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

Hepatocyte growth factor (HGF) and hemodialysis: physiopathology and clinical implications

Hepatocyte growth factor (HGF) is a pleiotropic cytokine which exerts a variety of effects on several cells, being involved in the regulation of many biological processes, such as inflammation, tissue repair, morphogenesis, angiogenesis, tumour propagation, immunomodulation of viral infections and cardio-metabolic activities. Patients undergoing regular hemodialysis (HD) present elevated levels of HGF, mainly due to the leukocyte activation associated with HD treatment. High HGF levels might account for specific clinical features of HD patients, i.e. mild liver damage in course of HCV-infection and high cardiovascular risk profile. Moreover, in patients with acute kidney injury, the induction of HGF may represent a crucial step to promote renal recovery, which can have important prognostic consequences in the short and long-term. In this review we discuss the mechanisms underlying HGF production in HD patients, the role of HGF in this particular patient population and the potential clinical implications derived from the study of HGF in HD patients.

Effect of hemodialysis schedules and membranes on hepatocyte growth factor and hepatitis C virus RNA levels

Hemodialysis induces production of the hepatocyte growth factor (HGF) and decrease of serum hepatitis C virus (HCV) RNA in patients with HCV infection, but it is not known if the hemodialysis schedule or type of membrane affect both the HGF production and HCV viremia. The effects on both parameters of alternate-day intermittent hemodialysis and short-daily hemodialysis and high and low flux membranes were investigated in 41 patients treated by hemodialysis. Sixteen (39%) patients were anti-HCV positive and 11 (69%) had HCV RNA. Twenty-six patients were on alternate-day intermittent and 15 on short-daily hemodialysis. High flux membranes were used for 29 patients and low flux membranes for 12 patients. A decrease in HCV RNA was observed at the end of hemodialysis (8.6 x 10(5) +/- 1.1 x 10(6) IU/ml vs. 4.4 x 10(5) +/- 7.3 x 10(5) IU/ml, P = 0.003). The proportion of HCV RNA decrease was similar in patients dialyzed with both schedules and with both types of membranes. The HGF levels increased from 2,605.9 +/- 1,428.7 to >8,000 pg/ml at 15 min. At the end of the session, the HGF levels decreased to 5,106.7 +/- 2,533.9 pg/ml. The HGF levels at the start of the next session were similar to those at baseline (2,680.0 +/- 1,209.3 pg/ml). The increase and dynamics of the HGF levels were similar in patient's hemodialyzed with both schedules and with both types of membranes. These results suggest that changes in HCV RNA and HGF levels during hemodialysis are not influenced by the schedule or type of membrane used.

Expression of p53/HGF/c-met/STAT3 signal in fetuses with neural tube defects

Neural tube defects (NTD) are morphogenetic alterations due to a defective closure of neural tube. Hepatocyte growth factor (HGF)/c-met system plays a role in morphogenesis of nervous system, lung, and kidney. HGF/c-met morphogenetic effects are mediated by signal transducers and activators of transcription (STAT)3 and both HGF and c-met genes are regulated from p53. The aim of our study was to analyze mRNA and protein expressions of p53, HGF, c-met, and STAT3 in fetuses with NTD. By reverse transcriptase-polymerase chain reaction and immunohistochemistry, we analyzed neural tissues from four NTD fetuses and the corresponding non-malformed lungs, kidneys and placentas. We found a reduced mRNA expression of HGF/c-met/STAT3 pathway, in the malformed nervous systems and placentas. The reduced expression of this pathway correlated with the absence of p53 in all these samples. On the contrary, detectable expression levels of p53, HGF, c-met, and STAT3 were observed in non-malformed lungs and kidneys obtained from the same fetuses. Comparable results were obtained by immunohistochemistry, with the exception of p53, which was undetected in all fetal tissues. In conclusion, in NTD fetuses, both the defective neural tube tissue and the placenta have a reduction in all components of the p53/HGF/c-met/STAT3 cascade. This raises the possibility of using the suppression of these genes for early diagnosis of NTD especially on chorionic villus sampling.

Hepatocyte growth factor controls the proliferation of cultured epidermal melanoblasts and melanocytes from newborn mice

Mouse epidermal melanoblasts and melanocytes preferentially proliferated from disaggregated epidermal cell suspensions derived from newborn mouse skin in a serum-free melanocyte-proliferation medium (MDMD) and melanoblast-proliferation medium (MDMDF) supplemented with dibutyryl adenosine 3':5'-cyclic monophosphate (DBcAMP) and/or basic fibroblast growth factor (bFGF). Pure cultured primary melanoblasts and melanocytes were further cultured with MDMD/MDMDF supplemented with hepatocyte growth factor (HGF) from 14 days (keratinocyte depletion). The HGF increased the number of melanoblasts and melanocytes, but not the percentage of differentiated melanocytes in the melanoblast-melanocyte population in the absence of keratinocytes. Flow cytometry analysis showed that melanoblasts and melanocytes in the S and/or G2/M phases of the cell cycle were increased by the treatment with HGF. Moreover, an anti-HGF antibody supplemented to MDMD/MDMDF from the initiation of the primary culture (in the presence of keratinocytes) inhibited the proliferation of melanoblasts and melanocytes, but not the differentiation of melanocytes. These results suggest that HGF is a keratinocyte-derived factor involved in regulating the proliferation of epidermal melanoblasts and melanocytes from newborn mice in cooperation with cAMP elevators and/or bFGF.

Hepatocyte growth factor upregulates alpha2beta1 integrin in Madin-Darby canine kidney cells: implications in tubulogenesis

It has been well established that hepatocyte growth factor (HGF) induces branching tubule formation of Madin-Darby canine kidney (MDCK) cells cultured in collagen gel. Tubulogenesis per se requires the involvement of cell proliferation, migration, focalization proteolysis, cell-cell interaction and differentiation. However, signaling pathways and proteins involved in HGF-induced tubulogenesis by MDCK cells have not been thoroughly studied. Because cell-matrix interactions play important roles in tubulogenesis, we analyzed whether HGF altered the expression of extracellular matrix receptor (alpha2, alpha3, beta1 and alphavbeta3 integrin). We found that among those proteins examined, alpha2beta1 integrin levels were enhanced by HGF. HGF-induced upregulation of alpha2beta1 integrin was mediated via upregulation of alpha2 integrin mRNA abundance. Cycloheximide blocked the HGF-induced increase in alpha2 integrin mRNA expression. To understand the signaling pathways leading to an HGF-induced increase in alpha2beta1 integrin levels, PD98059 (MEK1 inhibitor), LY294002 (PI3-kinase inhibitor), and GF109203X (PKC inhibitor) were used. We found that PD98059 blocked the HGF-induced increase in alpha2beta1 integrin expression. Furthermore, 5E8 (specific anti-alpha2beta1 integrin antibody) was employed to elucidate the potential role of HGF-induced upregulation of alpha2beta1 integrin in branching morphogenesis. 5E8 did not alter HGF-induced scattering effects but disrupted HGF-induced branching tubulogenesis in collagen gel via inhibition of cell-cell interactions and growth. Taken together, HGF upregulates alpha2beta1 integrin expression via an indirect pathway, the results of which contribute to the regulation of cell-cell interactions and cell growth during branching morphogenesis in collagen gel.

