Steroid hormone regulation of specific messenger RNA and protein synthesis in eucaryotic cells

Effect of gonadal steroids on progesterone receptor, estrogen receptor, and vitellogenin expression in male turtles (Chrysemys picta)

Hepatic vitellogenin (vtg) is a yolk precursor protein sequestered in follicular oocytes as nutrient supply for developing embryos in nonmammalian vertebrates. In prior research studies we have demonstrated that both progesterone (P) and testosterone (T) inhibit estrogen (E)-induced vitellogenesis in the male fresh water turtle (Chrysemys picta), and have suggested that these hormones may be involved in multihormonal regulation of vitellogenesis in the female turtle. However, the modes of action of progesterone and testosterone on estrogen-induced vitellogenesis are not known. We have proposed that progesterone inhibits vitellogenesis by modulation of progesterone receptor A (PRA) or B (PRB) isoforms and/or estrogen receptor (ER) gene transcription. In this study, we compare the vitellogenic responses of reproductively inactive male turtles to estradiol 17beta in the presence of exogenous testosterone or progesterone. Northern blot analysis was used to monitor the changes in vtg mRNA, ER mRNA, and PR mRNA expression; Western blotting to determine changes in PR isoform expression and a homologous ELISA for measurement of plasma vtg. Progesterone and testosterone reduced estrogen-induced vtg mRNA expression, but plasma vtg was not significantly reduced by these steroids. PRA and PRB were transcribed even though ER mRNA could not be detected, suggesting constitutive PR expression. However, in the presence of estradiol 17beta, both PR isoforms and mRNA transcripts were increased as a correlate of ER mRNA transcription, suggesting both transcriptional and translational effects; these effects were inhibited by testosterone and progesterone treatments. Since ER mRNA was sharply reduced by both testosterone and progesterone, and estradiol 17 beta increased PR mRNA transcription and translation, it is likely that the action of progesterone in reducing vtg mRNA is indirect via down regulation of ER mRNA, thus ER. This study provides further information on the role of progesterone and testosterone in the regulation of hepatic vitellogenesis, suggesting regulation of vitellogenesis mainly via modulation of hepatic ER mRNA.

Studies on the mechanism of glucocorticoid hormone induced alterations in rat thymic transcription--I. Evidence from reconstituted cross-over transcription assays that sequential increases and decreases in transcription are due to changes in the activity of RNA polymerase II rather than in the activity of chromatin template

In experiments to determine the mechanism of glucocorticoid induced decreases in thymic transcription, adrenalectomized rats were injected with hydrocortisone (50 mg/kg) or vehicle. Thymic nuclei were used to prepare chromatins and soluble nuclear extracts containing RNA polymerase II for cross-over experiments. With calf thymus DNA or rat thymic chromatins as templates limiting RNA polymerase II from rats treated with hydrocortisone 3 h previously had 130% of the [3H]UMP incorporating activity of RNA polymerase II from control vehicle treated rats. In contrast, limiting RNA polymerase II from rats treated with hydrocortisone 12 h previously had 40-50% of the [3H]UMP incorporating activity of RNA polymerase II from controls. When limiting calf thymus DNA or rat thymic chromatins were used in 12 h cross-over experiments. Individual RNA polymerases II produced equal [3H]UMP incorporations, but RNA polymerase II activity from hydrocortisone treated rats was again only 50% of control values. Thus with template saturation, RNA polymerase II from hydrocortisone treated rats could not transcribe rat thymic chromatin templates to the level achieved by RNA polymerase II from control rats. This suggests that the activity, rather than the amount, of RNA polymerase II from hydrocortisone treated rats is reduced. Double reciprocal plots of [3H]UMP incorporation on rat chromatins with increasing concentrations of RNA polymerases II were made at 12 h. The apparent Km for RNA polymerase II from animals treated with hydrocortisone was identical to that of RNA polymerase II from controls, but the Vmax of RNA polymerase II from hydrocortisone treated animals was reduced. These data suggest the presence of an inhibitor of transcription or an RNA polymerase II defective in its capacity to initiate and/or elongate RNA transcripts. Further experiments demonstrated that these effects were not due to steroid induced changes in ribonuclease or protease activities.

