Partial purification and characterization of hepatocyte growth factor from serum of hepatectomized rats

Lung may have an endocrine function producing hepatocyte growth factor in response to injury of distal organs

Hepatocyte growth factor (HGF) is a potent growth factor for various epithelial cells including mature hepatocytes and renal tubular cells. When 70% of the rat liver was excised, HGF mRNA in the intact lung markedly increased at 6 h later, then decrease to normal levels at 24 h. A similar marked increase of HGF mRNA was found in the lung of rats with hepatitis induced by CCl4. Moreover HGF mRNA in the intact lung also increased to about a 5 times higher level than the normal, within 12 h after unilateral nephrectomy. Isolated alveolar macrophages significantly expressed HGF mRNA, yet the amount remained unchanged after injury of the liver. The marked increase of HGF mRNA in lungs of partially hepatectomized rats remained even after removal of alveolar macrophages. In situ hybridization showed a marked increase of HGF mRNA signal found in endothelial cells in the lung after partial hepatectomy. We postulate that endothelial cells in the lung recognize damage of distal organs through a mediator and that lung-derived HGF may contribute to tissue repair or regeneration of injured organs, through endocrine-related mechanisms.

Hepatocyte growth factor is a paracrine factor for renal epithelial cells: Stimulation of DNA synthesis and Na,K-ATPase activity

The expressions of mRNAs of hepatocyte growth factor (HGF) and its receptor (c-met) and its effects were examined in cultured renal epithelial cell lines (OK, LLCPK1, and MDCK cells) and rat mesangial cells in primary culture. Northern blot analysis revealed the presence of HGF mRNA in mesangial cells, but not in epithelial cells. c-met mRNA was detected in epithelial cells, but not in mesangial cells. HGF stimulated [3H]-thymidine incorporation (DNA synthesis) dose-dependently in OK and LLCPK1 cells, but not in MDCK and mesangial cells. Ouabaine sensitive rubidium uptake (Na,K-ATPase activity) was stimulated by 63% with HGF (10 ng/ml) treatment for 16hr in MDCK cells. The results suggest that HGF is produced in the kidney, at least in mesangial cells and works on epithelial cells to stimulate the proliferation and/or to modify cell functions in a paracrine manner.

Membrane biochemistry and chemical hepatocarcinogenesis

Biochemical membrane alterations appearing during the process of chemical carcinogenesis are described. Emphasis is put on membrane composition, structure, and biogenesis. In this presentation the knowledge gained from experimental studies of liver and skin in the process of cancer development is acknowledged. Important biochemical changes have been reported in lipid composition, fatty acid saturation, constitutional enzyme expression, receptor turnover and oligomerization. Functional consequences of the altered membrane structure is discussed within the concepts of regulation of cell proliferation, regulation of membrane receptor expression, redox control, signal transduction, drug metabolism, and multidrug resistance. Data from malignant tumours and normal tissue are addressed to evaluate the importance of the alterations for the process and for the eventual malignant transformation.

Hepatocyte growth factor inhibits growth of hepatocellular carcinoma cells

Hepatocyte growth factor (HGF) is a potent mitogen for primary hepatocytes. Therefore, we examined HGF as a possible autocrine growth factor in hepatocellular carcinoma (HCC). We introduced an albumin-HGF expression vector into Fao HCC cells and transgenic mice. Expression of the albumin-HGF vector in Fao HCC cells inhibited their growth in vitro. In vivo, FaoHGF cells produced tumors that averaged 10% of the sizes of G418-resistant controls when transplanted into nude mice. In contrast, hepatocytes from transgenic mice expressing HGF grew more rapidly than did those from normal siblings. Further, growth of eight additional HCC cell lines was inhibited by the addition of recombinant HGF. Finally, of 35 tumor cell lines surveyed, only 6 cell lines expressed HGF mRNA, and no HCC cell line expressed HGF. Although HGF stimulates normal hepatocytes, it is a negative growth regulator for HCC cells.

Significance of serum human hepatocyte growth factor levels in patients with hepatic failure

Serum human hepatocyte growth factor levels were measured using a newly developed enzyme-linked immunosorbent assay kit in patients with liver diseases. Serum human hepatocyte growth factor levels were increased in correlation with derangements of prothrombin time, total bilirubin and other parameters reflecting hepatocellular dysfunction in 112 patients with chronic liver disease. The levels were positively correlated with serum AST and ALT levels in 59 of these patients whose prothrombin times were within the normal range. Abnormally increased serum human hepatocyte growth factor levels were found in 100% of the determinations in 16 patients with fulminant hepatic failure and in 80% of the determinations in 16 patients with chronic hepatic failure. The levels greater than 1 ng/ml, however, were found in 94% of determinations in the former group, but only in 16% of the determinations in the latter group. This difference was seen irrespective of prothrombin time or hepatic coma grades. In patients with fulminant hepatic failure serum human hepatocyte growth factor levels were increased immediately after plasma exchange using heparin as the anticoagulant in 71% of the determinations. This increase disappeared 12 hr after discontinuation of plasma exchange. In 17 of 39 patients with chronic renal failure who had no liver disease, serum human hepatocyte growth factor levels were abnormally increased before hemodialysis using heparin, and the levels were elevated immediately after hemodialysis in all the patients. The increase of serum human hepatocyte growth factor levels in hepatic failure may be the result of hepatocellular dysfunction and necrosis.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of effects of HGF and EGF on cellular calcium in rat hepatocytes

We compared the effects of HGF and EGF on cytoplasmic free calcium concentration, [Ca2+]c, and inositol trisphosphate production in rat hepatocytes. HGF induced a prompt and transient elevation of [Ca2+]c. EGF also induced an immediate increase in [Ca2+]c, the magnitude of which was greater than that by HGF. In contrast, in the presence of 1 microM extracellular calcium EGF increased [Ca2+]c to a lesser extent than HGF. When cells were pretreated with EGF, the effect of HGF on [Ca2+]c was greatly enhanced. However, such enhancement was not observed in medium containing 1 microM extracellular calcium. In hepatocytes prelabeled with [3H]-inositol, both HGF and EGF increased [3H]inositol trisphosphate. HGF and EGF acted synergistically to stimulate production of inositol trisphosphate. These results indicate that both HGF and EGF increase [Ca2+]c by a mechanism involving phosphoinositide turnover and that the actions of HGF and EGF on hepatocyte calcium metabolism are not totally identical.

