Scatter factor is a fibroblast-derived modulator of epithelial cell mobility

Tyrosine phosphorylation of beta-catenin and plakoglobin enhanced by hepatocyte growth factor and epidermal growth factor in human carcinoma cells

The effect of hepatocyte growth factor/scatter factor (HGF/SF) and epidermal growth factor (EGF) on cadherin-mediated adhesion of human carcinoma cells was studied. HGF/SF induced scattering of colonic adenocarcinoma HT29 and gastric adenocarcinomas MKN7 and MKN74 cells. Likewise, EGF induced scattering of HT29 and MKN7 cells. These cells expressed E-cadherin, which was concentrated at cell-cell contact sites. When the scattering of these cells was induced by HGF/SF or EGF, the E-cadherin concentration at cell-cell boundaries tended to decrease. Immunoblotting analyses, however, demonstrated that these growth factor treatments did not alter the expression of E-cadherin and E-cadherin-associated proteins, alpha- and beta-catenin and plakoglobin. beta-Catenin, plakoglobin and an unidentified 115-kDa molecule associated with E-cadherin were found to be phosphorylated at tyrosine residues, and these phosphorylations were enhanced by the growth factor treatments. These results suggest that HGF/SF and EGF may modulate the function of the cadherin-catenin system via tyrosine phosphorylation of cadherin-associated proteins.

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.

A large cell-adhesive scatter factor secreted by human gastric carcinoma cells

Human gastric carcinoma cell line STKM-1 secretes a large protein that induces scattering of a rat liver epithelial cell line (BRL) into disconnected individual cells in monolayer culture. This cell-scattering factor was purified from serum-free conditioned medium of STKM-1 cells and found to be composed of three disulfide-linked subunits of 140, 150, and 160 kDa. The 140-kDa peptide contains an amino acid sequence homologous to that of the laminin B2t chain. The native protein has an apparent molecular mass of > 1000 kDa and a pI of 5.0. In addition to the cell-scattering activity, the purified protein stimulates attachment of BRL cells to substrate and their migration. Similar effects have been observed toward various cell lines, including nontumorigenic epithelial, endothelial, and fibroblastic cell lines and human cancer cell lines. Similar cell-scattering activity was secreted by human squamous carcinoma and gastric carcinoma cell lines and nontumorigenic epithelial and endothelial cell lines. These results indicate that the protein, named "ladsin," is probably an extracellular matrix protein that regulates cell-cell and cell-substrate interactions and cell migration.

Molecular cloning and characterization of cDNA encoding mouse hepatocyte growth factor

A cDNA encoding mouse hepatocyte growth factor (HGF) has been cloned and completely sequenced by use of reverse transcriptase-polymerase chain reaction (RT-PCR) and subsequent cloning. Sequence analysis reveals that mouse HGF, similar to its human and rat counterparts, consists of 728 amino acids, and both the alpha- and beta-chains are encoded in a single open reading frame. Strong homology exists in the primary structure of HGF among the three species of mouse, rat and human (more than 90%), especially in Kringle 1 of the alpha chain which is assumed to be an essential domain for binding of HGF to its receptor, c-MET, a proto-oncogene product. Our results suggest the existence of evolutionary pressure to conserve the distinct structure, and presumably the biological functions, of HGF.

Immunohistochemical detection of hepatocyte growth factor/scatter factor in human cancerous and inflammatory lesions of various organs

Hepatocyte growth factor (HGF)/scatter factor (SF) is a multifunctional factor considered to be potentially involved in tissue regeneration, wound healing, embryogenesis, angiogenesis and cancer invasion. Here we examined immunohistochemically the distribution of HGF/SF in human tissues, including cancerous and inflammatory tissues, using anti-HGF antibody. HGF/SF accumulation was clearly detected in the extracellular matrix, particularly along the basement membrane, in cancerous and inflammatory tissues, but only a little was detected in normal tissues. HGF/SF is well known to have a strong affinity for heparin in vitro, and from the results of our immunohistochemical assay, we considered that HGF/SF was bound to heparin or heparan sulfate of the extracellular matrix and basement membrane. HGF/SF was well localized in cancerous and inflammatory lesions of human lung, liver and pancreas, and in apparently normal tissues of kidney, adrenal gland and pancreas obtained at autopsy. In lung, HGF/SF was localized along the basement membranes of cancer cell nests, in the extracellular matrix of the cancer cell surface, cancer stroma and tissues invaded by cancer, and the basement membranes of bronchial epithelium and capillary vessels in inflammatory stroma. Since HGF/SF makes some cancer cells more invasive in vitro, the accumulation of HGF/SF in cancerous tissue suggests that the invasiveness of some cancer cells may be increased by HGF/SF in vivo.

