Evidence for the identity of human scatter factor and human hepatocyte growth factor

Hepatocyte growth factor and the kidney: it is not just for the liver

Mesenchymal-epithelial interactions are important for many biological processes in epithelial organs such as the kidney. Hepatocyte growth factor (HGF) is a mesenchymally derived polypeptide cytokine that acts through its tyrosine kinase c-met receptor and is an important mediator of these interactions. This article reviews data showing the in vitro actions of HGF on renal epithelial cells that result in such diverse responses as mitogenesis, motogenesis, and morphogenesis. It also examines the in vivo evidence linking HGF and the c-met receptor to kidney development, regeneration following injury, and renal disease. Elucidating cellular mechanisms underlying the coordinated control of diverse HGF-induced phenotypic changes in renal epithelia in vitro should contribute to a clearer understanding of complex biological processes such as organogenesis, regeneration, and carcinogenesis in epithelial organs such as the kidney.

Stimulation of hepatocyte growth factor production by ascorbic acid and its stable 2-glucoside

Hepatocyte growth factor (HGF), a cytokine which is generally produced by mesenchymal cells, has mitogenic, motogenic and morphogenic activities in epithelial cells and it also has tumor-suppressing activities. Induction of HGF production may be involved in organ regeneration, wound healing and embryogenesis. We examined the effects of ascorbic acid (AsA), which stimulates the proliferation of fibroblasts, and its stable derivative, 2-O-alpha-D-glucopyranosyl-L-ascorbic acid (AA-2G), on HGF production by human skin fibroblasts. Basal HGF secretion was significantly stimulated by more than 0.1 mM AsA or AA-2G. Both vitamins synergistically enhanced HGF secretion stimulated by growth factors such as epidermal growth factor (EGF), platelet-derived growth factor (PDGF) and basic fibroblast growth factor (bFGF), cholera toxin and other inducers. Induction by EGF or bFGF was most markedly potentiated by the vitamins. HGF production by the KG-1 human leukemia cell line was also augmented by AsA or AA-2G. Another stable AsA derivative, ascorbic acid 2-phosphate (AA-2P) effectively promoted basal and EGF-induced HGF secretion by the fibroblasts, but ascorbic acid 2-sulfate (AA-2S) was much less effective. Intracellular AsA levels increased after the addition of AA-2G and AA-2P as well as AsA, but not after AA-2S. The effect of AA-2G was completely abrogated by the simultaneous addition of castanospermine, an alpha-glucosidase inhibitor, suggesting that the active form of AA-2G is AsA. Constitutive and EGF-induced HGF gene expression was also up-regulated after adding AsA or AA-2G to the cells. These results indicated that AsA acts alone or in synergy with several inducers to stimulate the production and gene expression of HGF in human skin fibroblasts and that the stable AsA derivative AA-2G is as effective as AsA in promoting HGF production.

Developmental roles of HGF/SF and its receptor, the c-Met tyrosine kinase

A number of developmental processes that involve cell migration, growth or morphogenesis depend on extracellular signals. A molecule that provides such signals, known as hepatocyte growth factor/scatter factor (HGF/SF), has attracted considerable interest in recent years because of its distinct structure, mechanism of activation and important roles throughout embryogenesis. This review discusses the main features of HGF/SF and its receptor, the product of the c-met protooncogene, and their role in embryogenesis.

Analysis of deleted variant of hepatocyte growth factor by alanine scanning mutagenesis: identification of residues essential for its biological function and generation of mutants with enhanced mitogenic activity on rat hepatocytes

To understand the structure-function relationship of hepatocyte growth factor (HGF) in more detail, we analyzed one of the other forms of HGF, deleted variant of HGF (dHGF), by alanine scanning mutagenesis. We show here that there are at least four sites important for dHGF to stimulate DNA synthesis in cultured adult rat hepatocytes, and that the residues of HGF essential for exerting its biological activity are not identical to those of dHGF. In addition, two mutants showed a decrease (approximately three-fold) in EC50 compared with wild-type dHGF in an assay of mitogenic activity on rat hepatocytes.

Growth factor-dependent activation of alphavbeta3 integrin in normal epithelial cells: implications for tumor invasion

Integrin activation is a multifaceted phenomenon leading to increased affinity and avidity for matrix ligands. To investigate whether cytokines produced during stromal infiltration of carcinoma cells activate nonfunctional epithelial integrins, a cellular system of human thyroid clones derived from normal glands (HTU-5) and papillary carcinomas (HTU-34) was employed. In HTU-5 cells, alphavbeta3 integrin was diffused all over the membrane, disconnected from the cytoskeleton, and unable to mediate adhesion. Conversely, in HTU-34 cells, alphavbeta3 was clustered at focal contacts (FCs) and mediated firm attachment and spreading. alphavbeta3 recruitment at FCs and ligand-binding activity, essentially identical to those of HTU-34, occurred in HTU-5 cells upon treatment with hepatocyte growth factor/scatter factor (HGF/SF). The HTU-34 clone secreted HGF/SF and its receptor was constitutively tyrosine phosphorylated suggesting an autocrine loop responsible for alphavbeta3 activated state. Antibody-mediated inhibition of HGF/SF function in HTU-34 cells disrupted alphavbeta3 enrichment at FCs and impaired adhesion. Accordingly, activation of alphavbeta3 in normal cells was produced by HTU-34 conditioned medium on the basis of its content of HGF/SF. These results provide the first example of a growth factor-driven integrin activation mechanism in normal epithelial cells and uncover the importance of cytokine-based autocrine loops for the physiological control of integrin activation.

Up-regulation of vascular endothelial growth factor induced by hepatocyte growth factor/scatter factor stimulation in human glioma cells

Recent findings suggest that hepatocyte growth factor/scatter factor (HGF/SF) contributes to the malignant progression of human gliomas. We investigated the effect of HGF/SF on vascular endothelial growth factor (VEGF) expression of c-Met/HGF receptor-positive human glioma cell lines. Treatment of the glioma cells with various concentrations of HGF/SF resulted in an enhanced secretion of VEGF proteins accompanying increased transcription of VEGF mRNA in a dose-dependent fashion. Since malignant gliomas frequently co-express HGF/SF and its receptor, these results suggest that HGF/SF could act as an indirect angiogenic factor through autocrine induction of VEGF expression and secretion in malignant gliomas.

Retinal pigment epithelial cells secrete and respond to hepatocyte growth factor

Hepatocyte growth factor (HGF) is normally expressed by mesenchymal cells while its receptor, c-Met, is expressed in epithelial cells. Since HGF is critically involved in epithelial-mesenchyme interactions and the retinal pigment epithelium (RPE) is present at the interface between the retina and choroid, this study was initiated to determine whether the RPE expresses or responds to HGF in vitro. Cultured adult and fetal human RPE expressed mRNA for HGF and c-Met by RT-PCR. ELISA assay demonstrated the secretion of HGF into RPE culture supernatants. Tyrosine phosphorylation of c-Met was constitutively found in 72 hour RPE cultures and could be rapidly induced in serum-starved cells by concentrated RPE supernatants. HGF was mitogenic for cultured RPE (100 ng/ml.) and stimulated their chemotaxis (maximal response at 50 ng/ml). RPE are one of only a very limited number of epithelia that express both HGF and its receptor, suggesting the possibility of an autocrine action for this growth factor.

