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

Interaction of adenosine 3',5'-cyclic monophosphate and tumor necrosis factor-alpha on serum amyloid A3 expression in mouse granulosa cells: dependence on CCAAT-enhancing binding protein-beta isoform

TNFalpha is an inflammatory-related cytokine that has inhibitory effects on gonadotropin- and cAMP-stimulated steroidogenesis and folliculogenesis. Because ovulation is an inflammatory reaction and TNF specifically induces serum amyloid A3 (SAA3) in mouse granulosa cells, the effect of cAMP on TNF-induced SAA3 promoter activity, mRNA and protein was investigated. Granulosa cells from immature mice were cultured with TNF and/or cAMP. TNF increased SAA3 promoter activity, mRNA, and protein, which were further increased by cAMP. cAMP alone increased SAA3 promoter activity, but SAA3 mRNA and protein remained undetectable. Thus, there appeared to be different mechanisms by which TNF and cAMP regulated SAA3 expression. SAA3 promoters lacking a nuclear factor (NF)-kappaB-like site or containing its mutant were not responsive to TNF but were responsive to cAMP. Among four CCAAT-enhancing binding protein (C/EBP) sites in the SAA3 promoter, the C/EBP site nearest the NF-kappaB-like site was required for TNF-induced SAA3. The C/EBP site at -75/-67 was necessary for responsiveness to cAMP. Dominant-negative C/EBP and cAMP response element-binding protein or short interfering RNA of C/EBPbeta blocked TNF- or cAMP-induced SAA3 promoter activity. The combination of TNF and cAMP increased C/EBPbeta protein above that induced by TNF or cAMP alone. Thus, cAMP in combination with TNF specifically induced C/EBPbeta protein, leading to enhanced SAA3 expression but requiring NF-kappaB in mouse granulose cells. In addition, like TNF, SAA inhibited cAMP-induced estradiol accumulation and CYP19 levels. These data indicate SAA may play a role in events occurring during the ovulation process.

Inflammation-induced recombinant protein expression in vivo using promoters from acute-phase protein genes

We report that promoters for two murine acute-phase protein (APP) genes, complement factor 3 (C3) and serum amyloid A3 (SAA3), can increase recombinant protein expression in response to inflammatory stimuli in vivo. To deliver APP promoter-luciferase reporter gene constructs to the liver, where most endogenous APP synthesis occurs, we introduced them into a nonreplicating adenovirus vector and injected the purified viruses intravenously into mice. When compared with the low levels of basal luciferase expression observed prior to inflammatory challenge, markedly increased expression from the C3 promoter was detected in liver in response to both lipopolysaccharide (LPS) and turpentine, and lower-level inducible expression was also found in lung. In contrast, expression from the SAA3 promoter was found only in liver and was much more responsive to LPS than to turpentine. After LPS challenge, hepatic luciferase expression increased rapidly and in proportion to the LPS dose. Use of cytokine-inducible promoters in gene transfer vectors may make it possible to produce antiinflammatory proteins in vivo in direct relationship to the intensity and duration of an individual's inflammatory response. By providing endogenously controlled production of recombinant antiinflammatory proteins, this approach might limit the severity of the inflammatory response without interfering with the beneficial components of host defense and immunity.

YY1 represses rat serum amyloid A1 gene transcription and is antagonized by NF-kappa B during acute-phase response

Serum amyloid A (SAA), one of the major acute-phase proteins, increases several hundredfold in concentration in plasma following acute inflammation, primarily as a result of a 200-fold increase in its transcriptional rate. Functional analysis of the rat SAA1 promoter has identified a 65-bp cytokine response unit (CRU; positions -135 to -71) that could confer cytokine responsiveness on a heterologous promoter. Within this CRU, two cis-regulatory elements, corresponding to NF-kappa B- and C/EBP-binding sites, were found to be functionally important and exerted synergistic effects on induced SAA1 expression. In this report, we show that a third transcription factor interacts with the CRU through a region located between the NF-kappa B- and C/EBP-binding sites. On the basis of its gel mobility shift patterns, ubiquitous binding activity, sequence specificity of DNA binding, zinc-dependent binding activity, and gel mobility supershift by specific antibodies, we concluded that this factor is identical to YY1. Methylation interference studies revealed that YY1 binding sequences overlapped with those of NF-kappa B, and gel mobility studies showed that NF-kappa binding to the CRU was effectively inhibited by YY1. Consistent with its presumed antagonistic role to NF-kappa B, YY1 exerted a negative effect on SAA1 expression, whereas disruption of its binding in the promoter elevated basal and cytokine-induced activities. Furthermore, overexpression of YY1 trans-repressed SAA1 promoter activity. Thus, our results demonstrate that SAA1 expression is tightly regulated by an on-off switch of activators and repressors, presumably to ensure that it is expressed only under appropriate physiological conditions.

