Glucocorticoid induction of egg white mRNAs in chick oviduct

Differential abundance of egg white proteins in laying hens treated with corticosterone

Stressful environments can affect not only egg production and quality but also gene and protein abundance in the ovary and oviduct in laying hens. The oviductal magnum of laying hens is the organ responsible for the synthesis and secretion of egg white proteins. The objective of this study was to investigate the effects of dietary corticosterone as a stress model on the abundance of proteins in the egg white and of mRNA and proteins in the magnum in laying hens. After a 14-day acclimation, 40 laying hens were divided into two groups which were provided for the next 14 days with either control (Control) or corticosterone (Stress) diet containing at 30 mg/kg. Corticosterone treatment resulted in increased feed intake (P ≤ 0.05) and decreased egg production. Two-dimensional electrophoresis (2DE) with MALDI-TOF/TOF MS/MS using eggs obtained on days 0 and 5 revealed differential abundance of egg white proteins by Stress: transiently expressed in neural precursors (TENP), hemopexin (HPX), IgY-Fcυ3-4, and extracellular fatty acid-binding protein (Ex-FABP) were decreased while ovoinhibitor and ovalbumin-related protein X (OVAX) were increased on days 5 vs 0 (P ≤ 0.05). Expression of mRNAs and proteins was also significantly modulated in the magnum of hens in Stress on day 14 (P ≤ 0.05). In conclusion, the current study provides the first evidence showing that dietary corticosterone modulates protein abundance in the egg white in laying hens, and it suggests that environmental stress can differentially modify expression of egg white proteins in laying hens.

Characterization of vitamin D-mediated induction of the CYP 24 transcription

Transcription of the CYP24 (25-hydroxyvitamin D(3)-24-hydroxylase) gene is known to be induced by 1alpha,25-dihydroxyvitamin D3 (1,25(OH)2D3). We studied the induction kinetics in detail in human skin-derived fibroblasts. While the basal transcription of this gene was very low, addition of 1,25(OH)2D3 increased the mRNA level by 50-fold within 1h. The induction reached as high as 20000-fold after 12h. DNA microarray analysis also indicated that the induction ratio of the CYP24 gene is exceptionally high among 3800 human genes examined. The increase of mRNA was caused by stimulation of the transcription, but not by stabilization of mRNA. 24(R),25-dihydroxyvitamin D3 (24,25(OH)2D3), a compound metabolically related to 1,25(OH)2D3, also stimulated the CYP24 gene transcription, though at much higher concentrations. However, this stimulation was significantly augmented by synergistic actions of 24,25(OH)2D3 and 1,25(OH)2D3, suggesting that 24,25(OH)2D3 or its metabolites might be playing some roles in the regulation of CYP24 gene transcription.

Regulation of Arctic char (Salvelinus alpinus) egg shell proteins and vitellogenin during reproduction and in response to 17beta-estradiol and cortisol

Estrogens induce both vitellogenin (Vtg) and egg shell (zona pellucida; ZP) protein synthesis in salmonids. However, while Vtg is strictly under estrogenic control, recent reports suggest that additional mechanisms are involved in ZP protein synthesis. During sexual maturation both estrogen and glucocorticoid levels increase in the circulation of female fish. As glucocorticoids have been shown to interfere with Vtg induction in fish we investigated whether cortisol (F) had similar effects on ZP regulation. In the present study we determined both the natural variation in Vtg and ZP during an annual reproductive cycle in female Arctic char (Salvelinus alpinus), and the effect of co-treatment of juvenile Arctic char with 17beta-estradiol (E2) and F. During sexual maturation the expression of Vtg and ZP correlated to plasma levels of E2 and F. Determination of Vtg and ZP protein levels following co-treatment with E2 and F showed that F antagonized E2 induction of Vtg. However, F was observed to potentiate the expression of ZP protein in the same fish. These results indicate that in Arctic char Vtg and ZP proteins are not regulated by the same mechanisms and suggest that ZP protein expression does not necessarily imply exposure to estrogenic compounds alone, and may thus not be ideally suited as a biomarker of exposure to estrogenic compounds.

