Identification of two distinct nuclear factors with DNA binding activity within the glucocorticoid regulatory region of the rat alpha-1-acid glycoprotein promoter

Multiplicity of Glucocorticoid Action in Inhibiting Allograft Rejection

Glucocorticoids (GCs) are used as immunosuppressive and antiinflammatory agents in organ transplantation and in treating autoimmune diseases and inflammatory disorders. GCs were shown to exert their antiproliferative effects directly through blockade of certain elements of an early membrane-associated signal transduction pathway, modulation of the expression of select adhesion molecules, and by suppression of cytokine synthesis and action. GCs may act indirectly by inducing lipocortin synthesis, which in turn, inhibits arachidonic acid release from membrane-bound stores, and also by inducing transforming growth factor (TGF)-β expression that subsequently blocks cytokine synthesis and T cell activation. Furthermore, by preferentially inhibiting the production of Th1 cytokines, GCs may enhance Th2 cell activity and, hence, precipitate a long-lasting state of tolerance through a preferential promotion of a Th2 cytokine-secreting profile. In exerting their antiproliferative effects, GCs influence both transcriptional and posttranscriptional events by binding their cytosolic receptor (GR), which subsequently binds the promoter region of cytokine genes on select DNA sites compatible with the GCs responsible elements (GRE) motif. In addition to direct DNA binding, GCs may also directly bind to, and hence antagonize, nuclear factors required for efficient gene expression, thereby markedly reducing transcriptional rate. The pleiotrophy of the GCs action, coupled with the diverse experimental conditions employed in assessing the GCs effects, indicate that GCs may utilize more than one mechanism in inhibiting T cell activation, and warrant careful scrutiny in assigning a mechanism by which GCs exert their antiproliferative effects. © 1998 Elsevier Science Inc.

Regulation of the rat UGT1A6 by glucocorticoids involves a cryptic glucocorticoid response element

Glucocorticoids precociously induce fetal rat UGT1A6 and potentiate polycyclic aromatic hydrocarbon (PAH)-dependent induction of this enzyme in vivo and in isolated rat hepatocytes. To establish whether induction was due to glucocorticoid receptor (GR), luciferase reporter vectors were tested in transfection assays with HepG2 cells. Using a reporter construct containing approximately 2.26 kilobases of the 5'-flanking region of the UGT1A6-noncoding leader exon (A1*), dexamethasone increased basal activity 3- to 7-fold in cells cotransfected with an expression plasmid for GR. PAH increased gene expression 23-fold, but the presence of dexamethasone only induced PAH-dependent expression by 1.5-fold, suggesting interaction between GR and the aryl hydrocarbon (Ah) receptor. Furthermore, the GR antagonist RU 38486 [17beta-hydroxy-11beta-(4-dimethylamino-phenyl)-17alpha-(prop-1-ynyl)-estra-4,9-dien-3-one] was a partial agonist that increased, rather than inhibited, basal activity 3-fold. 5'-deletion analysis defined the 5'-boundary for a functional glucocorticoid-responsive unit between base pairs -141 and -118 relative to the transcription start site. This region contains the Ah receptor response element (AhRE), and both PAH and glucocorticoid-dependent gene activation were lost when this area was deleted. Mutation of a single base pair located in the AhRE region simultaneously reduced induction by PAH and increased glucocorticoid induction. Thus, the sequences of both the AhRE and glucocorticoid response elements seem to overlap, suggesting that Ah receptor binding may decrease glucocorticoid-dependent induction due to interactions of these two cis-acting elements. Mutation of a putative GRE located between base pair -81 and -95 reduced, but did not completely eliminate, glucocorticoid-dependent induction of the reporter, suggesting that a nonclassic mechanism of induction is involved in this response.

Transcriptional and post-transcriptional mechanisms of glucocorticoid antiproliferative effects

