Cloning, genomic structure and chromosomal localization of the gene encoding mouse DNA helicase RECQL5beta

Understanding the Human RECQ5 Helicase-Connecting the Dots from DNA to Clinics

RECQ5, a member of the conserved RECQ helicase family, is the sole human RECQ homolog that has not been linked to a hereditary developmental syndrome. Nonetheless, dysregulation of RECQ5 has emerged as a significant clinical concern, being linked to cancer predisposition, cardiovascular disease, and inflammation. In cells, RECQ5 assumes a crucial role in the regulation of DNA repair pathways, particularly in the repair of DNA double-strand breaks and inter-strand DNA crosslinks. Moreover, RECQ5 exhibits a capacity to modulate gene expression by interacting with transcription machineries and their co-regulatory proteins, thus safeguarding against transcription-induced DNA damage. This review aims to provide an overview of the multifaceted functions of RECQ5 and its implications in maintaining genomic stability. We will discuss the potential effects of clinical variants of RECQ5 on its cellular functions and their underlying mechanisms in the pathogenesis of cancer and cardiovascular disease. We will review the impact of RECQ5 variants in the field of pharmacogenomics, specifically their influence on drug responses, which may pave the way for novel therapeutic interventions targeting RECQ5 in human diseases.

Alternative lengthening of telomeres: recurrent cytogenetic aberrations and chromosome stability under extreme telomere dysfunction

Human tumors using the alternative lengthening of telomeres (ALT) exert high rates of telomere dysfunction. Numerical chromosomal aberrations are very frequent, and structural rearrangements are widely scattered among the genome. This challenging context allows the study of telomere dysfunction-driven chromosomal instability in neoplasia (CIN) in a massive scale. We used molecular cytogenetics to achieve detailed karyotyping in 10 human ALT neoplastic cell lines. We identified 518 clonal recombinant chromosomes affected by 649 structural rearrangements. While all human chromosomes were involved in random or clonal, terminal, or pericentromeric rearrangements and were capable to undergo telomere healing at broken ends, a differential recombinatorial propensity of specific genomic regions was noted. We show that ALT cells undergo epigenetic modifications rendering polycentric chromosomes functionally monocentric, and because of increased terminal recombinogenicity, they generate clonal recombinant chromosomes with interstitial telomeric repeats. Losses of chromosomes 13, X, and 22, gains of 2, 3, 5, and 20, and translocation/deletion events involving several common chromosomal fragile sites (CFSs) were recurrent. Long-term reconstitution of telomerase activity in ALT cells reduced significantly the rates of random ongoing telomeric and pericentromeric CIN. However, the contribution of CFS in overall CIN remained unaffected, suggesting that in ALT cells whole-genome replication stress is not suppressed by telomerase activation. Our results provide novel insights into ALT-driven CIN, unveiling in parallel specific genomic sites that may harbor genes critical for ALT cancerous cell growth.

DNA helicase 3.6.4.12

EC number

 3.6.4.12

Systematic name

 ATP phosphohydrolase (DNA helix unwinding)

Recommended name

 DNA helicase

Synonyms

 3’ to 5’ DNA helicase <28> [35]

 3’-5’ DNA helicase <11> [55]

 3’-5’ PfDH <11> [55]

 5’ to 3’ DNA helicase <26,27> [19,42]

 AvDH1 <47> [37]

 BACH1 helicase <19> [34]

 BLM <3> [28]

 BLM protein <3> [28]

 BRCA1-associated C-terminal helicase <19> [34]

 BcMCM <8> [52]

 CeWRN-1 <43> [9]

 DDX25 <3,48> [36]

 DNA helicase 120 <7> [15]

 DNA helicase A <4> [8]

 DNA helicase E <5> [44]

 DNA helicase II <9> [7]

 DNA helicase III <4> [27]

 DNA helicase RECQL5β <44> [17]

 DNA helicase VI <3> [45]

 Dbp9p <46> (<46> a member of the DEAD box protein family [24]) [24]

 DmRECQ5 <1> [50]

 DnaB helicase <29> [23]

 E1 helicase <17> [58]

 GRTH/DDX25 <3,48> [36]

 HCoV SF1 helicase <23> [3]

 HCoV helicase <23> [3]

 HDH IV <3> [45]

 Hel E <5> [44]

 Hmi1p <40> [60]

 MCM helicase <6,5,38> [43,54]

 MCM protein <6,35> [43]

 MER3 helicase <22> [30]

 MER3 protein <22> [30]

 MPH1 <28> [35]

