Hepatocyte-stimulating factor, beta 2 interferon, and interleukin-1 enhance expression of the rat alpha 1-acid glycoprotein gene via a distal upstream regulatory region

Synthesis and activity of a novel inhibitor of nonsense-mediated mRNA decay

A new route to a tetracyclic lactam was developed and the product, called VG1, was found to inhibit nonsense-mediated mRNA decay at μM concentrations.

During efforts to prepare the known compound NMDI1, a new tetracyclic compound, called VG1, was prepared in six steps. This compound was found to have good activity as an inhibitor of nonsense-mediated mRNA decay.

Requirement for Stat5 in Thymic Stromal Lymphopoietin-Mediated Signal Transduction

Thymic stromal lymphopoietin (TSLP) is a newly identified cytokine that uniquely promotes B lymphopoiesis to the B220+/IgM+ immature B cell stage. In addition, TSLP shares many biological properties with the related cytokine IL-7. This can be explained by the finding that the receptor complexes for TSLP and IL-7 both contain the IL-7R α-chain; IL-7Rα is paired with the common γ-chain (γc) in the IL-7 receptor complex and the unique TSLP-R chain in the TSLP receptor complex. Although TSLP and IL-7 both induce tyrosine phosphorylation of the transcription factor Stat5, only IL-7-mediated signal transduction could be associated with activation of Janus family kinases (Jaks). Because Stat5 phosphorylation following cytokine stimulation is generally mediated by Jaks, the lack of Jak activation after TSLP treatment suggested the possibility that tyrosine-phosphorylated Stat5 may be nonfunctional. Herein, we demonstrate that TSLP induces a functional Stat5 transcription factor in that TSLP stimulation results in Stat5-DNA complex formation and transcription of the Stat5-responsive gene CIS. We also show that the TSLP receptor complex is functionally reconstituted using TSLP-R and IL-7Rα and that TSLP-mediated signal transduction requires Stat5. Moreover, TSLP-mediated signaling is inhibited by suppressor of cytokine signaling (SOCS)-1 and a kinase-deficient version of Tec but not by kinase-deficient forms of Jak1 and Jak2.

Protein tyrosine phosphatase 2 (SHP-2) moderates signaling by gp130 but is not required for the induction of acute-phase plasma protein genes in hepatic cells

Signals propagated via the gp130 subunit of the interleukin-6 (IL-6)-type cytokine receptors mediate, among various cellular responses, proliferation of hematopoietic cells and induction of acute-phase plasma protein (APP) genes in hepatic cells. Hematopoietic growth control by gp130 is critically dependent on activation of both STAT3 and protein tyrosine phosphatase 2 (SHP-2). To investigate whether induction of APP genes has a similar requirement for SHP-2, we constructed two chimeric receptors, G-gp130 and G-gp130(Y2F), consisting of the transmembrane and cytoplasmic domains of gp130 harboring either a wild-type or a mutated SHP-2 binding site, respectively, fused to the extracellular domain of the granulocyte colony-stimulating factor (G-CSF) receptor. Rat hepatoma H-35 cells stably expressing the chimeric receptors were generated by retroviral transduction. Both chimeric receptors transmitted a G-CSF-induced signal characteristic of that triggered by IL-6 through the endogenous gp130 receptor; i.e., both activated the appropriate JAK, induced DNA binding activity by STAT1 and STAT3, and up-regulated expression of the target APP genes, those for alpha-fibrinogen and haptoglobin. Notwithstanding these similarities in the patterns of signaling responses elicited, mutation of the SHP-2 interaction site in G-gp130(Y2F) abrogated ligand-activated receptor recruitment of SHP-2 as expected. Moreover, the tyrosine phosphorylation state of the chimeric receptor, the associated JAK activity, and the induced DNA binding activity of STAT1 and STAT3 were maintained at elevated levels and for an extended period of time in G-gp130(Y2F)-expressing cells following G-CSF treatment compared to that in cells displaying the G-gp130 receptor. H-35 cells ectopically expressing G-gp130(Y2F) were also found to display an enhanced sensitivity to G-CSF and a higher level of induction of APP genes. Overexpression of the enzymatically inactive SHP-2 enhanced the signaling by the wild-type but not by the Y2F mutant G-gp130 receptor. These results indicate that gp130 signaling for APP gene induction in hepatic cells differs qualitatively from that controlling the proliferative response in hematopoietic cells in not being strictly dependent on SHP-2. The data further suggest that SHP-2 functions normally to attenuate gp130-mediated signaling in hepatic (and, perhaps, other) cells by moderating JAK action.

Analysis of chromatin structure of rat alpha1-acid glycoprotein gene; changes in DNase I hypersensitive sites after thyroid hormone, glucocorticoid hormone and turpentine oil treatment

Transcription of the ratalpha1-acid glycoprotein (AGP) gene is activated by glucocorticoid, thyroid hormone (T3) and cytokines. Following these treatments, the chromatin structure of this gene was analyzed by means of digestion with DNase I or micrococcal nuclease. Four DNase I hypersensitive sites were observed in the 5'-upstream region of the rat AGP gene of liver cells. They were designated HS1, HS2, HS3 and HS4 (3'-->5'). After T3treatment the sensitivity of HS1 and HS2 increased and after dexamethasone (Dex) treatment that of all four sites did so. Three new sites appeared after turpentine oil treatment, while the sensitivities of HS3 and HS4 increased. We conclude that transcriptional activation of the gene by T3and Dex have very similar mechanisms, but that at the inflammation stage they become slightly different. The increase in sensitivity at HS1 and HS2 after T3treatment in vivo was successfully reproduced in a cell-free system by in vitro treatment with T3. HS1, HS2 and HS3 were also sensitive for micrococcal nuclease.

Role of lipopolysaccharide (LPS), interleukin-1, interleukin-6, tumor necrosis factor, and dexamethasone in regulation of LPS-binding protein expression in normal hepatocytes and hepatocytes from LPS-treated rats

Lipopolysaccharide (LPS)-binding protein (LBP) has been reported to be an acute-phase protein. LBP binds to LPS with a high affinity; LPS-LBP complexes then interact with the receptor CD14, resulting in increased expression of LPS-inducible genes. Hepatocytes represent a major source of LBP, but little is known about the regulation of rodent hepatocyte LBP synthesis. In these studies, undertaken to characterize hepatocyte LBP expression, we show that greater-than-20-fold increases in LBP mRNA levels in hepatocytes occurred following injection of LPS or turpentine in rats. In primary cultures of rat hepatocytes, the addition of interleukin-6 (IL-6) and LPS led to 4.5- and 3.2-fold stimulation in LBP mRNA levels, respectively. The induction of LBP by IL-6 or LPS was attenuated by dexamethasone. In contrast to IL-6 and LPS, in the presence of 10(-6) M dexamethasone, IL-1 and tumor necrosis factor (TNF) led to maximal LBP mRNA induction levels, 4.7- and 3.8-fold, respectively, suggesting that IL-6 and LPS stimulate LBP expression by mechanisms different from those of IL-1 and TNF. Similar induction levels of LBP mRNA were seen in rat H35 hepatoma cells for all four stimuli, and dexamethasone inhibited these responses. Dexamethasone alone increased the spontaneous induction in primary hepatocytes at early time points but suppressed induction at later time points. Furthermore, hepatocytes from rats treated with LPS in vivo exhibited a > 10-fold increase in mRNA expression in response to LPS and enhanced responses to TNF and IL-1. As with the normal hepatocytes, dexamethasone inhibited the LPS-dependent induction in the LPS-treated rat hepatocytes. These data suggest that LBP synthesis by hepatocytes is under the control of LPS, IL-1, TNF, IL-6, and glucocorticoids and that the LPS treatment primes hepatocytes for subsequent responses to LPS, TNF, and IL-1 for LBP synthesis.