YY1 represses rat serum amyloid A1 gene transcription and is antagonized by NF-kappa B during acute-phase response

Serum amyloid A (SAA), one of the major acute-phase proteins, increases several hundredfold in concentration in plasma following acute inflammation, primarily as a result of a 200-fold increase in its transcriptional rate. Functional analysis of the rat SAA1 promoter has identified a 65-bp cytokine response unit (CRU; positions -135 to -71) that could confer cytokine responsiveness on a heterologous promoter. Within this CRU, two cis-regulatory elements, corresponding to NF-kappa B- and C/EBP-binding sites, were found to be functionally important and exerted synergistic effects on induced SAA1 expression. In this report, we show that a third transcription factor interacts with the CRU through a region located between the NF-kappa B- and C/EBP-binding sites. On the basis of its gel mobility shift patterns, ubiquitous binding activity, sequence specificity of DNA binding, zinc-dependent binding activity, and gel mobility supershift by specific antibodies, we concluded that this factor is identical to YY1. Methylation interference studies revealed that YY1 binding sequences overlapped with those of NF-kappa B, and gel mobility studies showed that NF-kappa binding to the CRU was effectively inhibited by YY1. Consistent with its presumed antagonistic role to NF-kappa B, YY1 exerted a negative effect on SAA1 expression, whereas disruption of its binding in the promoter elevated basal and cytokine-induced activities. Furthermore, overexpression of YY1 trans-repressed SAA1 promoter activity. Thus, our results demonstrate that SAA1 expression is tightly regulated by an on-off switch of activators and repressors, presumably to ensure that it is expressed only under appropriate physiological conditions.

Induction of the mouse serum amyloid A3 gene by cytokines requires both C/EBP family proteins and a novel constitutive nuclear factor

Serum amyloid A (SAA) is a major acute-phase protein synthesized and secreted mainly by the liver. In response to acute inflammation, its expression may be induced up to 1,000-fold, primarily as a result of a 200-fold increase in the rate of SAA gene transcription. We have previously demonstrated that a 350-bp promoter fragment from the mouse SAA3 gene was necessary and sufficient to confer liver-specific and cytokine-induced expression. Deletion studies identified a distal response element that is responsible for the cytokine response and has properties of an inducible transcriptional enhancer. In this study, we further analyzed the distal response element and showed that it consists of three functionally distinct elements: the A element constitutes a weak binding site for C/EBP family proteins, the B element also interacts with C/EBP family proteins but with a much higher binding affinity, and the C element interacts with a novel constitutive nuclear factor, SEF-1. Site-specific mutation studies revealed that all three elements were required for maximum promoter activity. C/EBP alpha, C/EBP beta, and C/EBP delta were capable of interacting with elements A and B. Under noninduced conditions, C/EBP alpha was the major binding factor; however, upon cytokine stimulation C/EBP beta- and C/EBP delta-binding activities were dramatically increased and became the predominant binding factors. Consistent with these binding studies were the cotransfection experiments in which C/EBP beta and C/EBP delta were shown to be potent transactivators for the SAA3 promoter. Moreover, the transactivation required an intact B element despite the presence of other functional C/EBP-binding sites. Interestingly, although element C did not interact with C/EBP directly, it was nevertheless required for maximum transactivation by C/EBP delta. Our studies thus demonstrate that both C/EBP family proteins and SEF-1 are required to transactivate the SAA3 gene.