Identification of a novel cis-acting element for fibroblast-specific transcription of the FSP1 gene

The FSP1 gene encodes a filament-binding S100 protein with paired EF hands that is specifically expressed in fibroblasts. This led us to look for cis-acting elements in the FSP1 promoter that might engage nuclear transcription factors unique to fibroblasts. The first exon of FSP1 is noncoding, therefore, a series of luciferase reporter minigenes were created containing varying lengths of 5'-flanking sequence, the first intron, and the noncoding region of the second exon. A position and promoter-dependent proximal element between -187 and -88 bp was shown to be active in fibroblasts but not in epithelium. Sequence in the first intron from +777 to +964 had an enhancing effect that was not cell type specific. Hsv TK reporter constructs driven by this promoter/intron cassette in transgenic mice were coexpressed appropriately with FSP1 in tissue fibroblasts. Gel mobility shift competitor assays identified a novel domain, FTS-1 (fibroblast transcription site-1; TTGAT from -177 to -173 bp), that specifically interacts with nuclear extracts from fibroblasts. The necessity of this binding site was confirmed by site-specific mutagenesis. Database searches also turned up putative FTS-1 sites in the early promoter regions of other fibroblast expressed proteins, including the alpha1 and alpha2(I), and alpha1(III) collagens and the alphaSM-actin gene. We hypothesize that the selective engagement of FTS-1 elements may contribute to the mesenchymal phenotype of fibroblasts and perhaps other dedifferentiated cells.

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.

Activation of the urokinase plasminogen activator/urokinase plasminogen activator receptor system and redistribution of E-cadherin are associated with hepatocyte growth factor-induced motility of pancreas tumor cells overexpressing Met

Because hepatocyte growth factor (HGF) is a potent mitogen for normal human exocrine pancreas cells (NPCs) in vitro, we have analyzed the expression of HGF and its receptor, Met, in NPC and pancreas cancer cells and studied its effects in vitro. Using immunohistochemistry, Northern blotting, and reverse transcription-polymerase chain reaction, we examined the expression of HGF and Met in normal pancreas and pancreas cancer. Scatter assays, wound-healing assays, and migration through transwell filters were used to study HGF-stimulated motility of IMIM-PC-2 cancer cells. In tumors, HGF is mainly detected in stromal cells, whereas Met is overexpressed in cancer cells with an unpolarized distribution. In vitro, HGF stimulates motogenesis but not proliferation in cancer cells. Cell motility is accompanied by a rapid decrease in the cytoskeleton-bound E-cadherin, an acceleration of cellular adhesion to the substrate, an up-regulation of urokinase plasminogen activator (u-PA) RNA and protein, and a change in the solubility and proteolysis of the u-PA receptor. Cell motility is significantly reduced by inhibitors of u-PA proteolytic activity such as antibodies neutralizing u-PA activity, plasminogen activator inhibitor 1, and amiloride. These results show that a paracrine loop of HGF activation may participate in the development or progression of pancreas cancer. In vitro, the HGF-stimulated motogenesis of pancreas cancer cells involves the activation of the u-PA/u-PA receptor proteolytic system, suggesting its role in the invasive stages of tumor progression.

Evaluation of hepatocyte growth factor activator inhibitor expression in normal and malignant colonic mucosa

Gene expression of hepatocyte growth factor activator inhibitor (HAI), a recently identified Kunitz-type serine proteinase inhibitor, was analyzed in a series of human colorectal carcinoma cell lines and in human colorectal tissues. All of the 14 cell lines derived from adenocarcinoma of the colorectum expressed HAI in vitro, whereas a colon carcinoma cell line of neuroendocrine origin did not. In vivo, HAI was consistently expressed in the normal colorectal mucosa. Although the expression of HAI mRNA was conserved in adenocarcinoma tissues of the colorectum, the levels of expression were decreased in the adenocarcinoma tissues compared to the normal counterparts. There was a tendency towards an inverse correlation, albeit not well defined, between the amounts of HAI mRNA and the tumor progression. Immunohistochemical study indicated that HAI protein is present predominantly on the surface of epithelial cells of the colon and the immunoreactivity was decreased in the adenocarcinoma cells.

Human Hrs, a tyrosine kinase substrate in growth factor-stimulated cells: cDNA cloning and mapping of the gene to chromosome 17

Hrs is a 115kDa zinc finger protein which is rapidly tyrosine phosphorylated in cells stimulated with various growth factors. We previously purified the protein from a mouse cell line and cloned its cDNA. In the present study, we cloned a human Hrs cDNA from a human placenta cDNA library by cross-hybridization, using the mouse cDNA as a probe, and determined its nucleotide sequence. The human Hrs cDNA encoded a 777-amino-acid protein whose sequence was 93% identical to that of mouse Hrs. Northern blot analysis showed that the Hrs mRNA was about 3.0kb long and was expressed in all the human adult and fetal tissues tested. In addition, we showed by genomic Southern blot analysis that the human Hrs gene was a single-copy gene with a size of about 20kb. Furthermore, the human Hrs gene was mapped to chromosome 17 by Southern blotting of genomic DNAs from human/rodent somatic cell hybrids.

Serum concentration of hepatocyte growth factor in patients with metastatic breast cancer

The serum concentration of hepatocyte growth factor (HGF) was examined in 34 patients with metastatic breast cancer. Although no significant difference was observed between HGF concentration and the site of metastasis, serum HGF levels were slightly higher in patients with liver metastasis and in patients with multiple metastatic sites than in patients with other lesions. Significantly higher levels of serum HGF were observed in patients with progressive metastasis of breast cancer compared with those with stable metastasis. The patients with high HGF levels exhibited a significantly shorter survival rate than those with low HGF levels. Circulating HGF levels may be a useful indicator for the progression of metastatic lesions and the prognosis of patients with metastatic breast cancer.

Hepatocyte growth factor/scatter factor stimulates chemotaxis and growth of malignant mesothelioma cells through c-met receptor

Hepatocyte growth factor (HGF) and its receptor c-met are present in several human tissues but their expression in mesothelial cells has not been examined. In this study, we have investigated the expression of HGF and c-met in normal human mesothelial cells and 11 human malignant mesothelioma cell lines. Using RT-PCR and Western blotting we found that HGF is produced by 3/11 mesothelioma cell lines whereas c-met is expressed in 11/11 mesothelioma cell lines. In addition, c-met expression was also found in 6/6 cell samples obtained from pleural fluids of patients with mesothelioma. In contrast, neither normal cultured mesothelial cells nor mesothelial cells obtained directly from patients without mesothelioma expressed HGF nor c-met. We have also analysed the biological function of HGF and c-met in mesothelioma cell lines. Recombinant human (rh) HGF stimulated both directional (chemotactic) and random (chemokinetic) motility in all mesothelioma cell lines tested. Furthermore, mesothelioma serum free conditioned medium containing HGF stimulated mesothelioma cell migration. This effect could be blocked in the presence of neutralizing anti-HGF monoclonal antibodies (MAbs) in the assay. Addition of HGF to mesothelioma cells cultured on collagen type IV was associated with induction of bipolar shape and protrusion of prominent pseudopodia. We have also found that rhHGF was mitogenic for mesothelioma cells. Our findings suggest that expression of HGF/c-met is involved not only in mesothelioma progression but also in its growth and migration and that c-met expression found in mesothelioma cells taken directly from patients may be of diagnostic importance.

