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

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

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

Hepatocyte growth factor levels in bone marrow plasma of patients with leukaemia and its gene expression in leukaemic blast cells

Hepatocyte growth factor (HGF) has been known as a multiple function factor, which also stimulates early haematopoiesis. In this study, we found that HGF was expressed at both the RNA and protein levels in acute myeloid leukaemia (AML) and chronic myeloid leukaemia (CML). In patients with AML (n = 20) and CML (n = 5), bone marrow plasma HGF concentrations were 20.44 +/- 6.26 (mean +/- s.e.) ng ml-1 and 7.17 +/- 0.53 ng ml-1 respectively. These were significantly higher (P < 0.01) than the value for normal subjects (n = 26): mean 0.92 +/- 0.09 ng ml-1. Constitutive HGF production was observed in freshly prepared leukaemic blast cells from three patients with high HGF levels of bone marrow plasma. Expression of HGF mRNA was correlated with bone marrow plasma HGF levels. After complete remission was obtained in six patients, bone marrow plasma HGF levels were significantly decreased. In contrast, the HGF mRNA was less abundantly expressed in acute lymphoid leukaemia (ALL). In patients with ALL (n = 5), bone marrow plasma HGF concentration (0.69 +/- 0.14 ng ml-1) remained low within the value for normal subjects. These results suggest that some populations of myeloid lineage cells have the ability to produce HGF.

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

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

Growth factor regulation of integrin-mediated cell motility

Cell motility, a primary component of tumor cell invasion, is a continuum of sequential events in which the cell extends pseudopodia, forms nascent attachments, assembles and contracts the cytoskeleton, and finally, as it translocates forward, disengages distal adhesions. What triggers cells to move? Substratum contact mediated by integrin adhesion receptors is important, but other signals such as chemokinetic factors appear to be required for continued crawling. It is now apparent that integrins do not simply bind cells to matrix in a Velcro-like fashion, but also are potent signaling molecules. Initial engagement of integrins induces their condensation into focal contacts, forming anchors to the extracellular matrix and discrete signal-transducing complexes on the cytoplasmic surface. A number of growth factors, through either autocrine or paracrine pathways, can activate the cellular machinery that mobilizes the cell. Thus, these two classes of receptors--the integrin receptors that bind specific extracellular adhesion molecules, and growth factor receptors that bind their respective ligands--can regulate cell locomotion. Not surprisingly, there is 'cross-talk' between integrin and growth factor receptors that occurs through their common intracellular signaling pathways. In this way, each receptor type can either amplify or attenuate the other's signal and downstream response. An example of growth factor-induced motility is the epithelial-mesenchymal transition induced by hepatocyte growth factor/scatter factor (HGF/SF). When bound to its receptor, the c-met proto-oncogene product, HGF/SF induces a phenotypic conversion that appears to be an important aspect of tumor progression in malignant carcinomas. The motogenic response produced by HGF/SF in carcinoma cells occurs in discrete steps in which integrins and focal adhesion kinase (p125FAK) are first recruited to focal contacts. This is rapidly followed by cell spreading, disruption of focal adhesions and cell-cell contacts, and, finally, cell crawling. The precise mechanism by which growth factors such as HGF/SF and its receptor induce this motogenic response and modulate integrin function has not been clearly defined but appears to involve several signaling pathways. Understanding the process by which growth factor and integrin receptors interact and regulate motility may suggest novel targets for therapeutic intervention.

