Disease relevance of WRN

• No difference was seen in the subcellular localization of the WRN protein in a variety of normal and transformed human cell lines, including both carcinomas and sarcomas [1].
• WRN-/- cells showed hypersensitivities to genotoxic agents, such as 4-nitroquinoline 1-oxide, camptothecin and methyl methanesulfonate [2].
• Werner syndrome (WS) is a human premature aging disorder characterized by chromosomal instability [3].
• Of the five human RecQ helicases identified, three are associated with genetic disorders characterized by an elevated incidence of cancer or premature aging: Werner syndrome, Bloom syndrome, and Rothmund-Thomson syndrome [4].
• The genes responsible for these diseases, BLM and WRN, have been cloned and identified as homologs of the Escherichia coli recQ genes [5].

Psychiatry related information on WRN

• These disorders are xeroderma pigmentosum, Cockayne syndrome, trichothiodystrophy, Bloom syndrome, Werner syndrome, X-linked alpha-thalassemia/mental retardation syndrome, and Juberg-Marsidi syndrome [6].
• Prototypic examples being investigated by the author and his colleagues are the Werner syndrome and dementias of the Alzheimer type [7].
• The method can be used to rapidly determine telomere length in subsets of nucleated blood cells from patients with age-related diseases such as Down's syndrome, Alzheimer's disease and Werner syndrome [8].

High impact information on WRN

• Research on the Werner syndrome and a surprising number of other progeroid syndromes support the importance of the maintenance of genomic stability as a partial antidote to aging [9].
• This suggests that defects in the suppression of rearrangements involving divergent, repeated sequences may underlie the genome instability seen in BLM and WRN patients and in cancer cases associated with defects in these genes [10].
• Mut-7 of C. elegans, required for transposon silencing and RNA interference, is a homolog of Werner syndrome helicase and RNaseD [11].
• The premature ageing syndrome protein, WRN, is a 3'-->5' exonuclease [12].
• Werner syndrome (WS) is an uncommon autosomal recessive disorder characterized by premature aging [13].

Chemical compound and disease context of WRN

• The crude genotypic frequencies in gastric cancer patients were similar to those of the controls, but in the WRN codon 1367 polymorphisms the mean age tended to be higher in the Arg/Arg genotypes [14].
• We show here that antisense suppression of WRN in two human glioma cell lines reproduces hallmarks of the drug cytotoxicity profile of WS cells, namely, hypersensitivity to 4-nitroquinoline 1-oxide, camptothecin and hydroxyurea [15].
• We have examined the effect of age, dietary folate, and mutations in the Werner's syndrome helicase (WRN) and TRP53 genes on FXS repeat instability in mice [16].
• We prepared several monoclonal antibodies (mAbs) specific for the NH2- and COOH-terminal regions of the DNA helicase (WRN helicase) responsible for Werner's syndrome known as a premature aging disease [17].
• We investigated the association of a WRN gene polymorphism, namely c.4330 T --> C leading to an amino acid substitution from Cys to Arg, with bone density and lumbar spondylosis score in unrelated Japanese postmenopausal women (n = 377) [18].

Biological context of WRN

• We found that WRN associates with telomeres when dissociation of telomeric D loops is likely during replication and recombination [19].
• We show here that WRN functionally interacts with DNA polymerase delta (pol delta), a eukaryotic polymerase required for DNA replication and DNA repair [20].
• Our findings suggest that WRN may facilitate pol delta-mediated DNA replication and/or DNA repair and that disruption of WRN-pol delta interaction in WS cells may contribute to the previously observed S-phase defects and/or the unusual sensitivity to a limited number of DNA damaging agents [20].
• In addition, we show that a limited number of haplotypes are associated with the disease in both populations and that these haplotypes define clusters of apparently related haplotypes that may identify as many as eight or nine independent WRN mutations in these two populations [21].
• Here we present the results of a search for a region that exhibits linkage disequilibrium with the disorder, under the assumption that identification of such a region may provide an alternative method of narrowing down the location of WRN, the gene responsible for WS [21].

Anatomical context of WRN

• WS fibroblasts have an attenuated p53- mediated apoptotic response, and this deficiency can be rescued by expression of wild-type WRN [22].
• A physical interaction between WRN and FEN-1 is demonstrated by their co-immunoprecipitation from HeLa cell lysate and affinity pull-down experiments using a recombinant C-terminal fragment of WRN [3].
• We produced WRN-/-, BLM-/- and WRN(-/-)/BLM(-/-) mutants in the chicken B-cell line DT40 [2].
• Telomere instability in a human tumor cell line expressing a dominant-negative WRN protein [23].
• In contrast to WRN, BLM was expressed strongly in the testis and thymus [24].