Development of the adrenergic phenotype: increase in adrenal messenger RNA coding for phenylethanolamine-N-methyltransferase

Mechanisms regulating the developmental increase in the activity of adrenal phenylethanolamine-N-methyltransferase (PNMTase), an index of the adrenergic phenotype, were examined. Immunotitration indicated that the increase in catalytic activity in rat adrenal from birth to adulthood was attributable to increased numbers of PNMTase molecules, not enzyme activation. To determine whether the ontogenetic increase in PNMTase protein was associated with elevation of mRNA coding for PNMTase, cell-free translation was performed on total cellular mRNA obtained from adrenals at different ages. Translation in wheat-germ and reticulocyte lysate systems, followed by immunoprecipitation of the PNMTase product, NaDodSO4 gel electrophoresis, and fluorography, showed an 8-fold increase in the proportion of specific PNMTase mRNA relative to total mRNA in rat adrenals from birth to adulthood. Moreover, bovine adrenal medullae exhibited a 100-fold increase in PNMTase mRNA levels between embryonic life and adulthood. Consequently, the ontogenetic increase in adrenal PNMTase appears to be due to a developmental rise in specific mRNA coding for the protein.

Translation of phenylalanine hydroxylase-specific mRNA in vitro: evidence for pretranslational control by glucocorticoids

We have found that the induction of phenylalanine hydroxylase by hydrocortisone and serum in confluent cultures of H4-II-E-C3 rat hepatoma cells is accompanied by an increase in polysomal mRNA specific for phenylalanine hydroxylase, as measured by translation in a cell-free protein-synthesizing system. Thus, the induction is mediated largely, if not entirely, by a pretranslational mechanism, possibly by stimulation of the transcription of the phenylalanine hydroxylase gene.

Sterol ester hydrolase in Fusarium oxysporum

Two electrophoretically different forms of sterol ester hydrolase (EC 3.1.1.13) were obtained from the cytoplasmic extract of the mycelia of Fusarium oxysporum. The entities, estimated at 60,000 (I) and 15,000 (II) molecular weights, were obtained in Sephadex G100 column chromatography of the ammonium sulfate precipitate from the cytoplasmic extract. A third form III, 75,000 MW, was obtained from the culture filtrate. The activity of the enzyme was increased by Triton X-100 and was not inhibited by p-chloromercuribenzoate (PCMB), a sulfhydryl reagent. The enzymes I and II were inhibited differentially by NaCl. The optimal activities of forms I, II and III occurred at pH 4.8, pH 8.0 and pH 7.0, respectively. The apparent Km values of 7.7 X 10(-5), 8.3 X 10(-5) and 10.5 X 10(-5), respectively, indicate a similar order of affinity for cholesteryl oleate at pH 7.1. The rate of hydrolysis of cholesteryl esters were in the order: linoleate greater than oleate greater than valerate greater than butyrate greater than acetate. Cholesteryl benzoate and palmitate were not hydrolyzed. The properties of the microbial enzyme are discussed in relation.

Antimicrobial effects of clofibrate on the wheat pathogen Fusarium culmorum

The biological effects of clofibrate (ethyl p-chlorophenoxy-isobutyric acid) on the growth and metabolism of the soil-borne wheat pathogen Fusarium culmorum, were examined. In mid log phase (16 hr) cultures both phenylalanine uptake and secondary spore production were stimulated at 0.1 microM concentration; the net sterol content was reduced 50% at 0.35 microM; oxygen uptake was stimulated at 0.1 mM; growth was inhibited 50% at 0.1 mM concentration. Both phenylalanine and oxygen uptake were inhibited at 1.0 mM and pyruvate dehydrogenase activity was reduced 50% at 50 mM concentration of clofibrate. The data indicate that clofibrate affects a number of biological and enzyme systems. The inhibitory effect on the growth of the pathogen suggest a potential use of hypolipidemic agents like clofibrate as an antifungal agent for seed protection.