Induction of invasive growth in a gallbladder cancer cell line by hepatocyte growth factor in vitro

To study the mechanism of invasion and metastasis of gallbladder cancer cells, we established a cancer cell line, GB-d1, from a metastatic lymphnode of poorly differentiated adenocarcinoma of the gallbladder. GB-d1 cells proliferate well in a dish culture and form small cystic cell clusters in a collagen gel containing 10% fetal bovine serum. A conditioned medium of human embryonic lung fibroblasts (HEL) stimulated the proliferation of GB-d1 cells and induced cell scattering in the dish culture. In the gel culture, the conditioned medium induced a transformation of the spherical clusters to arborizating colonies with tubular projections that mimicked an invasion of cancer cells into the surrounding tissue. Similar results were obtained when 10 ng/ml of human recombinant hepatocyte growth factor (h-rHGF) was added to the culture medium. The proliferative and morphological changes induced by the conditioned medium were inhibited by antiserum against h-HGF. HEL and human gallbladder stromal fibroblast-like cells produced substantial levels of HGF in the culture media, while GB-d1 did not produce any detectable level of HGF. These results suggest that HGF promotes the invasive growth of gallbladder cancer cells in vitro, and it was also suggested that stromal fibroblasts may play an important role in the invasive progression of gallbladder cancer in a paracrine fashion.

The biology of hepatocyte growth factor/scatter factor

Hepatocyte growth factor, a potent mitogen for epithelial and other cell types, and scatter factor, a stimulant of epithelial cell motility are identical. In addition to these mitogenic and motogenic functions, the factor has been shown to be an epithelial morphogen and also has antiproliferative effects in some cancer cell lines. The membrane receptor for hepatocyte growth factor/scatter factor has been identified as the c-met proto-oncogene product.

Expression patterns of ornithine decarboxylase and c-met in growing Yoshida AH-130 hepatoma

The expression of the two proto-oncogenes ornithine decarboxylase and c-met was examined during various phases of growth of Yoshida AH-130 ascites hepatoma. Ornithine decarboxylase (ODC) and c-met mRNA levels declined progressively from day 5 (exponential growth-phase) until day 14 (quasi-stationary growth-phase). Transcription rate for both the genes remained constant between days 5 and 10, while decreasing at day 14. ODC activity was consistent with ODC mRNA level during hepatoma growth. In host liver, ODC mRNA accumulated 5 and 14 days after tumor transplantation, while c-met mRNA level was elevated until day 10 and diminished at day 14. ODC activity triplicated at day 14 in host liver. The progressive decline in the expression of ODC and c-met observed in hepatoma might be one of the mechanisms important for the control of tumor growth.

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.

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

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

The molecular pathogenesis of hepatocellular carcinoma

Some of the multiple factors involved in the molecular pathogenesis of hepatocellular carcinoma have been elucidated in recent years but no clear picture of how and in what sequence these factors interact at the molecular level has emerged yet. Transformation of hepatocytes to the malignant phenotype may occur irrespective of the aetiological agent through a pathway of chronic liver injury, regeneration and cirrhosis. The activation of cellular oncogenes, the inactivation of tumour suppressor genes and overexpression of certain growth factors contribute to the development of HCC. There is increasing evidence that the hepatitis B virus may play a direct role in the molecular pathogenesis of HCC. Aflatoxins have been shown to induce specific mutations of the p53 tumour suppressor gene thus providing a clue to how an environmental factor may contribute to tumour development at the molecular level.

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

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

The mouse hepatocyte growth factor-encoding gene: structural organization and evolutionary conservation

A mouse genomic phage library was screened by using a cDNA probe coding for mouse hepatocyte growth factor (HGF). Five overlapping genomic clones which contained the entire mouse HGF gene were isolated and characterized by restriction mapping, Southern hybridization and DNA sequencing. HGF spans about 65 kb and consists of 18 exons separated by 17 introns, similar to its human counterpart. The nucleotide (nt) sequences of the introns at the exon-intron junctions are GT-AG, analogous to those found in other eukaryotic genes. The exon-intron gene organization of HGF is highly homologous to that of several other genes encoding kringle-containing proteins, especially HGF-like protein and plasminogen. This result suggests that HGF probably evolved through gene duplication and/or exon shuffling events from an ancestral gene. Southern hybridization of genomic DNA from different species revealed that a high degree of homology exists among a variety of vertebrates, including chicken, when a mouse HGF cDNA was used as a probe. This evolutionary conservation of HGF strongly suggests that the protein may play an important role in normal cell physiology. Our current results on mouse HGF structure provide basic and detailed information to carry out further manipulation, such as gene targeting.

