Hepatotrophic growth factor in blood of mice treated with carbon tetrachloride

Phenobarbital suppresses growth and accelerates restoration of differentiation markers of primary culture rat hepatocytes in the chemically defined hepatocyte growth medium containing hepatocyte growth factor and epidermal growth factor

Phenobarbital (PB), a liver-tumor promoter, at a concentration of 3 mM dramatically inhibited the growth of adult rat hepatocytes in the chemically defined medium, HGM, with added hepatocyte growth factor (HGF) and epidermal growth factor (EGF). In concurrence with these findings, PB down-regulated expression of the HGF receptor (c-met) and suppressed production of the autocrine growth factor transforming growth factor-alpha (TGF-alpha). Furthermore, PB down-regulated expression of transcription factors associated with proliferation such as AP1 and NF-kappaB. In the presence of PB, hepatocytes remained morphologically differentiated and restoration of the expression of mature hepatocyte markers, such as albumin and cytochrome P450s (1A, 2B1/2, and 2E1), was accelerated after an initial phase of growth. Additionally, PB strongly suppressed expression of the mRNA for alpha-fetoprotein, a protein primarily expressed by fetal liver, and the accelerative effect of PB on restoration of mature hepatocyte markers showed a correlation with the up-regulation of the hepatocyte-enriched transcription factors HNF3 and HNF4. When the effects of PB on various extracellular matrix proteins were examined, the data indicated that PB specifically suppressed laminin and fibronectin production by hepatocytes, suggesting an important role for these proteins in growing hepatocyte cultures.

Gene expressions of c-met and hepatocyte growth factor in chronic liver disease and hepatocellular carcinoma

BACKGROUND/AIMS

The roles of c-met proto-oncogene and hepatocyte growth factor in human livers have not been shown.

METHODS

Gene expressions of both c-met and hepatocyte growth factor were quantified in livers with chronic active hepatitis and in cirrhotic livers with hepatocellular carcinoma as well as in normal controls, using competitive reverse transcription polymerase chain reaction.

RESULTS

C-met expression was significantly increased in chronic active hepatitis compared with control livers, and c-met expression in chronic active hepatitis correlated with serum alanine aminotransferase levels. Hepatocyte growth factor expression was increased in some patients with chronic active hepatitis compared with controls, and there was a significant correlation between c-met expression and hepatocyte growth factor expression. On the other hand, in hepatocellular carcinoma tissues, c-met expression was increased in some cases, while that in the surrounding non-carcinomatous tissues was similar to normal controls. Hepatocyte growth factor expression was not detected in the hepatocellular carcinoma tissues and was low in the surrounding non-carcinomatous tissues.

CONCLUSIONS

These findings suggest that hepatocyte growth factor may be involved in the regeneration of hepatocytes via paracrine mechanism in chronic active hepatitis, while in regulation of c-met expression in hepatocellular carcinoma tissues may be independent of hepatocyte growth factor stimulation.

Hepatocyte growth factor--pleiotropic cytokine produced by human leukemia cells

Hepatocyte growth factor (HGF) was identified, purified and molecularly cloned as a potent mitogen for mature rat hepatocytes in primary culture. It is one of the largest cytokines and is composed of disulfide-linked subunits of approximately 60 (heavy chain) and 35 kilodaltons (light chain). Recent observations revealed that HGF is mitogenic to various epithelial cells other than hepatocytes and to endothelial cells, and that it also acts as a motogen, morphogen and tumor-suppressor as well as a mitogen. These various biological activities of HGF are presumably transduced through the same receptor, c-Met, which is a member of the tyrosine kinase receptor family. Although it shows multiple biological activities on cells in culture, HGF is most likely the physiological hepatotrophic factor which triggers liver regeneration. It may also function as a renotrophic and pulmotrophic factor after tissue injury. HGF production in the liver, kidney and lung increases after injury to these organs. An elevated HGF level may act as an inducer of compensatory DNA synthesis. The regulation of HGF production is, therefore, important for the control of organ regeneration. HGF is produced mainly by mesenchymal cells such as fibroblasts and vascular smooth muscle cells. Various types of human leukemia cells also secrete HGF both in vitro and in vivo. Some biological activities of HGF on hematopoietic cells, including co-mitogenic activity on myeloid leukemia cell lines, were recently demonstrated. HGF gene expression and the protein production in leukemia and fibroblast cells are modulated by various cytokines and hormones. Those modulators may indirectly affect organ regeneration and other biological processes by controlling HGF production.