Simian virus 40 and polyoma virus stimulate overall cellular RNA and protein synthesis

In lytic infection with simian virus 40 and polyoma virus of monkey and mouse cells in tissue culture, synthesis of the viral tumor (T) antigens (T antigens) is rapidly followed by a mitogenic response of the host cell. The latter begins with virus-induced stimulation of overall cellular RNA and protein synthesis, leading to a substantial increase in cytoplasmic and nuclear RNA and protein. Stimulation begins within 1 hr after onset of T-antigen synthesis and also occurs if virus-induced DNA synthesis is blocked by metabolic inhibitors. The broad spectrum of biological and molecular effects induced by simian virus 40 and polyoma virus is, at least phenotypically, reminescent of the pleiotropic impact exerted on target cells by nonviral mitogens and by certain growth-promoting steroid and polypeptide hormones.

Diversity and complexity of uterine mRNA from rats of differing hormonal states

The diversity and complexity of the uterine mRNA population has been compared at two different stages of uterine growth and development in the rat. Analysis by cDNA hybridization to homologous mRNA indicates that there are 8000 different sequences expressed in the immature rat uterus responding to just 4 h of oestradiol-17 beta-induced growth while the fully developed uterus expresses 36 000 sequences. As a check on our results, the complexity is re-analysed by hybridization of mercurated mRNA to total unique DNA. Analysis by this method indicates that the hormone-stimulated immature rat uterus contains 12 000 poly(A)-containing mRNA sequences while the fully differentiated adult tissue contains 53 000 diverse sequences.

Qualitative and quantitative changes in uterine mRNA populations in response to oestradiol treatment of rats

The mRNA population of immature rat uteri, responding to different lengths of oestradiol-induced differentiation, have been compared by the technique of DNA hybridization with heterogeneous RNA. Over the first 4 h of hormone induction there are continuing qualitative and quantitative changes in the poly(A)-containing mRNA such that, by 4 h after oestradiol administration, the population bears little resemblance to that of the unstimulated animal. Between 2 h and 4 h after oestradiol administration, the most striking changes appear to be in sequences of intermediate abundance. The possible significance of these findings is discussed.

Characterization of uterine heterogeneous nuclear ribonucleic acid and the effect of oestradiol-17 beta on its synthesis

An early response to the administration of oestradiol-17 beta to immature rats is a dramatic stimulation in the synthesis of uterine hnRNA (heterogenous nuclear RNA). High-molecular-weight fractions of the hnRNA were purified and subfractionated on poly(U)-Sepharose into fractions that differed in their poly(A) content and their size profile on polyacrylamide gels. Oestrogen treatment of the rats stimulated the synthesis of all three fractions of high-molecular-weight hnRNA, but the kinetics of synthesis, degree of stimulation and size distribution of the newly synthesize RNA differed in each fraction.

Regulation of synthesis of a brain-specific protein in monolayer cultures of clonal rat glial cells

C6 cells were grown in monolayer culture under conditions permitting continued exponential cell division after attainment of a density at which extensive intercellular contacts were formed. An increase in the relative synthesis of S100 protein coincided with the time of formation of extensive intercellular contacts and preceded the onset of the stationary phase of growth by three generations. These observations suggested that the induction of S100 protein synthesis was mediated by cell contact and not by an arrest of cellular growth. The mechanism of this induction was first studied in a homologous non-initiating cell-free protein-synthesizing system from C6 cells, using fixed amounts of free amino acids or fully charged rat liver aminoacyl-tRNA as a source of precursors for protein synthesis. Real synthesis of total soluble proteins decreased as the cells progressed from logarithmic to stationary growth while synthesis of S100 protein increased during this period. The capacity of poly(A)+ RNA from logarithmic and stationary cultures to direct the synthesis of S100 protein was estimated in a cell-free protein-synthesizing system derived from wheat embryos. Increased synthesis of S100 protein in stationary cultures was directly correlated with an increase in translatable S100 protein mRNA.

