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

Hepatocyte growth factor/scatter factor induces a variety of tissue-specific morphogenic programs in epithelial cells

Hepatocyte growth factor/scatter factor (HGF/SF) is the mesenchymal ligand of the epithelial tyrosine kinase receptor c-Met. In vitro, HGF/SF has morphogenic properties, e.g., induces kidney epithelial cells to form branching ducts in collagen gels. Mutation of the HGF/SF gene in mice results in embryonic lethality due to severe liver and placenta defects. Here, we have evaluated the morphogenic activity of HGF/SF with a large variety of epithelial cells grown in three-dimensional collagen matrices. We found that HGF/SF induces SW 1222 colon carcinoma cells to form crypt-like structures. In these organoids, cells exhibit apical/basolateral polarity and build a well-developed brush border towards the lumen. Capan 2 pancreas carcinoma cells, upon addition of HGF/SF, develop large hollow spheroids lined with a tight layer of polarized cells. Collagen inside the cysts is digested and the cells show features of pancreatic ducts. HGF/SF induces EpH4 mammary epithelial cells to form long branches with end-buds that resemble developing mammary ducts. pRNS-1-1 prostate epithelial cells in the presence of HGF/SF develop long ducts with distal branching as found in the prostate. Finally, HGF/SF simulates alveolar differentiation in LX-1 lung carcinoma cells. Expression of transfected HGF/SF cDNA in LX-1 lung carcinoma and EpH4 mammary epithelial cells induce morphogenesis in an autocrine manner. In the cell lines tested, HGF/SF activated the Met receptor by phosphorylation of tyrosine residues. These data show that HGF/SF induces intrinsic, tissue-specific morphogenic activities in a wide variety of epithelial cells. Apparently, HGF/SF triggers respective endogenous programs and is thus an inductive, not an instructive, mesenchymal effector for epithelial morphogenesis.

The hepatocyte growth factor/scatter factor (HGF/SF) receptor, met, transduces a morphogenetic signal in renal glomerular fibromuscular mesangial cells

Previous studies have demonstrated that hepatocyte growth factor/scatter factor (HGF/SF) is secreted by mesenchymal cells and that it elicits motility, morphogenesis and proliferation of epithelia expressing the met receptor. We now report that HGF/SF may act as an autocrine factor in fibromuscular renal mesangial cells. These cells mechanically support glomerular endothelia, control the rate of plasma ultrafiltration and are implicated in the pathogenesis of a variety of chronic renal diseases. We detected met protein in the vascular stalk of metanephric glomeruli and in the mature mesangium. Mesangial lines from a mouse transgenic for a temperature-sensitive simian virus 40 T antigen expressed met mRNA and protein, and recombinant HGF/SF phosphorylated the met receptor tyrosine kinase. Cells were immortal in the permissive condition and HGF/SF enhanced proliferation in a defined medium. In the absence of the immortalising protein, division ceased and recombinant HGF/SF caused multipolar cells to become bipolar. The factor diminished stress fibres, their focal contacts and immunostaining for extracellular fibronectin, hence suggesting reduced substratum adhesion and enhanced motility. Mesangial lines also expressed HGF/SF mRNA and secreted bioactive factor; immunocytochemistry showed both ligand and receptor in individual cells. HGF/SF blocking antibody aggregated the cells, suggesting that mesangial-derived factor affects basal cell conformation in an autocrine manner. We conclude that mesangial cells express both HGF/SF and met, and the factor induces morphogenesis of cultured mesangial cells. Therefore HGF/SF may have an autocrine role in mesangial biology but further studies are now required to investigate the potential importance of the factor in vivo.

Hepatocyte growth factor-induced scatter of Madin-Darby canine kidney cells requires phosphatidylinositol 3-kinase

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 and scatter in response to CSF-1. However, cells expressing a mutant CSF-MET receptor containing a phenylalanine substitution for tyrosine 1356 were unable to scatter or form branching tubules following stimulation with CSF-1. Tyrosine 1356 is essential for the recruitment of multiple substrates including the p85 subunit of PI3-kinase, phospholipase C gamma, and Grb2. In this study, we have investigated the role of PI3-kinase and a downstream target of PI3-kinase, pp70S6K, in the induction of MDCK cell scatter in response to HGF/SF. Our results demonstrate that following stimulation with HGF/SF, activation of PI3-kinase but not pp70S6K is essential for MDCK cell scatter.

Hepatocyte growth factor/scatter factor expressed in follicular papilla cells stimulates human hair growth in vitro

Hepatocyte growth factor/scatter factor (HGF/SF) is a multifunctional polypeptide which acts as mitogen, motogen, or morphogen. In this study, we examined the effect of HGF/SF on human hair growth using organ and cell culture systems. HGF/SF was found to stimulate hair length and DNA synthesis in hair follicles at increasing concentrations up to 10 ng/ml (P < 0.05 and P < 0.01, respectively). HGF/SF stimulated [3H]thymidine incorporation by hair bulb-derived keratinocytes with the strongest response at 30 ng/ml of HGF/SF (P < 0.05). Cultured follicular papilla cells secreted HGF/SF, measured by an enzyme-linked immunoassay, in response to interleukin 1-alpha (IL1-alpha, 10 ng/ml), tumor necrosis factor-alpha (TNF-alpha, 10 ng/ml), or tetradecanoylphorbolacetate (100 nM) at levels ranging from 0.2 to 0.3 ng/mg protein/48 h. HGF/SF mRNA expressions, measured by the reverse transcription-polymerase chain reaction, were detected in follicular papilla cells, and were also stimulated by the three reagents. Transforming growth factor-beta (10 ng/ml) suppressed both protein and mRNA levels. These results suggest that hair follicle elongation induced by HGF/SF in organ culture occurs partly due to the mitogenic activity of HGF/SF expressed in follicular papilla cells on hair bulb-derived keratinocytes.