Hepatocyte growth factor/scatter factor activates the apoptosis signaling pathway by increasing caspase-3 activity in sarcoma 180 cells

Hepatocyte growth factor, which is now known to be the same protein as scatter factor, induced oligonucleosomal fragmentation of nuclear DNA of Sarcoma 180 cells and increased the activity of caspase-3, a key component in control of the apoptotic cell death pathway to about 2.6 times that in control cells on 48 hr incubation, but did not increase the activity of caspase-1. Both HGF-induced DNA fragmentation and caspase-3 activity were completely inhibited by co-incubation with an inhibitor of caspase-3, Ac-DEVD-H. In contrast, HGF did not affect the expression of the apoptosis suppressors Bcl-2 and Bcl-x. These results indicate that HGF activates the apoptosis signaling pathway by increasing caspase-3 activity in Sarcoma 180 cells.

HGF: its organotrophic role and therapeutic potential

Hepatocyte growth factor (HGF), originally implicated as a long-sought after hepatotrophic factor, supports epithelial branching duct formation in the developing lung as, a mesenchymal-derived morphogen. HGF elicits a potent organotrophic function for regeneration of organs including the liver, kidney and lung, through epithelial-stromal interactions. It prevents the onset or progress of hepatic fibrosis/cirrhosis, as well as the accompanying severe hepatic failure, and may become an effective drug for the treatment of fatty liver. HGF prevents the onset of acute and chronic renal failure, acts as pulmotrophic factor which enhances lung regeneration, and suppresses the onset of lung fibrosis. HGF may also be effective for treatment of vascular diseases, gastric ulcers, diabetes mellitus and neuronal diseases. Our results provide a new therapeutic strategy for treating such diseases.

HGF/SF in angiogenesis

Hepatocyte growth factor/scatter factor (HGF/SF) is a mesenchyme-derived cytokine that stimulates motility and invasiveness of epithelial and cancer cells. These responses are transduced through the c-met proto-oncogene product, a transmembrane tyrosine kinase that functions as the HGF/SF receptor. We have shown that HGF/SF is a potent angiogenic molecule and that its angiogenic activity is mediated primarily through direct actions on vascular endothelial cells. These include stimulation of cell migration, proliferation, protease production, invasion, and organization into capillary-like tubes. We further showed that HGF/SF is overexpressed in invasive human cancers, including breast cancer, relative to non-invasive cancers and benign conditions. In invasive breast cancers, the content of HGF/SF is strongly correlated with that of von Willebrand's factor, a marker of vascular endothelial cells. Furthermore, transfection of breast cancer and glioma cell lines with HGF/SF cDNA greatly enhanced the ability of these cells to grow as tumours in orthotopic sites in syngeneic or immunocompromized host animals. The increased growth rate of the HGF/SF-transfected cells was attributable, in part, to increased tumour angiogenesis. These findings suggest that HGF/SF may function as a tumour progression factor, in part by stimulating tumour cell invasiveness and in part by stimulating angiogenesis.

Differential expression of Met/hepatocyte growth factor receptor in subtypes of non-small cell lung cancers

Hepatocyte growth factor (HGF)/scatter factor (SF) is a multifunctional factor that stimulates epithelial cell motility, invasion and morphogenesis. Its receptor is a transmembrane tyrosine kinase encoded by the Met proto-oncogene. Several studies have suggested a possible role for HGF/Met in tumor development and progression. To investigate the potential roles of Met in human lung cancer biology, we have studied the mRNA and protein expression of Met in normal lung tissue, primary non-small cell lung carcinoma (NSCLC), and NSCLC cell lines. The results indicated a differential pattern of Met expression among various subtypes of NSCLC. The majority of squamous cell carcinoma (SQCC), either in vivo or in vitro, expressed Met mRNA and its protein product at levels much lower than or similar to normal lung tissue or bronchial epithelium. Moreover, SQCC characteristically over-expressed a variant Met mRNA which corresponds to a 5' partially deleted transcript produced by alternative splicing. In contrast, the expression of Met mRNA and its protein product in adenocarcinoma (ADC) and large cell undifferentiated carcinoma were more heterogeneous. Overexpression was demonstrated in approximately 35% and 20% of these subtypes of NSCLC, respectively. Among ADC, intermediate to high levels of Met immunoreactivity correlated with greater degree of tumor differentiation. Furthermore, an accentuation of Met immunoreactivity was often noted in cancer cells at the advancing edge of tumors. These findings support a role for Met in lung cancer cell invasion and differentiation in vivo, but its expression and functions may be modified by the differentiation phenotype of the tumor cells.

Hepatocyte growth factor (HGF) acts as a mesenchyme-derived morphogenic factor during fetal lung development

Mesenchymal-epithelial tissue interactions are important for development of various organs, and in many cases, soluble signaling molecules may be involved in this interaction. Hepatocyte growth factor (HGF) is a mesenchyme-derived factor which has mitogenic, motogenic and morphogenic activities on various types of epithelial cells and is considered to be a possible mediator of epithelial-mesenchymal interaction during organogenesis and organ regeneration. In this study, we examined the role of HGF during lung development. In situ hybridization analysis showed HGF and the c-met/HGF receptor gene to be respectively expressed in mesenchyme and epithelium in the developing lung. In organ cultures, exogenously added HGF apparently stimulated branching morphogenesis of the fetal lung. In contrast, HGF translation arrest or neutralization assays resulted in clear inhibition of epithelial branching. These results suggest that HGF is a putative candidate for a mesenchyme-derived morphogen regulating lung organogenesis. We also found that HGF is involved in epithelial branching, in collaboration with fibroblast growth factor (FGF) family molecule(s). In mesenchyme-free culture, HGF alone did not induce epithelial morphogenesis, however, addition of both HGF and acidic FGF (aFGF) or keratinocyte growth factor (KGF), ligands for the KGF receptor, induced epithelial branching more extensively than that was observed in explants treated with aFGF or KGF alone. In addition, the simultaneous inhibition of HGF- and FGF-mediated signaling using neutralizing antibody and antisense oligo-DNA resulted in drastic impairment of epithelial growth and branching. Possible interactions between HGF and FGFs or other growth factors in lung development is given consideration.

Hepatocyte growth factor plays a dual role in regulating skeletal muscle satellite cell proliferation and differentiation

The role of hepatocyte growth factor (HGF) and its receptor, c-met, in proliferation and differentiation of satellite cells was studied in primary cultures of chicken skeletal muscle satellite cells and a myogenic C2 cell line. HGF mRNA was expressed mainly in the myotubes of both cultures. The addition of conditioned medium derived from those cultures had a scattering effect on the canine kidney epithelial cell line, MDCK. In contrast, c-met mRNA levels decreased during cell differentiation of C2 and primary satellite cells. Application of exogenous HGF to chicken myoblasts resulted in their enhanced DNA synthesis. Among several growth factors, HGF was the first to induce DNA synthesis in quiescent satellite cells, thereby driving them into the cell cycle. Ectopic expression of chicken HGF in primary satellite cells suppressed the activation of muscle-regulatory gene reporter constructs MCK-CAT, MRF4-CAT, MEF2-CAT and 4Rtk-CAT, as well as the gene expression of MyoD and myogenin, and MHC protein expression. Ectopic MyoD reversed HGF's inhibitory effect on MCK transactivation. These data suggest that HGF inhibits cell differentiation by inhibiting the activity of basic helix-loop-helix (bHLH)/E protein heterodimers, thus inhibiting myogenic determination factor activity and subsequent muscle-specific protein expression. During muscle growth and regeneration, HGF plays a dual role in satellite-cell myogenesis, affecting both the proliferation and differentiation of these cells in a paracrine fashion.

