Induction of telomerase activity in stimulated human lymphocytes precedes expression of topoisomerase II alpha

Telomerase activity has been demonstrated in human immortal cell lines and in tumors, whereas it is generally absent from normal tissues, with the exception of germ cells. Low levels have also been detected in blood and skin cells. In this report we describe up-regulation of telomerase activity in normal human blood lymphocytes by mitogen stimulation. After 24 h of mitogen treatment a strong induction was detectable using the PCR-based telomeric repeat amplification protocol. The level of activity remained almost constant when the cultivation lasted 72 h. By contrast, topoisomerase II alpha was induced later with a maximum expression after 48-72 h. Our data show that telomerase can be induced in normal peripheral lymphocytes prior to expression of the S-phase typical protein topoisomerase II alpha indicating that telomere elongation might be initiated before DNA replication.