Progesterone receptor replenishment in T47D human breast cancer cells. Roles of protein synthesis and hormone metabolism

Progestin stimulation of manganese superoxide dismutase and invasive properties in T47D human breast cancer cells

Superoxide dismutase (SOD) occurs in two intracellular forms in mammals, copper-zinc SOD (CuZnSOD), found in the cytoplasm, mitochondria and nucleus, and manganese superoxide dismutase (MnSOD), in mitochondria. Changes in MnSOD expression (as compared to normal cells) have been reported in several forms of cancer, and these changes have been associated with regulation of cell proliferation, cell death, and metastasis. We have found that progestins stimulate MnSOD in T47D human breast cancer cells in a time and physiological concentration-dependent manner, exhibiting specificity for progestins and inhibition by the antiprogestin RU486. Progestin stimulation occurs at the level of mRNA, protein, and enzyme activity. Cycloheximide inhibits stimulation at the mRNA level, suggesting that progestin induction of MnSOD mRNA depends on synthesis of protein. Experiments with the MEK inhibitor UO126 suggest involvement of the MAP kinase signal transduction pathway. Finally, MnSOD-directed siRNA lowers progestin-stimulated MnSOD and inhibits progestin stimulation of migration and invasion, suggesting that up-regulation of MnSOD may be involved in the mechanism of progestin stimulation of invasive properties. To our knowledge, this is the first characterization of progestin stimulation of MnSOD in human breast cancer cells.

Immunohistochemical labelling of steroid receptors in normal and malignant human endometrium

For several years it was generally believed that only a single estrogen receptor (ER) and progesterone receptor (PR) existed. However, the discovery of a new ER (ERbeta) with specificity for estrogens has induced new insights in the estrogen signalling system. Moreover, PR is expressed as two major isoforms, PR-A and PR-B that arise from alternative transcriptional starting sites within the same gene. Although PR-A and PR-B were thought to occur in similar amounts, it is now clear that they are differentially expressed and thus have distinct functions in several human tissues, including human endometrium. The ER and PR expression and distribution pattern might play an important role in normal endometrial function and pathogenesis and the expression and relationship of the two distinct ER's and PR's could be of essential clinical implications. Moreover, the imbalance in ERalpha/ERbeta expression and the PR-A/PR-B ratio might play an important role in endometrial transition and subsequently influence endometrial pathogenesis. The knowledge of the pattern of steroid receptors in human endometrial tissue is of extreme importance, since it might start a new field in hormone therapy of endometrial cancer.

Focal subnuclear distribution of progesterone receptor is ligand dependent and associated with transcriptional activity

The progesterone receptor (PR) is a critical mediator of progesterone action in the female reproductive system. Expressed in the human as two proteins, PRA and PRB, the receptor is a ligand-activated nuclear transcription factor that regulates transcription by interaction with protein cofactors and binding to specific response elements in target genes. We previously reported that PR was located in discrete subnuclear foci in human endometrium. In this study, we investigated the role of ligand in the formation of PR foci and their association with transcriptional activity. PR foci were detected in mouse uterus and normal human breast tissues and were more abundant when circulating progesterone was high. In human malignant tissues, PR foci were aberrant: foci were larger in endometrial cancers than in normal endometrium, and in breast cancers hormone-dependence was decreased. Chromatin disruption also increased foci size and decreased ligand dependence, suggesting that altered nuclear architecture may contribute to the aberrant PR foci observed in endometrial and breast cancers. In breast cancer cells, movement of PR into foci required exposure to ligand and was blocked by transcriptional inhibitors and by prolonged inhibition of proteasomal degradation. Foci contained PR dimers, and fluorescence resonance energy transfer demonstrated that PR foci contained the highest concentration of receptor dimers in the nucleus. PR in foci colocalized with transcription factors and nascent RNA transcripts only in the presence of ligand, and inhibition of coactivator recruitment inhibited PR foci formation. The demonstration that focal distribution of PR within the nucleus is associated with transcription suggests a link between the subnuclear distribution of PR and its transcriptional activity that is likely to be important for normal cellular function of PR.

