The relationship of the estrogen receptor to the induction of vitellogenin in chicken and Xenopus liver

Selective promoter usage of the human estrogen receptor-alpha gene and its regulation by estrogen

Three promoters have been identified for the human estrogen receptor-alpha gene. The positions of promoters A and B are known whereas that of the recently identified promoter C is not. Cloning and hybridization experiments demonstrated that promoter C is located more than 21 kb upstream of promoter A. The use of the three promoters was examined in estrogen receptor-positive breast cancer cell lines, cell lines derived from other malignancies, and some normal tissues by RT-PCR and transient transfection. All estrogen-responsive breast cancer cell lines used all three promoters, apart from ZR-75 cells, which did not use promoter B in one of two sublines examined. Cell lines derived from other malignancies and other normal tissues that express lower levels of estrogen receptor-alpha showed more selective promoter usage. This suggests that the level of expression of estrogen receptor-alpha is determined by the number of promoters used, rather than the selective use of specific promoters. We also show that promoter C is used more widely than suggested by others. Analysis of a series of estrogen receptor-positive primary breast tumors showed that all three promoters were used in all the tumors. All three promoters were modulated by estrogen in estrogen-responsive breast cancer cell lines: all three promoters were down-regulated by estrogen in MCF-7 cells in which estrogens reduce receptor expression whereas all promoters used were upregulated in T47D, ZR-75, and EFM-19 cells in which estrogens increase receptor expression. This suggests that it is the repertoire of transcription factors present within a cell rather than the selective use of a specific promoter that determines whether estrogen receptor-alpha expression is increased or decreased by estrogen.

Identification and characterization of estrogen and progesterone receptors from the oviduct of the American alligator (Alligator mississippiensis)

A protein extract prepared from the egg shell fiber-secreting region of the oviduct of Alligator mississippiensis was assayed for the presence of receptors for estrogen and progesterone. In the presence of [3H]-estradiol-17 beta, the extract contained an estrogen-binding activity which reached equilibrium at 25 degrees C in 1 h. Scatchard analysis demonstrated that a single estrogen-binding activity was present in the extract with a Kd of 0.5 nM for [3H]estradiol-17 beta. A steroid specificity competition assay showed the estrogen binding activity strongly recognized estradiol-17 beta and diethylstilbestrol (DES) and weakly interacted with estrone, estriol, estradiol-17 alpha, and dihydrotestosterone (DHT). The estrogen binding activity did not recognize testosterone, dexamethasone or progesterone. The extract exhibited a DNA-binding activity that recognized an estrogen response element in a gel mobility shift assay. We have also identified a high affinity binding activity in the extract that specifically recognized the synthetic progestin R5020 with a Kd of 0.9 nM. This binding activity recognized 17 alpha-estradiol, dexamethasone, testosterone, and estriol. This activity did not recognize DHT, DES, or estradiol-17 beta. These data suggest the presence of estrogen and progesterone receptors in the oviduct of the alligator.

Estradiol receptor in the lizard liver (Podarcis s. sicula). Seasonal changes and estradiol and growth hormone dependence

This study shows that in the liver of the oviparous lizard, Podarcis s. sicula, the estrogen receptor (ER) level increases during the reproductive period (spring) when vitellogenesis occurs. This phenomenon interested both unfilled and filled ER present in the cytosolic and nuclear fractions. The increase in unfilled cytosolic and filled nuclear receptor was positively correlated to the plasma level of vitellogenin. The level of liver ER approximated that of mammalian liver ER and, therefore, it is higher than that reported for the liver of several nonmammalian species. At electrofocusing, liver ER distributes in two pH ranges (pH 6.5-7.5 and 8.0-8.8, respectively). The first form predominated in nuclei of reproductive females or of spayed estrogenized females and could represent the activated form of receptor. Ovariectomy was followed by a decrease in liver ER which can be induced in spayed females by estradiol administration. Pituitary growth hormone (GH) seemed to exert a synergic effect on estradiol liver estrogen receptor regulation. In lizards treated both with estradiol and GH, in fact, there was a significant increase in nuclear filled ER rather than an increase in the level of total nuclear ER.

