Species-specific changes in regulatory elements of mouse haptoglobin genes

Differential expression of bovine major acute phase proteins, cytokines and metabolic indicator genes in clinical endometritis cows

Among the uterine diseases, clinical endometritis (CE) is a major challenge to livestock farming as it causes sub- or infertility problems in dairy animals. The aim of this study was to evaluate the expression of cytokines (IL- 1β, TNF-α, IL-6, and IL-8), acute phase proteins [APPs; haptoglobin (Hp), serum amyloid A (SAA) and alpha-1 acid glycoprotein (AGP)] and energy indicators [leptin and insulin-like growth factor (IGF)-1] genes in uterine tissue of CE affected cows. The uterine biopsy from CE cows (4) and non-endometritis cows (4) was processed for quantitative real-time PCR to study the mRNA expression of these innate immune molecules. We observed that mRNA expression of SAA, IL-1β, IL-8 and leptin genes were significantly up-regulated while, TNF-α and IGF-I genes were significantly down-regulated in CE cows. It can be concluded that bovine APPs, cytokines and energy indicators genes are differentially expressed in CE affected cows.

Plasma clearance of hemoglobin and haptoglobin in mice and effect of CD163 gene targeting disruption

AIM

In humans, plasma haptoglobin (Hp) and the macrophage receptor CD163 promote a fast scavenging of hemoglobin (Hb). In the present study, we have compared the mouse and human CD163-mediated binding and uptake of Hb and HpHb complex in vitro and characterized the CD163-mediated plasma clearance of Hb in CD163 gene knockout mice and controls.

RESULTS

Contrary to human Hp, mouse Hp did not promote high-affinity binding to CD163. This difference between mouse and man was evident both by analysis of the binding of purified proteins and by ligand uptake studies in CD163-transfected cells. Plasma clearance studies in mice showed a fast clearance (half-life few minutes) of fluorescently labeled mouse Hb with the highest uptake in the kidney and liver. HPLC analysis of serum showed that the clearance curve exhibited a two-phase decay with a faster clearance of Hb than plasma-formed HpHb. In CD163-deficient mice, the overall clearance of Hb was slightly slower and followed a one-phase decay.

INNOVATION AND CONCLUSION

In conclusion, mouse Hp does not promote high-affinity binding of mouse Hb to CD163, and noncomplexed mouse Hb has a higher CD163 affinity than human Hb has. Moreover, CD163-mediated uptake in mice seems to only account for a part of the Hb clearance. The new data further underscore the fact that the Hp system in man seems to have a broader and more sophisticated role. This has major implications in the translation of data on Hb metabolism from mouse to man.

Identification and expression of liver-specific genes after LPS challenge in amphioxus: the hepatic cecum as liver-like organ and "pre-hepatic" acute phase response

Liver is present in all vertebrates and central to many physiological processes including processing of nutrients from ingested food, plasma protein synthesis, hormone production, and detoxification. However, its evolutionary origin remains open to date. Liver is also the principal organ of acute phase response (APR) but when the vertebrate-like APR regulatory network emerges during the chordate evolution is unknown. By combining global genome survey and qRT-PCR data sets, here, we clearly demonstrate the presence of the 58 vertebrate (zebrafish) liver-specific genes in amphioxus (hepatic cecum-specific genes) that are expressed in a tissue-specific manner in the hepatic cecum, the homolog of liver. Among these 58 hepatic cecum-specific genes, 52 genes respond to lipopolysaccharide challenge, which show similar expression profiles in both zebrafish and amphioxus. In addition, searching for binding sites for HNF and APR-associated transcription factors in promoter sequences for all the 58 hepatic cecum-specific genes and the 52 APR-related genes suggests that both HNF factors and APR-associated transcription factors in amphioxus form regulatory networks similar to those observed in zebrafish, regulating the hepatic cecum-specific genes and APR-related genes, respectively, via binding to their binding sites in the promoter regions. These similarities in liver/hepatic cecum-specific genes, APR, and regulatory networks between amphioxus and zebrafish supports the idea that hepatic cecum in amphioxus is the "pre-hepatic" organ homologous to vertebrate liver and acts as an immunological organ, playing an important role in APR.

