Repression by ARP-1 sensitizes apolipoprotein AI gene responsiveness to RXR alpha and retinoic acid

The gene coding for apolipoprotein AI (apoAI), a lipid binding protein involved in the transport of cholesterol and other lipids in the plasma, is expressed in mammals predominantly in the liver and the intestine. Liver-specific expression is controlled by synergistic interactions between transcription factors bound to three separate sites, sites A (-214 to -192), B (-169 to -146), and C (-134 to -119), within a powerful liver-specific enhancer located between nucleotides -222 and -110 upstream of the apoAI gene transcription start site (+1). Previous studies in our laboratory have shown that ARP-1, a member of the nuclear receptor superfamily whose ligand is unknown (orphan receptor), binds to site A and represses transcription of the apoAI gene in liver cells. In a more recent series of experiments, we found that site A is a retinoic acid (RA) response element that responds preferentially to the recently identified RA-responsive receptor RXR alpha over the previously characterized RA receptors RAR alpha and RAR beta. In this study we investigated the combined effects of ARP-1 and RXR alpha on apoAI gene expression in liver cells. Transient transfection assays showed that site A is necessary and sufficient for RXR alpha-mediated transactivation of the apoAI gene basal promoter in human hepatoma HepG2 cells in the presence of RA and that this transactivation is abolished by increasing amounts of cotransfected ARP-1. Electrophoretic mobility shift assays and subsequent Scatchard analysis of the data revealed that ARP-1 and RXR alpha bind to site A with similar affinities. These assays also revealed that ARP-1 and RXR alpha bind to site A as heterodimers with an affinity approximately 10 times greater than that of either ARP-1 or RXR alpha alone. Further transfection assays in HepG2 cells, using as a reporter a construct containing the apoAI gene basal promoter and its upstream regulatory elements (including site A) in their natural context, revealed that RXR alpha has very little effect on the levels of expression regardless of the presence or absence of RA. However, while ARP-1 alone or ARP-1 and RXR alpha together dramatically repress expression in the absence of RA, the repression by ARP-1 and RXR alpha together, but not ARP-1 alone, is almost completely alleviated in the presence of RA. These results indicate that transcriptional repression by ARP-1 sensitizes apoAI gene responsiveness to RXR alpha and RA and suggest that the magnitude of this responsiveness is regulated by the intracellular ratio of ARP-1 to RXR alpha. These observations raise the possibility that transcriptional repression is a general mechanism for switching gene transcription between alternative transcription activation pathways.

Regulation of albumin expression in fetal rat hepatocytes cultured under proliferative conditions: role of epidermal growth factor and hormones

Sustained production of plasma proteins, notably albumin, is a reliable indicator of the differentiated state of hepatocytes. In this work, we have developed a fetal hepatocyte culture system where studying the regulation of albumin expression in proliferating liver cells. Our results show that under proliferative conditions (i.e., in the presence of EGF) fetal hepatocytes maintain albumin production above control quiescent non-treated cells. Glucagon and noradrenaline have no effect on the proliferation induced by EGF in cultured fetal hepatocytes; however, they act synergistically with the growth factor, increasing intracellular albumin levels. The maximum response is obtained by treatment of cells with EGF and noradrenaline. The stimulatory noradrenergic effect is mimicked by agents that increase cyclic AMP levels (forskolin plus IBMX). However, vasopressin or phorbol esters have no effect on albumin production, neither alone nor in combination with EGF. Dexamethasone, which does not alter the proliferative induction of EGF, increases albumin content. This effect is independent of the proliferative status of the cells and is not enhanced by glucagon, noradrenaline, or cyclic AMP increasing agents. The hormonal changes observed in albumin production partially correlate with changes in mRNA levels. This is the first time that cyclic AMP increasing agents are shown to act synergistically with EGF, increasing the expression of this liver specific gene.

Hypercholesterolemia induces differential expression of rabbit apolipoprotein A and C genes

We have compared steady-state mRNA levels of apolipoproteins AI, AII, AIV, CI, CII and CIII in liver and small intestine of rabbits fed on a cholesterol-rich diet for up to 16 weeks. Apolipoprotein (apo) AIV mRNA was detected in both liver and small intestine, while apo AII was not detected in either organ. Apo CI, apo CII and apo CIII were expressed only in liver and apo AI mRNA was detected only in small intestine. In small intestine, apo AIV and apo AI mRNA levels increased to a maximum at the 4th and 12th week of treatment, respectively. In liver there was a parallel increase in the mRNA levels of apo AIV, apo CI, apo CII and apo CIII, with maximum levels after 4 weeks of treatment. A 3-fold increase was found in apo CII and apo CIII hepatic transcription rates between hypercholesterolemic and control rabbits after 4 weeks of treatment, no longer detectable after 8 weeks. However, no changes were found in apo AIV and apo CI transcription rates. Changes in apolipoprotein mRNA levels were accompanied by changes in plasma lipoprotein levels. Overall, these changes correlate well with the variations detected in the expression of the different apolipoprotein genes. Our results indicate that dietary cholesterol plays an important role in the regulation of these genes and that this regulation is tissue dependent.

Albumin gene expression is down-regulated by albumin or macromolecule infusion in the rat

A novel feedback regulatory mechanism operating on transcription of the albumin gene is described in the rat. In 1946, it was proposed that circulating colloids, including serum albumin, may affect the synthesis and/or secretion of albumin in the liver. The molecular basis for this proposed regulation has now been investigated by adding oncotically active macromolecules to the circulation of normal or genetically albumin-deficient Nagase analbuminemic rats (NAR) and analyzing the hepatic expression of genes, including albumin after 24 h. The transcription rate of the albumin gene was higher in NAR than in normal rats and was dramatically reduced by raising serum albumin to 1.6 g/dl. Intravenous infusion of albumin into normal rats also decreased transcriptional activity of the albumin gene by 50-60%, and this decrease correlated with changes in serum colloid osmotic pressure after albumin infusion. Inhibition of albumin gene transcription was also observed upon intravenous infusion of other protein or nonprotein macromolecules, such as gamma-globulin and dextran. This down-regulation appears to control the steady-state level of albumin mRNA in the liver. Aside from a concomitant decrease in apo E gene transcription after albumin or macromolecule infusion, there was no change in the transcription rate of other genes, including those exhibiting liver-preferred or -specific expression (e.g., tyrosine amino-transferase, cytochrome P-450, alpha 1-antitrypsin, apolipoproteins A-I and B, and transferrin) or general cellular expression (e.g., alpha-tubulin, pro alpha 2 collagen, and beta-actin). Feedback regulation of albumin gene expression by serum colloids may serve as a specific homeostatic mechanism to maintain the steady-state level of total protein in the circulation.