Growth of normal human hepatocytes in primary culture: effect of hormones and growth factors on DNA synthesis

Although the ability of hormones and growth factors to stimulate DNA synthesis in rat hepatocytes has been investigated extensively, no such study of human hepatocytes has been reported. Here we describe a series of experiments to identify those factors that regulate human hepatocyte DNA synthesis in vitro and which therefore may play a role in the control of human liver regeneration. Human hepatocytes were isolated from normal liver tissue obtained after graft reduction for transplantation into pediatric recipients. Cells were maintained in culture for up to 5 days, and DNA synthesis was determined. Hydroxyurea reduced [3H]thymidine incorporation into DNA by 95%, indicating replicative DNA synthesis. As previously found with rat hepatocytes, epidermal growth factor and transforming growth factor-alpha stimulated DNA synthesis at low nanomolar concentrations; transforming growth factor-alpha was slightly more potent. Although the overall rate of thymidine incorporation was lower than that for rodent cells, human hepatocytes were sensitive to lower concentrations of these growth factors, and the degree of stimulation was similar. Conversely, transforming growth factor-beta inhibited DNA synthesis at low picomolar levels. By contrast (unlike rat hepatocytes), arginine-vasopressin failed to initiate or potentiate DNA synthesis in human cells. These data indicate that normal human hepatocytes can respond to low concentrations of growth promoters or inhibitors, previously shown to have activity on rat hepatocytes. These factors may then play a role in control of human liver growth. However, important species differences are apparent, highlighting the limitations of extrapolating from animal studies to humans.

Identification of a fibroblast-derived epithelial morphogen as hepatocyte growth factor

We have previously shown that Madin-Darby canine kidney (MDCK) epithelial cells grown in collagen gels in the presence of fibroblasts or fibroblast-conditioned medium (CM) form branching tubules, instead of the spherical cysts that develop under control conditions. We now report that the fibroblast-derived molecule responsible for epithelial tubulogenesis is hepatocyte growth factor (HGF). First, addition of exogenous HGF to cultures of MDCK cells induces formation of epithelial tubules. Second, the tubulogenic activity of fibroblast CM is completely abrogated by antibodies to HGF. These results demonstrate that HGF, a polypeptide that was identified as a mitogen for cultured hepatocytes, has the properties of a paracrine mediator of epithelial morphogenesis, and suggest that it may play important roles in the formation of parenchymal organs during embryonic development.

Scatter factor from human embryonic lung fibroblasts is probably identical to hepatocyte growth factor

Human embryonic lung fibroblasts (MRC5) produced scatter factor which enhanced motility of Madin-Darby canine kidney (MDCK) epithelial cells and a factor which stimulates DNA synthesis of adult rat hepatocytes in primary culture. These activities were both completely neutralized by antibody against human hepatocyte growth factor (HGF). Human recombinant HGF induced a marked scattering of MDCK cells. Moreover, MRC5 cells highly expressed 6kb mRNA which hybridized with HGF cDNA probe and scatter factor cDNA cloned from the MRC5 cDNA library had the same sequence as that of HGF cDNA from human leukocytes. These results indicate that HGF possesses scatter factor activity and the scatter factor derived from the MRC5 cells is probably identical to HGF.

Hepatocyte growth factor has potent anti-proliferative activity in various tumor cell lines

Hepatocyte growth factor (HGF) has potent mitogenic activity for mature hepatocytes and various normal epithelial cells. We now have evidence that HGF at 1-10 ng/ml, strongly inhibits the growth of HepG2 hepatocellular carcinoma cells, B6/F1 melanoma cells and KB squamous carcinoma cells. These tumor cells express high affinity receptors for HGF with a Kd of 25-28 pM, similar to findings with hepatocytes. HGF at 1-100 ng/ml had no significant cytolytic effect on tumor cells. Therefore, the anti-proliferative effect of HGF on tumor cells seems to be cytostatic, not cytolytic. As HGF apparently has bidirectional effects on cell growth, the possibility that it can serve as an anti-tumor agent merits attention.

Hepatocyte growth factor: molecular structure and implications for a central role in liver regeneration

Hepatocyte growth factor (HGF) is a most potent factor for mature parenchymal hepatocytes in primary culture and may act as a trigger for liver regeneration. We purified HGF from rat platelets to homogeneity and cloned both human and rat HGF cDNA. HGF is a heterodimer molecule composed of the 69 kDa alpha-subunit and the 34 kDa beta-subunit. HGF has no amino acid sequence homology with other known peptide growth factors and possesses the highest potential among known growth factors to stimulate proliferation of hepatocytes in primary culture. HGF is derived from a single chain precursor of 728 amino acid residues and the precursor is proteolytically processed to form a two-chain mature HGF. The alpha-subunit of HGF contains 4 kringle structures and HGF has a homology (38%) with plasmin. Biologically active recombinant human HGF could be expressed from COS-1 cells and CHO cells transfected with cloned cDNA. HGF activity and the HGF mRNA level are markedly increased in the liver following insult such as hepatitis, by the administration of hepatotoxins, ischaemia, physical damage and partial hepatectomy. Moreover, HGF mRNA is induced in the lung and kidney, in the presence of liver injury. In situ hybridization revealed that HGF-producing cells in liver are non-parenchymal liver cells, presumably Kupffer and sinusoidal endothelial cells. Therefore, HGF from neighbouring cells (Kupffer and sinsuoidal endothelial cells) and distal organs (lung and kidney) may function as a trigger for liver regeneration by both a paracrine mechanism and an endocrine mechanism. HGF has mitogenic activity for renal tubular epithelial cells, epidermal melanocytes and keratinocytes as well as mature hepatocytes, and has the potential to promote cell migration for some epithelial cells, including normal human keratinocytes. Since cell growth and cell motility are relevant to tissue repair and embryogenesis, HGF may well have important roles in tissue repair and embryogenesis as well as in liver regeneration.

