title: Tethering telomeric double- and single-stranded DNA-binding proteins inhibits telomere elongation.
abstract: Mammalian telomeres are composed of G-rich repetitive double-stranded (ds) DNA with a 3' single-stranded (ss) overhang and associated proteins that together maintain chromosome end stability. Complete replication of telomeric DNA requires de novo elongation of the ssDNA by the enzyme telomerase, with telomeric proteins playing a key role in regulating telomerase-mediated telomere replication. In regards to the protein component of mammalian telomeres, TRF1 and TRF2 bind to the dsDNA of telomeres, whereas POT1 binds to the ssDNA portion. These three proteins are linked through either direct interactions or by the proteins TIN2 and TPP1. To determine the biological consequence of connecting telomeric dsDNA to ssDNA through a multiprotein assembly, we compared the effect of expressing TRF1 and POT1 in trans versus in cis in the form of a fusion of these two proteins, on telomere length in telomerase-positive cells. When expressed in trans these two proteins induced extensive telomere elongation. Fusing TRF1 to POT1 abrogated this effect, inducing mild telomere shortening, and generated looped DNA structures, as assessed by electron microscopy, consistent with the protein forming a complex with dsDNA and ssDNA. We speculate that such a protein bridge between dsDNA and ssDNA may inhibit telomerase access, promoting telomere shortening.
authors.affiliation: Department of Pharmacology and Cancer Biology, Duke University Medical Center, Durham, North Carolina 27710, USA.
authors.forename: Katherine T
authors.initials: KT
authors.lastname: Etheridge
authors.forename: Sarah A
authors.initials: SA
authors.lastname: Compton
authors.forename: Katharine S
authors.initials: KS
authors.lastname: Barrientos
authors.forename: Sezgin
authors.initials: S
authors.lastname: Ozgur
authors.forename: Jack D
authors.initials: JD
authors.lastname: Griffith
authors.forename: Christopher M
authors.initials: CM
authors.lastname: Counter
mesh_terms: D002460:Cell Line; D004247:DNA / Q000737:chemistry*; D004277:DNA, Single-Stranded / Q000737:chemistry*; D004268:DNA-Binding Proteins / Q000737:chemistry*; D005786:Gene Expression Regulation; D006801:Humans; D008856:Microscopy, Fluorescence; D008954:Models, Biological; D009687:Nuclear Proteins / Q000737:chemistry / Q000502:physiology*; D009690:Nucleic Acid Conformation; D011485:Protein Binding; D000089804:Shelterin Complex; D019098:Telomerase / Q000378:metabolism; D016615:Telomere / Q000648:ultrastructure; D034501:Telomere-Binding Proteins / Q000737:chemistry / Q000502:physiology*; D035321:Telomeric Repeat Binding Protein 1 / Q000737:chemistry / Q000502:physiology*; D035341:Telomeric Repeat Binding Protein 2 / Q000737:chemistry / Q000502:physiology*; D000091346:Tripeptidyl-Peptidase 1
chemical_list: D004277:DNA, Single-Stranded; D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; C440849:POT1 protein, human; D000089804:Shelterin Complex; C504753:TERF2 protein, human; D034501:Telomere-Binding Proteins; D035321:Telomeric Repeat Binding Protein 1; D035341:Telomeric Repeat Binding Protein 2; D000091346:Tripeptidyl-Peptidase 1; D004247:DNA; D019098:Telomerase; C000717267:TPP1 protein, human