Induction of the mouse serum amyloid A3 gene by cytokines requires both C/EBP family proteins and a novel constitutive nuclear factor

Serum amyloid A (SAA) is a major acute-phase protein synthesized and secreted mainly by the liver. In response to acute inflammation, its expression may be induced up to 1,000-fold, primarily as a result of a 200-fold increase in the rate of SAA gene transcription. We have previously demonstrated that a 350-bp promoter fragment from the mouse SAA3 gene was necessary and sufficient to confer liver-specific and cytokine-induced expression. Deletion studies identified a distal response element that is responsible for the cytokine response and has properties of an inducible transcriptional enhancer. In this study, we further analyzed the distal response element and showed that it consists of three functionally distinct elements: the A element constitutes a weak binding site for C/EBP family proteins, the B element also interacts with C/EBP family proteins but with a much higher binding affinity, and the C element interacts with a novel constitutive nuclear factor, SEF-1. Site-specific mutation studies revealed that all three elements were required for maximum promoter activity. C/EBP alpha, C/EBP beta, and C/EBP delta were capable of interacting with elements A and B. Under noninduced conditions, C/EBP alpha was the major binding factor; however, upon cytokine stimulation C/EBP beta- and C/EBP delta-binding activities were dramatically increased and became the predominant binding factors. Consistent with these binding studies were the cotransfection experiments in which C/EBP beta and C/EBP delta were shown to be potent transactivators for the SAA3 promoter. Moreover, the transactivation required an intact B element despite the presence of other functional C/EBP-binding sites. Interestingly, although element C did not interact with C/EBP directly, it was nevertheless required for maximum transactivation by C/EBP delta. Our studies thus demonstrate that both C/EBP family proteins and SEF-1 are required to transactivate the SAA3 gene.

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.

The human beta fibrinogen promoter contains a hepatocyte nuclear factor 1-dependent interleukin-6-responsive element

Acute-phase reactants are liver proteins whose synthesis is positively or negatively regulated during inflammation. The main mediators of this phenomenon are glucocorticoids and interleukin-6 (IL-6), a pleiotropic cytokine that also controls hematopoiesis. Functional analysis of several acute-phase reactant promoter regions has identified two major DNA motifs used by IL-6-regulated genes. The first one corresponds to a CTGG(G/A)AA sequence, and the other is a binding site for members of the C/EBP family of nuclear proteins. We have previously shown that the human beta fibrinogen (beta Fg) promoter contains an IL-6-responsive region, located between bp -150 and -67 (P. Huber, M. Laurent, and J. Dalmon, J. Biol. Chem. 265:5695-5701, 1990). In this study, using DNase I footprinting, mobility shift assays, and mutagenesis, we demonstrate that at least three subdomains of this region are necessary to observe a full response to IL-6. The most distal contains a CTGGGAA motif, and its mutation inhibits IL-6 stimulation. Another, which is able to interact with several distinct nuclear proteins, among them members of the C/EBP family, is dispensable for IL-6 induction but plays an important role in the constitutive expression of beta Fg. Finally, a proximal hepatocyte nuclear factor 1 binding site, already described as the major determinant of beta Fg tissue-specific expression, is also required for IL-6 stimulation. These results indicate a complex interplay between nuclear proteins within the beta Fg IL-6-responsive region and suggest a tight functional coupling between the tissue-specific and inducible elements.

The human beta fibrinogen promoter contains a hepatocyte nuclear factor 1-dependent interleukin-6-responsive element

Acute-phase reactants are liver proteins whose synthesis is positively or negatively regulated during inflammation. The main mediators of this phenomenon are glucocorticoids and interleukin-6 (IL-6), a pleiotropic cytokine that also controls hematopoiesis. Functional analysis of several acute-phase reactant promoter regions has identified two major DNA motifs used by IL-6-regulated genes. The first one corresponds to a CTGG(G/A)AA sequence, and the other is a binding site for members of the C/EBP family of nuclear proteins. We have previously shown that the human beta fibrinogen (beta Fg) promoter contains an IL-6-responsive region, located between bp -150 and -67 (P. Huber, M. Laurent, and J. Dalmon, J. Biol. Chem. 265:5695-5701, 1990). In this study, using DNase I footprinting, mobility shift assays, and mutagenesis, we demonstrate that at least three subdomains of this region are necessary to observe a full response to IL-6. The most distal contains a CTGGGAA motif, and its mutation inhibits IL-6 stimulation. Another, which is able to interact with several distinct nuclear proteins, among them members of the C/EBP family, is dispensable for IL-6 induction but plays an important role in the constitutive expression of beta Fg. Finally, a proximal hepatocyte nuclear factor 1 binding site, already described as the major determinant of beta Fg tissue-specific expression, is also required for IL-6 stimulation. These results indicate a complex interplay between nuclear proteins within the beta Fg IL-6-responsive region and suggest a tight functional coupling between the tissue-specific and inducible elements.

