Regulation of the recruitment of telomerase to telomeres in human cancer cells

Abstract

Telomerase activity allows normal cells to achieve immortality, which is one of the hallmarks of cancer. It is required to maintain telomere length to protect chromosome ends from being recognised as damaged DNA. The protein TCAB1 is necessary for telomerase trafficking to telomeres, while telomeric protein TPP1 is essential for its interaction with telomeres. However, the mechanisms regulating these proteins are poorly understood. This thesis identifies TPP1 as a novel disease-causing gene in humans. A mutation in the ‘TEL patch’ (the surface area of TPP1 that interacts with telomerase) is likely to have caused short telomeres in a family with inherited bone marrow failure. We demonstrated that other amino acids within the TEL patch, F209 and S210, are also vital for the recruitment of telomerase to telomeres. Mutational analysis demonstrated that phosphorylation of S255 of TPP1, possibly by ATM, regulates the function of TPP1 in recruiting telomerase to telomeres. Phosphorylation of S64 of TCAB1 was hypothesised to regulate its function in telomerase localisation to telomeres; while the involvement of phosphorylation of this residue remains undetermined, we demonstrated that this region of the protein is important. Furthermore, S491 of TCAB1 emerged as a residue that is potentially involved in regulating telomerase recruitment to telomeres. Additionally, this thesis also provided the first evidence for an association between nuclear actin polymerisation and telomerase recruitment to telomeres. Inhibition of actin polymerisation or nuclear import disrupted telomerase recruitment, suggesting a novel role for nuclear structural integrity in this process. Collectively, these data increase our understanding of the regulation of telomerase recruitment to telomeres by the proteins TCAB1, TPP1, and actin. This understanding will inform new strategies for development of cancer therapeutic drugs and for developing better diagnostics and treatments for telomere biology disorders.