Immunohistochemical analysis of atypical ductular reaction in the human liver, with special emphasis on the presence of growth factors and their receptors

AIMS/BACKGROUND

The objective of this study was to characterize the expression of transforming growth factor-alpha/epidermal growth factor receptor, hepatocyte growth factor/c-met, transforming growth factor-beta/Type I-II transforming growth factor-beta receptors, stem cell factor, urokinase plasminogen activator, smooth muscle actin, CD34 and alpha-fetoprotein in human liver samples with (sub)massive necrosis of different etiology containing atypical ductular reaction.

METHODS

Their presence was studied by immunohistochemistry on paraffin-embedded tissue sections.

RESULTS

Transforming growth factor-alpha and -beta, hepatocyte growth factor and their receptors were demonstrated in the ductules; additionally stem cell factor and urokinase plasminogen activator were also expressed. The atypical ductules were surrounded by smooth muscle actin-positive activated stellate cells.

CONCLUSION

These phenotypic similarities confirm that the atypical ductules in the human liver may be equivalent of oval cells in the rat liver, which are regarded as the progeny of stem cells. That is, the atypical ductular proliferation may correspond to a stem cell-fed regenerative process.

HGF promotes adhesion of ATP-depleted renal tubular epithelial cells in a MAPK-dependent manner

Hepatocyte growth factor (HGF) has been shown to enhance recovery from renal tubular ischemia. We investigated the possibility that HGF improves recovery by preventing ischemia-induced loss of cell adhesion. Murine inner medullary collecting duct-3 (mIMCD-3) cells subjected to 90% ATP depletion demonstrated a 55% decrease in adhesion, an effect that was completely reversed by the addition of HGF. Assays examining release of adherent cells revealed similar results with 30 min of ATP depletion causing loss of adhesion of 25% of mIMCD-3 cells and HGF completely reversing this effect. In contrast, HGF was unable to reverse the loss of adhesion of cells exposed to 99% ATP depletion. Examination of the mitogen-activated protein kinase (MAPK) signaling pathway revealed that HGF could induce extracellular signal-regulated kinase (ERK) phosphorylation in control and 90% ATP-depleted cells but not in 99% ATP-depleted cells. Inhibition of ERK activation with U0126 completely blocked the HGF-dependent reversal of ATP-depleted cell adhesion. Thus ATP-depleted cells demonstrate a marked decrease in cell adhesion that is reversible by the addition of HGF. This effect of HGF requires activation of the MAPK pathway.

Expression and localization of scatter factor/hepatocyte growth factor in human astrocytomas

Scatter factor/hepatocyte growth factor (SF/HGF) is a pleiotropic cytokine that has been implicated in glioma invasion and angiogenesis. The SF/HGF receptor, MET, has been found to be expressed in neoplastic astrocytes as well as in endothelial cells of the tumor vasculature. Both SF/HGF and MET expression have also been described to correlate with the malignancy grade of human gliomas. However, most glioblastoma cell lines lack SF/HGF expression, raising the question of the cellular origin of SF/HGF in vivo. Using in situ hybridization, we analyzed glioblastomas, anaplastic astrocytomas, diffuse astrocytomas, pilocytic astrocytomas, and normal brain for the expression of SF/HGF mRNA. We detected strong SF/HGF expression by the majority of the tumor cells and by vascular endothelial cells in all glioblastoma specimens analyzed. Combined use of in situ hybridization with fluorescence immunohistochemistry confirmed the astrocytic origin of the SF/HGF-expressiong cells. In contrast, CD68-immunoreactive microglia/macrophages, as well as vascular smooth muscle cells reactive to alpha-smooth muscle actin, lacked SF/HGF expression. In anaplastic, diffuse, and pilocytic astrocytomas, SF/HGF expression was confined to a subset of tumor cells, and signals were less intense than in glioblastomas. In addition, we detected SF/HGF mRNA in cortical neurons. SF/HGF expression was not up regulated around necroses or at tumor margins. MET immunoreactivity was observed in GFAP-expressing astrocytic tumor cells and endothelial cells as well as in a subset of microglia/macrophages. We conclude that in vivo, both autocrine and paracrine stimulation of tumor cells and endothelium through the SF/HGF-MET system are likely to contribute to tumor invasion and angiogenesis. Lack of SF/HGF expression by most cultured glioblastoma cells is not representative of the in vivo situation and most likely represents a culture artifact.

Expression of c-Met in developing rat hippocampus: evidence for HGF as a neurotrophic factor for calbindin D-expressing neurons

Hepatocyte growth factor-scatter factor (HGF) is expressed in different parts of the nervous system, and has been shown to exhibit neurotrophic activity. Here we show that c-Met, the receptor for HGF, is expressed in developing rat hippocampus, with the highest levels during the first postnatal weeks. To study the function of HGF, hippocampal neurons were prepared from embryonic rats and treated with different HGF concentrations. In these cultures, HGF increased the number of neurons expressing the 28-kDa calcium-binding protein (calbindin D) in a dose-dependent manner. The effect of HGF was larger than that observed with either brain-derived neurotrophic factor (BDNF) or neurotrophin-3 (NT-3), and cotreatment of the cultures with HGF and the neurotrophins was additive with respect to calbindin D neurons. Besides affecting the number of neurons, HGF significantly increased the degree of sprouting of calbindin D-positive neurons, suggesting an influence on neuronal maturation. BDNF and NT-3 stimulated neurite outgrowth of calbindin D neurons to a much smaller degree. In contrast to calbindin D neurons, HGF did not significantly increase the number of neurons immunoreactive with the neurotransmitter gamma-aminobutyric acid (GABA) in the hippocampal cultures. Immunohistochemical studies showed that c-Met-, calbindin D- and HGF-immunoreactive cells are all present in the dentate gyrus and partly colocalize within neurons. These results show that HGF acts on calbindin D-containing hippocampal neurons and increases their neurite outgrowth, suggesting that HGF plays an important role for the maturation and function of these neurons in the hippocampus.

Impaired response to hepatocyte growth factor in FRTL-5 rat thyroid cells expressing a functional hepatocyte growth factor receptor

The FRTL-5 rat thyroid cell line is widely used for studies of thyrocyte function and growth. The objective of the present study was to investigate the effects of hepatocyte growth factor (HGF) on FRTL-5 cells. HGF has previously been known to be a potent regulator of thyrocyte growth and differentiation. Met, the receptor for HGF was expressed in FRTL-5 cells, as well as in primary cultures of porcine thyrocytes included in the study as control. On HGF stimulation Met was tyrosine phosphorylated in both porcine and FRTL-5 cells, indicating an activation of the receptor. Addition of HGF induced changes of cell shape, scattering and proliferation of the porcine thyrocytes, but not in the FRTL-5 cells; yet, a functional coupling of Met to the p85 subunit of the phosphatidylinositol-3'-kinase (PI3'-K) in coprecipitation experiments, formation of focal adhesions detected in immunofluorescence staining with an antivinculin antibody, and induction of c-fos mRNA in Northern blot analysis was observed in FRTL-5 cells, showing a transduction of the HGF/Met signal. In summary, despite the expression of apparently functional Met, the FRTL-5 cells are unable to properly respond to HGF.

