Normal human cells can count the number of time they divide and eventually stop this process. This mechanism resides in the length of their telomeres, a DNA and protein structure present at the end of chromosomes. Telomeres are protecting chromosomes from degradation, like the plastic envelop present at the ends of our shoelaces. However in normal cells, telomeres cannot be replicated due to the absence of an enzyme called telomerase. When normal cells divide, telomeres become shorter which eventually leads to cell death, a bit like if one was chipping off a portion of the shoelaces until they are too short to be used. More than 85% of cancer cells have reactivated telomerase. We have evidences that normal human cells express a negative regulator of telomerase which is inactivated in tumor cells. The goal of our project is to identify this regulator and determine how cancer cells have eliminated it. This could lead to the development of new therapeutic approaches with very few side effects since normal cells do not express telomerase.