Glucocorticoid-mediated induction of alpha 1-acid glycoprotein: evidence for hormone-regulated RNA processing

Histone deacetylase inhibition attenuates cardiac hypertrophy and fibrosis through acetylation of mineralocorticoid receptor in spontaneously hypertensive rats

Inhibition of histone deacetylases (HDACs) by valproic acid (VPA) attenuates inflammatory, hypertrophic, and fibrotic responses in the hearts of spontaneously hypertensive rats (SHRs); however, the molecular mechanism is still unclear. We hypothesized that HDAC inhibition (HDACi) attenuates cardiac hypertrophy and fibrosis through acetylation of mineralocorticoid receptor (MR) in SHRs. Seven-week-old SHRs and Wistar-Kyoto rats were treated with an HDAC class I inhibitor (0.71% w/v in drinking water; VPA) for 11 weeks. Sections of heart were visualized after trichrome stain as well as H&E stain. Histone modifications, such as acetylation (H3Ac [acetylated histone 3]) and fourth lysine trimethylation (H3K4me3) of histone 3, and recruitment of MR and RNA polymerase II (Pol II) into promoters of target genes were measured by quantitative real-time polymerase chain reaction after chromatin immunoprecipitation assay. MR acetylation was determined by Western blot with anti-acetyl-lysine antibody after immunoprecipitation with anti-MR antibody. Treatment with VPA attenuated cardiac hypertrophy and fibrosis. Although treatment with VPA increased H3Ac and H3K4me3 on promoter regions of MR target genes, expression of MR target genes as well as recruitment of MR and Pol II on promoters of target genes were decreased. Although HDACi did not affect MR expression, it increased MR acetylation. These results indicate that HDACi attenuates cardiac hypertrophy and fibrosis through acetylation of MR in spontaneously hypertensive rats.

The acute phase response in the rodent

In the rodent, the general response to acute inflammation and tissue damage is characterized by a complex rearrangement in the pattern of concentrations of proteins in the plasma leading to an increase in the sedimentation rate of erythrocytes, an increase in leukocyte concentration in the bloodstream, and a decrease in the hematocrit. Body temperature changes only slightly or not at all. The reasons for the change in plasma concentrations of proteins are changes in their rates of synthesis in the liver. Degradation of plasma proteins is not affected. The details of the acute phase response evolved in the interaction of species with their environment. Therefore, it is not surprising to find differences in the details of the acute phase response among species. For example, alpha 2-macroglobulin is a strongly positive acute phase reactant in the rat, but not in the mouse; C-reactive protein is a strongly positive acute phase protein in the mouse, but is not found in the rat. An inducible acute phase cysteine proteinase inhibitor system, which has evolved from a primordial kininogen gene, has been observed so far only in the rat. The changes in the synthesis rates of acute phase proteins during inflammation are closely reflected by corresponding changes in intracellular mRNA levels. In the liver, the capacity to induce the acute phase pattern of synthesis and secretion of plasma proteins probably develops around birth. Changes in mRNA levels are brought about by changes in transcription rates or by changes in mRNA stability. Kinetics of mRNA changes during the acute phase response differ for individual proteins. The main signal compound for eliciting the acute phase response in liver seems to be interleukin-6/interferon-beta 2/hepatocyte stimulating factor, whereas interleukin-1 leads to typical acute phase changes in mRNA levels only for alpha 1-acid glycoprotein, albumin, and transthyretin. Plasma protein genes are expressed in various extrahepatic tissues, such as the choroid plexus, the yolk sac, the placenta, the seminal vesicles, and other sites. All these tissues are involved in maintaining protein homeostasis in associated extracellular compartments by synthesis and secretion of proteins. Synthesis and secretion of plasma proteins in paracompartmental organs other than the liver is not influenced by the acute phase stimuli.

The organophosphate-induced acute-phase response is characterized by synthesis of alpha 1-acid glycoprotein that exhibits an immunomodulatory effect

The organophosphorus compounds soman and paraoxon induce the acute-phase (AP) response. All phases of the AP response, from macrophage activation and stimulation of glucocorticoid secretion to AP protein expression appear to be under the control of similar molecular mechanisms to those during the turpentine-induced AP response. The AP protein content in the circulation 24 h after either soman, paraoxon or turpentine administration was injury-specific. Both soman and paraoxon poisoning were characterized by significantly increased synthesis of alpha(1)-acid glycoprotein (AGP) that displayed an immunomodulatory effect in vitro. This result suggests that after organophosphate poisoning AGP participates in vivo in a negative feedback mechanism that prevents over-activity of the immune system.

Inhibitory cis-element-mediated decay of human papillomavirus type 16 L1-transcript in undifferentiated cells

Production of human papillomavirus type 16 major capsid protein L1 in undifferentiated cells is negatively regulated by several yet unidentified cis-acting inhibitory RNA elements, among which a major element is located within the first 514 nucleotides of the L1-mRNA. By Northern blotting we examined effect of the major element on the steady-state level of mRNA transiently transcribed in 293T cells from the firefly luciferase (Fluc) gene combined with the L1 DNA fragment encoding the major element. As reported previously, the element down-regulated steady-state level of the mRNA. The most efficient down-regulation was achieved by insertion of the element near the 5' end of mRNA, resulting in an undetectable level of the mRNA. The longer the distance from the 5' end of the mRNA to the element, the weaker the down-regulation. The half-life of the mRNA having the element was similar to that of normal Fluc-mRNA. When the element near the 5' end was removed by splicing, the steady-state level of the resultant mRNA was raised to a readily detectable level. The steady-state level of RNA synthesized by RNA polymerase-I was not influenced by the presence of the element. Taken together, it is suggested that DNA region encoding the major inhibitory element does not disturb transcription and that the pre-mRNA is degraded by an RNA element-mediated mechanism after the splicing step in the course of mRNA maturation.

20-Hydroxyecdysone indirectly regulates Hemolin gene expression in Hyalophora cecropia

Development and innate immune defence are two vital processes that have been demonstrated to use the same or similar molecules and signalling pathways in insects. Hemolin is a moth haemolymph protein belonging to the immunoglobulin superfamily. It is strongly induced upon bacterial infection. However, recent studies indicate a developmental regulation of hemolin. We show that the steroid hormone 20-hydroxyecdysone (20E) can activate the expression of Hyalophora cecropia Hemolin (HcHemolin) in the fat body of diapausing pupae. Using the protein synthesis inhibitor cycloheximide we demonstrate that Hemolin up-regulation by 20E requires ongoing protein synthesis. Moreover, 20E enhances transcription of the Hemolin gene in response to bacteria. Comparing the upstream regions of Manduca sexta Hemolin (MsHemolin) and HcHemolin, we identified four putative regulatory sites. Two are putative hormone response elements (HREs), one with an imperfect inverted repeat (HRE-IR) and one with a monomeric site (HRE-M). An additional monomeric hormone receptor site (MRE) is present only in HcHemolin. The third conserved motif is similar to the interferon (IFN) regulatory factor binding element (IRF-E) and IFN-stimulated response element (ISRE). The fourth conserved element is a kappaB motif situated between the Cap-site and the TATA-box. Finally, by electrophoresis mobility shift assay we demonstrate that the HRE-IR forms specific complexes with nuclear extract proteins of normal pupae that increase after 20E stimulation.

