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

Involvement of growth factor receptor-bound protein-2 in rat hepatocyte growth

Growth factor receptor-bound protein-2 (GRB-2) is a protein linking receptor tyrosine kinase and Sos (Son of Sevenless gene; Ras GDP/GTP exchange protein), leading to activation of the Ras-mitogen-activated protein kinase (MAPK) cascade. So far, it remains unclear how GRB-2 plays a role in signal transduction pathways evoked by hepatotrophic factors. This study was attempted to evaluate the involvement of GRB-2 in signalling in rat hepatocyte growth. Using rat cultured hepatocytes stimulated by hepatotrophic factors and regenerating livers after partial hepatectomy (PH) we examined GRB-2-mediated linkage of hepatotrophic factor receptors to signal transducing molecules such as Sos or dynamin-II by immunoprecipitation and western blot analysis. In primary cultured hepatocytes stimulated with hepatocyte growth factor (HGF) or epidermal growth factor (EGF), GRB-2 linked HGF receptor or EGF receptor, respectively, to Sos which activated the mitogen-activated protein kinase (MAPK) cascade. In contrast, in primary cultured hepatocytes stimulated with insulin, GRB-2 linked insulin receptor substrate-1 (IRS-1) to dynamin-II as well as Sos. In the early phase after PH, GRB-2 activated the Ras-MAPK cascade by linking HGF receptor, IRS-1, or EGF receptor to Sos. In the late phase after PH, a complex of IRS-1-GRB-2 associated with dynamin-II, indicating that GRB-2 may transduce signals from IRS-1 to dynamin-II. We conclude that GRB-2 may play a role in transmitting signals from hepatotrophic factors to not only MAPK but also to other signalling pathways in hepatocyte growth.

Differential modulation of hepatocyte growth factor-stimulated motility by transforming growth factor beta1 on rat liver epithelial cells in vitro

We have previously shown that transforming growth factor-beta1 (TGF-beta1) enhances the epidermal growth factor- (EGF) and transforming growth factor-alpha (TGF-alpha)-stimulated motility of rat hepatocytes in an extracellular matrix (ECM)-dependent fashion (Stolz and Michalopoulos, 1997, J. Cell. Physiol., 170:57-68). We have extended this study to examine the effects of TGF-beta1 on hepatocyte growth factor (HGF) and EGF-stimulated motility of rat nonparenchymal liver epithelial cells (RLECs) in vitro and determined that chemotaxis, scattering, and monolayer wound healing by EGF was synergistically enhanced by TGF-beta1 on all ECMs examined. However, HGF-based motility, unlike EGF-stimulated motility, was modulated in an assay-dependent manner by TGF-beta1. HGF-stimulated chemotaxis was dramatically decreased by addition of TGF-beta1, but wound healing was synergistically enhanced by TGF-beta1 on all ECMs examined. HGF-based scattering was not consistently affected by TGF-beta1 on any ECM tested except on laminin, where scattering was often reduced by the concomitant addition of TGF-beta1. TGF-beta1 enhanced the motility associated with monolayer wound healing by HGF or EGF independent of DNA synthesis, because tritiated thymidine uptake was consistently reduced by 60% in the presence of TGF-beta1. The data indicate that HGF and EGF motility do not follow redundant signal-transduction pathways and that specific growth factor motility-related events, as measured by wound healing, scattering, and chemotaxis, are modulated independently by ECM and TGF-beta1.

Hepatic oval cell activation in response to injury following chemically induced periportal or pericentral damage in rats

Administration of 2-acetylaminofluorene (2-AAF) given before partial hepatectomy (PHx) results in suppression of hepatocyte proliferation and stimulation of oval cell proliferation. Our objective in this study was to examine the oval cell response and associated alpha-fetoprotein (AFP) gene expression by combining 2-AAF with selective damage of centrilobular regions (carbon tetrachloride [CCl4]) or periportal regions (allyl alcohol [AA]). Centrilobular damage results in a more enhanced oval cell response and AFP gene expression than periportal damage. Conversely, more intense proliferation of intraportal bile duct epithelia was seen with 2-AAF/AA than with 2-AAF/CCl4. The oval cell response and AFP gene expression was ranked as 2-AAF/ CCl4 > or = 2-AAF/PHx > 2-AAF/AA. AFP mRNA expression was also examined in an acute AA and CCl4 injury. We found very little AFP gene expression compared with the 2-AAF/hepatic injury models. To see a true oval cell response, the hepatocytes must be inhibited from proliferating. In addition, the results presented with the 2-AA/AA model suggest that the periportal matrix may be as important as the cells that populate the area.

Ethanolamine modulates the rate of rat hepatocyte proliferation in vitro and in vivo

A low molecular weight, heat-resistant hepatotrophic factor in an extract from the bovine intestinal mucosa was purified and identified as ethanolamine by structural analyses. The mode of action of ethanolamine in vitro and in vivo coincided with that of the crude extract of the tissue, indicating that ethanolamine is the active component. Ethanolamine synergistically elevated the stimulation of DNA synthesis in hepatocytes in primary culture when added together with a growth factor, such as epidermal growth factor, with the ED50 being 20 microM, although it showed little stimulatory effect by itself. Contrary to these in vitro results, the intraperitoneal administration of ethanolamine hydrochloride (24 mg of ethanolamine per kg of body weight) enhanced hepatocyte proliferation in regenerating rat livers after two-thirds hepatectomy without the administration of any growth factors. In the regenerating liver, hepatocyte proliferation may be initiated by an endogenous growth factor, but the supply of ethanolamine in circulation may not be sufficient for optimal hepatocyte proliferation; thus, the exogenous administration of ethanolamine may further enhance hepatocyte proliferation. Ethanolamine in circulation may be a humoral hepatotrophic factor.

