Down-regulation of telomerase activity in malignant lymphomas by radiationand chemotherapeutic agents

The effects of radiation and cytotoxic agents on telomerase activity in lym phoma cells were analyzed by a polymerase chain reaction-based telomeric re peat amplification protocol coupled with an enzyme-linked immunosorbent ass ay, reverse transcriptase-polymerase chain reaction for the expression of t he catalytic subunit of telomerase (hTERT), and by Western blot analysis in three lymphoma cell lines (Jurkat, Raji, CEM-6). Telomeric repeat amplific ation protocol-enzyme-linked immunosorbent assay demonstrated high basal le vels of telomerase activity in all cell lines compared to normal and activa ted peripheral blood lymphocytes. A significant decrease in telomerase acti vity was observed in all cell. lines after exposure to vincristine for 24 h ours. The decrease in telomerase activity paralleled the decrease in cell v iability in jurkat and CEM-6 cells but not in Raji cells. Radiation exposur e inhibited the telomerase activity of jurkat and CEM-6 cells whereas Raji cells were unaffected. Cell. cycle analysis demonstrated a significant G(2) /M arrest by cisplatin, VP-16, and vincristine. In contrast to the decline in telomerase activity, the level of hTERT RNA and protein increased. Furth ermore, the induction of hTERT was preceded by increased expression of the cyclin-dependent kinase inhibitor, p27/Kip1 protein, and p53. These results indicate that telomerase activity is down-regulated by anti-neoplastic age nts in lymphoma. cells, however expression of hTERT may not be correlated w ith telomerase activity. We also show that p27/Kip1 may be involved in the G(2)/M growth arrest induced by antineoplastic agents.