 NS3 <12,50> (<12,50> ambiguous [38,65,66]) [38,65,66]

 NS3 NTPase/helicase <14> (<14> ambiguous [67]) [67]

 NS3 protein <12> (<12> ambiguous [63]) [63]

 NTPase/helicase <12,16> (<12> ambiguous [61]) [61,64]

 PDH120 <7> [15]

 PIF1 <33> [51]

 PIF1 helicase <33> [51,53]

 PcrA <37> [20]

 PcrA helicase <37,41,49> [20,21,39]

 PcrASpn <41> [21]

 PfDH A <11> [55]

 Pfh1p <27> [42]

 RECQ5 <1> [49,50]

 RECQ5 helicase <1> (<1> small isoform [49]) [49]

 RECQL5b <44> [17]

 REcQ <31> [13]

 RSF1010 RepA <30> [5]

 RecG <45> [6]

 RecQ helicase <32> [56]

 RecQsim <32> [56]

 Rep52 <24> [40]

 Rrm3p <26> [19]

 Sgs1 <36> [29]

 Sgs1 DNA helicase <36> [29]

 TWINKLE <21> [33]

 Tth UvrD <20> [16]

 UvrD <20,42> [16,22]

 UvrD helicase <39> [18]

 WRN <18> [31]

 WRN RecQ helicase <18> [12]

 WRN helicase <18> [12]

 WRN protein <18> [12]

 WRN-1 RecQ helicase <43> [9]

 Werner Syndrome helicase <18> [31]

 Werner syndrome RecQ helicase <18> [12]

 dheI I <1> [46]

 dnaB <29> [23]

 hPif1 <33> [53]

 helicase DnaB <2> [10]

 helicase II <25> [25]

 helicase PcrA <49> [39]

 helicase UvrD <20> [16]

 helicase domain of bacteriophage T7 gene 4 protein <10> [47]

 non structural protein 3 <12> (<12> ambiguous [61,62]) [61,62]

 nonstructural protein 3 <12,14,50,51> (<12,14,50> ambiguous [38,63,65,66,67]; <51> ambigous [4]) [4,38,63,65,66,67]

 protein NS3 <12> (<12> ambiguous [62]) [62]

 scHelI <4> [26]

 urvD <25> [25]

RECQL5 helicase: connections to DNA recombination and RNA polymerase II transcription

The RecQ family of helicases are traditionally viewed as recombination factors, important for maintaining genome stability. RECQL5 is unique among these proteins in being associated with RNA polymerase II, the enzyme responsible for transcribing all protein-encoding genes in eukaryotes. Here, we describe the possible implications of recent studies and discuss models for RECQL5 function.

Recql5 plays an important role in DNA replication and cell survival after camptothecin treatment

Disruption of replication can lead to loss of genome integrity and increase of cancer susceptibility in mammals. Thus, a replication impediment constitutes a formidable challenge to these organisms. Recent studies indicate that homologous recombination (HR) plays an important role in suppressing genome instability and promoting cell survival after exposure to various replication inhibitors, including a topoisomerase I inhibitor, camptothecin (CPT). Here, we report that the deletion of RecQ helicase Recql5 in mouse ES cells and embryonic fibroblast (MEF) cells resulted in a significant increase in CPT sensitivity and a profound reduction in DNA replication after the treatment with CPT, but not other DNA-damaging agents. This CPT-induced cell death is replication dependent and occurs primarily after the cells had exited the first cell cycle after CPT treatment. Furthermore, we show that Recql5 functions nonredundantly with Rad51, a key factor for HR to protect mouse ES cells from CPT-induced cytotoxicity. These new findings strongly suggest that Recql5 plays an important role in maintaining active DNA replication to prevent the collapse of replication forks and the accumulation of DSBs in order to preserve genome integrity and to prevent cell death after replication stress as a result of topoisomerase I poisoning.

Recql5 and Blm RecQ DNA helicases have nonredundant roles in suppressing crossovers

In eukaryotes, crossovers in mitotic cells can have deleterious consequences and therefore must be suppressed. Mutations in BLM give rise to Bloom syndrome, a disease that is characterized by an elevated rate of crossovers and increased cancer susceptibility. However, simple eukaryotes such as Saccharomyces cerevisiae have multiple pathways for suppressing crossovers, suggesting that mammals also have multiple pathways for controlling crossovers in their mitotic cells. We show here that in mouse embryonic stem (ES) cells, mutations in either the Bloom syndrome homologue (Blm) or the Recql5 genes result in a significant increase in the frequency of sister chromatid exchange (SCE), whereas deleting both Blm and Recql5 lead to an even higher frequency of SCE. These data indicate that Blm and Recql5 have nonredundant roles in suppressing crossovers in mouse ES cells. Furthermore, we show that mouse embryonic fibroblasts derived from Recql5 knockout mice also exhibit a significantly increased frequency of SCE compared with the corresponding wild-type control. Thus, this study identifies a previously unknown Recql5-dependent, Blm-independent pathway for suppressing crossovers during mitosis in mice.

