Abstract
T-oligo, an 11-base oligonucleotide homologous to the 3'-telomeric overhang, is a novel, potent therapeutic modality in melanoma and multiple other tumor types. T-oligo is proposed to function in a manner similar to experimental disruption of the telomere overhang and induces DNA damage responses including apoptosis, differentiation and senescence. However, important components involved in T-oligo induced responses are not defined, particularly the role of p53, TRF1 and TRF2 in mediating the T-oligo induced responses. In MU, PM-WK, and MM-MC melanoma cells, exposure to T-oligo upregulates p53 expression and phosphorylation, resulting in cellular differentiation and activation of a caspase-mediated apoptotic cascade. However, siRNA-mediated knockdown of p53 completely blocks T-oligo induced differentiation and significantly decreases apoptosis, suggesting that p53 is an important mediator of T-oligo induced responses. In addition, we characterized the roles of telomere binding proteins, TRF1, TRF2, and tankyrase-1, in T-oligo induced damage responses. We demonstrate that tankyrase-1 activity is required for initiation of T-oligo induced damage responses including p53 phosphorylation and reduction of cellular proliferation. These results highlight TRF1, TRF2, tankyrase-1 and p53 as important elements in T-oligo mediated responses and suggest new avenues for research into T-oligo's mechanism of action.
Highlights
Telomeres and telomerase are areas of active research in tumor biology
These results suggest an integral role of p53 in T-oligo induced DNA damage responses
P53 expression and phosphorylation are hallmarks of the DNA damage response seen in cells exposed to DNA alkylating agents [39], exposure of the telomere overhang through disruption of the T-loop structure [40], and exposure to T-oligo [4, 20]
Summary
Telomeres and telomerase are areas of active research in tumor biology. Telomeres are structures that serve protective roles by allowing cells to distinguish chromosome ends from damaged DNA [1]. Administration of T-oligo, an 11-base oligonucleotide homologous to the 3′ telomeric overhang, has been proposed as both a cancer therapeutic [3], and a method to study DNA damage responses induced by disruption of the telomere [4, 5]. The T-loop caps and protects the telomere end through recruitment of the shelterin complex, composed of telomeric repeat binding factors 1 and 2 (TRF1 and TRF2), POT1, TIN1, TPP1 and RAP1 [6]. Expression of dominant negative TRF2 induces uncapping of the telomere overhang and initiates DNA damage responses, possibly by disruption of the T-loop and exposure of the telomere overhang, a process mediated in part through ATM and its effector protein p53 [5, 10]. Overexpression of TRF2 in telomerase negative cells www.impactjournals.com/oncotarget
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