Telomerase activity and telomeric states in cell proliferative and differentiative mechanisms.

Telomeres are DNA-protein complexes playing an important role in the maintenance of genome integrity. Telomerase is the enzyme acting as a template for addition of new telomeric repeats; this addition is essential for those cellular populationsthat have proliferative and differentiative potential. Telomerase and associated proteins are essential in responseto DNA damage. Moreover, telomere-associated proteins as TRF2 are involved in all signalling transduction pathway whichdrive cellular proliferation and differentiation. In somatic cells,shortening of telomeres contributes to the onset of senescence or apoptosis; tissues which require cellular renewal expresstelomerase activity in order to compensate telomeric shortening. Telomerase activity remains detectable in adult stem cellspopulations and in cells with high proliferative potential. Reactivationof telomerase activity may be a pathogenetic characteristic of neoplastic cellular population favouring tumoral proliferationand progression.