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

Cadherin-mediated cell-cell adhesion is perturbed by v-src tyrosine phosphorylation in metastatic fibroblasts

Rat 3Y1 cells acquire metastatic potential when transformed with v-src, and this potential is enhanced by double transformation with v-src and v-fos (Taniguchi, S., T. Kawano, T. Mitsudomi, G. Kimura, and T. Baba. 1986. Jpn. J. Cancer Res. 77:1193-1197). We compared the activity of cadherin cell adhesion molecules of normal 3Y1 cells with that of v-src transformed (SR3Y1) and v-src and v-fos double transformed (fosSR3Y1) 3Y1 cells. These cells expressed similar amounts of P-cadherin, and showed similar rates of cadherin-mediated aggregation under suspended conditions. However, the aggregates or colonies of these cells were morphologically distinct. Normal 3Y1 cells formed compacted aggregates in which cells are firmly connected with each other, whereas the transformed cells were more loosely associated, and could freely migrate out of the colonies. Overexpression of exogenous E-cadherin in these transformed cells had no significant effect on their adhesive properties. We then found that herbimycin A, a tyrosine kinase inhibitor, induced tighter cell-cell associations in the aggregates of the transformed cells. In contrast, vanadate, a tyrosine phosphatase inhibitor, inhibited the cadherin-mediated aggregation of SR3Y1 and fosSR3Y1 cells but had little effect on that of normal 3Y1 cells. These results suggest that v-src-mediated tyrosine phosphorylation perturbs cadherin function directly or indirectly, and the inhibition of tyrosine phosphorylation restores cadherin action to the normal state. We next studied tyrosine phosphorylation on cadherins and the cadherin-associated proteins, catenins. While similar amounts of catenins were expressed in all of these cells, the 98-kD catenin was strongly tyrosine phosphorylated only in SR3Y1 and fosSR3Y1 cells. Cadherins were also weakly tyrosine phosphorylated only in the transformed cells. The tyrosine phosphorylation of these proteins was enhanced by vanadate, and inhibited by herbimycin A. Thus, the tyrosine phosphorylation of the cadherin-catenin system itself might affect its function, causing instable cell-cell adhesion.

Cell adhesion in invasion and metastasis

Metastatic cells exhibit considerable flexibility in their adhesive interactions with other cells or components of the extracellular matrix. This review will describe the involvement of specific adhesion receptors, extracellular matrix molecules and cell dissociating cytokines in the metastatic cascade. We will particularly focus on disturbance of intercellular adhesion as a prerequisite for the release of invasive cells from carcinomas. We suggest that cell dissociation in these tumours is accomplished by loss of function or expression of the epithelial cell adhesion molecule E-cadherin, and through the activity of cell motility factors such as the scatter factor.

Expression of a human hepatocyte growth factor/scatter factor cDNA in MDCK epithelial cells influences cell morphology, motility, and anchorage-independent growth

The addition of exogenous hepatocyte growth factor (HGF)/scatter factor (SF) to MDCK epithelial cells results in fibroblastic morphology and cell motility. We generated HGF/SF producing MDCK cells by transfection with an expression plasmid containing human HGF/SF cDNA. Production of HGF/SF by these cells induced a change from an epithelial to a fibroblastic morphology and increased cell motility. In addition, the HGF/SF producing cells acquired efficient anchorage-independent growth in soft agar but did not form tumors in nude mice. The morphological change and the stimulation of the anchorage-independent growth were prevented by anti-HGF/SF antibody, suggesting that the factor is secreted and then exerts its effects through cell surface receptors.

Effect of scatter factor and hepatocyte growth factor on motility and morphology of MDCK cells

We investigated the effects of human placental scatter factor (hSF), mouse scatter factor (mSF) and recombinant human hepatocyte growth factor (HGF) on motility and morphology of individual Madin-Darby canine kidney cells using a computerized cell tracking system. All three factors increased the velocity of individual cells and the ratio of moving to stationary cells. Similarly, all three factors caused changes in morphologic features of cells, leading to increased area, flatness, and polarity. Increases in area and flatness but not polarity were slightly greater with HGF than with hSF or mSF. These results suggest that SFs and HGF have similar effects on motility and morphology of isolated epithelial cells.