Mammalian nonsense codons can be cis effectors of nuclear mRNA half-life

Frameshift and nonsense mutations within the gene for human triosephosphate isomerase (TPI) that generate a nonsense codon within the first three-fourths of the protein coding region have been found to reduce the abundance of the product mRNA that copurifies with nuclei. The cellular process and location of the nonsense codon-mediated reduction have proven difficult to elucidate for technical reasons. We show here, using electron microscopy to judge the purity of isolated nuclei, that the previously established reduction to 25% of the normal mRNA level is evident for nuclei that are free of detectable cytoplasmic contamination. Therefore, the reduction is likely to be characteristic of bona fide nuclear RNA. Fully spliced nuclear mRNA is identified by Northern (RNA) blot hybridization and a reverse transcription-PCR assay as the species that undergoes decay in experiments that used the human c-fos promoter to elicit a burst and subsequent shutoff of TPI gene transcription upon the addition of serum to serum-deprived cells. Finally, the finding that deletion of a 5' splice site of the TPI gene results predominantly but not exclusively in the removal by splicing (i.e., skipping) of the upstream exon as a part of the flanking introns has been used to demonstrate that decay is specific to those mRNA products that maintain the nonsense codon. This result, together with our previous results that implicate translation by ribosomes and charged tRNAs in the decay mechanism, indicate that nonsense codon recognition takes place after splicing and triggers decay solely in cis. The possibility that decay takes place during the process of mRNA export from the nucleus to the cytoplasm is discussed.

Mammalian nonsense codons can be cis effectors of nuclear mRNA half-life

Frameshift and nonsense mutations within the gene for human triosephosphate isomerase (TPI) that generate a nonsense codon within the first three-fourths of the protein coding region have been found to reduce the abundance of the product mRNA that copurifies with nuclei. The cellular process and location of the nonsense codon-mediated reduction have proven difficult to elucidate for technical reasons. We show here, using electron microscopy to judge the purity of isolated nuclei, that the previously established reduction to 25% of the normal mRNA level is evident for nuclei that are free of detectable cytoplasmic contamination. Therefore, the reduction is likely to be characteristic of bona fide nuclear RNA. Fully spliced nuclear mRNA is identified by Northern (RNA) blot hybridization and a reverse transcription-PCR assay as the species that undergoes decay in experiments that used the human c-fos promoter to elicit a burst and subsequent shutoff of TPI gene transcription upon the addition of serum to serum-deprived cells. Finally, the finding that deletion of a 5' splice site of the TPI gene results predominantly but not exclusively in the removal by splicing (i.e., skipping) of the upstream exon as a part of the flanking introns has been used to demonstrate that decay is specific to those mRNA products that maintain the nonsense codon. This result, together with our previous results that implicate translation by ribosomes and charged tRNAs in the decay mechanism, indicate that nonsense codon recognition takes place after splicing and triggers decay solely in cis. The possibility that decay takes place during the process of mRNA export from the nucleus to the cytoplasm is discussed.

Nonsense but not missense mutations can decrease the abundance of nuclear mRNA for the mouse major urinary protein, while both types of mutations can facilitate exon skipping

In an effort to understand the mechanisms by which nonsense codons affect RNA metabolism in mammalian cells, nonsense mutations were generated within the gene for the secretory major urinary protein (MUP) of mice. The translation of MUP mRNA normally begins within exon 1 and terminates within exon 6, the penultimate exon. Through the use of Northern (RNA) blot hybridization and assays that couple reverse transcription and PCR, a nonsense mutation within codon 50 of exon 2 or codon 143 of exon 5 was found to reduce the abundance of fully spliced, nuclear MUP mRNA to 10 to 20% of normal without an additional reduction in the abundance of cytoplasmic mRNA. In contrast, a nonsense mutation within codon 172 of exon 5 was found to have no effects on the abundance of MUP mRNA. These findings suggest that a boundary between nonsense mutations that do and do not reduce the abundance of nuclear mRNA exists within the exon preceding the exon that harbors the normal site of translation termination. In this way, the boundary is analogous to the boundary that exists within the penultimate exon of the human gene for the cytosolic enzyme triosephosphate isomerase. Assays for exon skipping, i.e., the removal of an exon as a part of the flanking introns during the process of splicing, reveal that 0.1, 2.0, and 0.1% of MUP mRNA normally lack exon 5, exon 6, and exons 5 plus 6, respectively. Relative to normal, the two nonsense mutations within exon 5 increase the abundance of RNA lacking exon 5 on average 20-fold and increase the abundance of RNA lacking exons 5 plus 6 on average 5-fold. Since only one of these nonsense mutations also reduces the abundance of fully spliced nuclear mRNA to 10 to 20% of normal, the two mechanisms by which a nonsense mutation can alter nuclear RNA metabolism must be distinct. The analysis of missense mutations within codons 143 and 172, some of which retain the nonsense mutation, indicates that the reduction in the abundance of fully spliced nuclear mRNA is dependent upon the premature termination of MUP mRNA translation, whereas skipping is attributable to nonsense mutation-mediated changes in exon 5 structure rather than to the premature termination of translation. The increase in exon 5 skipping by either the nonsense or missense mutations within codon 172 correlates with a decrease in the complementarity of exon 5 to U1 snRNA. This suggests that a 5' splice site may extend as far as 12 nucleotides into the upstream exon, which is, to our knowledge, the largest extension.

Purification and characterization of nucleolin and its identification as a transcription repressor

Expression of the acute-phase response genes, such as that for alpha-1 acid glycoprotein (AGP), involves both positive and negative transcription factors. A positive transcription factor, AGP/EBP, and a negative transcription factor, factor B, have been identified as the two most important factors responsible for the induction of the AGP gene. In this paper we report the purification, characterization, and identification of a B-motif-binding factor from the mouse hepatoma cell line 129p. The purified factor has been identified as nucleolin by amino acid sequence analysis. Biochemical and functional studies further established that nucleolin is a transcription repressor for regulation of AGP and possibly other acute-phase response genes. Thus, in addition to the many known functions of nucleolin, such as rRNA transcription, processing, ribosome biogenesis, and the shuttling of proteins between the cytoplasmic and nuclear compartments, it may also function as a transcriptional repressor.

Purification and characterization of nucleolin and its identification as a transcription repressor

Expression of the acute-phase response genes, such as that for alpha-1 acid glycoprotein (AGP), involves both positive and negative transcription factors. A positive transcription factor, AGP/EBP, and a negative transcription factor, factor B, have been identified as the two most important factors responsible for the induction of the AGP gene. In this paper we report the purification, characterization, and identification of a B-motif-binding factor from the mouse hepatoma cell line 129p. The purified factor has been identified as nucleolin by amino acid sequence analysis. Biochemical and functional studies further established that nucleolin is a transcription repressor for regulation of AGP and possibly other acute-phase response genes. Thus, in addition to the many known functions of nucleolin, such as rRNA transcription, processing, ribosome biogenesis, and the shuttling of proteins between the cytoplasmic and nuclear compartments, it may also function as a transcriptional repressor.