Regulation of rat haptoglobin gene expression is coordinated by the nuclear matrix

Using computer stress-induced duplex destabilization (SIDD) analysis and binding experiments, we identified a S/MAR element (-599/-200 bp) (Hp-S/MAR) adjacent to the cis-element (-165/-56 bp) in the rat haptoglobin gene. We examined its functional interactions with the lamins and lamin-associated proteins in the basal state and during acute-phase (AP) response-induced increased transcription. Colocalization, electrophoretic mobility shift assay (EMSA), and re-electrophoresis of nucleoprotein complexes, South-Western and Western blot analysis and coimmunoprecipitation experiments revealed that the lamins, PARP-1, C/EBP beta, and Hp-S/MAR assembled higher order complexes through direct lamin-Hp-S/MAR and probably PARP-1-Hp-S/MAR interactions although C/EBP beta did not bind to the Hp-S/MAR but established direct interaction with PARP-1. The transition from constitutive to increased haptoglobin gene transcription during the AP response was associated with quantitative and qualitative changes in Hp-S/MAR-protein interactions, respectively, observed as increased association of the lamin(s) with the Hp-S/MAR and as the appearance of a 90 kDa Hp-S/MAR-binding protein. Also, during the AP response the contact between C/EBP beta and PARP-1 established in the basal state was lost. DNA chromatography with the haptoglobin cis-element and Western blot analysis suggests that PARP-1 was a coactivator during constitutive and elevated transcription. The results show that the lamin components of the nuclear matrix form a network of functional, dynamic protein-protein and protein-Hp-S/MAR associations with multiple partners, and underline the involvement of PARP-1 in the regulation of haptoglobin gene transcription. We concluded that the interplay of these interactions fine tunes haptoglobin gene expression to meet the changing requirements of liver cells.

Metabolism and secretory function of white adipose tissue: effect of dietary fat

Approximately 40% of the total energy consumed by western populations is represented by lipids, most of them being ingested as triacylglycerols and phospholipids. The focus of this review is to analyze the effect of the type of dietary fat on white adipose tissue metabolism and secretory function, particularly on haptoglobin, TNF-α, plasminogen activator inhibitor-1 and adiponectin secretion. Previous studies have demonstrated that the duration of the exposure to the high-fat feeding, amount of fatty acid present in the diet and the type of fatty acid may or may not have a significant effect on adipose tissue metabolism. However, the long-term or short-term high fat diets, especially rich in saturated fatty acids, probably by activation of toll-like receptors, stimulated the expression of proinflammatory adipokines and inhibited adiponectin expression. Further studies are needed to investigate the cellular mechanisms by which dietary fatty acids affect white adipose tissue metabolism and secretory functions.

Evolution of the vertebrate twist family and synfunctionalization: a mechanism for differential gene loss through merging of expression domains

Twist genes are essential for embryonic development and are conserved from jellyfish to human. To study the vertebrate twist family and its evolution, the entire complement of twist genes was obtained for 9 representative species. Phylogenetic analysis showed that a single protochordate twist gene was duplicated at least twice before the teleost-tetrapod split to give rise to 3 ancestral genes, which were further duplicated or deleted, resulting in fluctuating number of twist paralogs in different vertebrate lineages. To find whether changes in gene copy number were associated with changes in gene function, embryonic expression patterns of twist orthologs were evaluated against the number of twist paralogs in different species. The results showed evidence for both neo- and subfunctionalization, and, in addition, for loss of an ancestral regulatory gene. For example, in Xenopus, twist2 was lost, but the twist1 paralog acquired, and therefore preserved, twist2 function. A general model is proposed to explain the data. In this process, termed synfunctionalization, one paralog acquires the expression domain(s) of another. The merging may lead to function shuffle. Alternatively, it may leave one paralog redundant and thus subject to deletion--while its function is retained by the surviving paralog(s). Synfunctionalization is a mechanism that, together with neo- and subfunctionalization, may work to establish equilibrium in the number of genes that regulate developmental processes; it may regulate the complexity of regulatory regions as well as gene copy number and therefore may play a role in evolution of gene function and the structure of genome.