Hepatocyte growth factor enhances intestinal mucosal cell function and mass in vivo

Hepatocyte growth factor (HGF), originally known to stimulate hepatocyte DNA synthesis, recently has been shown to enhance growth of intestinal epithelial cells in vitro. However, there have been no studies on the effect of HGF on the function of intestinal epithelial cells in vivo. This study was designed to examine the effect of systemically administrated HGF on intestinal epithelial cell mass and function. Twenty young adult male Sprague-Dawley rats underwent placement of jugular venous catheters connected to subcutaneously placed osmotic minipumps. The rats were divided into four groups based on the contents in the osmotic pump: Group 1 (control, n = 5), normal saline; Group 2 (n = 5), HGF 75 microg/kg/d; Group 3 (n = 5), HGF 150 microg/kg/d; and Group 4 (n = 5), HGF 300 microg/kg/d. After a 14 day infusion, [C14] galactose and [C14] glycine absorption were measured in a 10-cm segment of mid small intestine using an in vivo closed-recirculation technique. Mucosal DNA content and protein content of the same small bowel segment were determined for each group. With all three doses, HGF significantly increased DNA content (P < .01) and protein content (P < .05). HGF also significantly increased galactose absorption (P < .01) with all three doses. Glycine absorption was increased with a dose of 75 (P < .05) and 150 microg/kg/d (P < .01), but not at a dose of 300 microg/kg/d. These data demonstrate that HGF can increase intestinal epithelial cell mass and function in vivo. HGF may be clinically useful in patients with short bowel syndrome.

Enhanced expression of hepatocyte growth factor/c-Met by myocardial ischemia and reperfusion in a rat model

BACKGROUND

Hepatocyte growth factor (HGF) is a multifunctional factor implicated in tissue regeneration, wound healing, and angiogenesis. Circulating HGF is reportedly elevated during the early stage of myocardial infarction. However, its precise effect on the heart is unknown. To evaluate the regulation of HGF in ischemically damaged myocardium, the production of HGF and its high-affinity receptor, c-Met, was studied in a rat model of myocardial ischemia and reperfusion.

METHODS AND RESULTS

The plasma concentration of HGF began to increase within 1 hour of reperfusion after 1 hour of ischemia. The peak level was reached at 3 hours after reperfusion. Northern blotting revealed that HGF mRNA expression in the heart was augmented threefold at 24 and 48 hours and remained elevated by twofold at 120 hours after the myocardium was reperfused. The signal for c-met, high-affinity HGF receptor mRNA, was also upregulated parallel to upregulation for HGF. In the kidney, liver, lung, and spleen, HGF mRNA was also maximally increased at 12 hours after reperfusion. However, c-met was not upregulated in these organs. Immunohistochemical studies disclosed that capillary endothelial and interstitial cells, including infiltrating macrophages, were intensely stained for HGF, whereas capillary endothelial cells in the reperfused myocardium were positive for c-Met.

CONCLUSIONS

This study is the first to show that myocardial ischemia and reperfusion induced HGF expression in various organs in vivo. These results indicate that HGF/c-Met plays a role in capillary endothelial cell regeneration in the ischemically injured heart.

Regeneration of Sarcophaga imaginal discs in vitro: implication of 20-hydroxyecdysone

When the 3/4 sectors of leg imaginal discs of Sarcophaga were cultured in vitro in the presence of 2.5 x 10(-8) M 20-hydroxyecdysone, wound healing and restoration of their morphology occurred. This concentration of ecdysone was critical for wound healing and was 40 times lower than that necessary for inducing differentiation of imaginal discs in vitro. Lost positional values revealed by expression of the wingless gene were found to show partial recovery under these conditions. These results suggest that a low titer of ecdysone is essential for the regeneration of imaginal discs.

Hepatocyte growth factor in assessment of acute pancreatitis: comparison with C-reactive protein and interleukin-6

Serum levels of hepatocyte growth factor (HGF), C-reactive protein (CRP), and interleukin-6 (IL-6) were determined at the time of admission in 38 patients with acute pancreatitis. The clinical utility of HGF for the detection of severe pancreatitis and for predicting prognosis, bacterial infection (infected pancreatic necrosis or sepsis), and organ dysfunction (liver, kidney, and lung) during the clinical course of acute pancreatitis was compared with the clinical utility of CRP and IL-6 by analysis of receiver operator characteristic (ROC) curves. The optimum cutoff levels of HGF for severity, prognosis, infection, hepatic dysfunction, renal dysfunction, and respiratory dysfunction were 0.9, 1.1, 1.0, 1.1, 1.1, and 1.0 ng/ml, respectively. HGF was as useful as CRP and more useful than IL-6 for detection of severe pancreatitis and for predicting hepatic dysfunction. Moreover, HGF was more useful than CRP or IL-6 for predicting prognosis, renal dysfunction, and respiratory dysfunction. However, for predicting infection, CRP was more useful than HGF. These results suggest that serum HGF levels on admission may be a useful new clinical parameter for determining the prognosis of acute pancreatitis and that HGF may be closely related to the organ dysfunction of acute pancreatitis.

