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Abstract
Human shelterin components POT1 and TPP1 form a stable heterodimer that protects telomere ends from ATR-dependent DNA damage responses and regulates telomerase-dependent telomere extension. Mice possess two functionally distinct POT1 proteins. POT1a represses ATR/CHK1 DNA damage responses and the alternative non-homologous end-joining DNA repair pathway while POT1b regulates C-strand resection and recruits the CTC1-STN1-TEN1 (CST) complex to telomeres to mediate C-strand fill-in synthesis. Whether POT1a and POT1b are involved in regulating the length of the telomeric G-strand is unclear. Here we demonstrate that POT1b, independent of its CST function, enhances recruitment of telomerase to telomeres through three amino acids in its TPP1 interacting C-terminus. POT1b thus coordinates the synthesis of both telomeric G- and C-strands. In contrast, POT1a negatively regulates telomere length by inhibiting telomerase recruitment to telomeres. The identification of unique amino acids between POT1a and POT1b helps us understand mechanistically how human POT1 switches between end protective functions and promoting telomerase recruitment.
Highlights
Human shelterin components Protection of Telomeres 1 (POT1) and TPP1 form a stable heterodimer that protects telomere ends from ATR-dependent DNA damage responses and regulates telomerasedependent telomere extension
To understand how the POT1a and POT1b proteins contribute to telomere maintenance, we bred Pot1aF/F, Pot1b−/− and p53F/F mice to generate Pot1aF/F; Pot1b −/−; p53F/F and Pot1aF/F; Pot1b+/−; p53F/F mouse embryonic fibroblasts (MEFs)
Since telomerase processivity appears identical in the presence of either POT1aTPP1 or POT1b-TPP1, our results suggest that both POT1a and POT1b are proficient to promote telomerase processivity in this in vitro assay
Summary
Human shelterin components POT1 and TPP1 form a stable heterodimer that protects telomere ends from ATR-dependent DNA damage responses and regulates telomerasedependent telomere extension. We demonstrate that POT1b, independent of its CST function, enhances recruitment of telomerase to telomeres through three amino acids in its TPP1 interacting C-terminus. The identification of unique amino acids between POT1a and POT1b helps us understand mechanistically how human POT1 switches between end protective functions and promoting telomerase recruitment. A major question in the telomere field is how telomeres are able to protect chromosome ends from being recognized as damaged DNA while still functioning as substrates for telomerase-mediated telomere elongation. C Quantification of the indicated types of fusions per chromosome in Pot1b−/− sarcomas of the indicated generations. H Detection of G-overhangs (native gel) and total telomere lengths (denature gel) by TRF Southern in G3 Pot1b−/− sarcomas expressing the indicated constructs. Numbers indicate relative G-overhang and total telomere signals, with telomere signals set to 1.0 for cells expressing GFP
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