Detection of candidates for cancer cell motility inhibitory protein in the Dunning adenocarcinoma model

The more differentiated components of a primary tumor may produce substances that reduce the growth rate and metastatic potential of more aggressive components. In the Dunning R-3327 prostatic adenocarcinoma model, cancer cell motility is required for metastatic potential. Medium conditioned by the non-motile, non-metastatic G subline contains proteins of molecular weight 50-100 kDa that inhibited the motility of the highly motile, highly metastatic MAT-LyLu subline. G subline-conditioned medium was separated by DEAE-cellulose chromatography using a linear gradient of 0-0.5 M NaCl in 100 mM Tris at pH 8.3. The motility inhibitory activity of G-conditioned medium was localized to column fractions 51-70 that contained 18% of the applied protein and only 6.5% of the proteins secreted by the G cells. Analysis of pooled fractions 51-60 and 61-70 by two-dimensional gel electrophoresis identified five protein families, with a total of 12 charged proteins of molecular weights approximating 66, 54, 50, 41 and 34 kDa, that were not present or present in reduced quantities in column fractions that did not inhibit motility. Isolation and identification of motility inhibitory protein may prove it the first substance discovered that is produced by a more differentiated component of a neoplasm that directly inhibits a metastasis-associated property.

Growth factor-induced tyrosine phosphorylation of Hrs, a novel 115-kilodalton protein with a structurally conserved putative zinc finger domain

The activation of growth factor receptor tyrosine kinases leads to tyrosine phosphorylation of many intracellular proteins which are thought to play crucial roles in growth factor signaling pathways. We previously showed that tyrosine phosphorylation of a 115-kDa protein is rapidly induced in cells treated with hepatocyte growth factor. To clarify the structure and possible function of the 115-kDa protein (designated Hrs for hepatocyte growth factor-regulated tyrosine kinase substrate), we purified this protein from B16-F1 mouse melanoma cells by anti-phosphotyrosine immunoaffinity chromatography and determined its partial amino acid sequences. On the basis of the amino acid sequences, we molecularly cloned the cDNA for mouse Hrs. The nucleotide sequence of the cDNA revealed that Hrs is a novel 775-amino-acid protein with a putative zinc finger domain that is structurally conserved in several other proteins. This protein also contained a proline-rich region and a proline- and glutamine-rich region. The expression of Hrs mRNA was detected in all adult mouse tissues tested and also in embryos. To analyze the Hrs cDNA product, we prepared a polyclonal antibody against bacterially expressed Hrs. Using this antibody, we showed by subcellular fractionation that Hrs is localized to the cytoplasm; we also showed that that tyrosine phosphorylation of Hrs is induced in cells treated with epidermal growth factor or platelet-derived growth factor. These results suggest that Hrs plays a unique and important role in the signaling pathway of growth factors.

Differential intrastromal invasion by normal ocular surface epithelia is mediated by different fibroblasts

For most mucosal epithelia including the ocular surface, it is generally believed that wound healing is executed by epithelial migration on the plane of erosion or ulceration. In explant cultures, we incidentally observed the phenomenon of intrastromal invasion by corneal, limbal and conjunctival epithelial cells even when cell migration on plastics was promoted. Homotypic and heterotypic tissue recombinants between corneal and conjunctival epithelial cells and their stroma revealed that this phenomena was dependent on viable mesenchymal cells and was more active in conjunctival stroma than corneal stroma. Using organotypic cultures in which 3T3 fibroblasts were incorporated in collagen gel, we noted that this phenomenon was fibroblast-dependent and up-regulated by lifting the culture to the air-fluid interphase. The extent of intrastromal invasion was decreased if 3T3 fibroblasts were treated with increasing concentrations of mitomycin C. The invading epithelial islands retained the same basal and suprabasal epithelial phenotypes as those of the surface epithelial layers using several anti-keratin monoclonal antibodies. Using 5-fluorouracil (5-FU) to eliminate the rapid-cycling, i.e. transient amplifying progenitor basal cells, we further noted that this phenomenon could still be produced by 5-FU-resistant slow-cycling progenitor cells of corneal, limbal and conjunctival explants. In organotypic cultures, conjunctival fibroblasts were more active than corneal fibroblasts in inducing corneal or conjunctival epithelial invasion. As such intrastromal invasion can experimentally be produced by normal non-transformed adult epithelial cells and mediated by fibroblasts, this in vitro phenomenon may be useful for studying the epithelial-mesenchymal interactions operating during embryonic development and post-natal wound healing.

Expression and loss of heterozygosity of c-met proto-oncogene in primary breast cancer

The c-met proto-oncogene encodes the receptor to hepatocyte growth factor-scatter factor (HGF-SF), a mesenchyme-derived cytokine with cell-dissociating, invasion, and angiogenic properties. The expression of c-met in breast cancer is the subject of controversy; 111 primary breast cancers were examined for LOH of c-met by Southern blot electrophoresis. c-met expression was measured in a further 40 patients with breast cancer and in 8 patients with benign breast disease by flow cytometry. LOH of c-met was detected in only 4% of informative breast cancers. Expression of c-met was significantly greater in patients with breast cancer than in those with benign breast disease (P < 0.01, Mann-Whitney). There was no correlation however between increased c-met expression and clinicopathological prognostic variables. These results do not support the role of c-met as a tumour suppressor gene in breast cancer but suggest increased receptor expression in malignant breast disease. The significance of this increased expression in breast cancer is the subject of further investigation.

Sequential requirement of hepatocyte growth factor and neuregulin in the morphogenesis and differentiation of the mammary gland

We have examined the role of two mesenchymal ligands of epithelial tyrosine kinase receptors in mouse mammary gland morphogenesis. In organ cultures of mammary glands, hepatocyte growth factor (HGF, scatter factor) promoted branching of the ductal trees but inhibited the production of secretory proteins. Neuregulin (NRG, neu differentiation factor) stimulated lobulo-alveolar budding and the production of milk proteins. These functional effects are paralleled by the expression of the two factors in vivo: HGF is produced in mesenchymal cells during ductal branching in the virgin animal; NRG is expressed in the mesenchyme during lobulo-alveolar development at pregnancy. The receptors of HGF and NRG (c-met, c-erbB3, and c-erbB4), which are expressed in the epithelial cells, are not regulated. In organ culture, branching morphogenesis and lobulo-alveolar differentiation of the mammary gland could be abolished by blocking expression of endogenous HGF and NRG by the respective antisense oligonucleotides; in antisense oligonucleotide-treated glands, morphogenesis could again be induced by the addition of recombinant HGF and NRG. We thus show that two major postnatal morphogenic periods of mammary gland development are dependent on sequential mesenchymal-epithelial interactions mediated by HGF and NRG.