Synergistic enhancement of EGF, but not HGF, stimulated hepatocyte motility by TGF-beta 1 in vitro

The ability of TGF-beta 1 (transforming growth factor-beta 1) to suppress growth factor induced proliferation of many cell types in vitro is well documented; however, TGF-beta 1 increases within a similar time frame as the hepatocyte mitogens HGF (hepatocyte growth factor), EGF (epidermal growth factor), and TGF-alpha (transforming growth factor-alpha) prior to hepatocyte proliferation during liver regeneration. This has raised the issue that TGF-beta 1 may have effects on hepatocytes additional to mito-inhibition and that these effects may be relevant to the regenerative process. To this end, we examined the effect of TGF-beta 1 on both the mitogenesis and the motility of growth factor stimulated primary rat hepatocytes and the hepatoblastoma cell line HepG2 in vitro. TGF-beta 1 significantly enhanced the chemotactic motility of EGF or TGF-alpha, and not HGF, stimulated hepatocytes on a collagen I substratum. TGF-beta 1 was not chemotactic when added alone and decreased the DNA synthesis of all hepatocyte cultures to near control levels. HepG2 cells were chemotactic toward HGF, EGF, and TGF-beta 1 alone and displayed an additive chemotactic response when TGF-beta 1 was added to either HGF or EGF. Additionally, HepG2 cells were refractory to the growth stimulatory effects of HGF or EGF and the growth inhibitory effects of TGF-beta 1. Hepatocytes plated onto other collagen-containing substrates (collagen IV, Matrigel, or ECL, an entactin-collagen IV-laminin matrix), but not on fibronectin or laminin alone, also displayed enhanced EGF stimulated motility by TGF-beta 1. The data indicate that an additional, novel role for TGF-beta 1 during liver tissue remodeling following PHx may include the synergistic enhancement EGF stimulated hepatocyte motility responses, and this enhancement is observed only on collagen-containing extracellular matrices.

Human hepatocyte growth factor in alcoholic liver disease: a comparison with change in alpha-fetoprotein. Department of Veterans Affairs Cooperative Study Group 275

To evaluate the hepatic regenerative response in patients with alcoholic liver disease, sera from 263 patients with severe alcoholic hepatitis and/or cirrhosis were analyzed for hepatocyte growth factor (HGF) and alpha-fetoprotein (AFP). HGF concentration was elevated above healthy controls in 95% of the patients (median level = 2.4 ng/ml), whereas AFP tended to be depressed below controls (median level = 4.1 ng/ml). Correlations with parameters of liver injury (i.e., ascites, encephalopathy, AST bilirubin, and protime) all showed a more significant correlation with HGF concentrations than those of AFP. Patients with HGF levels below the mean (4 ng/ml) exhibited significantly better survival (median survival = 35 months vs. 8.5 months for those with HGF > or = 4 ng/ml; p = 0.007). Serum HGF levels were associated with various specific histologic features of alcoholic hepatitis that included, but were not exclusively related to, necrosis.

Treatment with a novel lipid A analogue, FS-112, and partial hepatectomy causes submassive liver necrosis and impaired liver regeneration in mice

A novel experimental model of submassive liver necrosis with impaired regeneration has been established. A novel lipid A analogue, FS-112, was injected intravenously into male BALB/c mice, followed 2 days later by a 70% partial hepatectomy. Over the next 9 days, mice became severely jaundiced, with a peak total bilirubin (TBil) concentration of (mean +/- s.d.) 12.9 +/- 2.1 mg/dL 7 days postoperatively. In contrast, the TBil concentration in vehicle-treated mice remained less than 2 mg/dL. Significant elevations of L-alanine:2-oxoglutarate aminotransferase (ALT) were also observed 3-7 days after the operation in mice pretreated with FS-112, compared with mice pretreated with the vehicle. Submassive liver necrosis was observed with extensive mononuclear cell infiltration in mice treated with FS-112 and subjected to partial hepatectomy. Furthermore, both the BrdU and the proliferating cell nuclear antigen (PCNA) labelling index (LI) 1 day following partial hepatectomy in mice pretreated with FS-112 (8.6 +/- 4.3 and 7.9 +/- 4.2%, respectively) were significantly lower than levels in vehicle-treated mice (25.8 +/- 3.8 and 26.5 +/- 10.5%, respectively). The time course of changes in the BrdU LI in liver specimens from mice treated with both FS-112 and partial hepatectomy did not increase, even 3, 5, and 7 days postoperatively. Excellent liver regeneration with a PCNA LI 10-fold higher than the resting level was observed in mice treated with D-galactosamine hydrochloride. These results strongly suggest that this animal model of submassive liver necrosis may be suitable for clarifying the mechanisms of impaired liver cell regeneration often seen in fulminant hepatitis.

31P NMR measurements of the effects of unsaturated fatty acids on cellular phospholipid metabolism

31P NMR measurements on extracts prepared from a variety of cultured mammalian cell lines and primary rat hepatocytes have shown changes in the levels of several phospholipid metabolites after incubation of cells with unsaturated fatty acids. These data suggest a possible link between the accumulation of neutral lipid and the changes in phospholipid metabolite concentrations that have been observed in some tumor cells and other rapidly growing tissues such as the regenerating liver and mitogen-stimulated lymphocytes.

Hepatocyte growth factor/scatter factor is present in most pleural effusion fluids from cancer patients

Pleural effusion samples were obtained from 55 patients with malignant disease, including patients with primary lung cancers and those with a variety of other tumours metastatic to the pleura. The effusions were assayed for the presence of hepatocyte growth factor/scatter factor (HGF/SF), by both ELISA and bioassay. The presence of malignant cells in the effusions was also assessed. Detectable amounts of the factor, as judged by both criteria, were found in over 90% of all the effusions, including those from patients with a wide variety of carcinomas and also lymphomas. A wide range of HGF/SF levels were found for all tumour classes, some effusions containing high levels above 4 ng ml-1. It is concluded that tumours within the pleura and adjacent lung tissue are usually exposed to biologically significant levels of HGF/SF.

Hepatocyte growth factor enhancement of preneoplastic hepatic foci development in rats treated with diethylnitrosamine and N-ethyl-N-hydroxyethylnitrosamine

Effects of hepatocyte growth factor were investigated in a two-stage rat liver carcinogenesis protocol. Male F344 rats were first treated with diethylnitrosamine (200 mg/kg, i.p.) and then, starting two weeks later, with N-ethyl-N-hydroxyethylnitrosamine (EHEN) for 6 weeks at a dose of 0.01% in drinking water. Hepatocyte growth factor, which was injected i.v. at a dose of 200 micrograms/kg body weight one (at week 3) or two times (at weeks 3 and 4) during EHEN administration, significantly increased the development of preneoplastic glutathione S-transferase placental form-positive foci. Although the observed effects of hepatocyte growth factor were weaker than that of the two-thirds partial hepatectomy (PH) performed at week 3, the present results suggest that the enhancing effects of PH performed during the promotion stage may be largely mediated through induction of hepatocyte growth factor.