Comparative analysis of expression of hepatocyte growth factor and its receptor, c-met, in gliomas, meningiomas and schwannomas in humans

Expression of hepatocyte growth factor (HGF) and c-met, a proto-oncogene that encodes a receptor for HGF, was examined in 45 cases of human primary intracranial tumors by means of RT-PCR. In gliomas, HGF and c-met mRNAs were preferentially expressed in high-grade tumors. Co-expression of both genes was observed in glioblastomas (6/15) and in one anaplastic astrocytoma (1/5) but not in low-grade astrocytomas (0/3). By contrast, the c-met gene was consistently expressed in meningiomas (12/14) and schwannomas (8/8). The presence of c-Met protein was confirmed in the tumor cells of glioblastoma, meningioma and schwannoma by immunohistochemical staining. Moreover, all of the schwannoma cases co-expressed the HGF gene. These observations suggest that HGF/c-met expression is somehow related to the disease progression in gliomas, whereas c-Met protein might have an important fundamental biological role in meningioma and schwannoma. Moreover, since all of the schwannoma cases concomitantly expressed the ligand (HGF) and the receptor (c-met) genes, HGF may act in an autocrine fashion in schwannoma.

Structural and functional characterization of the mouse c-met proto-oncogene (hepatocyte growth factor receptor) promoter

The c-met gene encoding Hepatocyte Growth Factor Receptor is predominantly expressed in epithelial cell types and overexpressed in a variety of human and mouse neoplastic tissues and cell lines. To understand the molecular mechanisms of the transcriptional regulation of this gene, we have cloned and functionally characterized the mouse c-met promoter region. Transient transfection analysis using a series of 5'-end deletion met-CAT chimeric constructs in epithelial (C-33A) and fibroblast (NIH3T3) cell lines demonstrated that the c-met promoter acts in a cell-type specific manner. These experiments also localized functionally important regulatory regions at -1390 to -279, relative to the transcription start site, which exert repressive activity, and at -278 to -77 which exhibit enhancing effects on c-met promoter activity. Further analysis by electrophoretic mobility shift assays using specific competitors and antibodies identified Sp1 protein binding to two cognate response elements at -221 and -124 within the enhancer region. Cotransfection experiments revealed that Sp1 stimulated promoter activity of the met-CAT constructs containing the two Sp1 binding sites. These results demonstrate that Sp1 is actively involved in the transcriptional regulation of the c-met promoter.

Expression of the hepatocyte growth factor and c-met in normal thyroid, non-neoplastic, and neoplastic nodules

We have examined the coexpression of hepatocyte growth factor (HGF) and its receptor (HGF-R or c-met) in an archival series of 63 paraffin-embedded thyroid specimens plus one lymph node metastasis. By immunocytochemistry, we found undetectable expression of both the ligand and the receptor in 10 normal thyroids and 9 nonpapillary malignant nodules [5 follicular carcinomas, 1 poorly differentiated (insular) carcinoma, 3 undifferentiated (anaplastic) carcinomas]. Of 10 non-neoplastic nodules (colloid nodules) and 17 benign neoplastic nodules, 3 of 10 colloid nodules, 2 of 10 follicular adenomas, and 2 of 7 oncocytic adenomas showed a weak but distinct staining (1+ score in a scale from 0 to 4+) of both HGF and c-met in a modest proportion of cells (1% to 3%). In these 7 cases, expression of HGF was always stromal and expression of c-met limited to the membrane of the follicular cells. Of 3 malignant nodules derived from aberrant growth of the parafollicular C cells (medullary thyroid cancer or MTC), 2 were positive (6% of cells). In these 2 cases, the expression of HGF (3+) was not stromal, but in both the membrane and cytoplasm of the parafollicular cells, while that of c-met (3+) was restricted to the membrane. In contrast to all of the above, of 14 papillary carcinomas (PTC) encompassing 5 histological variants (conventional; follicular; oncocytic; with foci of solid growth; diffuse sclerosing) plus 1 neck lymph node metastasis of 1 conventional PTC, 12 (86%) expressed HGF, and 13 (93%) expressed c-met. With the exception of 2 negative cases, HGF was detected in 15% to 46% of the cells. The highest percentage (46%) pertained to conventional PTC cases with abundant peritumoral lymphocyte infiltration, indicating that some lymphokine(s) may recruit PTC cells for HGF expression in a paracrine fashion. With the exception of one negative case, c-met was found in 43% to 80% of the cells, both at levels from intense (3+) to very intense (4+). The immunostaining for HGF was stromal in 25%, membranous in 8%, cytoplasmic in 8%, and both membranous and cytoplasmic in 59% of the PTC-positive cases. The immunostaining for c-met was membranous in 43% and both membranous and cytoplasmic in 57% of the PTC-positive cases. In the lymph node metastasis and in the diffuse sclerosing variant of PTC (the most aggressive variant), the coexpression of HGF/c-met was lost, in that only c-met was expressed on membranes in both cases. We conclude that the HGF/c-met system is activated (by overexpression of both components) in the vast majority of PTC. In most PTC the interaction of HGF and its receptor (c-met) is autocrine, not paracrine.

Tumor angiogenesis, hepatocyte growth factor, and c-Met expression in endometrial carcinoma

BACKGROUND

This study was designed to evaluate the significance of tumor angiogenesis and angiogenic factors such as hepatocyte growth factor (HGF) and c-Met in determining the prognoses of 93 patients with endometrial carcinoma.

METHODS

By immunohistochemical staining, this retrospective study investigated tumor angiogenesis, HGF expression, and c-Met expression, using one tissue slide that was representative of the invasive edge of the tumor. To evaluate tumor angiogenesis, the microvessels within the primary endometrial carcinoma were highlighted by staining their endothelial cells immunohistochemically for von Willebrand factor (VWF). The microvessels were then counted in the most intense areas of neovascularization. HGF and c-Met were identified with specific antibodies. Tumor angiogenesis, HGF expression, and c-Met expression were correlated with both the prognostic variables for and the survival of endometrial carcinoma.

RESULTS

A high microvessel count (> or = 110 in a 0.90 mm2 area) was significantly correlated with surgical Stage III and IV, histologic Grade 3, positive lymph node involvement, and shorter patient survival. Expression of c-Met was significantly correlated with surgical Stage III and IV, histologic Grade 3, and shorter survival. HGF expression was significantly correlated with surgical Stage III and IV by semiquantitative analysis. Multivariate analysis showed that surgical Stage III and IV, histologic Grade 3, the score for myometrial invasion > 1/2, and a high microvessel count were independent indicators of the prognoses of patients with endometrial carcinoma.

CONCLUSIONS

Both tumor angiogenesis, measured by the microvessel count, and c-Met expression were significant prognostic indicators for patients with endometrial carcinoma.