Requirement of Rrm3 helicase for repair of spontaneous DNA lesions in cells lacking Srs2 or Sgs1 helicase

The Rrm3 DNA helicase of Saccharomyces cerevisiae interacts with proliferating cell nuclear antigen and is required for replication fork progression through ribosomal DNA repeats and subtelomeric and telomeric DNA. Here, we show that rrm3 srs2 and rrm3 sgs1 mutants, in which two different DNA helicases have been inactivated, exhibit a severe growth defect and undergo frequent cell death. Cells lacking Rrm3 and Srs2 arrest in the G(2)/M phase of the cell cycle with 2N DNA content and frequently contain only a single nucleus. The phenotypes of rrm3 srs2 and rrm3 sgs1 mutants were suppressed by disrupting early steps of homologous recombination. These observations identify Rrm3 as a new member of a network of pathways, involving Sgs1 and Srs2 helicases and Mus81 endonuclease, suggested to act during repair of stalled replication forks.

Analysis of helicase activity and substrate specificity of Drosophila RECQ5

RecQ5 is one of five RecQ helicase homologs identified in humans. Three of the human RecQ homologs (BLM, WRN and RTS) have been linked to autosomal recessive human genetic disorders (Bloom syndrome, Werner syndrome and Rothmund-Thomson syndrome, respectively) that display increased genomic instability and cause elevated levels of cancers in addition to other symptoms. To understand the role of RecQ helicases in maintaining genomic stability, the WRN, BLM and Escherichia coli RecQ helicases have been characterized in terms of their DNA substrate specificity. However, little is known about other members of the RecQ family. Here we show that Drosophila RECQ5 helicase is a structure-specific DNA helicase like the other RecQ helicases biochemically characterized so far, although the substrate specificity is not identical to that of WRN and BLM helicases. Drosophila RECQ5 helicase is capable of unwinding 3' Flap, three-way junction, fork and three-strand junction substrates at lower protein concentrations compared to 5' Flap, 12 nt bubble and synthetic Holliday junction structures, which can be unwound efficiently by WRN and BLM.

An unusual mutation in RECQ4 gene leading to Rothmund-Thomson syndrome

Rothmund-Thomson syndrome (OMIM #268400) is a severe autosomal recessive genodermatosis: characterised by growth retardation, hyperpigmentation and frequently accompanied by congenital bone defects, brittle hair and hypogonadism. Mutations in helicase RECQ4 gene are responsible for a subset of cases of RTS. Only six mutations have been reported, thus, far and each affecting the coding sequence or the splice junctions. We report the first homozygous mutation in RECQ4 helicase: 2746-2756-delTGGGCTGAGGC in IVS8 responsible for the severe phenotype associated with RTS in a Malaysian pedigree. We report also a 5321 G-->A transition in exon 17 and the updated list of the RECQ4 gene mutations.

Drosophila melanogaster RECQ5/QE DNA helicase: stimulation by GTP binding

The Drosophila melanogaster RECQ5/QE gene encodes a member of the DNA helicase family comprising the Escherichia coli RecQ protein and products of the human Bloom's, Werner's, and Rothmund-Thomson syndrome genes. The full-length product of RECQ5/QE was expressed in the baculovirus system and was purified. Gel filtration experiments indicated that RECQ5/QE was present in an oligomeric state. The RECQ5/QE protein hydrolyzed ATP and even more actively GTP in the presence of single-stranded DNA. ATP drove the DNA helicase activity of RECQ5/QE, whereas GTP had little effect. GTP exhibited a stimulatory effect on DNA unwinding when it was used together with ATP. This effect was more apparent with non-hydrolyzable GTP analogs, such as GTPgammaS and GMPPNP. These results indicate that GTP binding to RECQ5/QE triggers its DNA helicase activity. GTP binding increased the rate of strand separation without affecting the S(0.5) (K(m)) values for the substrates during the DNA helicase reaction. The data collectively suggest that the RECQ5/QE protein is activated upon GTP binding through the ATP-binding site.