Unique epithelial cell production of hepatocyte growth factor/scatter factor by putative precancerous intestinal metaplasias and associated "intestinal-type" biliary cancer chemically induced in rat liver

Recently, we observed that Met, the receptor for hepatocyte growth factor/scatter factor (HGF/SF), is overexpressed in epithelial cells of both early-appearing intestinal metaplastic glands in precancerous hepatic cholangiofibrotic tissue and neoplastic glands in later developed intestinal-type of cholangiocarcinoma originated from the furan rat model of cholangiocarcinogenesis when compared with normal and hyperplastic intrahepatic biliary epithelia. We now show that HGF/SF is also aberrantly expressed in a manner closely paralleling that of its receptor in the neoplastic epithelial cells of furan-induced rat cholangiocarcinomas and in a majority of metaplastic epithelial cells within earlier formed precancerous hepatic cholangiofibrotic tissue. Using in situ hybridization and reverse transcription-polymerase chain reaction (RT-PCR), we further showed specific expression of HGF/SF messenger RNA (mRNA) in a novel rat cholangiocarcinoma epithelial cell line overexpressing Met. This cholangiocarcinoma cell line, termed C611B, was established from tumorigenic cells isolated from a furan-induced transplantable tumor. Moreover, we detected by in situ hybridization strong expression of HGF/SF mRNA transcripts in the cancerous epithelial glands of cholangiocarcinoma developed in recipient rats after in vivo cell transplantation of C611B cells. In contrast, mRNA transcripts and protein immunoreactivity for this cytokine were not detected in hepatocytes and biliary epithelial cells in adult normal rat liver nor in rat hyperplastic intrahepatic biliary epithelium. Our results clearly show that HGF/SF becomes aberrantly expressed in cholangiocarcinoma epithelium and in putative precancerous intestinal metaplastic epithelium induced in the liver of furan-treated rats.

Hepatocyte growth factor/scatter factor-induced intracellular signalling

Hepatocyte growth factor (HGF) identical to scatter factor (SF) is a glycoprotein involved in the development of a number of cellular phenotypes, including proliferation, mitogenesis, formation of branching tubules and, in the case of tumour cells, invasion and metastasis. This fascinating cytokine transduces its activities via its receptor encoded by the c-met oncogene, coupled to a number of transducers integrating the HGF/SF signal to the cytosol and the nucleus. The downstream transducers coupled to HGF/MET, most of which participate in overlapping pathways, determine the development of the cell's phenotype, which in most cell types is dual.

Hepatocyte growth factor overexpression in the islet of transgenic mice increases beta cell proliferation, enhances islet mass, and induces mild hypoglycemia

Hepatocyte growth factor (HGF) is produced in pancreatic mesenchyme-derived cells and in islet cells. In vitro, HGF increases the insulin content and proliferation of islets. To study the role of HGF in the islet in vivo, we have developed three lines of transgenic mice overexpressing mHGF using the rat insulin II promoter (RIP). Each RIP-HGF transgenic line displays clear expression of HGF mRNA and protein in the islet. RIP-mHGF mice are relatively hypoglycemic in post-prandial and fasting states compared with their normal littermates. They display inappropriate insulin production, striking overexpression of insulin mRNA in the islet, and a 2-fold increase in the insulin content in islet extracts. Importantly, beta cell replication rates in vivo are two to three times higher in RIP-HGF mice. This increase in proliferation results in a 2-3-fold increase in islet mass. Moreover, the islet number per pancreatic area was also increased by approximately 50%. Finally, RIP-mHGF mice show a dramatically attenuated response to the diabetogenic effects of streptozotocin. We conclude that the overexpression of HGF in the islet increases beta cell proliferation, islet number, beta cell mass, and total insulin production in vivo. These combined effects result in mild hypoglycemia and resistance to the diabetogenic effects of streptozotocin.

Expression of Hepatocyte Growth Factor (HGF) and its Receptor (MET) in Medullary Carcinoma of the Thyroid

The tyrosine kinase receptor encoded by the MET oncogene has the unusual property of mediating the invasive growth of epithelial cells upon binding with the hepatocyte growth factor (HGF). The MET/HGF receptor is known to be overexpressed in thyroid carcinomas originated from follicular cells, but has not been reported in C cell tumors. To investigate the role of HGF and of its receptor (encoded by MET oncogene) in medullary carcinoma of the thyroid (MCT), we studied the expression of HGF and MET in 20 cases by means of different techniques. By RT-PCR, HGF mRNA was found in 10/20 cases, while MET mRNA presence was demonstrated in 8/20, of which 7 also expressed HGF. Northern blot analysis and in situ hybridization were performed in selected cases and confirmed RT-PCR data in some cases, although the lower sensitivity of these procedures did not allow the identification of all RT-PCR positive cases. By immunohistochemistry (using specific monoclonal antibodies) HGF was demonstrated in 8/9 RT-PCR positive cases and a monoclonal to MET immunostained 5/6 RT-PCR positive cases. All receptor positive cases also expressed the ligand in the same tumor cell population. These findings demonstrate MET and HGF co-expression in a subset of MCT, in which autocrine/paracrine circuits may be active. No correlation was found between HGF/MET expression and clinico-pathological parameters, except for the more common multifocality of HGF/MET positive MCT. Whether the potential activation of MET in MCT is responsible for local invasion and malignant evolution is to be further investigated, especially in multifocal and aggressive tumors.

Growth-factor-dependent migration of human lung-cancer cells

Human lung tumors express different types of growth-factor receptors and corresponding ligands that might modulate several biological functions such as proliferation, differentiation, adhesion, and chemotaxis. In the present study, we have investigated the expression of different growth-factor receptors and their ligands in 5 established human lung-cancer cell lines. Using RT-PCR, we found that IGF-II/mannose-6-phosphate (M6P), c-met, EGF and c-kit receptors are expressed in 5/5 human lung-cancer cell lines. In order to investigate the biological function of these receptors, we performed Boyden-chamber assays using various growth factors as chemo-attractants. Human non-small-cell-lung-cancer cells (non-SCLC) migrated to recombinant human (rh)IGF I and IGF II at concentrations ranging from 1 to 1000 ng/ml, to HGF at 10 to 100 ng/ml, to EGF at 1 to 100 ng/ml and SCF at 1 to 50 ng/ml. In addition, we performed Boyden-chamber assays using U-1810-, U-1752- and Wart-derived serum-free conditioned medium as chemo-attractants. Serum-free conditioned medium stimulated migration of producer cells in a dose-dependent manner. The autocrine motility stimulating effect of U-1810-derived serum-free conditioned medium could be inhibited by 50% in the presence of neutralizing ahIGF-II antibodies in the assay, suggesting a possible autocrine motility loop in vitro.

