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Treatment of MCF-7 cells, a human mammary carcinoma cell line, with phorbol ester [12-O-tetradecanoylphorbol-13-acetate (TPA)] or calcium ionophore (A23187) was associated with striking effects on levels of estrogen receptor (ER) mRNA, specific binding of 17β-[3H]estradiol ([3H]E2), and immunoreactive ER.

TPA (10−7 M) caused a time-dependent reduction of ER mRNA which was below the level of detection after 9 h. Similar effects of TPA appeared at levels of specific binding of [3H]E2 as well as immunoreactive ER. In contrast, TPA induced an increase in mRNA for β-actin. Incubation of MCF-7 cells with increasing concentrations of TPA (1011-10−7 M) was associated with biphasic effects on ER mRNA and proteins. Levels of immunoreactive progesterone receptors (PR) were induced by E2 (10−9 M) in a time-dependent manner. In the presence of TPA (10−7 M), where ER levels were suppressed, no induction of PR was observed.

Removal of TPA (10−7 M) after 10 h (ER mRNA) or 22 h (ER proteins) of treatment was associated with a continued suppression of both mRNA and protein levels during the entire incubation period (48 h).

Treatment with A23187 (2 × 10−7 M) also caused a timedependent down-regulation of levels of ER mRNA and proteins. These effects occurred somewhat more slowly than those of TPA. Levels of β-actin mRNA were not changed by this treatment.

These results indicate that changes in estrogen sensitivity are mediated by calcium-dependent protein kinases in human mammary carcinoma MCF-7 cells.

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Copyright © 1991 by The Endocrine Society
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