Glucocorticoids (GCs) are used as immunosuppressive and anti-inflammatory agents in treating organ transplantation rejection, autoimmune diseases, (hematological) cancers, and inflammatory disorders. GCs exert their effects through a multitude of mechanisms, the most significant of which is inhibition of cytokine production, and for some cytokines their effects on target cells. Paradoxically, GCs also upregulate the expression of (pro-inflammatory) high-affinity cytokine receptors on target cells in the face of lost ligand (cytokine) stimulation. GC inhibition of cytokine expression occurs at both transcriptional and post-transcriptional levels. GCs acted transcriptionally by binding their cytosolic receptor (GR), thereby facilitating its nuclear translocation and subsequent binding to the promoter region of cytokine genes on sites compatible with GC response element (GRE) motifs, which in turn directly or indirectly regulated gene expression. In addition to direct DNA binding, GCs acted post-transcriptionally by: (1) antagonism of nuclear factors required for efficient gene expression either directly or through induction of the expression of specific transcription factor antagonists, (2) altered Th lineage development by favouring the generation of (anti-inflammatory) Th2 cells and suppressing the induction or the activity of established (pro-inflammatory) Th1 cells, and (3) stimulating the expression of transforming growth factor (TGF)-beta, an immunosuppressive cytokine which inhibited cytokine production. However, these mechanisms are not mutually exclusive, since GCs may utilize more than one mechanism in exerting their anti-proliferative effect.

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.

Point mutations within 663-666 bp of intron 6 of the human TDO2 gene, associated with a number of psychiatric disorders, damage the YY-1 transcription factor binding site

Single base mutations G-->A at position 663 and G-->T at position 666 of intron 6 of the human tryptophan oxygenase gene (TDO2) are associated with a variety of psychiatric disorders [Comings, D.E. et al. (1996) Pharmacogenetics 6, 307-318]. Binding of rat liver nuclear extract proteins to synthetic double-strand oligonucleotides corresponding to three allelic states of the region between 651 bp and 680 bp of human TDO2 intron 6 has been studied by gel shift assay. It has been demonstrated that to each allelic state of the region there corresponds a specific set of proteins that interacts with it. With the aid of computer analysis and using specific anti-YY-1 antibodies it has been shown that both mutations damage the YY-1 transcription factor binding site.

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.

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 heme oxygenase-2 by glucocorticoids in neonatal rat brain: characterization of a functional glucocorticoid response element

Heme oxygenase-2 (HO-2) is constitutively expressed in mammalian tissues; together with HO-1 (HSP32) it catalyzes the cleavage of heme to produce biliverdin IX alpha, CO and Fe. Detection of a consensus sequence of the glucocorticoid response element (GRE) in the promoter region of the HO-2 gene prompted the present study which has investigated the role of glucocorticoids (Gcs) in the regulation of HO-2 protein and transcript development in the newborn rat brain and has examined the promoter activity of the GRE in HeLa cells. Using in situ hybridization histochemistry, we noted a pronounced increase in signal for HO-2 mRNA in the brain of 14-day-old rats postnatally treated with corticosterone (5 microg/g, 4 x, starting 24-36 h after birth). And, using immunohistochemistry, a striking increase in neuronal HO-2 immunostaining in treated brains was detected. The HO-2 GRE was tested for responsiveness to dexamethasone (DX) using both a promoterless CAT expression vector, and a heterologous promoter containing luciferase expression vector in HeLa cells. The HO-2 promoter containing the GRE and transcription start site induced CAT reporter gene activity in response to DX, whereas mutation or deletion in the GRE abolished hormone responsiveness. Similarly, constructs containing the GRE conferred responsiveness to DX in an orientation-independent manner and increased relative luciferase activity. Further, specific binding of glucocorticoid receptor protein to the GRE was observed; binding could be competed out only by excess cold GRE and not by mutated HO-2 GRE, or AP1. HO-2 mRNAs (approximately 1.3 and approximately 1.9 kb) increased in HeLa cells treated with DX (5 microM), the level reached a maximum at 24 h. DX did not effect HO-1 mRNA level. The increase in the HO-2 transcript was accompanied by an increase in HO-2 protein, as assessed by Western blot analysis, and an increase in HO activity, as measured by bilirubin formation. Also, an increase in intensity of immunostaining was noted in DX-treated HeLa cells. We conclude that the GRE present in the HO-2 gene promoter region is functional, and propose the direct involvement of the adrenal glucocorticoids in modulation of HO-2 gene expression. In the context of biological functions of heme degradation products, we suggest that this regulation may be of significance, particularly to the neurons.

