title: FEN1 ensures telomere stability by facilitating replication fork re-initiation.
abstract: Telomeres are terminal repetitive DNA sequences whose stability requires the coordinated actions of telomere-binding proteins and the DNA replication and repair machinery. Recently, we demonstrated that the DNA replication and repair protein Flap endonuclease 1 (FEN1) is required for replication of lagging strand telomeres. Here, we demonstrate for the first time that FEN1 is required for efficient re-initiation of stalled replication forks. At the telomere, we find that FEN1 depletion results in replicative stress as evidenced by fragile telomere expression and sister telomere loss. We show that FEN1 participation in Okazaki fragment processing is not required for efficient telomere replication. Instead we find that FEN1 gap endonuclease activity, which processes DNA structures resembling stalled replication forks, and the FEN1 interaction with the RecQ helicases are vital for telomere stability. Finally, we find that FEN1 depletion neither impacts cell cycle progression nor in vitro DNA replication through non-telomeric sequences. Our finding that FEN1 is required for efficient replication fork re-initiation strongly suggests that the fragile telomere expression and sister telomere losses observed upon FEN1 depletion are the direct result of replication fork collapse. Together, these findings suggest that other nucleases compensate for FEN1 loss throughout the genome during DNA replication but fail to do so at the telomere. We propose that FEN1 maintains stable telomeres by facilitating replication through the G-rich lagging strand telomere, thereby ensuring high fidelity telomere replication.
authors.affiliation: Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, Missouri 63110.
authors.forename: Abhishek
authors.initials: A
authors.lastname: Saharia
authors.affiliation: Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, Missouri 63110.
authors.forename: Daniel C
authors.initials: DC
authors.lastname: Teasley
authors.affiliation: Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, Missouri 63110.
authors.forename: Julien P
authors.initials: JP
authors.lastname: Duxin
authors.affiliation: Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, Missouri 63110.
authors.forename: Benjamin
authors.initials: B
authors.lastname: Dao
authors.affiliation: Division of Endocrine and Oncologic Surgery, Department of Surgery, Washington University School of Medicine, St. Louis, Missouri 63110.
authors.forename: Katherine B
authors.initials: KB
authors.lastname: Chiappinelli
authors.affiliation: Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, Missouri 63110; Department of Medicine, Washington University School of Medicine, St. Louis, Missouri 63110. Electronic address: sheila.stewart@wustl.edu.
authors.forename: Sheila A
authors.initials: SA
authors.lastname: Stewart
mesh_terms: D002453:Cell Cycle / Q000502:physiology; D004247:DNA / Q000235:genetics / Q000378:metabolism*; D004261:DNA Replication / Q000502:physiology*; D045585:Flap Endonucleases / Q000235:genetics / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D053484:RecQ Helicases / Q000235:genetics / Q000378:metabolism; D016615:Telomere / Q000235:genetics / Q000378:metabolism*
chemical_list: C022262:Okazaki fragments; D004247:DNA; D045585:Flap Endonucleases; C468317:FEN1 protein, human; D053484:RecQ Helicases