Epithelial morphogenesis

The identification of protein factors, such as epimorphin, scatter factor, and activin, that induce epithelial branching and convergent extension-like movements in embryonic tissues are important breakthroughs in our understanding of the role of mesenchyme in epithelial morphogenesis. Moreover, the development of simple in vitro epithelial cell systems that undergo morphogenesis in response to these factors should provide a means to investigate the cellular and molecular bases of the morphogenetic movements themselves. Although many different cellular processes are involved in such morphogenetic behaviors, cell rearrangement is a particularly intriguing one that will be important to study further. Several considerations lead to the prediction that a dynamic regulation of cell-cell adhesion is likely to play a central role in cell rearrangements and epithelial morphogenesis. Ultimately, a greater issue to be addressed is how the different cellular mechanisms participating in epithelial morphogenesis are coordinated and regulated, so as to generate the diverse patterns found in various epithelia.

Scatter factor is a glycoprotein but glycosylation is not required for its activity

Scatter factor (SF) is a protein produced by fibroblasts, smooth muscle cells, and human placenta which scatter cohesive epithelial cell colonies and increases cellular motility. SF bound to concanavalin A and other lectins with high affinity. SF could also be stained with a glycoprotein specific stain. Incubation of producer cells (N-ras-transformed 3T3), with tunicamycin homolog A1 did not have any significant effect on the secretory activity of SF. The treatment of SF with N- and O-glycanases as well as endoglycosidase H had no effect on its activity. However, treatment of target (Madin Darby canine kidney) cells with tunicamycin A1, abolished the scattering response. These studies suggest that scatter factor is a glycoprotein, but glycosylation is not required for its secretion or activity by the producer cells; however, glycosylation of proteins in the target cells is required for SF action.

Phorbol ester-induced secretion of human hepatocyte growth factor by human skin fibroblasts and its inhibition by dexamethasone

Human skin fibroblasts secreted a certain amount of human hepatocyte growth factor (hHGF), as determined by an enzyme-linked immunosorbent assay for hHGF. This hHGF secretion was remarkably stimulated by protein kinase C (PKC)-activating phorbol esters, which was inhibited by the simultaneous addition of dexamethasone. Pretreatment with phorbol 12-myristate 13-acetate (PMA) caused a down-regulation in hHGF secretion. hHGF secreted by the PMA-treated cells showed a potent hepatocyte growth-promoting activity which was neutralized by an anti-hHGF antiserum. These results indicate both that PMA-treated human skin fibroblasts produce biologically active hHGF and the possible involvement of PKC activation in this process.

The effect of interferon-gamma on the invasiveness of HT-180 cells

It has been shown that tumour necrosis factor-alpha (TNF-alpha) induces the gene expression of collagenase and enhances the invasiveness of many cell types. However, we have previously demonstrated that interferon-gamma (IFN-gamma) induces the chemotactic response of cells and we have studied the in vitro effects of both cytokines on invasive migration using a human fibrosarcoma cell line (HT-1080). Invasive migration occurred with HT-1800 cells through a basement membrane equivalent (matrigel) and collagen type I gel. Pre-incubation of cells with increasing concentrations of IFN-gamma resulted in a dose-dependent reduction of this invasive migration. TNF-alpha considerably enhanced the invasiveness of HT-1080 cells and of fibroblasts. This effect could be significantly diminished by the pre-incubation of cells with IFN-gamma. Inhibition of invasiveness did not appear to be due to an altered binding to the barriers or altered collagenolytic activity of these cells, as shown by attachment and collagenase assays. These data support the concept that IFN-gamma can reduce the invasiveness of transformed cells which contributes to its in vivo anti-neoplastic effect.