A ubiquitous factor is required for C/EBP-related proteins to form stable transcription complexes on an albumin promoter segment in vitro

The liver-enriched transcription factor CCAAT/enhancer binding protein (C/EBP) binds to numerous liver-specific promoters, yet the mechanism by which the protein stimulates transcription has not been described. The serum albumin promoter, which is liver specific, contains a strong C/EBP-binding site tightly juxtaposed to a binding site for the ubiquitous factor nuclear factor-Y (NF-Y). The binding of C/EBP impairs the binding of NF-Y; yet surprisingly, this arrangement leads to strong synergistic activation of a minimal promoter in liver nuclear extracts. Transcriptional synergism is manifested by NF-Y facilitating the ability of C/EBP to form preinitiation complexes that are stable through multiple rounds of transcription. Binding by itself, C/EBP stimulates transcription weakly without forming stable complexes, and moving the NF-Y binding site 10 bp away from the C/EBP site increases NF-Y binding in the presence of C/EBP but reduces the efficiency of stable complex formation and transcriptional synergism. These findings show that C/EBP requires precise positioning next to a ubiquitous factor for optimal formation of stable complexes and provides a model to understand the dramatic activation of the albumin gene in hepatic development.

Selective translational control and nonspecific posttranscriptional regulation of ribosomal protein gene expression during development and regeneration of rat liver

Mammalian liver development is accompanied by a transition from rapid growth in the fetus to a quiescent state in the adult. However, extensive proliferation can be induced in the adult liver by partial hepatectomy. In this study, we examined the regulation of ribosomal protein (rp) gene expression in the developing and regenerating rat liver. Our results indicate that the translation of rp mRNAs is selectively repressed by about 70% upon development from fetal to adult life, as illustrated by the decrease in ribosomal loading. In addition, the relative abundance of these mRNAs, like that of several other, but not all, housekeeping mRNAs, declines during development through a posttranscriptional mechanism. When liver cells commence growth following partial hepatectomy, translation of rp mRNAs is resumed to near-maximal capacity, as judged by their very efficient recruitment into polysomes. The concomitant increase in the abundance rp mRNAs under these circumstances is achieved by a posttranscriptional mechanism. The apparent fluctuations in the translation efficiency of rp mRNAs are accompanied by parallel changes in the expression of the genes encoding the initiation factors eIF-4E and eIF-4A. Our results indicate that selective translational control of rp mRNAs in mammals is not confined to manipulated cells in culture but constitutes an important regulatory mechanism operating in vivo in the course of liver development and regeneration.

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

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

Impaired hepatic apolipoprotein B and E translation in streptozotocin diabetic rats

Studies of streptozotocin-induced diabetes in rats have demonstrated that hepatic apo B and apo E production are reduced. To determine if reductions are related to decreases in hepatic mRNAs, we performed blotting analysis of total liver RNA with rat apo B, apo E, and albumin cDNA probes. The expected reduction in albumin mRNA levels to 48% of control livers occurred in diabetic rat liver, while apo B and apo E mRNA levels were unchanged. The proportion of translational stop codon (BSTOP) mRNA averaged 43% of total in diabetic rats similar to control levels. Long-term labeling experiments using [35S]methionine in primary cultures of rat hepatocytes and specific immunoprecipitations demonstrated production of apo B and apo E, and albumin by hepatocytes from diabetic rats was reduced to 37%, 53%, and 23% of controls. Pulse-chase studies, together with mRNA analyses, suggest that reduced hepatic secretion of apo B and apo E in diabetics is primarily a result of impaired translation and not intracellular degradation. Ribosome transit studies directly confirmed the prolonged elongation rates for apo B and apo E mRNAs in hepatocytes derived from diabetic rats. This effect was more pronounced on apo BH (higher molecular weight) than on apo BL (lower molecular weight). Treatment of diabetic rats with insulin for 7 d led to normalization of hepatic albumin mRNA levels with no substantial change in apo E mRNA levels. In contrast, insulin treatment resulted in significant increases in hepatic apo B mRNA over control levels. Results suggest hepatic albumin and apo B mRNA levels are responsive to insulin in the diabetic state.

At least two distinct epigenetic mechanisms are correlated with high-frequency "switching" for APRT phenotypic expression in mouse embryonal carcinoma stem cells

A series of clones displaying high frequency "switching" phenotypes for expression of the adenine phosphoribosyltransferase (aprt) gene were previously isolated from the P19 mouse embryonal carcinoma stem cell line. Most clones contained only one aprt allele. We report here the characterization of each of these clones with regards to enzymatic activity, mRNA steady state levels, DNA methylation, and chromatin conformation. When clones were selected for resistance to the purine analog 2,6-diaminopurine, which requires markedly reduced levels of APRT enzymatic activity, two distinct classes were observed. The first class was associated with reduced or undetectable levels of aprt mRNA, hypermethylation of the 5' CpG island, and a closed chromatin conformation within this region. When clones of this class were selected for reacquisition of APRT enzymatic activity they were found to have increased mRNA levels, a hypomethylated CpG island, and an open chromatin conformation. In contrast, the second class of clones displayed wild-type levels of mRNA, CpG island hypomethylation, and an open chromatin conformation regardless of whether they were selected for the presence or absence of APRT enzymatic activity. The implications of these results for general mechanisms of epigenetic change in somatic cells and the possibility that expression of the mouse aprt gene may be developmentally regulated are discussed.

Selective translational control and nonspecific posttranscriptional regulation of ribosomal protein gene expression during development and regeneration of rat liver

Mammalian liver development is accompanied by a transition from rapid growth in the fetus to a quiescent state in the adult. However, extensive proliferation can be induced in the adult liver by partial hepatectomy. In this study, we examined the regulation of ribosomal protein (rp) gene expression in the developing and regenerating rat liver. Our results indicate that the translation of rp mRNAs is selectively repressed by about 70% upon development from fetal to adult life, as illustrated by the decrease in ribosomal loading. In addition, the relative abundance of these mRNAs, like that of several other, but not all, housekeeping mRNAs, declines during development through a posttranscriptional mechanism. When liver cells commence growth following partial hepatectomy, translation of rp mRNAs is resumed to near-maximal capacity, as judged by their very efficient recruitment into polysomes. The concomitant increase in the abundance rp mRNAs under these circumstances is achieved by a posttranscriptional mechanism. The apparent fluctuations in the translation efficiency of rp mRNAs are accompanied by parallel changes in the expression of the genes encoding the initiation factors eIF-4E and eIF-4A. Our results indicate that selective translational control of rp mRNAs in mammals is not confined to manipulated cells in culture but constitutes an important regulatory mechanism operating in vivo in the course of liver development and regeneration.