Glutamine Stimulates Argininosuccinate Synthetase Gene Expression through Cytosolic O-Glycosylation of Sp1 in Caco-2 Cells

Glutamine stimulates the expression of the argininosuccinate synthetase (ASS) gene at both the level of enzyme activity and mRNA in Caco-2 cells. Searching to identify the pathway involved, we observed that (i) the stimulating effect of glutamine was totally mimicked by glucosamine addition, and (ii) its effect but not that of glucosamine was totally blocked by 6-diazo-5-oxo-l-norleucine (DON), an inhibitor of amidotransferases, suggesting that the metabolism of glutamine to glucosamine 6-phosphate was required. Moreover, run-on assays revealed that glucosamine was acting at a transcriptional level. Because three functional GC boxes were identified on the ASS gene promoter (Anderson, G. M., and Freytag, S. O. (1991) Mol. Cell Biol. 11, 1935-1943), the potential involvement of Sp1 family members was studied. Electrophoretic mobility shift assays using either the Sp1 consensus sequence or an appropriate fragment of the ASS promoter sequence as a probe demonstrated that both glutamine and glucosamine increased Sp1 DNA binding. Immunoprecipitation-Western blot experiments demonstrated that both compounds increased O-glycosylation of Sp1 leading to its translocation into nucleus. Again, the effect of glutamine on Sp1 was inhibited by the addition of DON but not of glucosamine. Taken together, the results clearly demonstrate that the metabolism of glutamine through the hexosamine pathway leads to the cytosolic O-glycosylation of Sp1, which, in turn, translocates into nucleus and stimulates the ASS gene transcription. Collectively, the results constitute the first demonstration of a functional relationship between a regulating signal (glutamine), a transcription factor (Sp1), and the transcription of the ASS gene.

mRNA instability in the nucleus due to a novel open reading frame element is a major determinant of the narrow tissue specificity of folate receptor alpha

The folate receptor type alpha (FR-alpha) is a promising tumor marker and target. Here, we investigate the mechanistic basis for the tumor specificity and vast overexpression of FR-alpha. Among representative FR-alpha-positive (HeLa and JAR) and FR-alpha-negative (MG63, Caki1, and HT3) cell lines, the transcription rates of the endogenous FR-alpha gene, as well as the FR-alpha promoter activity, were relatively weak and comparable, but the FR-alpha transcript was abundant only in total RNA and nuclear RNA from the FR-alpha-positive cells. Rous sarcoma virus (RSV) promoter-driven expression of the FR-alpha gene was 7 to 30 times greater in the FR-alpha-positive than in FR-alpha-negative cells, both at the protein and mRNA levels, independently of intron sequences. Through the use of chimeric FR-alpha/FR-beta cDNAs, the above pattern of FR-alpha expression was attributed to a 60-bp sequence in the FR-alpha open reading frame. This sequence element, when placed in the 5' untranslated region of RSV promoter-luciferase, decreased the reporter expression approximately 7- to 20-fold in FR-alpha-negative cells (MG63, Caki1, HT3, BG1, and MCF7) relative to FR-alpha-positive cells (HeLa, JAR, and JEG3). Substitution of this FR-alpha element in FR-beta increased the in vivo degradation rate of the transcript in the nuclei of MG63 cells but not in the nuclei of HeLa cells or in the cytosol of MG63 or HeLa cells. The results reveal an efficient mechanism by which a novel sequence element causes differential transcript degradation in the nucleus to ensure narrow tissue specificity for a gene (e.g., that for FR-alpha) whose transcription is weak and relatively nonselective. FR-alpha exhibited constitutive mRNA and protein synthesis during the cell cycle and a slow protein turnover, presumably ensuring a high steady-state level of the receptor in cells that could override the nuclear mRNA instability determinant.

Nopp140 is a mediator of the protein kinase A signaling pathway that activates the acute phase response alpha1-acid glycoprotein gene

The acute phase response (APR) in liver during inflammation is one of the well known examples for elucidating the signaling pathways that lead to the combinatorial regulation of gene expression. The APR is exemplified by alpha(1)-acid glycoprotein gene (agp) expression. A number of transcription factors, including CCAAT/enhancer-binding protein beta (C/EBPbeta), glucocorticoid receptor, cAMP-response element-binding protein (CREB), and Nopp140, are known to participate in its induction. The underlying mechanism of Nopp140 and other factors for regulating agp expression remains unclear. Here we demonstrate that protein kinase A (PKA)-dependent phosphorylation of Nopp140, together with C/EBPbeta, induces agp gene expression synergistically. The cooperative activation of the agp gene by Nopp140 and forskolin is sensitive to inhibition by PKI. Results from biochemical and functional characterizations of Nopp140 mutants defective in PKA phosphorylation sites suggest that PKA-dependent Nopp140 phosphorylation is important for its role in agp gene activation. Furthermore, maximal activation of the agp gene by PKA-phosphorylated Nopp140 depends on the presence of CREB and C/EBPbeta. The participation of CREB in the activation is, however, independent of its PKA-mediated phosphorylation. In summary, we demonstrate the existence of a novel Nopp140-mediated PKA signaling pathway that leads to the activation of agp, one of the major acute phase response genes.

Role of glucocorticoids in the maturation of the rat renal Na+/H+ antiporter (NHE3)

BACKGROUND

Neonates have a lower Na+/H+ antiporter activity on the apical membrane of proximal tubule than that of adults. The maturational increase in Na+/H+ antiporter activity occurs at the time when there is a rise in serum glucocorticoid levels in rats. The purpose of the present study was to examine whether glucocorticoids are responsible for the postnatal increase in Na+/H+ antiporter activity.

METHODS

Nine-day-old Sprague-Dawley rats were compared with rats studied at 30 days of age who had either a sham operation or adrenalectomy (ADX) at nine days of age and with rats that had an adrenalectomy and physiologic corticosterone replacement (ADX-Cort) to determine whether glucocorticoid deficiency prevented the maturational increase in Na+/H+ antiporter activity. Na+/H+ antiporter activity was measured in proximal convoluted tubules perfused in vitro by the change in cell pH (pHi) following luminal sodium removal. NHE3 mRNA abundance was measured using Northern blot analysis, and NHE3 protein abundance was measured by immunoblot.

RESULTS

Na+/H+ antiporter activity was 93.8 +/- 17.7, 157.0 +/- 18.0, 356.7 +/- 29.9, and 402.5 +/- 14.5 pmol/mm. min in nine-day-old, ADX, ADX-Cort, and sham control groups, respectively. The ADX-Cort and sham control were higher than the 9-day-old and the 30-day-old ADX group (P < 0.05). Brush-border membrane NHE3 protein abundance in the nine-day-old and ADX groups were sixfold less than ADX-Cort and sham control groups (P < 0.001). Nine-day-old neonates had fivefold less renal cortical NHE3 mRNA than the ADX, ADX-Cort, and sham-operated control groups (P < 0.01).