RNA synthesis and processing as a measure of phenotypic variability in cytodifferentiation and neoplasia

Neoplastic cell lines exhibit RNA synthesis and process patterns which are related to phenotypic attributes more complex than merely the rate of proliferation. Mouse neuroblastoma cells of the same genotype but different differentiated states have different ribosomal RNA precursor processing patterns, while plasmacytoma cells of different genotypes but the same differentiated state have the same pre-ribosomal RNA processing pattern. In addition, our observations indicate that chromatin-associated RNA is involved in cytodifferentiation and is closely related to phenotypic variability. When neuroblastoma cells are induced to differentiate, there is a 2- to 3-fold increase in the labeling of chromatin-associated RNA. Both of the differentiated cell lines, human myeloma and mouse neuroblastoma, have slow-labeling, stable chromatin-associated RNA while this same fraction from HeLa cells is labeled rapidly and is unstable.

Translation of mRNA from rat-liver polysomes into tyrosine aminotransferase and tryptophan oxygenase in a protein-synthesizing system from wheat germ. Effects of cortisol on the translatable levels of mRNA for these two enzymes

Messenger RNA was isolated from rat liver polysomes by phenol/chloroform extraction and subsequent oligo(dT)-cellulose chromatography. The mRNA was translated in a protein-synthesizing system in vitro derived from wheat germ. The system was optimized in respect to Mg2+ and K+. The presence of spermidine or spermine is necessary for the synthesis of polypeptides having molecular weights of over 20 000. In the absence of the bases only small molecular weight products are formed. The amount of protein synthesized is linearly dependent on the amount of mRNA added up to concentrations of 80 mug mRNA/ml. The synthesis of tyrosine aminotransferase and tryptophan oxygenase in the system in vitro has been demonstrated by specific immunoprecipitation and sodium-dodecylsulfate polyacrylamide gel electrophoresis of the precipitate with enzyme proteins as marker. The amount of specific product formed is linearly dependent on the amount of mRNA present. The amount of translatable tyrosine aminotransferase mRNA and tryptophan oxygenase mRNA increases after administration of hydrocortisone to adrenalectomized rats. At low doses of hormone (2 mg/100 g body weight) maximal values are observed at 4 h, control levels being reached at 6-8 h after hormone application. With higher doses of hydrocortisone (20 mg/100 g body weight) maximal values are attained at 6 h, tending to control levels 14 h after treatment. The enzyme activity curves are parallel to the mRNA curves, the peak of enzyme activity occurring 2 h after the peak of mRNA activity.

Genetic, endocrine, and viral aspects of AKR leukemogenesis

In the AKR strain of mice a high incidence of spontaneous lymphoid leukemia develops before 12 months of age. Genetic, viral, and endocrine factors interact during development to produce the syndrome. Many of the deficiencies of AKR mice are associated with gene action in chromosome 17, at or near the major histocompatibility locus. It is suggested that low steroid levels and high thyroxin levels during an early period of development are an essential part of the syndrome. Specifically, induction of a polymerase enzyme and regulation of the extent of its action by hormones are postulated to favor appearance of C-type particles and accumulation of a population of undifferentiated lymphoid stem cells. Immunodeficiency and leukemic transformation result.

Synthesis of the brain-specific S-100 protein in a cell-free system from wheat embryo programmed with poly(A)-containing RNA from rabbit brain

Polyadenylated polysomal RNA was prepared from rabbit cerebral hemispheres using phenol extraction and chromatography on oligo(dT)-cellulose. This RNA directed the synthesis of the brain-specific S-100 protein in cell-free extracts from wheat embryo. S-100 protein was absent from the products of endogenous incorporation and from a reaction programmed with kidney mRNA. These results suggest that S-100 protein mRNA contains a poly(adenylic acid) sequence and rule out the necessity of a brain-specific factor for translation of -S100 protein mRNA.

Lineages, quantal cell cycles, and the generation of cell diversity

Most theories of determination or differentiation assume that embryonic cells differ from mature cells. Embryonic cells are thought to have metastable control mechanisms. These labile controls are believed to become progressively more stabilized as the cells differentiate. Zygote, blastula, neural plate, limb bud, somite, or ‘stem’ cells are conceived of as undifferentiated, totipotent, or multipotential cells. As such, these cells supposedly have available for activation a larger repertoire of phenotypic programmes than their progeny. A necessary corollary to this view is that the activation of one particular phenotypic programme out of the many available is a function of instructive exogenous inducing molecules.