Telomerase Activity in HL-60 Cells After Treatment with Differentiating Agents

Kim, In Ho; Kim, Sook Ja; Cheong, Hee Jeong; Park, Sung Kyu; Lee, Gyu Taeg; Won, Jong Ho; Suh, Won Suk; Baick, Seung Ho; Hong, Dae Sik; Park, Hee Sook

Abstract

BACKGROUND
Telomeres are repetitive DNA fragments at the termini of chromosomes functioning as stabilizing elements of the DNA. A ribonucleoprotein polymerase, called telomerase, is responsible for the synthesis of such telomeric repeats in embryo and germ cells. During ontogenesis of most normal human somatic cells, there exists a physiological telomerase repressing mechanism. In contrast, malignant cells are characterized by an unlimited progressive potential. Certain physiological agents, such as all-trans retinoic acid (ATRA), 13-cis retinoic acid (13-cisRA), 1alpha-25 dihydroxy vitamin D3 (VD3) and cytosine arabinoside (Ara-C), promote further differentiation of leukemic cells into mature granulocytes and monocytes and subsequently undergo apoptosis.
METHODS
To determine if a potential linkage is present between telomerase regulation and the differentiation of malignant hematopoietic cells, the changes in telomerase activity during the maturation of HL-60 cells induced by ATRA, 13-cisRA, VD3 and Ara-C were investigated.
RESULTS
Differentiating agents induce HL-60 cells to differentiate into CD11b+ granulocytes and monocyte/macrophages, respectively. Approximately 98% of HL-60 cells acquired the expression of CD11b+ antigen after ATRA, 13-cisRA or Ara-C treatment for 5 days. After 1 day treatment with differentiating agents, no significant difference in telomerase activity was shown between untreated and treated HL-60 cells. A dramatic inhibition of telomerase activity occurred at 3 days treatment of ATRA compared to untreated HL-60 cells. Longer treatment for 5 days with differentiating agents resulted in further decrease of telomerase activity. However, telomerase activity in HL-60 cells was decreased slightly by the VD3 or Ara-C treatment, even though for 5 days. No evidence of differentiation and slight decrease of telomerase activity were observed in ATRA-treated K-562 cells for 5 days. These decrease of telomerase activity were dependent on the incubation time and dose.
CONCLUSION
These data clearly show the role of telomerase activity during the differentiation of HL-60 cells. This in vitro model can be useful for studies of the mechanisms controlling telomerase activity and in the search for physiological telomerase modulators.