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

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

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

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

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

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

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

Diverse aspects of metanephric development

Mammalian nephrogenesis constitutes a series of complex developmental processes in which there is a differentiation and rapid proliferation of pluripotent cells leading to the formation of a defined sculpted tissue mass, and this is followed by a continuum of cell replication and terminal differentiation. Metanephrogenesis ensues with the intercalation of epithelial ureteric bud into loosely organized metanephric mesenchyme. Such an interaction is reciprocal, such that the intercalating ureteric bud induces the conversion of metanephric mesenchyme into an epithelial phenotype, while the mesenchyme stimulates the iterations of the ureteric bud. The induced mesenchyme then undergoes a series of developmental stages to form a mature glomerulus and tubular segments of the kidney. Coincidental with the formation of these nephric elements, the developing kidney is vascularized by the process of vasculogenesis and angiogenesis. Thus, the process of metanephric development is quite complex, and it involves a diverse group of molecules who's biological activities are inter-linked with one another and they regulate, in a concerted manner, the differentiation and maturation of the mammalian kidney. This diverse group of molecules include extracellular matrix (ECM) proteins and their receptors, ECM-degrading enzymes and their inhibitors, growth factors and their receptors, proto-oncogenes and transcription factors. A large body of literature data are available, which suggest a critical role of these molecules in metanephric development, and this review summarizes the recent developments that relate to metanephrogenesis.

Differential requirement of Grb2 and PI3-kinase in HGF/SF-induced cell motility and tubulogenesis

Hepatocyte growth factor/scatter factor (HGF/SF) is a multifunctional cytokine that induces mitogenesis, motility, invasion, and morphogenesis of several epithelial and endothelial cell lines in culture. The receptor for HGF/SF has been identified as the Met tyrosine kinase. To investigate the signaling pathways that are involved in these events, we have generated chimeric receptors containing the extracellular domain of the colony stimulating factor-1 (CSF-1) receptor fused to the transmembrane and intracellular domains of the Met receptor (MET). Madin-Darby canine kidney (MDCK) epithelial cells, expressing the CSF-MET chimera dissociate, scatter and form branching tubules in response to CSF-1. However, cells expressing a mutant CSF-MET receptor containing a phenylalanine substitution for tyrosine 1356 (Y1356F) are unable to scatter or form branching tubules following stimulation with CSF-1. Tyrosine 1356 is essential for the recruitment of multiple substrates including Grb2, the p85 subunit of PI3-kinase, and PLC gamma. To investigate the role of these signaling pathways, we have generated a mutant receptor that selectively fails to associate with Grb2, and have treated MDCK cells with potent inhibitors of PLC gamma, PI3-kinase, and p70S6K, a downstream target of PI3-kinase. Our results implicate pathways downstream from PI3-kinase in cell dissociation and scatter, whereas pathways downstream from Grb2 are required for branching tubulogenesis in MDCK cells.

Activating mutations for the met tyrosine kinase receptor in human cancer

Recently, mutations in the Met tyrosine kinase receptor have been identified in both hereditary and sporadic forms of papillary renal carcinoma. We have introduced the corresponding mutations into the met cDNA and examined the effect of each mutation in biochemical and biological assays. We find that the Met mutants exhibit increased levels of tyrosine phosphorylation and enhanced kinase activity toward an exogenous substrate when compared with wild-type Met. Moreover, NIH 3T3 cells expressing mutant Met molecules form foci in vitro and are tumorigenic in nude mice. Enzymatic and biological differences were evident among the various mutants examined, and the somatic mutations were generally more active than those of germ-line origin. A strong correlation between the enzymatic and biological activity of the mutants was observed, indicating that tumorigenesis by Met is quantitatively related to its level of activation. These results demonstrate that the Met mutants originally identified in human papillary renal carcinoma are oncogenic and thus are likely to play a determinant role in this disease, and these results raise the possibility that activating Met mutations also may contribute to other human malignancies.

Implantation of C6 astrocytoma spheroid into collagen type I gels: invasive, proliferative, and enzymatic characterizations

A three-dimensional model has been developed in which C6 astrocytoma spheroids of defined sizes are embedded into collagen type I gels. The authors have monitored cell invasive behavior; obtained quantitative data on cell invasion, proliferation, and enzymatic activity; assessed cell-cell interactions by altering the spheroid size used; and studied cell-matrix interactions by modifying the matrix components. Their results show that C6 astrocytoma cells detach from the spheroid surface and invade the gel as single cells by means of a system that appears to be dependent on metalloprotease function. These invasive cells have a low proliferative index. Larger spheroids with central hypoxic microregions possess cells that invade the gel at faster rates; this could be correlated with the release of increased collagen type I degrading activity. Extracellular matrix proteins, such as laminin, fibronectin, and collagen type IV have no significant influence on invasive activity, whereas hyaluronic acid decreases and human central nervous system myelin increases invasion. New strategies directed at the treatment of malignant gliomas must take into account the subpopulation of malignant cells located long distances from the major tumor mass. The spheroid invasion model may provide specific insights into the behavior of these invasive cells.

Functional and biophysical characterization of recombinant human hepatocyte growth factor isoforms produced in Escherichia coli

Hepatocyte growth factor (HGF) is a pluripotent secreted protein that stimulates a wide array of cellular targets, including hepatocytes and other epithelial cells, melanocytes, endothelial and haematopoietic cells. Multiple mRNA species transcribed from a single HGF gene encode at least three distinct proteins: the full-length HGF protein and two truncated HGF isoforms that encompass the N-terminal (N) domain through kringle 1 (NK1) or through kringle 2 (NK2). We report the high-level expression in Escherichia coli of NK1 and NK2, as well as the individual kringle 1 (K1) and N domains of HGF. All proteins accumulated as insoluble aggregates that were solubilized, folded and purified in high yield using a simple procedure that included two gel-filtration steps. Characterization of the purified proteins indicated chemical and physical homogeneity, and analysis by CD suggested native conformations. Although the K1 and N-terminal domains of HGF have limited biological activity, spectroscopic evidence indicated that the conformation of each matched that observed when the domains were components of biologically active NK1. Both NK1 and NK2 produced in bacteria were functionally equivalent to proteins generated by eukaryotic systems, as indicated by mitogenicity, cell scatter, and receptor binding and activation assays. These data indicate that all four bacterially produced HGF derivatives are well suited for detailed structural analysis.