Identification of human hepatocellular carcinoma-related proteins by proteomic approaches

Hepatocellular carcinoma (HCC) is the most common malignant liver tumor. Analysis of human serum from HCC patients using two-dimensional gel electrophoresis (2DE) combined with nano-high-performance liquid chromatography electrospray ionization tandem mass spectrometry (nano-HPLC-ESI-MS/MS) identified fourteen different proteins differentially expressed between HCC patients and the control group. Twelve proteins were up-regulated and two down-regulated. By using nano-HPLC-MS/MS system to analyze proteome in human serum, 317 proteins were identified, twenty-nine of which to high confidence levels (protein matched at last two unique peptide sequences). Of these twenty-nine proteins, six were present only in HCC patients and may serve as biomarkers for HCC.

Pyrrolidine dithiocarbamate inhibits interleukin-6 signaling through impaired STAT3 activation and association with transcriptional coactivators in hepatocytes

Interleukin (IL)-6 is a proinflammatory cytokine that has been implicated in the expression of acute phase plasma proteins and hepatic insulin resistance through activation of the JAK/STAT3 pathway. Although previous studies have demonstrated that pyrrolidine dithiocarbamate (PDTC) exerts protection against inflammatory responses, its role in the regulation of IL-6 receptor signaling remains unclear. Here we show that treatment of cultured HepG2 hepatoma cells with PDTC inhibits IL-6-stimulated tyrosine phosphorylation and subsequent nuclear translocation of STAT3 in a dose- and time-dependent fashion. No inhibition of JAK-1 activity was observed. To provide insight into PDTC signaling, we constructed a conditionally active STAT3 by fusing it with the ligand binding domain of the estrogen receptor (STAT3-ER). In the presence of 4-hydroxytamoxifen STAT3-ER was translocated in the nucleus of HepG2 cells in a phosphorylation-independent manner, and treatment with PDTC mitigated the response. Although STAT3 coprecipitated with heat-shock protein 90 (Hsp90) in control cells, coprecipitation of the two proteins was greatly reduced after PDTC treatment or after exposure to geldanamycin, an Hsp90 inhibitor. As a result there was a decrease in IL-6-induced association of STAT3 with the transcriptional coactivators FOXO1a and C/EBPbeta together with significant reduction in the expression of SOCS-3 protein and that of two major acute phase plasma proteins. Importantly, treatment of HepG2 cells and a primary culture of rat hepatocytes with PDTC restored insulin responsiveness that was abrogated by IL-6. These studies are consistent with the ability of PDTC to down-regulate IL-6-induced STAT3 activation by altering the stability of STAT3-Hsp90 complex.

Identification of neutrophil gelatinase-associated lipocalin (NGAL) as a discriminatory marker of the hepatocyte-secreted protein response to IL-1beta: a proteomic analysis

The liver is the major source of proteins used throughout the body for various functions. Upon injury or infection, an acute phase response (APR) is initiated in the liver that is primarily mediated by inflammatory cytokines such as interleukin-1beta (IL-1beta) and interleukin-6. Among others, the APR is characterized by an altered protein synthetic profile. We used two-dimensional gel electrophoresis to study the dynamics of changes in protein synthesis in hepatocytes exposed to these inflammatory cytokines. Protein profiles were quantified using image analysis and further analyzed using multivariate statistical methods. Our results indicate that IL-1beta and IL-6 each induces secreted protein responses with distinct dynamics and dose-dependence. Parallel stimulation by IL-1beta and IL-6 results in a protein pattern indistinguishable from the IL-1beta pattern, indicating a dominant effect of IL-1beta over IL-6 at the doses tested. Multidimensional scaling (MDS) of correlation distances between protein secretion levels revealed two protein pairs that are robustly co-secreted across the various cytokine stimulation conditions, suggesting shared regulatory pathways. Finally, we also used multivariate alternating conditional expectation (MACE) to identify transformation functions that discriminated the cytokine-stimulated and untreated hepatocyte-secreted protein profiles. Our analysis indicates that the expression of neutrophil gelatinase-associated lipocalin (NGAL) was sufficient to discriminate between IL-1beta and IL-6 stimulation. The combination of proteomics and multivariate analysis is expected to provide new information on the cellular regulatory networks involved in generating specific cellular responses.