Nonsense but not missense mutations can decrease the abundance of nuclear mRNA for the mouse major urinary protein, while both types of mutations can facilitate exon skipping

In an effort to understand the mechanisms by which nonsense codons affect RNA metabolism in mammalian cells, nonsense mutations were generated within the gene for the secretory major urinary protein (MUP) of mice. The translation of MUP mRNA normally begins within exon 1 and terminates within exon 6, the penultimate exon. Through the use of Northern (RNA) blot hybridization and assays that couple reverse transcription and PCR, a nonsense mutation within codon 50 of exon 2 or codon 143 of exon 5 was found to reduce the abundance of fully spliced, nuclear MUP mRNA to 10 to 20% of normal without an additional reduction in the abundance of cytoplasmic mRNA. In contrast, a nonsense mutation within codon 172 of exon 5 was found to have no effects on the abundance of MUP mRNA. These findings suggest that a boundary between nonsense mutations that do and do not reduce the abundance of nuclear mRNA exists within the exon preceding the exon that harbors the normal site of translation termination. In this way, the boundary is analogous to the boundary that exists within the penultimate exon of the human gene for the cytosolic enzyme triosephosphate isomerase. Assays for exon skipping, i.e., the removal of an exon as a part of the flanking introns during the process of splicing, reveal that 0.1, 2.0, and 0.1% of MUP mRNA normally lack exon 5, exon 6, and exons 5 plus 6, respectively. Relative to normal, the two nonsense mutations within exon 5 increase the abundance of RNA lacking exon 5 on average 20-fold and increase the abundance of RNA lacking exons 5 plus 6 on average 5-fold. Since only one of these nonsense mutations also reduces the abundance of fully spliced nuclear mRNA to 10 to 20% of normal, the two mechanisms by which a nonsense mutation can alter nuclear RNA metabolism must be distinct. The analysis of missense mutations within codons 143 and 172, some of which retain the nonsense mutation, indicates that the reduction in the abundance of fully spliced nuclear mRNA is dependent upon the premature termination of MUP mRNA translation, whereas skipping is attributable to nonsense mutation-mediated changes in exon 5 structure rather than to the premature termination of translation. The increase in exon 5 skipping by either the nonsense or missense mutations within codon 172 correlates with a decrease in the complementarity of exon 5 to U1 snRNA. This suggests that a 5' splice site may extend as far as 12 nucleotides into the upstream exon, which is, to our knowledge, the largest extension.

Multiple regions within the cytoplasmic domains of the leukemia inhibitory factor receptor and gp130 cooperate in signal transduction in hepatic and neuronal cells

The receptor for leukemia inhibitory factor (LIFR), in combination with the signal-transducing subunit for interleukin-6-type cytokine receptors, gp130, and LIF, activates transcription of acute-phase plasma protein genes in human and rat hepatoma cells and the vasoactive intestinal peptide gene in a human neuroblastoma cell line. To identify the regions within the cytoplasmic domain of LIFR that initiate signal transduction independently of gp130, we constructed a chimeric receptor by linking the extracellular domain of the granulocyte colony-stimulating factor receptor (G-CSFR) to the transmembrane and cytoplasmic domain of human LIFR. The function of the chimeric receptor protein in transcriptional activation was assessed by G-CSF-mediated stimulation of cotransfected cytokine-responsive reporter gene constructs in hepatoma and neuroblastoma cells. By using the full-length cytoplasmic domain and mutants with progressive carboxy-terminal deletions, internal deletions, or point mutations, we identified the first 150 amino acid residues of LIFR as the minimal region necessary for signaling. The signaling reaction appears to involve a cooperativity between the first 70-amino-acid region containing the two sequence motifs conserved among hematopoietin receptors (box 1 and box 2) and a critical sequence between residues 141 and 150 (box 3). Analogous analyses of the cytoplasmic domains of G-CSFR and gp130 indicated similar arrangements of functional domains in these receptor subunits and the requirement of a box 3-related motif for signaling.

Multiple regions within the cytoplasmic domains of the leukemia inhibitory factor receptor and gp130 cooperate in signal transduction in hepatic and neuronal cells

The receptor for leukemia inhibitory factor (LIFR), in combination with the signal-transducing subunit for interleukin-6-type cytokine receptors, gp130, and LIF, activates transcription of acute-phase plasma protein genes in human and rat hepatoma cells and the vasoactive intestinal peptide gene in a human neuroblastoma cell line. To identify the regions within the cytoplasmic domain of LIFR that initiate signal transduction independently of gp130, we constructed a chimeric receptor by linking the extracellular domain of the granulocyte colony-stimulating factor receptor (G-CSFR) to the transmembrane and cytoplasmic domain of human LIFR. The function of the chimeric receptor protein in transcriptional activation was assessed by G-CSF-mediated stimulation of cotransfected cytokine-responsive reporter gene constructs in hepatoma and neuroblastoma cells. By using the full-length cytoplasmic domain and mutants with progressive carboxy-terminal deletions, internal deletions, or point mutations, we identified the first 150 amino acid residues of LIFR as the minimal region necessary for signaling. The signaling reaction appears to involve a cooperativity between the first 70-amino-acid region containing the two sequence motifs conserved among hematopoietin receptors (box 1 and box 2) and a critical sequence between residues 141 and 150 (box 3). Analogous analyses of the cytoplasmic domains of G-CSFR and gp130 indicated similar arrangements of functional domains in these receptor subunits and the requirement of a box 3-related motif for signaling.

Distinct regions of the human granulocyte-colony-stimulating factor receptor cytoplasmic domain are required for proliferation and gene induction

Using two different cell systems, we show that the cytoplasmic domain of the granulocyte-colony-stimulating factor receptor (G-CSFR) may be composed of at least two functional regions. The first, within the membrane-proximal 57 amino acids, is absolutely required to deliver a proliferative signal. This region contains two sequence motifs conserved between members of the hematopoietin receptor family. The second functional region resides between amino acids 57 and 96. This region is required for the induction of acute-phase plasma protein gene expression when the G-CSFR is transfected into human hepatoma cell lines. The G-CSFR-transfected hepatoma cells respond to G-CSF by increasing the production of the same set of plasma proteins as stimulated by interleukin-6, suggesting that the two cytokines share a common signal transduction pathway.

Participation of the transcription factor C/EBP delta in the acute-phase regulation of the human gene for complement component C3

C3, the third component of complement, is critical in the host immune response in that it is involved in both the classical and alternative pathways of complement activation. We have previously shown that a region (bp -127 to -70) within the C3 promoter is indispensable for conferring interleukin 1 (IL-1) responsiveness to this gene. A sequence comparison reveals two CCAAT/enhancer binding protein (C/EBP) consensus sequences, basic DNA binding region and leucine zippers 1 and 2 (bZIP1 and bZIP2), within this region. Site-directed mutagenesis of the more 3' C/EBP site (bZIP1) in the C3 promoter significantly reduced the basal level of expression and the IL-1 responsiveness of the reporter gene, whereas mutation in the second, more 5', C/EBP consensus sequence (bZIP2) had a minimal effect on basal expression and IL-1 inducibility. Electrophoretic-mobility-shift assays, with and without antibodies to the different C/EBP proteins that "supershift" protein-DNA complexes, demonstrated that proteins binding at the 3' C/EBP site formed several complexes. Antibodies to C/EBP alpha supershifted the majority of complexes formed with extracts from control cells. Antibodies directed against C/EBP delta supershifted the major IL-1-inducible complexes. Western immunoblot analyses showed that the level of C/EBP delta protein was increased dramatically in the nuclei of Hep 3B2 cells after 4 h of IL-1 treatment. When Hep 3B2 cells were cotransfected with a C/EBP delta expression vector and a construct with a C3 promoter and a reporter gene, C/EBP delta was able to trans-activate the C3 promoter in an IL-1-responsive manner. The data strongly suggest that C/EBP delta is the major protein responsible for regulating the acute-phase expression of the human C3 gene.

Distinct regions of the human granulocyte-colony-stimulating factor receptor cytoplasmic domain are required for proliferation and gene induction

Using two different cell systems, we show that the cytoplasmic domain of the granulocyte-colony-stimulating factor receptor (G-CSFR) may be composed of at least two functional regions. The first, within the membrane-proximal 57 amino acids, is absolutely required to deliver a proliferative signal. This region contains two sequence motifs conserved between members of the hematopoietin receptor family. The second functional region resides between amino acids 57 and 96. This region is required for the induction of acute-phase plasma protein gene expression when the G-CSFR is transfected into human hepatoma cell lines. The G-CSFR-transfected hepatoma cells respond to G-CSF by increasing the production of the same set of plasma proteins as stimulated by interleukin-6, suggesting that the two cytokines share a common signal transduction pathway.

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.