Differential regulation of keratinocyte growth factor and hepatocyte growth factor/scatter factor by different cytokines in human corneal and limbal fibroblasts

Corneal epithelial stem cells and transient amplifying cells are located in the limbal and corneal regions, respectively. In a serum-free medium with or without different cytokines, limbal fibroblasts consistently produced greater levels of keratinocyte growth factor (KGF) transcript and protein than corneal fibroblasts, whereas corneal fibroblasts produced greater levels of hepatocyte growth factor/ scatter factor (HGF/SF) transcript and protein than limbal fibroblasts. Expression of HGF/SF transcript and protein was up-regulated mildly by epidermal growth factor (EGF), transforming growth factor-alpha (TGF-alpha), or platelet-derived growth factor B (PDGF-BB) but markedly by interleukin-1 beta (IL-1 beta) and was more pronounced in limbal than in corneal fibroblasts. Expression of KGF transcript was down-regulated by EGF, TGF-alpha, and PDGF-BB, was markedly up-regulated by IL-1 beta, and was more pronounced in limbal than in corneal fibroblasts. Expression of KGF protein was up-regulated markedly by IL-1 beta and moderately by PDGF-BB, especially in limbal fibroblasts. TGF-beta 1 uniquely turned off transcript and protein expression of HGF/SF and KGF in corneal fibroblasts. Although its transcript levels were similarly down-regulated in limbal fibroblasts, KGF protein levels were paradoxically up-regulated by TGF-beta 1 when added alone or with TGF-alpha or IL-1 beta. These data indicate that KGF and HGF/SF, two fibroblast-derived epithelial mitogens, are expressed differentially by limbal and corneal fibroblasts and are modulated by cytokines activated during epithelial-mesenchymal interactions, suggesting that they may play a different role in modulating corneal epithelial stem cells and transient amplifying cells.

Chromosomal localization of rat hepatocyte growth factor (Hgf) and HGF receptor (Met) and characterization of HGF receptor cDNA

The Met protooncogene encodes the tyrosine kinase receptor for the hepatocyte growth factor (HGF), a potent mitogen for hepatocytes and other epithelial cells produced by mesenchymal cells. Many of the studies on the physiologic and neoplastic growth of the liver, as well as other organs, have been performed in the rat. Therefore, chromosomal mapping of the rat Hgf gene and the gene of its receptor is of particular value. To achieve this, a probe of the coding part of rat HGF cDNA was used to isolate four genomic probes from a lambda phage rat genomic library. These probes were used to map the Hgf gene to Chromosome (Chr) 4q12 by the FISH technique. To obtain a probe for the mapping of the HGF receptor/Met gene, we cloned the complete coding region of the rat HGF receptor mRNA. Complementary DNA (cDNA) was synthesized with reverse transcriptase from total RNA for use as a template for the PCR. The two PCR primers were designed based on human and mouse sequences and were located in the flanking regions of the open reading frame of the HGF receptor mRNA. Amplification resulted in a band of an estimated size of 4.1 kb, which was cloned and sequenced. The nucleotide sequence showed about 93% and 85% homology compared with mouse and human HGF receptor sequences, respectively. A full-length probe of the coding part of the cDNA was used to map the rat HGF receptor/Met gene to Chr 4q21 by the FISH technique. Therefore, the rat Hgf and HGF receptor/Met genes are located relatively close to each other, in a way similar to humans but not mice.

C-met proto-oncogene expression in benign and malignant human renal tissues

PURPOSE

Hepatocyte growth factor/scatter factor (HGF/SF) is a potent mitogen to renal epithelial cells in vitro and in vivo. HGF/SF signals through its receptor which is coded by the c-met proto-oncogene. We hypothesized that altered expression of the HGF/SF receptor, c-met, may be involved in the pathogenesis of certain renal cell carcinomas. Our objectives were to 1) assess the presence and localization of c-met protein in benign and malignant human renal tissues, and 2) correlate the presence of c-met protein with renal carcinoma histological subtype, tumor stage and tumor grade.

MATERIALS AND METHODS

Immunohistochemical analysis of c-met protein was performed in 41 normal and malignant human renal samples.

RESULTS

c-met Immunostaining was detected in the normal kidney tissue in all 41 samples. In the normal kidney c-met immunostaining was limited to the cell membrane and/or cytoplasm of epithelial cells in specific tubular segments, including the proximal convoluted tubule, thin and thick limbs of the loop of Henle, and the collecting duct. The glomeruli, distal convoluted tubule and stroma were consistently negative for c-met staining. c-met Immunostaining was detected in 68% of renal cell carcinomas and was more common in higher nuclear grade cancers (p < 0.034).

CONCLUSIONS

The c-met receptor is present in specific tubular segments in the normal kidney and is frequently expressed in higher nuclear grade renal cancers, suggesting a role in renal carcinoma progression. Future studies should evaluate the biological significance of the HGF/ SF-c-met pathway in normal renal physiology, and renal cancer growth and progression.

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

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

Expression of interleukin-1beta in human breast carcinoma

BACKGROUND

Interleukin 1beta (IL-1beta) is a multifunctional cytokine that up-regulates the inflammatory response. It is not known whether IL-1beta plays a major role in human malignancy. To determine whether IL-1beta might be involved in breast carcinoma progression, the authors measured the IL-1beta content in tissue extracts from >200 invasive breast carcinomas and smaller numbers of ductal carcinoma in situ (DCIS) and benign lesions.

METHODS

IL-1beta content was measured by an enzyme-linked immunoadsorbent assay and analyzed to determine whether these values were correlated with the contents of scatter factor (SF) (an invasogenic and angiogenic cytokine), von Willebrand's factor (VWF) (a marker of endothelium), thrombospondin-1 (TSP1) (an antiadhesive and antiangiogenic glycoprotein), and tumor necrosis factor-alpha (TNF alpha) (another proinflammatory cytokine). Studies were also performed to determine whether IL-1beta content was correlated with other pathologic and immunochemical variables that have been utilized or proposed as prognostic indicators for breast carcinoma.