CONCLUSIONS

These data demonstrate that glucocorticoids play a role in the postnatal maturation of the proximal tubule Na+/H+ antiporter activity and brush-border membrane NHE3 protein abundance. Glucocorticoid deficiency does not completely prevent the maturational increase in Na+/H+ antiporter activity and does not affect NHE3 mRNA abundance.

Human alpha-1-glycoprotein and its interactions with drugs

For about half a century, the binding of drugs to plasma albumin, the "silent receptor," has been recognized as one of the major determinants of drug action, distribution, and disposition. In the last decade, the binding of drugs, especially but not exclusively basic entities, to another plasma protein, alpha 1-acid glycoprotein (AAG), has increasingly become important in this regard. The present review points out that hundreds of drugs with diverse structures bind to this glycoprotein. Although plasma concentration of AAG is much lower than that of albumin, AAG can become the major drug binding macromolecule in plasma with significant clinical implications. Also, briefly reviewed are the physiological, pathological, and genetic factors that influence binding, the role of AAG in drug-drug interactions, especially the displacement of drugs and endogenous substances from AAG binding sites, and pharmacokinetic and clinical consequences of such interactions. It can be predicted that in the future, rapid automatic methods to measure binding to albumin and/or AAG will routinely be used in drug development and in clinical practice to predict and/or guide therapy.

Mechanisms of differential transferrin receptor expression in normal hematopoiesis

We have investigated the expression of transferrin receptor (TfR) iron regulatory protein-1 (IRP-1) and iron regulatory protein-2 (IRP-2) in liquid suspension culture of purified hematopoietic progenitor cells (HPCs) induced by a growth factor stimulus to proliferation and unilineage differentiation/maturation through the erythroid, granulocytic, monocytic and megakaryocytic lineages. In initial HPC differentiation, TfR expression is induced in both erythroid and granulopoietic cultures. In late HPC differentiation (i.e. starting from day 5 of culture) and then differentiated precursor maturation, the TfR gene is highly expressed in the erythroid lineage, whereas it is sharply downmodulated in the granulopoietic, monocytopoietic and megakaryocytic series. The elevated TfR expression in erythroid cells is: (a) mediated through a high rate of TfR gene transcription; (b) modulated by intracellular iron levels; (c) mediated by TfR mRNA stabilization through the iron regulatory protein (IRP), in that IRP-1 activity is high in erythroid lineage as compared to the levels observed in other hemopoietic lineages; and (d) dependent on exogenous erythropoietin (Epo) (this is indicated by the marked TfR and IRP-1/IRP-2 downmodulation after Epo starvation). Interestingly, analysis of IRP-1 and IRP-2 expression during hemopoietic differentiation showed that: (a) IRP-1 expression was maintained during all steps of erythroid differentiation, while it was lost in the other hemopoietic lineages; (b) IRP-2 expression was observed during all stages of hemopoietic differentiation in all four lineages. However, IRP-1 and IRP-2 expression and activity are induced when monocytes, which express only low levels of IRP-1 and IRP-2, are induced to maturation to macrophages. These studies indicate that: (a) in normal erythropoiesis, the hyperexpression of TfR, starting from early erythroid HPC differentiation, is Epo-dependent and mediated via transcriptional and post-transcriptional mechanisms; (b) in the granulopoietic, monocytopoietic and megakaryocytic pathways, the TfR is first induced and then downmodulated (the latter phenomenon is mediated via transcriptional suppression of the TfR gene and IRP inactivation).

Alpha-1-acid glycoprotein

Alpha-1-acid glycoprotein (AGP) or orosomucoid (ORM) is a 41-43-kDa glycoprotein with a pI of 2.8-3.8. The peptide moiety is a single chain of 183 amino acids (human) or 187 amino acids (rat) with two and one disulfide bridges in humans and rats,respectively. The carbohydrate content represents 45% of the molecular weight attached in the form of five to six highly sialylated complex-type-N-linked glycans. AGP is one of the major acute phase proteins in humans, rats, mice and other species. As most acute phase proteins, its serum concentration increases in response to systemic tissue injury, inflammation or infection, and these changes in serum protein concentrations have been correlated with increases in hepatic synthesis. Expression of the AGP gene is controlled by a combination of the major regulatory mediators, i.e. glucocorticoids and a cytokine network involving mainly interleukin-1 beta (IL-1 beta), tumour necrosis factor-alpha (TNF alpha), interleukin-6 and IL-6 related cytokines. It is now well established that the acute phase response may take place in extra-hepatic cell types, and may be regulated by inflammatory mediators as observed in hepatocytes. The biological function of AGP remains unknown; however,a number of activities of possible physiological significance, such as various immunomodulating effects, have been described. AGP also has the ability to bind and to carry numerous basic and neutral lipophilic drugs from endogenous (steroid hormones) and exogenous origin; one to seven binding sites have been described. AGP can also bind acidic drugs such as phenobarbital. The immunomodulatory as well as the binding activities of AGP have been shown to be mostly dependent on carbohydrate composition. Finally, the use of AGP transgenic animals enabled to address in vivo, functionality of responsive elements and tissue specificity, as well as the effects of drugs that bind to AGP and will be an useful tool to determine the physiological role of AGP.

AMP-activated protein kinase counteracted the inhibitory effect of glucose on the phosphoenolpyruvate carboxykinase gene expression in rat hepatocytes

The effect of AMP-activated protein kinase (AMPK) in the regulation of the phosphoenolpyruvate carboxykinase (PEPCK) gene expression was studied in isolated rat hepatocytes. Activation of AMPK by AICAR counteracted the inhibitory effect of glucose on the PEPCK gene expression, both at the mRNA and the transcriptional levels. It is proposed that a target for AMPK is involved in the inhibitory effect of glucose on PEPCK gene transcription.

Inducible Expression and Regulation of the α1-Acid Glycoprotein Gene by Alveolar Macrophages: Prostaglandin E2 and Cyclic AMP Act as New Positive Stimuli

We have reported that α1-acid glycoprotein (AGP) gene expression was induced in lung tissue and in alveolar type II cells during pulmonary inflammatory processes, suggesting that local production of this immunomodulatory protein might contribute to the modulation of inflammation within the alveolar space. Because AGP may also be secreted by other cell types in the alveolus, we have investigated the expression and the regulation of the AGP gene in human and rat alveolar macrophages. Spontaneous AGP secretion by alveolar macrophages was increased 4-fold in patients with interstitial lung involvement compared with that in controls. In the rat, immunoprecipitation of [35S]methionine-labeled cell lysates showed that alveolar macrophages synthesize and secrete AGP. IL-1β had no effect by itself, but potentiated the dexamethasone-induced increase in AGP production. RNase protection assay demonstrated that AGP mRNA, undetectable in unstimulated cells, was induced by dexamethasone. Conditioned medium from LPS-stimulated macrophages as well as IL-1β had no effect by themselves, but potentiated the dexamethasone-induced increase in AGP mRNA levels. In addition to cytokines, PGE2 as well as dibutyryl cAMP increased AGP mRNA levels in the presence of dexamethasone. When AGP expression in other cells of the monocyte/macrophage lineage was examined, weak and no AGP production by human blood monocytes and by rat peritoneal macrophages, respectively, were observed. Our data showed that 1) AGP expression is inducible specifically in alveolar macrophages in vivo and in vitro; and 2) PGE2 and cAMP act as new positive stimuli for AGP gene expression.

