Cell cycledependent modulation of telemerase activity in tumor cells

Abstract

Telomerase is a ribonucleoprotein complex that is thought to add telomeric repeats onto the ends of chromosomes during the replicative phase of the cell cycle. We tested this hypothesis by arresting human tumor cell lines at different stages of the cell cycle. Induction of quiescence by serum deprivation did not affect telomerase activity. Cells arrested at the G₁/S phase of the cell cycle showed similar levels of telomerase to asynchronous cultures; progression through the S phase was associated with increased telomerase activity. The highest level of telomerase activity was detected in S-phase cells. In contrast, cells arrested at G₂/M phase of the cell cycle were almost devoid of telomerase activity. Diverse cell cycle blockers, including transforming growth factor β 1 and cytotoxic agents, also caused inhibition of telomerase activity. These results establish a direct link between telomerase activity and progression through the cell cycle.