Deregulation of estrogen induced telomerase activity in tamoxifen-resistant breast cancer cells

  • Authors:
    • Woo-Chan Park
    • Hong Liu
    • Jennifer MacGregor Schafer
    • V. Craig Jordan
  • View Affiliations

  • Published online on: November 1, 2005     https://doi.org/10.3892/ijo.27.5.1459
  • Pages: 1459-1466
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Abstract

Telomerase, a ribonucleoprotein enzyme that functions as a reverse transcriptase, is detected exclusively in immortal cells such as germ cells, stem cells and cancer cells. Telomerase activity is present in almost all human cancers. Telomerase activation is considered to be essential to maintain the integrity of the replicating tumor cell and to establish immortality. Based on this concept antiestrogen should initially regulate estrogen-stimulated telomerase but the enzyme would be expected to be constitutive in tamoxifen-resistant tumor cells. We have studied the estrogen regulation of telomerase in T47D:A18 breast cancer cells with a TRAPEZE Telomerase detection kit. Estradiol significantly increased telomerase activity after a 2-day treatment. Telomerase activity induced by estradiol was up to 10-fold higher within 4 days. Antiestrogens 4-hydroxytamoxifen (4-OHT) and ICI 182,780 were inactive alone and significantly blocked estradiol-stimulated increase in telomerase. These effects were correlated with changes in cell replications and changes in the cell cycle. In contrast, 4-OHT resistant T47D:A18 cells (T47D:A18/4-OHT, cultured in 1 µM 4-OHT for 6 months) grew spontaneously and had no changes in the cell cycle with estrogen treatment. The estrogen receptor (ERα) was present and still regulated at an estrogen responsive luciferase reporter gene with estrogen despite the fact that progesterone receptor was not increased in response to estradiol in T47D:A18/4-OHT cells. However, telomerase activity was increased about 40-fold in T47D:A18/4-OHT cells and this was not regulated by ICI 182,780. We conclude that the differential regulation of telomerase gene might be an important transition for tamoxifen resistance in T47D:A18 breast cancer cells.

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November 2005
Volume 27 Issue 5

Print ISSN: 1019-6439
Online ISSN:1791-2423

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Spandidos Publications style
Park W, Liu H, MacGregor Schafer J and Jordan VC: Deregulation of estrogen induced telomerase activity in tamoxifen-resistant breast cancer cells. Int J Oncol 27: 1459-1466, 2005.
APA
Park, W., Liu, H., MacGregor Schafer, J., & Jordan, V.C. (2005). Deregulation of estrogen induced telomerase activity in tamoxifen-resistant breast cancer cells. International Journal of Oncology, 27, 1459-1466. https://doi.org/10.3892/ijo.27.5.1459
MLA
Park, W., Liu, H., MacGregor Schafer, J., Jordan, V. C."Deregulation of estrogen induced telomerase activity in tamoxifen-resistant breast cancer cells". International Journal of Oncology 27.5 (2005): 1459-1466.
Chicago
Park, W., Liu, H., MacGregor Schafer, J., Jordan, V. C."Deregulation of estrogen induced telomerase activity in tamoxifen-resistant breast cancer cells". International Journal of Oncology 27, no. 5 (2005): 1459-1466. https://doi.org/10.3892/ijo.27.5.1459