Hepatocyte growth factor remains as an inactive single chain after partial hepatectomy or unilateral nephrectomy

Hepatocyte growth factor (HGF) is a potent mitogen for hepatocytes and renal tubular epithelial cells. HGF is proteolytically activated in the tissue injured by hepatotoxin or nephrotoxin, suggesting that HGF functions as a crucial growth factor for tissue regeneration following hepatotoxin- or nephrotoxin-induced injury. In this study, we analyzed the molecular form of HGF after partial hepatectomy or after unilateral nephrectomy. The active form of HGF was not detected under our experimental conditions after these operations. Thus, HGF may play little role in liver regeneration after partial hepatectomy and in compensatory renal enlargement after unilateral nephrectomy.

Epiregulin. A novel epidermal growth factor with mitogenic activity for rat primary hepatocytes

Epiregulin, a novel epidermal growth factor (EGF)-related growth regulating peptide, was purified from conditioned medium of the mouse fibroblast-derived tumor cell line NIH3T3/clone T7. It was a 46-amino-acid single chain polypeptide, and its amino acid sequence exhibited 24-50% amino acid sequence identity with sequences of other EGF-related growth factors. Epiregulin exhibited bifunctional regulatory properties: it inhibited the growth of several epithelial tumor cells and stimulated the growth of fibroblasts and various other types of cells. Epiregulin bound to the EGF receptors of epidermoid carcinoma A431 cells much more weakly than did EGF, but was nevertheless much more potent than EGF as a mitogen for rat primary hepatocytes and Balb/c 3T3 A31 fibroblasts. These findings suggest that epiregulin plays important roles in regulating the growth of epithelial cells and fibroblasts by binding to receptors for EGF-related ligands.

Expression of HGF and TGF-beta 1 mRNA after partial hepatectomy in rats with liver cirrhosis

Hepatocyte growth factor (HGF) is a potent mitogen for the maturation of hepatocytes in vitro which plays a role in liver regeneration in vivo. In addition, transforming growth factor-beta 1 (TGF-beta 1) is also a potent regulator of liver regeneration. In attempting to clarify the mechanisms related to liver regeneration after partial hepatectomy, we investigated the expression of HGF and TGF-beta 1 in rats with liver cirrhosis (LC). A rat model of LC was prepared using carbon tetrachloride (CCl4). The expression of HGF mRNA in both the LC and control groups showed a similar time-course with the highest expression seen at 18h after a 70% hepatectomy. The expression of TGF-beta 1 mRNA peaked at 18h after partial hepatectomy in the LC group and at 48h in the control group. The 5-bromo-2'-deoxyuridine (BrdU) labeling index for the LC group at 24, 48, and 72 h after partial hepatectomy was 9.2%, 5.9%, and 1.8%, while for the control group it was 7.0%, 11.7%, and 6.8%, respectively. The BrdU labeling index in the LC group was thus suppressed earlier than that in the control group. We therefore postulate that regeneration of the remnant liver in the presence of LC accelerates immediately after partial hepatectomy, but the extent of regeneration is insufficient because of an early cessation due to an early expression of TGF-beta 1.

Expression of hepatocyte growth factor and transforming growth factor beta 1 mRNA in P. acnes and lipopolysaccharide-treated rats

Hepatocyte growth factor (HGF), a potent hepatocyte mitogen in vitro, triggers hepatocyte regeneration after partial hepatectomy and acute liver cell necrosis induced by chemicals. In contrast, transforming growth factor beta 1 inhibits hepatocyte proliferation in vitro and suppresses liver regeneration in vivo. We assessed the expression of HGF and TGF beta 1 mRNA in an endotoxin-related hepatic cell necrosis model. Intravenous injection of Gram-negative lipopolysaccharide (LPS) into rats previously given heat-killed Propionibacterium acnes induced endotoxin-related hepatic cell necrosis. In this model, serum ALT began to rise to more than 100IU as early as 3 h after LPS injection, reaching 300IU 12h after injection. HGF mRNA levels in the liver did not increase significantly until 5h after LPS injection; at 12h, they had increased about threefold compared with controls. TGF beta 1 mRNA expression increased threefold after P. acnes treatment alone and increased further after LPS injection. In the spleen, HGF mRNA levels increased within 3h, but in the lung no increase in HGF mRNA was observed. Early elevation of liver TGF beta 1 mRNA levels and delayed elevation of HGF mRNA levels, with low expression of HGF in the lung, may play a role in the pathogenesis of endotoxin-related hepatic necrosis.

Differing distribution of hepatocyte growth factor-positive cells in the liver of LEC rats with acute hepatitis, chronic hepatitis and hepatoma

Using anti-rat hepatocyte growth factor (HGF) antibody, we investigated the distribution of HGF-positive cells in the liver tissues of LEC rats at various phases of liver diseases. During the phase of fulminant hepatitis, HGF-positive cells increased remarkably, and many of them were localized at the portal triads; these cells were identified from their shape as non-epithelial cells. A reduced number of HGF-positive cells was observed during the phase of chronic hepatitis, while no HGF-positive cells were seen in the tissue of cholangiofibrosis. During the phase of carcinoma, staining revealed that both the hepatocellular carcinoma cells and the non-epithelial cells in cancerous liver tissue were HGF-positive. These results suggest that, in LEC rats, HGF may play an important role in the regeneration of hepatocytes as well as in the development of hepatocellular carcinoma.

