Tamoxifen accelerates proteasomal degradation of O6- methylguanine DNA methyltransferase in human cancer cells

Ching Chuan Kuo, Jin Fen Liu, Her Shyong Shiah, Ma Li-Chen, Jang Yang Chang

Research output: Contribution to journalArticle

19 Citations (Scopus)

Abstract

Tamoxifen, a synthetic triphenyl-ethylene compound, is a member of a class of anticancer drugs known as selective estrogen receptor modulators. It may block tumor growth by mimicking estrogen and binding to the estrogen receptors, preventing cancerous growth. Clinical studies have demonstrated that a combination chemo/hormonal therapy regimen with tamoxifen and O 6-alkylating drugs increased the tumor response rate in cancer patients. The mechanism of action of this combined regimen remains undefined. In this study, we demonstrated that treatment of human colorectal HT-29 carcinoma cells with tamoxifen decreased the repair activity and expression level of O6-methylguanine DNA methyltransferase (MGMT) protein in a concentration- and time-dependent manner. This inhibition was also shown in other malignant human cells, regardless of their estrogen receptor status. Furthermore, MGMT inactivation by tamoxifen was associated with a significantly increased susceptibility of cells to 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU). No alteration in MGMT mRNA levels was observed in tamoxifen-treated cells. The half-life of MGMT protein was markedly decreased in the presence of tamoxifen. Tamoxifen-induced MGMT degradation could be blocked by MG-132, a proteasome inhibitor. An increased level of ubiquitinated MGMT protein was found after tamoxifen treatment. We conclude that tamoxifen decreased the MGMT protein level by accelerating protein degradation through the ubiquitin-dependent proteasomal pathway. These findings provide a strong rationale for combined chemo/hormonal therapy with tamoxifen and BCNU in the treatment of human cancers.

Original languageEnglish
Pages (from-to)2293-2300
Number of pages8
JournalInternational Journal of Cancer
Volume121
Issue number10
DOIs
Publication statusPublished - Nov 15 2007
Externally publishedYes

Fingerprint

Methyltransferases
Tamoxifen
Protein Methyltransferases
DNA
Neoplasms
Carmustine
Terphenyl Compounds
Estrogen Receptors
O-(6)-methylguanine
Selective Estrogen Receptor Modulators
Therapeutics
HT29 Cells
Proteasome Inhibitors
Growth
Ubiquitin
Pharmaceutical Preparations
Proteolysis
Half-Life
Estrogens
Carcinoma

Keywords

  • BCNU
  • MGMT
  • Proteasomal pathway
  • Tamoxifen
  • Ubiquitination

ASJC Scopus subject areas

  • Oncology
  • Cancer Research

Cite this

Tamoxifen accelerates proteasomal degradation of O6- methylguanine DNA methyltransferase in human cancer cells. / Kuo, Ching Chuan; Liu, Jin Fen; Shiah, Her Shyong; Li-Chen, Ma; Chang, Jang Yang.

In: International Journal of Cancer, Vol. 121, No. 10, 15.11.2007, p. 2293-2300.

Research output: Contribution to journalArticle

Kuo, Ching Chuan ; Liu, Jin Fen ; Shiah, Her Shyong ; Li-Chen, Ma ; Chang, Jang Yang. / Tamoxifen accelerates proteasomal degradation of O6- methylguanine DNA methyltransferase in human cancer cells. In: International Journal of Cancer. 2007 ; Vol. 121, No. 10. pp. 2293-2300.
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