Browsing by Author "Beattie, Tara L."

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    ATRX as a Regulator of Telomerase Activity in Cancer Cells
    (2020-03) Briggs, Sophie; Beattie, Tara L.; Cairncross, Gregory J.; Riabowol, Karl T.; Grewal, Savraj S.
    Telomere maintenance is the central process governing cellular immortality. The two distinct pathways – 1) telomerase activity and 2) the alternative lengthening of telomeres (ALT) – result in telomere elongation and allow cells to evade normal cellular ageing mechanisms. Both telomere maintenance pathways can become activated through gene mutations, leading to genetically unstable cells capable of unlimited proliferation. Expression of the chromatin remodeling protein ATRX is lost in almost all ALT+ cancers, suggesting a role for ATRX in ALT repression, however its exact role in telomere maintenance remains unclear. This thesis provides novel evidence suggesting ATRX acts to resolve telomeric G-quadruplexes (G4), thereby facilitating telomerase activity and indirectly repressing ALT. Using RNA interference in human cancer cell lines and a novel DNA ELISA-based technique, the data presented here establish that loss of ATRX expression results in increased G4 at the telomere. This G4 enrichment correlates with a reduction in telomerase activity in vitro which is exacerbated following treatment with the G4 stabilizing agent, Pyridostatin. Further, loss of the full-length ATRX isoform alone does not directly correlate with the ALT phenotype in the selected cell panel. However, a truncated ATRX isoform, ATRXt, was found to be expressed in all selected telomerase+ cells and shown to maintain key functions of the full-length protein. Therefore, alternative ATRX isoforms may act to facilitate telomerase activity through G4 resolution, even in the absence of full-length protein. Taken together, these data provide novel evidence identifying ATRX as an important factor facilitating telomerase-mediated telomere elongation through G4 resolution at the telomere.
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    Characterising the Role of the Smc5/6 Complex at Telomeres
    (2021-01-29) McLaren, William David John; Beattie, Tara L.; Zaremberg, Vanina; Riabowol, Karl T.
    Smc5/6 is a member of the SMC family of proteins alongside cohesin and condensin. The complex has previously described roles in DNA repair and more recently a role in telomere binding and maintenance. Here, I demonstrate novel genetic interactions between the Smc5/6 complex and a nuclear pore complex protein Nup170. Both Nup170 and Esc1 have previously been shown to be necessary for telomere maintenance and these two proteins form a complex alongside Sir4, a well-defined regulator of heterochromatin at the telomeres. Loss of Nup170 when combined with a DNA binding-defective mutant of Nse3, a core component of the Smc5/6 complex, leads to increases in subtelomeric gene expression and loss of telomere clustering. It was observed that by combining a deletion mutant of Nup170 with an Nse3 mutant leads to a decrease in survival when exposed to the DNA damage inducing agent MMS as well as an increase in subtelomeric gene expression. Observing Rap1GFP clusters as a readout for telomere clustering shows no change between nse3-1 single mutant and the nup170Δ/nse3-1 double mutant. This indicates that both Smc5/6 and Nup170 operate together to maintain normal telomere function and that they operate in the same pathway to cluster telomeres. These findings help to further elucidate the role of the Smc5/6 complex in maintaining telomere clustering, suppressing expression of subtelomeric genes at telomeres and interactions with Nup170.
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    Mindfulness-based cancer recovery and supportive-expressive therapy maintain telomere length relative to controls in distressed breast cancer survivors
    (Wiley, 2014-11-03) Beattie, Tara L.; Speca, Michael; Degelman, Erin S.; Fick, Laura J.; Tamagawa, Rie; Faris, Peter; Giese-Davis, Janine; Carlson, Linda E.
    Group psychosocial interventions including mindfulness-based cancer recovery (MBCR) and supportive-expressive group therapy (SET) can help breast cancer survivors decrease distress and influence cortisol levels. Although telomere length (TL) has been associated with breast cancer prognosis, the impact of these two interventions on TL has not been studied to date.
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    The Role of Telomere Clustering and Compaction in Cellular Senescence
    (2020-06-02) Adam, Nanda Johanna; Riabowol, Karl T.; Beattie, Tara L.; Goodarzi, Aaron A.; Shutt, Timothy E.; Patel, Kamala D.; Autexier, Chantal
    Chronological age is highly correlated with the development of numerous diseases, including cancer. Thus, delaying the onset of cellular aging should increase healthspan and reduce the period of morbidity that is seen as one approaches maximal lifespan. One of the main contributors to age-related diseases is replicative senescence, which is induced by a telomere-specific DNA damage response. This highly regulated pathway is modulated by an interplay between telomere length and shelterin proteins, such as Telomere Repeat-binding Factor 2 (TRF2). Since telomeres shorten with each cell division, telomere length has been used as a biomarker for cellular aging. However, many cancer cells display short telomeres despite their continued replicative capability. This indicates that cells can extend their cellular lifespan with relatively short telomeres if other factors are in place. Here, we have developed a method for 3D quantitative immunofluorescence microscopy of telomeres in interphase cells that includes image acquisition, processing and analysis to accurately determine telomere count, length and volume. Using this technique, we observed that long telomeres in telomerase-immortalized cells as well as DNA damage positive-telomeres in replicatively senescent cells can cluster, resulting in lower telomere counts. Analysis of individual telomeres by super-resolution microscopy techniques showed that telomeres in senescent cells have significantly more damage foci and are less dense when compared to low passage replicating cells. Alternatively, cell strains with short telomeres, but elevated TRF2 levels, showed more telomere compaction which correlated with an absence of DNA damage responses and increased replicative lifespan. These results show that telomere compaction, rather than average telomere length, may be more indicative of both cellular senescence and immortality, and provides novel insights into the key mechanisms involved in the development of age-related diseases due to the accumulation of senescent cells.
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    UV-inducible alternative splicing of PIG3
    (2006) Nicholls, Chris D.; Beattie, Tara L.; Robbins, Stephen