Expression of glutathione S-transferase during rat liver development

The ontogeny of rat liver glutathione S-transferase (EC 2.5.1.18) (GSTs) during foetal and postnatal development was investigated. The GSTs are dimers, the subunits of which belong to three multigene families, Alpha (subunits 1, 2, 8 and 10), Mu (subunits 3, 4, 6, 9 and 11) and Pi (subunit 7) [Mannervik, Alin, Guthenberg, Jennsson, Tahir, Warholm & Jörnvall (1985) Proc. Natl. Acad. Sci. U.S.A. 82, 7202-7206; Kispert, Meyer, Lalor, Coles & Ketterer (1989) Biochem. J. 260, 789-793]. There is considerable structural homology within each gene family, with the result that whereas reverse-phase h.p.l.c. successfully differentiates individual subunits, immunocytochemical and Northern-blotting analyses may only differentiate families. Enzymic activity, h.p.l.c. and Northern blotting indicated that expression of GST increased from very low levels at 12 days of foetal growth to substantial amounts at day 21. At birth, GST concentrations underwent a dramatic decline and remained low until 5-10 days post partum, after which they increased to adult levels. During the period under study, GST subunits underwent differential expression. The Mu family had a lower level of expression than the Alpha family, and, within the Alpha family, subunit 1 was more dominant in the adult than the foetus. Subunit 2 is the major form in the foetus. Most noteworthy were subunits 7 and 10, which were prominent in the foetus, but present at low levels post partum. Immunocytochemical analysis of the 17-day foetal and newborn rat livers showed marked differences in the distribution of GSTs in hepatocytes. In the 17-day foetal liver Pi greater than Alpha greater than Mu whereas in the newborns Alpha greater than Mu much greater than Pi. Erythropoietic cells were not stained for any of the three GST families. Steady-state mRNA concentrations in the foetus correlated with the relative transcription of the Alpha, Mu and Pi class genes. However, in those genes expressed post partum, namely the Alpha and Mu class, low transcriptional activity was associated with high concentrations of mRNA. This suggests that there is a switch from transcriptional control to post-transcriptional control at birth. GST 7-7 appears to be regulated predominantly by transcription throughout the period of liver development under observation.

Fibrogenesis in cirrhosis. Potential for therapeutic intervention

Liver cirrhosis is an end stage of several diseases that affect the liver chronically. It is characterized, among other things, by excess collagen deposition, distortion of liver architecture, tissue malfunction and hemodynamic alterations. Many of the complications of cirrhosis may result from excess matrix-deposition. Therefore, prevention of collagen accumulation or removal of collagen deposits could ameliorate the disease. In this article we discuss the pathophysiology of liver fibrosis and we describe various compounds with antiinflammatory and antifibrogenic activity. We discuss their possible mechanism of action and we describe animal and clinical studies in which these compounds have been utilized.

Long-term improvement of hypercholesterolemia after ex vivo gene therapy in LDLR-deficient rabbits

Familial hypercholesterolemia (FH) is an inherited disorder in humans that is caused by a deficiency of low density lipoprotein receptors (LDLRs). An animal model for FH, the Watanabe Heritable Hyperlipidemic rabbit, was used to develop an approach for liver-directed gene therapy based on transplantation of autologous hepatocytes that were genetically corrected ex vivo with recombinant retroviruses. Animals transplanted with LDLR-transduced autologous hepatocytes demonstrated a 30 to 50 percent decrease in total serum cholesterol that persisted for the duration of the experiment (122 days). Recombinant-derived LDLR RNA was harvested from tissues with no diminution for up to 6.5 months after transplantation.

Colchicine antimitosis abolishes CCl4 autoprotection

A subtoxic dose of CCl4 is known to destroy liver microsomal cytochrome P-450 and this is widely accepted as the mechanism of CCl4 autoprotection. Circumstantial evidence suggests that while cytochrome P-450 is significantly decreased, this mechanism alone cannot explain the phenomenon of autoprotection. Previous studies have established that hepatocellular regeneration is stimulated as early as 6 hr after the administration of a low dose of CCl4. If the early phase stimulation of hepatocellular regeneration by the protective dose is indeed the mechanism of autoprotection, then ablation of this early phase of tissue healing by colchicine should result in an abolishment of autoprotection. Present studies were conducted to test this conceptual premise. The protection afforded by a low dose of CCl4 (LCCl4, 100 microliter/kg, ip) on the toxic effects of a subsequently administered moderately toxic dose of CCl4 (HCCL4, 2.5 ml/kg, ip) was established in male Sprague-Dawley rats. The protective dose provided 100% protection, whereas only 62.5% survival was observed when the corn oil vehicle was administered instead of the protective dose of LCCl4. Colchicine administration (1 mg/kg, ip in saline) 2 hr prior to the injection of LCCl4 led to a complete loss of autoprotection resulting in 100% mortality in rats given the HCCl4. Earlier studies have established that colchicine selectively suppresses the early phase of hepatocellular regeneration at 6 hr without influencing the second phase at 36-48 hr. The consequence of colchicine antimitosis on the toxicological endpoints of liver injury was evaluated by serum enzyme elevations and by histopathological examination of the liver during a time course of 6, 24, 48, 72, and 96 hr after the administration of HCCl4. In the autoprotection regime, after only a transient and modest elevation of serum alanine and aspartate transaminases, complete recovery occurred by 96 hr. Hepatocellular necrosis was consistently lower compared to all other groups. Colchicine preadministration in the autoprotection regime resulted in significantly greater and progressive elevation of the serum enzymes and a correspondingly commensurate progression of hepatic lesion. Toxic effects of HCCl4 alone were more rapidly and maximally augmented by colchicine preadministration. The role of hepatocellular regeneration in autoprotection was evaluated by 3H-thymidine incorporation in hepatocellular nuclear DNA and by morphometric estimation of mitotic index. While HCCl4 alone resulted in some stimulation of 3H-thymidine incorporation and mitosis, the regenerative activity observed with prior LCCl4 administration was remarkably greater, particularly at 48 hr. Colchicine preadministration in either of these 2 protocols decisively obtunded the stimulated regenerative activities essentially abolishing the tissue healing mechanisms.(ABSTRACT TRUNCATED AT 400 WORDS)

Albumin mRNA expression in human liver diseases and its correlation to serum albumin concentration

The expression of albumin mRNA in human liver samples was investigated in order to understand the molecular mechanism of albumin gene expression in various liver diseases. Albumin mRNA in acute hepatic failure and decompensated liver cirrhosis was reduced significantly compared to normal control liver (P less than 0.05). Serum albumin concentration is closely correlated with albumin mRNA content (r = 0.895, P less than 0.01). These data suggest that albumin concentration is mainly regulated at albumin mRNA level in the liver despite the presence of other regulatory mechanisms and that expression of albumin mRNA level is correlated with disease severity. But in several cases there was a discrepancy between albumin mRNA level and severity of liver disease, so further investigation of the regulatory factors of albumin gene expression should be performed.