RESULTS

The most important findings of these studies were: 1) immunoreactive IL-1beta was detected in approximately 90% of invasive breast carcinomas; 2) IL-1beta levels were significantly higher in invasive carcinomas than in a group of DCIS and benign lesions; 3) high IL-1beta content in invasive carcinomas was significantly associated with higher contents of SF, VWF, and TSP1, but not TNF alpha; and 4) there was a trend toward higher IL-1beta content in invasive carcinomas with a group of other parameters that suggest a biologically more aggressive tumor (estrogen receptor negativity, high tumor grade, p53 positivity, and bcl-2 negativity); and the proportion of invasive tumors with these characteristics was significantly increased in a subgroup of tumors having very high IL-1beta content. The authors also found a correlation between high IL-1beta content and CD68 positivity, suggesting that macrophages may account for some of the IL-1beta present in human breast carcinoma tissue.

CONCLUSIONS

These findings suggest that significant titers of IL-1beta are present within the microenvironment of most breast carcinomas and that a high IL-1beta content is often associated with tumor invasiveness and with other pathologic features suggestive of an aggressive tumor biology.

Macrophage stimulating protein (MSP) binds to its receptor via the MSP beta chain

Macrophage stimulating protein (MSP) is a 78-kDa disulfide-linked heterodimer belonging to the plasminogen-related kringle protein family. MSP activates the RON receptor protein-tyrosine kinase, which results in cell migration, shape change, or proliferation. A structure-activity study of MSP was performed using pro-MSP, MSP, MSP alpha and beta chains, and a complex including the first two kringles and IgG Fc (MSP-NK2). Radioiodinated MSP and MSP beta chain both bound specifically to RON. The Kd of 1.4 nM for MSP beta chain is higher than the reported Kd range of 0.6-0.8 nM for MSP. Pro-MSP, MSP alpha chain, and MSP-NK2 did not bind. Only MSP stimulated RON autophosphorylation. Although the beta chain bound to RON and partially inhibited MSP-induced RON phosphorylation in kidney 293 cells, it did not induce RON phosphorylation. Pro-MSP, MSP alpha chain, or MSP-NK2 failed to activate RON, consistent with their inability to bind to the RON receptor. Functional studies showed that only MSP induced cell migration, and shape change in resident macrophages, and growth of murine keratinocytes. Our data indicate that the primary receptor binding domain is located in a region of the MSP beta chain, in contrast to structurally similar hepatocyte growth factor, in which the receptor binding site is in the alpha chain. However, full activation of RON requires binding of the complete MSP disulfide-linked alphabeta chain heterodimer.

Serum hepatocyte growth factor/scatter factor levels in small cell lung cancer patients

Serum hepatocyte growth factor/scatter factor (HGF/SF) levels were measured in 25 patients with small cell lung cancer (SCLC), 16 patients with benign lung diseases and 15 healthy subjects with an enzyme-linked immunosorbent assay. The patients with SCLC did not have bacterial or interstitial pneumonia. Patients with benign lung diseases included eight with bacterial pneumonia, three with interstitial pneumonia, and five with benign lung tumor. Serum HGF/SF levels were significantly higher in patients with SCLC (mean +/- S.D.: 0.40 +/- 0.17 ng/ml) than in healthy subjects (0.26 +/- 0.093 ng/ml) (P = 0.0083). Patients with bacterial pneumonia had significantly higher serum HGF/SF (0.52 +/- 0.19 ng/ml) than did those with benign lung tumors (0.27 +/- 0.058 ng/ml) and healthy subjects (P = 0.013 and P = 0.0019, respectively). By clinical stage of SCLC, HGF/SF levels were 0.34 +/- 0.12 and 0.47 +/- 0.20 ng/ml in patients with limited disease and extensive disease, respectively; this difference was not significant (P = 0.080). Although serum HGF/SF levels were increased in patients with SCLC, this increase might not have been related to tumor burden.

Scatter factor/hepatocyte growth factor expression enhances human glioblastoma tumorigenicity and growth

We have shown previously that the multifunctional cytokine scatter factor/hepatocyte growth factor (SF/HGF) is elevated in human malignant gliomas. In this study we investigated how human SF/HGF expression affects the malignancy of the U373 human glioblastoma cell line in vivo and in vitro. Human SF/HGF gene transfer increased U373 glioblastoma tumorigenicity by > or = 20-fold and enhanced the growth rate of intracerebral U373 xenografts by 3- to 8-fold. SF/HGF expression had no effect on the proliferation of glioblastoma cell monolayers but increased their anchorage-independent colony formation in soft agar by 5- to 8-fold. These results are the first to show that SF/HGF expression by human glioblastoma cells enhances their growth dysregulation in vitro and malignancy in vivo.

Paracrine regulation of germinal center B cell adhesion through the c-met-hepatocyte growth factor/scatter factor pathway

T cell-dependent humoral immune responses are initiated by the activation of naive B cells in the T cell areas of the secondary lymphoid tissues. This primary B cell activation leads to migration of germinal center (GC) cell precursors into B cell follicles where they engage follicular dendritic cells (FDC) and T cells, and differentiate into memory B cells or plasma cells. Both B cell migration and interaction with FDC critically depend on integrin-mediated adhesion. To date, the physiological regulators of this adhesion were unkown. In the present report, we have identified the c-met-encoded receptor tyrosine kinase and its ligand, the growth and motility factor hepatocyte growth factor/scatter factor (HGF/SF), as a novel paracrine signaling pathway regulating B cell adhesion. We observed that c-Met is predominantly expressed on CD38(+)CD77(+) tonsillar B cells localized in the dark zone of the GC (centroblasts). On tonsil B cells, ligation of CD40 by CD40-ligand, induces a transient strong upregulation of expression of the c-Met tyrosine kinase. Stimulation of c-Met with HGF/SF leads to receptor phosphorylation and, in addition, to enhanced integrin-mediated adhesion of B cells to both VCAM-1 and fibronectin. Importantly, the c-Met ligand HGF/SF is produced at high levels by tonsillar stromal cells thus providing signals for the regulation of adhesion and migration within the lymphoid microenvironment.