Binding of scatter factor to epithelial cell membrane protein: identification of its receptor

Binding of scatter factor (SF) to the surface protein of Madin-Darby canine kidney (MDCK) cells was investigated. The factor has a specific affinity for membrane proteins of MDCK cells and could be purified 10-20-fold using a membrane protein-affinity chromatographic procedure. The binding was pH- and salt-dependent. The factor did not bind to columns prepared with membrane proteins from non responder cells or with bovine serum albumin. Further purification to homogeneity was achieved using reverse phase and immunoaffinity chromatography. The factor dissociated into 92, 62 and 34/32 kDa bands on SDS-PAGE under reducing conditions. A 230 kDa protein band, the receptor-SF complex, was observed when radiolabeled SF was crosslinked to surface proteins of MDCK cells and the complexes were subjected to electrophoresis. The binding of radiolabeled SF to the MDCK cells was decreased in presence of excess unlabeled SF. These observations suggest that the binding of SF to surface proteins of MDCK cells is specific and occurs predominantly to a 150 kDa protein.

Autocrine motility factor and its receptor: role in cell locomotion and metastasis

The ability to locomote and migrate is fundamental to the acquisition of invasive and metastatic properties by tumor cells. Autocrine motility factor (AMF) is a 55 kD cytokine produced by various tumor cells which stimulates their in vitro motility and in vivo lung colonizing ability. AMF stimulates cell motility via a receptor-mediated signalling pathway. Signal transduction following binding of AMF to its receptor, a cell surface glycoprotein of 78 kD (gp78) homologous to p53, is mediated by a pertussis toxin sensitive G protein, inositol phosphate production and the phosphorylation of gp78. Cell surface gp78 is localized to the leading and trailing edges of motile cells but following cell permeabilization is found within an extended network of intracellular tubulovesicles. Gp78 tubulovesicles colocalize with microtubules and extension of the tubulovesicular network to the cell periphery is dependent on the presence of intact microtubules. Gp78 labeled vesicles can be induced to translocate between the cell center and periphery by altering intracellular pH as previously described for tubulovesicles labeled by fluid phase uptake. Anti-gp78 mAb added to viable motile cells is localized to large multivesicular bodies which, with time, relocate to the leading edge. Binding of AMF to its receptor induces signal transduction, similar to chemotactic stimulation of neutrophil mobility, as well as the internalization and transport of its receptor to the leading edge stimulating pseudopodial protrusion and cell motility.

Hepatocyte growth factor inhibits growth of hepatocellular carcinoma cells

Hepatocyte growth factor (HGF) is a potent mitogen for primary hepatocytes. Therefore, we examined HGF as a possible autocrine growth factor in hepatocellular carcinoma (HCC). We introduced an albumin-HGF expression vector into Fao HCC cells and transgenic mice. Expression of the albumin-HGF vector in Fao HCC cells inhibited their growth in vitro. In vivo, FaoHGF cells produced tumors that averaged 10% of the sizes of G418-resistant controls when transplanted into nude mice. In contrast, hepatocytes from transgenic mice expressing HGF grew more rapidly than did those from normal siblings. Further, growth of eight additional HCC cell lines was inhibited by the addition of recombinant HGF. Finally, of 35 tumor cell lines surveyed, only 6 cell lines expressed HGF mRNA, and no HCC cell line expressed HGF. Although HGF stimulates normal hepatocytes, it is a negative growth regulator for HCC cells.