Synergistic action of interleukin-6 and glucocorticoids is mediated by the interleukin-6 response element of the rat alpha 2 macroglobulin gene

One class of genes coding for the acute-phase proteins (acute-phase genes) is induced by interleukin 6 (IL-6) through the human transcription factor NF-IL-6 and its rat homolog IL-6-DBP/LAP. A second class, represented by the rat alpha 2 macroglobulin gene, utilizes a different IL-6 response element (IL-6-RE) and different DNA-binding proteins interacting with this element, the so-called IL-6-RE binding proteins (IL-6 RE-BPs). Human Hep3B and HepG2 hepatoma, U266 myeloma, and CESS lymphoblastoid cells contain IL-6 RE-BPs that form complexes, with the IL-6-RE, with gel mobilities indistinguishable from those of the corresponding complexes of rat liver cells. The ability to form these complexes was induced by IL-6 in human hepatoma cells with a maximum reached after 4 h and required ongoing protein synthesis. Multiple copies of an 18-bp element containing the IL-6-RE core were sufficient to confer both induction by IL-6 and a synergistic induction by IL-6 plus glucocorticoids to minimal promoters. The synergism was blocked by the receptor antagonist RU486 and thus was dependent on the glucocorticoid receptor (GR). However, the 18-bp element contained no consensus GR-binding site, and recombinant GR did not bind at this sequence. Therefore, the synergism was probably achieved by an indirect effect of a glucocorticoid-activated intermediate gene on the IL-6 RE-BPs. The rat IL-6 RE-BP had a molecular weight of 102 +/- 10 kDa and was thus distinct from NF-IL-6 and IL-6-DBP/LAP. Therefore, IL-6 must activate two different classes of liver acute-phase genes through at least two different nuclear DNA-binding proteins: NF-IL-6/IL-6-DBP/LAP and the IL-6 RE-BP.

Synergistic action of interleukin-6 and glucocorticoids is mediated by the interleukin-6 response element of the rat alpha 2 macroglobulin gene

One class of genes coding for the acute-phase proteins (acute-phase genes) is induced by interleukin 6 (IL-6) through the human transcription factor NF-IL-6 and its rat homolog IL-6-DBP/LAP. A second class, represented by the rat alpha 2 macroglobulin gene, utilizes a different IL-6 response element (IL-6-RE) and different DNA-binding proteins interacting with this element, the so-called IL-6-RE binding proteins (IL-6 RE-BPs). Human Hep3B and HepG2 hepatoma, U266 myeloma, and CESS lymphoblastoid cells contain IL-6 RE-BPs that form complexes, with the IL-6-RE, with gel mobilities indistinguishable from those of the corresponding complexes of rat liver cells. The ability to form these complexes was induced by IL-6 in human hepatoma cells with a maximum reached after 4 h and required ongoing protein synthesis. Multiple copies of an 18-bp element containing the IL-6-RE core were sufficient to confer both induction by IL-6 and a synergistic induction by IL-6 plus glucocorticoids to minimal promoters. The synergism was blocked by the receptor antagonist RU486 and thus was dependent on the glucocorticoid receptor (GR). However, the 18-bp element contained no consensus GR-binding site, and recombinant GR did not bind at this sequence. Therefore, the synergism was probably achieved by an indirect effect of a glucocorticoid-activated intermediate gene on the IL-6 RE-BPs. The rat IL-6 RE-BP had a molecular weight of 102 +/- 10 kDa and was thus distinct from NF-IL-6 and IL-6-DBP/LAP. Therefore, IL-6 must activate two different classes of liver acute-phase genes through at least two different nuclear DNA-binding proteins: NF-IL-6/IL-6-DBP/LAP and the IL-6 RE-BP.

Insulin is a prominent modulator of the cytokine-stimulated expression of acute-phase plasma protein genes

Several endocrine hormones which influence liver metabolism are known to increase in activity during the acute phase of injury or inflammation. We determined whether these hormones have the potential to influence acute-phase protein production in human and rat hepatoma cells. Catecholamines, glucagon, growth hormone, triiodothyronine, and cyclic nucleotides individually or in combination did not modulate the basal or the interleukin-1 (IL-1)-, IL-6-, and dexamethasone-stimulated levels of acute-phase plasma proteins. Insulin, however, was found to be a rapid, nonspecific, and dose-dependent inhibitor of the cytokine and glucocorticoid stimulation of acute-phase protein gene expression and to exert its effect at the transcriptional level. The insulin inhibition applied to all cytokines tested but to various degrees, depending upon the particular acute-phase gene. Insulin resulted in an early and prominent increase in the transcription of genes encoding the AP-1 components of JunA, JunB, and c-Fos, as has been observed for other growth factors. However, the effect of insulin on C/EBP beta was unexpected and paradoxical: while insulin completely inhibited the transcriptional activation of the C/EBP beta gene in cytokine- and dexamethasone-treated cells, the level of cytoplasmic C/EBP beta RNA was elevated. Quantitation of C/EBP beta mRNA by Northern (RNA) blot analysis and of C/EBP beta DNA binding activity by Southwestern (DNA-protein) blot analysis showed that insulin, when combined with cytokines and dexamethasone, stimulated both the mRNA and DNA binding activity by a factor of 1.6 compared with that of cells treated with cytokines and dexamethasone alone. Transient transfection of H-35 and HepG2 cells with a chloramphenicol acetyltransferase (CAT) gene expression vector containing the C/EBP beta response element also resulted in a 1.5-fold increase of C/EBP beta-mediated transcription in insulin-treated cells. Transfection of CAT gene constructs containing increasing lengths of heptaglobin gene 5' flanking sequences indicated that insulin inhibition of IL-6 stimulation required the presence of the region from -4100 to -1030. These results suggest that insulin has the potential to control the transcription of acute-phase genes by at least two separate mechanisms.

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.

[Hepatology. New research results in its significance for the understanding of liver diseases]

By two exemplary clinical situations--acute viral hepatitis, acute-phase reaction of the liver--the significance of basic research for the understanding of clinical phenomena and for the development of new diagnostic and therapeutic procedures is demonstrated. The very different phenomena following infection with the hepatitis-B-virus can be explained by the variation in the interactions of virus and liver cell, by the immune reaction of the host, and by mutants of the virus. The reaction of the liver to an extrahepatic infection is mediated by interleukin-6, and characterized by an alteration in protein metabolism. The synthesis of acute-phase proteins is increased. The proteins confine the local injury and establish the homeostasis of the organism.

A 58-base-pair region of the human C3 gene confers synergistic inducibility by interleukin-1 and interleukin-6

We have cloned the promoter for the human third component of complement (C3) gene and have identified sequences involved in its regulation during the acute-phase response. A construct linking 199 bp of the C3 promoter to the firefly luciferase gene was found to be very responsive to interleukin-1 (IL-1) and modestly responsive to interleukin-6 (IL-6) by transfection analysis in the human hepatoma line Hep3B2. Simultaneous treatment with the two cytokines showed a strong synergy between the actions of the two molecules. A 58-bp fragment (-127 to -70 bp) was shown by 5' and 3' deletional mutagenesis to contain cis-acting elements that mediated both the IL-1 response and the IL-1-plus-IL-6 synergistic response of this promoter. When coupled to a heterologous promoter, this fragment enabled the synergistic induction by IL-1 plus IL-6. Sequences homologous to the palindrome ACATTGCACAATCT, which mediates the induction of the IL-6 gene by IL-1 (S. Akira, H. Isshiki, T. Sugita, O. Tanabe, S. Kinoshita, Y. Nishio, T. Nakajima, T. Hirano, and T. Kishimoto, EMBO J. 9:1897-1906, 1990), and the core sequence of the IL-6-responsive element of the rat alpha 2-macroglobulin gene (CTGGGA; M. Hattori, L. J. Abraham, W. Northemann, and G. H. Fey, Proc. Natl. Acad. Sci. USA 87:2364-2368, 1990) are contained within this fragment in immediate juxtaposition and partially overlapping. Site-directed mutagenesis within this homology region drastically reduced the inducibility of the C3 promoter by either cytokine. DNase I footprinting analysis defined a binding site for the transcription factor CCAAT/enhancer-binding protein (C/EBP), which included the IL-1-responsive element-like sequence. No differences were seen between the footprints generated by using extracts from unstimulated and IL-1-stimulated Hep3B2 cells. However, gel retardation analyses revealed two IL-1-specific bands. The data suggest that the induction by IL-1 is mediated by a factor belonging to the family of C/EBP-related proteins.