Rapid induction of mRNAs for liver regeneration factor and insulin-like growth factor binding protein-1 in primary cultures of rat hepatocytes by hepatocyte growth factor and epidermal growth factor

Liver regeneration factor belongs to the leucine-zipper family of transcription factors. It was originally cloned and characterized through differential screening of a regenerating rat liver cDNA library. The mRNA for liver regeneration factor-1 is barely detectable in normal rat liver but is dramatically induced after two-thirds hepatectomy, with a peak 1 to 3 hr after surgery. The nature of the signaling molecule(s) for this rapid induction is not known. It has been suggested that the liver regeneration factor-1 protein product, through complex interactions with other transcription factors such as c-Jun and Jun-B, controls expression of genes that are required during the G1 phase of hepatic growth. Hepatocyte growth factor has been shown to be the most potent mitogen for hepatocytes in vitro and in vivo. Plasma levels of hepatocyte growth factor rapidly (within 30 min) increase after loss of hepatic parenchyma induced by partial hepatectomy or carbon tetrachloride treatment. It has been postulated that hepatocyte growth factor plays a crucial role in stimulating the hepatocyte to enter the cell cycle. In this communication, we report that addition of pure hepatocyte growth factor to primary cultures of rat hepatocytes in the absence of serum and insulin results in rapid and transient induction of liver regeneration factor-1 mRNA (more than 20-fold) with a peak of expression 1 hr after treatment. The levels of jun-B and c-fos mRNAs, which are also known to be induced during the early hours of liver regeneration, were also increased after treatment of isolated hepatocytes with hepatocyte growth factor.(ABSTRACT TRUNCATED AT 250 WORDS)

Expression of hepatocyte growth factor mRNA, and c-met mRNA (hepatocyte growth factor receptor) in human liver tumours

We have quantified mRNA for the hepatocyte growth factor and its putative receptor the c-met proto-oncogene protein product, in a series of human primary and secondary liver tumours and adjacent non-neoplastic liver. In all hepatocellular cancers, hepatocyte growth factor 6 kb mRNA expression was less (mean 23.93% +/- 6.33% S.E.M. n = 7) in the tumours than in the adjacent normal liver. Both relative over- and under-expression of c-met transcripts were found in tumour tissue compared to non-neoplastic liver. Thus hepatocellular cancer tissue does not over-express mRNA for hepatocyte growth factor, though this growth factor might play a role in hyperproliferative states leading to liver cancer.

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)

The Met proto-oncogene mesenchymal to epithelial cell conversion

Coexpression of the human Met receptor and its ligand, hepatocyte growth factor/scatter factor (HGF/SF), in NIH 3T3 fibroblasts causes the cells to become tumorigenic in nude mice. The resultant tumors display lumen-like morphology, contain carcinoma-like focal areas with intercellular junctions resembling desmosomes, and coexpress epithelial (cytokeratin) and mesenchymal (vimentin) cytoskeletal markers. The tumor cells also display enhanced expression of desmosomal and tight-junction proteins. The apparent mesenchymal to epithelial conversion of the tumor cells mimics the conversion that occurs during embryonic kidney development, suggesting that Met-HGF/SF signaling plays a role in this process as well as in tumors that express both epithelial and mesenchymal markers.

Regulating factors of liver regeneration after hepatectomy

The factors regulating liver regeneration were studied by measuring changes in the liver volume and serum hepatocyte growth factor (HGF) levels after hepatectomy. Changes in the liver volumes were studied in 68 hepatectomized patients, including (A) hepatoma patients who had chronic hepatitis or liver cirrhosis (n = 44) and (B) metastatic liver cancer patients who had normal liver parenchyma (n = 24). The hepatic volume increased by 13.8% of the remnant hepatic volume in group A and by 49.1% in group B. The examined factors included the percentage of resected liver volume (%RLV) and the results of laboratory tests. Regression analysis showed that in group A, both %RLV (beta = 0.46) and the serum total bilirubin (T-Bil) level (beta = -0.33) correlated significantly with the extent of liver regeneration and that in group B, only %RLV (beta = 0.78) correlated significantly with the regeneration. Serum HGF levels after hepatectomy were studied in 21 hepatectomized patients, including 11 hepatoma patients and 10 patients with some types of metastatic liver cancer. Serum HGF levels increased significantly after surgery in all 21 patients. Regression analysis, however, showed that the change in HGF was related to liver cirrhosis (beta = 0.46) and to the maximal postoperative T-Bil level (beta = 0.51) but not to the extent of liver regeneration after hepatectomy. These results suggest that liver regeneration is regulated primarily by factors relating to the percentage of the resected liver parenchyma and that serum HGF levels do not directly relate to liver regeneration after surgery.

Transforming growth factor-alpha expression during liver regeneration after partial hepatectomy and toxic injury, and potential interactions between transforming growth factor-alpha and hepatocyte growth factor