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

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

Transformations between epithelium and mesenchyme: normal, pathological, and experimentally induced

In this review, we define the two major tissue types, epithelium and mesenchyme, and we describe the transformations (transdifferentiations) of epithelium to mesenchyme (EMT) and mesenchyme to epithelium (MET) that occur during embryonic development. The differentiation of the metanephric blastema provides a striking example of MET. Differentiation of metanephric epithelium is promoted by matrix molecules and receptors (nidogen, laminins, alpha 6 integrins), hepatic growth factor/scatter factor, and products of the genes wnt-1, wnt-4, and Pax-2. Transformation of MDCK epithelium to mesenchyme-like cells is promoted in vitro by antibodies to E-cadherin, products of v-src, v-ras, and v-mos, and by manipulation of the epithelium on collagen gels. Suspension in collagen gel, transforming growth factors, and c-fos have also been shown to promote EMT in epithelia. We present studies from our laboratory showing that alpha 5 beta 1 integrin has a role in the EMT of lens epithelium that is brought about by suspension in collagen gel. Our laboratory has also shown that transfection with the E-cadherin gene induces embryonic corneal fibroblasts to undergo MET and that this MET is enhanced by interaction of the differentiating epithelium with living fibroblasts. This review calls attention to the roles that EMT and MET might have in kidney pathologies and urges further study of the involvement of these phenomena in renal development, renal injury, and renal malignancy.

Concomitant expression of hepatocyte growth factor (HGF), HGF activator and c-met genes in human glioma cells in vitro

Three new cell lines of human glioblastoma have been established. These cells co-expressed hepatocyte growth factor (HGF) and its receptor, c-Met, genes in vitro. Reverse-transcriptase/polymerase-chain reaction study revealed that the cells also expressed gene for HGF activator, a recently cloned serine proteinase, suggesting that HGF might have a role in glioma cells in vitro as an autocrine factor. The activator mRNA was also detected in other well-established glioma cell lines, glioma tissues and normal brain. The concomitant expression of HGF, HGF activator and c-met was also detected in one glioblastoma case in vivo out of five tested.

Human peri-tumoral and lung fibroblasts produce paracrine motility factors for recently established human sarcoma cell strains

Paracrine motogenic cytokines secreted by normal cells can stimulate metastatic cell invasion. For example, human fibroblasts secrete hepatocyte growth factor/scatter factor (HGF/SF), which stimulates paracrine migration of epithelial and certain carcinoma cells, and migration-stimulating factor (MSF), which stimulates autocrine migration of fibroblasts from certain breast carcinomas. We found that human peri-tumoral and lung fibroblasts secrete motility-stimulating activity for several recently established human sarcoma cell strains. Motility of lung metastasis-derived SYN-I sarcoma cells was preferentially stimulated by human lung and peri-tumoral fibroblast motility-stimulating factors (FMSFs). FMSFs were non-dialyzable, susceptible to trypsin and sensitive to dithiothreitol. Cycloheximide inhibited accumulation of FMSF activity in conditioned medium; however, addition of cycloheximide to the migration assay did not significantly affect motility-stimulating activity. Purified HGF/SF, rabbit anti-hHGF and RT-PCR analysis of peri-tumoral and lung fibroblast HGF/SF mRNA expression indicated that FMSF activity was unrelated to HGF/SF. Partial purification of FMSF by gel exclusion chromatography revealed several peaks of activity, suggesting multiple FMSF molecules or complexes. Since human soft tissue sarcomas have a distinctive hematogenous metastatic pattern (predominantly lung), FMSF may play a role in this process independent of HGF/SF.

HGF/SF: a potent cytokine for mammary growth, morphogenesis and development

The mammary gland is a renewing tissue in which morphogenetic processes and differentiation occur cyclically during the menstrual cycle, pregnancy and lactation. These events have been shown to be dependent upon epithelial-mesenchymal interactions. Studies of the effects of individual factors, their cellular source and their target cell populations in the different developmental stages of the mammary gland are greatly facilitated by the accessibility of this organ and the application of new techniques that allow purification of the major epithelial and stromal components of this tissue. Here we demonstrate that HGF/SF and its cellular receptor, c-met, are expressed and regulated temporally during mouse mammary development and differentiation. We show that human and mouse mammary fibroblasts produce HGF/SF and that HGF/SF is not only mitogenic but morphogenic and motogenic for both human and mouse mammary epithelial cells. We have found that human luminal and myoepithelial cells express c-met differentially and that HGF/SF has different effects on these two mammary epithelial cell populations. HGF/SF is mitogenic for luminal cells but not myoepithelial cells, and morphogenic to myoepithelial cells but not luminal cells. This is discussed in the context of the proliferative compartments in the normal mammary gland and the potential role of the myoepithelial cells to act as the skeleton for ductal development.

Tyrosine phosphorylation regulates the adhesions of ras-transformed breast epithelia

Transformed epithelial cells often are characterized by a fibroblastic or mesenchymal morphology. These cells exhibit altered cell-cell and cell-substrate interactions. Here we have identified changes in the adhesions and cytoskeletal interactions of transformed epithelial cells that contribute to their altered morphology. Using MCF-10A human breast epithelial cells as a model system, we have found that transformation by an activated form of ras is characterized by less developed adherens-type junctions between cells but increased focal adhesions. Contributing to the modified adherens junctions of the transformed cells are decreased interactions among beta-catenin, E-cadherin, and the actin cytoskeleton. The ras-transformed cells reveal elevated phosphotyrosine in many proteins, including beta-catenin and p120 Cas. Whereas in the normal cells beta-catenin is found in association with E-cadherin, p120 Cas is not. In the ras-transformed cells, the situation is reversed; tyrosine-phosphorylated p120 Cas, but not tyrosine-phosphorylated beta-catenin, now is detected in E-cadherin complexes. The tyrosine-phosphorylated beta-catenin also shows increased detergent solubility, suggesting a decreased association with the actin cytoskeleton. p120 Cas, whether tyrosine phosphorylated or not, partitions into the detergent soluble fraction, suggesting that it is not tightly bound to the actin cytoskeleton in either the normal or ras-transformed cells. Inhibitors of tyrosine kinases decrease the level of tyrosine phosphorylation and restore a normal epithelial morphology to the ras-transformed cells. In particular, decreased tyrosine phosphorylation of beta-catenin is accompanied by increased interaction with both E-cadherin and the detergent insoluble cytoskeletal fraction. These results suggest that elevated tyrosine phosphorylation of proteins such as beta-catenin and p120 Cas contribute to the altered adherens junctions of ras-transformed epithelia.

