Changes in cytosol and nuclear progesterone receptor concentrations in the rabbit uterus and their relation to induction of progesterone-regulated uteroglobin

Human larynx expresses isoforms of the oestrogen receptor

Commercially available enzyme immunoassays (EIAs) were used for oestrogen (ER) and progesterone (PR) receptor determination in the cytosol fraction of 118 human larynx cancer specimens and in the corresponding histologically proven non-malignant tissues. Fifty-one ER positive cancerous samples had corresponding non-cancerous tissues also expressing the receptor. A high resolution isoelectric focusing (IEF) technique followed by immunoblotting with the H222 anti-ER monoclonal antibody was used to evaluate the presence of ER isoforms in the 51 ER positive human larynx cancer specimens and in their corresponding non-malignant tissues. In both tissues, four ER isoforms were detected, with isoelectric points (pI) similar to those obtained in breast and endometrium carcinomas (6.1, 6.3, 6.6 and 6.8). A significant difference in the expression of ER isoforms between cancerous and non-cancerous tissue was found; precisely, the 94.1% of the ER positive non-malignant specimens co-expressed the four isoforms while they were detected in only the 35.5% of the malignant specimens (P < 0.0001 by Fisher's exact test). In larynx cancer, the concentration values of ER and PR did not correlate, nevertheless tumours co-expressing the four ER isoforms had PR levels significantly higher than those which did not (P = 0.02 by Mann-Whitney Wilcoxon sum rank test). To investigate the possibility that the isoforms of the monomeric 4S form of the ER (those with pI 6.3, 6.6, and 6.8) could dimerise, a cold agarose gel electrophoresis technique was used on IEF-separated ER isoforms. In summary, the evidence shows that all the isoforms are able to form homodimers and that the isoforms at pI 6.3 and 6.8 are able to dimerise with that at pI 6.6 but, under the same experimental conditions, they do not form the 6.3/6.8 heterodimer. It was concluded that: (1) the four isoforms of the ER are co-expressed by the non-malignant human larynx and the cancer loses the capacity to express some of them; (2) the complete complement of ER isoforms (all four) is needed for PR expression; (3) the monomeric 4S isoform with pI 6.6 has the capacity to form homo- and heterodimers, while the remaining two are only able to homodimerise.

Expression of estrogen receptor and its messenger ribonucleic acid in the MCF-7 cell line: multiparametric analysis of its processing and regulation by estrogen

Experimentally, a portion of the detectable cellular estrogen receptor (ER) is seen to disappear in human breast cancer cells submitted to estradiol treatment. In this study, we have applied several detection methods to analyze the loss (processing) then the replenishment of ER in the MCF-7 cell line. Radioligand exchange assay and enzyme immunoassay revealed an accumulation of ER in the nuclei with a concomitant depletion in cytosol shortly after the addition of estradiol in cell culture. Then, a time-dependent decrease of ER level in the nuclear compartment without rescue in the cytosol was observed. When an immunocytochemical assay was performed on whole cells treated with estradiol, a similar decrease of ER number was shown, indicating that a decrease in the extractability of estradiol-filled ER was not involved in the processing. Analysis of ER mRNA also indicated that the estrogen treatment induces a time-dependent decrease of its expression. Measurement of [35S]methionine-labeled ER following the arrest of the hormone treatment suggested that ER replenishment was due to newly synthesized receptors. Sucrose gradient experiments confirmed the generation of small molecular forms of ER, following its binding with estradiol. All these data are indicative of estrogen-receptor complex degradation. We also confirm that estrogen regulates ER level through the decrease of its mRNA expression.