Regulation of haptoglobin gene expression in 3T3-L1 adipocytes by cytokines, catecholamines, and PPARgamma

Factors which regulate expression of the haptoglobin (acute phase reactant) gene in adipocytes have been examined using 3T3-L1 cells. Haptoglobin expression was observed by Northern blotting in each of the major white adipose tissue depots of mice (epididymal, subcutaneous, mesenteric, and perirenal) and in interscapular brown fat. Expression occurred in mature adipocytes, but not in the stromal-vascular fraction. In 3T3-L1 cells, haptoglobin mRNA was detected from day 4 after the induction of differentiation into adipocytes. Lipopolysaccharide and the cytokines, TNFalpha and interleukin-6, resulted in substantial increases in haptoglobin mRNA in 3T3-L1 adipocytes; the increase (7-fold) was highest with TNFalpha. Increases in haptoglobin mRNA level were also induced by dexamethasone, noradrenaline, isoprenaline, and a beta3-adrenoceptor agonist. In contrast, haptoglobin mRNA was reduced by nicotinic acid and the PPARgamma agonist, rosiglitazone. RT-PCR showed that the haptoglobin gene was expressed in human adipose tissue (subcutaneous, omental). It is concluded that haptoglobin gene expression in adipocytes is stimulated by inflammatory cytokines, glucocorticoids, and the sympathetic system, while activation of the PPARgamma nuclear receptor is strongly inhibitory.

Haptoglobin, an inflammation-inducible plasma protein

Sterile tissue injury or infection initiates a local inflammatory response that mobilizes a systemic acute phase reaction resulting in, among other things, the induction of genes encoding the acute phase plasma proteins (APPs). In all vertebrates, a common set of APPs is increased and exerts essential protective functions. Haptoglobin (HP), one of the major APPs, acts as a high-affinity hemoglobin-binding protein and antioxidant. Liver is the major site of HP synthesis; however, regulated, low level expression is also detected in other organs. Induction of the Hp gene is mediated by interleukin-6-type cytokines and is synergistically enhanced by glucocorticoids. Growth stimulation of hepatic cells in vivo or in vitro suppresses the Hp gene-inducing effects of inflammatory cytokines. Receptors for IL-6 cytokines mediate induction of the Hp gene by the transcription factors signal transducer and activator of transcription-3 (STAT3) and CAAT/enhancer binding protein beta (C/EBPbeta), but attenuate the stimulation through co-activated STAT5 and mitogen-activated protein kinases, ERK-1 and ERK-2. The specificity by which the related cytokines, IL-6, oncostatin M, and leukemia inhibitory factor, regulate Hp gene transcription is determined by the profile of the cytokine receptor subunits expressed on the target cells and the relative extents by which these receptors activate the intracellular signaling pathways. The current hypothesis is that HP exerts an anti-inflammatory activity and that by the degree with which HP attenuates the inflammatory process, including the production of IL-6 cytokines, it determines the level and duration of acute phase expression of the Hp gene.

Involvement of CCAAT/enhancer-binding protein alpha in haptoglobin gene expression by all-trans-retinoic acid

Several acute-phase plasma proteins, including haptoglobin (Hp), are induced in the liver in response to inflammation. Recently, we found that Hp gene expression is up-regulated by all-trans-retinoic acid (ATRA) in the extrahepatic monocytic cell line, THP-1. To investigate the molecular mechanism underlying ATRA-induced Hp gene expression, we analyzed the induction of transcription factor CCAAT/enhancer-binding protein (C/EBP) isoforms in ATRA-stimulated THP-1 cells and their binding to the Hp promoter. Western blot analysis showed that treatment with ATRA increased C/EBPalpha and beta expression, but decreased that of C/EBPdelta. Electrophoretic mobility shift and supershift assays demonstrated that only C/EBPalpha of the C/EBP isoforms bound to the C/EBP DNA-binding sites in the Hp promoter. Furthermore, when ATRA-dependent Hp induction was inhibited by sodium butyrate or auranofin, induction of C/EBPalpha, but not C/EBPbeta, was also diminished. These results suggest that C/EBPalpha is involved in the activation of Hp gene expression by ATRA in human monocytic cells.