The progestational and androgenic properties of medroxyprogesterone acetate: gene regulatory overlap with dihydrotestosterone in breast cancer cells

Introduction

Medroxyprogesterone acetate (MPA), the major progestin used for oral contraception and hormone replacement therapy, has been implicated in increased breast cancer risk. Is this risk due to its progestational or androgenic properties? To address this, we assessed the transcriptional effects of MPA as compared with those of progesterone and dihydrotestosterone (DHT) in human breast cancer cells.

Method

A new progesterone receptor-negative, androgen receptor-positive human breast cancer cell line, designated Y-AR, was engineered and characterized. Transcription assays using a synthetic promoter/reporter construct, as well as endogenous gene expression profiling comparing progesterone, MPA and DHT, were performed in cells either lacking or containing progesterone receptor and/or androgen receptor.

Results

In progesterone receptor-positive cells, MPA was found to be an effective progestin through both progesterone receptor isoforms in transient transcription assays. Interestingly, DHT signaled through progesterone receptor type B. Expression profiling of endogenous progesterone receptor-regulated genes comparing progesterone and MPA suggested that although MPA may be a somewhat more potent progestin than progesterone, it is qualitatively similar to progesterone. To address effects of MPA through androgen receptor, expression profiling was performed comparing progesterone, MPA and DHT using Y-AR cells. These studies showed extensive gene regulatory overlap between DHT and MPA through androgen receptor and none with progesterone. Interestingly, there was no difference between pharmacological MPA and physiological MPA, suggesting that high-dose therapeutic MPA may be superfluous.

Conclusion

Our comparison of the gene regulatory profiles of MPA and progesterone suggests that, for physiologic hormone replacement therapy, the actions of MPA do not mimic those of endogenous progesterone alone. Clinically, the complex pharmacology of MPA not only influences its side-effect profile; but it is also possible that the increased breast cancer risk and/or the therapeutic efficacy of MPA in cancer treatment is in part mediated by androgen receptor.

Progestin regulation of 11beta-hydroxysteroid dehydrogenase expression in T-47D human breast cancer cells

This study examined the enzymatic characteristics and steroid regulation of the glucocorticoid-metabolizing enzyme 11beta-hydroxysteroid dehydrogenase (11beta-HSD) in the human breast cancer cell line T-47D. In cell homogenates, exogenous NAD significantly increased the conversion of corticosterone to 11-dehydrocorticosterone, while NADP was ineffective. There was no conversion of 11-dehydrocorticosterone to corticosterone either with NADH or NADPH demonstrating the lack of reductase activity. In keeping with these results, RT-PCR analysis indicated a mRNA for 11beta-HSD2 in T-47D cells, while 11beta-HSD1 mRNA levels were undetectable. In T-47D cells treated for 24 h with medroxyprogesterone acetate (MPA), 11beta-HSD catalytic activity was elevated 11-fold, while estrone (E(1)), estradiol (E(2)) and the synthetic glucocorticoid dexamethasone (DEX) were ineffective. The antiprogestin mifepristone (RU486) acted as a pure antagonist of the progestin-enhanced 11beta-HSD activity, but did not exert any agonistic effects of its own. In addition, RT-PCR analysis demonstrated that MPA was a potent inducer of 11beta-HSD2 gene expression, increasing the steady-state levels of 11beta-HSD2 mRNA. Taken together, these results demonstrate that 11beta-HSD2 is the 11beta-HSD isoform expressed by T-47D cells under steady-state conditions and suggest the existence of a previously undocumented mechanism of action of progestins in breast cancer cells.