Hepatocyte growth factor in transgenic mice: effects on hepatocyte growth, liver regeneration and gene expression

Attention has recently been focused on hepatocyte growth factor as a major candidate factor in liver regeneration because it is the most potent known mitogen for hepatocytes in vitro. However, hepatocyte growth factor also displays diverse activities in vitro as scatter factor, as an epithelial morphogen, as a pluripotent mitogen and as a growth inhibitor. Consequently, we developed transgenic mice that expressed hepatocyte growth factor under the control of albumin regulatory sequences to examine its in vivo role in hepatocyte growth. Hepatocytes of these mice expressed increased levels of hepatocyte growth factor as an autocrine growth factor. Hepatocyte growth factor was a potent stimulus for liver repair; the livers of hepatocyte growth factor-transgenic mice recovered completely in half the time needed for their normal siblings after partial hepatectomy. This transgenic model also enabled us to study the chronic effects of hepatocyte growth factor expression. During several months of observation, the labeling index of hepatocytes in albumin-hepatocyte growth factor mice was doubled, and liver DNA content was increased compared with that in wild-type mice. To identify intermediate signaling pathways for hepatocyte growth factor that might regulate this increased growth response, we examined transgenic mice for changes in expression of genes that are known to be regulated during liver regeneration. We found that levels of c-myc and c-jun mRNA were increased in the hepatocyte growth factor-transgenic mice. In additional experiments the increased c-myc expression was the consequence of increased transcription rates as seen in nuclear run-on and myc-CAT reporter gene experiments. We conclude that hepatocyte growth factor increases growth and repair processes when expressed for long periods in the liver and that c-myc and c-jun may be important intermediaries in the hepatocyte growth response caused by hepatocyte growth factor.

Partial purification and characterization of 'injurin-like' factor which stimulates production of hepatocyte growth factor

We have previously reported the evidence for presence of a humoral factor 'injurin', which induces expression of the hepatocyte growth factor (HGF) gene in MRC-5 human embryonic lung fibroblasts. We have now purified a factor from porcine liver which stimulates HGF production but differs from injurin. When injurin activity was measured as a stimulatory effect on HGF production by MRC-5 cells, this activity was found in various acid extracts from porcine tissues, including liver, kidney, brain, and lung, and acid extracts from the liver was used for purification. When the acid extract was applied to Q-Sepharose anion-exchange chromatography, 50-60% of the total injurin activity was absorbed to the column and the remaining activity was detected in the flow through fractions. Injurin activity was eluted from the Q-Sepharose column by NaCl concentration gradient with four peaks at 0.5-0.6 M, 0.7-0.8 M, 0.9-1.2 M. 1.5-2.0 M NaCl, thereby suggesting that the factor exists in heterogenous or various forms in tissues. The major active fractions were combined and applied to Mono-Q FPLC anion-exchange chromatography. Injurin activity eluted with a single peak at 0.9-1.5 M NaCl and this activity was 4286 fold purified from the starting extract. Addition of this fraction to MRC-5 cells increased the amount of HGF pulse-labeled with [35S]methionine to a 3-4-fold higher level than that seen in control cells, whereas it had no significant effect on HGF mRNA levels. Therefore, this factor seems to stimulate HGF synthesis affecting translational processes and is distinct from the previously characterized injurin which stimulates HGF gene expression. Chemical treatments and SDS-polyacrylamide gel electrophoresis of this injurin-like factor indicated that injurin-like factor is a acid- and heat-stable non-proteinous factor with an apparent M(r) of 8-15 kDa. Since the injurin activity of the factor was decreased by heparinase treatment, the factor may be a polysulfated glycosaminoglycan related to heparin or to heparan sulfate. These results suggest that HGF production may be regulated by this non-proteinous injurin-like factor and that this factor may also play an important role in the regeneration of organs, through translationally enhancing HGF production.