Morphogenesis of the avian trunk neural crest: use of morphological techniques in elucidating the process

Morphological data generated from light and electron microscopy form the basis of our understanding of avian morphogenesis. Because chicken embryos are readily and cheaply obtained and are easily accessible for experimental manipulation, morphogenetic processes have been studied extensively in this species. Such studies have allowed us to identify the cells involved during morphogenesis, observe the shape changes or cellular translocations that accompany a morphogenetic process, and determine the timing of these events. Elucidation of the molecular basis of morphogenesis has awaited the integration of several additional approaches. Among these are experimental embryology, which has allowed us to understand cellular behavior associated with morphogenesis; immunocytochemistry, which has identified the macromolecular cues that regulate cell movements and the environmental factors that control them; and molecular techniques, which will permit us eventually to clarify the genetic regulation of morphogenesis. Although current research in development is heavily biased towards molecular biology, morphological studies continue to frame the questions that are now being addressed using molecular techniques. This review focuses on the cells of the neural crest as a model system where questions of avian morphogenesis have been profitably addressed.

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.

Gastrulation in the mouse embryo: ultrastructural and molecular aspects of germ layer morphogenesis

Ultrastructural studies and lineage analyses of gastrulating mouse embryos have revealed that different morphogenetic tissue movements are involved in the formation of the three definitive germ layers. Definitive ectoderm is formed by epibolic expansion of the pre-existing progenitor population in the embryonic ectoderm. Formation of the mesoderm and the endoderm is initiated by cellular ingression at the primitive streak. The mesodermal layer is established by cell migration and cell sheet spreading, but the endoderm is formed by replacing the original primitive endodermal population. To this date, genes that are expressed during mouse gastrulation mostly encode cell surface adhesion or signalling molecules, growth factors and their receptors, and putative transcriptional factors. Their precise role during gastrulation remains to be investigated.

Expression of the c-Met/HGF receptor in human melanocytic neoplasms: demonstration of the relationship to malignant melanoma tumour progression

The c-MET proto-oncogene encodes the receptor for the Hepatocyte Growth Factor/Scatter Factor, which is known to mediate mitogenic, motogenic and invasive responses of several cell types. We have analysed by immunohistochemistry and biochemically the expression of c-MET in benign and malignant melanocytic lesions. The Met/HGF receptor which in the melanocytic lineage displays the structural features of the authentic receptor was undetectable in tissue melanocytes and in nevocytic nevi. Only four out of 23 primary melanomas scored positive. Expression was increased to a significant level in 17 out of the 44 metastatic lesions examined. The c-MET expression was homogeneous in multiple metastases from the same patients. Comparative analyses showed both lack of correlation with the expression of the tumour progression associated ICAM-1 adhesion molecule and, in 23% of cases, co-expression with the c-KIT encoded receptor. These findings show that the c-MET gene is expressed at late stages of melanoma progression and suggest that the presence of Met/HGF receptor may contribute to the acquisition of an invasive phenotype.

The role of cell adhesion molecules in cancer invasion and metastasis

Invasion and metastasis of tumor cells is the primary cause for the fatal outcome of cancer diseases. A striking feature of metastatic cells is the considerable flexibility in their adhesive interactions with other cells or components of the extracellular matrix. This review will describe the involvement of specific cell adhesion receptors, extracellular matrix molecules, and cell dissociating cytokines in the metastatic cascade. We will particularly focus on disturbance of intercellular adhesion as a prerequisite for the release of invasive cells from carcinomas. We suggest that cell dissociation in these tumors is accomplished by loss of function or expression of the epithelial cell adhesion molecule E-cadherin, and through the activity of cell motility factors, like scatter factor.

Scatter factor/hepatocyte growth factor and its receptor, the c-met tyrosine kinase, can mediate a signal exchange between mesenchyme and epithelia during mouse development

Scatter factor/hepatocyte growth factor (SF/HGF) has potent motogenic, mitogenic, and morphogenetic activities on epithelial cells in vitro. The cell surface receptor for this factor was recently identified: it is the product of the c-met protooncogene, a receptor-type tyrosine kinase. We report here the novel and distinct expression patterns of SF/HGF and its receptor during mouse development, which was determined by a combination of in situ hybridization and RNase protection experiments. Predominantly, we detect transcripts of c-met in epithelial cells of various developing organs, whereas the ligand is expressed in distinct mesenchymal cells in close vicinity. In addition, transient SF/HGF and c-met expression is found at certain sites of muscle formation; transient expression of the c-met gene is also detected in developing motoneurons. SF/HGF and the c-met receptor might thus play multiple developmental roles, most notably, mediate a signal given by mesenchyme and received by epithelial. Mesenchymal signals are known to govern differentiation and morphogenesis of many epithelia, but the molecular nature of the signals has remained poorly understood. Therefore, the known biological activities of SF/HGF in vitro and the embryonal expression pattern reported here indicate that this mesenchymal factor can transmit morphogenetic signals in epithelial development and suggest a molecular mechanism for mesenchymal epithelial interactions.