Interaction of antiprogestins with progesterone receptors in rat uterus

Cytosolic and nuclear progesterone receptors (PRc and PRn) under antiprogestin treatment were measured in rat deciduoma and compared with values for contralateral (nondeciduomatous) rat uterine tissue. Uterine PRc and PRn of the progesterone treated group were 101 +/- 8.7 and 4770 +/- 590 fmol/mg DNA respectively. After treatment with antiprogestins STS-557, 5 alpha-DNE, (5 alpha-dihydronorethisterone), 5 alpha-DNG (5 alpha-dihydronorgestrel), RU-22092 and RU-16556, PRc in the nondeciduomatous control horn ranged from 127 to 377 fmol/mg DNA and PRn from 2785 to 17925 fmol/mg DNA. In the decidual tissue, PRc decreased significantly (4.6 +/- 0.8 fmol/mg DNA) on 5 alpha-DNG treatment as compared with the progesterone alone treatment group (147 +/- 3.8). PRn in decidual tissue also decreased maximally on 5 alpha-DNG treatment. These results suggest that the interaction of antiprogestins may not be identical in control uterine tissue and in deciduoma.

Tissue specific effects of progesterone on progesterone and estrogen receptors in the female urogenital tract

The effect of progesterone administration on progesterone and estrogen receptors in the uterus, vagina and urethra of rabbits was studied. After 24 h of progesterone treatment the concentration of cytosolic progesterone receptors decreased to about 25% of the control value in the uterus, whereas no significant change in receptor concentration was observed in the vagina or the urethra. The concentration of the nuclear progesterone receptor did not change in any of the three tissues studied. The apparent dissociation constant (Kd) of nuclear progesterone receptor increased after progesterone treatment in all three tissues. Although the Kd of the cytosolic progesterone receptor also increased in all tissues, the difference was significant for only the vagina and urethra. The concentration of cytosolic estrogen receptors in the uterus decreased significantly (P less than 0.001) after progesterone treatment whereas the Kd value increased slightly (P less than 0.05). In vagina or the urethra, there was no change in either estrogen receptor concentration or Kd values after progesterone treatment. These data clearly showed that the reduction by progesterone of progesterone and estrogen receptor concentrations occurs only in the uterus and not in the vagina or the urethra.

Progesterone-dependent binding of a trans-acting factor to the uteroglobin promoter

A trans-acting factor that specifically binds to the uteroglobin (UG) gene promoter has been identified. Binding activity was absent in non-target tissues (lung, liver) in HeLa cell nuclear extracts, and in target tissue (endometrium) in the absence of progesterone. Mixing experiments revealed an inhibitor of promoter binding in the absence of progesterone and in nonspecific nuclear extracts. Inhibition of binding in the endometrium was reversed by the action of progesterone. The results suggest that binding of a transcription regulatory factor to the UG promoter switches from negative to positive with the action of progesterone. The binding activity corresponds to the expression of the UG gene and this protein may be, therefore, a coordinately regulated trans-acting factor which regulates UG in a tissue-specific manner.

Progesterone (P) receptor dynamics in estrogen primed normal human cervix following P injection

Progesterone (P) receptor levels were measured in the cytosol and in the 0.4 M KCl nuclear extract in human cervical tissues with [3H]-R5020 as a ligand and the results compared with those obtained in the myometrium and endometrium of the same uteri. Tissue samples were obtained from 28 women, grouped as follows: group A, 12 premenopausal controls; group B, 7 perimenopausal women who received estrogen 7 to 11 days before operation; and group C, 9 perimenopausal and postmenopausal women who received estrogen as in group B plus P injection 1 to 3 hours before operation. Estrogen administration resulted in a significant rise in total P receptor levels in the cervix, compared with the endometrium and myometrium. P injection after estrogen priming resulted in down-regulation of the P receptor in the cervix to undetectable levels, whereas in the endometrium and myometrium it resulted only in redistribution of the P receptor, with higher nuclear levels and lower cytosol levels. These results indicate the possibility of a different mechanism of regulation of the P receptor in the human cervix, compared with that in the endometrium and myometrium.

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.