Hepatocyte growth factor elevates the activity levels of glycolipid sulfotransferases in renal cell carcinoma cells

Accumulation of sulfoglycolipids associated with markedly elevated activity levels of glycolipid sulfotransferases has previously been demonstrated in the human renal cell carcinoma cell line, SMKT-R3. To elucidate the regulatory mechanisms of sulfoglycolipid synthesis in SMKT-R3 cells, the effects of various growth factors on the metabolic enzymes of sulfoglycolipids were investigated. Hepatocyte growth factor (HGF) significantly increased the activity levels of the sulfotransferases in a dose-dependent manner, but did not change that of arylsulfatase A, which hydrolyzes sulfoglycolipids. Scatchard analysis of 125I-HGF binding to SMKT-R3 cells indicated that the cells expressed high-affinity receptors for HGF with a Kd of 36 pM and 750 sites/cell. Furthermore, metabolic labeling with [35S]sulfate revealed that the addition of HGF to the culture medium of the cells resulted in an increment of sulfoglycolipid synthesis. Therefore, these observations suggest that HGF can function as a regulatory factor in sulfoglycolipid synthesis through the modulation of the sulfotransferase activity levels in renal cell carcinoma cells. In addition, HGF stimulated the proliferation and motility of SMKT-R3 cells, suggesting that HGF has multiple biological activities in renal cell carcinoma cells.

c-met mRNA overexpression in human hepatocellular carcinoma

This study was aimed at assessing the presence of c-met overexpression in human hepatocellular carcinoma and at determining whether this feature is associated with a definite clinical or pathological characteristic. Expression of c-met was determined by Northern-blot hybridization of a specific probe (human met proto-oncogene) in 18 tumoral and nontumoral liver samples obtained in 18 cirrhotic patients with hepatocellular carcinoma submitted to surgical treatment. Eight of the 18 hepatocellular carcinomas exhibited c-met overexpression, with an increase ranging between 2-fold and 10-fold when compared by densitometry with the surrounding liver. By contrast, in the remaining 10 cases c-met expression was almost identical to that of the surrounding nontumoral liver tissue. Overexpression of c-met was not related to either the age, sex, etiology or functional status of the underlying liver disease, or to the size of the tumor, to its differentiation degree or to the presence of pseudocapsule invasion and existence of additional neoplastic nodules. These data indicate that almost half of the human hepatocellular carcinomas exhibit c-met overexpression. Nevertheless, the biological relevance of this characteristic is not known.

Breast carcinoma: a collective disorder

The development and differentiation of the epithelial component of glandular tissues such as the breast is regulated by two apparently unrelated processes. One of these is presumed to be epithelial cell collective autonomous, that is, it is mediated by gene products which act directly on the epithelial cells. An important component of autonomous regulation is the functional expression of homotypic cell-cell adhesion molecules such as cadherins. The second process is non-autonomous and involves an inductive effect of the neighboring mesenchymal cell collective. An important component of non-autonomous regulation is the aggregation/condensation of mesenchyme closely associated with the epithelium. We propose that molecular alterations in autonomous and non-autonomous pathways are important causes and indicators respectively of breast cancer progression and that these two fundamental regulators of epithelial collective organization are in fact inter-dependent. For example, we show that the expression of hepatocyte growth factor (HGF), an epithelially targeted mesenchymally derived morphogenic factor is regulated by mesenchymal cell density (condensation) and by factors released from epithelial cells. Breast epithelial cells produce factors which inhibit and stimulate HGF expression. The inhibitory factor is transforming growth factor beta (TGF-beta) and the activation state of TGF-beta is a crucial element in HGF homeostasis. The balance of negative and positive HGF regulators is markedly affected by the growth conditions and differentiation state of the epithelial cells. The expression of the HGF receptor, met, is high in normal breast epithelial cells and in dedifferentiated (ER negative) tumor cells but is reduced or lost in ER positive well differentiated epithelial cells. Our results indicate that the expression of at least one epithelial morphogen, HGF, is inter-dependently regulated by mesenchymal condensation and by factors released by neighboring epithelial cells.