Effects of insulin-like growth factor-I, estrogen, glucocorticoid, and transferrin on the mRNA contents of ovalbumin and conalbumin in primary cultures of quail (Coturnix coturnix japonica) oviduct cells

The effects of estrogen, dexamethasone, insulin-like growth factor-I (IGF-I), and transferrin on the messenger RNA (mRNA) contents of ovalbumin and conalbumin in primary cultures of quail oviduct cells were investigated. In the absence of one of the above hormones or factors, a decrease in ovalbumin mRNA was prominent. In particular, removal of IGF-I and transferrin caused a significant effect. Studies using a combination of estrogen, dexamethasone, IGF-I and transferrin indicated that IGF-I cooperates with estrogen or dexamethasone and transferrin works with dexamethasone. Specifically, IGF-I enhanced ovalbumin synthesis or increased cellular ovalbumin mRNA content depending on its concentration in the medium in the presence of estrogen. However, the effects of estrogen, dexamethasone, IGF-I, and transferrin were not similarly observed with conalbumin mRNA. These results show that ovalbumin synthesis is controlled by estrogen or glucocorticoid with IGF-I or transferrin and that cellular ovalbumin mRNA content is also regulated by these hormones or transferrin. In contrast, conalbumin synthesis and cellular content of conalbumin mRNA are not affected by these hormones under the conditions of the present study.

Content of glucocorticoid receptor and arginase in gastric cancer and normal gastric mucosal tissues

The content of glucocorticoid receptor (GR) and arginase in human gastric cancer and the corresponding normal gastric mucosal tissues was determined. Among the 25 patients studied, the GR content in gastric cancer tissues was 33.2 +/- 10.2 fmol/mg protein versus 7.6 +/- 3.4 fmol/mg protein in gastric mucosal tissues. This difference is statistically significant (P less than 0.005). Of the 25 paired samples, 19 cancer tissues contained GR, whereas only seven of the normal mucosal tissues had GR. The level of arginase in gastric cancer tissues in 19 patients was assayed, it was 26.6 +/- 4.2 ng/mg protein which is also significantly higher than that in normal gastric mucosal tissues (13.5 +/- 1.8 ng/mg protein) (P less than 0.005). Since glucocorticoids and arginase are potent immune suppressive agents, the increased level of GR and arginase in gastric cancer tissue suggest that these glucocorticoid-related factors in gastric cancer tissue may play a partial role in regulating cellular immunity.

Evidence of estrogen receptors in normal human osteoblast-like cells

In seven strains of cultured normal human osteoblast-like cells, a mean of 1615 molecules of tritium-labeled 17 beta-estradiol per cell nucleus could be bound to specific nuclear sites. The nuclear binding of the labeled steroid was temperature-dependent, steroid-specific, saturable, and cell type-specific. These are characteristics of biologically active estrogen receptors. Pretreatment with 10 nanomolar estradiol in vitro increased the specific nuclear binding of progesterone in four of six cell strains, indicating an induction of functional progesterone receptors. RNA blot analysis demonstrated the presence of messenger RNA for the human estrogen receptor. The data suggest that estrogen acts directly on human bone cells through a classical estrogen receptor-mediated mechanism.

Effects of estradiol and dexamethasone on choline acetyltransferase activity in various rat brain regions

Estradiol, administered to ovariectomized rats, increased choline acetyltransferase (ChAT) activity in the caudate nucleus, cortex, hippocampus, and hypothalamus, suggesting possibly widespread central cholinergic involvement in estrus-related behavior. Dexamethasone also, except in hypothalamus, increased ChAT activity, notably (50%) in hippocampus. ChAT activity changes did not correlate with reported regional hormone receptor density. Estradiol's effect in the caudate suggests that hormone receptor and affected enzyme may not necessarily coexist intraneuronally.