Engineered mutants of HGF/SF with reduced binding to heparan sulphate proteoglycans, decreased clearance and enhanced activity in vivo

BACKGROUND

Although a number of growth factors bind cell-surface heparan sulphate proteoglycans (HSPGs), the role of this interaction is unclear except for fibroblast growth factor which requires HSPG binding for signalling. Hepatocyte growth factor/scatter factor (HGF/SF) plays important roles in mammalian development and tissue regeneration and acts on target cells through a specific receptor tyrosine kinase encoded by the c-met proto-oncogene. This factor also binds HSPGs with high affinity, but conflicting data have been reported on the role of HSPG binding in HGF/SF signalling.

RESULTS

To map the binding sites for HSPG and the Met receptor in HGF/SF, we have engineered a number of HGF/SF mutants in which several clusters of solvent-accessible residues in the hairpin structure of the amino-terminal domain or in kringle 2 have been replaced. Two of the mutants (HP1 and HP2) showed greatly decreased (more than 50-fold) affinity for heparin and HSPGs but retained full mitogenic and motogenic activities on target cells in culture. Furthermore, when compared with wild-type HGF/SF, the HP1 mutant exhibited a delayed clearance from the blood, higher tissue levels and a higher induction of DNA synthesis in normal, adult murine liver.

CONCLUSIONS

These results establish the following: the binding sites in HGF/SF for Met and for HSPGs can be dissociated by protein engineering; high-affinity binding of HGF/SF to HSPGs is not essential for signalling; one role of HSPG binding in the HGF/SF system appears to be sequestration and degradation of the growth factor; and HGF/SF mutants with decreased affinity for HSPGs exhibit enhanced activity in vivo.

Hepatocyte growth factor stimulates the invasion of gallbladder carcinoma cell lines in vitro

Human gallbladder cancer is highly malignant and its prognosis is usually poor depending on the extent of surrounding tissue invasion. We examined in vitro the invasive activity of four gallbladder cancer cell lines (GB-d1, GB-h3, GB-d2 and FU-GBC-1) in the absence or presence of hepatocyte growth factor (HGF). In type 1 collagen gel culture, HGF stimulated cell proliferation and induced an invasive phenotype of arborizing structures in GB-d1, GB-h3 and GB-d2. In a Matrigel invasion assay, invasion was also induced in three of these cell lines by HGF but not in FU-GBC-1. Cellular motility was, however, stimulated by HGF in all of the four cell lines to various extents. Zymography for proteolytic enzymes demonstrated high levels of type IV collagenase and urokinase-type plasminogen activator (u-PA) activity in GB-d1, GB-h3 and GB-d2 even in the absence of HGF. In the presence of HGF, the 72 kDa type IV collagenase (MMP-2) activity of GB-h3 and u-PA activities of GB-d1, GB-h3 and GB-d2 were enhanced. In contrast, the MMPs and PAs activities of FU-GBC-1 were faint irrespective of the addition of HGF. A Western blot analysis demonstrated higher levels of 190 kDa c-MET product (HGF receptor) of GB-d1, GB-h3 and GB-d2 than that of FU-GBC-1. The invasion in the Matrigel assay stimulated by HGF was inhibited by protease inhibitors, aprotinin and FOY-305, as well as by anti-HGF antibody. These results thus suggest that, in addition to the importance of the proteolytic activity, the cellular motility induced via the HGF/HGF-receptor system is essential for the invasive progression of gallbladder carcinoma cells.

Stimulatory effects of hepatocyte growth factor on hemopoiesis of SCF/c-kit system-deficient mice

In this study, we report that W/W mutant mice, which have severe macrocytic anemia caused by a deficit of extracellular domain in c-kit molecules and therefore die perinatally, have hemopoietic stem cells (HSCs) and mature hematolymphoid cells in the bone marrow (BM), thymus, and spleen, although there are significant decreases in cell counts. Moreover, the mitogen-induced proliferative response, mixed lymphocyte reaction, and anti-SRBC plaque formation of spleen cells in W/W mice are similar to those in age-matched +/? littermates and normal mice, suggesting that the SCF/c-kit system is necessary for cell proliferation but not essential for HSCs to differentiate. We next examine the stimulatory effects of hepatocyte growth factor (HGF) on hemopoiesis in W/W mice. HGF has a stimulatory effect on the colony formation (CFU-C) of W/W BM cells when cultured using either a methylcellulose assay (containing cytokines) or a long-term culture (LTC) assay. A similar stimulatory effect of HGF is observed in the other W or SI locus-mutant mice (W/Wv and SI/SId mice), which show less severe anemia than W/W. The numbers of nonadherent cells and cobblestone colonies significantly increase in the LTCs using their BM cells. In addition, in vivo administration of HGF shows a transient increase in the CFU-C counts in BM cells and peripheral blood cells. RBC, WBC, and platelet counts also increased. These results suggest that the SCF/c-kit system is not essential to hemopoiesis but that a compensatory system such as the HGF/c-met system functions in the SCF/c-kit system-deficient mice.

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.

Increased serum concentrations of human hepatocyte growth factor in proliferative diabetic retinopathy

Human hepatocyte growth factor (hHGF) is a powerful inducer of angiogenesis. We investigated the relationship between serum hHGF concentrations and proliferative diabetic retinopathy, the major characteristic of which is retinal neovascularization. Serum hHGF concentrations were measured in diabetic (n = 135) and nondiabetic subjects (n = 80). The mean serum hHGF concentration in diabetic subjects without retinopathy was lower than that in nondiabetic subjects [0.041 +/- 0.003 ng/mL (n = 62) vs. 0.080 +/- 0.010 ng/mL (n = 80); P < 0.05], but was not different from that in diabetic subjects with background retinopathy (0.058 +/- 0.007 ng/mL; n = 26) or preproliferative retinopathy (0.048 +/- 0.010 ng/mL; n = 10). The mean serum hHGF concentration was increased in subjects with proliferative retinopathy who had not undergone photocoagulation (0.213 +/- 0.025 ng/mL; n = 24), but not in those who had undergone photocoagulation (0.040 +/- 0.008 ng/mL; n = 13). Circulating hHGF may be involved in the mechanism of neovascularization in the proliferative diabetic retinopathy, and measurement of serum hHGF may be helpful in predicting the presence of proliferative retinopathy in diabetic subjects.

