The molecular basis for telomerase trafficking in human cancer cells
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Telomerase is the enzyme responsible for synthesizing the repetitive DNA of telomeres. In most human tissues, telomerase activity is confined to prenatal development. However, in the vast majority of cancers, telomerase is reactivated. This is critical to prolonged tumor maintenance and proliferation. Our lab is primarily concerned with understanding the molecular basis for the intracellular trafficking of the core components of human telomerase: human telomerase RNA (hTR), and human telomerase reverse transcriptase (hTERT). Significant progress has been made in identifying and characterizing the trafficking patterns that telomerase components follow throughout the cell cycle. This dissertation work focuses on understanding the mechanisms responsible for telomerase recruitment to the telomere. We hypothesized that telomerase recruitment is facilitated by dynamic association of the enzyme with core telomere binding proteins. Fluorescence microscopy based in vivo localization studies were employed in a variety of assays to assess the intrinsic roles of telomerase components, as well as factors residing at telomeres, in facilitating recruitment to telomere ends. In pursuit of this overall objective, it was determined that the hTERT N-DAT domain, TCAB1 (recently discovered telomerase component that resides at Cajal bodies), and TPP1 (one of six core telomere binding proteins), work together to facilitate telomerase recruitment. We also discovered novel coilin-positive nuclear bodies; we call telomerase induced bodies (TIBs). These TIBs are specific to telomerase components and are found at telomeres. hTERT mutants incapable of inducing TIBs are deficient in the ability to traffic to telomeres. This suggests that TIBs play a critical role in telomerase delivery to telomeres. Collectively, the findings contained within this thesis support a model whereby telomerase recruitment to telomeres involves dynamic interactions between telomerase components and at least one recruitment factor residing at the telomere.