Interleukin 6 enhances a cellular activity that functionally substitutes for E1A protein in transactivation

An interleukin 6 (IL-6)-regulated cellular activity in HepG2 cells is found to functionally substitute for the transcriptional transactivator product of the adenovirus transforming gene E1A in transactivating E1A-dependent and E1A-responsive viral early genes. Mutant viruses deficient in E1A expression replicate in HepG2 cells. Induction with IL-6 leads to significant enhancement of synthesis of viral early E1B and E2ae mRNAs by greater than 30-fold and increases viral replication to the wild-type levels. The E1A-substituting activity activates E1A-responsive promoters in transient transfection, and this transcriptional activity is regulated by IL-6 induction. Formation of distinct protein-promoter complexes by binding of proteins in nuclear extracts prepared from HepG2 cells to the E1A-dependent E2ae promoter further supports the possibility that this activity may be a nuclear component in the IL-6 signal transduction pathway.

Reduced and oxidized glutathione contents in adult rat hepatocytes under various culture conditions

Reduced and oxidized glutathione contents of adult rat hepatocytes in pure culture and in co-culture with rat epithelial cells were measured under various medium conditions. To the standard medium fetal calf serum, nicotinamide, H2SeO3, dimethylsulphoxide or no supplements were added. For freshly isolated hepatocytes, intracellular contents of 24 +/- 7 nmol reduced and 0.7 +/- 0.2 nmol oxidized glutathione/mg cellular protein were obtained, respectively. In pure culture as well as in co-culture and regardless of the medium conditions involved, the protein content stays constant during the culture time with the exception of a decrease in protein content after 6 days of pure culture, caused by deterioration and loss of the hepatocytes. In both culture systems, an initial increase in intracellular reduced glutathione levels was observed, followed by a decrease and a quick normalisation in co-culture. On the contrary, in pure culture, the decrease was slower, but not transient and a stabilized situation was never reached. The various supplementations of the culture media had no significant effect on the intracellular reduced glutathione contents of both culture systems. As far as the intra- and the extracellular oxidized glutathione contents and the extracellular reduced form are concerned, these were only present in small amounts.

Synergistic interactions between transcription factors control expression of the apolipoprotein AI gene in liver cells

The gene coding for apolipoprotein AI (apoAI), a plasma protein involved in the transport of cholesterol and other lipids in the plasma, is expressed predominantly in liver and intestine. Previous work in our laboratory has shown that different cis-acting elements in the 5'-flanking region of the human apoAI gene control its expression in human hepatoma (HepG2) and colon carcinoma (Caco-2) cells. Hepatocyte-specific expression is mediated by elements within the -256 to -41 DNA region relative to the apoAI gene transcription start site (+1). In this study it was found that the -222 to -110 apoAI gene region is necessary and sufficient for expression in HepG2 cells. It was also found that this DNA region functions as a powerful hepatocyte-specific transcriptional enhancer. Gel retardation and DNase I protection experiments showed that HepG2 cells contain proteins that bind to specific sites, sites A (-214 to -192), B (-169 to -146), and C (-134 to -119), within this enhancer. Site-directed mutagenesis that prevents binding of these proteins to individual or different combinations of these sites followed by functional analysis of these mutants in HepG2 cells revealed that protein binding to any one of these sites in the absence of binding to the others was not sufficient for expression. Binding to any two of these sites in any combination was sufficient for only low levels of expression. Binding to all three sites was essential for maximal expression. These results indicate that the transcriptional activity of the apoAI gene in liver cells is dependent on synergistic interactions between transcription factors bound to its enhancer.

Extracellular signals that regulate liver transcription factors during hepatic differentiation in vitro

A complex cell culture environment has been shown to maintain the differentiated state of hepatocytes, yet the mechanisms by which environmental cues selectively maintain liver-specific gene transcription have been unknown. In this paper we show that the hepatic environment regulates the activities of at least three liver-enriched transcription factors, eE-TF, eG-TF/HNF3, and eH-TF, that activate the mouse serum albumin enhancer. eE-TF is a heat-stable factor that has a DNA-binding specificity similar to that of the liver transcription factor C/EBP, but is a distinct protein. eG-TF/HNF3 contributes to the liver-specific transcription of several other serum protein genes. eH-TF binds to a TGTTTGC sequence that occurs at regulatory sites of the albumin promoter, the hepatitis B virus enhancer, and other hepatic genes. eE-TF, eG-TF/HNF3, and eH-TF are regulated by different combinations of the following cell culture conditions: a hormonally defined serum-free medium; an extracellular matrix gel; and a transformation-competent simian virus 40 large T antigen. We propose a regulatory network model to explain how cues from the cell lineage and the extracellular environment coordinately help maintain the activities of transcription factors involved in hepatocyte differentiation.

Extracellular signals that regulate liver transcription factors during hepatic differentiation in vitro

A complex cell culture environment has been shown to maintain the differentiated state of hepatocytes, yet the mechanisms by which environmental cues selectively maintain liver-specific gene transcription have been unknown. In this paper we show that the hepatic environment regulates the activities of at least three liver-enriched transcription factors, eE-TF, eG-TF/HNF3, and eH-TF, that activate the mouse serum albumin enhancer. eE-TF is a heat-stable factor that has a DNA-binding specificity similar to that of the liver transcription factor C/EBP, but is a distinct protein. eG-TF/HNF3 contributes to the liver-specific transcription of several other serum protein genes. eH-TF binds to a TGTTTGC sequence that occurs at regulatory sites of the albumin promoter, the hepatitis B virus enhancer, and other hepatic genes. eE-TF, eG-TF/HNF3, and eH-TF are regulated by different combinations of the following cell culture conditions: a hormonally defined serum-free medium; an extracellular matrix gel; and a transformation-competent simian virus 40 large T antigen. We propose a regulatory network model to explain how cues from the cell lineage and the extracellular environment coordinately help maintain the activities of transcription factors involved in hepatocyte differentiation.