Non-autocrine, constitutive activation of Met in human anaplastic thyroid carcinoma cells in culture

Activation of Met by its ligand HGF has been shown to elicit both mitogenic and motogenic responses in thyrocytes in vitro. In the present study we have investigated the expression of Met in human anaplastic thyroid carcinoma cells in culture. There was a variation in expression level and size of Met in the different cell lines; high Met expression was found in four cell lines, compared to non-neoplastic human thyrocytes. Treatment with glucoproteinase F showed that the size differences observed were due to variances in the degree of glycosylation. Interestingly, in cell lines with high expression of Met, the receptor proteins were found to be constitutively tyrosine phosphorylated. None of these cell lines expressed HGF mRNA, and addition of suramin did not affect the level of tyrosine phosphorylation of Met in unstimulated cells, suggesting the absence of autocrine stimulatory pathways. Furthermore, we did not observe MET gene amplification, activating mutations or phosphatase defects. The tyrosine phosphorylated receptors appeared functionally active since the receptors associated with the adaptor molecule Shc. In summary, we have found ligand-independent constitutively activated Met in four out of six anaplastic thyroid carcinoma cell lines.

Expression of hepatocyte growth factor (HGF) and HGF receptor (c-met) proteins in liver diseases: an immunohistochemical study

BACKGROUND

Hepatocyte growth factor (HGF) is a potent mitogen for hepatocytes in vivo as well as in vitro. Serum levels of HGF vary in liver diseases, reflecting liver damage and dysfunction. However there are no studies reporting expression of HGF and HGF receptor (c-met protein) simultaneously in various liver diseases.

METHODS

To clarify the clinical significance of HGF/c-met protein expression in liver diseases, liver tissues from 62 patients consisting of 7 with acute hepatitis (AH), 20 with chronic hepatitis (CH), 9 with liver cirrhosis (LC) and 26 with hepatocellular carcinoma (HCC) were immunohistochemically examined.

RESULTS

Intense staining of HGF was observed in patients from AH, CH and LC, although no immunoreactivity was seen in HCC. The expression of c-met protein was higher in patients with HCC and AH than in those with CH (p < 0.05). A correlation of immunoreactivity between HGF and c-met protein was not observed expect in patients with LC (p < 0.01). The extent of c-met expression had no correlation with differentiation of HCC, tumour size, presence of portal invasion, or serum AFP levels.

CONCLUSION

The results of the present study suggest that HGF plays an important role in human liver diseases, mostly in a manner independent of c-met protein expression.

Expression of the hepatocyte growth factor-like protein gene in human hepatocellular carcinoma and interleukin-6-induced increased expression in hepatoma cells

Human hepatocellular carcinoma is one of the most frequent malignant tumors. It may occur following exposure to various agents, including viruses and chemical carcinogens; however, the underlying mechanisms of the hepatocarcinogenesis are not known. The present study is the result of our search for genes which may be abundantly expressed in human primary liver carcinoma. One of these genes was found to encode the human hepatocyte growth factor-like protein (HGFLP), also known as macrophage-stimulating protein. HGFLP is structurally homologous to hepatocyte growth factor, a potent growth factor for liver. HGFLP mRNA was also found to be overexpressed in a hepatoblastoma sample and in a sample of subacute fulminant hepatic necrosis. In a study on the effects of cytokines on the expression of HGFLP, we found that IL-6 increased expression of HGFLP mRNA in Hep G2 cells, but IL-1alpha, IL-1beta and TNF-alpha had no effect. An increase in HGFLP could be the result of inflammation and/or tissue injury and its overexpression may prove to be useful as an indicator of hepatoma.

Serum hepatocyte growth factor as an index of disease status of patients with colorectal carcinoma

To evaluate the clinical significance of serum levels of hepatocyte growth factor (HGF) in colorectal cancer patients, we measured the venous and portal concentrations of HGF in 60 patients. The tissue concentrations in the tumour and adjacent normal mucosa were also determined. The serum HGF concentration for the peripheral venous blood of the patients was significantly higher than that in normal controls. The content of HGF in cancer tissue was also significantly higher than that in normal mucosa, and it was correlated with the serum HGF concentration for the peripheral venous blood. The serum concentration of HGF reflected pathological features, including tumour size and lymph node or liver metastasis, and it showed an association with various preoperative nutritional parameters and the preoperative haemoglobin level. The serum HGF concentration was also correlated with the serum concentrations of immunosuppressive acidic protein and interleukin-6, indices of the host's immunological condition. Serum HGF seems to be a useful index of the disease status of patients with colorectal carcinoma.

Hepatocyte growth factor (HGF/SF) in Alzheimer's disease

Hepatocyte growth factor (HGF/SF), is a heparin-binding polypeptide which stimulates DNA synthesis in a variety of cell types and also promotes cell migration and morphogenesis. HGF/SF mRNA has been found in a variety of tissues, including brain. In a previous study, we showed that basic fibroblast growth factor (bFGF), another heparin-binding protein is increased in Alzheimer's disease (AD), and appears to be associated with the heparan-sulfate proteoglycans bound to B/A4 amyloid (Biochem. Biophys. Res. Commun. 171 (1990) 690-696). In the present study, we examined the distribution of HGF/SF in 4% paraformaldehyde fixed samples of prefrontal cortex from control and Alzheimer patients, in order to assess the possibility that HGF/SF may be found in association with the pathologic changes which occur in Alzheimer's disease. A specific polyclonal antibody directed against HGF/SF revealed widespread HGF/SF-like immunoreactivity in both the cerebral cortex and white matter. Confocal microscopy confirmed that HGF/SF could be found in both GFAP positive astrocytes and LN3 positive microglia cells, as well as rare scattered cortical neurons. In the AD cases studied, the immunoreactivity was increased within both the astrocytes and microglial cells surrounding individual senile plaques. No staining was seen within the neurofibrillary tangles. Western blot analysis confirmed the normal molecular form of HGF/SF in Alzheimer's disease. Quantitative ELISA assay demonstrated a significant increase in HGF/SF in AD relative to age matched controls. These studies confirm the presence of HGF/SF immunoreactivity within neurons, astrocytes and microglial cells. They also indicate that HGF/SF may be increased within senile plaques as a function of the gliosis and microglial proliferation which occurs in association with these structures in Alzheimer's disease.

Expression of HGF and cMet in the developing and adult brain

Hepatocyte growth factor (HGF) was recently recognized as a potential neurotrophic factor in the developing brain. We studied expression of HGF and its receptor using Northern blot analysis and in situ hybridization for mRNA and double immunofluorescent laser confocal microscopy. HGF and cMet messages were abundant in the hippocampus of both human and rat brains. In this region, both messages were localized in the neuronal layer. Segregation of HGF predominantly in the hippocampal CA3-4 and cMet in CA1 supports the hypothesis that HGF may mediate important neurotrophic functions in both developing and adult brains.