Cell swelling increased the alpha2-macroglobulin gene expression in cultured rat hepatocytes

The effect of cell swelling on the expression of the alpha2-macroglobulin (alpha2M) gene was studied in hepatocytes in culture. Hypoosmolarity induced an increase (3-fold increase) in the level of alpha2M mRNA through a corresponding stimulation of the rate of transcription of the alpha2M gene. The addition of raffinose (100 mM) corrected the effect of hypoosmolarity at both mRNA and transcriptional level, demonstrating that cell swelling per se was responsible for the observed effect on the expression of the alpha2M gene. Moreover, the effect of cell swelling was additive to that of interleukin 6, a major mediator of the acute-phase response.

Estrogen regulation of peptidylglycine alpha-amidating monooxygenase messenger ribonucleic acid levels by a nuclear posttranscriptional event

Peptidylglycine alpha-amidating monooxygenase (PAM; EC 1.14.17.3) is a bifunctional protein containing two enzymes that act sequentially to catalyze the conversion of glycine-extended peptides into COOH-terminal amidated peptides. We have previously shown that PAM messenger RNA (mRNA) levels in the anterior pituitary of intact cycling adult female rats showed changes inversely related to the physiological variations of plasma estrogen levels during the estrous cycle. Chronic treatment of ovariectomized (OVX) rats with 17beta-estradiol was accompanied by a 4.5 +/- 0.5-fold decrease in total PAM mRNA and a 2-fold decrease in PAM activity in the anterior pituitary gland. To investigate the cellular site at which 17beta-estradiol acts to affect the PAM mRNA, we made parallel measurements of the relative levels of PAM mRNA and nuclear precursor RNA and the relative rate of gene transcription after treatments designed to alter the estrogen status. The transcription rate experiments indicated that these 17beta-estradiol effects were not due to reduced PAM gene activity, suggesting that a posttranscriptional mechanism was involved. The most common mechanism of posttranscriptional regulation affects cytoplasmic mRNA stability. Primary rat pituitary cell cultures from OVX and OVX-17beta-estradiol-treated rats in the presence of actinomycin D showed that 17beta-estradiol treatment decreased the half-life of PAM mRNA from 15-16 h to 8-9 h. There was no effect of 17beta-estradiol on PAM mRNA poly(A) tail length or site of polyadenylation. However, in this study the down-regulation of PAM was identified as a nuclear event. Analysis of nuclear RNA with probes specific for PAM intron sequences shows that decreased PAM expression after 17beta-estradiol treatment was largely due to intranuclear destabilization of the primary transcript. The levels of nuclear precursor RNA were decreased roughly 5- to 6-fold in OVX + 17beta-estradiol compared with OVX rats. The decrease in PAM mRNA is blocked by cycloheximide, indicating that its requires new protein synthesis. Mechanisms that would generate such an effect include altered stability of unprocessed message in the nucleus. The proportional changes observed in the nuclear precursor and mRNA levels suggest that the site of control is at the level of stability of the nuclear precursor RNA for PAM mRNA.

The glucocorticoid receptor regulates the binding of C/EPBbeta on the alpha-1-acid glycoprotein promoter in vivo

A complex interaction between the Glucocorticoid Receptor (GR), C/EBPbeta, and other transcription factors activate the Alpha-1 Acid Glycoprotein (AGP) promoter in HTC(JZ-1) rat hepatoma culture cells. This effect is mediated by the so-called Steroid Responsive Unit (SRU) of the AGP promoter that contains several binding sites for C/EBP transcription factors, some of which overlap with the Glucocorticoid Responsive Element (GRE). Our in vivo footprinting experiments revealed that the GRE- and the C/EBP-binding sites were already occupied glucocorticoid dependently in HTC(JZ-1) cells 10 min after dexamethasone administration (10(-6) M). Furthermore, local changes in the chromatine structure shown by the appearance of DNAse I hypersensitive sites (HS sites) also took place. These changes were probably dependent on a tissue-specific organization of the chromatine at the SRU because they were not detectable in a different glucocorticoid-responsive cell line (PC12) that did not express AGP. Here, we have also shown that withdrawal of dexamethasone or addition of the anti-glucocorticoid RU486 were able to revert the pattern induced by dexamethasone in vivo. The disappearance of the protected region and the hypersensitive sites, typical of the hormone activated promoter, confirmed the necessity of the GR to be bound by the agonist and the inability of the GR-antagonist complex to bind the DNA. By functional assays, we showed that the occupancy of the SRU by these transcriptional proteins in vivo correlated with the activation of the AGP gene transcription. With these results, we have shown that one of the functions of the GR to activate transcription of the AGP gene is to recruit C/EBPbeta and to maintain it bound at its target DNA sequences (SRU). This process was not accomplished by RU486.

Regulation of argininosuccinate synthetase mRNA level in rat foetal hepatocytes

Expression of the hepatic gene for argininosuccinate synthase (ASS), one of the key enzymes of the urea cycle, was analysed during the perinatal period in the rat. To this end, the amount of specific mRNA was measured in the liver at various stages of development and in cultured foetal hepatocytes maintained in different hormonal conditions. The ASS mRNA was first detected in 15.5-day foetuses and its level increased concomitantly with a rise in the enzyme activity, suggesting that the appearance of the ASS activity reflects the turning on of specific gene transcription. This was demonstrated by run-on assay which showed an enhanced rate of transcription of the ASS gene during the perinatal period. When foetal hepatocytes were cultured with dexamethasone, a dose-dependent increase in ASS mRNA was measured, which was completely abolished by actinomycin D addition. The transcription rate of the gene was increased about twofold in the presence of the steroid, as measured by nuclear run-on assay. This transcriptional action could additionally require a protein factor since it could be inhibited by the simultaneous addition of puromycin. Insulin or glucagon respectively repressed or enhanced the dexamethasone-induced accumulation of ASS mRNA when added simultaneously with the steroid for 24 h. This developmental regulation of the ASS mRNA by glucocorticoids, insulin and glucagon could account for the modulation of the enzyme activity previously observed in vivo and in vitro in the foetal liver.

Identification and characterization of a nucleolar phosphoprotein, Nopp140, as a transcription factor

Expression of the alpha-1 acid glycoprotein (AGP) gene (agp) is activated by a key transcription factor, AGP/enhancer-binding protein (AGP/EBP, commonly called C/EBP beta), in the liver during the acute-phase response. In addition to this positive regulation, agp is negatively regulated by nucleolin (T. H. Yang et al., Mol. Cell. Biol. 14:6068-6074, 1994). Other factors involve in positive regulation of the agp gene are poorly characterized. In a systematic search for factors that may interact with AGP/EBP, we have identified Nopp 140, a phosphoprotein of 140 kDa, by immunoaffinity chromatography. Nopp 140 not only functions as a transcriptional activator per se but also interacts with AGP/EBP to synergistically activate the agp gene in an AGP/EBP-binding motif-dependent manner. In addition to interacting with AGP/EBP, Nopp140 interacts specifically with TFIIB. Distinct regions of Nopp140 that interact with AGP/EBP and TFIIB have been characterized. The sequence of Nopp140 contains several stretches of serine- and acidic amino acid-rich sequences which are also found in ICP4 of herpes simplex virus type 1, a known transcription factor that interacts with TFIIB. The physical interaction between TFIIB and wild-type Nopp140 or several deletion mutants of Nopp140 correlates with the ability of Nopp140 to activate the agp gene synergistically with AGP/EBP. Thus, the molecular mechanism for agp gene activation may involve the interaction of AGP/EBP and TFIIB mediated by coactivator Nopp140.