Preferential stimulation of human progesterone receptor B expression by estrogen in T-47D human breast cancer cells

Human progesterone receptor (PR) expression is controlled by two promoter regions giving rise to transcripts encoding PR A and B proteins. It is unknown whether estrogen and progesterone, the major physiological modulators of PR expression, exert their effects equally on the PR promoters. The aim of this study was to analyze estrogen and progestin effects on PR promoters, PR-encoding transcripts, and PR A and B proteins in T-47D human breast cancer cells. The progestin ORG 2058 caused a prolonged decrease in transcription of the PR gene and also abrogated estrogen stimulation of PR transcription. Estradiol (E2) treatment increased the activity of the B but not the A promoter transfected into T-47D cells. ORG 2058 had no effect on the basal or E2-stimulated activity of either promoter. E2 caused a preferential increase in transcripts derived from promoter B, whereas progestins decreased the levels of all PR transcripts. E2 preferentially increased the concentration of the PR B protein and caused a decrease in the PR A/B ratio. This demonstration that estrogen and progestin independently control the synthesis of transcripts arising from the PR promoters and that estrogen alters the cellular PR A/B ratio provides possible mechanisms underlying the cell and tissue specificity of PR regulation.

Progestin stimulation of thymidine kinase in the human breast cancer cell line T47D

Our laboratory has previously reported that progestins stimulate growth of the human breast cancer cell line T47D. In an attempt to probe further into this stimulation, we are investigating progestin effects on thymidine kinase (EC 2.7.1.21), an enzyme known to be involved in growth regulation. This report relates our finding that progestins stimulate thymidine kinase activity, at physiological progestin concentrations, in a dose-responsive manner. Estradiol-17 beta also stimulates, but testosterone, hydrocortisone and aldosterone do not. The antiprogestin RU486 inhibits progestin stimulation, but also stimulates on its own. Maximal by 24 h, the progestin stimulation then falls off with time. Experiments with actinomycin D and cycloheximide suggest that the thymidine kinase stimulation depends on new RNA and protein synthesis. These data shed further light on progestin stimulation of the growth of human breast cancer. To our knowledge, this is the first report of progestin stimulation of thymidine kinase in human breast cancer cells.

Progestin induction of 17 beta-hydroxysteroid dehydrogenase enzyme protein in the T-47D human breast-cancer cell line

Steroid regulation of 17 beta-hydroxysteroid dehydrogenase (17-HSD) was studied in the T-47D human breast-cancer cell line, using a radioimmunoassay. In addition, 3 mRNA species (2.4, 1.4, and 0.9 kb) specific for the enzyme were shown to be present in these cells. All the synthetic progestins tested (ORG 2058, R5020, medroxyprogesterone acetate) significantly increased the immunoreactive enzyme protein concentration, while other types of steroids, such as testosterone, oestradiol and dexamethasone, were ineffective. The progestin-specific induction of 17-HSD was dose-related and was maximum in about 5 days. An antiprogestin, RU 486, when used in combination with synthetic progestins, blocked the progestin-induced increase of 17-HSD concentration very effectively. A good correlation was observed in the different experiments between the enzyme activity and the immunoreactive 17-HSD concentration. We conclude that progestins induce 17-HSD in T-47D cells and that the induction occurs via an increased accumulation of enzyme protein.

Progestins and androgens stimulate lipid accumulation in T47D breast cancer cells via their own receptors

