Telomeres are heterochromatic DNA-protein structures that protect the ends of linear chromosomes from being recognized as sites of DNA damage and help maintain genomic integrity. The shelterin complex that binds telomeres is vital for regulating telomere length and function, disruption of which can lead to ageing and tumorigenesis. About 90% of human cancers activate telomerase to maintain telomere length, which allows these cells to have unlimited proliferation. The remaining 10% of cancers use a telomerase-independent mechanism that relies on homologous recombination for telomere synthesis, known as alternative lengthening of telomeres or ALT. TRF1, a component of the shelterin complex that binds directly to telomeric DNA, has been implicated in telomere maintenance in both telomerase-positive and negative cancer cells. The function of TRF1 is regulated in part by post-translational modifications, such as phosphorylation. TRF1 phosphorylation at T371 has been implicated in regulating TRF1 functions in mitosis and in the repair of DNA double strand breaks in telomerase-positive cells. The results presented in this thesis demonstrate that TRF1 phosphorylation at T371 is also important in ALT cells and is regulated by DNA damage response factors. T371 phosphorylation is required for the functional assembly of ALT-associated PML bodies and the production of C-circles, which are hallmarks of ALT cancer cells. The results presented in this thesis also suggest that the dimerization and DNA binding capabilities of TRF1 are required for the functional assembly of ALT-associated PML bodies. The work presented here identifies a novel role of TRF1 in ALT activity, which provides further insight into telomere regulation mechanisms in this subset of cancer.

Master of Science (MSc)

Thesis