| Telomerase synthesizes telomeric sequences and is minimally composed of a reverse transcriptase (RT) (TERT) and RNA (TR). We reconstituted heterologous mouse and human TERT-TR and chimeric mTERT-hTERT-hTR complexes in vitro and in immortalized human alternative lengthening of telomere (ALT) cells. Our data suggest that species-specific determinants of activity, processivity, and telomere function map not only to TR, but also to the TERT component. hTERT-hTR, but not heterologous TERT-TR complexes, nor chimeric mTERT-hTERT-hTR complexes, significantly reduced the percentage of chromosomes without telomeric signals in ALT cells. Moreover, heterologous and chimeric complexes were defective in recruitment to telomeres. Our results suggest a requirement for several hTERT domains and interaction with multiple proteins for proper recruitment of telomerase to the shortest telomeres in human ALT cells. The ability of hTERT to elongate short mouse telomeres, and the inability of mTERT to elongate short human telomeres suggest that mechanisms regulating recruitment and activity of hTERT at short telomeres may be less stringently regulated than mechanisms regulating mTERT recruitment and activity at short telomeres. Results such as these may lead to the design of better strategies for inhibiting telomerase and validation using rodent models. For example, TERT domains that confer similar functions in human and mouse cells may be better targets than domains with species-restricted functions.;We also tested the specificity of a novel class of platinum(II) G-quadruplex stabilizers at inhibiting telomerase activity. We showed that these ligands efficiently stabilize telomeres and inhibit telomerase activity with comparable potency to telomestatin (a potent telomerase inhibitor). Additionally, these ligands may present a potent dual action strategy to not only inhibit telomerase function, but also disrupt telomere function and assembly. Accordingly, targeting telomere function may be more easily validated in mouse models. |