Hepatocyte growth factor/scatter factor, liver regeneration and cancer metastasis

Hepatocyte growth factor (HGF) is the most potent stimulator of hepatocyte growth and DNA synthesis identified; it is now known to be the same molecule as scatter factor, which increases the motility of a variety of cell types. HGF is becoming recognized as one of the most important factors in the regulation of liver regeneration after surgical resection or chemical damage. HGF is produced by several tissues, including neoplasms; it can therefore provide a stimulus for increased motility of malignant cells by both a paracrine and autocrine mechanism. The receptor for HGF has been identified as the product of the oncogene c-met, raising the possibility that this gene plays a key role in facilitating cellular invasion. HGF may therefore be important not only for liver cell growth but also in metastasis. This article summarizes the current position of research on HGF, and presents both clinical and scientific evidence that strongly implicates this factor in liver regeneration and cancer invasion and metastasis.

Hepatocyte growth factor-like protein is identical to macrophage stimulating protein

Although the hepatocyte growth factor-like protein (HLP) shares a 50% homology with the hepatocyte growth factor, the biological function of HLP has remained unknown. Addition of conditioned medium of COS-7 cells transfected with the expression plasmid for HLP cDNA to cultures of resident peritoneal macrophages induced specific activation of macrophages, and the factor which stimulates macrophages was purified from the conditioned medium. The purified protein showed M(r) of 85 kDa on SDS-PAGE, and this M(r) is in agreement with that of macrophage-stimulating protein (MSP) previously purified from human serum, as well as with the predicted M(r) of HLP. Amino acid composition of the purified protein coincided with the compositions of human HLP and MSP. Together with the finding that the partial amino acid sequences of MSP are highly homologous to that of HLP, we conclude that the biological function of HLP is to activate macrophages and that HLP and MSP are identical molecules.

The Met receptor tyrosine kinase transduces motility, proliferation, and morphogenic signals of scatter factor/hepatocyte growth factor in epithelial cells

Depending on the target cells and culture conditions, scatter factor/hepatocyte growth factor (SF/HGF) mediates several distinct activities, i.e., cell motility, proliferation, invasiveness, tubular morphogenesis, angiogenesis, or cytotoxicity. A small isoform of SF/HGF encoded by a natural splice variant, which consists of the NH2-terminal hairpin structure and the first two kringle domains but not the protease homology region, induces cell motility but not mitogenesis. Two types of SF/HGF receptors have recently been discovered in epithelial cells, the high affinity c-Met receptor tyrosine kinase, and low affinity/high capacity binding sites, which are probably located on heparan sulfate proteoglycans. In the present study, we have addressed the question whether the various biological activities of SF/HGF are transduced into cells by a single type of receptor. We have here examined MDCK epithelial cells transfected with a hybrid cDNA encoding the ligand binding domain of the nerve growth factor (NGF) receptor and the membrane-spanning and tyrosine kinase domains of the Met receptor. We demonstrate that all biological effects of SF/HGF upon epithelial cells such as the induction of cell motility, proliferation, invasiveness, and tubular morphogenesis can now be triggered by the addition of NGF. Thus, it is likely that all known biological signals of SF/HGF are transduced through the receptor tyrosine kinase encoded by the c-Met protooncogene.

Properties and functions of scatter factor/hepatocyte growth factor and its receptor c-Met

Scatter factor (SF), a cell motility factor with a multimodular structure, is identical to hepatocyte growth factor (HGF), a potent mitogen of various cell types. The receptor for SF/HGF has recently been identified as the c-Met proto-oncogene product, a transmembrane receptor tyrosine kinase. Depending on the target cells and culture conditions, SF/HGF has several distinct activities in vitro, i.e., it induces cell motility, proliferation, invasiveness, tubular morphogenesis, angiogenesis, or cytotoxicity. In vivo, SF/HGF might be involved in tissue regeneration, tumor progression, and embryological processes.

