[Telomere and telomerase in the differentiation of leukemic cell lines].

By using three hematopoietic cell lineages including myelomonocytic, erythroblastic and megakaryocytic differentiation, downregulation of telomerase activity was found to be a general response to the induction of differentiation. The decrease in telomerase activity occurred as early as 24h when HL-60 and K562 cells were cultured in the presence of VD3, ATRA and hemin and completely disappeared after 3 days. On the other hand MEG-01 cells showed dramatic inhibition of telomerase activity after 6 days of culture with TPA. Analysis of telomeric DNA in HL-60 cells and K562 cells demonstrated no remarkable loss of telomeric DNA with cellular differentiation while loosing telomerase activity. The repression of telomerase is one of many molecular events during the complex process of cellular differentiation, and testing of additional cell lines that are capable of differentiation will be helpful for understanding the mechanisms of telomerase control.