title: AKTIP/Ft1, a New Shelterin-Interacting Factor Required for Telomere Maintenance.
abstract: Telomeres are nucleoprotein complexes that protect the ends of linear chromosomes from incomplete replication, degradation and detection as DNA breaks. Mammalian telomeres are protected by shelterin, a multiprotein complex that binds the TTAGGG telomeric repeats and recruits a series of additional factors that are essential for telomere function. Although many shelterin-associated proteins have been so far identified, the inventory of shelterin-interacting factors required for telomere maintenance is still largely incomplete. Here, we characterize AKTIP/Ft1 (human AKTIP and mouse Ft1 are orthologous), a novel mammalian shelterin-bound factor identified on the basis of its homology with the Drosophila telomere protein Pendolino. AKTIP/Ft1 shares homology with the E2 variant ubiquitin-conjugating (UEV) enzymes and has been previously implicated in the control of apoptosis and in vesicle trafficking. RNAi-mediated depletion of AKTIP results in formation of telomere dysfunction foci (TIFs). Consistent with these results, AKTIP interacts with telomeric DNA and binds the shelterin components TRF1 and TRF2 both in vivo and in vitro. Analysis of AKTIP- depleted human primary fibroblasts showed that they are defective in PCNA recruiting and arrest in the S phase due to the activation of the intra S checkpoint. Accordingly, AKTIP physically interacts with PCNA and the RPA70 DNA replication factor. Ft1-depleted p53-/- MEFs did not arrest in the S phase but displayed significant increases in multiple telomeric signals (MTS) and sister telomere associations (STAs), two hallmarks of defective telomere replication. In addition, we found an epistatic relation for MST formation between Ft1 and TRF1, which has been previously shown to be required for replication fork progression through telomeric DNA. Ch-IP experiments further suggested that in AKTIP-depleted cells undergoing the S phase, TRF1 is less tightly bound to telomeric DNA than in controls. Thus, our results collectively suggest that AKTIP/Ft1 works in concert with TRF1 to facilitate telomeric DNA replication.
authors.affiliation: Dipartimento di Biologia e Biotecnologie, Sapienza-Università di Roma, Roma, Italy; Istituto Pasteur Fondazione Cenci Bolognetti, Sapienza-Università di Roma, Roma, Italy.
authors.forename: Romina
authors.initials: R
authors.lastname: Burla
authors.affiliation: Dipartimento di Biologia e Biotecnologie, Sapienza-Università di Roma, Roma, Italy; Istituto Pasteur Fondazione Cenci Bolognetti, Sapienza-Università di Roma, Roma, Italy.
authors.forename: Mariateresa
authors.initials: M
authors.lastname: Carcuro
authors.affiliation: Dipartimento di Biologia e Biotecnologie, Sapienza-Università di Roma, Roma, Italy; Istituto Pasteur Fondazione Cenci Bolognetti, Sapienza-Università di Roma, Roma, Italy.
authors.forename: Grazia D
authors.initials: GD
authors.lastname: Raffa
authors.affiliation: Dipartimento di Biologia e Biotecnologie, Sapienza-Università di Roma, Roma, Italy; Istituto Pasteur Fondazione Cenci Bolognetti, Sapienza-Università di Roma, Roma, Italy.
authors.forename: Alessandra
authors.initials: A
authors.lastname: Galati
authors.affiliation: Dipartimento di Fisica, Sapienza-Università di Roma, Roma, Italy.
authors.forename: Domenico
authors.initials: D
authors.lastname: Raimondo
authors.affiliation: Istituto Nazionale Tumori Regina Elena, Rome, Italy.
authors.forename: Angela
authors.initials: A
authors.lastname: Rizzo
authors.affiliation: Dipartimento di Biologia e Biotecnologie, Sapienza-Università di Roma, Roma, Italy; Istituto Pasteur Fondazione Cenci Bolognetti, Sapienza-Università di Roma, Roma, Italy.