The effects of estrogen, insulin and dexamethasone on the synthesis and secretion of egg white proteins in primary cultured oviduct cells of laying Japanese quail (Coturnix coturnix japonica)

1. The effects of estrogen, insulin and dexamethasone on the synthesis of egg white proteins were investigated by employing primary cultured oviduct cells of laying Japanese quails. 2. It was demonstrated that oviduct cells require insulin and dexamethasone, besides estrogen, to synthesize and secrete egg white proteins maximally.

Expression of the avian c-erb B (EGF receptor) protooncogene during estrogen-promoted oviduct growth

Expression of cellular erb B protooncogene messenger RNAs has been analyzed in the oviducts of immature chicks during estrogen-promoted growth. Hybridization of oviduct total cellular RNA with viral-derived erb B oncogene probes demonstrated significant expression of c-erb B mRNA in oviduct cells of untreated chicks. Daily administration of estrogen (diethylstilbestrol) to chicks results in marked oviduct growth but did not appreciably affect expression levels of c-erb B messenger RNA in oviducts after 2, 4 or 6 days of treatment. Withdrawal of chicks from estrogen treatment resulted in termination of oviduct growth. However, c-erb B messenger RNAs were detectable in the nonproliferative tissue at 5 days after hormone withdrawal. Readministration of diethylstilbestrol, progesterone or diethylstilbestrol plus progesterone to hormone-withdrawn birds (secondary stimulation) also did not affect c-erb B messenger RNA levels in the oviduct. These results demonstrate significant expression of the cellular erb B (epidermal growth factor receptor) gene in the avian oviduct. However, EGF receptor messenger RNA synthesis is not modulated in the oviduct by steroid hormones.

Characterization of the chromatin acceptor sites for the avian oviduct progesterone receptor using monoclonal antibodies

Monoclonal antibodies (MAb) against the chromatin acceptor sites for the avian oviduct progesterone receptor were prepared with highly purified hen oviduct acceptor proteins reconstituted to hen DNA. Addition of the MAbs to a cell-free assay blocked progesterone receptor from chick oviduct (PRov) binding to native-like acceptor sites on nucleoacidic protein (NAP) representing a partially deproteinized chromatin, which has been shown to be enriched in these binding sites. However, the antibodies do not block PRov binding to pure DNA, nor do they affect the receptor itself. Estrogen receptor binding to NAP was not inhibited, supporting a receptor specificity of the PRov acceptor sites as reported previously from direct competition studies. These data support earlier studies showing that (1) the reconstituted PRov acceptor sites resemble the native sites, (2) the acceptor sites are receptor specific, and (3) the PRov binding sites of NAP are different from those of pure DNA. While some animal-species specificity in the PRov binding inhibition was observed, no tissue specificity was seen. Direct binding of the antibodies to native acceptor sites was demonstrated in an enzyme-linked immunosorbent assay (ELISA) system. The antibodies showed little recognition of free acceptor protein or DNA alone, indicating specificity for the protein-DNA complex. A partial evolutionary conservation of the nuclear acceptor sites for PRov was shown by the fact that about 50% of the inhibition seen with hen NAP was obtained with NAPs from several other species, and this partial cross-reactivity of the MAbs with the same NAPs from other animal species was also seen in the ELISA.