E-cadherin: a marker for differentiation and invasiveness in prostatic carcinoma

Considerable controversy exists concerning the value of histomorphological data in the assessment of the malignant potential of prostatic carcinomas. We investigated the expression pattern of E-cadherin in human prostate at the translational level. E-cadherin is a specific epithelial cell-cell adhesion molecule which has previously been found to be expressed in well-differentiated non-invasive carcinoma cell lines but is lost in many poorly differentiated invasive cell lines. The E-cadherin expression pattern in the prostate samples was correlated with histopathological findings in the same specimens. We found strong E-cadherin expression in normal prostate and benign prostatic hyperplasia. A decrease in or loss of E-cadherin was seen in 13 of 14 locally advanced and in 8 of 9 poorly differentiated prostatic carcinomas. We conclude that downregulation of E-cadherin expression plays a role in prostate carcinogenesis and invasiveness.

Structure, genetic mapping, and expression of the mouse Hgf/scatter factor gene

The cytokine termed hepatocyte growth factor or scatter factor (HGF/SF) has been implicated in embryonic development and liver regeneration. Mouse HGF/SF cDNA clones were obtained by screening a mouse liver cDNA library with synthetic oligonucleotides, as well as by using the method of reverse transcription-polymerase chain reaction (RT-PCR) with mRNA isolated from adult mouse brain. Sequence analysis of mouse HGF/SF cDNA clones spanning the entire coding region revealed an overall amino acid identity of 90% and 98% with human and rat HGF, respectively. Using mouse HGF antisense RNA as a probe, we observed the expression of HGF/SF mRNA in the liver, kidney, whole brain and cerebellum of adult mice as well as in day 9 and day 10 mouse embryos. The mouse HGF/SF cDNA was utilized for mapping Hgf to the centromeric region of mouse Chromosome 5 in apparent close proximity to the reeler mutation by the analysis of two multilocus crosses. The relationship of Hgf to the reeler mutation is discussed. The availability of mouse HGF/SF cDNA clones should facilitate further analysis of HGF/SF function during development.

A novel recognition motif for phosphatidylinositol 3-kinase binding mediates its association with the hepatocyte growth factor/scatter factor receptor

The pleiotropic effects (mitogenesis, motogenesis, and morphogenesis) elicited by hepatocyte growth factor/scatter factor (HGF/SF) are mediated by the activation of the tyrosine kinase receptor encoded by the MET proto-oncogene. Following autophosphorylation, the receptor associates with the p85/110 phosphatidylinositol (PI) 3-kinase complex in vivo and in vitro. By a combination of two complementary approaches, competition with synthetic phosphopeptides and association with Tyr-Phe receptor mutants, we have identified Y-1349 and Y-1356 in the HGF/SF receptor as the binding sites for PI 3-kinase. Y-1349VHV and Y-1356VNV do not conform to the canonical consensus sequence YXXM for PI 3-kinase binding and thus define YVXV as a novel recognition motif. Y-1349 and Y-1356 are located within the C-terminal portion of the HGF/SF receptor and are phosphorylation sites. The affinity of the N- and C-terminal src homology region 2 (SH2) domains of p85 for the phosphopeptides including Y-1349 and Y-1356 is 2 orders of magnitude lower than that measured for Y-751 in the platelet-derived growth factor receptor binding site. However, the closely spaced duplication of the novel recognition motif in the native HGF/SF receptor may allow binding with both SH2 domains of p85, thus generating an efficient docking site for PI 3-kinase. In agreement with this model, we have observed that a phosphopeptide including both Y-1349 and Y-1356 activates PI 3-kinase in vitro.

Keratinocyte growth factor and hepatocyte growth factor/scatter factor are heparin-binding growth factors for alveolar type II cells in fibroblast-conditioned medium

Epithelial-mesenchymal interactions mediate aspects of normal lung growth and development and are important in the restoration of normal alveolar architecture after lung injury. To determine if fibroblasts are a source of soluble growth factors for alveolar type II cells, we investigated the effect of fibroblast-conditioned medium (CM) on alveolar type II cell DNA synthesis. Serum-free CM from confluent adult human lung fibroblasts was concentrated fivefold by lyophilization. Type II cells were isolated from adult rats by elastase dissociation and incubated with [3H]thymidine and varying dilutions of concentrated CM and serum from day 1 to 3 of culture. Stimulation of type II cell DNA synthesis by fibroblast-CM was maximal after 48 h of conditioning and required the presence of serum. The activity of the CM was eliminated by boiling and by treatment with trypsin, pepsin, or dithiothreitol and was additive with saturating concentrations of acidic fibroblast growth factor, epidermal growth factor, and insulin. The growth factor activity bound to heparin-Sepharose and was eluted with 0.6 and 1.0 M NaCl. Neutralizing antibody studies demonstrated that the primary mitogens isolated in the 0.6 and 1.0 M NaCl fractions were keratinocyte growth factor (KGF, fibroblast growth factor 7) and hepatocyte growth factor/scatter factor (HGF/SF), respectively. HGF/SF was demonstrated in the crude CM and KGF was detected in the 0.6 M NaCl eluent by immunoblotting. Northern blot analysis confirmed that the lung fibroblasts expressed both KGF and HGF/SF transcripts. Human recombinant KGF and HGF/SF induced a concentration- and serum-dependent increase in rat alveolar type II cell DNA synthesis. We conclude that adult human lung fibroblasts produce at least two soluble heparin-binding growth factors, KGF and HGF/SF, which promote DNA synthesis and proliferation of rat alveolar type II cells in primary culture. KGF and HGF/SF may be important stimuli for alveolar type II cell proliferation during lung growth and after lung injury.