Defective posttranslational processing activates the tyrosine kinase encoded by the MET proto-oncogene (hepatocyte growth factor receptor)

The MET proto-oncogene encodes a 190-kDa disulfide-linked heterodimeric receptor (p190 alpha beta) whose tyrosine kinase activity is triggered by the hepatocyte growth factor. The mature receptor is made of two subunits: an alpha chain of 50 kDa and a beta chain of 145 kDa, arising from proteolytic cleavage of a single-chain precursor of 170 kDa (pr170). In a colon carcinoma cell line (LoVo), the precursor is not cleaved and the Met protein is exposed at the cell surface as a single-chain polypeptide of 190 kDa (p190NC). The expression of the uncleaved Met protein is due to defective posttranslational processing, since in this cell line (i) the proteolytic cleavage site Lys-303-Arg-Lys-Lys-Arg-Ser-308 is present in the precursor, (ii) p190NC is sensitive to mild trypsin digestion of the cell surface, generating alpha and beta chains of the correct size, and (iii) the 205-kDa insulin receptor precursor is not cleaved as well. p190NC is a functional tyrosine kinase in vitro and is activated in vivo, as shown by constitutive autophosphorylation on tyrosine. The MET gene is neither amplified nor rearranged in LoVo cells. Overlapping cDNA clones selected from a library derived from LoVo mRNA were sequenced. No mutations were present in the MET-coding region. These data indicate that the tyrosine kinase encoded by the MET proto-oncogene can be activated as a consequence of a posttranslational defect.

Defective posttranslational processing activates the tyrosine kinase encoded by the MET proto-oncogene (hepatocyte growth factor receptor)

The MET proto-oncogene encodes a 190-kDa disulfide-linked heterodimeric receptor (p190 alpha beta) whose tyrosine kinase activity is triggered by the hepatocyte growth factor. The mature receptor is made of two subunits: an alpha chain of 50 kDa and a beta chain of 145 kDa, arising from proteolytic cleavage of a single-chain precursor of 170 kDa (pr170). In a colon carcinoma cell line (LoVo), the precursor is not cleaved and the Met protein is exposed at the cell surface as a single-chain polypeptide of 190 kDa (p190NC). The expression of the uncleaved Met protein is due to defective posttranslational processing, since in this cell line (i) the proteolytic cleavage site Lys-303-Arg-Lys-Lys-Arg-Ser-308 is present in the precursor, (ii) p190NC is sensitive to mild trypsin digestion of the cell surface, generating alpha and beta chains of the correct size, and (iii) the 205-kDa insulin receptor precursor is not cleaved as well. p190NC is a functional tyrosine kinase in vitro and is activated in vivo, as shown by constitutive autophosphorylation on tyrosine. The MET gene is neither amplified nor rearranged in LoVo cells. Overlapping cDNA clones selected from a library derived from LoVo mRNA were sequenced. No mutations were present in the MET-coding region. These data indicate that the tyrosine kinase encoded by the MET proto-oncogene can be activated as a consequence of a posttranslational defect.

Identification of a fibroblast-derived epithelial morphogen as hepatocyte growth factor

We have previously shown that Madin-Darby canine kidney (MDCK) epithelial cells grown in collagen gels in the presence of fibroblasts or fibroblast-conditioned medium (CM) form branching tubules, instead of the spherical cysts that develop under control conditions. We now report that the fibroblast-derived molecule responsible for epithelial tubulogenesis is hepatocyte growth factor (HGF). First, addition of exogenous HGF to cultures of MDCK cells induces formation of epithelial tubules. Second, the tubulogenic activity of fibroblast CM is completely abrogated by antibodies to HGF. These results demonstrate that HGF, a polypeptide that was identified as a mitogen for cultured hepatocytes, has the properties of a paracrine mediator of epithelial morphogenesis, and suggest that it may play important roles in the formation of parenchymal organs during embryonic development.

Comparison of autocrine mechanisms promoting motility in two metastatic cell lines: human melanoma and ras-transfected NIH3T3 cells