Associations of WRN with chemical compounds

• Genetic complementation studies indicate that human WRN rescues dna2-1 mutant phenotypes of growth, cell cycle arrest and sensitivity to the replication inhibitor hydroxyurea or DNA damaging agent methylmethane sulfonate [25].
• The results demonstrate that BLM and WRN proteins exhibit similar sensitivity profiles to these DNA-binding ligands and are most potently inhibited by the structurally related minor groove binders distamycin A and netropsin (K(i) </=1 microM) [26].
• The presence of aphidicolin inhibited CPT-induced WRNp foci strongly but not bleomycin-induced foci [27].
• In pursuit of a functional interaction between WRN and PARP-1, we found that WS cells are deficient in the poly(ADP-ribosyl)ation pathway after they are treated with the DNA-damaging agents H2O2 and methyl methanesulfonate [28].
• Moreover, Trichostatin A delays the re-entry of WRN into the nucleolus at late times after irradiation [29].

Physical interactions of WRN

• Werner syndrome protein interacts with human flap endonuclease 1 and stimulates its cleavage activity [3].
• WRN interacts physically and functionally with the recombination mediator protein RAD52 [30].
• The Pso4 mRNA splicing and DNA repair complex interacts with WRN for processing of DNA interstrand cross-links [31].
• In vitro studies also indicate that PCNA binds to a region in the N terminus portion of the WS protein containing a potential 3'-5' exonuclease domain [32].
• These results indicate that the WRN/PARP-1 complex plays a key role in the cellular response to oxidative stress and alkylating agents, suggesting a role for these proteins in the base excision DNA repair pathway [28].
• We show that SIRT1 interacts with WRN both in vitro and in vivo; this interaction is enhanced after DNA damage [33].

Enzymatic interactions of WRN

• Here, we show that WRN is phosphorylated through an ATR/ATM dependent pathway in response to replication blockage [34].
• WRN is phosphorylated in vivo after treatment of cells with DNA-damaging agents in a pathway that requires DNA-PKcs [35].
• Exogenous expression of exonuclease domain-deleted WRN interferes with the repair of radiation-induced DNA damages [36].

Co-localisations of WRN

• BLM is found primarily in nuclear domain 10 except during S phase when it colocalizes with the Werner syndrome gene product, WRN, in the nucleolus [37].
• In cells arrested in S phase with hydroxyurea, WRN exits the nucleolus and colocalizes with p53 in the nucleoplasm [38].
• In human cells, we report that WRN co-localizes and physically interacts with the critical telomere maintenance protein TRF2 [39].
• In response to gamma-irradiation or mitomycin C, WRN leaves the nucleoli and co-localizes with the Mre11 complex in the nucleoplasm [40].
• Werner's syndrome protein (WRN) migrates Holliday junctions and co-localizes with RPA upon replication arrest [41].

Regulatory relationships of WRN

• These data support the hypothesis that p53 can induce apoptosis through the modulation of specific DExH-containing DNA helicases and may have implications for the cancer predisposition observed in WS patients [22].
• WS protein (WRN) dramatically stimulates the rate of FEN-1 cleavage of a 5' flap DNA substrate [3].
• The exonucleolytic and endonucleolytic cleavage activities of human exonuclease 1 are stimulated by an interaction with the carboxyl-terminal region of the Werner syndrome protein [42].
• In the 5' upstream region, one Sp1 site and several AP 2 sites exist near the capping site, suggesting that the expression of RECQL4 is regulated by a housekeeping-type promoter similar to WRN [43].
• Furthermore, WRN RNAi-induced DNA damage was suppressed by overexpression of the telomere-binding protein TRF2 [44].

Other interactions of WRN

• p53-mediated apoptosis is attenuated in Werner syndrome cells [22].
• These conditions, however, did not prevent the DNA damage response in BLM-ablated cells, suggesting a distinct role for WRN in DNA homeostasis in vivo [44].
• Thus, the genomic instability observed in WRN-/- cells may be at least partially attributed to the lack of interactions between the WRN protein and human nucleases including EXO-1 [42].
• Here we report a novel physical and functional interaction between WRN and the homologous recombination mediator protein RAD52 [30].
• By comparative Northern blot analysis, we show that the RECQL4 transcripts are severely down-regulated in the cells from RTS patients, similar to our previous observation for WRN transcripts in cells from Werner patients [43].

Analytical, diagnostic and therapeutic context of WRN

• By using enzyme-linked immunosorbent assay (ELISA) to examine physical interaction between WRN and the same deletion mutants, we found that the WRN-binding motif is located within amino acids 100-300 and overlaps with the single-stranded DNA binding domain (amino acids 150-450) [45].
• RESULTS: Using immunocytochemistry, we found that WRNp forms distinct nuclear foci in response to DNA damaging agents, including camptothecin (CPT), etoposide, 4-nitroquinolin-N-oxide and bleomycin [27].
• Like its RecQ helicase family member, WRN, the defective protein in Werner syndrome, dissection of the BLM protein revealed that its HRDC domain is sufficient for its recruitment to the damaged sites [46].
• Results from coimmunoprecipitation studies indicate that WRN is associated with replication protein A (RPA) and p53 in vivo before and after treatment with the replication inhibitor hydroxyurea or gamma-irradiation that introduces DNA strand breaks [47].
• Second, the exonuclease co-purifies with the 160-kDa WRN protein and its associated DNA helicase and ATPase activities through successive steps of ion exchange and affinity chromatography, suggesting that all three activities are physically associated [48].

References