Transfer of motogenic and invasive response to scatter factor/hepatocyte growth factor by transfection of human MET protooncogene

The MET protooncogene encodes p190MET, a tyrosine kinase which is the receptor for a molecule known as scatter factor or hepatocyte growth factor (SF/HGF). This molecule has different biological activities, including stimulation of cell motility, promotion of matrix invasion and, in some cells, mitogenesis. We have cloned the full-length MET cDNA and transfected it into NIH 3T3 fibroblasts. Stable transfectants expressed the p190MET receptor together with two previously described truncated forms of 140 and 130 kDa lacking the tyrosine kinase domain. All three forms bound radiolabeled SF/HGF. The factor stimulated tyrosine kinase activity of the transfected p190MET and induced changes in cell shape, migration in Boyden chambers, and invasion of collagen matrices in vitro. The motile and invasive phenotype was transient and strictly dependent on the presence of SF/HGF. The factor did not stimulate either cell growth or thymidine incorporation in transfected cells, while it promoted colony formation in soft agar in the presence of 5% fetal calf serum. These data show that, in the presence of its ligand, the MET receptor expressed in fibroblasts induces cells to pursue a motogenic-invasive rather than a proliferative program.

Expression of the proto-oncogenes c-met and c-kit and their ligands, hepatocyte growth factor/scatter factor and stem cell factor, in SCLC cell lines and xenografts

We examined a panel of 25 small cell lung cancer (SCLC) cell lines and nude mouse xenografts for expression of the proto-oncogenes c-met and c-kit, and for expression of the corresponding ligands, hepatocyte growth factor (HGF) (also known as scatter factor (SF)), and stem cell factor (SCF), respectively. Expression of mRNA was detected by Northern blotting, and c-met and c-kit protein expression was detected by Western blotting and immunocytochemistry. c-met and c-kit mRNA was expressed in 22 of the examined cell lines or xenografts, and coexpression of the two proto-oncogenes was observed in 20 tumours. Expression of c-met and c-kit protein paralleled in the mRNA expression. HGF/SF mRNA was expressed in two of the examined tumours, and only one of these also expressed the c-met proto-oncogene. SCF mRNA was expressed in 19 of the examined tumours, and in 18 of these coexpression of c-kit and SCF was present. The high percentage of SCLC tumours expressing c-met and c-kit indicates that these proto-oncogenes may have an important function in this disease. The rare coexpression of c-met and HGF/SF is evidence that an autocrine regulatory pathway is not present for this receptor/ligand system in SCLC, while the frequent coexpression of c-kit and SCF indicates that this receptor/ligand system may have an autocrine function in SCLC.

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

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

A functional domain in the heavy chain of scatter factor/hepatocyte growth factor binds the c-Met receptor and induces cell dissociation but not mitogenesis

We recently found that scatter factor (SF), a cell motility factor with a multimodular structure, is identical to hepatocyte growth factor (HGF), a potent mitogen of various cell types. SF/HGF is the ligand of the c-Met receptor tyrosine kinase. Here we used transient expression of naturally occurring and in vitro mutagenized cDNAs of SF/HGF to delineate the protein domains necessary for biological activity and binding to the c-Met receptor. (i) A single-chain SF/HGF resulting from the destruction of the protease cleavage site between heavy and light chain (Arg-494--> Gln) was largely inactive, indicating that proteolytic cleavage is essential for acquisition of the biologically active conformation. (ii) A SF/HGF splice variant encoding a protein with a 5-amino acid deletion in the first kringle domain was as highly active as the wild-type molecule. (iii) The separately expressed light chain (with serine protease homology) was inactive in all assays tested. (iv) The separate heavy chain as well as a naturally occurring splice variant consisting of the N terminus and the first two kringle domains bound the c-Met receptor, stimulated tyrosine auto-phosphorylation, and induced scattering of epithelial cells but not mitogenesis. These data indicate that a functional domain in the N terminus/first two kringle regions of SF/HGF is sufficient for binding to the Met receptor and that this leads to the activation of the downstream signal cascade involved in the motility response. However, the complete SF/HGF protein seems to be required for mitogenic activity.

