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Relationship between tamoxifen-induced transforming growth factor beta 1 expression, cytostasis and apoptosis in
R R Perry1, Y Kang, B R Greaves
1Division of Surgical Oncology, Eastern Virginia Medical School, Norfolk 23507, USA.
Abstract:
Previously we have shown that tamoxifen (TAM) induces morphological and biochemical changes typical of apoptosis in oestrogen receptor (ER)-positive MCF-7 or ER-negative MDA-231 human breast cancer cells. In this study the effects of TAM on expression of transforming growth factor beta 1 (TGF-beta 1) were correlated with the effects on cell cycle kinetics and apoptosis. TAM had similar biphasic effects on both cell lines. Short-term (< 6 h) TAM incubation resulted in a slight decrease in TGF-beta 1 protein despite an increase in TGF-beta 1 mRNA and was associated with an increase in cells in S-phase. No apoptotic effects were noted. Longer (> or = 12 h) TAM incubation induced TGF-beta 1 protein (about 3-fold) and mRNA expression (about 2-fold) in both cell lines, and was associated with G1/G0 blockade and induction of apoptosis. The accumulation of TAM-induced TGF-beta 1 mRNA was increased by cycloheximide, but was not affected by 17 beta-oestradiol. Long-term incubation with TAM had no significant effect on TGF-beta 1 gene copy number. TAM-induced internucleosomal DNA cleavage was inhibited in both cell lines by the addition of an anti-TGF-beta 1 antibody. TAM has dose- and time-dependent effects on TGF-beta 1 expression associated with changes in cell cycle kinetics. These effects are independent of ER status and may be the result of a direct regulatory effect of TAM on TGF-beta 1 transcription. It also appears that induction of TGF-beta 1 plays an important role in TAM-induced apoptosis in breast cancer cells.
Insights
Tamoxifen (TAM) affects breast cancer cells by altering transforming growth factor beta 1 (TGF-beta 1) expression, leading to cell cycle changes and apoptosis. These effects are independent of oestrogen receptor status and highlight TGF-beta 1's role in TAM-induced cell death.
Area of Science:
- Oncology
- Molecular Biology
- Cell Biology
Background:
- Tamoxifen (TAM) is a widely used drug for breast cancer treatment.
- TAM is known to induce apoptosis in both oestrogen receptor (ER)-positive and ER-negative breast cancer cells.
- The precise mechanisms underlying TAM's effects on cell cycle kinetics and apoptosis require further elucidation.
Purpose of the Study:
- To investigate the correlation between tamoxifen's effects on transforming growth factor beta 1 (TGF-beta 1) expression and its impact on cell cycle kinetics and apoptosis in human breast cancer cells.
- To determine if these effects are dependent on oestrogen receptor (ER) status.
- To explore the role of TGF-beta 1 in tamoxifen-induced apoptosis.
Main Methods:
- Treatment of MCF-7 (ER-positive) and MDA-231 (ER-negative) human breast cancer cells with tamoxifen (TAM) for varying durations.
- Assessment of TGF-beta 1 mRNA and protein levels using quantitative methods.
- Analysis of cell cycle kinetics via flow cytometry.
- Induction and inhibition of apoptosis using specific agents and antibodies.
- Evaluation of TGF-beta 1 gene copy number.
Main Results:
- TAM exhibited biphasic effects on TGF-beta 1 expression and cell cycle progression in both cell lines.
- Short-term TAM exposure (< 6 h) decreased TGF-beta 1 protein but increased mRNA, correlating with S-phase increase and no apoptosis.
- Longer TAM exposure (>= 12 h) induced both TGF-beta 1 protein (3-fold) and mRNA (2-fold), leading to G1/G0 blockade and apoptosis.
- TAM-induced DNA cleavage was significantly inhibited by an anti-TGF-beta 1 antibody.
- Effects were independent of ER status.
Conclusions:
- Tamoxifen exerts dose- and time-dependent effects on TGF-beta 1 expression, influencing breast cancer cell cycle kinetics.
- The induction of TGF-beta 1 appears to be a key mediator in tamoxifen-induced apoptosis, irrespective of ER status.
- Tamoxifen may directly regulate TGF-beta 1 transcription, contributing to its anti-cancer effects.