Molecular cloning of a transcription factor, AGP/EBP, that belongs to members of the C/EBP family

A C/EBP-like transcription factor, AGP/EBP, that binds to three distinct motifs in the 5'-flanking region of alpha 1-acid glycoprotein gene (AGP) has been identified. Here we report the cloning and properties of cDNA corresponding to mouse AGP/EBP. AGP/EBP and C/EBP share 87% amino acid sequence homology in the "leucine zipper" and its associated DNA-binding domains, while their sequences outside these domains and the sizes of their mRNAs are different. Unlike the limited expression of C/EBP in tissues and cells, AGP/EBP appears to be ubiquitously expressed in tissues like lung, spleen, kidney, heart, testis, and liver and cell lines like p388D1, 129P (hepatoma cell line of C3H/HeJ), FO (mouse myeloma), and L929. Antibody against cloned and expressed AGP/EBP which was raised in rabbits could recognize AGP/EBP from nuclear extract of a number of cells and tissues. On the basis of our findings about the structural relationship and the similarity of motif recognition, we propose that a family of C/EBP-like transcription factors exists.

A 58-base-pair region of the human C3 gene confers synergistic inducibility by interleukin-1 and interleukin-6

We have cloned the promoter for the human third component of complement (C3) gene and have identified sequences involved in its regulation during the acute-phase response. A construct linking 199 bp of the C3 promoter to the firefly luciferase gene was found to be very responsive to interleukin-1 (IL-1) and modestly responsive to interleukin-6 (IL-6) by transfection analysis in the human hepatoma line Hep3B2. Simultaneous treatment with the two cytokines showed a strong synergy between the actions of the two molecules. A 58-bp fragment (-127 to -70 bp) was shown by 5' and 3' deletional mutagenesis to contain cis-acting elements that mediated both the IL-1 response and the IL-1-plus-IL-6 synergistic response of this promoter. When coupled to a heterologous promoter, this fragment enabled the synergistic induction by IL-1 plus IL-6. Sequences homologous to the palindrome ACATTGCACAATCT, which mediates the induction of the IL-6 gene by IL-1 (S. Akira, H. Isshiki, T. Sugita, O. Tanabe, S. Kinoshita, Y. Nishio, T. Nakajima, T. Hirano, and T. Kishimoto, EMBO J. 9:1897-1906, 1990), and the core sequence of the IL-6-responsive element of the rat alpha 2-macroglobulin gene (CTGGGA; M. Hattori, L. J. Abraham, W. Northemann, and G. H. Fey, Proc. Natl. Acad. Sci. USA 87:2364-2368, 1990) are contained within this fragment in immediate juxtaposition and partially overlapping. Site-directed mutagenesis within this homology region drastically reduced the inducibility of the C3 promoter by either cytokine. DNase I footprinting analysis defined a binding site for the transcription factor CCAAT/enhancer-binding protein (C/EBP), which included the IL-1-responsive element-like sequence. No differences were seen between the footprints generated by using extracts from unstimulated and IL-1-stimulated Hep3B2 cells. However, gel retardation analyses revealed two IL-1-specific bands. The data suggest that the induction by IL-1 is mediated by a factor belonging to the family of C/EBP-related proteins.

Molecular cloning of a transcription factor, AGP/EBP, that belongs to members of the C/EBP family

A C/EBP-like transcription factor, AGP/EBP, that binds to three distinct motifs in the 5'-flanking region of alpha 1-acid glycoprotein gene (AGP) has been identified. Here we report the cloning and properties of cDNA corresponding to mouse AGP/EBP. AGP/EBP and C/EBP share 87% amino acid sequence homology in the "leucine zipper" and its associated DNA-binding domains, while their sequences outside these domains and the sizes of their mRNAs are different. Unlike the limited expression of C/EBP in tissues and cells, AGP/EBP appears to be ubiquitously expressed in tissues like lung, spleen, kidney, heart, testis, and liver and cell lines like p388D1, 129P (hepatoma cell line of C3H/HeJ), FO (mouse myeloma), and L929. Antibody against cloned and expressed AGP/EBP which was raised in rabbits could recognize AGP/EBP from nuclear extract of a number of cells and tissues. On the basis of our findings about the structural relationship and the similarity of motif recognition, we propose that a family of C/EBP-like transcription factors exists.

The permissive role of glucocorticoids on interleukin-1 stimulation of angiotensinogen gene transcription is mediated by an interaction between inducible enhancers

The acute-phase activation of the rat angiotensinogen (rAT) gene in liver cells is a transcriptional event mediated through an interleukin-1-inducible, NF kappa B-binding, cis-acting element (the acute-phase response element [APRE]). Using a cell culture model for the acute-phase response, we showed that the increase in angiotensionogen mRNA in H35 rat hepatoma cells requires costimulation with glucocorticoids and cytokines. Stably transfected rAT promoter-luciferase reporter genes were also activated by cytokines only in the presence of glucocorticoids. This permissive role of glucocorticoids is dependent on the expression of functional glucocorticoid receptors, because in HepG2 cells naturally deficient in such receptors, rAT gene-luciferase reporter constructs responded to interleukin-1 only when cotransfected with an expression vector for the glucocorticoid receptor. Point mutations in the two rAT gene glucocorticoid response elements located adjacent to the APRE led to loss of interleukin-1 inducibility. Induction of luciferase activity in transfected cells occurred even in the presence of cycloheximide, demonstrating that this synergistic response did not depend on new protein synthesis. Thus, a direct interaction between the interleukin-1-inducible NF kappa B-binding APRE and glucocorticoid response elements, located in cis, underlies the acute-phase activation of the rAT gene.

The permissive role of glucocorticoids on interleukin-1 stimulation of angiotensinogen gene transcription is mediated by an interaction between inducible enhancers

The acute-phase activation of the rat angiotensinogen (rAT) gene in liver cells is a transcriptional event mediated through an interleukin-1-inducible, NF kappa B-binding, cis-acting element (the acute-phase response element [APRE]). Using a cell culture model for the acute-phase response, we showed that the increase in angiotensionogen mRNA in H35 rat hepatoma cells requires costimulation with glucocorticoids and cytokines. Stably transfected rAT promoter-luciferase reporter genes were also activated by cytokines only in the presence of glucocorticoids. This permissive role of glucocorticoids is dependent on the expression of functional glucocorticoid receptors, because in HepG2 cells naturally deficient in such receptors, rAT gene-luciferase reporter constructs responded to interleukin-1 only when cotransfected with an expression vector for the glucocorticoid receptor. Point mutations in the two rAT gene glucocorticoid response elements located adjacent to the APRE led to loss of interleukin-1 inducibility. Induction of luciferase activity in transfected cells occurred even in the presence of cycloheximide, demonstrating that this synergistic response did not depend on new protein synthesis. Thus, a direct interaction between the interleukin-1-inducible NF kappa B-binding APRE and glucocorticoid response elements, located in cis, underlies the acute-phase activation of the rAT gene.

