Telomere position effect in normal human cells

Replication of human somatic cells is accompanied by progressive shortening of telomeres, which finally leads to the activation of a DNA damage response and the phenotype of senescence. Senescent cells are characterized by a viable growth arrest and an altered expression profile that are suggested to affect integrity and function of tissues thus contributing to organismal aging and age-related pathologies. The finding that telomere-adjacent genes are usually repressed and can be activated by epigenetic remodeling of the chromatin upon telomere shortening (telomere position effect, TPE) has lead to the intriguing notion that telomere length itself might regulate the onset of changes associated with aging. In the human system, TPE so far has only been studied in tumor cell lines with reporter genes adjacent to artificially seeded telomeres lacking subtelomeric regions. Therefore, the objective of this project is to investigate TPE in a more "natural" system, in normal human cells. Following specific aims will be pursued: First, it will be verified that TPE actually exists in normal human diploid cells, using a reporter system. Second, endogenous genes regulated by TPE will be identified in several normal human cell strains with a microarray containing the most telomeric candidate genes of all human chromosomes. Third, a screen for factors required for establishment and maintenance of TPE will be performed in a human tumor cell line harboring a telomere-adjacent reporter construct using an shRNA library. The identified genes will then be tested in normal diploid human cells, both with regard to a reporter construct and to endogenous genes regulated by TPE. Further investigation will strongly depend on the specific factors identified in aim 2 and 3. All together, the results of this project will help to elucidate the mechanisms leading to the dysfunctional phenotype of aged cells, which is indispensable for targeted therapeutic interventions to counteract the adverse side effects of aging.