| Telomerase is a specialized ribonucleoprotein complex that uses its RNA subunit to synthesize the repetitive G-rich DNA found at the 3' ends of chromosomes. Most cancer cells, approximately 90%, upregulate telomerase to attain cellular immortalization, whereas, telomerase activity is undetected in normal somatic cells. Due to the differential expression pattern of telomerase between normal and tumor cells, telomerase has received significant attention as a universal cancer target. Additionally, since telomerase is expressed in stem cells during all stages of life, telomerase has been linked to the process of aging and age-related diseases. Despite the great interest in telomerase, current understanding of telomerase and its regulation remains limited. The research presented here elucidates how important factors of different cellular processes play a role in the regulation of telomerase at the post-translational level.In the first part of this dissertation, we identified and characterized promising compounds as telomerase inhibitors. One such class of compounds, tanshinone derivatives, proved to inhibit telomerase due to their ability to undergo redox cycling and generate reactive oxygen species. Studies using ortho-quinone containing compounds further indicated that reactive oxygen species can damage telomerase by oxidizing its protein subunit. Inactivation of telomerase by these compounds was sensitive to catalase, suggesting that H2O2 is a mediator of their inhibition. Results from these studies, reported in Chapter 3, indicate that telomerase is sensitive to oxidative damage and that this regulation can be implicated in both cancer and aging.In addition to identifying telomerase inhibitors, we were interested in the identification of cellular pathways that control telomerase function. Chapter 4 reports studies showing that caspases are negative regulators of telomerase. Telomerase was shown to be cleaved by caspases-6 and -7 both in vitro and in apoptotic cancer cells. Additionally, mutagenesis studies suggested that caspase resistant hTERT mutants have different effects on apoptosis threshold in cancer cells.These studies provide a basis to better understand how telomerase is regulated in the processes of cancer, aging, and age-related disorders. Further understanding of the biological significance of such post-translational regulations of telomerase will provide a rational approach toward modulating the enzyme and improving therapeutic treatment. |
