The TEL patch of telomere protein TPP1 mediates telomerase recruitment and processivity

Abstract

Human chromosome ends are capped by shelterin, a protein complex that protects the natural ends from being recognized as sites of DNA damage and also regulates the telomere-replicating enzyme, telomerase1–3. Shelterin includes the heterodimeric POT1-TPP1 protein, which binds the telomeric single-stranded DNA tail4–9. TPP1 has been implicated both in recruiting telomerase to telomeres and in stimulating telomerase processivity (the addition of multiple DNA repeats after a single primer-binding event)9–14. Determining the mechanisms of these activities has been difficult, especially because genetic perturbations also tend to affect the essential chromosome end-protection function of TPP115–17. Here we identify separation-of-function mutants of TPP1 that retain full telomere-capping function in vitro and in vivo, yet are defective in binding telomerase. The seven separation-of-function mutations map to a patch of amino acids on the surface of TPP1, the TEL patch, that both recruits telomerase to telomeres and promotes high-processivity DNA synthesis, indicating that these two activities are manifestations of the same molecular interaction. Given that the interaction between telomerase and TPP1 is required for telomerase function in vivo, the TEL patch of TPP1 provides a new target for anti-cancer drug development.

Phosphorylation of TPP1 regulates cell cycle-dependent telomerase recruitment

“…This interaction depends on the OB fold of TPP1 (15)(16)(17)(18)20). Recent studies have identified the residues that are required for the interface of TPP1-telomerase interaction (20)(21)(22). Our results thus far support the model that phosphorylation of S111 increases the telomerase activity that complexes with TPP1.…”

“…4A). Consistent with previous reports (20)(21)(22), several of the residues that are required for the interface of TPP1-telomerase interaction, including D166, E168, E169, E171, and E215, reside on the same face of the TPP1 3D structure (Fig. 4A).…”

“…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). Recently, key residues that define the interface for human TPP1 OB foldtelomerase interaction have been identified (20)(21)(22). However, these experiments were performed in asynchronous cells and did not address how telomerase was recruited to and extend telomeres at late S/G 2 .…”

Telomerase enzymatic component hTERT shortens long telomeres in human cells

“…[18][19][20][21][22][23] We examined its role on hTERT-mediated telomere shortening. TPP1 knockdown did not affect average TL in SAOS2 (P = 0.72) and had no significant effect on the length of very long telomeres on 11q (Fig.…”

Direct Single-Stranded DNA Binding by Teb1 Mediates the Recruitment of Tetrahymena thermophila Telomerase to Telomeres

“…Together with RAP1 and the TIN2 and TPP1 proteins, which bridge TRF1 and TRF2 to POT1, the telomeric-DNA-binding proteins create a network of complexes that block DNA damage response activation (14). Interestingly, TPP1 also interacts with telomerase as an essential step of recruitment in a manner physiologically restricted to S phase of the cell cycle (12,(16)(17)(18)(19). In fission yeast, the dsDNA-binding protein Taz1 takes the place of TRF1 and TRF2, Pot1 binds to the single-stranded DNA overhang, and Rap1, Poz1, and Tpz1 function as bridging proteins that link Taz1 to Pot1 (20,21).…”