Transcriptional induction of rat liver apolipoprotein A-I gene expression by glucocorticoids requires the glucocorticoid receptor and a labile cell-specific protein

Treatment with glucocorticoids increases the concentration of plasma high-density lipoprotein (HDL), which is inversely correlated to the development of atherosclerosis. Previously, we demonstrated that repeated administration of glucocorticoids increases apolipoprotein (apo) A-I gene expression and decreases apoA-II gene expression in rat liver. In the present study, the mechanism of glucocorticoid action on hepatic apoA-I and apoA-II expression was studied. A single injection of rats with dexamethasone increased hepatic apoA-I mRNA levels within 6 h and further increases were observed after 12 h and 24 h. In contrast, liver apoA-II mRNA levels gradually decreased after dexamethasone treatment to less than 25% control levels after 24 h. In rat primary hepatocytes and McARH8994 hepatoma cells, addition of dexamethasone increased apoA-I mRNA levels in a time-dependent and dose-dependent manner, whereas apoA-II mRNA levels were unchanged. Simultaneous addition of the glucocorticoid antagonist RU486 prevented the increase in apoA-I mRNA levels after dexamethasone treatment, which suggests that the effects of dexamethasone are mediated through the glucocorticoid receptor. Inhibition of transcription by actinomycin D and nuclear-run-on experiments in McARH8994 cells and primary hepatocytes showed that dexamethasone induced apoA-I, but not apoA-II, gene transcription. Transient-transfection assays in McARH8994 cells with a chloramphenicol acetyl transferase vector driven by the rat-apoA-I-gene promoter demonstrated that the proximal apoA-I promoter could be induced by dexamethasone, and this effect could be abolished by simultaneous treatment with RU486. However, in COS-1 cells, apoA-I promoter transcription was not induced by dexamethasone or cotransfected glucocorticoid receptor. In addition, the induction of apoA-I gene transcription by dexamethasone was blocked by the protein-synthesis inhibitor cycloheximide, which suggests the presence of a labile protein involved in apoA-I gene activation by dexamethasone. In conclusion, our results demonstrate that dexamethasone regulates rat apoA-I, but not apoA-II, gene expression through direct action on the hepatocyte. The induction of apoA-I gene transcription by dexamethasone requires the glucocorticoid receptor and a labile cell-specific protein.

Specificity of action of a herpes virus VP16/tetracycline-dependent trans-activator in mammalian cell cultures

In this work, we have studied the activity of a tetracycline modulatable trans-activator (tTA) generated by fusing the DNA binding domain of the tetracycline repressor to the trans-activation domain of the Herpes simplex virus protein 16 (HSV VP16) (plasmid pUHD15-1Neo). In the three different cell lines studied (HTC, rat hepatoma; T47D, human breast cancer; SK-N-BE, human neuroblastoma), the expression of the luciferase gene under the control of a tetracycline operator sequence (plasmid pUHC13-3) was used as a control of the incorporation and the functionality of the trans-activator. Clones selected from these cells responded in a time and dose-dependent manner to the withdrawal of tetracycline. In all these clones, the tTA trans-activator not only modulates the activity of the luciferase gene, but also modulates the activity of a number of endogenous proteins, including C/EBP beta, the glucocorticoid receptor (GR), and SP1. In the transfected cells, the level of these transcription factors was strongly inhibited in the presence of tetracycline and was highly increased after tetracycline removal. Electrophoresis mobility shift assay (EMSA) and footprint experiments proved that the induced proteins are perfectly efficient in binding the DNA. Their transcriptional activity was also determined. In HTC/A9 cells, the level of the chloramphenicol acetyltransferase (CAT) expression driven by the promoter of the alpha 1-glycoprotein (AGP) gene was strongly enhanced at 72-84 hr following removal of tetracycline from the growth media. The accumulation of the endogenous AGP mRNA also increased at 84 hr. In the T47D/TA11 and SK-N-BE/C2.6 cells, a general activation of protein synthesis was also evidenced.

Long-term culture of HepG2 hepatoma cells as a model for liver acute phase response during chronic inflammation. Effects of interleukin-6, dexamethasone and retinoic acid

HepG2 cells were cultured for 7 days in serum-free medium in the presence of interleukin-6 (IL-6), retinoic acid (RA) or dexamethasone (DX), and some plasma proteins secreted to the media were determined by electroimmunoassay whereas the contents of specific mRNAs in the cells was evaluated by Northern blot hybridization. Interleukin-6 maximally stimulated synthesis of alpha-1-antichymotrypsin between days 1 and 3 whereas the response of fibrinogen was delayed to days 3 to 7. Retinoic acid increased the effect of IL-6 on alpha-1-antichymotrypsin (ACT) and fibrinogen (FBG) on the level of both proteins and mRNAs. Synthesis of albumin was slightly inhibited by IL-6 and RA, and synthesis of transferrin was increased by RA but not by IL-6. Dexamethasone had small enhancing effect on the action of IL-6. These results suggest that long-term HepG2 cultures may provide an experimental model for liver acute phase response during chronic inflammation.