A novel recognition motif for phosphatidylinositol 3-kinase binding mediates its association with the hepatocyte growth factor/scatter factor receptor

The pleiotropic effects (mitogenesis, motogenesis, and morphogenesis) elicited by hepatocyte growth factor/scatter factor (HGF/SF) are mediated by the activation of the tyrosine kinase receptor encoded by the MET proto-oncogene. Following autophosphorylation, the receptor associates with the p85/110 phosphatidylinositol (PI) 3-kinase complex in vivo and in vitro. By a combination of two complementary approaches, competition with synthetic phosphopeptides and association with Tyr-Phe receptor mutants, we have identified Y-1349 and Y-1356 in the HGF/SF receptor as the binding sites for PI 3-kinase. Y-1349VHV and Y-1356VNV do not conform to the canonical consensus sequence YXXM for PI 3-kinase binding and thus define YVXV as a novel recognition motif. Y-1349 and Y-1356 are located within the C-terminal portion of the HGF/SF receptor and are phosphorylation sites. The affinity of the N- and C-terminal src homology region 2 (SH2) domains of p85 for the phosphopeptides including Y-1349 and Y-1356 is 2 orders of magnitude lower than that measured for Y-751 in the platelet-derived growth factor receptor binding site. However, the closely spaced duplication of the novel recognition motif in the native HGF/SF receptor may allow binding with both SH2 domains of p85, thus generating an efficient docking site for PI 3-kinase. In agreement with this model, we have observed that a phosphopeptide including both Y-1349 and Y-1356 activates PI 3-kinase in vitro.

The hepatocyte growth factor and its receptor

Hepatocyte growth factor/scatter factor (HGF/SF) is secreted by cells of mesodermal origin and shows powerful mitogenic, motogenic and morphogenic activities on epithelial and endothelial cells. It is a heparin-binding polypeptide with an alpha/beta heterodimeric structure, showing structural homologies with enzymes of the blood clotting cascade. HGF binds with high affinity to the receptor encoded by the MET protooncogene (p190MET). The MET receptor is a heterodimer of two disulfide-linked subunits (alpha and beta); the alpha subunit is extracellular, while the beta is transmembrane and endowed with tyrosine kinase activity. The HGF-triggered signalling is mediated by different cytoplasmic effectors, including phosphatidylinositol 3-kinase, phospholipase C-gamma, and Src-related tyrosine kinases. p190MET is expressed in several normal epithelial tissues (e.g., liver, gastrointestinal tract, kidney) and is often overexpressed in neoplastic cells. p190MET expression has been reported also in central nervous system microglia, a monocyte-derived cell population. We recently found that p190MET is expressed in selected peripheral blood cell populations, such as macrophages. The amount of both mRNA and protein is barely detectable, while it is dramatically increased upon activation. These findings suggest that HGF may play a role in hemopoietic cell signaling, during activation and differentiation of blood cell lineages.

Soluble factors from human hair papilla cells and dermal fibroblasts dramatically increase the clonal growth of outer root sheath cells

Depending on environmental influences, follicular outer root sheath (ORS) cells in vivo can differentiate either towards interfollicular keratinocytes or, as demonstrated in the rat vibrissa, hair matrix cells. Crucial regulators of both their proliferation and differentiation are the mesenchymal cells of the respective tissues. The interactions of human ORS cells with human hair papilla cells (HPC) or human dermal fibroblasts (HDF) were studied using a two-chamber model separating the two cell types either by a microporous membrane or additionally by a medium layer. The results of 3H-thymidine incorporation studies indicated that ORS cell growth was markedly enhanced in co-culture with either HPC or HDF, the highest stimulatory effect resulting when ORS cells were in close association with the mesenchymal cells. No correlation was found between ORS cell proliferation and IL-6 production in the co-culture system, thus pointing to the secretion by HPC and HDF of growth-promoting soluble factors that are different form IL-6 as well as from EGF, bFGF and insulin present in the culture medium.

