Superinduction of c-fos gene expression by estrogen in cultured guinea-pig endometrial cells requires priming by a cycloheximide-dependent mechanism.

Abstract

The c-fos gene expression is rapidly induced by various mitogenic agents and protein synthesis inhibitors in many cell types. Estradiol-17 beta can induce c-fos gene expression in breast cancer cell lines and in the uterus in vivo, but not in cultured guinea-pig endometrial cells. Using this model, we investigated whether a protein synthesis inhibitor, cycloheximide, could induce the c-fos gene and permit a superinduction by estrogens. In the presence of cycloheximide (10 micrograms/ml), protein synthesis was inhibited at 95% within the first hour. From 190 min after the addition of estradiol-17 beta or diethylstilbestrol (10(-8) M) and cycloheximide (10 micrograms/ml), there was a significant increase (ranging from 3- to 5-fold) of the c-fos messenger RNA level (2.2 kilobase in size), compared with the level in cells treated with cycloheximide alone. Nonestrogenic steroid hormones and estradiol-17 alpha were unable to induce c-fos gene expression in the presence of cycloheximide. The effect of estradiol-17 beta observed in the presence of cycloheximide was completely abolished by 4-hydroxy-tamoxifen or by Ly 156758 or by ICI 164384 (10(-6) M). The c-fos mRNAs were rather stable in cells treated with cycloheximide for 2 h (half-life = 51 +/- 6 min) and there was no further increase in the c-fos messenger RNA stability after the addition of cycloheximide plus estradiol-17 beta (half-life = 40 +/- 3 min). The overall results suggest a response at the transcriptional level. In conclusion, cycloheximide transmits activating signals to the c-fos gene which act as priming elements to allow the estrogen action in cultured guinea-pig endometrial cells.

Stimulation of GCMa and syncytin via cAMP mediated PKA signaling in human trophoblastic cells under normoxic and hypoxic conditions

“…4A). This increase of GCMa transcripts is comparable to an increase of transcript amounts of several proteins in response to cycloheximide treatment, like c‐fos [29], presumably due to mRNA stabilization. Syncytin transcript levels increased slightly after cAMP treatment for up to 8 h (Fig.…”

During development, 17alpha-estradiol is a potent estrogen and carcinogen.

“…Even though the binding for type I estrogen receptor sites by E2-177a is diminished, it is unable to compete for type II sites (22). The induction of gene expression such as c-fos in rat uterus and guinea pig endometrium is specific for E2-17P (23,24 the mesenchyme cannot be discounted (5,(13)(14)(15)19). Other possible nongenomic mechanisms of action for E2-17a include conversion to E2-17P (27), common reactive metabolites with E2-17P (5,(11)(12)(13), aneuploidy (5,(7)(8)(9), and the rapid release of intracellular calcium (28).…”

A pharmacological review of raloxifene

“…In this regard, raloxifene also blocks the uterinestimulatory effects of tamoxifen in rats [40] . Other stimulatory effects of estrogen in the uterine endometrium are antagonized by raloxifene as well including endometrial c-fos expression [41] and glycogen synthesis [42] . Raloxifene also antagonizes chlamydial H .…”