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

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

Control of invasive growth by hepatocyte growth factor (HGF) and related scatter factors

Hepatocyte growth factor (HGF) is the prototype of a family of structurally related soluble molecules, named scatter factors (SFs). These control a complex genetic programme leading to cell-dissociation, migration in the extracellular matrix, growth, acquisition of polarity and tubule formation. This programme is pivotal during the embryonic development of epithelial and some mesodermal-derived tissues. In the adult HGF sustains cell survival and regeneration. A structurally related molecule, originally identified as macrophage stimulating protein (MSP), triggers the same complex genetic programme in epithelial and neural cells. The receptors for HGF and MSP are the tyrosine kinases encoded by the homologous genes MET and RON. As a distinctive feature, these receptors act via a two-phosphotyrosine docking site, capable of concomitant activation of multiple intracellular transducers and signalling pathways. In a number of malignant tumours, MET and RON constitutively sustain the genetic programme of scattering, leading to invasive growth and metastatic phenotype. Four MET-related receptors have been recently identified (the SEX protein family). These molecules are predominantly expressed during development and are likely to mediate repelling cues between cells of different type.

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

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

Identification and characterization of motility stimulating factor secreted from pancreatic cancer cells: role in tumor invasion and metastasis

Cell motility is an important factor in the process of invasion and metastasis of tumor. In this study, the relationship between cell motility and experimental metastatic potential was examined using two human pancreatic cancer cell lines, SW1990 and PANC-1. Serum-free conditioned medium from the highly metastatic cell line SW1990 was found to contain a factor that stimulated the migration of and induced a fibroblast-like morphological change in the weakly metastatic cell line PANC-1. Preincubation of PANC-1 cells with SW1990 conditioned medium (SW-C.M.) induced liver metastasis following splenic injection of PANC-1 cells in nude mice, although no liver metastasis was observed without pretreatment of SW-C.M. This factor, temporarily termed PDMF (pancreatic cancer-derived motility factor) is a heparin non-binding protein having a molecular weight of 40 kDa calculated by gel-filtration HPLC which acts not only chemotactically but also chemokinetically, and also acts mainly in a paracrine fashion. However, this factor had no effect on the proliferation of PANC-1 cells; it therefore appears to be a so-called motility factor. Only TGF-beta1 and IL-6 were recognized in the SW-C.M. among cytokines thought to stimulate cell motility. These cytokines stimulated the motility of PANC-1 cells, but differed from PDMF in the neutralizing test with antibody against these cytokines. Results of characterization and preliminary purification suggest that this factor may be a novel motility factor. The above findings suggest that this motility factor may play an important role in the invasion and metastasis of pancreatic cancer, and complete purification of it will be useful in elucidating the mechanism of progression of cancer and designing a strategy for inhibition of invasion and metastasis of pancreatic cancer.

Expression of hepatocyte growth factor/scatter factor and its receptor, MET, suggests roles in human embryonic organogenesis

Hepatocyte growth factor/scatter factor (HGF/SF) is secreted by mesenchymal cells and elicits proliferation, motility, differentiation, and morphogenesis of epithelia and other cells. These effects are mediated by binding to MET, a receptor tyrosine kinase. Genetically engineered mice lacking HGF/SF die in utero due to a failure of placental and hepatocyte differentiation, but little information exists regarding the expression of this signaling system in human development. Using reverse transcriptase-polymerase chain reaction, Western blots, and immunohistochemistry, we report that HGF/SF and MET are expressed during critical early periods of human organogenesis from 6 to 13 wk of gestation. Organs that expressed both genes included liver, metanephric kidney, intestine, and lung, each of which develop by inductive interactions between mesenchyme and epithelia. Of all organs studied, the placenta contained the highest levels of HGF/SF protein, and MET was detected in trophoblastic cells of chorionic villi as early as the 5th wk of gestation. Finally, examination of a human multicystic dysplastic kidney demonstrated that malformed, hyperproliferative tubules expressed MET, whereas HGF/SF protein was immunolocalized to the same epithelia and also to the surrounding undifferentiated cells. Hence HGF/SF might be an important growth factor in normal human embryogenesis and may additionally play a role in human organ malformations.

Differential response of fetal and adult fibroblasts to cytokines: cell migration and hyaluronan synthesis

Previous studies have indicated that fetal skin fibroblasts display an elevated level of migratory activity compared to adult cells and that this may result from inherent differences in the production of hyaluronan (HA) by these cells. Data presented in this communication indicate that the elevated level of fetal fibroblast migration into 3D-collagen gels and HA synthesis by these cells were not affected by epidermal growth factor (EGF), platelet-derived growth factor (PDGF), acidic fibroblast growth factor (aFGF) or basic fibroblast growth factor (bFGF). In contrast, both cell migration and HA synthesis by fetal fibroblasts were inhibited by transforming growth factor-betal (TGF-beta1). Adult fibroblasts responded to these cytokines in a distinct fashion: i.e. cell migration and HA synthesis were stimulated by EGF, PDGF, aFGF and bFGF, but remained unaffected by TGF-beta1. Gel-filtration chromatography revealed that these effects of cytokines on HA synthesis were predominantly confined to the production of high molecular mass (&gt;106 kDa) species. Co-exposure of cells to both cytokines and Streptomyces hyaluronidase revealed that (1) the elevated migration of control fetal fibroblasts was inhibited by hyaluronidase, (2) this inhibition was partially restored by co-exposure to EGF, PDGF, aFGF and bFGF, but remained unaffected by TGF-beta1, (3) the migration of control adult fibroblasts was unaffected by hyaluronidase and partially stimulated by EGF, aFGF and bFGF (when compared to the effects of these cytokines on cells cultured in the absence of hyaluronidase) and (4) neither PDGF nor TGF-beta1 affected the migration of hyaluronidase-treated adult cells. Linear regression analysis revealed a significant correlation between cell migration and HA synthesis by both fetal and adult fibroblasts in the presence and absence of cytokines (r2=0.9277, P&lt;0.0001), with the exception of adult fibroblasts exposed to PDGF. Taken together, these findings suggest that (1) the migration of fetal and adult fibroblasts is differentially modulated by exogenous cytokines and (2) with the possible exception of the effects of PDGF on adult fibroblasts, cytokine-induced modulation of cell migration appears to utilise both HA-dependent and HA-independent pathways.