Transforming growth factor-alpha and hepatocyte growth factor are important stimulators of hepatocyte proliferation. In this series of experiments we sought to measure the expression of transforming growth factor-alpha mRNA by hepatocytes in response to toxic liver injury produced by carbon tetrachloride or galactosamine and to perform a more detailed analysis of transforming growth factor-alpha expression after partial hepatectomy. We also explored the interactions of transforming growth factor-alpha and hepatocyte growth factor in their effects on hepatocytes in vitro and tested the ability of these factors to stimulate endogenous transforming growth factor-alpha production by hepatocytes. In previous work we have used oligonucleotide probes to measure transforming growth factor-alpha mRNA expression after partial hepatectomy. In this study we used a rat transforming growth factor-alpha cDNA probe and found that the level of liver transforming growth factor-alpha mRNA increases 4 hr after partial hepatectomy, shows peak expression at 18 hr and returns to the normal level by 36 to 48 hr. Measurement of the corresponding peptide in the liver by means of radioimmunoassay shows that the level of transforming growth factor-alpha rises by 12 hr, peaks at 24 hr and remains significantly increased at 48 hr compared with the levels in sham-operated rats. Carbon tetrachloride and galactosamine are known to produce different patterns of acute liver injury, with maximal hepatocyte DNA synthesis at 48 hr and 5 days, respectively. After carbon tetrachloride administration the profiles of the transforming growth factor-alpha and hepatocyte growth factor mRNA expression are similar, each showing two peaks: the first at 12 hr and the second at 48 hr. In contrast, after galactosamine-induced liver injury the expression patterns of transforming growth factor-alpha and hepatocyte growth factor mRNAs differ: hepatocyte growth factor shows a major peak at 24 hr, with a smaller increase at 5 days, whereas transforming growth factor-alpha begins to increase after 2 days, with a single peak occurring at 5 days. In primary hepatocyte cultures, transforming growth factor-alpha and hepatocyte growth factor appear to have complementary effects. The maximal hepatocyte nuclear labeling index induced by hepatocyte growth factor was 42%; the addition of transforming growth factor-alpha increased this to 74%. Exogenous transforming growth factor-alpha, but not hepatocyte growth factor, stimulates the production of the transforming growth factor-alpha peptide by hepatocytes.(ABSTRACT TRUNCATED AT 400 WORDS)

Expression of hepatocyte growth factor mRNA during oval cell activation in the rat liver

The customary wave of hepatocyte regeneration which occurs in the rat liver after two-thirds partial hepatectomy can be abolished by oral administration of the carcinogen 2-acetylaminofluorene. Instead, regeneration is achieved through the proliferation and differentiation of potential stem cells (oval cells) which appear to emanate from the portal space. Ultrastructural studies have illustrated the undifferentiated nature of these cells in the first 3 days after resection, but very rapidly they acquire features of small hepatocytes or biliary epithelia. Oval cell progeny can form either cohesive columns of cells within sinusoids which may later differentiate into new hepatic plates, or single cells that can insinuate within existing plates. Using a 35S antisense riboprobe to hepatocyte growth factor (HGF) mRNA, the synthesis of HGF mRNA was observed in sinusoid-lining cells. There were few HGF mRNA-expressing cells in the liver removed at resection, but numbers steadily increased in the remnant over the next 7 days. In particular, an almost nine-fold increase in the density of HGF mRNA-producing cells occurred in the periportal areas, resulting in approximately double the density present within the centrilobular parenchyma. The superabundance of HGF-producing cells in the immediate vicinity of oval cell proliferation and differentiation strongly suggests that this growth factor is involved in all aspects of stem cell behaviour--proliferation, migration, and differentiation, through a paracrine mechanism.

Expression of the hepatocyte growth factor receptor in the regenerating rat liver

The c-met oncogene product is a cell-surface receptor, which ligand is believed to be the hepatocyte growth factor. We studied the expression of c-met oncogene in the regenerating rat liver after either partial hepatectomy or CCl4-induced liver injury. Northern blot analysis showed that after partial hepatectomy the transcripts of c-met decreased at 8 h, reached the minimum at 36 h, and returned to the steady level on the seventh day. In contrast with the hepatectomized liver, the transcripts of c-met increased after CCl4 treatment. These observations suggest that c-met transcription may be regulated differently depending on regeneration signals.

Decrease in the hepatic clearance of hepatocyte growth factor in carbon tetrachloride-intoxicated rats

To examine whether a decrease in hepatic uptake, clearance or both of hepatocyte growth factor contributes to increased plasma hepatocyte growth factor levels, we kinetically analyzed hepatic hepatocyte growth factor handling using rats with carbon tetrachloride-induced liver injury in both in vivo and perfused liver systems. After the intravenous administration of tracer 125I-hepatocyte growth factor, the time profile of trichloroacetic acid-precipitable 125I-hepatocyte growth factor was analyzed, and tissue clearance and total body plasma clearance were determined. For the tissues examined (liver, kidney, lung, spleen and adrenal), liver and adrenal clearance of 125I-hepatocyte growth factor decreased significantly. It was found that the hepatic clearance explains the bulk of the total body plasma clearance. The hepatic clearance and the total body clearance decreased to minimums (approximately 40% of control) 24 hr after carbon tetrachloride administration and recovered to near-control values over a 6-day period. At 24 hr after carbon tetrachloride administration, a single-pass liver perfusion of 125I-hepatocyte growth factor was performed, and its results were compared with the control results. After a 15-min perfusion of 125I-hepatocyte growth factor, we washed the liver sequentially with heparin and then with acid buffer to separately determine the cell-surface-bound and internalized 125I-hepatocyte growth factor. In carbon tetrachloride-intoxicated rats, both the acid-washable binding and the internalized 125I-hepatocyte growth factor dropped to almost half of the control values, but the decrease in heparin-washable binding was minimal. In contrast, when 125I-hepatocyte growth factor was perfused with excess unlabeled hepatocyte growth factor (135 pmol/L), mostly saturating the cell-surface receptors, the change in cell-surface-bound 125I-hepatocyte growth factor and internalized 125I-hepatocyte growth factor in carbon tetrachloride-intoxicated rats was minimal. This finding, along with our previous finding that the cell-surface hepatocyte growth factor receptors are greatly down-regulated in carbon tetrachloride-intoxicated rats, suggests that the hepatic clearance of hepatocyte growth factor through receptor-mediated endocytosis decreases in carbon tetrachloride-intoxicated rats. The decrease in the hepatic clearance of hepatocyte growth factor could be one of the causes of the elevated hepatocyte growth factor level in the circulating blood in liver diseases.