Regulation of mouse serum amyloid A gene expression in transfected hepatoma cells

Expression of mouse serum amyloid A (SAA1, -2, and -3) mRNAs can be induced up to 1,000-fold in the liver in response to acute inflammation. This large increase is primarily the result of a 200-fold increase in the rates of SAA gene transcription. To analyze the cis-acting regulatory element(s) responsible for regulating transcription, we fused 306 base pairs of the mouse SAA3 promoter to a reporter gene, the chloramphenicol acetyltransferase (CAT) gene, and transfected this chimeric DNA into cultured cells. In transient expression assays, this 5' sequence was sufficient to confer cell-specific expression: CAT activity was readily detectable when the construct was transfected into liver-derived cells but was not detectable in nonliver cells. Furthermore, when liver cells transfected with this construct were treated with conditioned media prepared from activated mixed lymphocyte cultures or with recombinant interleukin-1, a 10- to 15-fold increase in CAT activity was detected. Deletion analyses showed two regions of interest: a proximal region that enhanced CAT expression in a cell-specific manner and a distal region that conferred responsiveness to both conditioned media and recombinant interleukin-1. This distal responsive element had properties of an inducible transcriptional enhancer, and deletion of the proximal cell-specific region rendered the distal element responsive to stimulation by conditioned media in nonliver cells.

Interaction of a liver-specific factor with an enhancer 4.8 kilobases upstream of the phosphoenolpyruvate carboxykinase gene

We have previously identified a series of five DNase-I hypersensitive (HS) sites within and around the rat phosphoenolpyruvate carboxykinase (PEPCK) gene. The far upstream region has now been sequenced, and the tissue-specific HS site has been mapped more precisely at 4,800 base pairs upstream of the transcription start site of the PEPCK gene. DNA fragments that include the HS site were cloned upstream of various promoters to test whether these regions modulate transcription of the chloramphenicol acetyltransferase reporter gene. Chloramphenicol acetyltransferase activity was enhanced when the DNA fragment encompassing the upstream HS site was linked to various lengths of the PEPCK promoter or to the heterologous simian virus 40 promoter. This upstream region in conjunction with the proximal promoter, which may contain a tissue-specific element, conferred maximum activation in H4IIE hepatoma cells, which express the endogenous PEPCK gene. When these experiments were performed in XC cells, in which the gene is not expressed, transcriptional activation by the upstream element was still significant. Evidence of a specific protein-DNA interaction, using DNA mobility shift and DNase I footprinting assays, was obtained only when using H4IIE cell nuclear extracts. Competition assay showed that the interacting factor may be similar or identical to the liver-specific factor HNF3. We suggest that this protein factor binds to DNA within the HS site and interacts with the proximal promoter region to control tissue-specific high-level expression of the PEPCK gene.

Regulation of mouse serum amyloid A gene expression in transfected hepatoma cells

Expression of mouse serum amyloid A (SAA1, -2, and -3) mRNAs can be induced up to 1,000-fold in the liver in response to acute inflammation. This large increase is primarily the result of a 200-fold increase in the rates of SAA gene transcription. To analyze the cis-acting regulatory element(s) responsible for regulating transcription, we fused 306 base pairs of the mouse SAA3 promoter to a reporter gene, the chloramphenicol acetyltransferase (CAT) gene, and transfected this chimeric DNA into cultured cells. In transient expression assays, this 5' sequence was sufficient to confer cell-specific expression: CAT activity was readily detectable when the construct was transfected into liver-derived cells but was not detectable in nonliver cells. Furthermore, when liver cells transfected with this construct were treated with conditioned media prepared from activated mixed lymphocyte cultures or with recombinant interleukin-1, a 10- to 15-fold increase in CAT activity was detected. Deletion analyses showed two regions of interest: a proximal region that enhanced CAT expression in a cell-specific manner and a distal region that conferred responsiveness to both conditioned media and recombinant interleukin-1. This distal responsive element had properties of an inducible transcriptional enhancer, and deletion of the proximal cell-specific region rendered the distal element responsive to stimulation by conditioned media in nonliver cells.

Interaction of a liver-specific factor with an enhancer 4.8 kilobases upstream of the phosphoenolpyruvate carboxykinase gene

We have previously identified a series of five DNase-I hypersensitive (HS) sites within and around the rat phosphoenolpyruvate carboxykinase (PEPCK) gene. The far upstream region has now been sequenced, and the tissue-specific HS site has been mapped more precisely at 4,800 base pairs upstream of the transcription start site of the PEPCK gene. DNA fragments that include the HS site were cloned upstream of various promoters to test whether these regions modulate transcription of the chloramphenicol acetyltransferase reporter gene. Chloramphenicol acetyltransferase activity was enhanced when the DNA fragment encompassing the upstream HS site was linked to various lengths of the PEPCK promoter or to the heterologous simian virus 40 promoter. This upstream region in conjunction with the proximal promoter, which may contain a tissue-specific element, conferred maximum activation in H4IIE hepatoma cells, which express the endogenous PEPCK gene. When these experiments were performed in XC cells, in which the gene is not expressed, transcriptional activation by the upstream element was still significant. Evidence of a specific protein-DNA interaction, using DNA mobility shift and DNase I footprinting assays, was obtained only when using H4IIE cell nuclear extracts. Competition assay showed that the interacting factor may be similar or identical to the liver-specific factor HNF3. We suggest that this protein factor binds to DNA within the HS site and interacts with the proximal promoter region to control tissue-specific high-level expression of the PEPCK gene.

Structure, hormonal regulation, and identification of the interleukin-6- and dexamethasone-responsive element of the rat haptoglobin gene

Hepatic expression of the haptoglobin (Hp) gene in mammalian species is stimulated severalfold during an acute-phase reaction. To identify the molecular mechanism responsible for this regulation, the single-copy rat Hp gene has been isolated. The genomic sequences showed a high degree of homology with the primate Hp gene. Activity of the rat Hp gene was increased in cultured liver cells by interleukin-1 (IL-1), IL-6, and glucocorticoids. The genomic Hp gene sequence spanning from -6500 to +6500, when transiently introduced into human hepatoma (HepG2) cells, directed IL-6- and dexamethasone-stimulated expression of rat Hp mRNA and protein. No response to IL-1 was detected, suggesting that the corresponding regulatory element(s) might lie outside of the tested gene sequences. An IL-6- and dexamethasone-responsive element has been localized to the promoter proximal region -146 to -55. Although the nucleotide sequences of this rat Hp gene region showed substantial divergence from that of the human gene, analysis of sequential 5' and 3' deletion constructs indicated an arrangement of functional IL-6 response elements in the rat Hp promoter sequence comparable to that of the human homolog. The magnitude of IL-6 regulation through the rat Hp gene promoter was severalfold lower than that of the human Hp gene. The reduced activity could be ascribed to a single-base difference in an otherwise conserved sequence corresponding to an active element in the human gene. The IL-6 response of the rat Hp element was improved severalfold by substituting that base with the human nucleotide.

Structure, hormonal regulation, and identification of the interleukin-6- and dexamethasone-responsive element of the rat haptoglobin gene

Hepatic expression of the haptoglobin (Hp) gene in mammalian species is stimulated severalfold during an acute-phase reaction. To identify the molecular mechanism responsible for this regulation, the single-copy rat Hp gene has been isolated. The genomic sequences showed a high degree of homology with the primate Hp gene. Activity of the rat Hp gene was increased in cultured liver cells by interleukin-1 (IL-1), IL-6, and glucocorticoids. The genomic Hp gene sequence spanning from -6500 to +6500, when transiently introduced into human hepatoma (HepG2) cells, directed IL-6- and dexamethasone-stimulated expression of rat Hp mRNA and protein. No response to IL-1 was detected, suggesting that the corresponding regulatory element(s) might lie outside of the tested gene sequences. An IL-6- and dexamethasone-responsive element has been localized to the promoter proximal region -146 to -55. Although the nucleotide sequences of this rat Hp gene region showed substantial divergence from that of the human gene, analysis of sequential 5' and 3' deletion constructs indicated an arrangement of functional IL-6 response elements in the rat Hp promoter sequence comparable to that of the human homolog. The magnitude of IL-6 regulation through the rat Hp gene promoter was severalfold lower than that of the human Hp gene. The reduced activity could be ascribed to a single-base difference in an otherwise conserved sequence corresponding to an active element in the human gene. The IL-6 response of the rat Hp element was improved severalfold by substituting that base with the human nucleotide.