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

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

The in vitro motility of human gliomas increases with increasing grade of malignancy

BACKGROUND

Malignant gliomas are a highly invasive disease with a dismal prognosis despite aggressive therapeutic interventions.

METHODS

The authors tested the hypothesis that increasing in vitro motility of human glial tumors correlates with increasing grade of malignancy. A radial dish assay was used to quantitatively assess the brain tumor cell motility of 14 low passage cell lines derived from human glial tumors of varied malignancy, and 3 cell lines derived from human glia. The egress of cells from a central region of high tumor cell density to a region of lower tumor cell density was determined at various time points. A motility coefficient (MC), the slope of distance traveled against time, was generated by simple linear regression analysis.

RESULTS

The MC increased with the increased histologic grade of malignancy. Generation of a t-statistic was used to determine the significance of differences in motility among 5 histopathologic groups: 10 glioblastoma (World Health Organization Grade IV) cell lines (mean MC, 0.00396), 2 mixed anaplastic oligoastrocytoma (Grade III) cell lines (mean MC, 0.00382), 1 anaplastic astrocytoma (Grade III) cell line (mean MC, 0.00295), 1 Grade I glioma cell line (mean MC, 0.00206), and 3 human glial cell lines (mean MC, 0.00110).

CONCLUSIONS

The radial dish assay provided a reproducible method for quantitatively assessing brain tumor cell motility. The higher MC observed with the malignant human glioma cell lines correlated with the tendency of these tumors to invade into adjacent brain tissue. The potential to inhibit glial tumor motility may provide an important therapeutic avenue in the future.

Immunogold labeling of oncogenic and tumor related proteins

Immunogold labeling electron microscopy technique has been used to study the ultrastructural localization of oncogenic proteins: Mos, Met, Ski, and the tumor-associated protein, Muc1, as well as their relationship with other tumor-related proteins. By pre- and postembedding immunogold labeling electron microscopy techniques, we showed that the Mos protein pp39mos colocalized with microtubule bundles, suggesting that microtubulin or microtubule-associated protein(s) may be the substrate of Mos. Met protein was labeled at the microvilli of the lumen that are formed in cultured T47D cells, implying its potential involvement in lumen formation. Ski localization experiments revealed a unique globular structure "Ski body" that is present inside the nucleus of interphase chicken embryo fibroblast infected with Ski cDNA FB29 and FB2-29. Ski bodies were also found scattered in the cytoplasm of metaphase FB29 and FB2-29 Ski expressing chicken embryo fibroblasts. In T47D cells, tumor-associated protein Muc1 was associated with both the plasma membrane and the membranes of secretory vesicles in the cytoplasm. In MUC1 infected NIH3T3 cells, however, labeling showed that in addition to the plasma membrane and the membranes of secretory vesicles, some Muc1 gold spheres were seen inside the secretory vesicles, suggesting that the subcellular localization of the protein may vary in different cell types.

Comparative study of hepatocyte growth factor/scatter factor and keratinocyte growth factor effects on human keratinocytes

Hepatocyte growth factor/scatter factor (HGF/SF) and keratinocyte growth factor (KGF, also designated FGF-7) are paracrine growth factors secreted by mesenchymal cells and active on a variety of epithelial cell types. In this study, the biologic responses of keratinocytes to these paracrine growth factors were compared. Stimulation of mitogenesis, migration, plasminogen activator (PA) activity, and fibronectin production were examined using human foreskin keratinocytes cultured in serum-free MCDB 153 medium. Although the two factors stimulated a similar level of proliferation when cells were maintained for 5 d in 1.8 mM Ca++, the peak effect of KGF, observed at 10 ng/ml, was approximately threefold higher than that of HGF/SF when cells were in medium containing 0.15 mM Ca++. Both agents promoted the migration of cells in low-calcium medium (0.08 mM Ca++). However, the magnitude of the response was approximately twofold greater for HGF/SF at 10 ng/ml than KGF at the same concentration. None of the matrix proteins such as type I collagen, type IV collagen, laminin, or fibronectin either stimulated or suppressed HGF/SF- or KGF-stimulated keratinocyte migration. Both factors stimulated PA activity of the cell extracts, especially urokinase-type, with similar potencies. Promoted PA activity was maximal with the addition of 10 ng/ml of either factor. Neither factor increased the production of fibronectin under conditions in which transforming growth factor-beta 1 was active. These results indicate that HGF/SF and KGF, both recognized as paracrine growth factors, elicit distinctive patterns of response by keratinocytes, implying that they have different roles in epidermal physiology.

Hepatocyte growth factor/scatter factor modulates cell motility, proliferation, and proteoglycan synthesis of chondrocytes

Hepatocyte growth factor/scatter factor (HGF/SF) is a multifunctional growth factor that promotes proliferation, motility, and morphogenesis in epithelial cells. Recently the HGF receptor, c-met protooncogene product, has been shown to be expressed in developing limb buds (Sonnenberg, E., D. Meyer, M. Weidner, and C. Birchmeiyer, 1993. J. Cell Biol. 123: 223-235), suggesting that some populations of mesenchymal cells in limb buds respond to HGF/SF. To test the possibility that HGF/SF is involved in regulation of cartilage development, we isolated chondrocytes from knee joints and costal cartilages of 23-d embryonic and 4-wk-old rabbits, and analyzed the effects of HGF/SF on migration and proliferation of these cells. We found that HGF/SF stimulated migration of cultured articular chondrocytes but did not scatter limb mesenchymal fibroblasts or synovial fibroblasts in culture. HGF/SF also stimulated proliferation of chondrocytes; a maximum three-fold stimulation in DNA synthesis was observed at the concentration of 3 ng/ml of HGF/SF. Moreover, HGF/SF had the ability to enhance proteoglycan synthesis in chondrocytes. The responsiveness of chondrocytes to HGF/SF was also supported by the observation that they expressed the HGF/SF receptor. Addition of the neutralizing antibody to rat HGF/SF affected neither DNA synthesis nor proteoglycan synthesis in rat chondrocytes, suggesting a paracine mechanism of action of HGF/SF on these cells. In situ hybridization analysis showed that HGF/SF mRNA was restrictively expressed in the areas of future joint regions in developing limb buds and in the intercostal spaces of developing costal cartilages. These findings suggest that HGF/SF plays important roles in cartilage development through its multiple activities.