Induction of hepatocyte growth factor/scatter factor by interferon-gamma in human leukemia cells

Induction of hepatocyte growth factor/scatter factor (HGF/SF) may be one of the critical steps in organ regeneration, wound healing, and embryogenesis. We previously reported the production of HGF/SF from various human leukemia cell lines and a high level of the growth factor in blood and bone marrow plasma from patients with various types of leukemia. We determined here the effects of hematopoietic cytokines on HGF/SF production in human leukemia cell lines, KG-1, a myeloid cell line, and RPMI-8226, a B cell line. Interferon (IFN)-gamma remarkably stimulated HGF/SF production in both cell lines at concentrations of more than 0.1 or 1 IU/ml. IFN-alpha and IFN-beta were as effective as IFN-gamma in RPMI-8226 cells, but less than IFN-gamma in KG-1 cells. HGF/SF gene expression in KG-1 cells was also up-regulated by IFN-gamma. Granulocyte colony-stimulating factor (G-CSF), granulocyte/macrophage colony-stimulating factor (GM-CSF), interleukin (IL)-5 and IL-6 had no effect on HGF/SF production in the 2 leukemia cell lines. We also determined the effects of HGF/SF inducers known for human fibroblasts on the growth factor production in leukemia cells. Out of phorbol 12-myristate 13-acetate (PMA), cholera toxin, IL-1 beta, and tumor necrosis factor (TNF)-alpha, the former three were as effective as IFN-gamma in KG-1 cells, but only TNF-alpha stimulated HGF/SF production in RPMI-8226 cells, whose effect was less than those of IFN-alpha, IFN-beta, and IFN-gamma. The effect of IFN-gamma in KG-1 cells was synergistic with that of PMA. In contrast with the effect in leukemia cells, HGF/SF induction by IFN-gamma in human skin fibroblasts was much less than that by PMA or cholera toxin. These results indicated that IFN-gamma is a potent inducer of HGF/SF in human leukemia cells. This finding suggests the presence of a homeostatic control mechanism in liver regeneration and repair: hepatic injury, DNA synthesis inhibition, or apoptosis caused by IFN-gamma is subsequently overcome by cytokine-induced HGF/SF, a potent promoter of liver DNA synthesis.

Expression of the HGF/SF receptor, c-met, and its ligand in human colorectal cancers

The c-met proto-oncogene product is a receptor tyrosine kinase that mediates the effects of the multifunctional cytokine hepatocyte growth factor/scatter factor (HGF/SF). We have studied the expression of both the c-met receptor and HGF/SF at both the protein and message level in colorectal cancer tissues of varying disease stage. All of the tumors displayed an overexpression of the c-met mRNA compared to their normal tissue counterparts while 16 of 21 tissues (75%) displayed up-regulation of c-met protein. No HGF/SF mRNA or protein could be detected in either tissue type. Viable tumor cells extracted from cancer tissue exhibited increased motility in response to HGF/SF stimulation demonstrating that c-met was functionally active. No correlation between expression of c-met and tumor stage or degree of differentiation was observed. HGF/SF is known to be a potent stimulator of tumor cell motility and invasion, two cellular properties essential for the metastatic development of cancers. The overexpression of the HGF/SF receptor in colorectal cancers may result in an increased sensitivity to HGF/SF, which may confer an enhanced metastatic potential to the cancer cells within the tumor body.

HGF/NK4 is a specific antagonist for pleiotrophic actions of hepatocyte growth factor

We prepared a specific antagonist for hepatocyte growth factor (HGF) and designated it HGF/NK4. HGF/NK4 is composed of N-terminal 447 amino acids of the alpha-chain of HGF, thus contains the N-terminal hairpin domain and subsequent four kringle domains. HGF/NK4 competitively inhibited the specific binding of HGF to the receptor. Importantly, HGF/NK4 neither stimulated DNA synthesis of primary cultured rat hepatocytes (mitogenesis) nor induced cell scattering (motogenesis) and branching tubulogenesis (morphogenesis) of MDCK renal epithelial cells, however, HGF/NK4 almost completely inhibited the mitogenic, motogenic, and morphogenic activities of HGF. HGF/NK4 also suppressed tyrosine phosphorylation of the c-Met/HGF receptor induced by HGF. Apparently this is the first documentation of a specific antagonist which abrogates the mitogenic, motogenic, and morphogenic activities of HGF.

Simultaneous or delayed administration of hepatocyte growth factor equally represses the fibrotic changes in murine lung injury induced by bleomycin. A morphologic study

Hepatocyte growth factor (HGF) is a humoral mediator of epithelial-mesenchymal interactions, acting on a variety of epithelial cells as mitogen, motogen, and morphogen. Exogenous HGF acts as a hepatotrophic factor and a renotrophic factor during experimental injury. To investigate whether HGF has a pulmotrophic function, human recombinant HGF was administered to C57BL/6 mice with severe lung injury by bleomycin (BLM). Low dose simultaneous and continuous administration of HGF (50 micrograms/mouse/7 d) with BLM (100 mg/mouse/7 d) repressed fibrotic morphological changes at 2 and 4 wk. Ashcroft score showed a significant difference in lung fibrosis with and without HGF at 4 wk (3.7 +/- 0.4 versus 4.9 +/- 0.3, p < 0.05). Furthermore, either simultaneous or delayed administration of high dose HGF (280 micrograms/mouse/14 d) equally repressed fibrotic changes by BLM when examined at 4 wk (Ashcroft score: 2.6 +/- 0.4 and 2.4 +/- 0.2 versus 4.1 +/- 0.2, p < 0.01). Hydroxyproline content in the lungs was significantly lower in mice with either simultaneous or delayed administration of high dose HGF as compared to those administered BLM alone (121.8 +/- 8.1% and 113.2 +/- 6.2% versus 162.7 +/- 4.6%, p < 0.001). These findings indicate that exogenous HGF acts as a pulmotrophic factor in vivo and prevents the progression of BLM-induced lung injury when administered in either a simultaneous or delayed fashion. HGF may be a potent candidate to prevent or treat lung fibrosis.

Functional characterization of domains contained in hepatocyte growth factor-like protein

To delineate the functional protein domains necessary for the biological activity of hepatocyte growth factor-like protein (HGFL), we created various site-directed and deletion mutated cDNAs coding for this protein. Wild-type and mutated versions of HGFL were produced after transfection of the corresponding cDNAs into tissue culture cells. The biological importance of the domains within HGFL was then examined by addition of recombinant wild-type or mutant forms of HGFL to assays aimed at elucidating regions involved in the stimulation of DNA synthesis, the induction of shape changes in macrophages, and the ability to stimulate cell scattering. Mutant proteins lacking the serine protease-like domain (light chain) were not biologically active in any of the assays tested and could not compete with wild-type HGFL in cell scattering experiments. These data, in addition to direct enzyme-linked immunosorbent assay analyses, suggest that the light chain may play an important role in the interaction of HGFL with its receptor, Ron. Elimination of the proposed protease cleavage site between the heavy and light chains (by mutation of Arg-483 to Glu) produced a protein with activity comparable to wild-type HGFL. Further studies with this mutated protein uncovered an additional proteolytic cleavage site that produces biologically active protein. Deletion of the various kringle domains or the amino-terminal hairpin loop had various effects in the multiple assays. These data suggest that the heavy chain may play a pivotal role in determining the functional aspects of HGFL.

Existence of two nonlinear elimination mechanisms for hepatocyte growth factor in rats

Nonlinearity in the overall elimination of hepatocyte growth factor (HGF) was examined in rats. After intravenous administration, the plasma clearance (CLplasma) of HGF exhibited a dose-dependent biphasic reduction with high- and low-affinity components. If we consider our previous finding that both receptor-mediated endocytosis (RME) and a low-affinity uptake mechanism, probably mediated by heparan sulfate proteoglycan (HSPG), in the liver are major HGF clearance mechanisms, it may be that saturation of CLplasma at lower and higher doses represents saturation of RME and HSPG-mediated uptake, respectively. At an HGF dose (1.46 nmol/kg), which completely saturates the high-affinity component, CLplasma was almost completely reduced when HGF was premixed with heparin. However, CLplasma was reduced by heparin to, at most, one-fifth that after HGF alone in a dose near the linear range (3.66 pmol/kg). Saturation of CLplasma for HGF premixed with heparin was monophasic and nonlinear only at the lowest HGF doses. In vitro, high-affinity binding of [35S]heparin to HGF was found, showing that one HGF molecule binds to the penta- or hexasaccharide unit. Because mitogenic activity of HGF has been reported in the presence of heparin, these results suggest that heparin mainly inhibits low-affinity HGF uptake by complexing with HGF, whereas its effect on RME is relatively minor.