Marked stimulation of growth and motility of human keratinocytes by hepatocyte growth factor

Effect of hepatocyte growth factor (HGF) on normal human epidermal keratinocytes cultured under conditions of low Ca2+ (0.1 mM, growth-promoting condition) and physiological Ca2+ (1.8 mM, differentiation-promoting condition) was investigated. In low Ca2+, HGF markedly enhanced the migration of keratinocytes while it suppressed cell growth and DNA synthesis in a dose-dependent manner. In contrast, HGF enhanced the migration, cell growth, and DNA synthesis of keratinocytes cultured under conditions of physiological Ca2+. The maximal stimulation of DNA synthesis (2.4-fold stimulation) in physiological Ca2+ was seen at 2.5-5 ng/ml HGF and the stimulatory effect of HGF was suppressed by transforming growth factor-beta 1. Analysis of the HGF receptor using 125I-HGF as a ligand showed that human keratinocytes expressed a single class of specific, saturable receptor for HGF in both low and physiological Ca2+ conditions, exhibiting a Kd = 17.3 pM and approximately 690 binding sites/cell under physiological Ca2+. Thus, HGF is a potent factor which enhances growth and migration of normal human keratinocytes under conditions of physiological Ca2+. HGF may play an important role in epidermal tissue repair as it enhances both the migration and growth of keratinocytes.

Artificial liver. State of the art

If an effective hepatic assist system existed, it could serve as a bridge to transplantation. Most of the patients waiting for liver transplantation have chronic liver insufficiency but are not in hepatic coma. Various hepatic assist systems have been used to salvage patients with acute liver insufficiency. Most attempts have been disappointing. The methods used have included plasma exchange, plasma adsorption, double filtration, cryofiltration, thermofiltration, the combination of plasma exchange and amino acid hemodialysis, and others. For patients with chronic liver disease with moderate liver function impairment and limited to one or only a few areas of metabolic abnormality, a hepatic assist might allow the life of the patient to be maintained temporarily. The application of hepatic assist methods for chronic liver disease patients treated at the Cleveland Clinic has been encouraging. One of the patients who suffered from sclerosing cholangitis has maintained a near-normal life for almost five years by 170 plasma treatments. This is in spite of the fact that, at the onset of treatment, the patient was nearly comatose. Unfortunately, this patient did not wish to receive a liver transplantation. Based upon this experience, the concept of a bridge to transplantation approach to hepatic assist devices appears feasible. In addition, it is speculated that hepatic assistance during the early recovery stage of liver transplantation and during mild episodes of rejection may be useful.

ELISA for F-TCF (human hepatocyte growth factor/hHGF)/fibroblast-derived tumor cytotoxic factor antigen employing monoclonal antibodies and its application to patients with liver diseases

For determination of fibroblast-derived tumor cytotoxic factor, F-TCF (human hepatocyte growth factor/hHGF), sensitive two-step sandwich enzyme-linked immunosorbent assay (ELISA) employing monoclonal antibodies was developed. Microplates were coated with monoclonal antibody (P1C8) and bound F-TCF was quantitated with the second monoclonal antibody (P2D6) linked to peroxidase. The standard curve for F-TCF was found to be linear in the range of 0.16 to 10 ng of F-TCF per ml. The assay was specific for F-TCF but not for plasminogen. The assay can be used for determination of F-TCF antigen in both human plasma and serum. The variation of absorbance was little in duplicate samples. Recoveries of exogenous F-TCF added to serum or plasma samples showed theoretical values. F-TCF antigen levels in 21 healthy volunteers was found to be 0.56 +/- 0.43 ng/ml. In contrast, mean F-TCF levels in patients with liver diseases were all higher than those of healthy subjects. This ELISA system has the advantage of using a sensitive and reproducible set of monoclonal antibodies, and is a useful method for monitoring F-TCF levels in patients with liver diseases.

Assignment of the hepatocyte growth factor (HGF) to chromosome 7q22-qter

The hepatocyte growth factor (HGF) is thought to be important in the growth of hepatocytes during normal foetal liver growth and following liver damage. The human gene encoding HGF has been mapped to chromosome 7 and shown to be localized in the region q22-qter.

Organization of the human hepatocyte growth factor-encoding gene

Human genomic phage libraries were screened for the human hepatocyte growth factor (HGF)-encoding gene (HGF) using a cDNA encoding the human protein as a probe. Characterization of the clones revealed that this gene is composed of 18 exons interrupted by 17 introns spanning approx. 70 kb. The first exon contains the 5'-untranslated region and the signal peptide. The next ten exons encode the alpha-chain which contains four kringle structures. Each kringle domain is encoded by two exons as observed in other kringle-containing proteins. The twelfth exon contains the short spacer region between the alpha- and beta-chains and the remaining six exons comprise the beta-chain. The beta-chain is structurally similar to the catalytic domains of serine proteases; amino acid substitutions in the active site were found. The organization of the HGF gene is highly homologous to those of the serine proteases involved in blood coagulation and fibrinolysis, especially with that of plasminogen. This suggests that the human HGF gene is evolutionally related to these genes.

Possible endocrine control by hepatocyte growth factor of liver regeneration after partial hepatectomy

Hepatocyte Growth Factor (HGF), which is a most potent growth factor for primary cultured hepatocytes, may act as a trigger for liver regeneration. After 70% of the rat liver was removed, HGF activity in the remnant liver began to increase within 24 h. In parallel with the activity, the HGF mRNA level in the remnant liver increased at 12 h after the operation and reached a maximum at 24 h. Increases in HGF activity and in the mRNA level were much lower and later than those in the liver of rats with hepatitis induced with CCl4. However, the first increase in HGF activity in the plasma of hepatectomized rats was noted 3 h after the resection, that is much earlier than the initial DNA synthesis in the remnant liver. Thus, while HGF production was induced in the remnant liver during regeneration after partial hepatectomy, the initial trigger may not be the liver-derived HGF, rather, it may be HGF derived from extrahepatic organs, via blood circulation.

Expression of hepatocyte growth factor mRNA in regenerating rat liver after partial hepatectomy

Hepatocyte Growth Factor (HGF) is a potent complete mitogen for primary cultures of hepatocytes in vitro. There is strong evidence that this novel growth factor may mediate hepatocyte regeneration after liver damage. We have shown previously that the amount of immunoreactive HGF markedly increases in the serum of rats soon after partial hepatectomy or CCl4 administration. In the present paper, we demonstrate that the level of HGF mRNA in rat liver also dramatically increases from 3 to 6 hours post hepatectomy, peaks at 12 hr and gradually returns to undetectable levels by 72 to 96 hours post hepatectomy. In separate experiments, DNA synthesis (in vivo) was determined in rat liver remnants after partial hepatectomy. DNA synthesis peaked 24 hr after hepatectomy, 12 hr after the peak of HGF mRNA expression. These results suggest that HGF may be one of the major early signals that triggers hepatocyte proliferation during liver regeneration.