Synergistic interactions between transcription factors control expression of the apolipoprotein AI gene in liver cells

The gene coding for apolipoprotein AI (apoAI), a plasma protein involved in the transport of cholesterol and other lipids in the plasma, is expressed predominantly in liver and intestine. Previous work in our laboratory has shown that different cis-acting elements in the 5'-flanking region of the human apoAI gene control its expression in human hepatoma (HepG2) and colon carcinoma (Caco-2) cells. Hepatocyte-specific expression is mediated by elements within the -256 to -41 DNA region relative to the apoAI gene transcription start site (+1). In this study it was found that the -222 to -110 apoAI gene region is necessary and sufficient for expression in HepG2 cells. It was also found that this DNA region functions as a powerful hepatocyte-specific transcriptional enhancer. Gel retardation and DNase I protection experiments showed that HepG2 cells contain proteins that bind to specific sites, sites A (-214 to -192), B (-169 to -146), and C (-134 to -119), within this enhancer. Site-directed mutagenesis that prevents binding of these proteins to individual or different combinations of these sites followed by functional analysis of these mutants in HepG2 cells revealed that protein binding to any one of these sites in the absence of binding to the others was not sufficient for expression. Binding to any two of these sites in any combination was sufficient for only low levels of expression. Binding to all three sites was essential for maximal expression. These results indicate that the transcriptional activity of the apoAI gene in liver cells is dependent on synergistic interactions between transcription factors bound to its enhancer.

Distinct developmental regulatory mechanisms for two members of the aldolase gene family

The aldolase isozyme family is composed of three members, A, B, and C, which are encoded by separate genes. The proteins are expressed in a tissue-restricted manner during development and in the adult. To elucidate the regulation of aldolase mRNA in the mouse liver, we analyzed its expression by a number of methods including Northern blot, RNA dot blot, and nuclear run-on assays. Our experiments demonstrate that the expression of aldolase A in the liver is primarily regulated by post-transcriptional control. In contrast, we found that changes in the level of aldolase B mRNA are due to changes in the rate of initiation of transcription. In addition, we examined the regulation of aldolase expression in the adult kidney. We found that although the kidney has eight times more aldolase B than the liver, the rate of initiation of transcription is similar in both tissues. Also, the rate of initiation of transcription of aldolase A is the same in the adult kidney and liver although there is 40 times more steady state aldolase A mRNA in the kidney than in the liver.

Chemistry and biology of alpha-fetoprotein

Alpha-Fetoprotein (AFP) is a product of specific fetal tissues and of neoplastic cells of hepatocyte or germ cell origin in adults. This protein belongs to a gene family that is phylogenetically most closely related to serum albumin. Its primary, secondary, and tertiary structural aspects appear similar to the three-domain concept proposed for the latter protein. The primary sequence of AFP departs most widely from serum albumin in the first 135 amino acid residues, with about 42% of the remaining 590 residues of the human proteins being identical. Some evidence exists that there are limited sequence differences in the AFP of a given animal species. AFP shows considerable charge heterogeneity that appears to relate mostly to its glycoid moiety. The proteins of some species such as the rat show more pronounced heterogeneities than that of humans. The variations in extent and type of glycosylations are evidenced by differences in the binding to various lectins. These interactions are being extensively explored in attempts to differentiate the sources of the protein produced by various normal and neoplastic cells and may provide valuable diagnostic methods. AFP, like serum albumin, shows relatively strong binding affinities for a variety of ligands. The most notable difference is the strong preferential binding of polyunsaturated fatty acids by AFP. This protein may play a role in transporting these substances to developing and to malignant cells. Various agents affect the synthesis of this protein both by specific fetal tissues and by neoplastic cells. Marked differences in the responses of cells, particularly those of neoplastic types, are indicative of variations in the genetic factors responsible for control of its synthesis. The subject of the genomic repression of the synthesis of AFP seen in fetal life upon maturation of the liver and the reoccurrence of synthesis upon malignant conversion of hepatocytes and of certain germ cells are of particular interest. The regulation of the closely related AFP and albumin genes is providing a powerful and attractive model to examine molecular events in the activation and inactivation of specific genes during development and in oncogenic processes. Extensive measurements of AFP during pregnancy and in the course of neoplasias, notably hepatoma, are being made to aid in following changes in such developments. Various specific physiological roles for this protein are also being proposed. One of these is its possible action in the regulation of immune processes.(ABSTRACT TRUNCATED AT 400 WORDS)

Role of hepatocellular regeneration in CCl4 autoprotection

The destruction of liver microsomal cytochromes P450 by a previously administered low dose of CCl4 has been widely accepted as the mechanism of CCl4 autoprotection. However, circumstantial evidence suggests that this mechanism cannot completely explain the phenomenon of autoprotection. The protective effect of a low dose of CCl4 (0.3 ml/kg, po) on the lethal effect of a subsequently administered high dose (5 ml/kg, po) was established in male Sprague Dawley rats. The protective dose permitted 100% survival, whereas only 15% survival was observed without it. Hepatotoxicity, measured by serum enzyme elevations (aspartate transaminase, alanine transaminase, and sorbitol dehydrogenase) and histopathological changes 24 hr after the treatment with high dose, was similar in both the groups, even though the protective dose had significantly decreased liver microsomal cytochromes P450 (to 62% of normal) and associated enzymes, aminopyrine demethylase and aniline hydroxylase. Rats pretreated with CoCl2 to decrease hepatic microsomal cytochrome P450 to 44% of normal levels did not show a significant protection from the hepatotoxicity of high dose of CCl4. Previous studies have established that hepatocellular regeneration is stimulated within 6 hr after the administration of a low dose of CCl4. Based on this observation, a premise that autoprotection results from augmented recovery from injury rather than decreased injury appears likely. Hence, the role of hepatocellular regeneration was evaluated by following 3H-thymidine incorporation in hepatocellular nuclear DNA, labelling index by autoradiography, and by morphometric estimation of mitotic index. After administration of the protective dose of CCl4, stimulated nuclear DNA synthesis measured by 3H-thymidine incorporation into nuclear DNA was increased and this remained high even after subsequent administration of high dose of CCl4. Forty-eight hr after the administration of a lethal dose of CCl4 alone (5 ml/kg, po), labelling index was slightly increased, but mitotic index was not increased. In the surviving rats (15%), both labelling index and mitotic index were significantly elevated after an additional 24 hr. In rats receiving the protective dose, a significantly greater elevation of labelling index as well as mitotic index occurred 48 hr after the administration of the same lethal dose of CCl4. These results suggest that hepatocellular regeneration stimulated by the protective dose, as a biological response recruited to overcome the accompanying limited injury, may augment and sustain tissue repair processes to permit tissue restoration even after the massive liver injury elicited by the subsequent large dose of CC14.

