Pot1 and cell cycle progression cooperate in telomere length regulation

Department of Molecular Genetics, Biochemistry and Microbiology, University of Cincinnati College of Medicine, PO Box 0524, Cincinnati, Ohio 45267-0524, USA.
Nature Structural & Molecular Biology (Impact Factor: 13.31). 02/2008; 15(1):79-84. DOI: 10.1038/nsmb1331
Source: PubMed


Removal of the vertebrate telomere protein Pot1 results in a DNA damage response and cell cycle arrest. Here we show that loss of chicken Pot1 causes Chk1 activation, and inhibition of Chk1 signaling prevents the cell cycle arrest. However, arrest still occurs after disruption of ATM, which encodes another DNA damage response protein. These results indicate that Pot1 is required to prevent a telomere checkpoint mediated by another such protein, ATR, that is most likely triggered by the G-overhang. We also show that removal of Pot1 causes exceptionally rapid telomere growth upon arrest in late S/G2 of the cell cycle. However, release of the arrest slows both telomere growth and G-overhang elongation. Thus, Pot1 seems to regulate telomere length and G-overhang processing both through direct interaction with the telomere and by preventing a late S/G2 delay in the cell cycle. Our results reveal that cell cycle progression is an important component of telomere length regulation.

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Available from: Dmitri Churikov, Dec 29, 2015
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    • "Another group of SMH-like proteins (AtTRB1– 3) binds specifically with telomeric DNA with unknown functionality [6]. Fascinatingly, physical association was also reported between AtPOT1b and AtTRB1–3 [7] which may be involved through Telo bind domain [8] [9]. Thus AtTRB1-3 might be a key player in arbitrating structural modifications in AtPOT1b to strongly hold DNA. "
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    ABSTRACT: POT from Arabidopsis thaliana is a member of shelterin complex and belongs to Telo_bind protein family. Three homologs are reported, namely, AtPOT1a, AtPOT1b, and AtPOT1c, where AtPOT1b is involved in genomic stability and chromosome end protection by providing necessary grip to G-rich region of telomeric DNA for telomerase assembly. Telomeric binding factors (TRB1–3) physically interact with POT with no known functionality. In this work attempt has been made to elucidate the reason behind the interaction by analyzing molecular docking interaction between AtPOT1b and AtTRB1–3, which yielded potential residues, which could play essential role in structural modification. 3 ns molecular simulation helped to look into structural stability and conformational dynamics portraying domain movements. AtTRB’s interaction with AtPOT1b provoked structural changes in AtPOT1b, thereby increasing the affinity for single strand DNA (ssDNA) as compared to double strand DNA (dsDNA). Although the obtained results require experimental evidence they can act as a guide in tracing the functions in other organisms. The information provided in this paper would be helpful in understanding functions of TRB1–3 with respect to genomic stability.
    Full-text · Article · Feb 2014
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    • "Work with chimeric proteins showed that the difference between POT1a/b resides in their DNA-binding domains (Palm et al. 2009), pointing to the ssDNA-binding features of these proteins as crucial for ATR repression. Because the ATR pathway is activated following binding of RPA to ssDNA, a simple RPA exclusion model has been proposed (Guo et al. 2007; Lazzerini Denchi and de Lange 2007; Churikov and Price 2008). According to this model, the presence of POT1 on the single-strand telomeric DNA (either the 3′ overhang when the telomere is in an open state or the D loop in the t-loop configuration) would block RPA from binding and thereby prevent the activation of the ATR signaling pathway (de Lange 2009). "
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    ABSTRACT: The symphony of the human genome concludes with a long Gregorian chant of TTAGGG repeats. This monotonous coda represents one of the most complex problems in chromosome biology: the question of how cells distinguish their natural chromosome ends from double-strand breaks elsewhere in the genome. McClintock's classic finding of chromosome breakage-fusion-bridge cycles, first reported by her at one of the early Cold Spring Harbor Laboratory Symposia (the ninth), served as a prelude to this question. The 75th Cold Spring Harbor Laboratory Symposium marks the completion of a series of mouse gene deletion experiments that revealed DNA-damage-response pathways that threaten chromosome ends and how the components of the telomeric shelterin complex prevent activation of these pathways.
    Preview · Article · May 2011 · Cold Spring Harbor Symposia on Quantitative Biology
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    • "by us and others (Denchi and de Lange, 2007; Barrientos et al., 2008; Guo et al., 2007; Churikov and Price, 2008), in which POT1 prevents activation of the ATR pathway by blocking the binding of RPA to the single-stranded TTAGGG repeats. In agreement with this RPA exclusion model, RPA appears at telomeres and is required for activation of the ATR kinase once "
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    ABSTRACT: We previously proposed that POT1 prevents ATR signaling at telomeres by excluding RPA from the single-stranded TTAGGG repeats. Here, we use a Shld1-stabilized degron-POT1a fusion (DD-POT1a) to study the telomeric ATR kinase response. In the absence of Shld1, DD-POT1a degradation resulted in rapid and reversible activation of the ATR pathway in G1 and S/G2. ATR signaling was abrogated by shRNAs to ATR and TopBP1, but shRNAs to the ATM kinase or DNA-PKcs did not affect the telomere damage response. Importantly, ATR signaling in G1 and S/G2 was reduced by shRNAs to RPA. In S/G2, RPA was readily detectable at dysfunctional telomeres, and both POT1a and POT1b were required to exclude RPA and prevent ATR activation. In G1, the accumulation of RPA at dysfunctional telomeres was strikingly less, and POT1a was sufficient to repress ATR signaling. These results support an RPA exclusion model for the repression of ATR signaling at telomeres.
    Preview · Article · Nov 2010 · Molecular cell
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