Native and recombinant human hepatocyte growth factors are highly potent promoters of DNA synthesis in both human and rat hepatocytes

Human hepatocyte growth factor (hHGF) has recently been expressed as a recombinant polypeptide from Chinese hampster ovary cell transfectants. Using a primary rat hepatocyte bioassay, we have tested the biological activity of recombinant hHGF and compared it with native hHGF. Dose-response curves were almost identical, with half-maximal stimulation of DNA synthesis at 1-2 ng/ml (equivalent to approximately 10 pM). S-phase labeling index was similarly enhanced and numerous mitotic cells were observed. Recombinant and native hHGF also stimulated DNA synthesis and S-phase labeling index in primary adult human hepatocytes. Human cells were more responsive than rat hepatocytes, with recombinant hHGF slightly more potent than native hHGF (half-maximal stimulation 0.3 and 0.6 ng/ml, respectively). Since HGF levels rise in patients with fulminant hepatic failure and in animals after partial hepatectomy or administration of hepatotoxins, situations where liver regeneration occurs, HGF is suggested to play a key role in regulation of hepatic growth. The high potency of the factor on human hepatocytes reinforces its candidacy as a critical mitogen in human liver growth. The availability of a recombinant hHGF opens the way for in vivo experimental studies and to the possibility of using hHGF as a clinical therapeutic agent, either alone or in combination with other factors.

Twenty-one percent partial hepatectomy. In vivo rat model for the study of liver regeneration

We describe a new model of submaximal stimulation of liver regeneration in the rat. Removal of the right lateral lobes in the rat produced a 21% hepatectomy. The measurement accuracy of the incorporation rate of [14C]thymidine into DNA 24 h after 21% hepatectomy (n = 32) was less than that after the standard 34% hepatectomy (n = 32), with S.D./mean being 35% and 130%, respectively (F-test, p less than 0.025). This model was able to detect regeneration-stimulation activity present in liver cytosol extract and serum of 68% hepatectomized rats. Using this model we identified a subfraction of rat serum achieved after treatment of serum with ethanol and ion-exchange column, which had a highly stimulatory effect. Stimulation obtained with serum from hepatectomized pigs showed that these factors are not species specific.

Identification and change in the receptor for hepatocyte growth factor in rat liver after partial hepatectomy or induced hepatitis

Specific binding of 125I-labeled human recombinant HGF to the primary cultured rat hepatocytes or liver plasma membranes was observed to be temperature- and time-dependent. Scatchard analysis indicated the presence of a single class of high affinity receptors with a dissociation constant (Kd) of 24-32 pM, a value in good accord with half maximum dose for HGF activity and a receptor density of about 500-600 sites/cell. Affinity cross-linking of the receptor with 125I-HGF revealed the HGF receptor in rat liver membranes to be a polypeptide of Mr approximately 220,000. After partial hepatectomy, specific binding of 125I-HGF to the membranes of residual livers decreased by 60-70% between 3 and 6 h, and was scanty at 12 h after hepatectomy. After one week, the binding was recovered to the 1.7 fold level in the untreated rat liver. This rapid down-regulation of HGF receptors was also observed in plasma membranes of rat livers in the presence of hepatitis induced by CCl4. We propose that HGF which can be immediately supplied to the liver after hepatic injury will function as a trigger for regeneration of this organ.

Hepatocyte growth factor is a potent stimulator of human melanocyte DNA synthesis and growth

Hepatocyte growth factor (HGF) is a potent mitogen for adult rat hepatocytes in primary culture. HGF stimulates growth and DNA synthesis of normal human epidermal melanocytes in culture. The maximal stimulation of DNA synthesis by 4.0-fold occurred with 10 ng/ml HGF. This stimulatory effect was additive with both acidic and basic fibroblast growth factors, while it was inhibited by transforming growth factor-beta 1. Melanocytes expressed a single class of specific, high-affinity receptors for HGF with a Kd of 22 pM and approximately 120 receptors/cell. Thus, HGF is a potent mitogen for normal human epidermal melanocytes.

Induction of DNA replication and cell growth in rat liver by obstructive jaundice

Obstructive jaundice, produced by ligating the common bile duct, induced a transient DNA replication followed by cell proliferation in rat liver. At 48 h after the operation, DNA polymerase alpha activity started to increase and reached its maximum level (more than twice the control) at day 4. At day 7, the enzyme level had decreased to the control level. Pulse-labeling experiment using radioactive thymidine showed that the rate of DNA synthesis increased approximately 2.5-fold in the same pattern as that of DNA polymerase alpha. The mitotic index in hepatocytes also increased 10-fold at day 4 and then decreased. The proliferation of liver cells induced by obstructive jaundice mimics the regeneration of partially hepatectomized liver, although the response was slightly delayed and the proliferation was transient.

Hepatocyte growth factor is a potent mitogen for cultured rabbit renal tubular epithelial cells

Hepatocyte growth factor (HGF), which is a potent growth factor of adult rat hepatocytes in primary culture, also strongly stimulated DNA synthesis of rabbit renal tubular epithelial cells in secondary culture. Its mitogenic activity was dose-dependent, being detectable at 3 ng/ml and maximal at 30 ng/ml. Over 20% of the cells were shifted to the S-phase by HGF alone, judging by the labeling index. HGF had additive effects with EGF, acidic fibroblast growth factor (a-FGF), and insulin. Transforming growth factor-beta 1 (TGF-beta 1) strongly inhibited DNA synthesis of renal tubular cells stimulated by HGF. The growth of renal tubular epithelial cells was also regulated by cell density: DNA synthesis stimulated by HGF was high at lower cell density and was strongly suppressed at high cell density. These results suggest that HGF may act as a renotropic factor in compensatory renal growth or renal regeneration in vivo.