The HMC-1 human mast cell line expresses the hepatocyte growth factor receptor c-met

Hepatocyte growth factor (HGF) was originally characterized as a strong inducer of liver regeneration. However, it is now clear that HGF and its receptor, the proto-oncogene c-met, can be expressed in many other tissues, and that HGF can mediate diverse biological activities. We investigated the expression and function of c-met in a human mast cell line (HMC-1). We found that HMC-1 cells express c-met and that c-met expression can be upregulated by treatment of the cells with phorbol 12-myristate 13-acetate (PMA). Although HGF did not detectably influence the proliferation or morphology of HMC-1 cells, HGF inhibited the cells' ability to release tumor necrosis factor-alpha (TNF-alpha) in response to stimulation with PMA and the calcium ionophore, A23187. These results add the inhibition of TNF-alpha production to the other recognized effects of HGF/c-met on cellular function.

Early role of Fsp1 in epithelial-mesenchymal transformation

A seamless plasticity exists among cells shifting between epithelial and mesenchymal phenotypes during early development and again later, in adult tissues, following wound repair or organ remodeling in response to injury. Fsp1, a gene encoding a fibroblast-specific protein associated with mesenchymal cell morphology and motility, is expressed during epithelial-mesenchymal transformations (EMT) in vivo. In the current study, we identified several cytokines that induce Fsp1 in cultured epithelial cells. A combination of these factors, however, was most efficacious at completing the process of EMT. The optimal combination identified were two of the cytokines classically associated with fibrosis, i.e., transforming growth factor-beta1 (TGF-beta1) and epidermal growth factor (EGF). To confirm that it was the induction of Fsp1 by these cytokines mediating EMT, we used antisense oligomers to block Fsp1 production and subsequently measured cell motility and markers of EMT phenotype. The antisense oligomers suppressed Fsp1 expresison and epithelial transformation; therefore, we conclude that the appearance of Fsp1 is an important early event in the pathway toward EMT.

Hemodynamic effects of scatter factor in conscious rats

Scatter factor (SF), also known as hepatocyte growth factor, is a potent mitogen that has been suggested to exhibit greater efficacy than vascular endothelial growth factor (VEGF) in rabbits with hindlimb ischemia. Our study examined the effects of SF on cardiovascular hemodynamics and compared the responses to VEGF. Hemodynamic parameters were monitored before and after administration of SF or VEGF in conscious, instrumented rats. Intravenous injection of SF produced a dose-related reduction in mean arterial pressure (MAP) and increase in heart rate (HR). These responses were significantly attenuated by pretreatment with N omega-nitro-L-arginine methyl ester a nitric oxide (NO) synthase inhibitor, suggesting the depressor effect of SF may be mediated by NO. SF (250 micrograms/kg) reduced stroke volume and cardiac output, but did not affect the maximal first derivation of left ventricular pressure (dP/dt), suggesting that the reduction in cardiac output is caused by decreased stroke volume that probably results from a reduction in venous return. Compared with SF, VEGF produced greater hypotensive and tachycardic responses and greater reductions in stroke volume and cardiac output, indicating that SF has fewer side effects on hemodynamics. Although both growth factors might reduce venous return, SF decreased hematocrit presumably through venodilation, whereas VEGF increased hematocrit as a result of vascular hyperpermeability.

Growth and differentiation factors inhibit the migratory phenotype of cultured neonatal rat hepatocytes induced by HGF/SF

Previous studies have demonstrated that neonatal rat hepatocytes cultured in a serum-free medium adopt a fibroblast-like morphology and form a well-developed vimentin network. By immunoblotting, phase-contrast microscopy, and immunolocalization studies we report here that hepatocyte growth factor (HGF) induces a pronounced migratory/scatter phenotype in neonatal hepatocytes in primary culture. These fibroblast-like cells are highly elongated and adopt a pronounced spindle shape in the presence of this growth factor. Most of them coexpress vimentin and cytokeratin intermediate filaments. Both EGF and TGF-beta1 also induced vimentin expression in cytokeratin-positive cells but this effect was not correlated with a change of epithelial phenotype. Only in DMSO-supplemented cultures was vimentin expression of hepatocytes inhibited and no coexpression was observed in the presence of this factor. Remarkably, the effect induced by HGF was totally inhibited when DMSO, TGF-beta1, or EGF was added to HGF-supplemented cultures. Epithelial sheets of well-defined hepatocytes were observed with these combinations although the complete epithelial morphology was achieved by combining DMSO with a growth factor. Taken together these results suggest that growth and differentiation factors modulate the migratory effect of HGF/SF in hepatocytes.

Hepatocyte growth factor (HGF/SF) is a muscle-derived survival factor for a subpopulation of embryonic motoneurons

Muscle-derived factors are known to be important for the survival of developing spinal motoneurons, but the molecules involved have not been characterized. Hepatocyte growth factor/scatter factor (HGF/SF) plays an important role in muscle development and motoneuron axon outgrowth. We show that HGF/SF has potent neurotrophic activity (EC50=2 pM) for a subpopulation (40%) of purified embryonic rat motoneurons. Moreover, HGF/SF is an essential component of muscle-derived support for motoneurons, since blocking antibodies to HGF/SF specifically inhibited 65% of the trophic activity of media conditioned by C2/C7 skeletal myotubes, but did not inhibit the trophic activity secreted by Schwann cell lines. High levels of expression of the HGF/SF receptor c-Met in the spinal cord are restricted to subsets of motoneurons, mainly in limb-innervating segments. Consistent with this distribution, cultured motoneurons from limb-innervating brachial and lumbar segments showed a more potent response to HGF/SF than did thoracic motoneurons. By the end of the period of motoneuron cell death, levels of c-Met mRNA in motoneurons were markedly reduced, suggesting that the effects of HGF/SF may be limited to the period of motoneuron cell death. HGF/SF may play an important role during motoneuron development as a muscle-derived survival factor for a subpopulation of limb-innervating motoneurons.

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.

Transcriptional induction of the agp/ebp (c/ebp beta) gene by hepatocyte growth factor

Hepatocyte growth factor (HGF) is a pleiotropic factor with mitogenic, morphogenic, motogenic, cytotoxic, or growth inhibitory activity. Although the signaling of HGF is mediated through the cell membrane receptor c-Met, the molecular mechanism of downstream signal transduction remains obscure. In this report, we present evidence that shows HGF can stimulate the expression of AGP/EBP (C/EBP beta) and NF-kappaB, which are both key transcription factors responsible for the regulation of many genes under stress conditions or during the acute-phase response. Biochemical and functional analysis indicates that the HGF-responsive element is located in the region -376 to -352 (URE1) of the 5'-upstream regulatory sequence of agp/ebp. Activation of NF-kappaB by HGF was observed to precede the induction of agp/ebp. Further studies indicate that NF-kappaB can cooperate with AGP/EBP or other members of the C/EBP family to activate the agp/ebp gene in both URE1 and URE2-dependent manner. These results suggest that the induction of the agp/ebp gene by HGF is mediated at least in part by its activation of NF-kappaB. The activated NF-kappaB then interacts with AGP/EBP, resulting in the induction of agp/ebp.