Detection and characterization of an activity which aligns mesodermal cells into parallel arrays

A cell line of mesodermal origin, FS9, was found to release a Cell Orienting Factor into its culture medium. In contrast with the random migration of controls, the orienting activity causes migrating mesenchymal cells to form an orderly "halo' surrounding tissue explants; individual cells and their cytoskeletons are elongated and parallel to each other but at right angle to the explant. No effect on the rate of cell movement was apparent. The orienting activity could be quantified by counting the number of cells found within strings radiating at right angles to a single tissue explant in the presence of FS9 conditioned medium or by using NIH image analysis. A dose dependent relationship with half maximal activity occurring at a 25% dilution of conditioned medium was observed. Cells that migrated randomly in the absence of conditioned medium became oriented within 4 h of exposure to 50% conditioned medium. Conversely, when the conditioned medium was removed, parallel alignment was rapidly lost. The orienting activity was found in conditioned media from a variety of mesodermal derivatives. Transformation of Balb/c 3T3 cells using EJ-ras oncogene led to augmented production of the activity. Furthermore, insulin was required in serum-free medium to support its production, Laminin, fibronectin and collagen and a range of pure cytokines, neither promoted nor inhibited orientation. Cell alignment was also unaffected by treatments which interfered with cell-substrate interactions and motility including the addition of the RGD peptide or anti-integrin beta 1 and beta 3 antibodies. A protein is likely to be involved since the activity was heat and trypsin sensitive and non-dialysable. The possibility is discussed that the orienting activity is a novel protein(s) which alters intercellular interactions to promote the formation of an aligned pattern by migrating mesenchymal cells.

Preventing the loss of competence for neural induction: HGF/SF, L5 and Sox-2

The response to neural induction depends on the presence of inducing signals and on the state of competence of the responding tissue. The epiblast of the chick embryo loses its ability to respond to neural induction by the organizer (Hensen's node) between stages 4 and 4+. We find that the pattern of expression of the L5(220) antigen closely mirrors the changes in competence of the epiblast in time and in space. For the first time, we describe an experiment that can extend the period of neural competence: when L5(220) expression is maintained beyond its normal time by implanting HGF/SF secreting cells, the competence to respond to Hensen's node grafts is retained. The host epiblast forms a non-regionalized neural tube, which expresses the pan-neural marker SOX-2 (a Sry-related transcription factor) but not any region-specific markers for the forebrain, hindbrain or spinal cord. Although HGF/SF secreting cells can mimic signals from Hensen's node that maintain L5 expression, they cannot rescue the ability of the node to induce anterior structures (which is normally lost after stage 4). The ectoderm may acquire stable neural characteristics during neural induction by going through a hierarchy of states: competence, neuralization and regionalization. Our findings allow us to start to define these different states at a molecular level, and show that the competence to respond to neural induction is not entirely autonomous to the responding cells, but can be regulated by extracellular signalling molecules.

The lipid products of phosphoinositide 3-kinase increase cell motility through protein kinase C

Phosphoinositide 3-kinase has been implicated as an activator of cell motility in a variety of recent studies, yet the role of its lipid product, phosphatidylinositol 1,4,5-trisphosphate (PtdIns-3,4,5-P3), has yet to be elucidated. In this study, three independent preparations of PtdIns-3,4,5-P3 were found to increase the motility of NIH 3T3 cells when examined utilizing a microchemotaxis chamber. Dipalmitoyl L-alpha-phosphatidyl-D-myo-inositol 3,4,5-triphosphate (Di-C16-PtdIns-3,4,5-P3) also produced actin reorganization and membrane ruffling. Cells pretreated with 12-O-tetradecanoylphorbol-13-acetate to cause down-regulation of protein kinase C (PKC) exhibited complete inhibition of cell motility induced by Di-C16-PtdIns-3,4,5-P3. These results are consistent with previous observations that PtdIns-3,4,5-P3 activates Ca2+-independent PKC isoforms in vitro and in vivo and provide the first demonstration of an in vivo role for the lipid products of the phosphoinositide 3-kinase. PtdIns-3,4,5-P3 appears to directly initiate cellular motility via activation of a PKC family member.

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

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

Wild-type but not mutant p53 activates the hepatocyte growth factor/scatter factor promoter

p53 transactivates the expression of a variety of genes by binding to specific DNA sequences within the promoter. We have investigated the ability of wild-type p53 and a non-DNA binding p53 mutant to activate the hepatocyte growth factor/scatter factor (HGF/SF) promoter using chloramphenicol acetyltransferase reporter constructs. We also used deletion sequences of the HGF/SF promoter to identify which regions, if any, were responsible for p53 binding. Our results show that wild-type but not mutant p53 activates the HGF/SF promoter when using -3000 and -755 bp upstream of the HGF/SF gene. This activation is lost when promoter sequences covering -365 and -239 bp are used. Analysis of the DNA sequence between -365 and -755 bp shows one putative p53 half-site with 80% homology to the consensus sequence and another half-site 3 bases downstream of this with 100% homology to the consensus sequence. In contrast to previously identified p53 binding DNA sequences, the downstream half-site is inverted. We propose that the HGF/SF promoter can be activated by wild-type p53 in vivo and that this could be as a result of a novel form of sequence-specific DNA binding.