Sequestration of a hepatocyte growth factor in extracellular matrix in normal adult rat liver

Perfusion of normal adult rat livers with Hanks' solution containing 1 M NaCl in situ led to the releasing of a large amount of hepatocyte growth factor (HGF). During the first 5 min of perfusion, the HGF content of the perfusate reached a maximum level, while the LDH activity due to release from the cells was negligible. The liver HGF content did not decrease with age. The liver HGF content in rats injured by CCl4 injection decreased temporarily and then recovered rapidly to a normal level. These results indicate that HGF is sequestered in the extracellular matrix in the subendothelial space in normal adult rat liver and its effect will be either neutralized or potentiated by other local factors.

Structure and function of hepatocyte growth factor

Hepatocyte growth factor (HGF), a potent mitogen for mature hepatocytes in primary culture, was first found in sera of partial hepatectomized rats and seems to be a hepatotrophic factor for liver regeneration which has not been purified over the past 30 years. HGF is composed of the 69 kDa alpha-subunit and the 34 kDa beta-subunit. Molecular cloning reveals that HGF is derived from a single chain precursor of 728 amino acid residues and it contains 4 kringle domains in the alpha-subunit. HGF gene spans about 70kb and consists of 18 exons and 17 introns. HGF is now thought to be a pleiotropic factor influencing a cell growth and cell motility for various epithelial cells. HGF receptor with Kd = 20-30pm is widely distributed in various epithelial cells including hepatocytes. HGF mRNA and HGF activity increase markedly in liver after various liver injuries and in kidney following unilateral nephrectomy or acute renal injury. Moreover, HGF mRNA is induced even in the intact lung in response to liver and kidney injury. In situ hybridization reveals that HGF-producing cells are mesenchymal cells such as Kupffer cells and sinusoidal endothelial cells in liver, fenestrated endothelial cells in kidney, and macrophages and endothelial cells in lung. Thus, HGF may play an important role as a paracrine or endocrine mediator through an epithelial-mesenchymal interaction in wound-healing, tissue or organ regeneration, morphogenesis and carcinogenesis.

Physicochemical characteristics of hepatic stimulatory factor prepared from cell free supernatant of hepatocyte cultures

We previously reported that the cell free supernatant of hepatocyte cultures contained a hepatic stimulatory factor, which increases survival time and stimulates liver regeneration in the galactosamine induced fulminant hepatic failure animal model. When hepatocytes were microencapsulated in an alginate matrix, the cell free supernatant outside the microcapsuled lacked the above stimulatory effects. However, the cell free content of microcapsules was able to increase both survival time and incorporation of 3H-thymidine in our animal model. This hepatic stimulatory factor has a molecular weight greater than albumin because alginate microcapsules allow the penetration of albumin but not the hepatic stimulatory factor. In this paper we report the molecular weight study and some other physiochemical characteristics of this factor. Using Sephacryl gel chromatography we showed that this factor has a molecular weight of over 110,000 D. This factor loses its hepatic stimulatory effect after heat or trypsin treatment. Although its elution profile on Sephacryl gel does not change after such treatments.

Identification and partial characterization of receptor binding sites for HGF on rat hepatocytes

Hepatocyte Growth Factor (HGF) (also known as Hepatopoietin A [HPTA] (1-9) is a heterodimeric heparin-binding polypeptide mitogen for hepatocytes distinct from other well-known growth factors. In this study, biologically active radioiodinated HGF was used to identify binding sites on intact hepatocytes in culture. The results show the presence of relatively low affinity binding sites due to the presence of heparin or heparin-like molecules and high affinity specific receptor binding sites on the cell surface of intact hepatocytes. Scatchard analysis of binding data indicates an apparent dissociation constant (Kd) of 3.5 nM with 120,000 sites per hepatocyte for the cell-surface receptor. Analysis of affinity cross-linked 125I-HGF-receptor complex by SDS-PAGE under non-reducing conditions reveals the presence of a distinct band with apparent Mr of 230,000. These data show that HGF exerts its biological effect on hepatocytes (stimulation of DNA synthesis) through a specific and unique cell-surface receptor.

Enhancing effect of S-(1,2-dicarboxyethyl)glutathione on epidermal growth factor-stimulated DNA synthesis in primary cultures of adult rat hepatocytes

A tripeptide S-(1,2-dicarboxyethyl)glutathione (DCE-GS) has been reported to be present in the lens, liver, and heart. Effects of DCE-GS and its derivatives and analogues on hepatocyte deoxyribonucleic acid (DNA) synthesis were examined using primary cultures of adult-rat hepatocytes. DCE-GS alone had no effect on DNA synthesis of hepatocytes. However, when DCE-GS was added with epidermal growth factor (EGF), the tripeptide effectively enhanced EGF-stimulated DNA synthesis of hepatocytes under the culture conditions of low cell density, but not high cell density. On the other hand, some esters and amides of DCE-GS and DCE-GS analogues showed a suppressive effect on DNA synthesis of hepatocytes in the absence of EGF. The derivatives and analogues together with EGF had no effect or rather a suppressive effect on stimulation of hepatocyte DNA synthesis by EGF. Therefore, the two carboxy groups in the substituent probably play an important role in the stimulative activity of DCE-GS. In addition, it seems likely that one of in vivo physiological roles of DCE-GS is related to liver regeneration.

Expression of hepatocyte growth factor gene in endothelial and Kupffer cells of damaged rat livers, as revealed by in situ hybridization

Hepatocyte growth factor (HGF) has been demonstrated to be synthesized and secreted by non-parenchymal liver cells for liver regeneration after hepatic injury. We performed in situ hybridization to identify HGF-producing cell types in rat liver hepatitis induced by administrating carbon tetrachloride as a hepatotoxin. We found that transcripts of the HGF gene are localized in the Kupffer and endothelial cells in normal livers and increased remarkably in the Kupffer cells of the damaged livers. Thus, HGF is concluded to be synthesized in the Kupffer and endothelial cells to repair the liver tissue in paracrine fashion. No significant increase in the transcripts of the HGF gene was observed in livers after partial hepatectomy, indicating that a mechanism on liver regeneration after the hepatectomy differs from that on liver repairs. Since the HGF gene expression was also found in lung and kidney, HGF may be a ubiquitous factor for tissue repairs.