Induction of rat alpha-1-acid glycoprotein by phenobarbital is independent of a general acute-phase response

Phenobarbital (PB) induces transcription of the alpha 1-acid glycoprotein (AGP) gene, one of the major positive acute-phase proteins, the expression of which is controlled by a specific combination of glucocorticoids and cytokines. This raises questions as to the involvement of glucocorticoids and cytokine pathways in the PB-mediated effect on AGP gene expression. We found that the pattern of whole-serum proteins in PB-treated rats differed markedly from that observed during a typical acute inflammatory response (in turpentine-treated rats): levels of some positive acute-phase proteins (APP) increased slightly (alpha 1-acid glycoprotein, haptoglobin, hemopexin and T-kininogen), while levels of alpha 2 macroglobulin, the most sensitive marker of the acute-phase reaction, decreased. Among the negative APP, neither albumin nor prealbumin decreased while CBG increased. The cytokines involved in AGP gene regulation (mainly IL1, IL6 and TNF alpha) do not therefore seem to mediate the effect of PB on acute-phase protein expression. Glucocorticoid involvement is also ruled out by the observed enhancement of the effect of PB on AGP expression in adrenalectomized animals. Our results suggest that phenobarbital acts on AGP expression by a mechanism independent of the inflammatory pathway.

Transcriptional control of genes that regulate glycolysis and gluconeogenesis in adult liver

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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.

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.

Cloning and structural characterization of a rabbit genomic DNA for alpha 1 acid glycoprotein

The gene for rabbit alpha 1 acid glycoprotein (AGP) has been isolated from a lambda EMBL3 genomic DNA library. Isolated clone contains a 12 Kbp fragment of rabbit genomic DNA. Restriction endonuclease mapping has localized the gene within a 4.2 Kbp fragment spanning two EcoRI sites. Southern blot analysis of the rabbit genomic DNA and its comparison with the cloned gene indicates that there is only one gene for AGP present per genome. DNA sequence analysis of the cloned gene indicates that the entire gene, TATA box to the polyadenylation signal, is located within the 4.2 Kbp region and contains six exons representing the full-length cDNA described earlier (1). The 5'-end of alpha 1-AGP gene sequences from rabbit, human, rat and mouse have been compared. Such analysis reveals two conserved regions located between -63 bp and -36 bp and -29 bp and -1 bp of putative transcription start site, which may play a role in transcriptional induction of this gene during acute response. In addition to this conserved domain, DNA sequence upstream of the major transcription start site contains a potential element for Sp1 binding and a 18 bp long palindrome sequence followed by a short repeating dinucleotide sequence, which may be important in the regulation of AGP gene induction.

AGP/EBP(LAP) expressed in rat hepatoma cells interacts with multiple promoter sites and is necessary for maximal glucocorticoid induction of the rat alpha-1 acid glycoprotein gene

Transcription of the rat alpha 1-acid glycoprotein (AGP) gene is induced by glucocorticoids. In addition to the glucocorticoid response element which maps to bases -120 to -107, sequences located between bases -106 to -42 have been shown to be necessary for hormone induction. We have previously identified multiple sites of C/EBP interaction with the AGP promoter in the region -106 to -64. In this study, we purify and identify a C/EBP family member, AGP/EBP(LAP), present in the rat hepatoma cell line HTC (JZ.1) which also binds to the C/EBP recognition sites in this region. Mutations in the recognition sites that prevent binding are analyzed, and the results suggest a positive as well as a possible inhibitory role for AGP/EBP(LAP) in the glucocorticoid induction of the gene in HTC (JZ.1) cells.

AGP/EBP(LAP) expressed in rat hepatoma cells interacts with multiple promoter sites and is necessary for maximal glucocorticoid induction of the rat alpha-1 acid glycoprotein gene

Transcription of the rat alpha 1-acid glycoprotein (AGP) gene is induced by glucocorticoids. In addition to the glucocorticoid response element which maps to bases -120 to -107, sequences located between bases -106 to -42 have been shown to be necessary for hormone induction. We have previously identified multiple sites of C/EBP interaction with the AGP promoter in the region -106 to -64. In this study, we purify and identify a C/EBP family member, AGP/EBP(LAP), present in the rat hepatoma cell line HTC (JZ.1) which also binds to the C/EBP recognition sites in this region. Mutations in the recognition sites that prevent binding are analyzed, and the results suggest a positive as well as a possible inhibitory role for AGP/EBP(LAP) in the glucocorticoid induction of the gene in HTC (JZ.1) cells.