Growth stimulation of rat fetal hepatocytes in response to hepatocyte growth factor: modulation of c-myc and c-fos expression

Hepatocyte growth factor, which is a potent growth factor for primary cultured adult hepatocytes, strongly stimulated DNA synthesis of rat fetal (20-day of gestation) hepatocytes. Its mitogenic capacity, measured as (3H)-thymidine incorporation into acid precipitable material was dose dependent, being detectable at 1 ng/ml and maximal at 5 ng/ml. Over 15% of the cells entered into S-phase and mitosis as judged by flow cytometric analysis of the cell cycle. HGF had additive effects with transforming growth factor-alpha, whereas transforming growth factor-beta strongly inhibited DNA synthesis of fetal hepatocytes stimulated by HGF. HGF induced c-fos and c-myc expression in a time-dependent manner, with a maximum at 30 min for c-fos and 8 h for c-myc. These results suggest that HGF may act as a proliferative factor during fetal liver growth.

Rapid and marked induction of hepatocyte growth factor during liver regeneration after ischemic or crush injury

Liver injuries induced by ischemia or physical trauma are characterized by noninflammatory damage frequently observed in a clinical setting. When the liver of rats was injured by ischemic treatment or physical crushing, necrotic tissue degeneration occurred in several sites of lobulus within 24 hr. Hepatocyte growth factor, a potent mitogen for adult rat hepatocytes in primary culture, was markedly induced in the livers of rats injured by ischemia or physical trauma. In both cases, the hepatocyte growth factor messenger RNA level in the injured liver reached about 10 to 20 times that of the normal level during 12 to 24 hr after liver injury. The increase in hepatocyte growth factor messenger RNA correlated well with the degree of liver damage as evaluated by serum ALT activity in the sera of rats. In situ hybridization showed that hepatocyte growth factor messenger RNA expression occurs in nonparenchymal liver cells, primarily in Kupffer cells of the ischemic liver. After the increase of hepatocyte growth factor messenger RNA in the injured liver, a marked compensatory hepatocyte DNA synthesis occurred 48 to 72 hr after these treatments. These results suggest that hepatocyte growth factor acts as a hepatotropic factor for liver regeneration after noninflammatory liver damage caused by ischemia and physical crush, probably through a paracrine mechanism.

Developmental changes in hepatocyte growth factor mRNA and its receptor in rat liver, kidney and lung

Hepatocyte growth factor (HGF) is a mesenchymal-derived factor which induces mitosis, cell movement and morphogenesis of tissue-like structure. We analyzed changes in HGF mRNA and its receptor, the c-met proto-oncogene product, in the liver, kidney and lung during late fetal and postnatal development in rats. In the liver, the HGF-mRNA level was very low during late gestation and in neonates, it increased remarkably and reached a maximum two weeks postnatally, to be followed by a decrease to 33% of the maximum. HGF mRNA in the kidney and lung was either undetectable or very low during late gestation and the neonatal period and increased markedly to reach a maximum, respectively, 3-4 weeks postnatally. HGF-mRNA level in the adult rat lung was fivefold higher than that in the liver and kidney. The number of HGF receptors on plasma membranes of these tissues was low in neonates but there was a rapid increase after birth and a maximum was reached within three weeks. The number of HGF receptors/ng plasma membrane protein at the maximal level was highest in the liver and lowest in the lung. c-met/HGF-receptor mRNA in the liver was also low during late-gestation or in early neonatal periods and increased postnatally. Since HGF-mRNA and HGF-receptor levels changed differently in liver, kidney and lung, the expression of HGF and its receptor may be independently regulated in each organ. However, in these organs, HGF mRNA and the HGF receptor increased within a few weeks of birth, HGF may play roles in organ growth, organ maturation and the maintenance of tissue homeostasis during the postnatal period, presumably through its potential to act as mitogen, motogen and morphogen.

Serum hepatocyte growth factor levels in hepatectomized and nonhepatectomized surgical patients

Serum hepatocyte growth factor levels were measured in hepatectomized and nonhepatectomized surgical patients. The levels were significantly increased and reached a maximum within 7 days after surgery in both groups, returning to preoperative levels 28 days after partial hepatectomy and 7 days after other operations. Multiple regression analysis showed that such maximal hepatocyte growth factor levels were significantly related to having liver cirrhosis and postoperative maximal serum total bilirubin and alanine aminotransferase levels and peripheral white blood cell counts in the hepatectomized group and to postoperative maximal peripheral white blood cell counts and serum C-reactive protein levels in the nonhepatectomized group. However, the levels showed no relation to the resected liver volume and increment of the remaining liver volume 28 days after partial hepatectomy. It is concluded that serum hepatocyte growth factor levels were increased after partial hepatectomy in association with hepatocellular dysfunction and necrosis and systemic inflammation. It is unlikely that the increase was related to liver regeneration.

Signal transduction during liver regeneration: role of insulin and vasopressin

The relationship between cell proliferation and inositol lipid turnover has been studied by comparing the steady state of inositol derivative metabolism in quiescent and regenerating rat hepatocytes isolated at 4 h (G1 phase of first cell cycle) and 24 h (onset of M phase) after partial hepatectomy. The effect of two hormones able to regulate hepatic regeneration, insulin and vasopressin, has been considered, and the results can be summarized as follows: (i) at 4 h after partial hepatectomy, the precursor incorporation into inositol polyphosphates and the particulate phospholipase C activity increase with respect to quiescent hepatocytes, whereas the content of 11, 4, 5P3 does not change, suggesting an increased turnover of this molecule in this step of cell cycle priming; (ii) 24 h after partial hepatectomy, the radioactivity linked to IP3 and IP4, as well as soluble and particulate phospholipase C activity, and IP3 content increase, suggesting the presence, at the onset of M phase, of second messenger accumulation; (iii) only 24 h after partial hepatectomy, the inositol derivative metabolism is affected by vasopressin; and (iv) insulin exerts a modulatory role on inositol polyphosphate production without involving membrane-bound PLC activity or phosphoinositide hydrolysis. These data suggest that inositol-derived signal molecules are associated with hepatic regeneration; moreover, the metabolic pathway of such compounds seems to be regulated so that only specific inositol phosphates are present in each step of the cell cycle.