Expression of scatter factor and c-met receptor in benign and malignant breast tissue

BACKGROUND

Scatter factor (SF), also known as hepatocyte growth factor, is an angiogenic cytokine that stimulates epithelial cell motility and invasion. Its receptor is a transmembrane tyrosine kinase encoded by the c-met protooncogene. Several prior experimental and clinical studies have suggested that SF might play a role in the development and progression of breast carcinoma. To investigate the possible involvement of SF and c-met in the evolution of breast carcinoma, the authors studied their expression in sections of human breast tissue.

METHODS

A variety of paraffin embedded tissue specimens (of normal breast tissue tissue, benign hyperplasia, ductal carcinoma-in-situ [DCIS], and invasive ductal carcinoma) from 125 patients were immunoperoxidase-stained using specific antisera against SF and c-met. The staining intensities of epithelial mammary cells were scored semiquantitatively, and the staining scores were analyzed as a function of tissue type. In addition, in situ hybridization to detect SF mRNA was performed for a small number of cancer sections.

RESULTS

Specific SF staining was observed in tumor cells, normal cell types (epithelium and vascular smooth muscle), and acellular stroma, whereas c- met staining was observed in tumor cells and normal cell types but not in stroma. Analysis of the staining scores of epithelial mammary cells revealed several patterns: (1) SF and c-met staining scores each increased in the following order: normal breast/benign hyperplasias (lowest) --> DCIS (higher) --> invasive carcinoma (highest); (2) normal-appearing mammary ducts and lobules in invasive cancer sections showed less SF and c-met staining than tumor cells in the same specimens but more staining than normal ducts and lobules in sections of normal breast tissue and benign hyperplasia; (3) within the DCIS and invasive cancer groups, SF and c-met staining scores were correlated; and (4) among 40 consecutive cases of DCIS, higher levels of SF and c-met staining showed a trend toward association with other features suggestive of aggressive tumor biology (comedo histology, high nuclear grade, p53 positivity, and bcl-2 negativity). In situ hybridization analysis revealed that the same cell types that expressed SF protein (including tumor cells) also expressed SF mRNA transcripts.

CONCLUSIONS

SF and c-met are overexpressed in breast carcinoma as compared with benign breast tissue, and they tend to be coexpressed in cancerous tissue. These findings are consistent with the idea that the SF:c-met ligand:receptor pair may have a role in breast carcinoma progression.

Hepatocyte growth factor alters the polarity of Madin-Darby canine kidney cell monolayers

Hepatocyte growth factor (HGF) and E-cadherin are important for epithelial morphogenetic events. We examined the effects of HGF on E-cadherin localization and interaction with beta-catenin in polarized Madin-Darby canine kidney (MDCK) cell monolayers grown on filters. Surface biotinylation experiments showed that HGF increases apically accessible E-cadherin. Confocal immunofluorescence microscopy of HGF-treated cells showed localization of E-cadherin at membrane domains contacting the apical compartment and an increase in accessibility of apically applied antibodies to lateral E-cadherin below the tight junction. Coimmunoprecipitation of beta-catenin/E-cadherin complexes showed that the amount of E-cadherin associated with beta-catenin increased during the first 24 h of HGF treatment with a return to baseline values after 48 and 72 h. Metabolic labeling showed that HGF increased the synthetic rate of beta-catenin and the amount of newly synthesized E-cadherin associated with immunoprecipitated beta-catenin, with the peak effect occurring after 12 h of treatment and returning to baseline after 24 h. HGF treatment inhibited transcytosis of immunoglobulin A by the polymeric immunoglobulin receptor. We conclude that HGF treatment of polarized MDCK cells grown on filters decreases cell polarity and alters E-cadherin/beta-catenin interaction and synthesis.

Hepatocyte Growth Factor/Scatter Factor Promotes Adhesion of Lymphoma Cells to Extracellular Matrix Molecules Via α4β1 and α5β1 Integrins

Hepatocyte growth factor (HGF )/scatter factor (SF ) is the ligand for a tyrosine kinase cell surface receptor encoded by the MET protooncogene (c-MET). HGF/SF can induce proliferation and motility in epithelial cells and promotes invasion of carcinoma cells and NIH3T3 fibroblasts transfected with both HGF/SF and c-MET genes. Our results show that HGF/SF and c-MET also play a role in adhesion and invasion of human lymphoma cells. c-MET mRNA is expressed in hemopoietic cells, such as hemopoietic progenitor cells (CD34+ cells) in bone marrow (BM) and mobilized peripheral blood, immature B cells in cord blood and BM, and germinal center B-centroblasts. In normal peripheral blood B cells, which are c-MET−, c-MET expression was induced by PMA, ConA, HGF/SF, and Epstein-Barr virus (EBV) infection. Using immunohistochemistry, we detected c-MET on the cell surface of large activated centroblasts in lymph nodes from patients with B-non–Hodgkin's lymphoma and Hodgkin's disease. In the latter group, c-MET expression correlated well with the presence of EBV. Because HGF/SF and c-MET promote metastasis of carcinoma cells, we studied the effects of c-MET stimulation by HGF/SF of B-lymphoma cells on properties relevant for metastasis, ie, adhesion, migration, and invasion. HGF/SF stimulated adhesion of the c-MET+ B-cell lines to the extracellular matrix molecules fibronectin (FN) and collagen (CN) in a dose dependent manner. However, adhesion to laminin was not affected by HGF/SF. Adhesion to FN was mediated by β1-integrins α4β1 (VLA4) and α5β1 (VLA5) since blocking antibodies against β1- (CD29), α4- (CD49d), or α5- (CD49e) integrin subunits, completely reversed the effect of HGF/SF. Furthermore, HGF/SF induced adhesion was abrogated by addition of genistein, which blocks protein tyrosine kinases, including c-MET. Addition of HGF/SF resulted in a sixfold increase in migration of c-MET B-lymphoma cells through Matrigel, compared to medium alone. In rat fibroblast cultures, HGF/SF doubled the number of c-MET+ B-lymphoma cells that invaded the fibroblast monolayer. In these adhesion, migration and invasion assays HGF/SF had no effect on c-MET− cell lines. In conclusion, c-MET is expressed or can be induced on immature, activated, and certain malignant B cells. HGF/SF increased adhesion of c-MET+ B-lymphoma cells to FN and CN, mediated via β1-integrins α4β1 and α5β1 , and furthermore promoted migration and invasion.