A natural hepatocyte growth factor/scatter factor autocrine loop in myoblast cells and the effect of the constitutive Met kinase activation on myogenic differentiation

As a rule, hepatocyte growth factor/scatter factor (HGF/SF) is produced by mesenchymal cells, while its receptor, the tyrosine kinase encoded by the met proto-oncogene, is expressed by the neighboring epithelial cells in a canonical paracrine fashion. In the present work we show that both HGF/SF and met are coexpressed by undifferentiated C2 mouse myoblasts. In growing cells, the autocrine loop is active as the receptor exhibits a constitutive phosphorylation on tyrosine that can be abrogated by exogenously added anti-HGF/SF neutralizing antibodies. The transcription of HGF/SF and met genes is downregulated when myoblasts stop proliferating and differentiate. The coexpression of HGF/SF and met genes is not exclusive to C2 cells since it has been assessed also in other myogenic cell lines and in mouse primary satellite cells, suggesting that HGF/SF could play a role in muscle development through an autocrine way. To analyze the biological effects of HGF/SF receptor activation, we stably expressed the constitutively activated receptor catalytic domain (p65(tpr-met)) in C2 cells. This active kinase determined profound changes in cell shape and inhibited myogenesis at both morphological and biochemical levels. Notably, a complete absence of muscle regulatory markers such as MyoD and myogenin was observed in p65(tpr-met) highly expressing C2 clones. We also studied the effects of the ectopic expression of human isoforms of met receptor (h-met) and of HGF/SF (h-HGF/SF) in stable transfected C2 cells. Single constitutive expression of h-met or h-HGF/SF does not alter substantially the growth and differentiation properties of the myoblast cells, probably because of a species-specific ligand-receptor interaction. A C2 clone expressing simultaneously both h-met and h-HGF/SF is able to grow in soft agar and shows a decrease in myogenic potential comparable to that promoted by p65(tpr-met) kinase. These data indicate that a met kinase signal released from differentiation-dependent control provides a negative stimulus for the onset of myogenic differentiation.

Scatter factor binds to thrombospondin and other extracellular matrix components

Scatter factor (SF) is an angiogenic growth factor that stimulates motility and invasion of carcinoma cells. SF is present in the extracellular matrix (ECM) of breast cancers, where it might act to promote tumor cell invasion and angiogenesis. To investigate how SF is incorporated into the ECM, we studied the binding of SF to various ECM components using a solid-phase binding assay based on the SF enzyme-linked immunosorbent assay. We found that SF binds to a variety of ECM molecules, with different binding capacities. The highest SF binding capacities were observed for thrombospondin-1 (TSP-1), fibronectin (Fn), and heparan sulfate proteoglycan, although SF did not bind to albumin. Mature two-chain SF and precursor single-chain SF bound approximately equally well to TSP-1 and Fn. Moreover, two SF alpha-chain peptides (NK1 and NK2) both bound to TSP-1 and Fn, suggesting that the whole SF molecule is not required for binding. Based on binding competition assays, TSP-1 exhibited higher affinity for SF than did nine other ECM molecules, including Fn and heparan sulfate proteoglycan. Although heparin in solution potently inhibited the binding of SF to TSP-1-coated surfaces, even very high concentrations of heparin could not elute SF already bound to TSP-1. SF binding was modulated by binding interactions among ECM molecules (TSP-1-Fn, TSP-1-collagen I, and Fn-collagen I), suggesting that the matrix capacity to bind SF depends upon its exact composition. SF bound in a dose-dependent fashion to ECMs secreted by three human breast carcinoma cell lines. Binding of SF to matrices from all three cell lines was significantly inhibited by preincubation of the matrices with antibodies against TSP-1, whereas antibodies against several other ECM components were less effective or ineffective in inhibiting SF binding. In addition, TSP-1 markedly inhibited chemotaxis of microvascular endothelial cells toward SF and SF-induced angiogenesis in the rat cornea neovascularization assay. Our findings suggest that 1) SF interacts with a variety of ECM components, 2) high affinity SF-TSP-1 interactions may mediate the binding of SF to the breast cancer matrix, and 3) the SF-TSP-1 interaction may contribute to modulation of angiogenesis. Possible implications of these findings for tumor angiogenesis are discussed.

Hepatocyte growth factor mRNA in human liver cirrhosis as evidenced by in situ hybridization

BACKGROUND

Hepatocyte growth factor (HGF) is a strong mitogen of hepatocytes, and HGF-producing cells have been reported to be Ito cells or endothelial cells in the sinusoid of the liver. No reports have been published about the localization of HGF mRNA in human liver cirrhosis.

METHODS

In situ hybridization (ISH) for HGF mRNA was performed in 5 normal liver and 16 human liver cirrhosis specimens, using 1 RNA probe and 3 oligonucleotide probes labeled with 35S.

RESULTS

A positive signal was obtained in 15 of these cases. In five normal liver specimens, signals of HGF mRNA were not obtainable. In 13 of the 15 cases of liver cirrhosis, HGF mRNA was present in the periphery of the regenerative nodules. This peripheral pattern was seen in regenerative nodules with irregular nodule to septal interfaces. Combined immunohistochemistry and ISH showed that vimentin and CD 68-positive cells consistent with macrophages expressed HGF mRNA in such cases. In three specimens with diffuse signal for HGF mRNA in the hepatic nodules, signals localized to the sinusoidal spaces. HGF mRNA-positive cells were spindled and polygonal in shape, suggesting endothelial, Kupffer, and/or Ito cells of origin. In the diffuse pattern the peripheral margins of the regenerative nodules appeared well-defined. In one case regenerative nodules with both diffuse and peripheral signal patterns were present in the same section. There was no relationship among HGF mRNA, etiology, and macroscopic appearance of liver cirrhosis.

CONCLUSIONS

HGF gene transcription in human liver cirrhosis nodules may be heterogeneous, probably related to the degree of activity of the regenerative nodules. HGF appears to be produced by the mesenchymal cells, including Ito cells, macrophages (Kupffer cells), and endothelial cells in human liver cirrhosis.

Neurotrophic effect of hepatocyte growth factor on central nervous system neurons in vitro

Although the expression of hepatocyte growth factor (HGF) and its receptor, proto-oncogene c-met, has been demonstrated in the central nervous system (CNS), the function of HGF in the CNS was not fully understood. In the present studies, we determined the effects of HGF on neuronal development in neocortical explant and mesencephalic neurons obtained from embryonic rat brain. HGF clearly enhanced neurite outgrowth in neocortical explants. In the mesencephalic culture, the number of tyrosine hydroxylase (TH)-positive neurons was significantly higher in the HGF-treated wells and the neurites of the TH-positive neurons appear to be more developed. Moreover, the dopamine uptake into mesencephalic neurons was also enhanced by HGF treatment, indicating that HGF promotes the survival and/or maturation of mesencephalic dopaminergic neurons. In both neocortical explants and mesencephalic neurons, c-met autophosphorylation was induced by HGF and MAP kinase activation was also detected in the neocortical explant. Furthermore, Western blot analysis of the cultured CNS cells revealed that HGF was expressed mainly in microglia. These results suggest that HGF from microglia has neurotrophic activity on the CNS neurons and plays significant roles in the development of the CNS.