Secretion of egg white proteins in primary cultured oviduct cells of laying Japanese quail (Coturnix coturnix japonica)

Oviduct (magnum) cells of laying Japanese quails (Coturnix coturnix japonica) were isolated after digestion of the magnum portion by collagenase and dispase and cultured in Dulbecco's modified Eagle medium (DME) supplemented with 10% fetal calf serum. The cultured cells formed a monolayer. Immunoperoxidase staining with antiovalbumin and anticonalbumin antibodies elucidated that more than 90% of the total population of the cells contained ovalbumin and conalbumin within the cytoplasm. The result shows that the cultured cells are composed mainly of tubular gland cells. Cells secreted ovalbumin and conalbumin continuously for several days. Secretion of these egg white proteins was confirmed to be inhibited by colchicine and vinblastine, which means that the microtubular system is involved in the secretion pathway of the proteins, as is widely accepted. Tunicamycin, an inhibitor of glycosylation of proteins, blocked the glycosylation of nascent ovalbumin molecules at a concentration of 5 micrograms/mL in the medium. However, immunoreactive ovalbumin was secreted under these conditions, without being glycosylated. This suggests that the carbohydrate moiety of ovalbumin is not essential for the secretion of ovalbumin. The secretion of ovalbumin was inhibited by brefeldin A, which is supposed to inhibit the transport of proteins from the rough endoplasmic reticulum to the Golgi apparatus. The present method of cultivating egg white-secreting cells will be useful in investigations of mechanisms and regulation of the synthesis and secretion of egg white proteins in birds.

Structural organization of the proopiomelanocortin gene in Xenopus laevis. 5'-end homologies within the toad and mammalian genes

This study reports the isolation and characterization of the entire proopiomelanocortin (POMC) gene of the amphibian Xenopus laevis. The Xenopus POMC gene consists of three exons of which the main exon 3 codes for all of the bioactive domains of the precursor protein. Intron A (2.6 kb) separates the segments encoding the 5'-untranslated mRNA region and intron B (2.5 kb) interrupts the protein-coding sequence near the signal peptide coding region. In that this structural organization of the Xenopus POMC gene is similar to those of the mammalian genes, apparently the POMC gene has been remarkably stable during 350 million years of vertebrate evolution. A comparative analysis of the 5'-flanking sequences of the Xenopus and mammalian POMC genes reveals the presence of several conserved regions. One of these regions is homologous with sequences located upstream of the capping sites of other glucocorticoid-regulated genes and another region contains a segment reminiscent of a viral enhancer consensus sequence.

c-mos upstream sequence exhibits species-specific enhancer activity and binds murine-specific nuclear proteins

Expression of the c-mos proto-oncogene is detected only in mouse and rat testis and ovaries. Its transcriptionally silent character suggested the involvement of sequences that cause repression of the c-mos expression. Evidence for such repressor sequences has been reported. Here we investigated the possibility that a cis-acting enhancer element(s) is responsible for the cell type-specific c-mos(rat) expression. We localized an enhancer close to (300 bases) the repressor sequences, which acts on heterologous promoters in an orientation-independent manner over large distances. Surprisingly, it shows species preference. Sequence analysis of the enhancer fragment indicated the presence of four blocks of nucleotides homologous to the simian virus 40 enhancer core sequence. Different nuclear proteins, some of which are expressed in murine but not in primate cells, bind to the enhancer DNA. They protect three closely associated areas from DNase I digestion, two of which are homologous to the simian virus 40 enhancer core sequence. The third protected sequence is located downstream from the two enhancer core blocks.

Specific binding of estrogen receptor to sites upstream and within the transcribed region of the chicken ovalbumin gene

By means of the DNA-cellulose competitive binding assay, the interaction of estrogen receptor complexed to 17 beta-estradiol with fragments of a cloned DNA region of the estrogen responsive chicken ovalbumin gene spanning from 1343 bps upstream to 373 bps within the transcribed region of the gene (p0V 1.7) was investigated. Only DNA fragments including either the 5'-flanking region from -21 to -140 bps or the region within the gene from +41 to +143 bps showed binding affinity for the estrogen receptor higher than calf thymus DNA. DNA fragments from human alpha 1-globin gene and glucocorticoid responsive murine mammary tumor provirus corresponding to the same DNA region investigated for ovalbumin showed affinity for the estrogen receptor no higher than that of calf thymus DNA. These results suggest that two specific binding sites for estrogen receptor are located upstream and within the ovalbumin gene, near the start-site of transcription. These receptor binding sites overlap with the 'estrogen response element' identified by Dean et al. (1) and the DNase I Hypersensitive region I found by Kaye et al. (2).

