Differential inhibition of telomerase activity during induction of differentiation in hematopoietic, melanoma, and glioma cells in culture.

Accumulating evidence indicates that telomerase activity is stringently repressed in normal human somatic cells but reactivated in cancers and immortal cells, suggesting that activation of telomerase activity may play a role in carcinogenesis and immortalization. Recently, down-regulation of telomerase activity by induction of differentiation has been reported for cells of pre-myelocytic and myelocytic leukemia as well as embryonic carcinoma. To gain further insight about the regulation of telomerase activity following induction of differentiation, telomerase activity was examined in a human hematopoietic progenitor cell line (D2), a melanoma cell line (CM73-36) and a glioma cell line (Ast812) before and after addition of differentiation inducing agents. The state of differentiation was assessed by growth inhibition and cell morphological maturation. Telomerase activity was assayed by a PCR-based telomeric repeat amplification protocol (TRAP). Our data show that telomerase activity was inhibited only in differentiation-induced D2 cells but not in differentiation-induced melanoma and glioma cells. A model for the differential inhibition of telomerase activity following induction of differentiation in different cancer cells will be presented.