Degradation of the Met tyrosine kinase receptor by the ubiquitin-proteasome pathway

The Met tyrosine kinase receptor is a widely expressed molecule which mediates pleiotropic cellular responses following activation by its ligand, hepatocyte growth factor/scatter factor (HGF/SF). In this communication we demonstrate that significant Met degradation is induced by HGF/SF and that this degradation can be blocked by lactacystin, an inhibitor of proteasome activity. We also show that Met is rapidly polyubiquitinated in response to ligand and that polyubiquitinated Met molecules, which are normally unstable, are stabilized by lactacystin. Both HGF/SF-induced degradation and polyubiquitination of Met were shown to be dependent on the receptor possessing intact tyrosine kinase activity. Finally, we found that a normally highly labile 55-kDa fragment of the Met receptor is stabilized by lactacystin and demonstrate that it represents a cell-associated remnant that is generated following the ligand-independent proteolytic cleavage of the Met receptor in its extracellular domain. This truncated Met molecule encompasses the kinase domain of the receptor and is itself tyrosine phosphorylated. We conclude that the ubiquitin-proteasome pathway plays a significant role in the degradation of the Met tyrosine kinase receptor as directed by ligand-dependent and -independent signals. We propose that this proteolytic pathway may be important for averting cellular transformation by desensitizing Met signaling following ligand stimulation and by eliminating potentially oncogenic fragments generated via extracellular cleavage of the Met receptor.

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

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

Regulation of angiogenesis by scatter factor

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

Expression of HGF, its receptor c-met, c-myc, and albumin in cirrhotic and neoplastic human liver tissue

Hepatocellular carcinoma (HCC) is a common type of cancer, with approximately 260,000 new cases each year, and liver cirrhosis is generally considered a major predisposing factor for HCC. However, specific changes of gene expression in liver cirrhosis and HCC remain obscure. The expression of genes for hepatocyte growth factor (HGF), its receptor c-met proto-oncogene, c-myc proto-oncogene, and albumin was analyzed. Gene expression was studied by PCR in seven normal human livers, nine cases of hepatitis C cirrhosis, 12 cases of alcoholic cirrhosis, two cases of liver adenoma, and 12 cases of HCC. HGF and c-met protein were revealed by immunofluorescent staining. HGF mRNA was not expressed in normal livers but was detected in adenomas, in 80% of HCC, and in some cirrhoses. Paraffin-embedded and fresh-frozen tissue samples yielded similar results. Immunohistochemical data correlated with PCR results regarding the overexpression of the HGF/c-met system in HCC. Albumin gene expression was decreased in HCC vs normal livers, consistent with altered function of tumor hepatocytes. The elevated expression of the HGF/c-met system in HCC may play a role in tumor development and/or progression. Tissue localization studies of HGF and its receptor c-met protein support the existence of both autocrine and paracrine mechanisms of action of HGF in HCC vs only a paracrine mechanism in normal liver.

Immunoreactivity for hepatocyte growth factor/scatter factor and its receptor, met, in human lung carcinomas and malignant mesotheliomas

Paraffin sections from 29 lung carcinomas (28 primary and 1 metastatic) and 9 pleural malignant mesotheliomas were immunostained with antisera to human hepatocyte growth factor/scatter factor (HGF/SF) and its receptor, met. For HGF/SF, immunoreactivity was demonstrated in all 9 mesotheliomas, 9 of 12 adenocarcinomas, and 7 of 10 squamous cell carcinomas. None of seven cases of small cell anaplastic carcinoma was positive. The adenocarcinomas frequently showed enhanced luminal staining, suggesting possible secretion of HGF/SF, and this pattern of staining was also seen occasionally in bronchial epithelium adjacent to the tumour. Stromal fibroblasts also showed immunoreactivity for HGF/SF in 6/8 cases of mesothelioma but in only 3/12 adenocarcinomas, 1/10 squamous cell carcinomas, and 1/4 small cell anaplastic carcinomas. All tumours stained for met, usually strongly. The staining was mainly cytoplasmic in nature, but some plasma membrane staining was usually evident. Adenocarcinomas showed strong luminal membrane staining, as did adjacent, histologically normal bronchial epithelium. This study demonstrates the presence of HGF/SF and met in most of the tumour types described, particularly mesotheliomas, and suggests that the HGF/SF/met signalling system may play a role in the development of these tumours, either by autocrine or by paracrine mechanisms.

Hepatocyte growth factor/scatter factor is an axonal chemoattractant and a neurotrophic factor for spinal motor neurons

In the embryonic nervous system, developing axons can be guided to their targets by diffusible factors secreted by their intermediate and final cellular targets. To date only one family of chemoattractants for developing axons has been identified. Grafting and ablation experiments in fish, amphibians, and birds have suggested that spinal motor axons are guided to their targets in the limb in part by a succession of chemoattractants made by the sclerotome and by the limb mesenchyme, two intermediate targets that these axons encounter en route to their target muscles. Here we identify the limb mesenchyme-derived chemoattractant as hepatocyte growth factor/scatter factor (HGF/SF), a diffusible ligand for the c-Met receptor tyrosine kinase, and we also implicate HGF/SF at later stages as a muscle-derived survival factor for motoneurons. These results indicate that, in addition to functioning as a mitogen, a motogen, and a morphogen in nonneural systems, HGF/SF can function as a guidance and survival factor in the developing nervous system.

Involvement of Livertine, a hepatocyte growth factor family member, in neural morphogenesis

The formulation of the nervous system in vertebrate embryos involves extensive morphogenetic movements that include the folding of the neural tube and the migration of neural crest cells. Changes in cell shape and cell movements underlie neural morphogenesis but the molecular mechanisms involved in these processes in vivo are not well understood. Here, we show that a new member of the hepatocyte growth factor family, which we name Livertine, is expressed in frog embryos in neural cells including neural crest and midline neural plate cells which are undergoing pronounced morphogenetic movements. The ectopic expression of Livertine perturbs gastrulation and leads to positional changes in injected cells without apparently changing cell type. These results suggest that one of the normal functions of Livertine is the control of neural morphogenesis in the vertebrate embryo.