Using electron microscopy, in the human breast cancer cell line T47D, the synthetic progestin R5020, and 5 alpha-dihydrotestosterone were shown to increase significantly the number of lipid droplets per cell section compared to control cells or estradiol- and dexamethasone-treated cells. Lipid accumulation, as measured by Oil Red O dying and by [2-14C]acetate incorporation, was observed at concentrations as low as 10 pM R5020 and 1 nM 5 alpha-dihydrotestosterone, and was always more abundant after progestin treatment. The progestin antagonist RU486 inhibited, in a dose-dependent manner, lipid accumulation initiated by the two hormones, whereas the androgen antagonist flutamide inhibited only the effect initiated by 5 alpha-dihydrotestosterone. Cytoplasmic lipid droplets accumulation was not observed in the BT20 breast cancer cell line, which contains neither progesterone nor androgen receptors. These results indicate that progestins and androgens increase lipid accumulation by interacting with their own receptor. Chromatographic analysis of [2-14C]acetate labeled lipids showed that R5020 and 5 alpha-dihydrotestosterone enhanced the accumulation of cellular triglycerides at least in part by increasing their synthesis and decreased the quantity of lipids released into the medium. To conclude, we have shown that progestins and androgens, via their own receptor, can induce the same triglyceride accumulation in T47D cells. This effect follows fatty acid synthetase induction and precedes cell growth inhibition, two responses also triggered by progestin and androgen in these cells.

Comparative effects of 17 beta-estradiol, progestin R5020, tamoxifen and RU38486 on lactate dehydrogenase activity in MCF-7 human breast cancer cells

The effects of 17 beta-estradiol (estradiol), synthetic progestin R5020 and their antagonists, tamoxifen (Tam) and synthetic RU38486 on lactate dehydrogenase (LDH) activity in MCF-7 human breast cancer cells during the growth period were studied. A specially developed quantitative cytochemical assay was used; LDH activity is expressed per cell, and is thus independent of the positive and negative growth effects of the hormones and antagonists. Estradiol and R5020 stimulated LDH activity after similar exposures (6-48 h) and the stimuli were concentration dependent over the range 10(-7) M to 10(-10) M. As for the antagonists, RU38486 stimulated LDH activity in much the same way as estradiol and R5020; Tam alone, on the other hand, does not stimulate LDH, but when added to estradiol, Tam inhibits estradiol mediated LDH activation. When present at half-stimulant concentration, estradiol + R5020 and estradiol + RU38486 exhibit additive effects on LDH activity. Thus LDH appears to be an interesting tool for the study of hormone and antagonist effects in MCF-7 breast cancer cells.

Progesterone metabolism in T47Dco human breast cancer cells--II. Intracellular metabolic path of progesterone and synthetic progestins

We show here that progesterone added to the medium of proliferating T47Dco human breast cancer cells is metabolized with a half life of 2-4h. The final metabolic product, 5 alpha-pregnan-3 beta,6 alpha-diol-20-one, (P-metabolite) is released into the medium. This structure suggested that the intracellular metabolism of progesterone involves the enzymes 5 alpha-reductase, 3 beta-hydroxysteroid dehydrogenase, and 6 alpha-hydroxylase. To investigate this pathway, the cells were incubated with a variety of potential substrates. In addition to progesterone, only precursors with the 5 alpha-configuration served as substrates for the enzymes leading to P-metabolite formation. Some precursors with a 5 beta-configuration were also metabolized by T47Dco cells. This metabolism reflected activity by either 3 beta-hydroxysteroid dehydrogenase and/or 6 alpha-hydroxylase but, in contrast to progesterone metabolism, the rates were different and the products were often mixtures. In T47Dco and MCF-7 human breast tumor cells, the reduction at C-3 followed by 6 alpha-hydroxylation, appear to be the major, and possibly only, route of progesterone metabolism. In contrast, preliminary data suggest that in normal human breast epithelial cells, this is not an exclusive route. Androgens are partially subject to the same metabolic enzymes, but synthetic progestins are not metabolized by T47Dco during an 18 h incubation.