Sulphated proteoglycan is required for collecting duct growth and branching but not nephron formation during kidney development

Kidney epithelia have separate origins; collecting ducts develop by ureteric bud growth and arborisation, nephrons by induced mesenchyme-epithelium transition. Both express sulphated glycosaminoglycans (GAGs) which are strikingly upregulated during nephron differentiation. However, sodium chlorate, an inhibitor of GAG sulphation, and the GAG-degrading enzymes heparitinase plus chondroitinase, did not prevent nephron development. In contrast, ureteric bud growth and branching were reversibly inhibited by the above reagents, the inhibition correlating quantitatively with sulphated GAG deprivation caused by a range of chlorate concentrations. Growth and branching could be independently restored during GAG deprivation by hepatocyte growth factor and phorbol-12-myristate acetate (PMA) respectively. Together these signalling effectors stimulated both branch initiation and growth. Thus growth and morphogenesis of ureteric bud involve distinct signalling pathways both regulated by GAGs.

The murine stk gene product, a transmembrane protein tyrosine kinase, is a receptor for macrophage-stimulating protein

Macrophage-stimulating protein (MSP) was originally identified as an inducer of murine resident peritoneal macrophage responsiveness to chemoattractants. We recently showed that the product of RON, a protein tyrosine kinase cloned from a human keratinocyte library, is the receptor for MSP. Similarity of murine stk to RON led us to determine if the stk gene product is the murine receptor for MSP. Radiolabeled MSP could bind to NIH 3T3 cells transfected with murine stk cDNA (3T3/stk). Binding was saturable and was inhibited by unlabeled MSP but not by structurally related proteins, including hepatocyte growth factor and plasminogen. Specific binding to STK was demonstrated by cross-linking of 125I-labeled MSP to membrane proteins of 3T3/stk cells, which resulted in a protein complex with a molecular mass of 220 kDa. This radiolabeled complex comprised 125I-MSP and STK, since it could be immunoprecipitated by antibodies to the STK beta chain. Binding of MSP to stk cDNA-transfected cells induced tyrosine phosphorylation of the 150-kDa STK beta chain within 1 min and caused increased motile activity. These results establish the murine stk gene product as a specific transmembrane protein tyrosine kinase receptor for MSP. Inasmuch as the stk cDNA was cloned from a hematopoietic stem cell, our data suggest that in addition to macrophages and keratinocytes, a cell in the hematopoietic lineage may also be a target for MSP.

The biology of hepatocyte growth factor/scatter factor

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

The role of the microtubular system in the cell response to HGF/SF

The effects of the microtubular drugs colcemid and taxol on the morphological changes induced by hepatocyte growth factor/scatter factor (HGF/SF) in MDCK cells were studied. Dynamic changes in the area and shape of individual cells were assessed by morphometric methods whereas alterations of the cytoskeleton were assessed by immunomorphological methods. The results suggest that there are two components in the response to HGF/SF: (a) activation of the extension of lamellae leading to cell spreading; and (b) reorganization of microtubules leading to polarization of cell shape. The latter response is highly sensitive to microtubular drugs, especially taxol. HGF/SF induced spreading in taxol-treated MDCK cells but these cells retained a non-polarized discoid shape and a pattern of actin microfilament bundles characteristic of the untreated cells. Colcemid and taxol did not prevent HGF/SF-induced migration of cells in Boyden chambers but completely inhibited the outgrowth of multicellular strands and tubules from cell aggregates in collagen gels. These results show that enhanced lamella formation in response to HGF/SF without polarization of cell shape is sufficient to induce cell motility. In contrast, microtubule-dependent polarization is essential for complex morphogenetic responses such as tubulogenesis in collagen gels.

Three patterns of cytokine expression potentially involved in epithelial-fibroblast interactions of human ocular surface

Signals transmitted from mesenchyme to epithelia or vice versa constitute the basis of reciprocal epithelial-mesenchymal interactions. As a first step toward understanding epithelial-mesenchymal interactions on the ocular surface where the transit amplifying cell-containing corneal epithelium is anatomically separated from the stem cell-containing limbal epithelium, we sought to characterize the expression patterns of cytokines and their receptors by primary epithelial and early-passaged fibroblast cultures of human cornea and limbus. Northern hybridization with oligonucleotide and cDNA probes to a total of 25 cytokines and 12 of their receptors revealed that the positively expressed cytokines could be divided into the following four patterns. Type I: TGF-alpha, IL-1 beta, and PDGF-B were expressed exclusively by epithelial cells but their respective receptors EGFR and IL-1R were predominantly and PDGFR-beta was exclusively expressed by fibroblasts. Type II: IGF-I, TGF-beta 1, -beta 2, LIF, and bFGF, and their receptors were expressed by both epithelial cells and fibroblasts. FGFR-1 (flg) and FGFR-2 (bek) were expressed more by fibroblasts and bFGF was expressed more by corneal than limbal epithelial cells. Type III: keratinocyte growth factor (KGF) and hepatocyte growth factor (HGF) were expressed exclusively by fibroblasts and their respective receptors, KGFR and c-met, were predominantly expressed by epithelial cells. Combined with RT-PCR, the quantity of KGF and KGFR transcripts was highest in limbal fibroblasts and epithelial cells, respectively. In contrast, the quantity of HGF and HGFR (c-met) transcripts was highest in corneal fibroblasts and epithelial cells, respectively. Type IV: M-CSF and IL-8 were expressed by fibroblasts and/or epithelial cells but their receptors were not expressed by epithelial cells nor fibroblasts, but by immune or inflammatory cells. In addition to these potential paracrine actions, autocrine actions mediated by TGF-alpha/EGFR, IL-1 beta/IL1-R, and bFGF/FGFR-1 were more expressed by corneal than limbal epithelial cells. Immunofluorescence staining on human corneoscleral cryosections confirmed that EGFR and bFGF were not expressed by the limbal basal epithelium, but expressed strongly by the corneal epithelium, a pattern consistent with Northern hybridization. These results indicate that ocular surface epithelial cells and fibroblasts can express a myriad of cytokines, among which the first three patterns constitute the network of potential epithelial-mesenchymal cytokine dialogues. The difference of certain cytokine expression between corneal and limbal regions suggests that this network participates in normal epithelial growth and differentiation, and plays an important role in wound healing.