Interaction of c-myc with transforming growth factor alpha and hepatocyte growth factor in hepatocarcinogenesis

Double transgenic mice bearing fusion genes consisting of mouse albumin enhancer/promoter-mouse c-myc cDNA and mouse metallothionein 1 promoter-human TGF-alpha cDNA were generated to investigate the interaction of these genes in hepatic oncogenesis and to provide a general paradigm for characterizing the interaction of nuclear oncogenes and growth factors in tumorigenesis. Coexpression of c-myc and TGF-alpha as transgenes in the mouse liver resulted in a tremendous acceleration of neoplastic development in this organ as compared to expression of either of these transgenes alone. The two distinct cellular reactions that occurred in the liver of the double transgenic mice prior to the appearance of liver tumors were dysplastic and apoptotic changes in the existing hepatocytes followed by emergence of multiple focal lesions composed of both hyperplastic and dysplastic cell populations. These observations suggest that the interaction of c-myc and TGF-alpha, during development of hepatic neoplasia contributes to the selection and expansion of the preneoplastic cell populations which consequently increases the probability of malignant conversion. These studies have now been extended to examine the interaction of hepatocyte growth factor (HGF) with c-myc during hepatocarcinogenesis in the transgenic mouse model. While sustained overexpression of c-myc in the liver leads to cancer, coexpression of HGF and c-myc in the liver delayed the appearance of preneoplastic lesions and prevented malignant conversion. Similarly, tumor promotion by phenobarbital was completely inhibited in the c-myc/HGF double transgenic mice whereas phenobarbital was an effective tumor promoter in the c-myc single transgenic mice. The results indicate that HGF may function as a tumor suppressor during early stages of liver carcinogenesis, and suggest the possibility of therapeutic application for this cytokine. Furthermore, we show for the first time that interaction of c-myc with HGF or TGF-alpha results in profoundly different outcomes of the neoplastic process in the liver.

Dimerization of Fab fragments enables ready screening of phage antibodies that affect hepatocyte growth factor/scatter factor activity on target cells

A number of applications of antibodies in diagnosis and therapy require multivalent reagents either because of the polymeric nature of the antigens or because biological activity depends on an effect on the formation of homodimeric species. Here, we report a procedure for mass screening of phage-derived monomeric antibody fragments that depend on valency for activity. As a model system, a set of 13 phage-derived human Fab fragments were first selected against mouse and human recombinant hepatocyte growth factor/scatter factor (HGF/SF), a high molecular weight polypeptide growth factor related to the blood protease plasminogen and involved in development and cancer. These Fab fragments were subsequently screened for an effect on HGF/SF activity either as monomeric fragments or after dimerization with a monoclonal antibody (9E10) directed against a peptide tag on the fragments. Fab were identified that either inhibited or enhanced HGF/SF activity on target cell lines, but dimerization was required for this effect. The approach proposed should facilitate mass screening of phage-derived antibody fragments that depend on multiple valency for activity.

Transforming growth factor-beta and hepatocyte growth factor produced by gastric fibroblasts stimulate the invasiveness of scirrhous gastric cancer cells

Scirrhous gastric carcinoma is characterized by cancer cells that infiltrate rapidly in the stroma with extensive growth of fibroblasts. In the present study, we examined the effect of gastric fibroblasts on the invasiveness of a scirrhous gastric cancer cell line, OCUM-2D, using an invasion assay. Gastric fibroblast-derived conditioned medium (CM) significantly stimulated the invasiveness of OCUM-2D cells, as did transforming growth factor-beta (TGF-beta) and hepatocyte growth factor (HGF). The stimulating activity of gastric fibroblast-derived CM was inhibited significantly by anti-TGF-beta neutralizing antibody or anti-HGF neutralizing antibody. TGF-beta and HGF were detected in the gastric fibroblast-derived CM, and TGF-beta receptor and C-met (HGF receptor) were expressed on OCUM-2D cells. Thus, TGF-beta and HGF produced by gastric fibroblasts appear to affect the invasiveness of scirrhous gastric cancer cells. TGF-beta was also detected in the conditioned medium derived from OCUM-2D cells, though HGF was not. TGF-beta appears to affect the invasiveness of OCUM-2D cells in both paracrine and autocrine fashions.

Effect of phosphorylated rat fetuin on the growth of hepatocytes in primary culture in the presence of human hepatocyte-growth factor. Evidence that phosphorylated fetuin is a natural modulator of hepatocyte-growth factor

Rat fetuin, a counterpart of human alpha 2-HS glycoprotein and bovine fetuin, that is synthesized and secreted by hepatocytes is mostly phosphorylated, though rat fetuin isolated from bone matrix does not contain phosphorus. A rat 63-kDa phosphorylated N-glycoprotein (pp63) is the phosphorylated form of rat fetuin and pp63 has been shown to inhibit insulin-receptor tyrosine kinase activity. Therefore, we examined the effect of phosphorylated rat fetuin (phosphofetuin) on DNA synthesis in rat hepatocytes in culture in the presence of human hepatocyte-growth factor (HGF), since the human receptor of HGF, c-Met, is known to contain a tyrosine-kinase domain in its intracellular domain. We found that phosphofetuin from conditioned medium of rat-hepatocyte cultures dose-dependently decreased HGF-stimulated DNA synthesis in hepatocytes, whereas addition of non-phosphorylated rat fetuin had no effect. Addition of anti-(rat fetuin) Ig to the culture medium increased HGF-stimulated DNA synthesis by hepatocytes. Immunoprecipitation and cross-linking experiments showed that phosphofetuin bound to human HGF. We found that phosphofetuin interfered with binding of HGF to its specific receptor(s). These observations suggest that phosphofetuin synthesized by hepatocytes may be a natural modulator of HGF as a chalone, and that regulation of expression of phosphofetuin by growth factors and cytokines may be involved in liver regeneration under inflammatory conditions, such as in hepatitis.

Regulation of angiogenesis by scatter factor

Scatter factor (SF, hepatocyte growth factor) is a cytokine that stimulates motility, proliferation, and morphogenesis of epithelia. These responses are transduced through a tyrosine kinase receptor that is encoded by a proto-oncogene (c-met). SF is a potent angiogenic molecule, and its angiogenic activity is mediated, in part, through direct actions on endothelial cells. These include stimulation of cell motility, proliferation, protease production, invasion, and organization into capillary-like tubes. SF also stimulates the proliferation of smooth muscle cells and pericytes, cell types that also participate in the formation of capillaries and other microvessels. SF is chronically overexpressed in tumors, and it is postulated SF may function as a tumor angiogenesis factor. SF production in tumors may be due, in part, to an abnormal tumor: stroma interaction in which tumor cells secrete soluble proteins (SF-inducing factors) that stimulate stromal cell SF production and in part to autocrine production by the tumor cells themselves. Recent studies suggest a linkage between tumor suppressors (anti-oncogenes) and inhibition of angiogenesis. We hypothesize that tumor suppressor gene mutations may contribute to activation of an SF-->c-met signalling pathway, leading to an invasive and angiogenic tumor phenotype. Modulation of this pathway may provide clinically useful methods of enhancing or inhibiting angiogenesis.