title: Werner syndrome protein suppresses the formation of large deletions during the replication of human telomeric sequences.
abstract: Werner syndrome (WS) is a disorder characterized by features of premature aging and increased cancer that is caused by loss of the RecQ helicase WRN. Telomeres consisting of duplex TTAGGG repeats in humans protect chromosome ends and sustain cellular proliferation. WRN prevents the loss of telomeres replicated from the G-rich strand, which can form secondary G-quadruplex (G4) structures. Here, we dissected WRN roles in the replication of telomeric sequences by examining factors inherent to telomeric repeats, such as G4 DNA, independently from other factors at chromosome ends that can also impede replication. For this we used the supF shuttle vector (SV) mutagenesis assay. We demonstrate that SVs with [TTAGGG]6 sequences are stably replicated in human cells, and that the repeats suppress the frequency of large deletions despite G4 folding potential. WRN depletion increased the supF mutant frequency for both the telomeric and non-telomeric SVs, compared with the control cells, but this increase was much greater (27-fold) for telomeric SVs. The higher SV mutant frequencies in WRN-deficient cells were primarily due to an increase in large sequence deletions and rearrangements. However, WRN depletion caused a more dramatic increase in deletions and rearrangements arising within the telomeric SV (70-fold), compared with non-telomeric SV (8-fold). Our results indicate that WRN prevents large deletions and rearrangements during replication, and that this role is particularly important in templates with telomeric sequence. This provides a possible explanation for increased telomere loss in WS cells.
authors.affiliation: Department of Environmental and Occupational Health, University of Pittsburgh Graduate School of Public Health, Pittsburgh, PA, USA.
authors.forename: Rama Rao
authors.initials: RR
authors.lastname: Damerla
authors.forename: Kelly E
authors.initials: KE
authors.lastname: Knickelbein
authors.forename: Steven
authors.initials: S
authors.lastname: Strutt
authors.forename: Fu-Jun
authors.initials: FJ
authors.lastname: Liu
authors.forename: Hong
authors.initials: H
authors.lastname: Wang
authors.forename: Patricia L
authors.initials: PL
authors.lastname: Opresko
mesh_terms: D001483:Base Sequence; D045744:Cell Line, Tumor; D004261:DNA Replication; D005090:Exodeoxyribonucleases / Q000235:genetics / Q000378:metabolism*; D054856:G-Quadruplexes; D015321:Gene Rearrangement; D017930:Genes, Reporter; D016153:Genes, Suppressor; D005822:Genetic Vectors / Q000235:genetics / Q000378:metabolism; D006801:Humans; D008969:Molecular Sequence Data; D016296:Mutagenesis; D012343:RNA, Transfer / Q000235:genetics / Q000378:metabolism; D053484:RecQ Helicases / Q000235:genetics / Q000378:metabolism*; D012091:Repetitive Sequences, Nucleic Acid; D017384:Sequence Deletion; D016615:Telomere / Q000235:genetics / Q000378:metabolism*; D014898:Werner Syndrome / Q000201:enzymology / Q000235:genetics; D000071657:Werner Syndrome Helicase
chemical_list: C096275:supF tRNA; D012343:RNA, Transfer; D005090:Exodeoxyribonucleases; D053484:RecQ Helicases; C098785:WRN protein, human; D000071657:Werner Syndrome Helicase