Expression of hepatocyte growth factor receptor (c-met) mRNA in primary cultures of human hepatocytes

Aim-To investigate the regulation of hepatocyte growth factor (HGF) receptor (c-met) gene expression in isolated primary human hepatocytes.Methods-Primary hepatocytes were maintained in monolayer culture for up to 72 hours in serum-free medium. They were treated with growth factors and the level of HGF, c-met and reduced glyceraldehyde-phosphate dehydrogenase mRNA expression determined by northern blot analysis.Results-Hepatocytes expressed a single 9 kilobase c-met gene transcript whilst HGF mRNA analysis was negative. Addition of HGF and epidermal growth factor, both potent mitogens for human hepatocytes, enhanced c-met mRNA expression approximately twofold within 24 hours, after which levels returned to normal. In non-growth factor treated cells, transforming growth factor-beta (TGFbeta) had little effect upon c-met mRNA levels. However, TGFbeta inhibited the HGF induced increase in c-met mRNA levels.Conclusions-These results indicate that hepatocytes which proliferate in response to HGF demonstrate levels of c-met mRNA which are subject to growth factor modulation and suggest an important means of growth regulatory control.

Factors controlling growth, motility, and morphogenesis of normal and malignant epithelial cells

Factors that control epithelial growth, motility, and morphogenesis play important roles in malignancy and in normal development. Here we discuss the molecular nature and the function of two types of molecules that control the development and maintenance of epithelia: Components that regulate epithelial cell adhesion; and soluble factors and their receptors that regulate growth, motility, differentiation, and morphogenesis. In development, the establishment of epithelial cell characteristics and organization is crucially dependent on cell adhesion and the formation of functional adherens junctions. The integrity of adherens junctions is frequently disturbed late in tumor progression, and the resulting loss of epithelial characteristics correlates with the metastatic potential of carcinoma cells. Various soluble factors that induce epithelial growth, motility, or differentiation in cell culture, function via tyrosine kinase receptors. We concentrate here on receptors that are expressed exclusively or predominantly on epithelia, and on ligands that are derived from the mesenchyme. In development, these receptors and their ligands function in mesenchymal-epithelial interactions, which are known to govern growth, morphogenesis, and differentiation of epithelia. During tumor development, mutations or overexpression of the receptors are frequently observed; these alterations contribute to the development and progression of carcinomas.

In vivo response of hepatocytes to growth factors requires an initial priming stimulus

Although growth factor effects have been studied in cultured hepatocytes, little information exists as to whether these factors can trigger hepatocyte replication in vivo. In this study we infused epidermal growth factor, transforming growth factor-alpha and hepatocyte growth factor directly into the portal vein of rats for 24 hr to see whether they could induce DNA synthesis in normal livers or in livers subjected to one-third hepatectomy. Infusion of transforming growth factor-alpha or epidermal growth factor at doses up to 80 micrograms/24 hr had little effect on hepatic DNA synthesis in normal liver, whereas the monomeric and heterodimeric forms of hepatocyte growth factor generally produced increases of less than threefold in hepatic DNA synthesis. In contrast, after one-third hepatectomy infusion of epidermal growth factor, transforming growth factor-alpha or hepatocyte growth factor produced dose-dependent increases in hepatic DNA synthesis. At a dose of 40 micrograms/24 hr, epidermal growth factor increased DNA synthesis threefold, whereas transforming growth factor-alpha or hepatocyte growth factor increased DNA synthesis to greater than six times that in rats that had undergone hepatectomy alone. Furthermore, infusion of these growth factors, with or without one third-hepatectomy, induced the expression of transforming growth factor-alpha mRNA in the liver. The pattern of protooncogene expression induced by one-third hepatectomy was studied to determine the effect of this procedure in sensitizing the liver to the growth factors. Compared with the well-characterized two-thirds hepatectomy system, there was a similar but smaller increase in c-myc expression but no induction of c-jun expression.(ABSTRACT TRUNCATED AT 250 WORDS)