Expression of HGF mRNA in human rejecting kidney as evidenced by in situ hybridization

In situ hybridization was performed to demonstrate hepatocyte growth factor (HGF) mRNA in two patients with normal kidney and in 23 patients with allograft nephrectomy. In situ hybridization was combined with immunohistochemistry to identify HGF-producing cells. In the two patients with normal kidney, no HGF mRNA was obtainable. In 15 of the 23 allograft patients, signals of HGF mRNA were detectable. In six of these 15 patients, the signals were present mainly at the medullocortex junction, and in the other nine patients at the cortex and/or medulla. Strong and frequent signals were present in gland-like structures in 15 cases. Some scattered signals were also present in the fibrosed glomeruli in five cases, in the thickened intimas of large arteries in three cases, and in the arterial muscle coats of two cases. Combined immunohistochemistry and in situ hybridization showed that HGF mRNA-positive cells in gland-like arrangements were also positive for cytokeratin and negative for factor VIII. Cells with HGF mRNA signal and located in the arterial media were also positive for actin. These findings suggest that HGF mRNA is transcribed both in the urinary tubular epithelium and in the mesenchymal cells (fibroblasts, and smooth muscle cells in chronic vascular rejection and endothelial cells and/or mesangial cells in transplant glomerulopathy) in human rejecting kidney.

Biliary proliferation and adaptation in furan-induced rat liver injury and carcinogenesis

Distinctive intrahepatic biliary adaptation responses occur in the liver of rats subjected to select hepatotoxic and/or carcinogenic treatments with the nongenotoxic cholangiocarcinogenic agent furan. Specifically, metaplastic small intestinal-like glands closely resembling in their cellular composition the crypts of Lieberkühn of normal rat small intestine were selectively derived from putative hyperplastic bile ductule-like progenitor structures in the right and caudate liver lobes of young adult Fischer-344 male rats given furan by gavage at a daily dose of 30-45 mg/kg body weight, 5 times weekly, over a 2-6-wk treatment period. Longer term chronic administration of furan at 30 mg/kg/day for 9-19 wk resulted in the preferential development of primary hepatic adenocarcinomas, which arose at 70-100% incidences from right/caudate liver lobes and which were characterized by small intestine mucosal cell differentiation. Interestingly, the neoplastic glands of these "intestinal-type" hapatic tumors demonstrated strongly positive immunochemical reactions for both hepatocyte growth factor/scatter factor and its c-met encoded receptor and were immunohistochemically positive for transforming growth factor beta 1 (TGF-beta 1) and for mannose-6-phosphate/insulin-like growth factor II receptor, implicated in the activation of latent TGF-beta 1. In contrast, a different pattern of aberrant bile ductular cell differentiation was noted to occur in the atrophied right liver lobe of moribund Fischer-344 male rats that were chronically exposed over a 10-14-day period to a severely hepatotoxic dose of furan (60 mg/kg/day). Under this latter experimental condition, rare yet distinct cholangiolar-like structures composed of biliary epithelial cells and typically a single ductular hepatocytic cell in various stages of maturation specifically formed in association with an extensive hyperplastic bile ductular reaction. Very similar cholangiolar-like structures also appeared in areas of preexisting hyperplastic bile ductule tissue at 3-5 days following the administration of a single hepatonecrogenic dose of CCl4 to rats that 4-6 wk earlier had been subjected to a bile duct ligation. In addition, a novel rat model was developed in which furan combined in a unique synergistic manner with bile duct ligation to induce the replacement of almost all of liver with well-differentiated hyperplastic bile ductules without evidence of differentiation along either metaplastic small intestine mucosal cell or ductular hepatocyte lineages. Bile ductular epithelial cell isolated from bile duct-ligated/furan-treated rats were further observed to be organized in the form of bile duct-like structures in vitro under specific conditions of primary cell culture and in vivo following their cell transplantation into the inguinal fat pads of sygeneic recipient rats. Overall, these findings serve to exemplify the remarkable plasticity that may be exhibited by certain proliferating biliary cell populations in liver in response to specific types of severe hepatic injury and/or during cholangiocarcinogenesis.

Hepatocyte growth factor is the most potent endogenous stimulant of rabbit gastric epithelial cell proliferation and migration in primary culture

Various growth factors are suggested to be involved in gastric mucosal repair. Our previous studies have shown that exogenous hepatocyte growth factor (HGF) has a proliferative effect on gastric epithelial cells. In the present study, comparison of the maximum proliferative effects and the optimum concentrations of several growth factors revealed that HGF was the most potent mitogen for gastric epithelial cells, as is the case for hepatocytes. Restitution of gastric epithelial cell monolayers was assessed using a round wound restitution model. HGF was the most effective agent for facilitating gastric epithelial restitution among those tested. A binding assay revealed specific binding of HGF to its receptor on gastric epithelial cells. Northern blot analysis confirmed the expression of specific HGF receptor mRNA (c-met) by gastric epithelial cells but not by gastric fibroblasts. To investigate endogenous HGF production, we determined the effect of gastric fibroblast-conditioned medium on epithelial proliferation and restitution. The conditioned medium produced similar effects to HGF and its activity was neutralized by an anti-HGF antibody. In addition, expression of HGF mRNA was detected in gastric fibroblasts but not in gastric epithelial cells. Our immunohistochemical study confirmed these in vitro data by means of demonstrating the existence and localization of HGF at human native gastric mucosa. HGF was localized at fibroblasts under the epithelial cell layer around gastric ulcers. These results suggest that HGF may be a potent endogenous promotor of gastric epithelial cell proliferation and migration, and may contribute to gastric mucosal repair through a paracrine mechanism.

Biological activation of pro-HGF (hepatocyte growth factor) by urokinase is controlled by a stoichiometric reaction

Hepatocyte growth factor (HGF) is a paracrine inducer of morphogenesis and invasive growth in epithelial and endothelial cells. HGF is secreted by mesenchymal cells as an inactive precursor (pro-HGF). The crucial step for HGF activation is the extracellular hydrolysis of the Arg494-Val495 bond, which converts pro-HGF into alpha beta-HGF, the high-affinity ligand for the Met receptor. We previously reported that the urokinase-type plasminogen activator (uPA) activates pro-HGF in vitro. We now show that this is a stoichiometric reaction, and provide evidence for its occurrence in tissue culture. Activation involves the formation of a stable complex between pro-HGF and uPA. This complex was isolated from the in vitro reaction of pure uPA with recombinant pro-HGF, as well as from the membrane of target cells, after sequential addition of uPA and pro-HGF. On the cell membrane, the uPA-HGF complex was bound to the Met receptor. Monocytic cell lines, and primary monocytes after adhesion, activated efficiently pro-HGF both on their surface and in the culture medium. This activation was inhibited by anti-catalytic anti-uPA antibodies, and occurred by a stoichiometric reaction. The stoichiometry of the activation reaction suggests that the biological effects of HGF can be titrated in vivo by the level of uPA activity. Adequate amounts of uPA can be locally provided by the macrophages, which would condition the tissue microenvironment by rendering HGF bioavailable to its target cells.