Controlled induction of focal adhesion disassembly and migration in primary fibroblasts

Fibroblast migration is an integral component of biological processes such as wound healing and embryogenesis. Previous experiments examining fibroblast locomotion from tissue explants have shown that migrating fibroblasts lack, or contain only transient, focal adhesions (focal contacts). Focal adhesions are specialized regions of tight cell-matrix interaction, assembled by a complex process of transmembrane signalling. Although the explant model has been used for studying several aspects of fibroblast locomotion, it is limited by the lack of control over migration, and only a small percentage of the cells actually locomoting. Therefore, we have developed an in vitro model for cultured fibroblast strains where the presence or absence of focal adhesions can be manipulated, and in the latter case 70% of these cells become locomotory. The stimulus used to decrease the percentage of cells containing focal adhesions, and hence enhance locomotion, was newborn rat heart-conditioned medium (HCM). Addition of HCM to rat embryo fibroblasts induced both chemokinesis and chemotaxis. Cells disassembled focal adhesions on a variety of extracellular matrix substrates after approximately 6 h of stimulation with HCM; conversely, removal of HCM promoted reformation of focal adhesions within 12–24 h. HCM-stimulated fibroblasts which lacked focal adhesions concomitantly lacked F-actin stress fibers and focal concentrations of vinculin and talin. Therefore, fibroblast migration can be readily controlled in an on-off manner through conditioned medium, which influences the absence or presence of focal adhesions.

The expression of invasive behavior of differentiated squamous carcinoma cell line evaluated by an in vitro invasion model

In order to elucidate the factors contributory to the expression of invasiveness of oral squamous cell carcinoma, we conducted biochemical and morphological comparisons of well differentiated squamous carcinoma cell line OSC-19 (oral squamous cell carcinoma) and undifferentiated carcinoma cell line KB, both cultured on 3T3 cell-embedded collagen gel (in vitro invasion model). OSC-19 cells invaded 3T3 cell-embedded collagen gel, while KB cells and OSC-19 cells on 3T3 cell-free gel matrix were less invasive. Cultured OSC-19 cells were characterized by lower proliferating activity, lower secretion of laminin and higher secretion of fibronectin than those of KB cells. Although the basement membrane with deposition of laminin and type IV collagen was formed, it was discontinuous at the invasion front. Gelatin zymography and western blotting showed matrix metalloproteinases (MMP), i.e., 72 kDa gelatinase (MMP-2) and 92 kDa gelatinase (MMP-9). Gelatinolytic activity was assayed, and was higher in OSC-19 cells than in KB cells or OSC-19 cells of the 3T3 cell-free model. By immunohistochemical analysis, MMP-2-positive cells were found scattered in both cell lines without any preferential localization, and the positivity for MMP-9 was localized in the invasion front of OSC-19 cells. These results strongly suggest that the invasiveness of squamous cell carcinoma is well correlated with cell-matrix adhesion by fibronectin and with focal elaboration of metalloproteinases, especially MMP-9, which play a major role in degrading the extracellular matrix components.

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.

Autocrine factors, type IV collagenase secretion and prostatic cancer cell invasion

Motility factors play a major role in tumor cell invasion and metastases. The biochemical properties of various motility factors; the receptor mediated mechanism of action; the role of microtubules; the potential influence of oncogenes; and the influence of motility factors on type IV collagenase secretion and invasion are discussed. We report on expression of a 70 kDa motility factor, termed invasion stimulating factor (ISF), in human prostatic PC-3 sublines. Boyden chamber chemotactic assays and measurements of type IV collagenase synthesis and secretion suggest that an ISF-receptor dependent mechanism influences tumor cell invasion and protease secretion. Taken together, the evidence that autocrine motility factors play an essential role in tumor cell invasion and metastases is compelling.

Tyrosine kinase receptors in the control of epithelial growth and morphogenesis during development

The c-ros, c-met and c-neu genes encode receptor-type tyrosine kinases and were originally identified because of their oncogenic potential. However, recent progress in the analysis of these receptors and their respective ligands indicate that they do not mediate exclusively mitogenic signals. Rather, they can induce cell movement, differentiation or morphogenesis of epithelial cells in culture. Interestingly, the discussed receptors are expressed in embryonal epithelia, whereas direct and indirect evidence shows that the corresponding ligands are produced in mesenchymal cells. In development, signals given by mesenchymal cells are major driving forces for differentiation and morphogenesis of epithelia; embryonal epithelia are generally unable to differentiate without the appropriate mesenchymal factors. The observed activities of these receptor/ligand systems in cultured cells and their expression patterns indicate that they regulate epithelial differentiation and morphogenesis also during embryogenesis and suggest thus a molecular basis for mesenchymal epithelial interactions.

Scatter factor induces blood vessel formation in vivo

Scatter factor (also known as hepatocyte growth factor) is a glycoprotein secreted by stromal cells that stimulates cell motility and proliferation. In vitro, scatter factor stimulates vascular endothelial cell migration, proliferation, and organization into capillary-like tubes. Using two different in vivo assays, we showed that physiologic quantities of purified native mouse scatter factor and recombinant human hepatocyte growth factor induce angiogenesis (the formation of new blood vessels). The angiogenic activity was blocked by specific anti-scatter factor antibodies. Scatter factor induced cultured microvascular endothelial cells to accumulate and secrete significantly increased quantities of urokinase, an enzyme associated with development of an invasive endothelial phenotype during angiogenesis. We further showed that immunoreactive scatter factor is present surrounding sites of blood vessel formation in psoriatic skin. These findings suggest that scatter factor may act as a paracrine mediator in pathologic angiogenesis associated with human inflammatory disease.