Proteinases and proteinase inhibitors as modulators of animal cell growth

1. Three distinct lines of evidence indicate that proteinases are involved in the growth of cultured animal cells. 2. Endogenous growth-related proteinases have been identified, and exogenous proteinases can also stimulate cell proliferation, probably by different mechanisms. In some cases, higher concentrations of proteinases are cytotoxic. 3. Proteinase inhibitors, not surprisingly, inhibit cell growth, but can also be mitogenic at sub-inhibitory concentrations. 4. There must, therefore, be at least three major cellular processes in which proteinases or proteinase inhibitors can operate to exert a direct effect on cell proliferation. 5. Details of one action of an exogenous proteinase, typified by thrombin and the thrombin receptor, are becoming clear at the molecular level, but thrombin probably activates at least two intracellular signalling systems, as well as acting as a growth inhibitor in some situations. 6. Much remains to be investigated in other examples.

Hepatocyte growth factor down-regulates the alpha-fetoprotein gene expression in PLC/PRF/5 human hepatoma cells

Hepatocyte growth factor (HGF) is a potent mitogen for hepatocytes; however, in certain human hepatoma cell lines, the growth is inhibited by HGF. In the present study, the effect of HGF on the alpha-fetoprotein (AFP) gene expression was analyzed in PLC/PRF/5 human hepatoma cells. HGF did not inhibit cell proliferation, but dose-dependently suppressed AFP secretion at the concentrations of 10 ng/ml or less. By Northern blot analysis, the levels of AFP mRNA were suppressed by HGF, whereas the levels of beta-actin mRNA used as a control did not show any significant changes. In the transient chloramphenicol acetyltransferase plasmid transfection assays, the AFP promoter activity was repressed by HGF, in contrast, the AFP enhancer activity was not affected by HGF. These results suggest that the AFP gene expression is down-regulated by HGF through the suppression of its promoter activity in human hepatoma cells.

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

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

Differential expression of hepatocyte growth factor, transforming growth factor-alpha and transforming growth factor-beta 1 messenger RNAs in two experimental models of liver cell proliferation

Hepatocyte growth factor, a potent hepatocyte mitogen in vitro, appears to trigger hepatocyte regeneration after partial hepatectomy and after acute liver cell necrosis. Transforming growth factor-alpha and transforming growth factor-beta 1 may also be involved in the control of liver regeneration. In this study we assessed possible roles of hepatocyte growth factor, transforming growth factor-alpha and transforming growth factor-beta 1 on liver cell proliferation in vivo, using a model of choline deficiency that is associated with liver cell necrosis and a model of a hypolipidemic agent (4-chloro-6-(2,3 xylidino)-2-pyrimidinylthio (N-beta-hydroxyethyl) acetamide) without liver necrosis. Male F344 rats were fed a choline-deficient diet or 0.16% 4-chloro-6-(2,3 xylidino)-2-pyrimidinylthio (N-beta-hydroxyethyl) acetamide diet for 6 and 4 wk, respectively. Rats were killed periodically, and the expression of hepatocyte growth factor messenger RNA in the liver, lung and kidney was determined by Northern-blot analysis. The levels of transforming growth factor-alpha and transforming growth factor-beta 1 messenger RNAs in the liver were also determined. Feeding a choline-deficient diet for 1 to 6 wk led to gradual increases in the levels of hepatocyte growth factor, transforming growth factor-alpha and transforming growth factor-beta 1 messenger RNAs in the liver. Feeding a 4-chloro-6-(2,3 xylidino)-2-pyrimidinylthio (N-beta-hydroxyethyl) acetamide diet for 3 days and 2 wk induced marked enhancement of liver cell proliferation as judged by hepatocyte 5-bromo-2-deoxyuridine incorporation.(ABSTRACT TRUNCATED AT 250 WORDS)

Regulation of cell growth and motility by hepatocyte growth factor and receptor expression in various cell species