Stress activated protein kinase p38 is involved in IL-6 induced transcriptional activation of STAT3

The pleiotropic cytokine interleukin-6 (IL-6) induces acute phase protein expression in HepG2 human hepatoma cells and promotes the growth of mouse B9 hybridoma. The signaling cascades leading to these biological functions are only partially known. We analysed the involvement of MAPK homologues in IL-6 transduction pathways and found that interleukin-6 triggered activation of p38 stress-activated protein kinase (p38) but not of jun kinase. p38 activity was required for biological functions including acute phase protein secretion from HepG2 hepatoma and proliferation of B9 hybridoma cells. Using a reporter gene construct containing a 190 bp promoter fragment of the acute phase protein haptoglobin we found that p38 is involved in transcriptional activation of the haptoglobin promoter by STAT3 but not by NF-IL6. Thus, we present evidence for a role of p38 in IL-6 induced functions and a possible cross-talk between this MAPK homologue and the STAT pathway.

Involvement of polyomavirus enhancer activator 3 in the regulation of expression of gamma-glutamyl transpeptidase messenger ribonucleic acid-IV in the rat epididymis

Gamma-glutamyl transpeptidase (GGT) mRNA-IV and polyomavirus enhancer activator 3 (PEA3) mRNA are highly expressed in the initial segment of the rat epididymis, and both are regulated by testicular factors. PEA3 protein in rat initial segment nuclear extracts has been shown to bind to a PEA3/Ets binding motif, which is derived from the partially characterized GGT mRNA-IV promoter region. This suggests that PEA3 may be involved in regulating transcription from the rat GGT mRNA-IV gene promoter in the initial segment. Using DNA oligonucleotide primers and DNA sequencing analysis, an approximately 1500-basepair (bp) DNA sequence at the 5' region of the promoter was obtained. Using transient transfection, PEA3 activated transcription of the rat GGT mRNA-IV promoter only in cultured epididymal cells from the rat initial segment, but not in Cos-1 or NRK-52E cells. Promoter deletion analysis indicated that a PEA3/Ets binding motif between nucleotides -22 and -17 is the functional site for PEA3 to activate transcription of GGT promoter IV and that an adjacent Sp1 binding motif is also required to maintain promoter IV activity in epididymal cells. Transcriptional activation of promoter IV was shown to be epididymal cell-specific and PEA3-specific. In addition, PEA3 may act as a weak repressor for transcription of promoter IV, probably using a PEA3/Ets binding motif(s) distal to the transcription start site. A model of how PEA3 is involved in the regulation of transcription of GGT promoter IV in epididymal cells is proposed.

Targeted disruption of the mouse ferrochelatase gene producing an exon 10 deletion

Protoporphyria is a disease characterized by a deficiency in ferrochelatase, the terminal enzyme in the heme biosynthetic pathway, which catalyzes the chelation of iron and protoporphyrin to form heme. Clinical symptoms arise from an accumulation of protoporphyrin behind the partial enzyme block and include photosensitivity and sometimes hepatobiliary disease. Protoporphyria is described as an dominant disease, yet patients exhibit decreased ferrochelatase activities of 15-30% of normal, not 50% as might be expected. Missense, nonsense, and splicing mutations have been identified in ferrochelatase cDNA from protoporphyric patients. In this study we introduce an exon 10 deletion, an analogous mutation to that described in some protoporphyric patients, into the mouse embryonic stem (ES) cell genome via homologous recombination. Targeted ES cells were confirmed by Southern blot analysis. Expression of wild-type and exon 10-deleted mRNA was demonstrated by reverse transcriptase-polymerase chain reaction (RT-PCR) and cDNA sequencing. Ferrochelatase levels were analyzed by immunoblotting. Ferrochelatase activity was measured by the chelation of zinc and mesoporphyrin, and by the decrease in protoporphyrin accumulation after adding delta-aminolevulinic acid. In the exon 10 +/- ES cells there is expression of both wild-type and exon 10-deleted mRNA, a 50% decrease in cross-reactive material with an anti-ferrochelatase antibody, and an approximate 50% decrease in ferrochelatase activity compared to wild-type ES cells. Therefore, an exon 10 deletion alone is insufficient to decrease ferrochelatase activity to the levels in protoporphyric patients. This suggests that requirement of an additional mutation to decrease the expression of the wild-type allele.