Monocyte-conditioned media possess a novel factor which increases motility of cancer cells

A number of cytokines have been reported to increase the cell motility (scatter) of cohesive cell colonies. We report here a novel scattering factor produced by human monocytes. Media from both stimulated and non-stimulated human monocytes or the monocytic cell line, U937, increased the cell motility of 2 human colon-cancer cell lines, HT115 and HT29, but not the canine epithelial cell line MDCK. Motility was assayed by cell dissociation from carrier beads and colony scattering. HT115 cells were strongly scattered by the conditioned media but not by interleukins IL-1, 2, 4, 6, 8, 10, TNF alpha, TGF beta, EGF, GM-CSF, IGF-I, PDGF, interferon-gamma. This factor is distinct from hepatocyte growth factor/scatter factor (HGF/SF), since the activity was not blocked by anti-HGF/SF antibody. The activity was reduced by treatment with acid, heat, trypsin and dithiothreitol; this, together with gel filtration, suggests that the factor is a protein (MW 40 to 60 kDa). This new factor, which is secreted from monocytes and the monocytic cell line, U937, has the ability to increase the motility of cancer cells and may be important in controlling the behaviour of tumours in vivo.

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.

Differences in chemotaxis to fibronectin in weakly and highly metastatic tumor cells

We have examined the chemotactic ability of tumor cell lines with different metastatic potential to plasma fibronectin in Transwell chamber assay. Human renal carcinoma cells with highly metastatic potential, SN12 C-2, chemotactically migrated to fibronectin (10 micrograms/ml) about three-fold more strongly than weakly metastatic SN12 C-4 cells. Similarly, murine melanoma B16-BL6 cells (highly metastatic) showed higher motility to soluble fibronectin in comparison with weakly metastatic B16-F1 cells. Anti-VLA-alpha 3 and beta 1 antibodies potently blocked the chemotaxis of both highly and weakly metastatic cells (SN12 C-2 and C-4) to fibronectin. This implies that the migration of both C-2 and C-4 cells to fibronectin is basically mediated by VLA-3 receptor. In contrast, the anti-VLA-alpha 5 antibody and RGDS peptide significantly inhibited the chemotaxis of SN12 C-2 cells to fibronectin, but did not affect weakly metastatic SN12 C-4 cells. These results suggest that the chemotactic ability to fibronectin positively correlates with the metastatic potential in SN12 and B16 cell lines, and that VLA-5 receptor is concerned in the motility of highly metastatic SN12 C-2 cells to soluble fibronectin.

Human lung cancer cell line producing hepatocyte growth factor/scatter factor

Hepatocyte growth factor (HGF)/scatter factor (SF) is a cytokine which is produced by mesenchymal cells and stimulates the motility of some epithelial cells, including cancer cells and vascular endothelial cells. Two human lung cancer cell lines, PC-1 and PC-13, were found to produce a protein which was indistinguishable from HGF/SF with regard to biological activities and immunological characteristics, although they were derived from epithelial cells. In general, highly aggressive cancer cells often show some mesenchymal characteristics, and production of HGF/SF by cancer cells is also considered as a phenomenon of acquisition of mesenchymal phenotype, which may be involved in cancer invasion and progression. These cell lines showed no apparent response to exogenous HGF/SF. In addition, no c-met proto-oncogene product was detectable in these cells by Western blot analysis. Although the function of HGF/SF produced by cancer cells, either autocrine or paracrine stimulation, remains to be studied, this is the first report to describe cancer cells producing HGF/SF.

Extracellular proteolytic cleavage by urokinase is required for activation of hepatocyte growth factor/scatter factor

The extracellular protease urokinase is known to be crucially involved in morphogenesis, tissue repair and tumor invasion by mediating matrix degradation and cell migration. Hepatocyte growth factor/scatter factor (HGF/SF) is a secretory product of stromal fibroblasts, sharing structural motifs with enzymes of the blood clotting cascade, including a zymogen cleavage site. HGF/SF promotes motility, invasion and growth of epithelial and endothelial cells. Here we show that HGF/SF is secreted as a single-chain biologically inactive precursor (pro-HGF/SF), mostly found in a matrix-associated form. Maturation of the precursor into the active alpha beta heterodimer takes place in the extracellular environment and results from a serum-dependent proteolytic cleavage. In vitro, pro-HGF/SF was cleaved at a single site by nanomolar concentrations of pure urokinase, generating the active mature HGF/SF heterodimer. This cleavage was prevented by specific urokinase inhibitors, such as plasminogen activator inhibitor type-1 and protease nexin-1, and by antibodies directed against the urokinase catalytic domain. Addition of these inhibitors to HGF/SF responsive cells prevented activation of the HGF/SF precursor. These data show that urokinase acts as a pro-HGF/SF convertase, and suggest that some of the growth and invasive cellular responses mediated by this enzyme may involve activation of HGF/SF.