Progesterone metabolism in T47Dco human breast cancer cells--I. 5 alpha-pregnan-3 beta,6 alpha-diol-20-one is the secreted product

Progesterone is a major hormone controlling normal breast development and function. In breast cancer, progesterone may be involved in tumor growth regulation, and the concentration of the intracellular receptor proteins for progesterone are used to distinguish hormone dependent from autonomous tumors. We have been studying the cytoplasmic and nuclear distribution of progesterone receptors after progesterone treatment of cultured T47Dco human breast cancer cells. Anomalous behavior of the receptors, when progesterone was compared to synthetic progestins, suggested that progesterone was being rapidly metabolized by the cells. We have now studied this metabolism in detail. When progesterone is added to medium of proliferating cells, it disappears with a half life of 2-4 h. A single metabolite (P-metabolite) is quantitatively released into the medium, but its release is delayed 10-14 h. The quantitative conversion of progesterone to P-metabolite was confirmed using two independent methods: gas chromatography with internal standards, and 14C-radioisotope measurements. We have used gas chromatography, gas chromatography/mass spectrometry, thin layer chromatography and nuclear magnetic resonance to identify the final metabolic product released into the medium as 5 alpha-pregnan-3 beta,6 alpha-diol-20-one.

Evidence for nuclear processing of progesterone receptors in rat placenta

The distribution of the progesterone receptor (Rp) in cytosolic and nuclear compartments of placenta has been studied in intact and ovariectomized (Ovx) rats on the 14th day of pregnancy. Removal of estradiol (E) and progesterone (P) by Ovx caused a 50% decrease in progesterone receptors from cytosolic and nuclear compartments. Estradiol replacement restored binding to intact levels. Progesterone, given 19 h after E, induced an additional 3-fold increment in the number of cytosolic and nuclear binding sites 1 h later. Four hours after progesterone the number of receptor sites in the placenta fell 60%, signifying processing. This was followed 4 h later by reversal of processing mechanisms leading to full recovery of nuclear and cytoplasmic binding sites. Actinomycin D (0.6 mg/ani) was found to have no influence on these events. On the other hand cycloheximide (0.5 mg/ani) completely prevented processing of binding sites when administered at the same time as progesterone or 2 h before, but did not influence the unmasking of nuclear sites which occurred 1 h after a progesterone challenge. The cycloheximide block to processing was partial when given 2 or 3 h after progesterone (61 and 43% complete, respectively). The full complement of receptors was processed when cycloheximide treatment was delayed 3.75 h after progesterone administration. These findings have led to the view that processing represents rapid and reversible changes in binding properties of the receptor rather than a gain or loss of receptor protein per se. The findings of this study suggest that a hypothetical substance, "processin", whose production is blocked by cycloheximide binds to the receptor and in some undefined manner inhibits ligand-receptor interaction within 4 h after an in vivo progesterone challenge. Nuclear accumulation of receptor induced by progesterone was not accompanied by cytoplasmic depletion of receptor nor was the apparent loss of processed nuclear receptor due to recycling of receptor to cytoplasm. We propose that nuclear receptors continually recycle within the nucleus in masked and unmasked states regulated by delicate interplay between progesterone and processin.

Estrogen responsiveness of fetal guinea pig uterine cells in culture

Cells from the uterus of the guinea pig fetus have been grown as a monolayer culture in serum-containing medium. Cells from the first subculture showed high concentrations of progesterone receptor (PR; 9.3-13.8 pmol/mg DNA) even after 9 days in medium containing charcoal-treated serum and estradiol did not induce any further increase. The antiestrogens, tamoxifen and monohydroxytamoxifen, both had an inhibitory effect which could be overcome by estradiol. The progestins, progesterone and R5020, as well as the antiprogestin, RU38486, also decreased the PR concentration. Estrogen receptor (ER) levels did not vary with the compounds tested but were found to be low compared to concentrations found in the fetal guinea pig uterus at 55-65 days of gestation. None of the compounds tested had any effect on the growth of the fetal uterine cells so that the modulation of PR concentrations was dissociated from the regulation of cell growth. It is concluded that estrogens are necessary but not sufficient factors in the control of PR levels in fetal uterine cells. The establishment of a culture system for separate types of fetal uterine cells will permit us to study in vitro the factors involved in the growth effects of estrogens and the control of PR synthesis.

