218. Lack of correlation between telomere length and telomerase activity and expression in leukemic cells

Telomerase is a ribonucleoprotein complex that allows cells to grow indefinitely and it is believed that reactivation of telomerase plays an important role in immortalization and carcinogenesis. The aim of this work was to analyze the telomerase expression and activity along with telomere length in leukemic cells at the moment of diagnosis and during therapy. Cells were isolated from peri-pheral blood and bone marrow of children with ALL and ANNL. Controls included normal peripheral blood lymphocytes and myeloblast cell line K562. Telomerase expression has been studied by RT-PCR using specific primers for telomerase reverse trancriptase gene (hTERT), telomerase template RNA (hTR) and telomerase associated protein gene (TP1). Telomerase repeat amplification protocol-TRAP and PCR-ELISA (Roche) were used for analysis of telomerase activity. For studying telomere length Telo TAGGG Telomere Length assay (Roche) was used. High telomerase expression and activity has been found in cells of ALL and ANLL as well as in myeloblast cell line K562. Only in some cases of peripheral blood lymphocytes from healthy individuals low telomerase expression and activity has been detected. Chemiluminescent detection of terminal restriction fragments (TRF) from DNA isolated from ALL cells showed variable pattem of telomere length. The ALL cell appeared to have both long and short telomere lengths, in contrast to normal lymphocytes producing limited pattem of TRF (short telomeres). The ANLL cells produced predominantly short telomere pattern despite high telomerase activity and expression. Telomerase activity was diminished in patients in remission during chemotherapy. Telomere length in ALL cells was shorter in remission as compared to the time of diagnosis. It can be concluded that high telomerase activity and expression in leukemic cells do not correlate with telomere length (TRF pattern). Grant support: The work was sponsored by KBN grants No 4P05B 072 17 and 6P05E 102 20