Lateral growth and terminal differentiation during repeated epidermal regeneration in vitro

By incubating multilayered primary cultures of human epidermal keratinocytes in a low calcium medium, the suprabasal layers can be stripped off leaving a basal cell monolayer. When this monolayer is refed normal calcium medium a reproducible series of cell kinetic, morphological and biochemical changes take place resulting in the regeneration of a multilayered tissue. The stripping procedure seems to induce the selective proliferation of a cohort of basal cells that is committed to vertical migration and rapid terminal differentiation. In contrast, when the basal cells are allowed to regenerate in the presence of the strong mitogen, cholera toxin, lateral growth and continued proliferation are favoured at the expense of the capacity of the cells to differentiate. Repeated stripping of the same cultures disclosed a considerable heterogeneity in the capacity of the basal cells to regenerate the suprabasal layers. The number of times the basal cells could restore the suprabasal layers after repeated stripping varied from four to nine times. A negative correlation between donor age and regenerative capacity was observed. The experiments with repeated stripping of the same cultures also showed that the capacity to proliferate and to restore the multilayering was fully retained for at least four cycles of stripping-regeneration, whereas the capacity to terminally differentiate was rapidly lost. It is suggested that the present system of regenerating epidermal tissue cultures may serve as an experimental model for the study of epidermal tissue homeostasis and cellular aging.

Tumorigenicity of the met proto-oncogene and the gene for hepatocyte growth factor

The met proto-oncogene is the tyrosine kinase growth factor receptor for hepatocyte growth factor/scatter factor (HGF/SF). It was previously shown that, like the oncogenic tpr-met, the mouse met proto-oncogene transforms NIH 3T3 cells. We have established NIH 3T3 cells stably expressing both human (Methu) and mouse (Metmu) met proto-oncogene products. The protein products are properly processed and appear on the cell surface. NIH 3T3 cells express endogenous mouse HGF/SF mRNA, suggesting an autocrine activation mechanism for transformation by Metmu. However, the tumor-forming activity of Methu in NIH 3T3 cells is very low compared with that of Metmu, but efficient tumorigenesis occurs when Methu and HGF/SFhu are coexpressed. These results are consistent with an autocrine transformation mechanism and suggest further that the endogenous murine factor inefficiently activates the tumorigenic potential of Methu. The tumorigenicity observed with reciprocal chimeric human and mouse receptors that exchange external ligand-binding domains supports this conclusion. We also show that HGF/SFhu expressed in NIH 3T3 cells produces tumors in nude mice.

Tumorigenicity of the met proto-oncogene and the gene for hepatocyte growth factor

The met proto-oncogene is the tyrosine kinase growth factor receptor for hepatocyte growth factor/scatter factor (HGF/SF). It was previously shown that, like the oncogenic tpr-met, the mouse met proto-oncogene transforms NIH 3T3 cells. We have established NIH 3T3 cells stably expressing both human (Methu) and mouse (Metmu) met proto-oncogene products. The protein products are properly processed and appear on the cell surface. NIH 3T3 cells express endogenous mouse HGF/SF mRNA, suggesting an autocrine activation mechanism for transformation by Metmu. However, the tumor-forming activity of Methu in NIH 3T3 cells is very low compared with that of Metmu, but efficient tumorigenesis occurs when Methu and HGF/SFhu are coexpressed. These results are consistent with an autocrine transformation mechanism and suggest further that the endogenous murine factor inefficiently activates the tumorigenic potential of Methu. The tumorigenicity observed with reciprocal chimeric human and mouse receptors that exchange external ligand-binding domains supports this conclusion. We also show that HGF/SFhu expressed in NIH 3T3 cells produces tumors in nude mice.

Hepatocyte growth factor is a potent angiogenic factor which stimulates endothelial cell motility and growth

Hepatocyte Growth Factor (HGF, also known as Scatter Factor) is a powerful mitogen or motility factor in different cells, acting through the tyrosine kinase receptor encoded by the MET protooncogene. Endothelial cells express the MET gene and expose at the cell surface the mature protein (p190MET) made of a 50 kD (alpha) subunit disulfide linked to a 145-kD (beta) subunit. HGF binding to endothelial cells identifies two sites with different affinities. The higher affinity binding site (Kd = 0.35 nM) corresponds to the p190MET receptor. Sub-nanomolar concentrations of HGF, but not of a recombinant inactive precursor, stimulate the receptor kinase activity, cell proliferation and motility. HGF induces repairs of a wound in endothelial cell monolayer. HGF stimulates the scatter of endothelial cells grown on three-dimensional collagen gels, inducing an elongated phenotype. In the rabbit cornea, highly purified HGF promotes neovascularization at sub-nanomolar concentrations. HGF lacks activities related to hemostasis-thrombosis, inflammation and endothelial cells accessory functions. These data show that HGF is an in vivo potent angiogenic factor and in vitro induces endothelial cells to proliferate and migrate.