An inducible 50-kilodalton NF kappa B-like protein and a constitutive protein both bind the acute-phase response element of the angiotensinogen gene

The rat angiotensinogen gene is induced in the course of the hepatic acute-phase response. We demonstrate that monocyte conditioned medium can stimulate transcription of a stably introduced reporter construct driven by 615 base pairs of the angiotensinogen 5'-flanking sequence, as well as the endogenous gene, in Reuber H35 cells. Point mutations of a cis-acting element, located 545 base pairs from the transcription start site and sharing sequence identity with known nuclear factor kappa B (NF kappa B)-binding sites, led to loss of cytokine inducibility. When cloned upstream of a minimal promoter, this cis-acting element imparted transcriptional inducibility by monocyte conditioned medium, interleukin-1, and tumor necrosis factor on a luciferase reporter gene in HepG2 cells. Two distinct proteins bound this element in vitro: a heat-stable, constitutively present, hepatic nuclear protein that gave rise to a DNase I-protected footprint covering the functionally defined element; and a binding protein of different mobility, induced by monocyte conditioned medium, which also recognized the NF kappa B-binding site of the murine kappa light-chain enhancer. UV cross-linking showed this inducible protein to have an apparent molecular mass of 50 kilodaltons, similar to that described for NF kappa B and distinct from the constitutively present protein that was shown by Southwestern (DNA-protein) blot to have a molecular mass of 32 kilodaltons. Methylation interference analysis showed that the induced species made contact points with guanine residues in the NF kappa B consensus sequence typical of NF kappa B. Induction of this binding activity did not require new protein synthesis, and 12-O-tetradecanoylphorbol-13-acetate could mimic the induction by cytokines. We thus provide direct evidence for involvement of NF kappa B or a similar factor in the hepatic acute-phase response and discuss the potential role of the presence of a constitutive nuclear factor binding the same cis element.

An inducible 50-kilodalton NF kappa B-like protein and a constitutive protein both bind the acute-phase response element of the angiotensinogen gene

The rat angiotensinogen gene is induced in the course of the hepatic acute-phase response. We demonstrate that monocyte conditioned medium can stimulate transcription of a stably introduced reporter construct driven by 615 base pairs of the angiotensinogen 5'-flanking sequence, as well as the endogenous gene, in Reuber H35 cells. Point mutations of a cis-acting element, located 545 base pairs from the transcription start site and sharing sequence identity with known nuclear factor kappa B (NF kappa B)-binding sites, led to loss of cytokine inducibility. When cloned upstream of a minimal promoter, this cis-acting element imparted transcriptional inducibility by monocyte conditioned medium, interleukin-1, and tumor necrosis factor on a luciferase reporter gene in HepG2 cells. Two distinct proteins bound this element in vitro: a heat-stable, constitutively present, hepatic nuclear protein that gave rise to a DNase I-protected footprint covering the functionally defined element; and a binding protein of different mobility, induced by monocyte conditioned medium, which also recognized the NF kappa B-binding site of the murine kappa light-chain enhancer. UV cross-linking showed this inducible protein to have an apparent molecular mass of 50 kilodaltons, similar to that described for NF kappa B and distinct from the constitutively present protein that was shown by Southwestern (DNA-protein) blot to have a molecular mass of 32 kilodaltons. Methylation interference analysis showed that the induced species made contact points with guanine residues in the NF kappa B consensus sequence typical of NF kappa B. Induction of this binding activity did not require new protein synthesis, and 12-O-tetradecanoylphorbol-13-acetate could mimic the induction by cytokines. We thus provide direct evidence for involvement of NF kappa B or a similar factor in the hepatic acute-phase response and discuss the potential role of the presence of a constitutive nuclear factor binding the same cis element.

Acute-phase reaction induces a specific complex between hepatic nuclear proteins and the interleukin 6 response element of the rat alpha 2-macroglobulin gene

Interleukin 6 (IL-6) was established as a transcriptional inducer of the rat alpha 2-macroglobulin gene, a prototype liver acute-phase gene. Maximum induction occurred when the 5' flanking sequences of this gene (position -209 to -43) directed expression from the gene's own TATA box and transcription start site. Removal of the hexanucleotide CTGGGA (position -164 to -159) abolished 60-70% of the hormonal induction in FAO1 rat hepatoma cells. This hexanucleotide was defined as the IL-6 response element (IL-6-RE). The IL-6-RE is well conserved in the cytokine-responsive regions of other acute-phase genes and serves as a binding site for nuclear proteins. A characteristic DNA-protein complex (complex I) was formed with nuclear proteins from normal rat livers. A different, hormone-inducible complex (complex II) was assembled specifically with nuclear proteins from acute-phase rat livers or from IL-6-treated human Hep 3B hepatoma cells. Complex II was competitively inhibited by oligonucleotides representing the conserved IL-6-RE sequence from other acute-phase genes. Thus, the proteins building complex II likely participate in a general signal transduction mechanism mediating the transcriptional activation by IL-6 of several acute-phase genes.

Interleukin-6 and the acute phase response

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Alpha interferon and gamma interferon stimulate transcription of a single gene through different signal transduction pathways

Interferons (IFNs) play a key role in the defense against virus infection and the regulation of cell growth and differentiation, in part through changes in specific gene transcription in target cells. We describe several differences between the signal transduction events that result in transcriptional activation of the human gene coding for a guanylate-binding protein (GBP) by alpha interferon (IFN-alpha) and gamma interferon (IFN-gamma). Activation by IFN-alpha was rapid, transient, and cycloheximide resistant. Activation by IFN-gamma was slower, sustained, and delayed by cycloheximide. IFN-gamma led to the formation of a stable intracellular signal which led to continued GBP transcription even if the ligand was withdrawn, whereas IFN-alpha-induced GBP transcription decayed rapidly if IFN-alpha was withdrawn. Perturbations of signaling pathways involving classical second messengers (cyclic AMP, Ca2+, protein kinase C) did not induce GBP transcription. However, various kinase inhibitors blocked the transcriptional response to IFN-gamma but not IFN-alpha, suggesting that a specific and possibly novel kinase is involved in gene activation by IFN-gamma.

Alpha interferon and gamma interferon stimulate transcription of a single gene through different signal transduction pathways

Interferons (IFNs) play a key role in the defense against virus infection and the regulation of cell growth and differentiation, in part through changes in specific gene transcription in target cells. We describe several differences between the signal transduction events that result in transcriptional activation of the human gene coding for a guanylate-binding protein (GBP) by alpha interferon (IFN-alpha) and gamma interferon (IFN-gamma). Activation by IFN-alpha was rapid, transient, and cycloheximide resistant. Activation by IFN-gamma was slower, sustained, and delayed by cycloheximide. IFN-gamma led to the formation of a stable intracellular signal which led to continued GBP transcription even if the ligand was withdrawn, whereas IFN-alpha-induced GBP transcription decayed rapidly if IFN-alpha was withdrawn. Perturbations of signaling pathways involving classical second messengers (cyclic AMP, Ca2+, protein kinase C) did not induce GBP transcription. However, various kinase inhibitors blocked the transcriptional response to IFN-gamma but not IFN-alpha, suggesting that a specific and possibly novel kinase is involved in gene activation by IFN-gamma.

Nuclear factors interacting with an interleukin-6 responsive element of rat alpha 2-macroglobulin gene

During acute inflammation, a group of liver-derived plasma proteins, acute phase proteins (APPs), increase in concentration. Interleukin-6 (IL-6) is responsible for this increase via the induction of APP gene expression. We have identified an IL-6 responsive cis-acting element (IL-6RE) of gene encoding a typical APP, rat alpha 2-macroglobulin (alpha 2M). The IL-6RE contains a sequence that is conserved among the 5'-flanking regions of various APP genes. Introduction of mutations into the conserved sequence revealed that the sequence, termed IL-6RE core, is a critical and essential component of IL6-RE. Nuclear factors binding to the IL-6RE core were identified in livers of normal and inflamed rats. Mobility shift pattern and DNase I footprinting profile indicated that the factors from normal and inflamed stages recognized the same sequence but were distinct from each other. These results suggested that the regulation of alpha 2M gene expression may involve mutually exclusive interaction of stage-specific trans-acting factors.