The antiprogesterone steroid RU-486 does not impair gonadotropin-stimulated luteal adenylyl cyclase activity or gonadotropin release by pituitary cells

Administration of the antiprogesterone synthetic steroid RU-486 (17 beta-hydroxy-11 beta-[4-dimethylaminophenyl-1]-17 alpha-[prop-l-ynyl]-estra-4,9-dien-3-one) in human and non-human primates induces menstruation and is promising as a new approach to fertility control. To explore the sites of action of RU-486, we investigated in this study the effects of RU-486 upon gonadotropin-stimulable adenylyl cyclase in membrane preparations obtained from human corpus luteum and upon LH and FSH release by a dispersed rat anterior pituitary cell culture. In the presence of a wide range of concentrations (10(-10) to 10(-6) M), RU-486 failed to alter basal or hCG-stimulated adenylyl cyclase activities under conditions allowing either maximal or submaximal hormonal activation. Additionally, enzyme stimulation by GMP-P(NH)P (100 microM), NaF (10 mM) or forskolin (100 microM) was not affected by a high concentration (10(-6) M) of RU-486. These data indicate that RU-486 does not affect gonadotropin receptor binding nor does it interfere with cAMP generation. It is unlikely, therefore, that the compound may modulate human luteal function through changes in plasma membrane lipid mobility or modifications of reactions occurring in plasma membranes as suggested for other steroids in several membrane systems. The present observations are compatible with previously published in vivo studies suggesting that RU-486 activity does not involve a direct antigonadotropic effect at the primate corpus luteum level. We also found that RU-486 (10(-12) to 10(-7) M) did not alter the basal release of gonadotropins by the pituitary cells, nor did the compound impair the response of these cells to maximally or submaximally effective concentrations of LHRH. Thus, these data suggest that the anti-reproductive actions of RU-486 involve no direct effect upon pituitary function. Taken together, these findings support the concept that RU-486 exerts its effects on the luteal phase exclusively by a local action upon the endometrium.

Benzo[a]pyrene metabolism in human T 47D mammary tumor cells: evidence for sulfate conjugation and translocation of reactive metabolites across cell membranes

Human mammary tumor T 47D cells were examined for their capacity to metabolize benzo[a]pyrene (BaP) to gain insight into potential metabolic pathways for BaP in human epithelial tissue. Confluent cultures metabolized 95% of 4 microM BaP after 24 h incubation. BaP metabolites were analyzed from culture medium since only residual amounts remained in cells. Tetraols/triols, dihydrodiols, quinones and phenols were either unconjugated or existed as sulfate conjugates. Glucuronide conjugation was minor. Remaining water-soluble (WS) metabolites could be extracted with butanol or removed from culture medium protein with methanol/water and suggestive evidence indicates these may be glutathione conjugates. A portion of BaP-WS metabolites were covalently bound to medium protein. This latter phenomenon is attributed to translocation of reactive BaP metabolites across cell membranes which could potentially occur in vivo during cellular processing of BaP.

Glucocorticoid receptor regulation

Glucocorticoids, like other classes of steroid hormones, must bind to cellular receptors in order to exert their effects. Because of this central role in mediating hormone action, it is important to elucidate those factors that control receptor content. The purpose of this minireview is to summarize the recent work that explores the mechanisms through which cells modulate their glucocorticoid receptor binding capacity.

A progestin effect on lactate dehydrogenase in the human breast cancer cell line T-47D

The human breast cancer cell line T-47D has high levels of progesterone receptor even in the absence of exogenously added estrogen. Because of this it is a good line in which to study aspects of progestin action. It has been shown by others that lactate dehydrogenase in MCF-7 cells is responsive to estrogen but not to progesterone. Other proteins in other systems have been found to be responsive to both estrogen and progesterone, often requiring priming by estrogen, presumably to produce sufficiently high quantities of progesterone receptor. Reasoning that lactate dehydrogenase in T-47D cells might be stimulated by progestins alone at physiological levels since these cells already have high levels of progesterone receptor, we now report that this is indeed the case.