Sex dimorphism and hormonal regulation of rat tissue kallikrein mRNA

The regulation of rat tissue kallikrein mRNA levels was investigated by RNA filter hybridization using a kallikrein cDNA probe and by in vitro translation of isolated RNA. The synthesis of a 37 kDa polypeptide has been hybrid-arrested by the tissue kallikrein cDNA in cell-free translation assays directed by submandibular mRNA and the quantitation of this protein was used as a measure of translational activity of kallikrein mRNA. In Northern blot analyses, relative kallikrein mRNA levels were found to be 60-fold higher in submandibular gland than in pancreas and 20-fold higher than in kidney. In addition, it was noted that kallikrein mRNA is differentially regulated in tissues from male and female animals. Rat submandibular gland kallikrein mRNA is 2-times more abundant in male animals as in females. This trend is reversed in kidney, where the kallikrein mRNA in females is twice that in male animals. Relative submandibular gland kallikrein mRNA levels were found to be responsive to hormonal manipulation as measured by both Northern blotting and cell-free translation assays. Castration of male animals resulted in a decrease of kallikrein mRNA which could be partially restored by treatment with thyroxine and almost completely restored by testosterone treatment. The submandibular gland kallikrein mRNA in normal female rats was increased up to 30% by administration of testosterone or thyroxine. Adrenalectomized female rats showed a decrease in submandibular kallikrein mRNA which was significantly increased by testosterone, thyroxine, aldosterone and cortisol, with the largest effect being a 2- to 2.4-fold increase in cortisol-treated rats. These results indicate that hormones regulate tissue kallikrein synthesis in the rat submandibular gland, at least in part, by altering kallikrein mRNA accumulation.

Hormonal induction of riboflavin carrier protein in the chicken oviduct and liver: a comparison of kinetics and modulation

Estrogen (E) induction of riboflavin carrier protein (RCP) in the chicken oviduct and liver was investigated to compare and contrast the kinetics, hormonal specificity and modulation of its elaboration in the 2 steroid-responsive tissues. During primary stimulation, continued daily E administration to immature female chicks elicited, after an initial lag, rapid growth and RCP content of the overduct; neither progesterone (P) nor testosterone (T) could substitute for E in this respect. Furthermore, P given along with E curtailed tissue growth and its RCP content, whereas E + T had a synergistic effect on tissue growth only. During secondary stimulation, E administration steeply enhanced both tissue weight and RCP content without any lag. Interestingly, P (but not T) could substitute for E in augmenting magnum RCP concentration to a comparable extent while a concomitant effect on tissue growth was less marked. In contrast, hepatic induction of RCP was absolutely E-specific during both primary and secondary stimulations. Secondary stimulation with either E or P of E-primed birds enhanced the rates of RCP synthesis in the oviduct relative to that of total protein, whereas in the liver only E was effective in this regard. The absolute rate of E-induced RCP synthesis in both the steroid-stimulated tissues was significantly higher than that of general protein elaboration.

Localization of the lipid intermediate pathway of protein glycosylation in oviduct cell types

