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Antiestrogens stimulate expression of transiently transfected and endogenous genes in rat pituitary tumor cell lines
1Howard Hughes Medical Institute Laboratory, Brigham and Women's Hospital, Boston, MA.
Abstract:
Tamoxifen, nafoxidine, and clomiphene (1 x 10(-5) M) cause 5- to 15-fold increases in transient expression of plasmids transfected into rat somatomammotrophic pituitary tumor cell lines. To be effective, the antiestrogen must be present during the calcium phosphate transfection though it does not enhance the nuclear uptake or stability of transfected plasmid. The effect occurs with mammalian (rat growth hormone, mouse metallothionein I) or viral (thymidine kinase, Rous sarcoma virus) promoters and is inhibited by prior exposure of cells to high concentrations of estradiol but not glucocorticoid, progesterone or testosterone. Cis-tamoxifen, a conformation with much lower affinity for the estrogen receptor, has only one-fifth the effect of tamoxifen. Neither estradiol nor diethylstilbestrol have similar effects. Tamoxifen also increases endogenous rat growth hormone mRNA in these pituitary tumor cell lines. Transient expression in a number of other cell lines (JEG-3, COS-7, PC-12) is unaffected by tamoxifen suggesting the effect may be cell-type specific though MCF-7 cells are slightly responsive. The mechanism for the potent stimulation of gene transcription by these agents is not apparent but may be relevant to the mechanism of action of these agents as estrogen antagonists in vivo.
Insights
Anti-estrogens like tamoxifen significantly boost gene expression in specific pituitary tumor cells. This effect, dependent on the estrogen receptor, highlights a novel mechanism for gene transcription regulation.
Area of Science:
- Molecular Biology
- Endocrinology
- Pharmacology
Background:
- Estrogen receptor (ER) antagonists are crucial in hormone-dependent therapies.
- Understanding the molecular mechanisms of ER antagonists is vital for optimizing their therapeutic use.
- Gene expression regulation is a complex process influenced by various cellular and external factors.
Purpose of the Study:
- To investigate the effect of anti-estrogens on gene expression in pituitary tumor cell lines.
- To elucidate the role of the estrogen receptor in mediating this gene expression modulation.
- To explore the potential therapeutic implications of anti-estrogen-induced gene transcription.
Main Methods:
- Transfection of plasmid DNA into rat somatomammotrophic pituitary tumor cell lines.
- Treatment with anti-estrogens (tamoxifen, nafoxidine, clomiphene) and other steroid hormones.
- Analysis of transient gene expression using various promoters (mammalian and viral).
- Assessment of endogenous gene expression (rat growth hormone mRNA).
Main Results:
- Tamoxifen, nafoxidine, and clomiphene increased transient plasmid expression 5- to 15-fold.
- The effect required the presence of anti-estrogens during transfection and was mediated by the estrogen receptor.
- Estradiol inhibited the anti-estrogen effect, while other steroids did not.
- Cis-tamoxifen showed reduced activity, supporting the role of estrogen receptor affinity.
- Tamoxifen also upregulated endogenous rat growth hormone mRNA.
- The effect was largely specific to pituitary tumor cell lines, with slight responsiveness in MCF-7 cells.
Conclusions:
- Anti-estrogens potently stimulate gene transcription in specific pituitary tumor cell lines.
- This stimulation is mediated through the estrogen receptor pathway.
- The findings suggest a novel mechanism of action for estrogen antagonists with potential therapeutic relevance.