Stimulation of the acute-phase response in simian virus 40-hepatocyte cell lines

Seven simian virus 40 (SV40)-hepatocyte cell lines were characterized with respect to the ability to express eight liver acute-phase genes. cDNA clones corresponding to albumin, serum amyloid A, alpha 1-acid glycoprotein, haptoglobin, alpha-, beta-, and gamma-fibrinogen, and alpha 1-major-acute-phase protein mRNAs were used in Northern (RNA) or slot blot analyses. In the noninduced state, six of the seven cell lines showed significant (i.e., liverlike) levels of constitutive expression of all genes examined except that expression of haptoglobin mRNA was considerable lower than in the normal liver. To examine whether these immortalized liver cells can respond appropriately to inflammatory mediators, cells were treated with conditioned medium from activated human monocytes or mixed lymphocyte cultures. Results showed that these SV40-hepatocyte cell lines responded to the conditioned media in culture by down-regulating albumin gene expression and up-regulating other acute-phase genes in a time- and dose-dependent manner. These results indicate that the SV40-hepatocytes retained not only the ability to express a number of acute-phase genes but also the ability to respond to external stimuli. The usefulness of these cell lines for analysis of the molecular mechanisms involved in the regulation of these acute-phase genes is discussed.

Identification of cis-acting sequences responsible for phorbol ester induction of human serum amyloid A gene expression via a nuclear factor kappaB-like transcription factor

We have analyzed the 5'-flanking region of one of the genes coding for the human acute-phase protein, serum amyloid A (SAA). We found that SAA mRNA could be increased fivefold in transfected cells by treatment with phorbol 12-myristate 13-acetate (PMA). To analyze this observation further, we placed a 265-base-pair 5' SAA fragment upstream of the reporter chloramphenicol acetyltransferase (CAT) gene and transfected this construct into HeLa cells. PMA treatment of these transient transfectants resulted in increased CAT expression. Nuclear proteins from PMA-treated HeLa cells bound to this DNA fragment, and methylation interference analysis showed that the binding was specific to the sequence GGGACTTTCC (between -82 and -91), a sequence previously described by R. Sen and D. Baltimore (Cell 46:705-716, 1986) as the binding site for the nuclear factor NF kappa B. In a cotransfection competition experiment, we could abolish PMA-induced CAT activity by using cloned human immunodeficiency virus long-terminal-repeat DNA containing the NF kappa B-binding sequence. The same long-terminal-repeat DNA containing mutant NF kappa B-binding sequences (G. Nabel and D. Baltimore, Nature [London] 326:711-713, 1987) did not affect CAT expression, which suggested that binding by an NF kappa B-like factor is required for increased SAA transcription.

Stimulation of the acute-phase response in simian virus 40-hepatocyte cell lines

Seven simian virus 40 (SV40)-hepatocyte cell lines were characterized with respect to the ability to express eight liver acute-phase genes. cDNA clones corresponding to albumin, serum amyloid A, alpha 1-acid glycoprotein, haptoglobin, alpha-, beta-, and gamma-fibrinogen, and alpha 1-major-acute-phase protein mRNAs were used in Northern (RNA) or slot blot analyses. In the noninduced state, six of the seven cell lines showed significant (i.e., liverlike) levels of constitutive expression of all genes examined except that expression of haptoglobin mRNA was considerable lower than in the normal liver. To examine whether these immortalized liver cells can respond appropriately to inflammatory mediators, cells were treated with conditioned medium from activated human monocytes or mixed lymphocyte cultures. Results showed that these SV40-hepatocyte cell lines responded to the conditioned media in culture by down-regulating albumin gene expression and up-regulating other acute-phase genes in a time- and dose-dependent manner. These results indicate that the SV40-hepatocytes retained not only the ability to express a number of acute-phase genes but also the ability to respond to external stimuli. The usefulness of these cell lines for analysis of the molecular mechanisms involved in the regulation of these acute-phase genes is discussed.

Identification of cis-acting sequences responsible for phorbol ester induction of human serum amyloid A gene expression via a nuclear factor kappaB-like transcription factor

We have analyzed the 5'-flanking region of one of the genes coding for the human acute-phase protein, serum amyloid A (SAA). We found that SAA mRNA could be increased fivefold in transfected cells by treatment with phorbol 12-myristate 13-acetate (PMA). To analyze this observation further, we placed a 265-base-pair 5' SAA fragment upstream of the reporter chloramphenicol acetyltransferase (CAT) gene and transfected this construct into HeLa cells. PMA treatment of these transient transfectants resulted in increased CAT expression. Nuclear proteins from PMA-treated HeLa cells bound to this DNA fragment, and methylation interference analysis showed that the binding was specific to the sequence GGGACTTTCC (between -82 and -91), a sequence previously described by R. Sen and D. Baltimore (Cell 46:705-716, 1986) as the binding site for the nuclear factor NF kappa B. In a cotransfection competition experiment, we could abolish PMA-induced CAT activity by using cloned human immunodeficiency virus long-terminal-repeat DNA containing the NF kappa B-binding sequence. The same long-terminal-repeat DNA containing mutant NF kappa B-binding sequences (G. Nabel and D. Baltimore, Nature [London] 326:711-713, 1987) did not affect CAT expression, which suggested that binding by an NF kappa B-like factor is required for increased SAA transcription.

Glucocorticoid and estrogen regulation of a rat T-kininogen gene

We have examined the regulation of a rat T-kininogen gene by glucocorticoid and estrogen. Expression of the endogenous gene in a rat hepatoma cell line is increased 5-fold and 2-fold in response to dexamethasone and 17 beta-estradiol-3-benzoate, respectively. Various deletion constructs of the 5' region of an isolated T-kininogen gene were fused to a chloramphenicol acetyltransferase (CAT) gene and introduced into the hepatoma cells by electroporation. Analysis of the CAT activity in cell extracts after treatment with glucocorticoid or estrogen revealed that a fragment from -167 to +52 is sufficient to confer full induction. An additional deletion in this region was unresponsive, while a larger fragment (-612 to -100) linked to a heterologous promoter did result in regulated expression. These results suggested that the sequence responsible for the hormonal response was located at -167 to -100 from the transcription start site. This 67 bp region contains a consensus for the core sequence of the glucocorticoid responsive element (GRE) and the estrogen responsive element (ERE). Interestingly these elements are located within 7 bp of each other and both sequences overlap a 16 bp palindrome that may be important in hormone receptor-DNA recognition.

Identification of the promoter sequences involved in the interleukin-6 dependent expression of the rat alpha 2-macroglobulin gene

The 5'-region of the rat alpha 2-macroglobulin gene has been characterized. A 5.6 kb Sal I - Xba I fragment containing the first 4 exons of the alpha 2-macroglobulin gene and 1.3 kb of its 5'-flanking region was sequenced. The putative transcriptional start site was determined by RNase protection and primer extension analysis. TATA- and CAAT-box equivalent sequences were found. A potential glucocorticoid receptor binding site was located on the antisense strand. DNA sequences containing the 5'-flanking region of the rat alpha 2-macroglobulin gene were linked to the gene coding for the bacterial chloramphenicol acetyltransferase and introduced into Hep G2 cells. In these transfected Hep G2 cells CAT activity could be induced by recombinant human interleukin-6. Deletion analyses have shown that the sequences between -852 and -777 as well as between -404 and -165 relative to the cap site, contain regulatory elements involved in the interleukin-6 dependent induction of the alpha 2-macroglobulin gene.