Oviduct tissue slices were incubated with [3H]-leucine or [3H]-mannose in the presence and absence of tunicamycin, a specific inhibitor of lipid-mediated protein glycosylation. Conditions were established where tunicamycin had maximal effect on [3H]-mannose incorporation (greater than 90% inhibition) but a minimal effect on [3H]-leucine incorporation (less than 10% inhibition) into total TCA-insoluble products. Analysis of incubated tissues by SDS-polyacrylamide gel electrophoresis revealed that in the absence of tunicamycin, [3H]-mannose was incorporated into only a few proteins, of which ovalbumin represented the major radiolabeled component. Tunicamycin markedly reduced the incorporation of [3H]-mannose into ovalbumin and other oviduct glycoproteins. In contrast, analysis by SDS-polyacrylamide gel electrophoresis showed that [3H]-leucine was incorporated into a variety of proteins in the absence of tunicamycin. The radioactivity profile of some of these proteins was shifted toward lower Mr when oviduct slices were incubated in the presence of tunicamycin, with only a minimal decrease in protein labeling. Light microscopic autoradiograms of tissue incubated with [3H]-leucine in either the presence or absence of tunicamycin exhibited extensive labeling of tubular gland and epithelial cells. In the absence of tunicamycin, these cell types also become markedly labeled with [3H]-mannose; however, incorporation of label in both cell types was substantially reduced in the presence of tunicamycin. Qualitatively, labeling of tubular gland cells appeared greater than that of epithelial cells, largely due to the concentration of silver grains over the dense population of secretory vesicles in the tubular gland cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Steroid hormone regulation of prostatic acid phosphatase expression in cultured human prostatic carcinoma cells

We have investigated the modulation of prostatic acid phosphatase expression in the human prostatic cancer cell line LNCaP in response to the natural androgens testosterone and dihydrotestosterone, the female sex steroid estradiol and the synthetic androgen R1881 (methyltrienolone). Testosterone and dihydrotestosterone at 1 microgram/ml enhance the acid phosphatase synthesis by a factor of 3.5, while a hundred-fold lower concentration of the synthetic androgen R1881 induces an almost five-fold increase in the expression of this enzyme. The stimulation by all androgens tested and estradiol was dose-dependent. The synthetic glucocorticoid triamcinolone acetonide does not modulate the prostatic acid phosphatase expression in LNCaP cells, neither alone nor in combination with R1881.

Chick oviduct glucocorticosteroid receptor. Specific binding of the synthetic steroid RU 486 and immunological studies with antibodies to chick oviduct progesterone receptor

The glucocorticosteroid receptor (GR) has been studied in oviduct cytosol prepared from estrogen-primed, 4-week-withdrawn chicken. The equilibrium dissociation constant was 6 nM for dexamethasone, and 18 300 receptor sites/cell were measured assuming that all cells contain identical concentrations of GR. Dexamethasone, used in most studies investigating glucocorticosteroid action, was found not to be the best GR ligand. The affinities of several natural and synthetic glucocorticosteroids for GR increased in the following order: cortisol less than deoxycorticosterone less than dexamethasone less than corticosterone less than triamcinolone acetonide. The synthetic steroid RU 486 was the most specific ligand of GR (its affinity was approximately equal to 10-fold higher than that of triamcinolone acetonide), while it did not bind either to plasma transcortin (which binds dexamethasone nor, surprisingly, to progesterone receptor (PR), contrary to what occurs in mammalian species. The molybdate-stabilized, 8-S form of GR was prepared from withdrawn chick oviduct, whole chick embryo or cultured chick embryo fibroblasts (which do not contain PR), and was labeled with either [3H]dexamethasone or [3H]RU 486. The sedimentation coefficient of radioactive ligand--8-S GR complexes was shifted towards heavier forms after incubation with polyclonal (IgG-G3) or monoclonal (BF4) antibodies generated against the molybdate-stabilized, 8-S form of the chick oviduct PR. Since neither IgG-G3 nor BF4 interacted with the steroid binding 4-S form of GR, it is suggested that these antibodies recognized a non-steroid binding protein common to molybdate-stabilized, 8-S forms of GR and PR.

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.

