AKTIP/Ft1, a New Shelterin-Interacting Factor Required for Telomere Maintenance

Romina Burla, Mariateresa Carcuro, Grazia D. Raffa, Alessandra Galati, Domenico Raimondo, Angela Rizzo, Mattia La Torre, Emanuela Micheli, Laura Ciapponi, Giovanni Cenci, Enrico Cundari, Antonio Musio, Annamaria Biroccio, Stefano Cacchione, Maurizio Gatti, Isabella Saggio

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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.

Original languageEnglish
Article numbere1005167
JournalPLoS Genetics
Volume11
Issue number6
DOIs
Publication statusPublished - Jul 1 2015

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ASJC Scopus subject areas

  • Genetics
  • Molecular Biology
  • Ecology, Evolution, Behavior and Systematics
  • Cancer Research
  • Genetics(clinical)

Cite this

Burla, R., Carcuro, M., Raffa, G. D., Galati, A., Raimondo, D., Rizzo, A., La Torre, M., Micheli, E., Ciapponi, L., Cenci, G., Cundari, E., Musio, A., Biroccio, A., Cacchione, S., Gatti, M., & Saggio, I. (2015). AKTIP/Ft1, a New Shelterin-Interacting Factor Required for Telomere Maintenance. PLoS Genetics, 11(6), [e1005167]. https://doi.org/10.1371/journal.pgen.1005167