Human hepatic regenerative stimulator substance: partial purification and biological characterization of hepatic stimulator substance from human fetal liver cells

Current support or replacement therapies for fulminant acute hepatic failure are frequently very disappointing. In this study, human hepatic stimulator substance--a liver-specific growth factor--was partially purified from human fetal liver cells and characterized by its biological effects. Almost 70-fold protein content was purified with an approximately 80-fold increase in specific growth stimulator activity. Human hepatic stimulator substance proved to be heat-stable, protease-sensitive, organ-specific and species-nonspecific. Human hepatic stimulator substance produced a two- to threefold increase of 3H-thymidine incorporation into hepatic DNA when injected intraperitoneally into growing weanling mice (nonhepatectomized) or regenerating rats (34% hepatectomy). The effects of hHSS in reversing the lethality of D-galactosamine (1.6 gm/kg body weight)-induced hepatic necrosis in rats were further evaluated. A survival rate of 4% (n = 24), 41% (n = 12, p less than 0.05), 33% (n = 12, p less than 0.05), 31% (n = 13, p less than 0.05) and 18% (n = 11, p greater than 0.05) was observed when the rats were injected with 4 ml of saline intraperitoneally, 4 ml of human intact fetal hepatocytes (2.4 x 10(8] intraperitoneally, 4 ml of human hepatic stimulator substance intraperitoneally, 2 ml of twofold concentrated human hepatic stimulator substance intravenously and 1 ml of fourfold human hepatic stimulator substance intramuscularly, respectively, 20 hr after poisoning.(ABSTRACT TRUNCATED AT 250 WORDS)

Primary structure of rat hepatocyte growth factor and induction of its mRNA during liver regeneration following hepatic injury

Overlapping cDNA clones for rat hepatocyte growth factor (rHGF) were isolated by cross-hybridization with the cloned cDNA for human hepatocyte growth factor (hHGF) and the nucleotide sequence of the cDNA was determined. The entire primary structure of rHGF was deduced from the sequence. Comparison of the amino acid sequences between rat and human HGFs revealed that the two sequences are highly conserved throughout the protein structures, suggesting that rat and human HGFs may be functionally similar. Responses of the rHGF mRNA during liver regeneration in rats were examined by Northern blot hybridization analysis with the aid of the cDNA probe for rHGF. The mRNA levels increased in the liver and spleen but not in the kidney after administration of carbon tetrachloride. At the maximum level of induction, the rHGF mRNA increased in the liver about 4.5-fold over its normal level. The mRNA levels also increased in the liver and spleen after administration of D-galactosamine. On the other hand, no obvious increase of the mRNA was observed in the liver and spleen after partial hepatectomy. These observations suggest that HGF may function as a regulator of liver regeneration following hepatic injury caused by hepatotoxins.

Isolation and expression of cDNA for different forms of hepatocyte growth factor from human leukocyte

Human leukocyte cDNA library was screened to isolate cDNA clones coding for hepatocyte growth factor using cDNA from human liver as a probe. Nucleotide and deduced amino acid sequences were analyzed for two of four clones obtained. One of them contained an open reading frame coding for a polypeptide chain of 728 amino acid residues like that of cDNA clone derived from human liver. In another clone a spontaneous deletion of 15 base pairs was found within the coding sequence. When expressed transiently using COS-1 cells both clones produced protein with similar biological activity against rat hepatocyte in vitro.

Hepatotropin mRNA expression in human foetal liver development and in liver regeneration

A 569 bp probe against the beta-chain of hepatotropin was used to examine expression of RNA for this growth factor in human adult and foetal liver, foetal kidney and pancreas, and rat liver after partial hepatectomy. Low level expression of a 6 kb RNA occurred in human adult and normal rat liver. 70% hepatectomy increased expression, peaking at 10 h and returning to near normal levels 24 h after resection. The 6 kb band was strongly expressed in human foetal liver, as compared with adult, but not in foetal kidney or pancreas, suggesting a major role for hepatotropin in both foetal development and regeneration of the liver.

Biological and immunological properties of human hepatocyte growth factor from plasma of patients with fulminant hepatic failure

We have recently purified human hepatocyte growth factor (hHGF), a heterodimer with molecular weight of about 83,000, from plasma of patients with fulminant hepatic failure (Gohda, E. et al., J. Clin. Invest. 81, 414-419, 1988). Biological and immunological properties of hHGF were examined. Out of the well-known growth factors tested, only epidermal growth factor (EGF) and transforming growth factor-alpha (TGF-alpha) stimulated DNA synthesis of adult rat hepatocytes in primary culture. hHGF enhanced the DNA synthesis at less than one-tenth of the molar concentrations of EGF and TGF-alpha. Half-maximal stimulations by hHGF, EGF and TGF-alpha were observed at 30, 400 and 900 pM, respectively. Maximal stimulation by TGF-alpha, however, was greater than those caused by hHGF and EGF. The effect of hHGF was additive with the maximal effects of EGF and TGF-alpha. Anti-hHGF antiserum was prepared in a rabbit by injecting with purified hHGF. This antiserum recognized nonreduced hHGF, but not reduced hHGF. The antiserum for hHGF did not inhibit growth-promoting activity of EGF, that was neutralized by incubation with anti-EGF antiserum. The activity of hHGF was completely inhibited by anti-hHGF antiserum, but not by anti-EGF antiserum. hHGF did not show any cross-reactivity to anti-EGF antiserum as measured by enzyme immunoassay for EGF. Thus, biological and immunological properties of hHGF are different from those of EGF and TGF-alpha.

Promoting effect of citrulline in hepatocarcinogenesis: possible mechanism in hypercitrullinemia

Hypercitrullinemia (adult type), believed to be one of the hereditary urea cycle disorders, is known to be complicated by hepatocellular carcinoma at a high incidence (approximately 14%). We investigated the relationship between this hypercitrullinemia and hepatocarcinogenesis. After the addition of citrulline, incorporation of tritiated thymidine into primary cultured hepatocytes of adult rat increased in a dose-dependent fashion in the range of 0.1 to 5 mmol/L. The citrulline-added group also showed significant increase in ornithine and polyamine contents in hepatocytes. The incidence of epithelial cell foci in the in vivo-in vitro tumor promotion analyzing system significantly rose in the group maintained with 5 mmol/L citrulline and in the group maintained with 1.5 mmol/L phenobarbital. These findings suggest the possibility that citrulline has a promotion effect on hepatocyte proliferation and that at high concentrations it plays the role of a hepatocarcinogenesis promoter.