Estrogen-like effects of combined dexamethasone and tamoxifen in the chick oviduct

The effects of dexamethasone alone on withdrawn chick oviduct weight, DNA, protein content and progesterone receptor concentration were barely detectable, whereas ovalbumin and conalbumin synthesis were increased. When dexamethasone and tamoxifen were combined, a marked increase of total proteins, including egg white proteins, DNA and wet weight occurred. Progesterone receptor also was increased. The most striking result was the stimulation of DNA polymerase-alpha activity by combined dexamethasone and tamoxifen, whereas either compound was completely ineffective.

Glucocorticoids inhibit the coordinated translation of alpha- and beta-globin mRNAs in Friend erythroleukemia cells

The dimethylsulfoxide (Me2SO)-mediated induction of hemoglobin synthesis in Friend erythroleukemia cells is inhibited by the glucocorticoids hydrocortisone, dexamethasone, and fluocinolone acetonide; hydrocortisone, at concentrations of 10(-5) to 10(-8) M inhibits by 90-30% and fluocinolone acetonide at concentrations of 10(-8) to 10(-11) M shows a greater than 90% inhibition. At these concentrations the hormones have no effect on cell growth or viability. In this study it has been shown that there is a group of proteins, including the alpha- and beta-globins, whose regulation is associated with the induction of Friend erythroleukemia cell differentiation, and that the expression of some of these, in addition to alpha- and beta-globin, is affected by glucocorticoids. The levels of alpha- and beta-globin mRNAs are very close to fully induced levels and preclude transcription as a major site for glucocorticoid control. In addition, it has been shown that glucocorticoids inhibit the translation of alpha- and beta-globin mRNAs, that the level of this inhibition is concentration dependent, and that the translation of beta-globin mRNA is slightly more sensitive to inhibition than the translation of alpha-globin mRNA. It is concluded that, although the translation of alpha- and beta-globin mRNA is a major site of inhibition by glucocorticoids, there is a detectable amount of alpha- and beta-globin synthesized. Thus, part of this mechanism may involve a differential sensitivity of alpha- and beta-globin mRNA translation which results in unequal amounts of globin synthesis and an overall more potent inhibition of hemoglobin formation.

Analysis of the coordinate expression of 3-hydroxy-3-methylglutaryl coenzyme A synthase and reductase activities in Chinese hamster ovary fibroblasts

Decreased activities of both 3-hydroxy-3-methylglutaryl coenzyme A (HMG CoA) synthase and HMG CoA reductase are observed in the presence of sterol in the Chinese hamster ovary (CHO) fibroblast. In three different genotypes of CHO cell mutants resistant to 25-hydroxycholesterol both enzyme activities exhibit a decreased response to 25-hydroxycholesterol compared to wild-type cells. Permanently repressed levels of both HMG CoA synthase and HMG CoA reductase activities are observed in another CHO mutant, phenotypically a mevalonate auxotroph. Mevinolin, a competitive inhibitor of HMG CoA reductase, has no effect on HMG CoA synthase activity measured in vitro. Incubation of CHO cells with sublethal concentrations of mevinolin produces an inhibition of the conversion of [14C]acetate to cholesterol and results in elevated levels of both HMG CoA synthase and HMG CoA reductase activities. Studies of CHO cells in sterol-free medium supplemented with cycloheximide indicate that continuous protein synthesis is not required for the maximal expression of HMG CoA synthase activity and provide an explanation for the lack of temporal similarity between HMG CoA synthase and reductase activities after derepression. These results support the hypothesis of a common mode of regulation for HMG CoA synthase and HMG CoA reductase activities in CHO fibroblasts.

