The goal of this proposal is to characterize the mechanism of telomerase-independent telomere maintenance. Although telomerase activation is the most common mechanism for maintenance of telomeric DNA, a subset of tumors and cell lines use a telomerase-independent mechanism, termed Alternative Lengthening of Telomeres (ALT), to sustain telomeric DNA. In telomerase-deficient yeast strains, telomere stabilization is achieved through recombination-based mechanisms. Similarly, although the molecular mechanism has yet to be established, the evidence from mammalian systems is consistent with ALT involving recombination. Based on data from yeast studies, it has been suggested that telomere recombination requires loss of the capping activity by which telomeres were originally defined. To test this hypothesis in mammalian cells, the structure of ALT telomeres will be determined using molecular biological methods and electron microscopy. Clarifying the structure of ALT telomeres will provide insight into the molecular mechanism of ALT. Secondly, factors involved in DNA recombination that are essential for telomere maintenance by ALT will be identified using dominant negative and knockdown approaches. These data will characterize the molecular requirements for ALT and will differentiate between possible recombination-based mechanisms. The only genetic alteration in mammalian cells linked to a predisposition to activate ALT is p53 status. Among its other functions, p53 has been shown to be involved in suppression of recombination. Thus, the role of p53 in regulating ALT will be characterized using temperature sensitive alleles of p53. These data will be the first that illustrate how alterations in a factor might predispose cells to ALT. Inhibition of telomerase has become an attractive target for future chemotherapeutic agents. However, ALT tumors would be refractory to these treatments. This proposal will identify structural changes and factors essential for activation of ALT and thus identify new potential targets for chemotherapeutic agents.

Agency
National Institute of Health (NIH)
Institute
National Cancer Institute (NCI)
Type
Research Project (R01)
Project #
5R01CA098087-03
Application #
6918606
Study Section
Radiation Study Section (RAD)
Program Officer
Pelroy, Richard
Project Start
2003-08-15
Project End
2007-07-31
Budget Start
2005-08-01
Budget End
2006-07-31
Support Year
3
Fiscal Year
2005
Total Cost
$280,963
Indirect Cost
Name
Fox Chase Cancer Center
Department
Type
DUNS #
073724262
City
Philadelphia
State
PA
Country
United States
Zip Code
19111
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Johnson, Jay E; Varkonyi, Robert J; Schwalm, Jaclyn et al. (2005) Multiple mechanisms of telomere maintenance exist in liposarcomas. Clin Cancer Res 11:5347-55
Razak, Zaineb R Abdul; Varkonyi, Robert J; Kulp-McEliece, Michelle et al. (2004) p53 differentially inhibits cell growth depending on the mechanism of telomere maintenance. Mol Cell Biol 24:5967-77