Glutamine inhibits the lowering effect of glucose on the level of phosphoenolpyruvate carboxykinase mRNA in isolated rat hepatocytes

The expression of phosphoenolpyruvate carboxykinase (P-pyruvate CK) was shown to be decreased by hypoosmolarity and increased by glutamine in perfused liver from fed rats [Newsome, W. P., Warskulat, U., Noe, B., Wettstein, M., Stoll, B., Gerok, W. & Häussinger, D. (1994) Biochem, J. 304, 555-560]. This work was undertaken to specify the mechanisms of glutamine action, using isolated hepatocytes from rats that had been starved for 24 h. At low concentrations (up to 5 mM), glutamine elicited a decrease in the level of P-pyruvate CK mRNA through cell swelling and, at higher concentrations, an increase in the mRNA level was observed. Experiments with combinations of glucose and glutamine or glucose and various amino acids demonstrated that glutamine counteracted the inhibitory effect of glucose on P-pyruvate CK mRNA at a transcriptional, level, and strongly suggested that the amide group of glutamine was involved in this effect. The metabolism of glucose was required for the reinforcement of the apparent stimulatory effect of glutamine, as demonstrated by the use of various sugars. Glucosamine, but not mannosamine, increased the level of P-pyruvate CK mRNA, as did glucose plus glutamine. These results suggest that the pathway leading from glucosamine-6-phosphate production might be responsible, at least partly, for the effect observed on P-pyruvate CK mRNA.

Regulation of tyrosine aminotransferase gene expression by glucocorticoids in quiescent and regenerating liver

Following 70% hepatectomy, the induction of tyrosine amino-transferase mRNA by glucocorticoids was marginal at 1.5 h, significantly impaired between 3 and 8 h and, at 16 h post-hepatectomy, reached a value approx. 5-fold the basal level, similar to the level observed in quiescent liver. The fold induction of the mRNA was accounted for by a similar fold activation of transcription of the gene by glucocorticoids in regenerating but not in quiescent liver; in the latter, activation of transcription was marginal in spite of glucocorticoid-induced hypersensitivity to cleavage by DNase I at the glucocorticoid-dependent enhancer of the gene. The possibility that in quiescent liver glucocorticoids act at a transcriptional step beyond initiation, increasing the rate of elongation or overcoming a blockage in elongation, was excluded. However, a similar fold induction was determined for total and nuclear tyrosine aminotransferase mRNA in the presence of glucocorticoids, suggesting that in quiescent liver glucocorticoids promote efficient maturation of the tyrosine aminotransferase primary transcript. Thus a glucocorticoid-induced nuclear post-transcriptional up-regulation apparently compensates for impaired activation of transcription of the tyrosine aminotransferase gene by glucocorticoids in quiescent liver.

Hypoosmolarity and glutamine increased the beta-actin gene transcription in isolated rat hepatocytes

The mechanism of action of hydration state was studied on beta-actin gene expression in isolated hepatocytes. Results obtained with Northern blot analysis and run on transcription assays show that hypoosmolarity increased and hyperosmolarity decreased the beta-actin mRNA level through a corresponding modulation of the rate of the gene transcription. Glutamine, which is known to induce cell swelling, also increased the beta-actin mRNA level in a dose-dependent manner and induced a stimulation of the beta-actin gene transcription. Thus, cell hydration state regulates gene expression in the liver through a transcriptional mechanism.

Hemin inhibits the interferon-beta-induced antiviral state in established cell lines

Hemin and other metalloporphyrins are known as very versatile compounds in nature, because they are able to carry out numerous functions in a free state or in association with specific proteins. When Friend murine erythroleukemia cells are treated with IFN-beta plus 100 microM hemin, the antiviral state is not observed, whereas the antiviral effect of IFN-gamma is unaffected by hemin treatment. This inhibitory effect of hemin is not restricted to erythroid cells. In fact, it is also observed in murine L929 and in human cell lines treated with IFN-beta. Neither trivalent iron in other forms nor hemin analogs (such as protoporphyrin IX or Sn(2+)-protoporphyrine IX) mimic this effect. Conversely, Co(3+)-protoporphyrin IX was as effective as hemin. At the transcriptional level, results obtained by run-on assays on nuclei from IFN-treated cells indicate that hemin does not completely inhibit IFN-beta induction of 2-5A synthetase gene(s) at 6 h of treatment but abolishes it at 24 h. In addition, hemin is able to inhibit the accumulation of IFN-induced 2-5A synthetase mRNAs. Experiments carried out to investigate the hemin effect on the early steps of the IFN signaling pathway indicate that hemin interferes with the ability of type I IFN to bind to its receptor, probably by a direct action on the IFN molecule.

The human inter-alpha-trypsin inhibitor genes respond differently to interleukin-6 in HepG2 cells

The effects of interleukin 6 (IL-6), the major inducer of the acute-phase reaction, on the expression of inter-alpha-trypsin inhibitor (ITI) genes were examined using human HepG2 hepatoma cells. The three ITI heavy-chain genes H1, H2 and H3 were transcriptionally regulated by IL-6 in a dose- and time-dependent manner. The treatment of HepG2 cells with IL-6 resulted in an increase of H1 and H3 mRNA levels and a decrease of H2 and L mRNA levels. Actinomycin D blocked the action of IL-6, suggesting that IL-6 regulated the H1, H2, H3 gene expression. Moreover, the kinetics of the ITI mRNA degradation in untreated and IL-6-treated cells confirmed these data. The nuclear run-on assay supports the regulatory effect of IL-6 at the transcription level of the L and H2 genes. Primer extension experiments showed that the effect of IL-6 on L, H2 and H3 mRNA synthesis was not related to the transcription starting point. Although H1, H2, H3 and L gene products are supposedly present in similar amounts in the ITI and pre-alpha-trypsin inhibitor molecules, the present work shows that these genes are regulated in a different manner, at least under the influence of IL-6.

Phenobarbital induction of alpha 1-acid glycoprotein in primary rat hepatocyte cultures

The serum level of rat alpha 1-acid glycoprotein is significantly increased by treatment with phenobarbital, and in vivo studies have shown that phenobarbital seems to act mainly at the transcriptional level. To show the direct mediating effect of phenobarbital on alpha 1-acid glycoprotein gene expression, we investigated the ability of primary cultured rat hepatocytes to respond to in vitro phenobarbital administration. Phenobarbital increased both alpha 1 acid glycoprotein secretion and corresponding mRNA levels in primary rat hepatocytes cultured on matrigel. Used in combination with interleukin-1, interleukin-6 and dexamethasone, phenobarbital had an additive or synergistic effect on alpha 1-acid glycoprotein synthesis. These results show that (a) phenobarbital acts directly on hepatocytes by increasing alpha 1-acid glycoprotein gene expression and (b) this effect is mediated by a specific mechanism independent of pathways involved in alpha 1-acid glycoprotein induction by interleukin-1, interleukin-6 and glucocorticoids.