Quantitative analysis of mRNA synthesis during early cortisol action on rat thymocytes: restricted size of a possible hormone response

Complete inhibition of cortisol-induced pycnosis was seen by actinomycin D and cycloheximide only when added during the initial period of hormone action. This phenomenon, being a characteristic of steroid hormone effects in general, is often taken as indirect evidence for early steroid-induced mRNA synthesis. The lack of direct evidence for this theory has been tested for significance. Approximately 133 newly synthesized mRNA molecules were found to accumulate in the cytoplasm/min/cell, suggesting an average synthesis rate for individual mRNA species of about 1 copy/h/cell. Electrophoretic fractionation of double labelled RNA failed to reveal any changes of the isotope ratio of single fractions during the first 15-45 min of cortisol action, within an experimental error corresponding to +/- 2- +/- 20 molecules/cell. Possible effects of cortisol are thus restricted to changes in the range of constitutive mRNA synthesis rates. In contrast, the RNA labelling pattern was differentially changed after 45 min treatment with 10(-5) M cycloheximide.

Expression of a chicken lysozyme recombinant gene is regulated by progesterone and dexamethasone after microinjection into oviduct cells

We transferred a chicken lysozyme gene recombinant by microinjection into primary cultures of chicken oviduct cells. The recombinant gene is a fusion between the lysozyme promoter, including 1.4 kb of upstream sequences, and the coding region of the gene for SV40 T antigen (plys-T). The expression of plys-T is stimulated by the steroid hormones progesterone and dexamethasone, but not by estradiol. The number of oviduct cells expressing coinjected or separately injected control genes is not increased by steroids. A deletion mutant lacking the lysozyme sequences between -161 and +15 does not express T antigen, indicating that transcription of plys-T starts within the lysozyme promoter region. By screening different cell types we found that microinjected plys-T is expressed in chicken oviduct cells but not in chicken macrophages or fibroblasts or in rat II fibroblasts.

A somatomedin-like peptide hormone is required during the estrogen-mediated induction of ovalbumin gene transcription

Expression of the ovalbumin gene in chicken oviduct explant cultures requires the presence of a somatomedin-like peptide hormone in addition to estrogen. Insulin, proinsulin and multiplication-stimulating activity (MSA) are equally active substitutes for this peptide hormone, and maximal induction requires about 0.5 micrograms/ml; fetal calf serum can partially substitute for these factors. The equipotency of insulin and proinsulin indicates that insulin receptors are not involved, and the activity of MSA suggests that the active receptor is specific for somatomedins. The permissive effect of the peptide factor occurs within 1-2 hr and is required for the initiation of estrogen-mediated transcription on the ovalbumin gene. In contrast, transcription from the conalbumin gene is fully induced by estrogen in the presence or absence of peptide factors or serum, despite the fact that these two egg white genes are both transcribed in the same cells in response to the same steroid hormones. We suggest that the interaction of a somatomedin with its membrane-bound receptor generates an intracellular signal that interacts specifically with the ovalbumin gene.

The ovalbumin gene family: hormonal control of X and Y gene transcription and mRNA accumulation

The ovalbumin gene family is composed of three genes, X, Y and ovalbumin, which are expressed in laying hen oviduct. We have analyzed the in vivo transcription products of X and Y genes and the effect of steroid hormones on their synthesis and accumulation. As in the case of ovalbumin, the complete gene transcripts and processing intermediates are present in the poly(A)+ RNA fraction. The mature RNAs are found in polysomes and are translated into proteins. The expression of X and Y genes is controlled by steroid hormones: X and Y RNAs are not detectable in oviducts from chicks withdrawn from estrogen stimulation, whereas in chicks stimulated with estrogen for 7 days, X RNA represents 0.3% and Y RNA 0.8% of ovalbumin mRNA. In laying hen, however, the levels of X and Y RNAs are about 2% of ovalbumin mRNA. After stimulation with other steroid hormones, alone or in combination, the level of X and Y RNA does not achieve that detected in laying hen. Progesterone has a much weaker effect on X RNA accumulation than on that of Y and ovalbumin mRNAs. Studies with isolated nuclei show that X and Y gene expression is regulated by hormones at the level of transcription. However, the differences observed between the transcription rates and the accumulation of X and Y mRNAs suggest that the expression of X and Y genes could also be controlled at the levels of RNA processing and/or mRNA stability.