Progesterone dependent uptake of uteroglobin by rabbit endometrium

Unlabeled or 3H-labeled UGL, isolated from rabbit lungs, was injected intraluminally into the uteri of ovariectomized low dose progesterone substituted and unsubstituted animals as well as into mated animals on the fifth day of pregnancy. It was offered to the endometrium, in this last case, in competition with endogenously synthesized UGL. 3H-labeled IgG served as a control. The animals were killed 24 h after the experiment. Immunohistograms and autoradiograms showed that UGL was taken up by the whole endometrium of the ovariectomized animals but only when progesterone was present. In the preimplantation uterus, uptake was limited to clusters of smaller cells accumulated in the lumen adjacent to the epithelium, whereas IgG remained within the uterine lumen, forming a dense layer on the endometrial surface.

Steroid receptor recycling and its possible role in the modulation of steroid hormone action

The fate of steroid-receptor complexes after their nuclear retention in target cells is not firmly established. Nuclear glucocorticoid- and androgen-receptor complexes could be recycled back to the cytosol in their responsive tissues, whereas this has not been clearly established for the case of progesterone and estrogen receptors. The models of steroid receptor recycling proposed so far involve release of chromatin-bound complexes into the cytosol, loss of steroid, and receptor inactivation. These receptors, however, can eventually be reactivated to a steroid binding form to reinitiate a cycle of steroid binding and further nuclear translocation. We propose that this model can represent a general aspect of steroid hormone action, provided that inactivation/reactivation processes occur in every steroid responsive system. A process involving a reversible receptor inactivation could play a major role in the control of steroid receptor recycling. It is proposed that a control on the extent of receptor available to steroid binding could result in a modulation of cellular responses to steroid hormones.

Uteroglobin: a model for the sutyd of progesterone action in mammals

Uteroglobin, a progesterone-binding protein, is expressed in several organs, principally endometrium and lung, of the rabbit and other rodents. The phasic activation of the uteroglobin gene in the endometrium during early pregnancy is regulated by progesterone, which contrasts with the constitutive, nonregulated expression of this gene in the lung. Thus, uteroglobin provides a useful model for the study of differential gene regulation by hormones as well as for the study of steroid-protein interactions.

Cytosol and nuclear estrogen and progesterone receptors in the rabbit endocervix

This report describes the measurement of estrogen and progesterone receptors in cytosols and nuclear fractions from endocervical tissue components. Unoccupied cytosol estrogen receptor levels as determined by Scatchard analysis of [3H]-estradiol binding data indicated a single class of high affinity binding sites for the epithelial-stromal complex (KD = 0.74 x 10(-9) M). Binding was specific for estrogen (estradiol greater than estriol greater than estrone) and unaffected by desoxycorticosterone, dihydrotestosterone and progesterone. Assays for total estrogen receptor verified that 71.6 +/- 5.3% of this 8S estrogen receptor is in the epithelial-stromal complex while the remaining approximately 28% is localized in the stroma and fibromuscular wall, with the cells of the complex containing the highest receptor concentration. In 5-day pseudopregnant and ovariectomized rabbits compared to estrous rabbits there was a 50% decrease in the cytosol estrogen receptor in the epithelial-stromal complex and a 30% decrease in the concentration of nuclear receptor. Cytosol and nuclear progesterone receptors were measured as an indicator of estrogen action in the rabbit endocervix. Cytosol progesterone receptor concentrations (fmol/mg DNA) in 5-day pseudopregnant and ovariectomized animals were reduced to approximately 35% of the concentration in estrous animals. Nuclear progesterone receptor concentrations decreased 65% in 5-day pseudopregnant and 90% in ovariectomized animals suggesting decreased receptor synthesis. Collectively these data support the concept that the rabbit endocervix may be directly regulated by estrogens.

5 alpha-Dihydrotestosterone-induced uteroglobin synthesis in rabbit uterus is not inhibited by antiandrogen administration but is prevented by estradiol

The physiological androgen, 5 alpha-dihydrotestosterone (DHT), enhances a progesterone-regulated protein (uteroglobin) synthesis in the rabbit uterus. In order to clarify the induction mechanism(s), rabbits were treated for 5 days with DHT alone or concomitantly with a nonsteroidal antiandrogen, RU 23908, or with different doses of estradiol. Uteroglobin content was measured in the uterine fluid by radioimmunoassay and uteroglobin mRNA activity in uterine tissues using cell-free translation in vitro. Uteroglobin induction elicited by DHT was inhibited by a small dose of estradiol, but not by antiandrogen. These results support the idea tha androgens bring about their action on uteroglobin synthesis via a mechanism involving uterine progesterone receptor.