Inflammation of the dam has different effects on the binding of maternal and fetal rat liver nucleoproteins to the rat haptoglobin gene promoter

Transcriptional regulation of binding interactions between nucleoproteins and the hormone response element (RE) of the rat haptoglobin (Hp) gene was investigated in adult and fetal livers of rats exposed to inflammation on day 19 of pregnancy. Nuclear extracts from the embryonal liver displayed a barely detectable binding-affinity for hormone RE, but in extracts from the adult liver it was noticeable. The acute phase reaction of the mother promoted an increase of Hp gene expression in both adult and fetal livers, relying on stage-specific changes in hormone RE binding activities of nucleoplasmic proteins. The results indicated that the elevation of Hp gene expression in fetal liver to the steady basal level found in adults required the induction of new trans-acting proteins, whereas an overexpression of this gene in adult acute phase liver relied essentially on an increase in the binding-affinity of the preexisting hormone RE binding proteins.

Human serum amyloid A genes are expressed in monocyte/macrophage cell lines

Serum amyloid A (apoSAA) is a family of proteins found, mainly associated with high density lipoproteins, in the blood plasma of mammals and at least one avian species, the Pekin duck. These proteins are present in small amounts under normal circumstances, but their concentration is capable of rising 100- to 1,000-fold in situations involving tissue injury or infection. Like classic acute phase proteins they are produced in the liver; however, expression of one of the apoSAA genes is known to occur in activated macrophages of mice. We examined three human macrophage precursor cell lines (THP-1, U-937, and HL-60), before and after differentiation with phorbol 12-myristate 13-acetate or 1 alpha,25-dihydroxy-vitamin D3, for apoSAA messenger (m)-RNA expression and found that: 1) induction of steady-state apoSAA mRNA by lipopolysaccharide, interleukin-1, or interleukin-6 required the presence of the synthetic glucocorticoid dexamethasone; 2) the three known active genes, apoSAA1, apoSAA2, and apoSAA4, were induced in THP-1 cells, whereas the pseudogene apoSAA3 was not; 3) differentiated and undifferentiated THP-1 cells expressed apoSAA mRNA, but U-937 cells expressed apoSAA mRNA (low levels) only after phorbol 12-myristate 13-acetate differentiation and HL-60 cells did not express apoSAA mRNA whether differentiated or not; 4) apoSAA protein was detectable immunologically at a low level in lyophilized medium from induced THP-1 cells. Our findings are compatible with the hypotheses that 1) apoSAA gene expression in human monocytes/macrophages in vivo is differentiation dependent; 2) activated macrophages provide a local source of apoSAA at sites of tissue injury or inflammation; 3) apoSAA is induced in tissue macrophages by local stimuli, under conditions that may not evoke the systemic acute phase response.

Characterization of a novel transcription complex required for glucocorticoid regulation of the rat alpha-1-acid glycoprotein gene

The liver alpha-1-acid glycoprotein (AGP) gene promoter contains several positive cis-acting sequences that are involved in the hormone regulation of its expression. We have characterized a new functionally important sequence located at -155 to -143 upstream from the glucocorticoid regulatory element (GRE, -120 to -105). At least three nuclear proteins bind to this sequence (CTGTGGGAACAG), called the upstream regulatory element (URE). One of these proteins, AGP nuclear factor 4 (ANF-4), is the major component of the DNA-protein complex we detected in footprint and electrophoresis mobility shift assay (EMSA) experiments using rat liver, HTC(JZ-1) rat hepatoma cell extracts and affinity-purified proteins. Another is C/EBP beta, which also binds to three elements downstream from the GRE. The third protein is shown to have a molecular weight of 102 kD. Deletions and site-directed mutagenesis demonstrated that this complex of proteins is involved in the positive hormonal regulation of AGP gene transcription. Binding experiments revealed that ANF-4 and C/EBP beta binding sites are partially overlapping and require the palindromic structure of the URE for high-affinity binding. Southwestern (DNA-protein blot analysis) and cross-linking experiments with nuclear extracts from rat liver and HTC(JZ-1) rat hepatoma cells, revealed two identical constitutive binding activities with molecular masses of 66 and 102 kD. We concluded that this transcription complex is composed of three distinct proteins, ANF-4, C/EBP beta, and a 102-kD protein, and that they play an important role for the hormone regulation of AGP.

Pretreatment with alpha 2-macroglobulin leads to recovery of rats exposed to a lethal scald

The effect of alpha 2-macroglobulin (alpha 2M) administration on the survival rate of lethally injured rats and molecular mechanisms regulating its hepatic expression after sublethal and lethal scalding were examined. Transcriptional activity of nuclei for the alpha 2M gene increased after a sublethal 20 per cent TBSA scald reaching a maximal three-fold increase by 12 h, whereas concentrations of the corresponding mRNA and protein attained the maximal nine- and 18-fold enhancements by 24 h, respectively. After the second, lethal scald, the plasma alpha 2M level increased during the first few hours, then dropped rapidly below the control value although the abundance of its mRNA was several fold enhanced. This anomaly was ascribed to inhibition of the alpha 2M mRNA translation caused by the second scald-induced disturbance of the haemodynamic equilibria. Eighty per cent of rats receiving alpha 2M prior to rescalding survived the second injury. Their recovery proceeded in parallel with normalization of the plasma volume and reactivation of the process of acute phase protein synthesis in the liver. A functional link between these events is discussed.

Induction of liver alpha-1 acid glycoprotein gene expression involves both positive and negative transcription factors

Expression of the alpha-1 acid glycoprotein (AGP) gene is liver specific and acute phase responsive. Within the 180-bp region of the AGP promoter, at least five cis elements have been found to interact with trans-acting factors. Four of these elements (A, C, D, and E) interacted with AGP/EBP, a liver-enriched transcription factor, as shown by footprinting analysis and by an anti-AGP/EBP antibody-induced supershift in a gel retardation assay. Modification of these sites by site-directed mutagenesis coupled with transfection analysis indicated that AGP/EBP binding to all of these sites resulted in positive regulation of the promoter. Dose-response data suggest that AGP/EBP binding to these sites results in the cooperative activation of the promoter. In contrast, functional assays showed that element B is a negative regulatory element; this element is recognized by heat-stable DNA-binding factors which are found in many cells and tissues. The regulation of these binding proteins was studied in rat liver treated with lipopolysaccharide (LPS), which induced an acute-phase reaction. We found that LPS treatment resulted in a two- to threefold increase in AGP/EBP activity and a severalfold decrease in the activity of factors that bind to element B in the liver. These results indicate that expression of the AGP gene can be regulated by both positive and negative factors and that the modulation of these factors can account for the LPS induction of the AGP gene.