Mutation of juxtamembrane tyrosine residue 1001 suppresses loss-of-function mutations of the met receptor in epithelial cells

Signals transduced by the met tyrosine kinase, which is the receptor for scatter factor/hepatocyte growth factor, are of major importance for the regulation of epithelial cell motility, morphogenesis, and proliferation. We report here that different sets of tyrosine residues in the cytoplasmic domain of the met receptor affect signal transduction in epithelial cells in a positive or negative fashion: mutation of the C-terminal tyrosine residues 13-16 (Y1311, Y1347, Y1354, and Y1363) reduced or abolished ligand-induced cell motility and branching morphogenesis. In contrast, mutation of the juxtamembrane tyrosine residue 2 (Y1001) produced constitutively mobile, fibroblastoid cells. Furthermore, the gain-of-function mutation of tyrosine residue 2 suppressed the loss-of-function mutations of tyrosine residue 15 or 16. The opposite roles of the juxtamembrane and C-terminal tyrosine residues may explain the suggested dual function of the met receptor in both epithelial-mesenchymal interactions and tumor progression.

Characterization of cancer cell dissociation factor in a highly invasive pancreatic cancer cell line

BACKGROUND

Two pancreatic cancer cell lines, the highly invasive and metastatic cell line PC-1.0 and the weakly invasive and rarely metastatic cell line PC-1, were established from a pancreatic ductal carcinoma induced by N-nitrosobis (2-oxopropyl) amine in a Syrian golden hamster.

METHODS

The cancer cell dissociation activity in serum-free conditioned medium of PC-1.0 cells was partially purified using a heparin column, a hydroxylapatite column, anion exchange, and gel filtration high-performance liquid chromatography. Several biologic properties of the partially purified activity were evaluated.

RESULTS

Two cell lines exhibited different growth morphologic changes in vitro: the weakly invasive cell line PC-1 formed islandlike colonies, and the highly invasive cell line PC-1.0 grew mainly as single cells. The conditioned medium of PC-1.0 cells induced dissociation of islandlike colonies and morphologic changes of PC-1 cells to elongated cells, with a high frequency of pseudopodia formation similar to the morphologic findings of PC-1.0 cells. The dissociation activity did not bind to the heparin column and had an apparent molecular mass of > 400 kDa, as deduced from gel filtration. Several immunoreactive proteinous bands were observed in immunoblotting analysis using a polyclonal blocking antibody. The partially purified activity enhanced cell motility, chemoinvasion, and cell adhesion to plastic plates and fibronectin.

CONCLUSIONS

Highly invasive and metastatic PC-1.0 cells produce a soluble proteinous factor, called "dissociation factor" (DF), which induces cell dissociation of weakly invasive and rarely metastatic PC-1 cells. It seems likely that DF has a role in tumor invasion and metastasis.

Association of p120, a tyrosine kinase substrate, with E-cadherin/catenin complexes

p120 was originally identified as a substrate of pp60src and several receptor tyrosine kinases, but its function is not known. Recent studies revealed that this protein shows homology to a group of proteins, beta-catenin/Armadillo and plakoglobin (gamma-catenin), which are associated with the cell adhesion molecules cadherins. In this study, we examined whether p120 is associated with E-cadherin using the human carcinoma cell line HT29, as well as other cell lines, which express both of these proteins. When proteins that copurified with E-cadherin were analyzed, not only alpha-catenin, beta-catenin, and plakoglobin but also p120 were detected. Conversely, immunoprecipitates of p120 contained E-cadherin and all the catenins, although a large subpopulation of p120 was not associated with E-cadherin. Analysis of these immunoprecipitates suggests that 20% or less of the extractable E-cadherin is associated with p120. When p120 immunoprecipitation was performed with cell lysates depleted of E-cadherin, beta-catenin was no longer coprecipitated, and the amount of plakoglobin copurified was greatly reduced. This finding suggests that there are various forms of p120 complexes, including p120/E-cadherin/beta-catenin and p120/E-cadherin/plakoglobin complexes; this association profile contrasts with the mutually exclusive association of beta-catenin and plakoglobin with cadherins. When the COOH-terminal catenin binding site was truncated from E-cadherin, not only beta-catenin but also p120 did not coprecipitate with this mutated E-cadherin. Immunocytological studies showed that p120 colocalized with E-cadherin at cell-cell contact sites, even after non-ionic detergent extraction. Treatment of cells with hepatocyte growth factor/scatter factor altered the level of tyrosine phosphorylation of p120 as well as of beta-catenin and plakoglobin. These results suggest that p120 associates with E-cadherin at its COOH-terminal region, but the mechanism for this association differs from that for the association of beta-catenin and plakoglobin with E-cadherin, and thus, that p120, whose function could be modulated by growth factors, may play a unique role in regulation of the cadherin-catenin adhesion system.

A role for HGF/SF in neural induction and its expression in Hensen's node during gastrulation

It was previously shown (Roberts, C., Platt, N., Streit, A., Schachner, M. and Stern, C. D. (1991) Development 112, 959–970) that grafts of Hensen's node into chick embryos enhanced and maintain expression of the L5 carbohydrate in neighbouring epiblast cells, and that antibodies against L5 inhibit neural induction by such a graft. We now show that L5 is initially widely expressed in the epiblast, but as neural induction proceeds it gradually becomes confined to and up-regulated in the early neural plate. L5 can therefore be considered as a marker for cells that are competent to respond to neural induction. We also show that Hepatocyte Growth Factor/Scatter Factor (HGF/SF) promotes the expression of L5 by extraembryonic epiblast in collagen gels after overnight culture. Explants cultured for several days in the presence of HGF/SF, as well as explants of prospective neural plate, can differentiate into cells with neuronal morphology expressing neuronal markers. To investigate whether HGF/SF is expressed in the chick embryo at appropriate stages of development, we produced specific cDNA probes and used them for in situ hybridization. We find that at the primitive streak stage, HGF/SF is expressed specifically in Hensen's node. We therefore propose that HGF/SF plays a role during the early steps of neural induction, perhaps by inducing or maintaining the competence of the epiblast to respond to neural inducing signals.