Cooperative effects of C/EBP-like and NF kappa B-like binding sites on rat serum amyloid A1 gene expression in liver cells

Serum amyloid A (SAA) is a major acute-phase protein synthesized and secreted mainly by the liver. In response to inflammation, its expression is increased by 1000-fold, primarily because of a 200-fold increase in the rates of SAA gene transcription. We have shown that when 304 bp of 5' flanking region of the rat SAA1 gene is fused to a reporter gene, the chloramphenicol acetyltransferase (CAT) gene, CAT activity is induced in a cell-specific manner in response to conditioned media prepared from activated mixed lymphocyte cultures and recombinant interleukin-1. In this study, deletion of the SAA1 promoter to -120 bp with respect to the transcriptional start site did not diminish promoter activity; however, deletion to -94 bp renders the promoter completely inactive. Functional analysis have demonstrated that a 66-bp DNA fragment spanning -138 bp to -73 bp could confer cytokine responsiveness to a heterologous thymidine kinase promoter. Within this 66-bp responsive element resided an NF kappa B-like-binding site and a C/EBP-like-binding site. Although each binding site alone could confer responsiveness when stimulated with conditioned media and TPA, the response was much weaker than that observed when both sites were present. Moreover, site-specific mutations of either binding site completely abolished SAA1 promoter activity. Taken together, these results suggest a functional importance for and cooperative interaction of these two nuclear-factor binding sites in the cytokine-induced expression of the rat SAA1 gene.

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.

Two adjacent C/EBP-binding sequences that participate in the cell-specific expression of the mouse serum amyloid A3 gene

Serum amyloid A (SAA) is a major acute-phase protein synthesized primarily in the liver. Its expression, very low in normal animals, is increased several hundredfold following acute inflammation. To examine DNA sequences involved in liver-specific expression, 5'-flanking regions of the mouse SAA3 gene were analyzed by transient transfection, band shift, and DNase I protection assays. We found that a 56-bp fragment immediately 5' to the TATA box spanning the region -93 to -38 relative to the transcription start site was sufficient to confer liver cell-specific transcriptional activation onto a heterologous promoter in a dose-dependent and orientation-independent manner. This DNA fragment could form DNA-protein complexes with heat-stable nuclear proteins, and the complexes formed could be specifically competed for by excess oligomers corresponding to the C/EBP- or DBP-binding sites but not by binding sites for three other liver-specific factors, HNF1, HNF3, and HNF4. Footprint analysis using Hep3B nuclear extracts revealed two adjacent footprint regions within this 56-bp fragment, the distal region having at least fivefold-greater affinity than the proximal region. Identical footprint patterns were observed when purified recombinant C/EBP protein was used. These results indicated that binding of C/EBP to this 56-bp fragment plays an important role in vivo in enhancing expression of the mouse SAA3 gene in hepatocytes.

Two adjacent C/EBP-binding sequences that participate in the cell-specific expression of the mouse serum amyloid A3 gene

Serum amyloid A (SAA) is a major acute-phase protein synthesized primarily in the liver. Its expression, very low in normal animals, is increased several hundredfold following acute inflammation. To examine DNA sequences involved in liver-specific expression, 5'-flanking regions of the mouse SAA3 gene were analyzed by transient transfection, band shift, and DNase I protection assays. We found that a 56-bp fragment immediately 5' to the TATA box spanning the region -93 to -38 relative to the transcription start site was sufficient to confer liver cell-specific transcriptional activation onto a heterologous promoter in a dose-dependent and orientation-independent manner. This DNA fragment could form DNA-protein complexes with heat-stable nuclear proteins, and the complexes formed could be specifically competed for by excess oligomers corresponding to the C/EBP- or DBP-binding sites but not by binding sites for three other liver-specific factors, HNF1, HNF3, and HNF4. Footprint analysis using Hep3B nuclear extracts revealed two adjacent footprint regions within this 56-bp fragment, the distal region having at least fivefold-greater affinity than the proximal region. Identical footprint patterns were observed when purified recombinant C/EBP protein was used. These results indicated that binding of C/EBP to this 56-bp fragment plays an important role in vivo in enhancing expression of the mouse SAA3 gene in hepatocytes.

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.