Overexpression and activation of hepatocyte growth factor/scatter factor in human non-small-cell lung carcinomas

Hepatocyte growth factor/scatter factor (HGF/SF) stimulates the invasive growth of epithelial cells via the c-MET oncogene-encoded receptor. In normal lung, both the receptor and the ligand are detected, and the latter is known to be a mitogenic and a motogenic factor for both cultured bronchial epithelial cells and non-small-cell carcinoma lines. Here, ligand and receptor expression was examined in 42 samples of primary human non-small-cell lung carcinoma of different histotype. Each carcinoma sample was compared with adjacent normal lung tissue. The Met/HGF receptor was found to be 2 to 10-fold increased in 25% of carcinoma samples (P = 0.0113). The ligand, HGF/SF, was found to be 10 to 100-fold overexpressed in carcinoma samples (P < 0.0001). Notably, while HGF/SF was occasionally detectable and found exclusively as a single-chain inactive precursor in normal tissues, it was constantly in the biologically-active heterodimeric form in carcinomas. Immunohistochemical staining showed homogeneous expression of both the receptor and the ligand in carcinoma samples, whereas staining was barely detectable in their normal counterparts. These data show that HGF/SF is overexpressed and consistently activated in non-small-cell lung carcinomas and may contribute to the invasive growth of lung cancer.

Interaction between Gab1 and the c-Met receptor tyrosine kinase is responsible for epithelial morphogenesis

The proteins Gab1 and the related DOS (for 'daughter of sevenless') each bind to substrates of tyrosine kinases like Grb2 or Corkscrew, and act in signalling pathways downstream of tyrosine kinase receptors. Here we show that Gab1 interacts directly with the c-met-encoded receptor tyrosine kinase but not with a number of other tyrosine kinases from different subfamilies. A newly identified proline-rich domain of Gab1 is responsible for the binding of this protein to the tyrosine-phosphorylated bidentate docking site in c-Met. Expression of Gab1 in epithelial cells is sufficient to induce the c-Met-specific activities, including branching morphogenesis. Thus we have discovered a new phosphotyrosine interaction domain in Gab1 and shown that Gab1 is the substrate of the c-Met receptor tyrosine kinase that mediates epithelial morphogenesis.

Expression of Met protein in thyroid tumours

Met protein is a transmembrane 190 kD heterodimer with tyrosine kinase activity, encoded by c-MET oncogene. It serves as a high affinity receptor for hepatocyte growth factor (HGF)/scatter factor (SF), a cytokine which stimulates cell proliferation, motility, and invasion. Expression of Met protein was investigated in 116 thyroid tumours using an anti-Met mouse monoclonal antibody (DQ-13) active on paraffin-embedded material. Reactivity for DQ-13 was observed in 77 per cent of papillary carcinomas, in 70 per cent of Hürthle cell tumours, and rarely in other tumours. The staining was either uniformly present throughout the tumour or limited to nests of infiltrating tumour cells. In some Hürthle cell tumours, prominent accumulation of the protein was observed in the Golgi area. Reactivity for Met protein was decreased or absent in poorly differentiated tumours and was not influenced by tumour size, presence of lymph node metastases, or age of the patient. Immunostaining for Ki-67 revealed that cytoplasmic accumulation of Met protein was not associated with enhanced proliferation of tumour cells. Overexpression of Met protein in thyroid papillary carcinoma may result in increased motility of tumour cells, which in turn may account for intraglandular multifocal dissemination and early lymph node metastasis.

Concomitant expression of hepatocyte growth factor/scatter factor and the receptor c-MET in human myeloma cell lines

Myeloma cell line supernatants were screened for their ability to inhibit the activity of transforming growth factor-beta (TGFbeta) in the mink lung cell (Mv-1-Lu) bioassay. Supernatant from the human myeloma cell line JJN-3 contained potent TGFbeta antagonistic activity. This activity was isolated and found to be associated with a 72-78-kDa glycoprotein. Specific polyclonal and monoclonal antibodies were generated toward the 72-78-kDa protein, and these antibodies precipitated the TGFbeta inhibitory activity from JJN-3 supernatant. Upon amino acid sequencing the protein appeared to be identical to hepatocyte growth factor (HGF), and some of the generated antibodies directly blocked the action of recombinant HGF in various assays. By HGF-specific polymerase chain reaction we demonstrated that HGF mRNA was expressed in five out of five tested myeloma cell lines. The level of HGF protein in supernatants showed great variation from >500 ng/ml in JJN-3 supernatant to a few ng/ml in the supernatants from other myeloma cell lines. The same five cell lines were also screened for expression the HGF receptor c-MET. Four of them expressed the receptor as shown by reverse transcriptase-polymerase chain reaction and Western blot. The receptor was shown to be constitutively phosphorylated in the human myeloma cell line JJN-3. This receptor could be dephosphorylated by anti-HGF antibodies, indicating the existence of an autocrine HGF loop in this cell line. We propose that HGF/c-MET may play a role in multiple myeloma.

The metastatic phenotype--prognostic implications

Strong efforts are being made in order to better understand the molecular mechanisms underlying cancer dissemination. We have attempted to summarise some of the findings in this area. A large number of differences in gene expression have been described in metastatic and non-metastatic cells. In the mouse B16 melanoma system, more than 50 different markers have been described. It is likely that many of these differences reflect the same genetic alteration (i.e. a mutation in a regulatory gene alters the expression of a set of co-regulated target genes). One could argue that it is more effective to study mutations in regulatory as opposed to expression of down-stream target genes. However, we feel that proto-oncogenes are less suitable as markers compared to target genes, since it is difficult to screen for mutations at multiple levels in regulatory pathways. In contrast, measuring the expression of a small number of target genes (i.e. one of the targets in Fig. 1), the expression of which are stimulated by upstream regulators, is accomplished more easily. It is anticipated that the future of optimised panels of independent markers will sharpen cancer diagnosis and lead to individualised therapy.