Scatter factor/hepatocyte growth factor is essential for liver development

Polypeptide growth factors are important effectors of cell growth and differentiation in vitro and are thought to be critical for processes such as specification of cell fate, tissue growth and organogenesis in vivo. Scatter factor/hepatocyte growth factor (SF/HGF) is the prototype of an emerging family of growth factors that resemble in their domain structure and mechanism of activation the blood proteinase plasminogen. The cellular responses of SF/HGF are mediated by the c-Met tyrosine kinase receptor. Here we report that mice lacking SF/HGF fail to complete development and die in utero. The mutation affects the embryonic liver, which is reduced in size and shows extensive loss of parenchymal cells. In addition, development of the placenta, particularly of trophoblast cells, is impaired. Thus, SF/HGF is essential for the development of several epithelial organs.

Placental defect and embryonic lethality in mice lacking hepatocyte growth factor/scatter factor

Hepatocyte growth factor/scatter factor (HGF/SF) functions as a mitogen, motogen and morphogen for a variety of cultured cells. The genes for HGF/SF and its receptor (the c-met proto-oncogene product) are expressed in many tissues during the embryonic periods and in the adult. HGF/SF is thought to mediate a signal exchange between the mesenchyme and epithelia during mouse development. To examine the physiological role of HGF/SF, we generated mutant mice with a targeted disruption of the HGF/SF gene. Here we report that homozygous mutant embryos have severely impaired placentas with markedly reduced numbers of labyrinthine trophoblast cells, and die before birth. The growth of trophoblast cells was stimulated by HGF/SF in vitro, and the HGF/SF activity was released by allantois in primary culture of normal but not mutant embryos. These findings suggest that HGF/SF is an essential mediator of allantoic mesenchyme-trophoblastic epithelia interaction required for placental organogenesis.

A two-dimensional model of cell movement. Well differentiated human rectal adenocarcinoma cells move as coherent sheets upon TPA stimulation

We previously found that 12-O-tetradecanoylphorbol-13-acetate (TPA)-enhanced invasion of Matrigel was associated with augmentation of cell motility but not with metalloproteinase activity in a highly metastatic variant (L-10) of human rectal adenocarcinoma cell line RCM-1. In the present study, with a two-dimensional cell motility assay, we investigated morphology of TPA-induced motility and biochemical pathways that may be involved in the induction of such a motile response to TPA. TPA induced active cell locomotion in L-10 cells with characteristic morphology: the cells moved outwards from the cell islands mainly as a localized coherent sheet of cells with few single moved out cells, but not cell proliferation. The front cells showed locomotor morphologies with front-tail polarity and well-spread leading lamella. Thus, this TPA-induced L-10 cell spreading and motility system seems to be a good model to investigate how well-differentiated adenocarcinoma cells move as cohesive cell nests. Agents which selectively modulate the adenylate cyclase or G protein-related pathways, e.g., 2',5'-dideoxyadenosine and pertussis toxin, had negligible effect upon motility. In contrast, the membrane-permeable synthetic diacylglycerol 1-oleoyl-2-acetyl-glycerol, which has been reported to activate protein kinase C (PKC) directly, could induce cell spreading and motility. Unexpectedly, PKC inhibitors staurosporine and H-7 enhanced TPA-induced cell spreading and motility. Staurosporine itself could induce cell spreading and motility. Taken together, these observations suggested possible involvement of PKC in TPA-induced L-10 cell spreading and motility and that staurosporine might have PKC agonist effect on induction of the spreading and motility.

Hepatocyte growth factor stimulates extensive development of branching duct-like structures by cloned mammary gland epithelial cells

Although epithelial-mesenchymal (stromal) interactions are thought to play an important role in embryonic and postnatal development of the mammary gland, the underlying mechanisms are still poorly understood. To address this issue, we assessed the effect of fibroblast-derived diffusible factors on the growth and morphogenetic properties of a clonally derived subpopulation (clone TAC-2) of normal murine mammary gland (NMuMG) epithelial cells embedded in collagen gels. Under control conditions, TAC-2 mammary gland epithelial cells suspended within collagen gels formed either irregularly shaped cell aggregates or short branching cord-like structures. Addition of conditioned medium from Swiss 3T3 or MRC-5 fibroblasts dramatically stimulated cord formation by TAC-2 cells, resulting in the development of an extensive, highly arborized system of duct-like structures, which in appropriate sections were seen to contain a central lumen. The effect of fibroblast conditioned medium was completely abrogated by antibodies against hepatocyte growth factor (also known as scatter factor), a fibroblast-derived polypeptide that we have previously shown induces tubulogenesis by Madin-Darby canine kidney epithelial cells. Addition of exogenous recombinant human hepatocyte growth factor to collagen gel cultures of TAC-2 cells mimicked the tubulogenic activity of fibroblast conditioned medium by stimulating formation of branching duct-like structures in a dose-dependent manner, with a maximal 77-fold increase in cord length at 20 ng/ml. The effect of either fibroblast conditioned medium or hepatocyte growth factor was markedly potentiated by the simultaneous addition of hydrocortisone (1 microgram/ml), which also enhanced lumen formation. These results demonstrate that hepatocyte growth factor promotes the formation of branching duct-like structures by mammary gland epithelial cells in vitro, and suggest that it may act as a mediator of the inducing effect of mesenchyme (or stroma) on mammary gland development.

Regulation of scatter factor/hepatocyte growth factor responses by Ras, Rac, and Rho in MDCK cells

Scatter factor/hepatocyte growth factor (SF/HGF) stimulates the motility of epithelial cells, initially inducing centrifugal spreading of cell colonies followed by disruption of cell-cell junctions and subsequent cell scattering. These responses are accompanied by changes in the actin cytoskeleton, including increased membrane ruffling and lamellipodium extension, disappearance of peripheral actin bundles at the edges of colonies, and an overall decrease in stress fibers. The roles of the small GTP-binding proteins Ras, Rac, and Rho in regulating responses to SF/HGF were investigated by microinjection. Inhibition of endogenous Ras proteins prevented SF/HGF-induced actin reorganization, spreading, and scattering, whereas microinjection of activated H-Ras protein stimulated spreading and actin reorganization but not scattering. When a dominant inhibitor of Rac was injected, SF/HGF- and Ras-induced spreading and actin reorganization were prevented, although activated Rac alone did not stimulate either response. Microinjection of activated Rho inhibited spreading and scattering, while inhibition of Rho function led to the disappearance of stress fibers and peripheral bundles but did not prevent SF/HGF-induced motility. We conclude that Ras and Rac act downstream of the SF/HGF receptor p190Met to mediate cell spreading but that an additional signal is required to induce scattering.