Expression of the protective proteins hemopexin and haptoglobin by cells of the neural retina

The blood-retinal barrier, consisting of retinal pigment epithelial cells and retinal endothelial cells, prevents hemopexin and haptoglobin, anti-oxidant protective plasma proteins normally synthesized by the liver, from entering the neural retina. If present, these proteins must, therefore, be made locally. The cell types within the retina in which hemopexin and haptoglobin mRNAs are made have been investigated. RNA was extracted from both the neural retina and pigment epithelium obtained by dissection of human donor eyes as well as from cultured pigment epithelial and photoreceptor cells. The mRNAs for both haptoglobin and hemopexin were detected, using reverse-transcriptase polymerase chain reaction, in the neural retina and cultured photoreceptors but not in pigment epithelial cells. The cellular location of these mRNAs was determined using in situ hybridization of sections of human retina which revealed that haptoglobin mRNA was located principally in the photoreceptor cells, cells of the inner nuclear layer and some cells of the ganglion cell layer. Hemopexin mRNA, previously shown to be made in the human neural retina (Hunt et al., 1996. Journal of Cellular Physiology 168: 71-80), is expressed by most of the cells of neural retina including the photoreceptors and, notably, the ganglion cells.

Comparison of promoters for the murine and human P-selectin genes suggests species-specific and conserved mechanisms for transcriptional regulation in endothelial cells

P-selectin, an adhesion receptor for leukocytes, is constitutively expressed in megakaryocytes and endothelial cells. Tumor necrosis factor-alpha (TNF-alpha) or lipopolysaccharide (LPS) increases synthesis of P-selectin in murine but not in human endothelial cells. To identify potential species-specific and conserved mechanisms for regulation of expression of P-selectin, we cloned the 5'-flanking region of the murine P-selectin gene and compared its features with those previously reported for the human gene. The murine and human genes shared conserved Stat-like, Hox, Ets, GATA, and GT-IIC elements. In the murine gene, a conserved GATA element bound to GATA-2 and functioned as a positive regulatory element, whereas a conserved Ets element bound to GA-binding protein and functioned as a negative regulatory element. Significantly, the murine P-selectin gene had several features not found in the human gene. These included an insertion from -987 to -649 that contained tandem GATA and tandem AP1-like sequences, which resembled enhancers in beta-globin locus control regions. Both tandem elements bound specifically to nuclear proteins. The murine gene lacked the unique kappaB site specific for p50 or p52 homodimers found in the human gene. Instead, it contained two tandem kappaB elements and a variant activating transcription factor/cAMP response element site, which closely resembled sites in the E-selectin gene that are required for TNF-alpha- or LPS-inducible expression. TNF-alpha or LPS augmented expression of a reporter gene driven by the murine, but not the human, P-selectin promoter in transfected endothelial cells. Deletional analysis of the murine 5'-flanking region revealed several sequences that were required for either constitutive or inducible expression. These data suggest that both species-specific and conserved mechanisms regulate transcription of the human and murine P-selectin genes.