Induction of serum-borne immunomodulatory factors in B6C3F1 mice by carbon tetrachloride. I. Carbon tetrachloride-induced suppression of helper T-lymphocyte function is mediated by a serum borne factor

Following carbon tetrachloride-induced liver injury, hepatotrophic factors are synthesized and released into the serum to facilitate the regeneration of damaged hepatic tissue. We investigated the possibility that immunosuppression could be mediated through induction of a serum factor(s) because in vivo exposure of B6C3F1 mice to carbon tetrachloride selectively inhibits T-cell-dependent immune responses. Addition of mouse serum (5% by volume) obtained from mice treated with carbon tetrachloride (250 or 500 mg/kg/day for 7 days) to naive spleen cell cultures markedly suppressed the sheep red blood cell antibody-forming cell response compared to controls (P < 0.01). Immunosuppression was observed in mice sensitized with sheep red blood cells 48 h, but not 24 or 72 h, following one dose of carbon tetrachloride (1000 mg/kg). Only serum isolated from mice 48 h following exposure to a single dose of carbon tetrachloride (1000 mg/kg) suppressed the antibody-forming cell response when added in vitro to spleen cell cultures. Biodistribution studies using [14C]-labelled carbon tetrachloride demonstrated that accumulation of the [14C]-label was primarily associated with excretory organs (liver, kidneys and lungs) but not with the serum, red blood cells, or spleen. Surprisingly, 24 and 48 h following exposure to [14C]-labelled carbon tetrachloride, an increase in radioactivity was detected in the thymus. The distinct profile of immunosuppressive activity associated with serum isolated from carbon tetrachloride-treated mice and the biodistribution studies clearly demonstrating a negligible amount of carbon tetrachloride or metabolites in the serum strongly implicate the role of a carbon tetrachloride-induced serum borne immunosuppressive factor.

Hepatocyte growth factor induces calcium mobilization and inositol phosphate production in rat hepatocytes

The effects of hepatocyte growth factor (HGF) on intracellular Ca2+ mobilization were studied using fura-2-loaded single rat hepatocytes. Hepatocytes microperfused with different amounts of HGF responded with a rapid concentration-dependent rise in the cytosolic free Ca2+ concentration with a maximum increase of 142% at 80 ng/ml of HGF. The lag period of the Ca2+ response was decreased with increasing HGF concentrations, being 64 +/- 12 s, 42 +/- 6 s, and 14 +/- 2 s, respectively, with 8, 20, and 80 ng/ml of HGF. The detailed pattern of Ca2+ transients, however, was variable. Out of 16 cells tested using 20 ng/ml of HGF, 68% showed sustained oscillatory responses, whereas other cells showed a sustained increase in the cytosolic-free Ca2+ upon exposure to HGF, which was dependent on the presence of extracellular Ca2+. HGF also induced Ca2+ entry across the plasma membrane. Mobilization of Ca2+ by HGF was accompanied by a rapid accumulation of inositol 1,4,5-trisphosphate (Ins 1,4,5-P3). The effects of HGF and epidermal growth factor (EGF) were comparable and partly additive for Ins 1,4,5-P3 production and for the sustained phase of Ca2+ mobilization. Preincubation of cells with 10 microM of genistein to inhibit protein tyrosine kinases abolished the HGF-induced Ca2+ response and also inhibited HGF-induced Ins 1,4,5-P3 production in rat liver cells. These data indicate that early events in the signal transduction pathways mediated by HGF and EGF have in common the requirements for tyrosine kinase activity, Ins 1,4,5-P3 production, and Ca2+ mobilization.