authors.forename: Mattia
authors.initials: M
authors.lastname: La Torre
authors.affiliation: Dipartimento di Biologia e Biotecnologie, Sapienza-Università di Roma, Roma, Italy; Istituto Pasteur Fondazione Cenci Bolognetti, Sapienza-Università di Roma, Roma, Italy.
authors.forename: Emanuela
authors.initials: E
authors.lastname: Micheli
authors.affiliation: Dipartimento di Biologia e Biotecnologie, Sapienza-Università di Roma, Roma, Italy; Istituto Pasteur Fondazione Cenci Bolognetti, Sapienza-Università di Roma, Roma, Italy.
authors.forename: Laura
authors.initials: L
authors.lastname: Ciapponi
authors.affiliation: Dipartimento di Biologia e Biotecnologie, Sapienza-Università di Roma, Roma, Italy; Istituto Pasteur Fondazione Cenci Bolognetti, Sapienza-Università di Roma, Roma, Italy.
authors.forename: Giovanni
authors.initials: G
authors.lastname: Cenci
authors.affiliation: Istituto di Biologia e Patologia Molecolari del CNR, Sapienza-Università di Roma, Roma, Italy.
authors.forename: Enrico
authors.initials: E
authors.lastname: Cundari
authors.affiliation: Istituto di Ricerca Genetica e Biomedica del CNR, Pisa, and Istituto Toscano Tumori, Firenze, Italy.
authors.forename: Antonio
authors.initials: A
authors.lastname: Musio
authors.affiliation: Istituto Nazionale Tumori Regina Elena, Rome, Italy.
authors.forename: Annamaria
authors.initials: A
authors.lastname: Biroccio
authors.affiliation: Dipartimento di Biologia e Biotecnologie, Sapienza-Università di Roma, Roma, Italy; Istituto Pasteur Fondazione Cenci Bolognetti, Sapienza-Università di Roma, Roma, Italy.
authors.forename: Stefano
authors.initials: S
authors.lastname: Cacchione
authors.affiliation: Dipartimento di Biologia e Biotecnologie, Sapienza-Università di Roma, Roma, Italy; Istituto Pasteur Fondazione Cenci Bolognetti, Sapienza-Università di Roma, Roma, Italy; Istituto di Biologia e Patologia Molecolari del CNR, Sapienza-Università di Roma, Roma, Italy.
authors.forename: Maurizio
authors.initials: M
authors.lastname: Gatti
authors.affiliation: Dipartimento di Biologia e Biotecnologie, Sapienza-Università di Roma, Roma, Italy; Istituto Pasteur Fondazione Cenci Bolognetti, Sapienza-Università di Roma, Roma, Italy; Istituto di Biologia e Patologia Molecolari del CNR, Sapienza-Università di Roma, Roma, Italy.
authors.forename: Isabella
authors.initials: I
authors.lastname: Saggio
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D051017:Apoptosis Regulatory Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002453:Cell Cycle / Q000235:genetics; D002478:Cells, Cultured; D004249:DNA Damage / Q000235:genetics; D004261:DNA Replication; D029721:Drosophila Proteins / Q000737:chemistry / Q000378:metabolism; D005347:Fibroblasts / Q000502:physiology; D016158:Genes, p53; D006801:Humans; D051379:Mice; D009687:Nuclear Proteins / Q000737:chemistry / Q000378:metabolism; D011506:Proteins / Q000235:genetics / Q000378:metabolism*; D016615:Telomere / Q000235:genetics / Q000378:metabolism*; D035321:Telomeric Repeat Binding Protein 1 / Q000378:metabolism; D035341:Telomeric Repeat Binding Protein 2 / Q000378:metabolism
chemical_list: C486377:AKTIP protein, human; D048868:Adaptor Proteins, Signal Transducing; D051017:Apoptosis Regulatory Proteins; D029721:Drosophila Proteins; C109729:Fts protein, mouse; D009687:Nuclear Proteins; D011506:Proteins; D035321:Telomeric Repeat Binding Protein 1; D035341:Telomeric Repeat Binding Protein 2; C000607218:peo protein, Drosophila