Deduced primary structure of rat hepatocyte growth factor and expression of the mRNA in rat tissues

The primary structure of rat hepatocyte growth factor (HGF) was elucidated by determining the base sequence of the complementary DNA (cDNA) of HGF. The cDNA for rat HGF was isolated by screening a liver cDNA library with oligonucleotides based on the partial N-terminal amino acid sequence of the beta subunit of purified rat HGF. HGF is encoded in an mRNA of about 6 kilobases. Both alpha and beta subunits of HGF are specified in a single open reading frame for a 728-amino acid protein with a calculated molecular weight of 82,904. The N-terminal part of HGF has a signal sequence and a prosequence with 30 and 25 amino acid residues, respectively. The mature heterodimer structure is derived proteolytically from this single pre-pro precursor polypeptide. The calculated molecular weights of the alpha and beta subunits are 50,664 and 25,883, respectively, and each subunit has two potential N-linked glycosylation sites. The amino acid sequence of HGF is 38% identical with that of plasminogen. The alpha subunit of HGF contains four "kringle" structures, and the beta subunit has 37% amino acid identity with the serine protease domain of plasmin. Northern blot analysis revealed that HGF mRNA was expressed in rat various tissues, including the liver, kidney, lung, and brain.

Tissue distribution of hepatopoietin-A: a heparin-binding polypeptide growth factor for hepatocytes

Hepatopoietin-A (HPTA) is a heparin-binding polypeptide growth factor which consists of a heavy and a light polypeptide chain with molecular weights of 70,000 and 35,000, respectively. It stimulates DNA synthesis in primary cultures of normal rat hepatocytes in serum-free medium. The complete purification and characterization of HPTA from rabbit serum were reported by us elsewhere. Recently we have determined the amino-terminal amino acid sequence of the rabbit HPTA light chain up to 24 residues and have shown that the sequence is not homologous with other known sequences. [N.B. Human hepatocyte growth factor, recently sequenced by two other groups, is the same molecular species as HPTA.] In the present paper we report the production of a neutralizing polyclonal antiserum raised in chicken against purified rabbit HPTA. This antiserum does not inhibit the mitogenic effect of other potent inducers of hepatocyte DNA synthesis (epidermal growth factor or acidic fibroblast growth factor), nor does it interact with these growth factors in an enzyme-linked immunosorbent assay (ELISA). The antibody recognizes HPTA, as was determined by Western immunoblotting. Since the tissue origin of HPTA is not known, this anti-HPTA antiserum was used to investigate the tissue distribution of HPTA in rabbits by immunohistostaining methods. Acinar cells of the pancreas, neurons of the brain, C cells of the thyroid, ductal cells of the salivary glands, and Brunners glands of the duodenum stained with anti-HPTA antibody. Liver, spleen, thymus, and kidney do not seem to contain appreciable amounts of HPTA. We confirmed these findings by extracting and purifying active HPTA from the stained tissues listed above. The anti-HPTA antibody recognizes HPTA purified from different tissues, as was determined by ELISA, Western immunoblotting, and immunoneutralization experiments.

Studies on the hyperplasia ('regeneration') of the rat liver following partial hepatectomy. Changes in lipid peroxidation and general biochemical aspects

Using the experimental model of partial hepatectomy in the rat, we have examined the relationship between cell division and lipid peroxidation activity. In rats entrained to a regime of 12 h light/12 h dark and with a fixed 8 h feeding period in the dark phase, partial hepatectomy is followed by a rapid regeneration of liver mass with cycles of synchronized cell division at 24 h intervals. The latter phenomenon is indicated in this study by pulses of thymidine kinase activity having maxima at 24 h, 48 h and 72 h after partial hepatectomy. Microsomes prepared from regenerating livers show changes in lipid peroxidation activity (induced by NADPH/ADP/iron or by ascorbate/iron), which is significantly decreased relative to that in microsomes from sham-operated controls, again at 24 h, 48 h and 72 h after the operation. This phenomenon has been investigated with regard to possible underlying changes in the content of microsomal fatty acids, the microsomal enzymes NADPH:cytochrome c reductase and cytochrome P-450, and the physiological microsomal antioxidant alpha-tocopherol. The cycles of decreased lipid peroxidation activity are apparently due, at least in part, to changes in microsomal alpha-tocopherol content that are closely associated in time with thymidine kinase activity.

Hepatotrophic growth factor in blood of mice treated with carbon tetrachloride

The presence of a human hepatocyte growth factor (hHGF)-like DNA-synthesis promoter in platelet-poor serum of mice with liver injury was examined. Activity of the serum for stimulating DNA synthesis in cultured rat hepatocytes was low in untreated or vehicle-treated mice, but markedly increased 24 h after carbon tetrachloride administration and then dropped to normal levels prior to the peak of liver DNA synthesis. The effect of the serum was additive with the maximal effects of mouse and human epidermal growth factors, but not with that of hHGF. The growth-stimulating factor in the mouse serum, like hHGF, had affinity for heparin and was heat-labile. These results indicate that the level of a serum hHGF-like hepatocyte growth factor increased in mice treated with carbon tetrachloride prior to liver regeneration.

Marked increase of HGF mRNA in non-parenchymal liver cells of rats treated with hepatotoxins

When experimental hepatitis was induced by administrating rats with hepatotoxins such as CCl4 and D-galactosamine, HGF mRNA increased dramatically in the injured liver. The increase of HGF mRNA was time- and dose-dependent. At 5 hr after CCl4-treatment, HGF mRNA was remarkably increased; it reached the maximum level at 10 hr and maintained at this level for 40 hr. On the contrary, in D-galactosamine-induced hepatitis, HGF mRNA started to increase from 24 hr after a long lag time. Moreover, HGF mRNA was expressed transiently, decreasing rapidly to the basal level after reaching the maximum level at 36 hr. The degree of induction of HGF mRNA correlates well to the degree of liver damage. In the liver, HGF mRNA could be detected in only non-parenchymal cells, not in parenchymal hepatocytes. These findings suggest that liver is a main producing organ of HGF for liver regeneration after hepatic injury, and HGF is synthesized and secreted by non-parenchymal liver cells so that it stimulates the growth of parenchymal hepatocytes to repair liver tissue in paracrine fashion.