Processing of hepatocyte growth factor to the heterodimeric form is required for biological activity

Hepatocyte growth factor is a plasminogen-like molecule with diverse biological effects. Although it is synthesized as a single chain polypeptide, it was originally purified as a disulfide-linked heterodimer which was generated by an internal proteolytic event. Subsequent work indicated that preparations consisting largely of the monomeric form also exhibited potent activity. By using a combination of protease inhibition and site-directed mutagenesis, we established that conversion of the single chain polypeptide to the heterodimer occurred during the bioassay and was required for mitogenic and motogenic activity.

The presence of hepatocyte growth factor in the developing rat

Hepatocyte growth factor (HGF), a heparin-binding polypeptide mitogen, stimulates DNA synthesis in adult rat and human hepatocytes and in several other cells of epithelial origin. Recently, it was determined that scatter factor (SF), a protein that has been shown to cause the dispersion and migration of epithelial cells in culture, is identical to HGF. Moreover, the receptor for HGF was identified as the product of the proto-oncogene, c-MET, a tyrosine kinase-containing transmembrane protein. c-MET expression has been reported in a variety of adult and embryonic mouse tissues. Similarly, we and others have demonstrated that HGF is expressed in various adult rat and human tissues. In the present study, the tissue distribution of HGF during rat development was determined by immunohistochemistry using an HGF-specific polyclonal antiserum. Between day 12 and day 19, immunoreactivity for HGF was present in various locations such as hematopoietic cells, somites, squamous epithelium of the esophagus and skin, periventricular germinal matrix of the brain, bronchial epithelium, renal collecting tubules and chondrocytes. After day 19, HGF immunoreactivity was also present in the pancreas, submaxillary glands and neural tissues. In addition to immunolocalizing HGF in tissue sections, bioreactive and immunoreactive HGF was extracted and purified from rat fetuses. Other studies demonstrated the presence of HGF and c-MET mRNA in total fetal rat, and in fetal and neonatal rat liver. Addition of purified HGF to fetal and neonatal rat liver cultures enriched for hepatocytes stimulated DNA synthesis up to six-fold over controls. These findings strongly suggest a pivotal role for this potent regulator of growth and development.

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.

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.

Detection of migration stimulating activity in wound fluid

Fetal skin fibroblasts produce a soluble "migration stimulating factor" (MSF) which is not made by their normal adult counterparts. MSF stimulates the migration of adult skin fibroblasts into 3D collagen gels, thus providing the basis of a convenient bioassay for its presence. We have previously reported that MSF stimulates hyaluronic acid (HA) synthesis by adult skin fibroblasts and that this effect on matrix deposition appears to be responsible for the observed increase in cell motility. In the present study, wound fluid samples were collected from 18 patients undergoing surgery for various nonmalignant conditions and these were then fractionated according to the protocol used to isolate MSF from fetal fibroblast-conditioned medium. Detectable levels of migration stimulating activity were present in 17/18 (94%) of these samples. Paired serum samples obtained both pre- and postoperatively from five patients with positive wound fluid samples were also analyzed for MSF activity; such activity was found in only 1/5 (20%) of the preoperative and 0/5 (0%) of the postoperative serum samples. These data suggest that the MSF present in wound fluid is not derived from a plasma transudate or from platelet degranulation, but may reflect the transient and localized reinitiation of MSF production by adult fibroblasts in response to wounding. Taken together with previous observations regarding the effect of MSF on fibroblast migration and HA synthesis, our data suggest a possible physiological function of MSF in the wound healing response. Previous studies have revealed that MSF is produced by a subpopulation of apparently persistent fetal-like skin fibroblasts obtained from breast cancer patients and is also found in the serum of these individuals. Wound fluid and serum samples were accordingly collected from patients undergoing surgery for various types of malignant conditions or with a previous history of cancer; detectable levels of MSF activity were found in 8/10 (80%) of these wound fluid samples, 2/3 (66.6%) of the preoperative, and 3/3 (100%) of the postoperative paired serum samples. These findings suggest that the presence of detectable serum levels of MSF is not restricted to breast cancer and may be a general feature of malignant disease.

The presence of scatter factor in patients with metastatic spread to the pleura

Pleural effusion fluid obtained from eleven patients with metastatic spread to the pleura was screened for the ability to cause the dispersal--'scattering'--of MDCK colonies in vitro. Four of these samples proved to be positive using this assay. Of these two had titres high enough to warrant further purification on a cation exchange Mono S column. Active material from both lung samples, eluted at the same positions as factor from cultured human lung fibroblasts (MRC-5) and human placenta but in a slightly different position to murine scatter factor. In both cases the semi-purified active agent was identified as hepatocyte growth factor/scatter factor (HGF/SF) using an ELISA detection system specific for human HGF/SF. This is the first report identifying the presence of significant amounts of HGF/SF in the pleura of patients where malignant spread has occurred.