182.3.1 The Ter sites and termination proteins 192.3.2 Models for orientation-specific fork arrest 203. Helicases in transcription 203.1 Assisted loading of E. coli RNAP by the sigma70 initiation factor 213.1.1 RNAP holoenzyme formation 233.1.2 Formation of closed promoter complexes RPc and RPi 243.1.3 Strand separation and the formation of the open complex 243.1.4 Promoter clearance 243.1.5 Conclusions 253.2 Transcript formation serves as a monitor (reporter) of RNAP helicase activity in the elongation phase of transcription 253.2.1 Structural aspects of transcription complex translocation 263.2.2 Transcript elongation is an approximately isoenergetic process 263.3 Termination of transcription 273.3.1 Intrinsic termination 273.3.2 Termination by transcription-termination helicase Rho 283.3.3 Conclusions 293.4 Loading of the Rho transcription-termination helicase 294. Helicases in nucleotide excision repair (NER) 304.1 The limited strand-separating activity of the UvrAB complex 314.2 UvrB is a DNA helicase adapted for NER 334.2.1 The ATP-binding site of UvrB is similar to that of other helicases 334.2.2 The putative DNA-binding site 334.3 UvrA as a UvrB loader 344.4 Assisted targeting of UvrAB to the transcribed strand of DNA sequences undergoing active transcription 344.4.1 Targeting of UvrAB to damaged DNA sites in the vicinity of promoters is assisted by RNAP 344.4.2 TRCF participates in the assisted targeting of UvrAB to a transcribing RNAP stalled by a DNA lesion 354.4.3 Conclusions 364.5 UvrC endonuclease is the reporter of UvrAB helicase activity in incision 364.6 Post-incision events 364.7 Mechanistic details of the helicase activity of UvrD 374.7.1 Structural organization and conformational changes 374.7.2 Translocation and unwinding activities 384.7.3 Step size of DNA unwinding 384.7.4 Oligomeric state 395. Helicases in recombination 395.1 Role of RecBCD and RecQ in the initiation of recombination 405.1.1 The RecBCD enzyme 405.1.1.1 Loading of RecBCD onto its DNA substrate does not require a separate loading protein 405.1.1.2 The endonuclease activity of RecD, and the binding of SSB protein, serve as reporters of RecBCD helicase activity 405.1.1.3 RecA can also serve as a reporter of RecBCD helicase activity 415.1.1.4 RecBCD step size and unwinding mechanism 415.1.1.5 RecBCD unwinding efficiency 425.1.2 The RecQ protein 435.2 Strand-exchange reaction catalyzed by RecA 435.2.1 The nucleoprotein filament 445.2.2 The strand-exchange reaction 465.2.2.1 A ‘minor-groove’ to ‘major-groove’ triple-helix transition 465.2.2.2 Role of the secondary DNA-binding site of RecA 465.2.2.3 SSB protein stimulates the strand-exchange reaction 465.2.2.4 Cost of the strand-exchange reaction 475.2.3 Conclusion: RecA is a ‘scaffolding’ protein that prepares DNA for a coupled unpairing–reannealing reaction 485.3 Role of the RuvAB helicase in processing recombination intermediates by a branch migration mechanism 485.3.1 A brief description of the RuvA and RuvB proteins 495.3.2 Crystal structures of RuvA and the RuvA–Holliday junction complex 505.3.3 RuvA as a scaffolding protein that prepares the homoduplex for strand separation 515.3.4 Branch migration mechanism 516. RNA unwindases in the spliceosome 526.1 RNA structural rearrangements within the spliceosome: an overview 526.2 The spliceosome consumes chemical free energy 546.3 RNA structural alterations require the concerted (or coupled) action of unwinding and reannealing proteins 546.4 The reannealing proteins of the spliceosome: contribution of the RNA recognition motifs (RRMs) 556.5 The RNA unwindases of the spliceosome 556.6 RNA targets of the RNA unwindases 567. Conclusions and overview 578. Acknowledgments 589. References 59In Part I of this review [Delagoutte & von Hippel, Quarterly Reviews of Biophysics (2002) 35, 431–478] we summarized what is known about the properties, mechanisms, and structures of the various helicases that catalyze the unwinding of double-stranded nucleic acids. Here, in Part II, we consider these helicases as tightly integrated (or coupled) components of the various macromolecular machines within which they operate. The biological processes that are considered explicitly include DNA replication, recombination, and nucleotide excision repair, as well as RNA transcription and splicing. We discuss the activities of the constituent helicases (and their protein partners) in the assembly (or loading) of the relevant complex onto (and into) the specific nucleic acid sites at which the actions of the helicase-containing complexes are to be initiated, the mechanisms by which the helicases (and the complexes) translocate along the nucleic acids in discharging their functions, and the reactions that are used to terminate the translocation of the helicase-containing complexes at specific sites within the nucleic acid ‘substrate’. We emerge with several specific descriptions of how helicases function within the above processes of genetic expression which, we hope, can serve as paradigms for considering how helicases may also be coupled and function within other macromolecular machines.
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Singh, Dharmendra Kumar, Venkateswarlu Popuri, Tomasz Kulikowicz, Igor Shevelev, Avik K. Ghosh, Mahesh Ramamoorthy, Marie L. Rossi, Pavel Janscak, Deborah L. Croteau, and Vilhelm A. Bohr. "The human RecQ helicases BLM and RECQL4 cooperate to preserve genome stability." Nucleic Acids Research 40, no. 14 (April 28, 2012): 6632–48. http://dx.doi.org/10.1093/nar/gks349.
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Popuri, Venkateswarlu, Csanád Z. Bachrati, Laura Muzzolini, Georgina Mosedale, Silvia Costantini, Elisa Giacomini, Ian D. Hickson, and Alessandro Vindigni. "The Human RecQ Helicases, BLM and RECQ1, Display Distinct DNA Substrate Specificities." Journal of Biological Chemistry 283, no. 26 (April 30, 2008): 17766–76. http://dx.doi.org/10.1074/jbc.m709749200.
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