Estradiol-binding molecules in the hepatocytes of the female water frog, Rana esculenta, and plasma estradiol and vitellogenin levels during the reproductive cycle

Estradiol-binding molecules have been found both in cytosol and nuclear extract of hepatocytes of the female green frog Rana esculenta. These molecules show the properties of an estradiol receptor (Re): high and specific affinity for estrogens (2.10-7.10 x 10(-10) M), stability of binding at 0 and 20 degrees, localization in the nucleus, and cytosolic versus nuclear binding shift in estradiol-treated frogs. In hepatocytes, both filled and unfilled Re is detectable in all stages of the R. esculenta annual cycle. It increases during the recovery phase (September to January) when vitellogenetic processes are active in the ovary. These changes are positively correlated with vitellogenin. Only nuclear filled Re, moreover, is positively correlated to level of circulating estradiol. This suggests a direct connection: plasma estradiol level versus nuclear filled Re versus plasma vitellogenin level.

Chromatin structural transitions and the phenomenon of vitellogenin gene memory in chickens

We have previously shown that the steroid hormone-mediated transcriptional activation of the chicken vitellogenin II gene (VTGII) in the liver is accompanied by a series of chromatin structural changes, including the formation of two sets of 5'-proximal nuclease-hypersensitive sites and the demethylation of a single 5'-flanking MspI site which lies within a region of DNA that recently has been shown by Jost and co-workers to specifically bind the estrogen receptor complex in vitro. To assay the stability and possible functional significance of these induced structural changes, we transiently activated the VTGII gene during embryonic development and then allowed the chickens to hatch and grow for various periods of time before analyzing their livers. By 7 weeks posthatching all of the induced 5'-flanking hypersensitive sites had decayed. Moreover, the loss of these sites occurred without consequence to the "memory effect," that is, these structural features did not need to be present in hormone withdrawn birds to allow this gene to be activated more rapidly in response to a secondary presentation of estradiol. Although the demethylation was more stable, it also appeared not to be the basis of the memory phenomenon. The birds that still exhibited memory after 25 weeks of hormone withdrawal were not more extensively demethylated within the receptor-binding site than were the birds which failed to show memory at this age. A similar uncoupling of these two parameters was also observed when embryos were first injected with submaximal doses of estradiol and then assayed 1 week after hatching; the chickens which acquired memory were not demethylated to any greater extent than those which did not acquire memory. Other parameters that may be relevant to memory are discussed.

Chromatin structural transitions and the phenomenon of vitellogenin gene memory in chickens

We have previously shown that the steroid hormone-mediated transcriptional activation of the chicken vitellogenin II gene (VTGII) in the liver is accompanied by a series of chromatin structural changes, including the formation of two sets of 5'-proximal nuclease-hypersensitive sites and the demethylation of a single 5'-flanking MspI site which lies within a region of DNA that recently has been shown by Jost and co-workers to specifically bind the estrogen receptor complex in vitro. To assay the stability and possible functional significance of these induced structural changes, we transiently activated the VTGII gene during embryonic development and then allowed the chickens to hatch and grow for various periods of time before analyzing their livers. By 7 weeks posthatching all of the induced 5'-flanking hypersensitive sites had decayed. Moreover, the loss of these sites occurred without consequence to the "memory effect," that is, these structural features did not need to be present in hormone withdrawn birds to allow this gene to be activated more rapidly in response to a secondary presentation of estradiol. Although the demethylation was more stable, it also appeared not to be the basis of the memory phenomenon. The birds that still exhibited memory after 25 weeks of hormone withdrawal were not more extensively demethylated within the receptor-binding site than were the birds which failed to show memory at this age. A similar uncoupling of these two parameters was also observed when embryos were first injected with submaximal doses of estradiol and then assayed 1 week after hatching; the chickens which acquired memory were not demethylated to any greater extent than those which did not acquire memory. Other parameters that may be relevant to memory are discussed.

[Characterization of specific receptors for estradiol, induction of vitellogenin and its mRNA in the liver of rainbow trout (Salmo gairdnerii)]

In all egg laying vertebrates, synthesis and use of vitellogenin (Vg) are intimately bound to the active phase of reproduction. In the liver of the rainbow trout (Salmo gairdnerii), Vg synthesis is influenced by estradiol (E2) which, we believe, acts through the classical mechanism of steroid hormone action. After binding of the hormone to a soluble specific receptor protein, the estradiol-receptor complex can interact with chromatin and modulate the expression of Vg genes, leading to increased synthesis of specific mRNA and Vg. We show here: (i) the presence of specific oestrogen receptors (dissociation constant KD congruent to 1.5 X 10(-9) M for E2) in the cytosol of the male trout liver. (ii) The male liver, offering, an ideal experimental control of "zero" background, we followed-in the liver of male trout--the kinetics of induction of Vg mRNA by hybridization with Vg cDNA, after E2 stimulation, and (iii) the apparition of Vg in the serum by using an original rocket immuno-electrophoretic technique. The male trout liver vitellogenin model and the original techniques we developed will be very useful to study the influence of endogenous and exogenous factors on the different steps (receptors, transcription, translation) of vitellogenesis regulation.