Inhibitory effects of acyclic retinoid (polyprenoic acid) and its hydroxy derivative on cell growth and on secretion of alpha-fetoprotein in human hepatoma-derived cell line (PLC/PRF/5)

Acyclic retinoid (polyprenoic acid) has a slightly different structure from retinoic acid. However, acyclic retinoid acts similarly to retinoic acid, because both bind to cellular retinoic acid-binding protein and cellular retinoid-binding protein. F-type, with the same strong binding affinity. We studied the effects of acyclic retinoid, the 7-hydroxy derivative of acyclic retinoid (7OH-acyclic retinoid) and retinoic acid on a human hepatoma-derived cell line PLC/PRF/5 (Alexander cells). Acyclic retinoid inhibited cell growth with an ID50 value of 14 microM, and reduced cell viability with an LD50 value of 86 microM. The ratios of LD50 value to ID50 value were 6.1 for acyclic retinoid, 2.4 for 7OH-acyclic retinoid and 1.4 for all-trans-retinoic acid. Taking this ratio as a parameter of relative cytotoxicity, we concluded that acyclic retinoid is the least toxic compound. Growth inhibition of cells by acyclic retinoid was associated with the incorporation of 3H-thymidine in the logarithmic phase. Acyclic retinoid reduced secretion of alpha-fetoprotein (AFP) and reciprocally increased secretion of albumin in the culture media, suggesting that acyclic retinoid influences gene expression of these proteins. Thus, acyclic retinoid, one of the less toxic retinoids, inhibits cell growth of human cancer cell line PLC/PRF/5 and appears to alter gene expression of AFP and albumin toward a "normal" direction.

Synergism between hepatic injuries and a nonhepatotropic reovirus in mice. Enhanced hepatic infection and death

Reovirus type 1, after intravenous inoculation in the adult mouse, is secreted via bile into the intestine in an infectious form. Although reovirus type 1 is rapidly removed from systemic circulation by the liver and the lung, very few hepatocytes express reovirus antigen during infection. In intestinal cells, reovirus replicates selectively in the crypts. This site preference may be due to active cell proliferation in the crypts. We hypothesized that the state of the cell may affect virus replication and tested this hypothesis by using chemical and surgical means to increase hepatic mitotic activity. Adult mice were treated with carbon tetrachloride or surgical trauma, inoculated with reovirus type 1 intravenously, and subsequently killed. Virus antigen was identified using a highly specific immunohistochemical technique. Liver sections were stained using immunoperoxidase with specific rabbit antireovirus antibody. Hepatotoxin and surgical trauma increase reovirus antigen detection in both Kupffer cells and hepatocytes. Only the sequential administration of CCl4 and virus caused mortality at doses sublethal for each alone. These data demonstrate a synergism between hepatic injury and reovirus which results in a significant increase in the magnitude of viral infection and contributes to mortality. Such synergism may be important in idiopathic liver disease.

Transcriptional and posttranscriptional regulation of apolipoprotein E, A-I, and A-II gene expression in normal rat liver and during several pathophysiologic states

Assessment of the relative transcription rates and mRNA steady-state levels for apolipoprotein genes E, A-I, and A-II has been performed in normal rat liver, during liver regeneration and following induction of cirrhosis, as well as in rats with inherited analbuminemia associated with hyperlipidemia. Apo E exhibits primarily transcriptional control with an additional component of posttranscriptional control, whereas Apo A-I is controlled primarily at the posttranscriptional level, thus indicating that these genes are regulated independently. The level of control for Apo A-II has not been determined, because of difficulty experienced in measuring the transcription rate of this gene. During liver regeneration, cirrhosis, and analbuminemia, there is a marked increase in the ratio of Apo A-I to Apo E mRNA, resulting from an increase in the Apo A-I mRNA steady-state level and a decrease in Apo E mRNA. These changes are similar in the three pathophysiologic states and seem to occur through a combination of transcriptional and posttranscriptional mechanisms.

Changes in gene expression after temporary renal ischemia

Temporary renal ischemia is followed by increased DNA synthesis and cell division as the kidney restores the continuity of the renal epithelium. We sought to characterize some of the changes in proto-oncogene and growth factor expression during this proliferative response. Northern analysis of polyadenylated RNAs of kidney cortical and outer stripe of outer medullary tissue from male Sprague-Dawley rats was performed following release of renal hilar clamping of 50 minutes duration. Ischemia produced an increase in c-fos mRNA that reached a peak at one hour and declined rapidly to control levels by four hours after release of the clamp. A similar rapid increase and decrease in early growth response 1 (Egr 1) mRNA was noted. The response of these immediate early genes was typical of their response to mitogens, suggesting that they served a similar role in renal cell regeneration. Levels of c-Ki-ras and glyceraldehyde phosphate dehydrogenase mRNA were unchanged. Renal preproEGF mRNA decreased at two hours, was virtually absent by 24 hours and remained low for at least four days after ischemia. Urinary excretion of EGF fell immediately after release of ischemia and before the decline in preproEGF mRNA or SNGFR, suggesting post-transcriptional affects of ischemia on renal EGF production. EGF excretion returned to only 50% of control by day 21. Specific 125I-EGF binding increased in membrane fractions of cortex, outer medulla and inner medulla as early as 24 hours after release of the clamp. Cortical 125I-EGF binding increased in the proximal tubule but not in the glomerulus.(ABSTRACT TRUNCATED AT 250 WORDS)

Liver gene expression during chronic dietary iron overload in rats

To clarify the pathogenesis of hepatic iron toxicity, we investigated the effect of chronic dietary iron overload on the expression of several genes in rat liver. After 10 wk of iron treatment, when only minor histological features of liver damage were appreciable, the level of pro-alpha 2(I)-collagen mRNA was already higher than in control liver and increased further at 30 wk of treatment. Also, the relative amount of L ferritin subunit mRNA was enhanced early by iron load and was even more elevated at the latest time point considered, whereas neither H ferritin subunit nor transferrin mRNA levels were affected by iron treatment. In contrast, after chronic iron treatment, no variations were found in the steady-state level of mRNAs transcribed from liver-specific and preferentially expressed genes (albumin, alpha-fetoprotein, apolipoprotein A-1), growth-related genes (c-myc, c-Ha-ras and c-fos) and stress-induced genes (heat shock protein 70). These results suggest that chronic dietary iron overload in rats can specifically activate target genes in the liver (i.e., L ferritin and procollagen) in the absence of either histological signs of severe liver damage or alterations in differentiated liver functions.