Induction of liver alpha-1 acid glycoprotein gene expression involves both positive and negative transcription factors

Expression of the alpha-1 acid glycoprotein (AGP) gene is liver specific and acute phase responsive. Within the 180-bp region of the AGP promoter, at least five cis elements have been found to interact with trans-acting factors. Four of these elements (A, C, D, and E) interacted with AGP/EBP, a liver-enriched transcription factor, as shown by footprinting analysis and by an anti-AGP/EBP antibody-induced supershift in a gel retardation assay. Modification of these sites by site-directed mutagenesis coupled with transfection analysis indicated that AGP/EBP binding to all of these sites resulted in positive regulation of the promoter. Dose-response data suggest that AGP/EBP binding to these sites results in the cooperative activation of the promoter. In contrast, functional assays showed that element B is a negative regulatory element; this element is recognized by heat-stable DNA-binding factors which are found in many cells and tissues. The regulation of these binding proteins was studied in rat liver treated with lipopolysaccharide (LPS), which induced an acute-phase reaction. We found that LPS treatment resulted in a two- to threefold increase in AGP/EBP activity and a severalfold decrease in the activity of factors that bind to element B in the liver. These results indicate that expression of the AGP gene can be regulated by both positive and negative factors and that the modulation of these factors can account for the LPS induction of the AGP gene.

1 alpha,25-dihydroxyvitamin D3 regulates the transcription of carbonic anhydrase II mRNA in avian myelomonocytes

Carbonic anhydrase II (CAII) is highly expressed in the osteoclast, where it is involved in the process of extracellular acidification required for bone resorption. We have previously shown that 1 alpha,25-dihydroxyvitamin D3 [1,25(OH)2D3], a steroid hormone that regulates the differentiation of macrophages and osteoclasts, induces the expression of CAII mRNA and protein in avian bone marrow cells. To determine whether this regulation occurred at the gene level, we have studied the effects of 1,25(OH)2D3 on CAII expression in a transformed myelomonocytic avian cell line (BM2). As observed in nontransformed cells, 1,25(OH)2D3 markedly increased CAII biosynthesis and mRNA levels. The increase in CAII mRNA was detected as early as 3 hr after adding the hormone (1.9-fold) and reached 4.7-fold by 48 hr. These effects were completely blocked by actinomycin D, and nuclear run-on analysis confirmed that 1,25(OH)2D3 increased the rate of CAII gene transcription. In contrast, induction of CAII mRNA expression was not affected by inhibition of protein synthesis with cycloheximide, and no significant changes in mRNA stability were seen. Thus, 1,25(OH)2D3 modulates CAII gene expression at the transcriptional level, and this effect does not require de novo synthesis of other gene products. These results suggest that activation of the CAII gene occurs early in the differentiation events triggered by vitamin D3 in myelomonocytic cells.

The expression of liver acute-phase protein genes during rat development and in response to inflammation of the dam

The hepatic expression of albumin (Al) and plasma acute phase protein genes (APP) was examined during the development of rat liver and in response to inflammation of the dam. Throughout the 10- to 20-day gestation period the level of alpha 2-macroglobulin (alpha 2M) mRNA in fetal liver exceeded twice that of the adult liver. The concentrations of the other APP and Al mRNAs were 10-30% of those of the adult liver between days 10 and 13 of gestation, then increased to values which ranged from 40% for haptoglobin (Hp) to 80% for Al and alpha 1-acid glycoprotein (AGP) mRNAs on day 19 of gestation. The transition of fetuses to an extrauterine environment was followed by a temporary overexpression of the Hp gene and an increase of the fibrinogen (Fb), AGP and thiostatin (TST) mRNAs to adult levels. Fetal liver responded to inflammation of the mother by a transcriptional induction of all of the investigated APP genes, except for the Fb gene whose level of expression remained unchanged. The pattern of individual APP genes expression in maternal and fetal livers was similar and characteristic for the acute phase reaction.

Post-transcriptional regulation of urokinase plasminogen activator gene expression occurs in the nucleus of BC1 rat mammary tumor cells

The regulation of urokinase plasminogen activator (uPA) expression was investigated in 2 highly metastatic rat mammary adenocarcinoma cell lines, BC1 and MAT 13762. BC1 cells were observed to synthesize, on average, 10 times less uPA enzyme and mRNA than MAT 13762 cells; however this difference was not accounted for by differences in uPA gene copy number/structure or in the rate of uPA gene transcription in the cell lines studied. Moreover, Northern blot analysis of invasive sub-populations derived in vitro from the BC1 cell line revealed levels of uPA expression similar to those of the parent, but a 3-fold elevation in expression of the metalloprotease gene, transin. Further investigation showed that treatment of BC1 cells with either of the protein synthesis inhibitors, cycloheximide or anisomycin, increased the level of both nuclear and cytoplasmic uPA RNA 6- to 18-fold in 4 hr, whilst inducing a maximum 2.6-fold increase in the rate of uPA gene transcription. This increase in uPA gene expression may therefore reflect, in part, an increase in the stability and/or processing of nuclear uPA transcripts. These results suggest that the degree of uPA gene expression does not correlate directly with BC1 tumor-cell invasion in vitro, and that the uPA gene is down-regulated, at least in part, post-transcriptionally in the nucleus of BC1 mammary tumor cells.

Modifications of hepatic alpha-1-acid glycoprotein and albumin gene expression in rats treated with phenobarbital

The serum level of alpha 1-acid glycoprotein (alpha 1-AGP) is significantly increased in various animal species by treatment with cytokines, glucocorticoids and phenobarbital. The mechanisms responsible for the cytokine-induced and glucocorticoid-induced increases are now well documented, but not so in the case of phenobarbital. The main purpose of this study was to assess whether phenobarbital acts on alpha 1-AGP synthesis in the liver at the transcriptional or translational level. Male Dark Agouti rats received 70 mg phenobarbital/kg daily for 7 days. The analysis of total hepatic RNA showed that a single injection of phenobarbital induced an 11-fold increase in phenobarbital-dependent cytochrome P450IIB mRNA, whereas seven injections of phenobarbital were required to induce a maximum 5.5-fold increase in alpha 1-AGP mRNA. Concurrently, the transcription rate of the alpha 1-AGP gene rose 3.5-fold. Hepatocytes isolated after the seventh injection of phenobarbital showed a threefold increased capacity to secrete alpha 1-AGP, corresponding to a 3.2-fold increased alpha 1-AGP mRNA content in the liver. In conditions in which its effect on the induction of alpha 1-AGP synthesis was maximum, phenobarbital caused a 30% reduction in liver albumin mRNA and in albumin secretion by isolated hepatocytes, resulting from a 60-70% reduction in the rate of transcription of the albumin gene measured in isolated nuclei. We conclude that the effect of phenobarbital on alpha 1-AGP and albumin gene expression occurs at the transcriptional rather than the translational level.