A comparison of diethylstilbestrol- and estradiol-17 beta-induced vitellogenesis in quail

Japanese quail were injected intramuscularly with .125 to 32 mumole/100 g body weight of estradiol-17 beta (E2) or diethylstilbestrol (DES). During the following 8 days, vitellogenesis was assessed in these birds by measuring plasma concentrations of protein-bound phosphorus (PBP; vitellogenin is a phosphoprotein), calcium, and total protein. Blood packed cell volumes were recorded also. Plasma PBP concentrations of E2-injected male and female quail increased to .83 and .96 mg/ml from control values of .004 and .12 mg/ml, respectively. Doses of 8 to 32 (males) or 4 to 32 (females) mumole E2/100 g body weight induced similar initial rates of vitellogenesis, but the duration of vitellogenesis increased with increasing doses of hormone. In male quail, low doses of DES (.5 to 4.0 mumole/100 g body weight) were more effective than equal doses of E2 in inducing increases in plasma PBP levels. However, the maximum PBP concentrations attained with high doses of DES were less than those attained with equal doses of E2 (.53 and .83 mg/ml, respectively).

Glucocorticoid receptor of X. laevis: possible effect of phosphorylation on hormone binding

The cytoplasmic glucocorticoid receptor of X. laevis liver has a high affinity for [3H]dexamethasone (Kd, 0.3 x 10(-8) M), and its binding specificity for a variety of steroids is similar to that found for mammalian glucocorticoid receptors. The ability of this receptor to bind [3H]-dexamethasone is stable at 0 degrees C but is rapidly lost at 10 and 20 degrees C. Alkaline phosphatase increases, whereas molybdate and tungstate decrease, the rate at which the binding activity is lost. These results are consistent with the loss of binding activity being due to dephosphorylation of the receptor. Binding of [3H]dexamethasone to the receptor does not alter the rate at which the binding activity is lost but does increase the stabilizing effect of molybdate. 100 mM molybdate lowers the apparent affinity of the receptor for [3H]dexamethasone, suggesting that molybdate can interact with the X. laevis glucocorticoid receptor. Addition of UTP, but not ATP, GTP or CTP, reactivates the receptor-binding activity, which indicates that the receptor may be phosphorylated by a UTP-dependent protein kinase.

Comparative study of the physiology of vitellogenesis in Japanese quail

1. During a study of vitellogenesis in the Japanese quail, male or female quail were given, intramuscularly, one to three doses of estradiol-17 beta (16 mumol/100 g body weight). 2. In treated males, the plasma concentrations of protein-bound P (PBP, a measure of the phosphate groups in vitellogenin), Ca, and total protein fluctuated in unison. 3. Packed cell volume (PCV) values varied approx, inversely as the PBP concentrations. 4. Maxima of approx. 0.85 mg PBP/ml occurred six, five, and four days after the primary, secondary, and tertiary injections. Following each maximum, the PBP concentrations declined rapidly to the 0.004 mg/ml level found in the plasma of untreated male quail. 5. During periods of elevated PBP levels, Ca and PBP were present in equimolar quantities. 6. When laying female quail were given a single injection of estradiol, the PBP concentration rose from 0.12 to 0.97 mg/ml. 7. PCV values for both male and female estrogen-treated quail decreased from approx. 0.50 to 0.30. The decreases in PCV values were attributed to increases in plasma volume as measured using 125I-labelled serum albumin. No marked change in total erythrocyte mass was measured using 51CrO2-(4) as the cell label. 8. Perhaps the decrease in plasma serum albumin concentrations reported by some investigators for estrogen-treated animals is due to dilution rather than to repression of serum albumin synthesis.

Vitellogenesis and the vitellogenin gene family

Vitellogenin is synthesized under estrogen control in the liver, extensively modified, transported to the ovary, and there processed to the yolk proteins lipovitellin and phosvitin. In the frog Xenopus laevis there are at least four distinct but related vitellogenin genes. The two genes A1 and A2 have a 95 percent sequence homology in their messenger RNA coding regions, and contain 33 introns that interrupt the coding region (exons) at homologous positions. Sequences and lengths of analogous introns differ, and many introns contain repetitive DNA elements. The introns in these two genes that have apparently arisen by duplication have diverged extensively by events that include deletions, insertions, and probably duplications. Rapid evolutionary change involving rearrangements and the presence of repeated DNA suggests that the bulk of the sequences within introns may not have any specific function.