Molecular cloning and expression of human hepatocyte growth factor

Hepatocyte growth factor (HGF) is the most potent mitogen for mature parenchymal hepatocytes in primary culture, and seems to be a hepatotrophic factor that acts as a trigger for liver regeneration after partial hepatectomy and liver injury. The partial purification and characterization of HGF have been reported. We have demonstrated that pure HGF from rat platelets is a new growth factor effective at concentrations as low as 1 ng ml-1. The effects of HGF and epidermal growth factor (EGF) are additive. The activity of HGF is not species-specific, although it does not stimulate growth in Swiss 3T3 fibroblasts. HGF has a relative molecular mass (Mr) of 82,000 and is a heterodimer composed of a large alpha-subunit of Mr 69,000 and a small beta-subunit of Mr 34,000. Here we report the amino-acid sequence of human HGF determined by complementary DNA cloning and the expression of biologically active human HGF from COS-1 cells transfected with cloned cDNA. The nucleotide sequence of the human HGF cDNA reveals that both alpha- and beta-chains are contained in a single open reading frame coding for a pre-pro precursor protein of 728 amino acids.

Further characterisation of 'hepatotropin', a high molecular weight hepatotrophic factor in rat serum

We report further characterisation of the hepatocyte growth factor 'hepatotropin' which is found in rat serum 24 h after partial hepatectomy. Hepatotropin enhances DNA synthesis in primary cultures of adult rat hepatocytes, and is of high molecular weight. Serum fractions were separated by gel filtration, heparin-sepharose affinity chromatography and ion-exchange chromatography. Sodium dodecylsulphate-polyacrylamide gel electrophoresis (SDS-PAGE) identified a band of apparent subunit relative molecular weight (Mr) 100,000 associated with biological activity, although purification to homogeneity has not been achieved. The activity is heat-labile, trypsin-sensitive, and stable to lyophilisation, but loses activity after dilution and reconcentration. In combination with known peptide hepatocyte growth modulators, hepatotropin acted synergistically with insulin and epidermal growth factor (EGF) but its action was not enhanced by glucagon. Studies on isolated rat hepatocyte membranes showed no evidence of enhanced phosphorylation of the EGF receptor by hepatotropin. The relationship of hepatotropin to previously described serum and platelet-derived growth factors is discussed.

Clinical significance of human hepatocyte growth factor in blood from patients with fulminant hepatic failure

We have recently found the presence of human hepatocyte growth factor in sera of patients with fulminant hepatic failure and have purified human hepatocyte growth factor from plasma of a patient with fulminant hepatic failure. In this paper, we report the clinical significance of human hepatocyte growth factor in blood from patients with fulminant hepatic failure. The effect of sera or plasma from 17 patients with fulminant hepatic failure on liver cell growth was examined by use of adult rat hepatocytes in primary cultures. Sera or plasma from 16 of the 17 patients with fulminant hepatic failure stimulated DNA synthesis in hepatocytes more effectively than normal human serum. The mean growth-promoting activity for the 17 patients with fulminant hepatic failure was about 16 times higher than that obtained for normal human serum. This growth-promoting activity of the patients' blood was not related to sex, age, clinical outcome of the patients or type of fulminant hepatic failure, but was intimately related to the clinical grade of hepatic coma. Sera or plasma with Grade III and IV coma showed stimulatory activity on DNA synthesis more markedly than sera or plasma from patients with coma of less than Grade II. In the surviving group, this activity decreased as the hepatic coma of patients improved. In fact, this activity of sera from patients at the recovery stage showed no significant increase compared with that of normal human serum. In the group of terminal patients, this activity increased as the coma developed.(ABSTRACT TRUNCATED AT 250 WORDS)

Human growth hormone stimulates liver regeneration in rats

To study the effect of human growth hormone (hGH) on liver regeneration in rats, 200 micrograms hGH was administered to partial hepatectomized rats twice a day for three days. The bw of hGH-treated rats was higher than that in untreated rats. After three day administration, the liver weight was 3.18 +/- 0.13 g, significant higher than that of untreated rats (2.68 +/- 0.17 g). Human GH also stimulated the mitosis in the liver. Serum insulin-like growth factor I (IGF-I) and albumin levels were significantly increased and urea nitrogen levels were significantly decreased in hGH-treated rats compared with those in untreated rats. When 120 micrograms/day IGF-I was continuously administered to partial hepatectomized rats for three days, the bw and the liver weight were not higher than those of controls. These data indicate that hGH directly stimulates liver regeneration and recover liver dysfunction in rats.

Enhancement in rats by the liver tumor promoter ethinyl estradiol of a serum factor(s) which is stimulatory for hepatocyte DNA synthesis

Fractionation of female rat serum or plasma on Sephadex G-200 revealed the presence of an activity stimulatory for hepatocyte DNA synthesis. Treatment of female rats with the liver tumor promoter ethinyl estradiol (EE) at 2.5 micrograms/day caused a 1.6 fold increase in the level of this activity at 24 hr in both serum and plasma. The stimulatory activity had a molecular weight of 135 kD, was sensitive to trypsin and heating and was not inhibited by the antiestrogen tamoxifen or antibody to epidermal growth factor (EGF). However, the pooled active fractions from EE-treated rats competed to a greater extent than comparable fractions from control rats for specific [125I]-EGF binding to rat liver membranes. These results demonstrate that treatment of female rats with EE, under conditions known to stimulate liver growth, caused an increase in level of a factor(s) stimulatory for hepatocyte DNA synthesis and whose activity may be mediated through the EGF receptor.

Stimulation of DNA synthesis in hepatocytes by Kupffer cells after partial hepatectomy

The role of Kupffer cells during reparative regeneration of rat liver was investigated with an in vitro experimental model. Conditioned media from primary cultures of Kupffer cells isolated from intact and regenerating liver were added to primary cultures of hepatocytes, and [3H]thymidine incorporation into DNA was studied. Kupffer cell-conditioned media from intact liver and regenerating remnant liver significantly stimulated DNA synthesis in hepatocytes as compared with control media (p less than 0.05). Moreover, the stimulating activity of Kupffer cells prepared from regenerating liver at 6 and 12 hr after partial hepatectomy was significantly higher than that of Kupffer cells from untreated rats (p less than 0.05). The activity was found in serum-free conditioned media. This stimulating activity exponentially increased as the increase of the number of the cultured cells, indicating that the stimulating activity was released directly by cultured Kupffer cells. These results suggest that Kupffer cells stimulate DNA synthesis in hepatocytes by producing and releasing certain factor(s) at an early stage of liver regeneration after partial hepatectomy.