Hepatocyte growth factor (HGF), a humoral mediator for regeneration of liver and kidney, possesses multiple biological activities. To investigate target cell specificity and to examine whether multiple actions of HGF are related to properties of the HGF receptor on target cells, we examined the effects of HGF on cell growth and motility and analyzed the HGF receptor in various species of cells. HGF stimulated growth and DNA synthesis of PAM212 (naturally immortalized mouse keratinocytes), Mv1Lu (mink lung epithelia), and A431 (human epidermoid carcinoma) cells, as well as mature hepatocytes, but inhibited those of IM-9 (human B-lymphoblasts). Conversely, HGF had a marked stimulatory effect on cell motility of MDCK (Mardin-Darby canine kidney epithelia) cells, but not on their growth. Also, HGF enhanced the motility of various species of cells, including A431, PAM212, HepG2 (human hepatoma), KB (human epidermoid carcinoma), and J-111 (human monocytes) cells. Scatchard analysis of 125I-HGF binding to hepatocytes indicated that the cells expressed both high- and low-affinity binding sites for HGF with Kd values of 23 and 260 pM, respectively. High-affinity HGF receptor with Kd values of 20-25 pM was detected at 40-720 sites/cell in MDCK, A431, PAM212, Lu99, and IM-9 cells, but not in fibroblasts and hematopoietic cells. In contrast, low-affinity binding sites were detected in all cell lines examined, even in those not responsive to HGF. Northern blots revealed that cells possessing a high-affinity HGF receptor expressed c-MET/HGF receptor mRNA. Therefore, HGF probably regulates both cell growth and motility of various types of epithelial cells and some types of mesenchymal cells. The multiple biological activities of HGF may be exerted through a high-affinity HGF receptor linked to multiple distinct intracellular signaling pathways.

Role of the adenylate cyclase, phosphoinositidase C and receptor tyrosyl kinase systems in the control of hepatocyte proliferation by hepatocyte growth factor

Hepatocyte growth factor (HGF) is the most potent known mitogen for hepatocytes in primary culture. However, the mechanisms through which HGF induces hepatocyte proliferation have not been defined. Here we have investigated the role of the adenylate cyclase, phosphoinositidase C and tyrosine kinase signalling systems in the control of hepatocyte proliferation by HGF using freshly isolated or cultured adult rat hepatocytes. We show that human recombinant HGF caused a dose-dependent increase in hepatocyte DNA synthesis with a maximal effect at 10 ng/mL and an EC50 of 5.9 ng/mL. HGF had no effect on hepatocyte adenylate cyclase activity or intracellular cAMP levels. Elevation of hepatocyte cAMP levels resulted in inhibition of HGF-stimulated DNA synthesis. HGF stimulated inositol phospholipid hydrolysis with a maximal effect at 25 ng/mL and potentiated the effect of vasopressin (10(-8) and 10(-9)M). HGF (100 ng/mL) caused an increase in the phosphorylation on tyrosine of an unknown hepatocyte protein with a molecular mass of 36 kDa. Thus, we have shown that HGF, like epidermal growth factor (EGF), can activate the phosphoinositidase C and tyrosine kinase systems in rat hepatocytes. As with EGF, these intracellular signalling systems may underlie HGF-induced hepatocyte proliferation.

The met proto-oncogene receptor and lumen formation

The met proto-oncogene product (Met) and its ligand, hepatocyte growth factor/scatter factor (HGF/SF), have been implicated in cell mitogenic response, cell motility, and the promotion of the ordered spatial arrangement of tissue. By means of confocal laser-scanning microscopy, it was shown that Met is expressed in cells bordering lumen-like structures that resemble ducts in the human mammary cell line T47D. In human breast tissue biopsies, Met staining was intense in normal cells bordering mammary ducts but was reduced in adjacent tumor tissue. Met staining in lumen-forming organs colocalizes with staining of antibody to phosphotyrosine, which suggests that the Met receptor and its substrates may be activated in lumen structures or ducts. HGF/SF treatment of human epithelial carcinoma cell lines resulted in the formation of lumen-like structures in vitro. Reduced expression of Met could be related to the extent of tumor cell differentiation.

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

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

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

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

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

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