[Physiopathologic implications of telomerase]

Telomerase is a specialized RNA-directed DNA polymerase that extends telomeres of eukaryotic chromosomes. Telomerase gene expression is active in germinal, stem and tumoral cells and repressed in normal human somatic cells. Activation of telomerase involves immortalization, while repression of this enzyme involves the shortening of telomeres in each round of chromosomal replication. Telomere shortening constitutes a mechanism for cells to control cell division and the entrance in the replicative senescence state. If the expression of this enzyme is forced, senescent human cells will extend their life span reaching the immortalization and malignization of the cells. Activation or depression of telomerase activity has important implications in aging and cancer therapy. Telomerase regulation is a multifactorial process in which telomerase expression, post-translational protein-protein interactions and protein phosphorylation are involved.