Breast Cancer Research and Treatment

, Volume 93, Issue 3, pp 227–236

Cyclic Induction of Senescence with Intermittent AZT Treatment Accelerates both Apoptosis and Telomere Loss

  • Hyun Jung Ji
  • Sun Young Rha
  • Hei Cheul Jeung
  • Sang Hwa Yang
  • Sung Whan An
  • Hyun Cheol Chung
Report

Abstract

Background. 3′-azido-2′,3′-dideoxythymidine (AZT) is phosphorylated intracellularly to 3′-azido-3′-deoxythymidine-5-triphosphate (AZT-TP), which is incorporated into telomeric DNA, thereby blocking chain elongation. AZT is also known to inhibit reverse transcriptase, as well as other cellular enzymes including DNA polymerase γ, thymidine kinase, and telomerase.

Methods. We induced cancer cell senescence by treating MCF-7 cells with AZT in dosages of IC10 and IC20 for an extended period (about 120 population doublings (PD)). We then investigated the sequential changes in cellular growth, expression of telomerase subunits and transcription factors (c-Myc, Mad1), telomerase activity and telomere length.

Results. Senescence, apoptosis, growth delay, inhibition of telomerase activity and shortening of telomere length were all observed in a dose- and time-dependent manner. After the onset of senescence, the apoptosis rate increased slowly during early PDs. In contrast to senescence, the apoptotic rate showed little change after AZT removal, while it increased suddenly and significantly in a dose-dependent manner upon the second introduction of AZT. Continuous shortening of the telomeric length was observed with AZT, and, upon re-exposure to AZT, shortening of the telomere occurred more rapidly than with first exposure. Of the telomerase subunits, telomerase reverse transcriptase (hTERT) and c-Myc were the first to show a reduction in activity after AZT treatment, followed by changes in hTER , Mad1 and hTEP-1.

Conclusion. Cyclic treatment with AZT initially suppressed hTERT and c-Myc, followed by suppression of hTER, Mad1 and hTEP-1. Furthermore, the treatment accelerated both telomere loss and apoptosis, even when administered at a senescence-inducing dosage level.

Key words

apoptosis hTERT senescence telomerase telomere 

Abbreviations

AZT

3′-azido-2′,3′-dideoxythymidine

AZT-TP

3-azido-3-deoxythymidine-5-triphosphate

CHAPS

3-[(3-cholamidopropyl)dimethylammonio]-1-propane-sulfonate

EGTA

ethylene glycol-bis(β-aminoethyl Ether)

hTER

telomerase RNA

hTERT

telomerase reverse transcriptase

TEP

telomerase-associated protein

TRAP

telomeric repeat amplification protocol

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Copyright information

© Springer 2005

Authors and Affiliations

  • Hyun Jung Ji
    • 1
    • 2
    • 4
  • Sun Young Rha
    • 1
    • 2
    • 4
  • Hei Cheul Jeung
    • 1
    • 2
    • 4
  • Sang Hwa Yang
    • 1
    • 4
  • Sung Whan An
    • 1
  • Hyun Cheol Chung
    • 1
    • 2
    • 3
    • 4
  1. 1.Cancer Metastasis Research Center, Young Cancer CenterYonsei University College of MedicineSeoulKorea
  2. 2.Brain Korea 21 Project for Medical ScienceYonsei University College of MedicineSeoulKorea
  3. 3.Department of Internal MedicineSeoulKorea
  4. 4.Yonsei University College of MedicineYonsei Cancer CenterSeoulKorea
  5. 5.Cancer Metastasis Research Center, Young Cancer CenterYonsei University College of MedicineSeoulKorea

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