DBP, a liver-enriched transcriptional activator, is expressed late in ontogeny and its tissue specificity is determined posttranscriptionally

The full-length cDNA for a transcriptional activator, DBP, that binds to the D site of the albumin promoter has been cloned. DBP belongs to a family of related transcription factors including Fos, Jun, CREB, and C/EBP, which share a conserved basic domain. However, unlike most other members of this family, DBP does not contain a "leucine zipper" structure. Among several rat tissues tested, significant levels of its protein are only observed in liver; yet, with the exception of testis, DBP mRNA is present in all of the examined tissues. DBP as well as its mRNA accumulate to significant levels only in adult animals. During chemically induced liver regeneration, DBP expression is rapidly down-regulated, suggesting that DBP may be involved in the proliferation control of hepatocytes. This cell growth-dependent expression of DBP, in contrast to its tissue specificity, appears to be controlled at the level of mRNA accumulation.

Exon skipping during splicing of albumin mRNA precursors in Nagase analbuminemic rats

Based on the observation that albumin transcripts accumulate in the liver nuclear RNA fraction of Nagase analbuminemic rats (NAR), it was proposed [Esumi, H., Takahashi, Y., Sato, S., Nagase, S. & Sugimura, T. (1983) Proc. Natl. Acad. Sci. USA 80, 95-99] [corrected] that a 7-base-pair deletion at the splice donor site of intron H-I of the albumin gene in these animals leads to impaired processing of albumin pre-mRNA. To identify the specific splicing abnormality, we examined the primary structure of cytoplasmic albumin mRNA across the junctions of exons G-H-I by RNase protection mapping, Northern blot hybridization, Southern blot analysis of polymerase chain reaction-amplified cDNA, and DNA sequencing. The major albumin mRNA species in NAR showed precise deletion of exon H, suggesting that this exon was skipped during albumin pre-mRNA processing. Since the intron G-H splice donor and acceptor sites and exon H sequence are normal, the finding of exon H skipping in NAR has important implications regarding the mechanism of splice site selection. Moreover, the NAR model provides an excellent system to study splicing in vivo in a higher animal.

Effects of 5-azacytidine and 5-aza-2-deoxycytidine on alphafetoprotein levels in mice

1. Production of alphafetoprotein in adult C3H mice was monitored by radial immunodiffusion both in controls, and in animals treated with carbon tetrachloride, 5-azacytidine, or 5-aza-2-deoxycytidine, either alone or in combination. 2. Carbon tetrachloride routinely induced alphafetoprotein synthesis in our experiments, but neither of the cytidine analogues showed any effects on the serum levels of this protein when administered alone. 3. Treatment of mice with either cytidine analogue prior to carbon tetrachloride injection markedly reduced the consequent production of alphafetoprotein, whereas if carbon tetrachloride injection was followed by a subsequent injection with either cytidine analogue, a markedly enhanced level of serum alphafetoprotein was detected. 4. It is suggested that carbon tetrachloride induces alphafetoprotein production in adult mice by inducing liver damage, followed by synthesis of the protein in the dividing and differentiating cells during recovery. We also propose that the cytidine analogues ablate this response by a cytotoxic effect on the liver cells when they are administered prior to the CCl4, but enhance the alphafetoprotein levels when administered after the CCl4 because they inhibit the methylation of cytidine residues in the recovery cell population in the liver and thus prevent early cessation of synthesis of the protein.

In vitro replication and expression of hepatitis B virus from chronically infected primary chimpanzee hepatocytes

Primary chimpanzee hepatocytes were maintained in vitro utilizing a serum-free medium. Hepatocyte functions were sustained throughout the culture period as demonstrated by the synthesis and secretion of liver-specific plasma proteins characteristic for differentiated hepatocytes. Hepatocyte cultures established from a chimpanzee chronically infected with human hepatitis B virus exhibited the synthesis and secretion of hepatitis B virus proteins into the medium. In addition, the de novo replication of hepatitis B virus was documented by the recovery of virus, exhibiting an endogenous DNA polymerase activity, from the tissue culture medium. Therefore, both the long-term maintenance of differentiated hepatocytes and the expression of hepatitis B virus from these primary cultures were sustained in the serum-free medium.

Regulation of interleukin 6 receptor expression in human monocytes and monocyte-derived macrophages. Comparison with the expression in human hepatocytes

IL-6 is a cytokine with pleiotropic biological functions, including induction of the hepatic acute phase response and differentiation of activated B cells into Ig-secreting plasma cells. We found that human peripheral blood monocytes express the IL-6-R, which is undetectable on the large majority of lymphocytes of healthy individuals. Stimulation of monocytes by endotoxin or IL-1 causes a rapid downregulation of IL-6-R mRNA levels and a concomitant enhancement of IL-6 mRNA expression. IL-6 itself was found to suppress the IL-6-R at high concentrations. A gradual decrease of IL-6-R mRNA levels was observed along in vitro maturation of monocytes into macrophages. We show that downregulation of IL-6-R mRNA levels by IL-1 and IL-6 is monocyte specific, since IL-6-R expression is stimulated by both IL-1 and IL-6 in cultured human primary hepatocytes. Our data indicate that under noninflammatory conditions, monocytes may play a role in binding of trace amounts of circulating IL-6. Repression of monocytic IL-6-R and stimulation of hepatocytic IL-6-R synthesis may represent a shift of the IL-6 tissue targets under inflammatory conditions.