The role of metabolism in carbon tetrachloride-mediated immunosuppression. In vitro studies

In vitro studies were performed to determine the role of metabolic bioactivation in mediating immunosuppression by CCl4. Direct addition of CCl4 to naive spleen cell cultures sensitized with either sheep erythrocytes, DNP-Ficoll or lipopolysaccharide (LPS) resulted in a marked inhibition of the antibody forming cell (AFC) response to all three of the selected antigens at 3.0 mM concentration in culture. However, this inhibition was primarily due to the direct cytotoxic effects of CCl4 on spleen cells following 3-5 days of culture in the presence of the chemical as evidenced by a decrease in cell number and viability and by the absence of selective effects on T-cell dependent humoral responses which is contradictory to the effects observed in vivo. Co-incubation of splenocytes for 1 h with primary hepatocytes, but not with subcellular metabolic activation systems, such as S9 or microsomes, enhanced the immunotoxic effects of CCl4 in vitro. Interestingly, a 3-h co-incubation of spleen cells with metabolically active hepatocytes in primary culture resulted in an even greater potentiation of the immunotoxic effects of CCl4 as determined by the T-cell dependent IgM AFC response. Conversely, under identical conditions, CCl4 did not suppress humoral responses to the polyclonal B-cell activator LPS which is in agreement with the effects produced by in vivo exposure to CCl4. It is important to emphasize that for the metabolic activation studies (i.e. co-incubation with either S9, microsomes or hepatocytes), spleen cells were washed free of CCl4 immediately following the co-incubation period. Control splenocyte cultures (i.e. no metabolic activation system) incubated in the presence of CCl4 alone at 3.0 mM over a 3-h time-period, had no effect on spleen cell function, number or viability. In agreement with our previous findings which indicate that pretreatment of mice with inducers and inhibitors of the mixed function oxygenase system prior to CCl4 administration modulated the immunotoxic effects of CCl4 in vivo, these results lead us to conclude that immunotoxicity by CCl4 requires metabolic activation.

Effects of protein kinase inhibitors on the mitogenic activity of human hepatocyte growth factor on rat hepatocytes in primary culture

To evaluate the role of protein phosphorylation reactions in signal transduction of human hepatocyte growth factor (hHGF), now known to be the same protein as the scatter factor and tumor cytotoxic factor, we examined the effects of various inhibitors of protein kinases on the mitogenic activity of hHGF on rat hepatocytes in primary culture. Genistein, a specific inhibitor of tyrosine kinase, dose-dependently inhibited the effect of hHGF in stimulating DNA synthesis of hepatocytes. By contrast, 1-(5-isoquinolinesulfonyl)-2- methylpiperazine (H7), a specific inhibitor of protein kinase C, potentiated the stimulatory effect of hHGF on DNA synthesis of hepatocytes. H7 was effective at over 2 micrograms/ml and potentiated the effect of hHGF over 2-fold at 20 micrograms/ml. On the other hand, an inhibitor of Ca++/calmodulin-dependent protein kinase inhibited both the basal and hHGF-stimulated DNA synthesis in the cells, whereas an inhibitor of cyclic nucleotide-dependent protein kinases had little effect on the action of hHGF. These results suggest that tyrosine phosphorylation is required for stimulation of hepatocyte DNA synthesis by hHGF and that the action of hHGF is negatively regulated by protein kinase C activation.