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

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

Characterization of the scatter factor/hepatocyte growth factor gene promoter. Positive and negative regulatory elements direct gene expression to mesenchymal cells

Scatter factor/hepatocyte growth factor (SF/HGF) and its receptor c-Met represent a paracrine signaling system involved in mesenchymal-epithelial interactions during development and during tumor progression. We have examined the promoters of the mouse and human SF/HGF genes by deletion mapping followed by CAT assays as well as by gel retardation and footprinting analysis. The promoter sequences are highly conserved (89.5% identity) up to position -453 from the major transcription start site but diverged considerably further upstream. Both promoters are active in mesenchymal but not epithelial cells thus reflecting the expression pattern of the SF/HGF gene in cells in vitro and in vivo. We have here identified two regulatory sequences in the SF/HGF promoter: a negative element at positions -239 to -258 and a positive element near the major transcription start site; specific deletions destroyed the activities of these elements. We were not able to localize elements on the SF/HGF promoter region that mediate the previously described effects of transforming growth factor beta, 12-O-tetradecanoylphorbol-13-acetate, and coculture of epithelial cells on SF/HGF gene expression. This study represents a first step toward understanding the intricately regulated and cell type-specific expression of the paracrine acting SF/HGF.

Stimulation and regulation of tumor cell motility in invasion and metastasis

In this review, the role of extracellular factors in the stimulation and regulation of tumor cell motility are discussed. Tumor cells respond in a motile fashion to a variety of external ligands including autocrine motility factors, growth factors, and components of the extracellular matrix. Since tumor cell motility is a necessary component of tumor invasion and metastasis, we speculate that these protein factors could play important regulatory roles in tumor motility at different stages of the metastatic cascade.

Stimulation of circus movement by activin, bFGF and TGF-beta 2 in isolated animal cap cells of Xenopus laevis

Lobopodium is a hyaline cytoplasmic protrusion which rotates circumferencially around a cell. This movement is called circus movement, which is seen in dissociated cells of amphibian embryos. Relative abundance of the lobopodia-forming cells changes temporally and spatially within Xenopus embryos, reflecting stage-dependent difference of morphogenetic movements. The lobopodia-forming activity of dissociated animal cap cells was stimulated strongly by activin and bFGF, and weakly by TGF-beta 2. In addition, activin A was found to stimulate cellular attachment to the substratum when the cultivation lasted long. Thus, mesoderm-inducing growth factors stimulate lobopodia formation and cellular movements which may be necessary for gastrulation and neurulation in Xenopus early embryos.

Epithelial-mesenchymal transitions in development and tumor progression

Epithelial-mesenchymal transitions play important roles in development and malignancy. Here we discuss molecular events in the control of such transitions: changes in cellular adhesion components, action of oncogenes and tyrosine kinase receptors, as well as activation of transcription factors. In development, epithelial-mesenchymal transitions take place in a temporally and spatially controlled manner, whereas in tumors these changes are highly uncontrolled. Loss of epithelial character is typically observed late in progression of human carcinomas, and correlates there with the acquisition of invasive and metastatic potential.

Regulation of HGF and HGFR gene expression

Hepatocyte growth factor and its receptor (the product of the c-met protooncogene) are believed to be necessary for the normal growth and development of many tissues and organs. This ligand/receptor system controls essential cellular responses such as cell proliferation and motility as well as morphogenesis and differentiation. HGF mRNA is expressed primarily in mesenchymal but not in epithelial cells while its receptor is predominately expressed in epithelial cells. This pattern of HGF and HGFR gene expression in combination with the unique biological effects of HGF on its target cells has led to the postulate that HGF is one of the long-sought mediators conveying cross-talk between the epithelial and stromal compartments of a given tissue. The expression of HGF and HGFR genes are unregulated in several types of human cancer; therefore, understanding the control mechanisms governing HGF and HGFR gene expression is of great clinical interest. Toward this goal, we have analyzed the effects of various physiological agents such as cytokines and hormones on the expression of HGF and the HGFR in a multitude of cell types in vitro. Moreover, we have cloned and analyzed the HGF promoter and its 5'-flanking region to uncover the basis for its inducible and cell-type specific expression at the transcriptional level. Our results indicate that HGF and HGFR gene expression is inducible and their expression is orchestrated in stromal and epithelial cells, respectively, by extracellular signals derived from steroid hormones as well as cytokines such as IL-1, IL-6, and TNF alpha.

Roles of hepatocyte growth factor/scatter factor and the met receptor in the early development of the metanephros

Several lines of evidence suggest that hepatocyte growth factor/scatter factor (HGF/SF), a soluble protein secreted by embryo fibroblasts and several fibroblast lines, may elicit morphogenesis in adjacent epithelial cells. We investigated the role of HGF/SF and its membrane receptor, the product of the c-met protooncogene, in the early development of the metanephric kidney. At the inception of the mouse metanephros at embryonic day 11, HGF/SF was expressed in the mesenchyme, while met was expressed in both the ureteric bud and the mesenchyme, as assessed by reverse transcription PCR, in situ hybridization, and immunohistochemistry. To further investigate the expression of met in renal mesenchyme, we isolated 13 conditionally immortal clonal cell lines from transgenic mice expressing a temperature-sensitive mutant of the SV-40 large T antigen. Five had the HGF/SF+/met+ phenotype and eight had the HGF/SF-/met+ phenotype. None had the HGF/SF+/met- nor the HGF/SF-/met- phenotypes. Thus the renal mesenchyme contains cells that express HGF/SF and met or met alone. When metanephric rudiments were grown in serum-free organ culture, anti-HGF/SF antibodies (a) inhibited the differentiation of metanephric mesenchymal cells into the epithelial precursors of the nephron; (b) increased cell death within the renal mesenchyme; and (c) perturbed branching morphogenesis of the ureteric bud. These data provide the first demonstration for coexpression of the HGF/SF and met genes in mesenchymal cells during embryonic development and also imply an autocrine and/or paracrine role for HGF/SF and met in the survival of the renal mesenchyme and in the mesenchymal-epithelial transition that occurs during nephrogenesis. They also confirm the postulated paracrine role of HGF/SF in the branching of the ureteric bud.