PTOP interacts with POT1 and regulates its localization to telomeres

Abstract

Telomere maintenance has been implicated in cancer and ageing, and requires cooperation between a multitude of telomeric factors, including telomerase, TRF1, TRF2, RAP1, TIN2, Tankyrase, PINX1 and POT1 (refs 1-12). POT1 belongs to a family of oligonucleotide-binding (OB)-fold-containing proteins that include Oxytricha nova TEBP, Cdc13, and spPot1, which specifically recognize telomeric single-stranded DNA (ssDNA). In human cells, the loading of POT1 to telomeric ssDNA controls telomerase-mediated telomere elongation. Surprisingly, a human POT1 mutant lacking an OB fold is still recruited to telomeres. However, the exact mechanism by which this recruitment occurs remains unclear. Here we identify a novel telomere protein, PTOP, which interacts with both POT1 and TIN2. PTOP binds to the carboxyl terminus of POT1 and recruits it to telomeres. Inhibition of PTOP by RNA interference (RNAi) or disruption of the PTOP-POT1 interaction hindered the localization of POT1 to telomeres. Furthermore, expression of the respective interaction domains on PTOP and POT1 alone extended telomere length in human cells. Therefore, PTOP heterodimerizes with POT1 and regulates POT1 telomeric recruitment and telomere length.

Cancer and aging: the importance of telomeres in genome maintenance

“…TIN2 does not bind telomeric DNA directly. Rather, TIN2 appears to tether TRF1 to POT1 by binding the bridge protein PTOP/PIP1 [53,54] (Fig. 2).…”

Structural Maintenance of Chromosomes Flexible Hinge Domain Containing 1 (SMCHD1) Promotes Non-homologous End Joining and Inhibits Homologous Recombination Repair upon DNA Damage

“…Immunofluorescence (IF), Western Blotting, and AntibodiesImmunofluorescence and Western blotting were carried out as previously described (22). For IF, cells grown on glass coverslips were fixed in 4% paraformaldehyde, permeabilized with 0.5% Triton X-100, and then blocked with 5% BSA before incubation with primary and secondary antibodies.…”

Phosphorylation of TPP1 regulates cell cycle-dependent telomerase recruitment

“…Analysis of HTC75 cells stably expressing control and FLAG-tagged wild-type and mutant TPP1 proteins by using the TRF assay was done as described (13,43).…”

“…Of the six proteins, TPP1 contains an N-terminal oligonucleotide-and oligosaccharide-binding (OB) fold and is tethered to telomeres through interactions with telomere DNA binding proteins TRF1, TRF2, and POT1 (13,14). Work from us and others has shown that the TPP1 OB fold interacts with the telomerase and is required for telomere recruitment of telomerase and high telomerase processivity (15)(16)(17)(18)(19).…”