Serum hepatocyte growth factor levels in liver diseases: clinical implications

Although recent studies have shown that hepatocyte growth factor (HGF) is a potent mitogen in vivo, the significance of serum HGF in liver diseases remains unclear. To clarify clinical significance of serum HGF in liver diseases, serum HGF was measured in 127 patients with liver diseases and in 200 healthy individuals, using a highly sensitive immunoradiometric assay (IRMA). This assay is specific for HGF and is sensitive enough to detect 0.1 ng/mL of HGF. Mean values for serum HGF in acute hepatitis (AH), chronic hepatitis (CH), liver cirrhosis (LC), hepatocellular carcinoma (HCC), primary biliary cirrhosis (PBC), fulminant hepatic failure (FHF), and normal controls were 0.45, 0.40, 1.05, 1.06, 0.44, 16.40, and 0.27 ng/mL, respectively. Serum HGF levels in these diseases were significantly increased compared with those in the controls (P < .001), and exhibited a positive correlation with total bilirubin, indocyanine green (ICG) test (R15), asparate aminotransferase (AST), and a negative correlation with albumin and prothrombin time (P < .001). Cirrhotic patients with modified Child class C had higher levels of serum HGF than those graded as modified Child class A or B (P < .001). In CH, serum HGF levels were significantly related to the histological activity index (HAI) score (P < .002). Seven patients with HCC who underwent transcatheter arterial embolization (TAE) exhibited a gradual increase in serum HGF levels up to day 4 after treatment; these higher levels were maintained until day 7, although AST reached a peak on day 2 and then decreased gradually.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Colony isolation and secondary culture of fetal porcine hepatocytes on STO feeder cells

The secondary culture of non-transformed parenchymal hepatocytes has not been possible. STO feeder cell-dependent secondary cultures of fetal pig hepatocytes were established by colony isolation from primary cultures of 26-d fetal livers. The liver cells had the typical polygonal morphology of parenchymal hepatocytes. They also spontaneously differentiated to form small biliary canaliculi between individual cells or progressed further to large multicellular duct-like structures or cells undergoing gross lipid accumulation and secretion. The secondary hepatocyte cultures expressed alpha-fetoprotein (AFP), albumin, and beta-fibrinogen mRNA, and conditioned medium from the cells contained elevated levels of transferrin and albumin. STO feeder cell co-culture may be useful for the sustainable culture of hepatocytes from other species.

Identification of a cell-type-specific transcriptional repressor in the promoter region of the mouse hepatocyte growth factor gene

Hepatocyte growth factor (HGF), a cytokine with multiple functions, exhibits cell-type-specific as well as cytokine- and steroid hormone-regulated expression. The HGF gene is known to be expressed predominately in mesenchymal but not in epithelial cells. In this study, we report the identification of a cell-type-specific transcriptional repressor in the promoter region of the mouse HGF gene, which is evidently responsible for the suppression of HGF expression in epithelial cells. Gel mobility shift assays and DNase I footprinting studies revealed that a 27-bp element (-16 to +11) around the transcription initiation site is responsible for the binding of a nuclear protein which is present in epithelial but not in mesenchymally derived cells. Further analysis of the binding activity of the DNA region with nuclear protein revealed that an approximately 19-bp sequence containing a unique palindromic structure (5'-AACCGACCGGTT-3') overlapped by a CAP box is essential for binding. Substitution of a single base (the contact site) within this region by site-directed mutagenesis resulted in total abrogation of the binding of the nuclear protein and a concomitant increase in the transcriptional activity of various lengths of HGF-chloramphenicol acetyltransferase fused genes when transfected into the epithelial cell line RL95-2 but not the mesenchymal cell line NIH 3T3. Southwestern (DNA-protein) analyses revealed that the nuclear protein which binds to this repressor element is a single polypeptide of approximately 70 kDa. Analysis of the nuclear extract prepared from regenerating mouse liver at various times after two-thirds partial hepatectomy by gel mobility shift assay revealed a substantial reduction (more than 75% within 3 h) in the binding of the repressor to its cognate binding site. Our results suggest that a cis-acting transcriptional repressor in the promoter region of the mouse HGF gene is involved in cell-type-specific regulation through binding to its cognate trans-acting protein which exists in epithelial cells but is absent in fibroblast cells.

Identification of a cell-type-specific transcriptional repressor in the promoter region of the mouse hepatocyte growth factor gene

Hepatocyte growth factor (HGF), a cytokine with multiple functions, exhibits cell-type-specific as well as cytokine- and steroid hormone-regulated expression. The HGF gene is known to be expressed predominately in mesenchymal but not in epithelial cells. In this study, we report the identification of a cell-type-specific transcriptional repressor in the promoter region of the mouse HGF gene, which is evidently responsible for the suppression of HGF expression in epithelial cells. Gel mobility shift assays and DNase I footprinting studies revealed that a 27-bp element (-16 to +11) around the transcription initiation site is responsible for the binding of a nuclear protein which is present in epithelial but not in mesenchymally derived cells. Further analysis of the binding activity of the DNA region with nuclear protein revealed that an approximately 19-bp sequence containing a unique palindromic structure (5'-AACCGACCGGTT-3') overlapped by a CAP box is essential for binding. Substitution of a single base (the contact site) within this region by site-directed mutagenesis resulted in total abrogation of the binding of the nuclear protein and a concomitant increase in the transcriptional activity of various lengths of HGF-chloramphenicol acetyltransferase fused genes when transfected into the epithelial cell line RL95-2 but not the mesenchymal cell line NIH 3T3. Southwestern (DNA-protein) analyses revealed that the nuclear protein which binds to this repressor element is a single polypeptide of approximately 70 kDa. Analysis of the nuclear extract prepared from regenerating mouse liver at various times after two-thirds partial hepatectomy by gel mobility shift assay revealed a substantial reduction (more than 75% within 3 h) in the binding of the repressor to its cognate binding site. Our results suggest that a cis-acting transcriptional repressor in the promoter region of the mouse HGF gene is involved in cell-type-specific regulation through binding to its cognate trans-acting protein which exists in epithelial cells but is absent in fibroblast cells.

Distinct morphological and mito-inhibitory effects induced by TGF-beta 1, HGF and EGF on mouse, rat and human hepatocytes

TGF-beta 1 is known as a potent inhibitor of proliferation of rat and human hepatocytes. In this study we show that the effects of TGF-beta 1 are quite different on mouse hepatocytes. In rat and human hepatocytes, TGF-beta 1 inhibited DNA synthesis and also inhibited the morphological changes induced by growth factors in rat and human hepatocytes. In contrast, addition of TGF-beta 1 to mouse hepatocytes resulted in pronounced alterations in morphology of these cells. These changes were similar to those induced by HGF and EGF. The induction of structural changes by TGF-beta 1 was noted only in mouse hepatocytes. Mouse hepatocytes were also much more resistant to the mito-inhibitory effect of TGF-beta 1. These findings suggest profound differences in hepatocyte growth regulation between these species and may relate to observed differences in susceptibility to carcinogenesis.