In vitro binding to an in vivo effect on the cytosol and nuclear progesterone receptors of various progestins, and their relationship to synthesis of uteroglobin in rabbit uterus

In vitro binding affinities of various progestins to cytosol and nuclear progesterone receptors of rabbit uterus were determined and correlated with the biological potency of these steroids. In addition, cytosol and nuclear progesterone receptor levels were measured after a 5-day administration of different progestins (0.5 mg/kg daily) with variable biologic activities. The receptor levels were compared with the biological response; the induction of uteroglobin synthesis. Cytosol and nuclear progesterone receptors had identical steroid binding properties (r = 0.98). The correlation between the in vitro binding affinity (cytosol or nuclear) and the in vivo biologic activity of the steroids was good (r = 0.73). After a 5-day treatment with progestins, the nuclear receptor concentration correlated n an inverse manner (r = -0.84) with the uterine fluid uteroglobin concentration. A similar, but slightly weaker correlation (r = -0.81) was also found for the cytosol receptor content and uteroglobin secretion. These data indicate that not only nuclear, but also cytosol progesterone receptor levels decrease in the rabbit uterus during chronic hormone action. Decline in the nuclear progesterone receptor content seemed to occur during treatment with all progestational steroids, while only progestins with high biological potency were capable of decreasing the cytosol receptor content.

Uteroglobin mRNA and levels of nuclear progesterone receptor in endometrium

To investigate the mechanism of induction of uteroglobin by progesterone, the relationship between uteroglobin mRNA (mRNAug) activity and nuclear progesterone receptor levels has been examined in rabbit endometrium during early pregnancy. mRNAug activity was assessed by translation in vitro of poly A-rich endometrial RNA and immunoprecipitation of the synthesized peptides using anti-uteroglobin antibodies. Progesterone receptor was determined in purified endometrial nuclei by Scatchard analysis of the specific binding of 3H-R5020 under exchange conditions. mRNAug activity reached a peak on Day 4 of pregnancy and declined thereafter up to Day 8. Nuclear progesterone receptor levels showed a slight rise on Day 2, then returned to baseline levels. When mRNAug activity was high, progesterone receptor levels had declined. A cause-and-effect relationship between nuclear progesterone receptors and specific mRNA or protein synthesis remains to be established.

Hormonal control of uteroglobin secretion and preuteroglobin mRNA content in rabbit endometrium

The cellular content of preuteroglobin mRNA in endometrium was measured by molecular hybridization to preuteroglobin cDNA, and compared with uteroglobin content in the uterine secretion as determined by radioimmunoassay. The following results were obtained. (1) A single injection of either estradiol or progesterone leads to a rapid accumulation of preuteroglobin mRNA in the endometrium, but has no effect on the cellular content of preuteroglobin mRNA in the lung. (2) The effect of progesterone on uteroglobin on secretion parallels its influence on preuteroglobin mRNA levels, but estradiol has a more pronounced effect on the mRNA content than on uteroglobin secretion. (3) 5 days after priming with estradiol, a single injection of progesterone leads to the accumulation of preuteroglobin mRNA sequences without measurable lag phase, whereas a lag period is found if progesterone is administered earlier after estradiol treatment. (4) In the endometrium of pseudopregnant rabbits there are around 10 000 molecules of preuteroglobin mRNA per epithelial cell as compared with 300 in control estrous rabbits, and 1000-2000 in animals treated with estradiol alone. (5) Following maximal induction, the apparent half-life of uteroglobin and its mRNA are inversely influenced by estrogens: estradiol accelerates the disappearance of uteroglobin from the uterine secretion, and retards the decay of preuteroglobin mRNA sequences in endometrium.