Nuclear synthesis of egg white protein messenger ribonucleic acids in chick oviduct: effects of the anti-estrogen tamoxifen on estrogen-, progesterone-, and dexamethasone-induced synthesis

Tamoxifen is a potent anti-estrogen in the chicken oviduct [Sutherland, R., Mester, J., & Baulieu, E.E. (1977) Nature (London) 267, 434-435]. Its action on egg white protein gene transcription was studied in isolated nuclei under various hormonal conditions. Injected alone to estrogen-primed and then withdrawn chickens, tamoxifen was unable to trigger gene transcription. After its administration together with or 6 h after diethylstilbestrol (a synthetic estrogen), tamoxifen stopped or suppressed the estrogen-dependent increase of ovalbumin and conalbumin gene transcription. On the contrary, when tamoxifen was given with progesterone or with dexamethasone (a synthetic glucocorticosteroid), two steroids that also increased specific transcription of the ovalbumin and conalbumin genes, there was an amplification effect that lasted up to 24-30 h. These results demonstrate that tamoxifen is active at the transcriptional level when inhibiting estrogen action and when increasing progesterone and dexamethasone effects on protein synthesis [Catelli, M. G., Binart, N., Elkik, F., & Baulieu, E. E. (1980) Eur. J. Biochem. 107, 165-172; Le Bouc, Y. (1983) Thèse de 3ème cycle, Université Paris VII]. The complexity of hormone-anti-estrogen interactions on transcriptional efficiency was also illustrated by the greater amplifying effect of tamoxifen on conalbumin than on ovalbumin gene transcription and by the lack of potentiation by the anti-estrogen of dexamethasone-dependent ovomucoid gene transcription. The role of tamoxifen-estrogen receptor complexes in these responses is discussed in view of their differential amount in chromatin in the presence of estrogen or of progesterone.

Steroidal regulation of rat uterine in vitro mRNA translation products

Total rat uterine mRNA was isolated following 1,2 or 3 days of estradiol, 3 days of progesterone, or 3 days of progesterone and estradiol treatment of immature animals. The mRNA translation products were analyzed by 2-dimensional electrophoresis. The results demonstrate that a number of mRNA products were affected by varying the hormonal conditions. Estradiol consistently caused an increase in mRNA in vitro translation products corresponding to polypeptides with mol. wt of 40,000 Daltons (p40), 59,000 Daltons (p59). A polypeptide with a mol. wt of 37,000 Daltons (p37) consistently decreases in concentration following estradiol administration. Progesterone, alone, caused a decrease in p37, p59, and a slight increase in p40. When progesterone was combined with estradiol we detected translation product levels similar to those seen following 1 day of estradiol treatment. Thus, the change in mRNA populations as a response of the immature rat uterus to estradiol and progesterone can be utilized to characterize the tissue's response to these hormones. This type of study also provides a method for detecting gene products which may possibly be utilized as potential markers to investigate estrogen and progesterone action.

Differential inhibition of protein synthesis: a possible biochemical mechanism of thalidomide teratogenesis