Comparative effects of hepatocyte growth factor and epidermal growth factor on motility, morphology, mitogenesis, and signal transduction of primary rat hepatocytes

Hepatocyte growth factor (HGF) and epidermal growth factor (EGF) are major hepatocyte mitogens, but HGF, also known as scatter factor (SF), has also been shown as a potent motogen for epithelial and endothelial cells. The mechanisms by which HGF is a stronger motogen compared to other mitogens are not understood. Here we report a comparative study of the effect of the two growth factors on cultured primary rat hepatocytes regarding their differential effects on morphology, mitogenicity, and motility as well as the phosphorylation of cytoskeletal-associated proteins. Using three different motility assays, both HGF and EGF increased the motility of hepatocytes, but HGF consistently elicited a significantly greater motility response than EGF. Additionally, HGF induced a more flattened, highly spread morphology compared to EGF. To examine if HGF and EGF phosphorylated different cytoskeletal elements as signal transduction targets in view of the observed variation in morphology and motility, primary cultures of 32P-loaded rat hepatocytes were stimulated by either HGF or EGF for up to 60 min. Both mitogens rapidly stimulated four isoforms of MAP kinase with similar kinetics and also rapidly facilitated the phosphorylation of cytoskeletal-associated F-actin. Two cytoskeletal-associated proteins, however, were observed to undergo rapid phosphorylation by HGF and not EGF during the time points described. One protein of 28 kDa was observed to become phosphorylated fivefold over controls, while the EGF-stimulated cells showed only a slight increase in the phosphorylation of this protein. Another protein with an apparent mwt of 42 kDa was phosphorylated 20-fold at 1 min and remained phosphorylated over 50-fold over control up to the 60 min time point. This protein was observed to become phosphorylated by EGF only after 10 min, and to a lesser extent (20-fold). Taken together, the data suggest that HGF and EGF stimulate divergent as well as redundant signal transduction pathways in the hepatocyte cytoskeleton, and this may result in unique HGF- or EGF-specific motility, morphology, and mitogenicity in hepatocytes.

Expression and functional interaction of hepatocyte growth factor-scatter factor and its receptor c-met in mammalian brain

Hepatocyte growth factor-scatter factor (HGF-SF) is a pleiotropic cytokine with mito-, morpho-, and motogenic effects on a variety of epithelial and endothelial cells. HGF-SF activity is mediated by the c-met protooncogene, a membrane-bound tyrosine kinase. Here, we demonstrate that both genes are expressed in developing and adult mammalian brains. HGF-SF mRNA is localized in neurons, primarily in the hippocampus, the cortex, and the granule cell layer of the cerebellum, and it is also present at high levels in ependymal cells, the chorioid plexus, and the pineal body. c-met is expressed in neurons, preferentially in the CA-1 area of the hippocampus, the cortex, and the septum, as well as in the pons. In the embryonic mouse, brain HGF-SF and c-met are expressed as early as days 12 and 13, respectively. Neuronal expression of HGF-SF is evolutionary highly conserved and detectable beyond the mammalian class. Incubation of septal neurons in culture with HGF-SF leads to a rapid increase of c-fos mRNA levels. The results demonstrate the presence of a novel growth factor-tyrosine kinase signaling system in the brain, and they suggest that HGF-SF induces a functional response in a neuronal subpopulation of developing and adult CNS.

Uptake and distribution of hepatocyte growth factor in normal and regenerating adult rat liver

We have previously shown that systemically injected hepatocyte growth factor (HGF) is primarily taken up by the liver. The present study shows that HGF injected systemically or through the portal circulation is retained primarily at periportal sites. The periportal retention of HGF seems to persist longer in regenerating liver. The percentage of the total HGF injected that was retained within the liver at 1 minute after injection varied with the dose. A maximal amount of 0.157 +/- 0.012 microgram of HGF per gram liver tissue is retained by normal liver. Analysis of the circulating form of HGF in the plasma showed a relative enrichment with time for the heterodimeric form of HGF. A portion of portally injected HGF, composed of both single chain and two chain (heterodimeric) form was excreted intact in the bile. This was found in both normal and regenerating liver. These studies show that the liver can sequester large amounts of HGF and that the sequestration occurs primarily at periportal sites. Our studies support the hypothesis that a nonlysosomal processing pathway for HGF is present in the liver.

Expression and localization of hepatocyte growth factor in rat submandibular gland

By combination of in situ hybridization and immunohistochemical techniques, the expression of hepatocyte growth factor (HGF) was demonstrated in the submandibular gland of rats. Both the mRNA signal and immunoreactivity for HGF were localized exclusively to the epithelial cells of granular convoluted tubules, whereas they were absent from the other components of the submandibular gland. In the granular convoluted tubule cells, HGF-immunoreactivity was localized to the apical secretory granules, which was further substantiated by immunoelectron microscopy. These results added HGF to the list of many growth factors that are produced in the rat submandibular gland and secreted into the saliva.

Cooperative roles of hepatocyte growth factor and plasminogen activator in tubular morphogenesis by human microvascular endothelial cells

Epidermal growth factor (EGF) or transforming growth factor-alpha (TGF-alpha) stimulated cell migration, chemotaxis, and the expression of tissue-type plasminogen activator (t-PA) in human omental microvascular endothelial (HOME) cells. Hepatocyte growth factor (HGF) stimulated cell proliferation, but had a negligible stimulatory effect on cell migration, the expression of t-PA and tube-like formation into collagen gel in HOME cells. Basic fibroblast growth factor stimulated cell proliferation, cell migration, tubulogenesis and the expression of urokinase-type plasminogen activator (u-PA) in bovine aortic endothelial (BAE) cells. HOME and BAE cells had both high- and low-affinity receptors for HGF. In BAE cells, u-PA activity and tube-like structures in collagen gel were induced in the presence of HGF alone. In contrast, in HOME cells, t-PA activity and tube-like structures were induced in the presence of TGF-alpha alone, but not in the presence of HGF alone. However, we observed a marked induction of tube formation by HOME cells when both t-PA and HGF were added simultaneously. In the model system for tumor angiogenesis, when HOME cells were co-cultured with a renal cancer cell line, KPK13, tube-like structures were induced in the presence of HGF:KPK13 cells expressed large amounts of t-PA mRNA. Our present study suggested that HGF in concert with active t-PA could be angiogenic in HOME cells.

Role of chemically induced cell proliferation in carcinogenesis and its use in health risk assessment

There is much interest in incorporating knowledge of biological mechanisms of carcinogenesis into assessments of health risks to humans posed by chemicals in the environment. Debate over the soundness of using data from animal bioassays conducted at minimally toxic doses or fractions thereof for predicting cancer risks to humans exposed to much lower doses has stimulated interest in the question of whether genotoxic or mitotic effects predominate in chemical carcinogenesis. Cell division plays a key role at each stage in the evolution of cancer, and it is well documented that increased rates of cell proliferation can escalate the risk of malignancy. This article examines the current understanding of both mechanisms by which chemicals provoke cell proliferation and the contribution of various kinetic patterns of cell proliferation to carcinogenesis.