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The ability to evade senescence is a hallmark of cancer. More recently senescence has been implicated in development and ageing as well as age-associated pathologies, suggesting a broader context for what was originally considered an in vitro artefact. With an ageing population and an increasing incidence of cancer, a better understanding of the mechanisms involved in senescence control is of huge interest. Telomere damage is a key driver of cellular senescence. Expression of a dominant negative mutant of TRF2 (TRF2ΔBΔM), one of the key components of the shelterin complex, depletes TRF2 from telomeres resulting in activation of the DNA damage response reminiscent of critical telomere shortening. The resultant persistent activation of DNA damage response pathways leads to the rapid development of a senescence phenotype. Using this method of prompt, homogeneous, premature senescence induction in primary human fibroblasts, a genome-wide loss of function shRNA screen was performed to identify novel regulators of senescence. Candidates identified in this primary screen were retested using an inducible form of the TRF2ΔBΔM system, and a high throughput siRNA custom library. Following a number of validation steps, XPO7, a nuclear exporter was identified as a potentially interesting candidate. Depletion of XPO7 extends the replicative lifespan of fibroblasts in culture and is capable of bypassing senescence induced by telomere damage, irradiation and oncogene expression (RasV12). Ectopic expression of XPO7 in proliferating primary fibroblasts triggers premature senescence with a characteristic senescence phenotype along with activation of a transcription pattern typical of oncogene induced senescence. Moreover, mutations in XPO7 are frequently observed in multiple cancer types including prostate cancer, ovarian cancer and some lymphomas, suggesting a potential role as a tumour suppressor. Open Access |