Glucocorticoids stimulate p21 gene expression by targeting multiple transcriptional elements within a steroid responsive region of the p21waf1/cip1 promoter in rat hepatoma cells

Glucocorticoids can induce a G1 arrest in the cell cycle progression of BDS1 rat hepatoma cells. In these cells, dexamethasone, a synthetic glucocorticoid, stimulated a rapid and selective increase in expression of the p21 cyclin-dependent kinase (CDK) inhibitor mRNA and protein and virtually abolished CDK2 phosphorylation of the retinoblastoma protein. Expression of the p27 CDK inhibitor, and other G1-acting cell cycle proteins, remained unaffected. Dexamethasone stimulated p21 promoter activity in a p53-independent manner that required functional glucocorticoid receptors. Transforming growth factor-beta, which also induced a G1 cell cycle arrest of the hepatoma cells, failed to elicit this response. Analysis of 5' deletions of the p21 promoter uncovered a glucocorticoid responsive region between nucleotides -1481 and -1184, which does not contain a canonical glucocorticoid response element but which can confer dexamethasone responsiveness to a heterologous promoter. Fine mapping of this region uncovered three distinct 50-60-base pair transcriptional elements that likely function as targets of glucocorticoid receptor signaling. Finally, ectopic expression of p21 had no effect on hepatoma cell growth in the absence of glucocorticoids but facilitated the ability of dexamethasone to inhibit cell proliferation. Thus, our results have established a direct transcriptional link between glucocorticoid receptor signaling and the regulated promoter activity of a CDK inhibitor gene that is involved in the cell cycle arrest of hepatoma cells.

Tissue, temporal and inducible expression pattern of haptoglobin in mice

Haptoglobin (Hp) is a member of the acute phase plasma proteins previously thought to be synthesized solely by the adult liver. The present study analyzes the tissue and temporal expression pattern of endogenous haptoglobin in the mouse and acute phase inducibility in various tissues. The liver is found to be the major site of haptoglobin expression but significant expression levels were also observed in the lung and skin. Acute phase induction by bacterial lipopolysaccharide (LPS) demonstrated that haptoglobin was induced not only in the liver but also in other tissues, including lung, skin, spleen, and kidney. Temporal analyses demonstrated that haptoglobin is expressed during embryogenesis in the liver and is inducible in various tissues surveyed throughout development. Transgenic mice that harbored a 1.05-kilobase (kb) region of the human haptoglobin promoter linked to two different reporter genes gave rise to lung-specific expression in the majority of transgenic lines with minimal liver expression. However, when induced with lipopolysaccharide, the 1.05-kb fragment contained the necessary elements for a response comparable to endogenous expression levels. In conclusion, these studies demonstrate that haptoglobin is not an adult liver specific gene, and its role as an acute phase reactant may well be more diverse than previously suspected.

The carboxyl-terminal region of STAT3 controls gene induction by the mouse haptoglobin promoter

Haptoglobin (HP) is one of the major acute phase plasma proteins in the mouse, and its synthesis is additively induced by interleukin (IL)-6 and glucocorticoids. STAT3 serves as the mediator of the IL-6 receptor signal and appears to contribute to the transcriptional induction of acute phase protein genes. The carboxyl-terminal region of STAT3, consisting of an acidic domain and containing a serine phosphorylation site, has been proposed to contribute to the induction process. To assess the role of STAT3 in the transcriptional control of the HP promoter, we applied two mutant forms of STAT3: one with a deletion of the carboxyl-terminal 55 amino acid residues, STAT3Delta55C, and the other with a substitution of serine 727 to alanine, STAT3SA. Like the wild-type STAT3, both mutant STAT3 forms are activated by the signal-transducing subunit of the IL-6 receptor, gp130, or by co-transfected IL-3 receptor. Ectopic expression and activation of wild-type STAT3 or STAT3SA in HepG2 hepatoma cells similarly enhance transcription through the IL-6-response element of the HP promoter. This enhancement is specific for STAT3 and cannot be reproduced by STAT1 or STAT5. In contrast, STAT3Delta55C inhibits IL-6-induced transcriptional activation. Interestingly, whereas receptor-activated STAT3 also enhances stimulation of the haptoglobin promoter by dexamethasone through the glucocorticoid receptor, activated STAT3Delta55C reduces the regulation below the level achieved by the glucocorticoid receptor alone. This transdominant action by STAT3Delta55C is dependent on a functional IL-6-responsive element. The data suggest that the carboxyl-terminal domain, but not its serine phosphorylation site of STAT3, is required for transcription as part of the hematopoietin receptor signaling as well as for cooperation with other transcription factors such as the glucocorticoid receptor.