A theory concerning the chemical and biochemical mechanisms of thalidomide teratogenesis is presented. A considerable body of evidence suggests that the glutarimide ring of thalidomide may exert its biological activity because of its resemblance to the imide pyrimidines thymine and uracil. In addition to the glutarimide ring, thalidomide contains a moderately reactive phthalimide moiety, which allows the spontaneous formation of various glutarimide derivatives in fetal tissues. A model is proposed in which the phthalimide group reacts with small nucleophiles, most likely the polyamines, to produce a derivative(s) having a similar biochemical potential to that of cycloheximide, a glutarimide which is a powerful inhibitor of the elongation phase of protein synthesis. Interference in the elongation phase results in the selective inhibition of the translation of messages which have a high translational efficiency. Evidence is reviewed concerning the differential inhibition or protein synthesis by cycloheximide and the effects of this inhibition on various biochemical and biological processes which are critical during development and differentiation. A similar biochemical activity by the putative thalidomide derivative(s) could explain its extreme teratogenic potential. A number of parallels between the biological effects of thalidomide and cycloheximide are discussed which support the idea that a similar biochemical activity is involved. The theory readily explains many of the observed biological effects of thalidomide including the large difference between fetal and adult toxicity. In addition, evidence is reviewed which suggests that the teratogenic properties of a number of drugs which are structurally related to thalidomide may have a common chemical basis due to the similarity of their imide core structures to thymine and uracil.

The physico-chemical properties of the AtT-20 cell's glucocorticoid receptor during depletion

Glucocorticoid agonists decrease the number of glucocorticoid receptors in the cloned AtT-20 mouse pituitary tumor cell. To investigate whether the structure of the receptor is altered during this process, we monitored the physico-chemical properties of the nuclear and cytosolic receptors undergoing depletion. Agarose chromatography, DEAE-cellulose chromatography and sucrose gradient ultracentrifugation were employed. Cells were sampled after 2, 24, 48 and 96 h incubation with 10 nM tritiated triamcinolone acetonide. Agarose chromatography yielded, in each case, a single receptor-containing peak that had a Stokes radius of 5.8 nm. Nuclear and cytosolic glucocorticoid receptors from each preparation eluted from DEAE-cellulose as a single, symmetric peak at a KCl concentration of 0.075 M. Sucrose gradient ultracentrifugation of all samples also yielded only a single peak. For each technique the amount of receptor recovered was inversely related to the length of intact cell incubation. Thus, depletion of the glucocorticoid receptor is not accompanied by observable changes in its size, surface charge or hydrodynamic properties. These results suggest that the first step of agonist-induced glucocorticoid receptor depletion in the AtT-20 cell involves the loss or alteration of the receptor's steroid-binding site.

A 250-kilodalton cellular protein is induced by progestins in two human breast cancer cell lines MCF7 and T47D

We have studied the effect of R5020, a synthetic progestin, on the biosynthesis of cellular proteins extracted from the MCF7 and T47D human breast cancer cells, using gel electrophoresis. R5020 stimulates the synthesis, as measured after [35S]-methionine labelling, and the accumulation, as shown by silver staining, of a protein of molecular weight approximately equal to 250,000. The increase of the labelled 250-kilodalton protein was rapid (3 hours) and after 3 days this protein represented approximately equal to 6% of the total cellular proteins (approximately equal to 1 microgram/150,000 cells). The induction of the 250-kilodalton protein was obtained by physiologically active concentrations of several progestins and high concentrations of 5 alpha-dihydrotestosterone but not by estradiol or dexamethasone. It was inhibited by R486 , a progestin antagonist, but not by flutamide, an androgen antagonist. These results indicate a mediation by the progesterone receptor. The 250-kilodalton protein appears to be an excellent probe to study in cell culture the mechanism of action of progestin on human cells.

Progestin-specific markers in human cell lines: biological and pharmacological applications

We review the progestin-specific responses (induced proteins, increased enzymatic activity) described in uterus, mammary tumours and human breast cancer cell lines established from pleural effusions. Recent data from our laboratory using the T47D breast cancer cell line are then given. They include: (a) a general methodology for evaluating the specific effects of steroids on the production of [35S]methionine-labelled proteins released into the culture medium; (b) results concerning the specificity of regulation by the progestins of a 48 000 dalton protein secreted by T47D cells; (c) the evidence for androgen-specific proteins in the same cells; (d) A discussion of the criteria required to define the receptor responsible for a particular effect of steroids. Lastly, we consider the general interest of progestin-regulated proteins in cell culture for pharmacology and biology.