Liver collagen mRNA and serum amino-terminal peptide of type III procollagen (PIIINP) levels in patients with alcoholic liver disease

We have investigated the alpha 1 (I), alpha 2 (I) and alpha 1 (III) liver collagen mRNA levels in 38 patients with alcoholic liver disease. The patients were divided into 3 groups according to the severity of their liver disease. Liver collagen mRNA levels were estimated by densitometric analysis after hybridization with the corresponding cDNA. Serum amino-terminal peptide of type III procollagen (PIIINP) was determined by radioimmunoassay in 30 patients. The results indicated that there was no increase but rather a decrease in the liver alpha 1 (I), alpha 2 (I) and alpha 1 (III) collagen mRNA in patients with the most severe liver lesions as compared to those with minimal changes. This decrease was significant for alpha 2 (I) and alpha 1 (III) cDNA probes. In contrast, serum PIIINP levels showed a positive correlation with the severity of the disease. Thus this study indicates that collagen accumulation in the liver as well as elevation of the serum PIIINP during the development of alcoholic liver disease probably reflects posttranscriptional events in collagen synthesis.

The liver as a self-organizing system. I. Theoretics of its representation

The liver is described as a composite system consisting of a set of operative creodic microunits open to a continuous flow of matter, energy and informations. Its dynamics depend on two interactive and interrelated subsystems with actions described as homopoiesis and homeorhesis, making it an autoisodiasostic system. The system's emergent (equifinal) or emergence states, operative potential, diffusion and reaction phenomena and compensation states are also formally described. For readers not familiar with the language of general system theory, of system dynamics and of categorical analysis, a glossary of some terms is provided.

Thyroid hormone effect on alpha-fetoprotein and albumin coordinate expression by a human hepatoma cell line

The action of triiodothyronine on the production of alpha-fetoprotein and albumin in serum-free cultures of Hep G2 human hepatoma cells was examined. Our data showed that a marked inhibition (up to 8-fold) of alpha-fetoprotein secretion and an increase in albumin (up to 4-fold) are produced by 10(-8) M triiodothyronine. These effects were slow in their onset and for completion required 20-25 days of treatment with the hormone. However, an exposure of the cells to triiodothyronine for only the first 4 h was sufficient to affect, in a similar way, the secretion of alpha-fetoprotein and albumin when measured 15 days after treatment. The secretion of the two proteins parallels their intracellular levels. The decrease in alpha-fetoprotein production can be explained by a reduction of the RNA coding for the protein. The same is essentially true also for albumin increased secretion and related mRNA expression.

Glucocorticoids induce transcription of ribosomal protein genes in rat liver

Transcription of rat liver ribosomal RNA is induced by glucocorticoids. In order to determine whether the expression of ribosomal protein genes is coordinately regulated, we measured the effect of dexamethasone on their transcription. Administration of this hormone to adrenalectomized rats led, within 1 h, to a 2.2-fold enhancement of transcription of liver ribosomal protein genes. To define the dexamethasone-responsive element, we isolated and tested mouse L32 gene sequences for the ability to confer glucocorticoid induction to the bacterial chloramphenicol acetyltransferase (CAT) gene in L cells. An 80 base pair region of the L32 gene, between nucleotide position -69 and +11, with respect to the start site of transcription, was sufficient for induction of the CAT gene by dexamethasone. Despite these stimulating effects, we have failed to detect elevation in the abundance of the ribosomal protein mRNAs both in rat liver and in mouse L cells. Possible interpretations for this seemingly ineffectual process are discussed.

In vitro and in vivo association of transforming growth factor-beta 1 with hepatic fibrosis

Despite extensive efforts, little progress has been made in identifying the factors that induce hepatic fibrosis. Transforming growth factor-beta (TGF-beta) has been shown to enhance collagen production, therefore its role in hepatic fibrosis was investigated. Treatment of cultured hepatic cells with TGF-beta 1 increased type I procollagen mRNA levels 13-fold due to post-transcriptional gene regulation. When two animal models of hepatic fibrosis, murine schistosomiasis and CCl4-treated rats, were examined, they both exhibited increased levels of TGF-beta 1 gene expression at times that somewhat preceded the increase in collagen synthesis. In contrast, in murine schistosomiasis, mRNA levels of tumor necrosis factor and interleukin-1 peaked early in the fibrogenic process. Immunohistochemical analysis showed TGF-beta 1 to be present in normal mouse liver and to be markedly increased in mice infected with schistosomiasis. TGF-beta 1 appeared in the hepatic parenchyma, primarily in hepatocytes. These findings strongly suggest a role for TGF-beta 1 in a pathophysiological state.

Regulation of interleukin-6 receptor expression in human monocytes and hepatocytes

Human blood monocytes normally express the interleukin-6 receptor. Treatment of cultured monocytes with endotoxin, interleukin-1 beta, or interleukin-6 results in a decrease in interleukin-6 receptor mRNA levels. Glucocorticoids aso cause a drop in monocytic interleukin-6 receptor mRNA levels. We also found interleukin-6 receptor expression in cultured human hepatocytes, but in contrast to monocytes, where interleukin-6 receptor mRNA is presented by the ligand and by interleukin-1, treatment of hepatocytes with interleukin-6 or interleukin-1 resulted in increased interleukin-6 receptor mRNA levels. Induction of interleukin-6 receptor mRNA in hepatocytes was less pronounced when glucocorticoids were omitted from the culture medium. We conclude that during noninflammatory homeostasis, blood monocytes are involved in binding of trace amounts of circulating interleukin-6. During inflammatory events, the main target of interleukin-6 may be changed from the monocytic population not only to activated B-cells, but also to the hepatocytes.

Reciprocal changes in serum albumin and alpha-fetoprotein levels in the recovery course of acute viral hepatitis stimulated by glucagon and insulin therapy: analysis of a double blind controlled trial

The records of 57 patients with acute viral hepatitis (28 given hormones and 29 placebo) in a double blind controlled trial of one week of glucagon and insulin therapy were analyzed. In the placebo group, SGPT values dropped after treatment with improved prothrombin time and serum levels of total bilirubin and albumin. In the hormone group, they changed similarly, except serum albumin levels which were reversed during treatment (P less than 0.05). There was a bottom line of serum albumin levels which preceded a peak of serum alpha-fetoprotein levels within one week in the placebo group, but was around the peak in the hormone group. There were 12 patients in the hormone group in whom serum alpha-fetoprotein levels rose with treatment and decreased after its discontinuation, and 5 in the placebo group (P less than 0.05). Such a change in serum alpha-fetoprotein levels was accompanied by decreased serum albumin levels in 6 of 10 patients given hormones and none of the 5 given placebo (P less than 0.05). These results indicate reciprocal changes in serum albumin and alpha-fetoprotein levels appearing during the recovery course of acute viral hepatitis, and suggest that this therapy may stimulate its development. Stimulation of liver regeneration by this therapy merits consideration.