Effect of dexamethasone on mRNA levels for 5-aminolevulinate synthase in different rat tissues

5-Aminolevulinate synthase mRNA levels from different tissues were quantitated by Northern blot hybridization analysis utilizing the rat liver 5-aminolevulinate synthase cDNA clone as probe. A 5-aminolevulinate synthase mRNA species of size 2.3 kb was seen in all the tissues examined. Densitometric scanning of the autoradiographs demonstrated that the adrenal gland contained the largest amount of 5-aminolevulinate synthase mRNA. Levels corresponding to approximately 50% of this amount were found in the small intestine, lung, heart, muscle and testes. In the liver and kidney the level was approximately 25% of that found in the adrenal gland. These results demonstrate the housekeeping role of this gene. Dexamethasone treatment for 1 day or 5 days dramatically induced 5-aminolevulinate synthase mRNA levels in the liver and small intestine, and to a lesser extent in lung, heart, kidney and muscle. Nuclear run-off experiments suggest that a post-transcriptional mechanism predominantly contributes to the dexamethasone-induced increase in 5-aminolevulinate synthase mRNA levels observed in the liver. Interestingly, in the steroidogenic tissues of the adrenal gland and testes, there was a substantial decrease in 5-aminolevulinate synthase mRNA levels after dexamethasone administration but the mechanism of this control remains to be investigated.

Posttranscriptional regulation of beta interferon expression in erythroid Friend cells treated with gamma interferon

Treatment of Friend erythroleukemia cells (FLC) with gamma interferon (IFN-gamma) in the presence of anti-IFN-beta antibodies reduces the effectiveness of the antiviral state and the induction of 2'-5'-oligoadenylate synthetase activity, indicating that the antiviral activity of IFN-gamma in FLC is in part mediated by the production of IFN-beta. Accordingly, IFN-gamma induces a less pronounced antiviral state in FLC resistant to IFN-alpha/beta than in wild-type cells. Moreover, while results of run-on assays indicate that both IFN-alpha and -beta genes are constitutively transcribed in these cells, FLC treatment with IFN-gamma induces only IFN-beta mRNA accumulation. These results indicate that posttranscriptional mechanisms are involved in the regulation of IFN-beta and -alpha expression by IFN-gamma. The low amounts of the induced IFN-beta synergize with IFN-gamma in mounting the potent antiviral effect.

Transcription of muscle-specific genes is repressed by reactivation of pp60v-src in postmitotic quail myotubes

Quail myogenic cells infected with temperature sensitive (ts) mutants of Rous sarcoma virus (RSV) exhibit a temperature-dependent transformation and block of differentiation. When the cells are allowed to differentiate at the restrictive temperature (41 degrees C) and then shifted back to the permissive temperature (35 degrees C), a sharp reduction in the accumulation of muscle-specific mRNAs is observed, following reactivation of the transforming protein pp60v-src. A kinetic analysis of this down-regulation reveals that the reduction in the accumulation of muscle-specific transcripts occurs fairly rapidly within 6 to 20 h after the shift back, depending on the mRNA analyzed. Studies on transcription of endogenous muscle-specific genes and a transfected chloramphenicol acetyltransferase reporter gene under the control of muscle-specific promoters, at the different temperatures, suggest that the oncogene exerts its control mainly at the transcriptional level. On the contrary, transcription of the CMD1 gene, the avian homolog of the mouse muscle regulatory MyoD gene, is not significantly affected by the oncogene both in proliferating myoblasts and in myotubes shifted back to 35 degrees C. These findings are consistent with the conclusion that v-src blocks myogenesis by controlling transcription of muscle-specific genes independently of cell proliferation. Furthermore, they suggest the existence of an alternative pathway, not requiring the silencing of CMD1 transcription, through which the oncogene exerts its effect.

Oligonucleotide inhibition of IL2R alpha mRNA transcription by promoter region collinear triplex formation in lymphocytes

The promoter region of the IL2R alpha gene 5' flanking sequence contains enhancer elements crucial for binding nuclear factors which upregulate transcription following T lymphocyte activation. A 3' exonuclease resistant oligonucleotide (3'A-IL28p, terminated by a free amine group at its 3' end) was designed to bind to the IL2R alpha promoter region from -273 to -246, forming a collinear triplex spanning the kappa B enhancer (-266 to -256) as well as most of the serum response element (CArG box, -251 to -244). The binding site specificity of this oligonucleotide was demonstrated in electrophoretic mobility shift assays and by inhibition of restriction endonuclease (HinfI) cleavage within the segment of the target DNA predicted to form a triplex with the oligonucleotide. Intact normal lymphocytes, preincubated for 2h with 3'A-IL28p, accumulated less IL2Ralpha mRNA relative to other mRNAs (c-myc, beta-actin, IL2R beta, IL-6) for up to 12h after PHA stimulation, than did lymphocytes treated with a control oligomer of similar composition but different sequence. Nuclear run-on studies demonstrated that the rate of IL2R alpha mRNA synthesis relative to c-myc and beta-actin was also selectively diminished by treatment with 3'A-IL28p. These experiments suggest that transcription of individual genes can be selectively modulated in living cells by sequence specific collinear triplex formation in regulatory enhancer sequences.

Transcription of muscle-specific genes is repressed by reactivation of pp60v-src in postmitotic quail myotubes

Quail myogenic cells infected with temperature sensitive (ts) mutants of Rous sarcoma virus (RSV) exhibit a temperature-dependent transformation and block of differentiation. When the cells are allowed to differentiate at the restrictive temperature (41 degrees C) and then shifted back to the permissive temperature (35 degrees C), a sharp reduction in the accumulation of muscle-specific mRNAs is observed, following reactivation of the transforming protein pp60v-src. A kinetic analysis of this down-regulation reveals that the reduction in the accumulation of muscle-specific transcripts occurs fairly rapidly within 6 to 20 h after the shift back, depending on the mRNA analyzed. Studies on transcription of endogenous muscle-specific genes and a transfected chloramphenicol acetyltransferase reporter gene under the control of muscle-specific promoters, at the different temperatures, suggest that the oncogene exerts its control mainly at the transcriptional level. On the contrary, transcription of the CMD1 gene, the avian homolog of the mouse muscle regulatory MyoD gene, is not significantly affected by the oncogene both in proliferating myoblasts and in myotubes shifted back to 35 degrees C. These findings are consistent with the conclusion that v-src blocks myogenesis by controlling transcription of muscle-specific genes independently of cell proliferation. Furthermore, they suggest the existence of an alternative pathway, not requiring the silencing of CMD1 transcription, through which the oncogene exerts its effect.

Hormonal modulation of a gene injected into rat heart in vivo

We demonstrate gene transfer into rat heart in vivo by the direct injection of plasmid DNA. Injection of gene constructs driven by retroviral and cellular promoters resulted in detectable levels of reporter gene activities. The cellular promoter and 5' flanking sequence (positions -613 to +32) were derived from the rat alpha-myosin heavy chain gene whose expression in vivo is restricted to cardiac muscle and is positively regulated by thyroid hormone. After DNA injection, activity of the firefly luciferase gene coupled to the myosin heavy chain promoter and regulatory sequence was detected in heart but not in skeletal muscle and was significantly increased in response to thyroid hormone treatment. Consequently, expression of injected genes can be targeted to specific cell types in vivo and can be modulated by the hormonal status of the animal. This approach provides a means of mapping the elements of genes that regulate their responses to complex stimuli that cannot be modeled in vitro.