The overall goal of this project is to understand how telomeres prevent the activation of the DNA damage response at chromosome ends. In the prior funding period we have made progress on defining this end- protection problem, establishing that the two main DNA damage response pathways, the ATM and ATR kinase signaling cascades, can be activated at chromosome ends when telomere protection is lost. In this proposal, we describe experiments designed to gain mechanistic insights into how telomeres repress the ATM and ATR kinases. Specifically, AIMs 1 and 2 will focus on two components of the telomeric shelterin complex, TRF2 and POT1, which we have shown to act independently to repress the ATM and ATR pathways at chromosome ends.
The third aim of this proposal is to examine how telomeres are duplicated by semi-conservative DNA replication. Our preliminary data indicates that telomeric repeats pose a considerable challenge to the replication fork, leading to replication fork arrest and phenotypes consistent with telomeres representing fragile sites. Thus, the data suggest that the protective telomeric DNA at chromosome ends comes at the cost of potential replication problems. TRF1, a third component of shelterin identified in our laboratory, was found to have a key role in facilitating the replication of telomeres. This new insight forms the basis of the work in AIM 3 where we will examine telomere replication in detail and address how TRF1 facilitates replication fork progression through the telomeric DNA. Together these experiments should reveal the basic principles by which the telomeric shelterin complex allows mammalian cells to maintain linear chromosomes without activating DNA damage signaling cascades. Human cells lose telomeric DNA with cell divisions and exhibit limited proliferation due to the eventual loss of telomere function. Understanding telomere function and the consequences of telomere deprotection is directly relevant to the limited life-span of primary human cells in vitro and will shed light on the finite ability of stem cells to replenish organ function in vivo. This research is therefore expected to improve the understanding of telomere- related diseases, such as dyskeratosis congenita, and diminished organ function with aging in normal individuals. Furthermore, the outcome of our experiments are relevant to human cancer since loss of telomere function is thought to be a driving force in the early stages of human tumorigenesis.

Public Health Relevance

We propose to define the mechanism by which telomeres protect the ends of human chromosomes. Telomere function is a key issue in human health because telomeres are lost with cell divisions and with age, resulting in diminished cell growth and impaired organ homeostasis. In several human diseases, the loss of telomeric DNA is exacerbated, leading to premature organ failure and death.

National Institute of Health (NIH)
National Institute on Aging (NIA)
Research Project (R01)
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Study Section
Cellular Mechanisms in Aging and Development Study Section (CMAD)
Program Officer
Guo, Max
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Rockefeller University
Anatomy/Cell Biology
Other Domestic Higher Education
New York
United States
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Doksani, Ylli; de Lange, Titia (2016) Telomere-Internal Double-Strand Breaks Are Repaired by Homologous Recombination and PARP1/Lig3-Dependent End-Joining. Cell Rep 17:1646-1656
de Lange, Titia (2015) A loopy view of telomere evolution. Front Genet 6:321
Tong, Adrian S; Stern, J Lewis; Sfeir, Agnel et al. (2015) ATM and ATR Signaling Regulate the Recruitment of Human Telomerase to Telomeres. Cell Rep 13:1633-46
Zimmermann, Michal; de Lange, Titia (2014) 53BP1: pro choice in DNA repair. Trends Cell Biol 24:108-17
Doksani, Ylli; de Lange, Titia (2014) The role of double-strand break repair pathways at functional and dysfunctional telomeres. Cold Spring Harb Perspect Biol 6:a016576
Frescas, David; de Lange, Titia (2014) Binding of TPP1 protein to TIN2 protein is required for POT1a,b protein-mediated telomere protection. J Biol Chem 289:24180-7
Zimmermann, Michal; Kibe, Tatsuya; Kabir, Shaheen et al. (2014) TRF1 negotiates TTAGGG repeat-associated replication problems by recruiting the BLM helicase and the TPP1/POT1 repressor of ATR signaling. Genes Dev 28:2477-91
Kabir, Shaheen; Hockemeyer, Dirk; de Lange, Titia (2014) TALEN gene knockouts reveal no requirement for the conserved human shelterin protein Rap1 in telomere protection and length regulation. Cell Rep 9:1273-80
Frescas, David; de Lange, Titia (2014) A TIN2 dyskeratosis congenita mutation causes telomerase-independent telomere shortening in mice. Genes Dev 28:153-66
Frescas, David; de Lange, Titia (2014) TRF2-tethered TIN2 can mediate telomere protection by TPP1/POT1. Mol Cell Biol 34:1349-62

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