Phorbol ester-induced secretion of human hepatocyte growth factor by human skin fibroblasts and its inhibition by dexamethasone

Human skin fibroblasts secreted a certain amount of human hepatocyte growth factor (hHGF), as determined by an enzyme-linked immunosorbent assay for hHGF. This hHGF secretion was remarkably stimulated by protein kinase C (PKC)-activating phorbol esters, which was inhibited by the simultaneous addition of dexamethasone. Pretreatment with phorbol 12-myristate 13-acetate (PMA) caused a down-regulation in hHGF secretion. hHGF secreted by the PMA-treated cells showed a potent hepatocyte growth-promoting activity which was neutralized by an anti-hHGF antiserum. These results indicate both that PMA-treated human skin fibroblasts produce biologically active hHGF and the possible involvement of PKC activation in this process.

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)

Human hepatocyte growth factor in blood of patients with fulminant hepatic failure. Basic aspects

Human hepatocyte growth factor (hHGF) was purified from the plasma of six patients with fulminant hepatic failure due to hepatitis B in two and non-A, non-B hepatitis in four. The purified hHGF from each patient contained two major protein bands having molecular weights of 79,000 and 86,000 and several minor bands having molecular weights between 76,000 and 92,000 on sodium dodecyl sulfate-polyacrylamide gel electrophoresis performed under nonreduced conditions. After reduction with 2-mercaptoethanol, three major bands having molecular weights of 58,000, 34,500, and 31,500 were evident. In addition, a band having a molecular weight of 21,000 was detected. hHGF activity was destroyed by its reduction. The hHGF purified from patients demonstrated a dose response in terms of an increase in DNA synthesis using cultured hepatocytes. The hHGF concentration in the plasma of the patients with grade III-IV hepatic coma was calculated to be in the range of 1.8-3.0 nM. Finally the heavy chain of hHGF was not recognized by an anti-human albumin antibody, indicating that hHGF is not biliprotein, an albumin-bilirubin complex, that has been reported to be a putative liver growth factor.

Human hepatocyte growth factor in blood of patients with fulminant hepatic failure. I. Clinical aspects

The levels of human hepatocyte growth factor (hHGF) in sera obtained from patients with various liver diseases were determined using adult rat hepatocytes maintained in primary culture. The mean hHGF activity for 22 patients with fulminant hepatic failure was about nine times greater than that found in normal human serum. The increase in serum hHGF activity seen in two patients with "acute-on-chronic" hepatitis was similar to that found in patients with fulminant hepatic failure. The serum level of hHGF from patients with acute hepatitis is related to the stage of their illness. The average value for 31 patients was about three times that of normal human serum. In some patients, the time course for the increase in serum hHGF activity was similar to that demonstrated for alpha-fetoprotein. The mean hHGF activity in serum for the 33 patients with chronic hepatitis and from 25 patients with liver cirrhosis was increased also compared with that of normal human serum. In addition, serum hHGF activity in three of seven patients studied after partial hepatectomy for a space-occupying lesion of the liver was increased. These data suggest that the increase in serum hHGF activity present in patients with various liver diseases reflects a self-defense mechanism that is involved in the process of liver cell regeneration.

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.

Induction of hepatocyte mitosis in intact adult rat by interleukin-1 alpha and interleukin-6

In the adult rat the liver is normally quiescent, but it proliferates rapidly in response to partial hepatectomy (PH). A hepatectomized rat is subjected to stress by the operation. We have examined the effects of acute phase cytokines. To investigate the mediation of hepatocyte growth, recombinant human interleukin-1 alpha (IL-1) and interleukin-6 (IL-6) were injected into male rats. Administration of IL-1 or IL-6 followed by NH4Cl and glucagon could induce hepatocyte mitosis 30 h after the first injection. This activity was lost when interleukins were exposed to 90 degrees C for 30 minutes. NH4Cl augmented the effects of IL-1 and IL-6. These results suggest that the IL-1 and IL-6 are important mediators of liver regeneration after PH. We present a hypothesis for the triggering mechanism of hepatocyte proliferation.