Marked induction of hepatocyte growth factor mRNA in intact kidney and spleen in response to injury of distant organs

Hepatocyte growth factor (HGF) is a potent mitogen for various epithelial cells, including mature hepatocytes and renal tubular cells. Here, HGF mRNA was found to be markedly increased in non-injured kidney and spleen, when the liver or kidney in rats was injured by 70% partial hepatectomy or unilateral nephrectomy. HGF mRNA increased to 3-4 fold higher level than the normal in the kidney and spleen as well as in the remnant liver after partial hepatectomy. Similarly, HGF mRNA markedly increased in the spleen as well as in the remnant kidney after unilateral nephrectomy. These results suggest that the onset of injury to the liver or kidney may be recognized by distal non-injured organs by the signalling of a humoral factor and that HGF derived from these organs may be involved in the regeneration of liver or kidney, through an endocrine mechanism.

Receptor phenotype underlies differential response of hepatocytes and nonparenchymal cells to heparin-binding fibroblast growth factor type 1 (aFGF) and type 2 (bFGF)

Heparin-binding fibroblast growth factors (HBGF) have been implicated in the regeneration of both parenchymal and nonparenchymal cells of the liver. The response to and phenotype of hepatocyte receptors for HBGF-1 (acidic fibroblast growth factor) and HBGF-2 (basic fibroblast growth factor) were compared to keratinocytes, fibroblasts, and endothelial cells. HBGF-1 stimulated DNA synthesis in hepatocytes, keratinocytes, fibroblasts, and endothelial cells whereas activity of HBGF-2 was limited to fibroblasts and endothelial cells. HBGF-2 antagonized the mitogenic activity of HBGF-1 for hepatocytes and keratinocytes. Hepatocytes and keratinocytes exhibited both high- and low-affinity, nonmatrix receptor sites for HBGF-1, but only low-affinity sites for HBGF-2. The mesenchymal cells displayed only high-affinity sites for both HBGF-1 and HBGF-2. Northern blot and immunochemical analysis revealed that the expression of HBGF receptor genes bek and flg are partitioned between normal hepatocytes and nonparenchymal cells, respectively. Expression of epithelial cell-specific, mesenchymal cell-derived HBGF-7 (keratinocyte growth factor) mRNA in regenerating liver tissue was undetectable relative to HBGF-1. The results support a multifunctional role of HBGF-1 acting through different receptor phenotypes in hepatocyte and nonparenchymal cells during liver regeneration.

Identification and characterization of "injurin," an inducer of expression of the gene for hepatocyte growth factor

The marked and rapid increase of hepatocyte growth factor (HGF) mRNA in the intact lung of rats after partial hepatectomy or unilateral nephrectomy suggests the existence of a humoral factor mediating a signal of injury to distal organs and may induce the expression of HGF gene in these organs. We have now identified a proteinous factor in the sera of rats with injury of liver or kidney that increases HGF mRNA in the intact lung. When the serum of rats with liver insult caused by partial hepatectomy or ischemic treatment was injected i.p. into normal noninjured rats, it induced a marked HGF mRNA expression in the lung of the recipient rats. The addition of serum from rats with various hepatic or renal injuries to MRC-5 human embryonic lung fibroblasts in culture also led to the induction of HGF mRNA expression, so that the production of HGF by MRC-5 cells after treatment with the sera was remarkably increased in the culture medium. However, serum from the normal intact rat induced no HGF production and no HGF mRNA in the lung in vivo and lung fibroblasts in vitro. This factor, which increases HGF production, was purified greater than 200-fold from sera of CCl4-treated rats. The factor proved to be an acid- and heat-stable protein with an apparent molecular mass of 10-20 kDa in SDS/PAGE. Its activity markedly increased within 3-6 hr in the plasma of rats after various treatments that injured the liver or kidney. These results suggest that the factor specifically appears in the blood of rats with organ injury and may be involved in organ regeneration through the potential to increase the synthesis of HGF. Since the factor seems to mediate various organ injuries, we named it "injurin."

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.

Modulation of acute phase protein synthesis in cultured rat hepatocytes by human recombinant hepatocyte growth factor

Human recombinant hepatocyte growth factor (HGF) added to primary cultures of rat hepatocytes stimulates synthesis of some acute phase proteins, especially alpha-2-macroglobulin. As indicated by changes in mRNA abundance HGF increases alpha-2-macroglobulin production at the pretranslational level. Interleukin-6, the main acute-phase cytokine, does not show synergy with HGF in enhancing synthesis of alpha-2-macroglobulin, and inhibits HGF-induced DNA-synthesis. On the other hand, dexamethasone potentiates the effects of HGF on synthesis of DNA and acute phase proteins by cultured rat hepatocytes.

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.

Deletion of kringle domains or the N-terminal hairpin structure in hepatocyte growth factor results in marked decreases in related biological activities

To determine the essential domain for biological activity in the hepatocyte growth factor (HGF) molecule, we prepared various mutated recombinant HGFs using site-directed mutagenesis, and examined the effects on DNA synthesis in hepatocytes, scattering of MDCK cells and the antiproliferative activity on HepG2 hepatoma cells. Native HGF and mutant HGFs, in which Gln534 and/or Tyr673 were respectively substituted for His and Ser to coincide with the catalytic triad amino acids in plasmin, markedly stimulated DNA synthesis of hepatocytes and scattering of MDCK cells but inhibited DNA synthesis of HepG2 cells. The mutant HGF deleted with the third or fourth kringle domain resulted in marked decrease of all three biological activities, while deletion of the N-terminal hairpin structure or the first or second kringle domain almost completely inactivated biological activities. We propose that the N-terminal hairpin structure and the first and second kringle domains are essential for biological activities of HGF and possibly for binding to its receptor.