Telomerase activity in normal human endothelial cells.

Telomerase, a ribonucleoprotein complex, adds hexameric repeats of 5' T T A G G G 3' to the ends of chromosomes called telomeres. Telomerase activity is present in germ cells but not in most somatic cells. An overwhelming majority of cancer cells show elevated levels of telomerase activity. Once thought to be cancer-cell specific, it is becoming apparent that many proliferating normal cells express telomerase activity. In this study, we demonstrate that normal human endothelial cells express telomerase activity: the activity is growth related. In quiescent, confluent cultures, the telomerase activity is repressed. Furthermore, the activity is lost upon subculturing of the endothelial cells in vitro. Finally, G2/M arrest induced by nocodazole treatment of endothelial cells abolished telomerase activity. Primary cultures of endothelial cells offer a powerful model to study the role, if any, of telomerase in normal cells.