Tumor-cell migration plays an essential role in invasion into surrounding tissues and the formation of metastatic colonies in distant organs. Metastatic human A2058 melanoma and ras-transfected NIH3T3 cells produce autocrine motility factors (AMFs) which stimulate their own motility, and the A2058 cell AMF (AMF/A2058) has been purified. In this study, we partially purified the AMF produced by N-ras-transfected NIH3T3 cells (AMF/NIH3T3) and compared it with AMF/A2058. The two AMFs differed in their gel filtration patterns and heat stability, although both elicited migration of N-ras-transfected NIH3T3 cells. The receptor for AMF/A2058 in A2058 cells is linked to a pertussis-toxin-sensitive GTP-binding protein. Pre-treatment of N-ras-transfected NIH3T3 cells with pertussis toxin also specifically blocked the promotion of motility by AMF/A2058, but did not affect the activity of AMF/NIH3T3. Stimulation of N-ras-transfected NIH3T3 cells by both AMFs elicited an additive response. Thus, the autocrine mechanisms of these two metastatic tumor cell lines are different with regard to the AMF molecules, receptors, and signal transduction pathways.

Scatter factor from human embryonic lung fibroblasts is probably identical to hepatocyte growth factor

Human embryonic lung fibroblasts (MRC5) produced scatter factor which enhanced motility of Madin-Darby canine kidney (MDCK) epithelial cells and a factor which stimulates DNA synthesis of adult rat hepatocytes in primary culture. These activities were both completely neutralized by antibody against human hepatocyte growth factor (HGF). Human recombinant HGF induced a marked scattering of MDCK cells. Moreover, MRC5 cells highly expressed 6kb mRNA which hybridized with HGF cDNA probe and scatter factor cDNA cloned from the MRC5 cDNA library had the same sequence as that of HGF cDNA from human leukocytes. These results indicate that HGF possesses scatter factor activity and the scatter factor derived from the MRC5 cells is probably identical to HGF.

Dominant and recessive genes involved in tumor cell invasion

The past year has been the discovery and further analysis of several genes and protein products that are critically involved in the generation of invasive and metastatic tumor cells. Like oncogenes and tumor suppressor genes, the genes responsible for invasive and metastatic phenotypes can function in a dominant or recessive fashion. In this review, particular emphasis will be given to the dominantly acting genes encoding the cell adhesion molecule CD44 and the motility factor scatter factor, and the recessively acting genes encoding the cell adhesion molecule E-cadherin and nm23.

Hepatocyte growth factor: molecular structure and implications for a central role in liver regeneration

Hepatocyte growth factor (HGF) is a most potent factor for mature parenchymal hepatocytes in primary culture and may act as a trigger for liver regeneration. We purified HGF from rat platelets to homogeneity and cloned both human and rat HGF cDNA. HGF is a heterodimer molecule composed of the 69 kDa alpha-subunit and the 34 kDa beta-subunit. HGF has no amino acid sequence homology with other known peptide growth factors and possesses the highest potential among known growth factors to stimulate proliferation of hepatocytes in primary culture. HGF is derived from a single chain precursor of 728 amino acid residues and the precursor is proteolytically processed to form a two-chain mature HGF. The alpha-subunit of HGF contains 4 kringle structures and HGF has a homology (38%) with plasmin. Biologically active recombinant human HGF could be expressed from COS-1 cells and CHO cells transfected with cloned cDNA. HGF activity and the HGF mRNA level are markedly increased in the liver following insult such as hepatitis, by the administration of hepatotoxins, ischaemia, physical damage and partial hepatectomy. Moreover, HGF mRNA is induced in the lung and kidney, in the presence of liver injury. In situ hybridization revealed that HGF-producing cells in liver are non-parenchymal liver cells, presumably Kupffer and sinusoidal endothelial cells. Therefore, HGF from neighbouring cells (Kupffer and sinsuoidal endothelial cells) and distal organs (lung and kidney) may function as a trigger for liver regeneration by both a paracrine mechanism and an endocrine mechanism. HGF has mitogenic activity for renal tubular epithelial cells, epidermal melanocytes and keratinocytes as well as mature hepatocytes, and has the potential to promote cell migration for some epithelial cells, including normal human keratinocytes. Since cell growth and cell motility are relevant to tissue repair and embryogenesis, HGF may well have important roles in tissue repair and embryogenesis as well as in liver regeneration.

Localization of hepatocyte growth factor in human and rat tissues: an immunohistochemical study

Hepatocyte growth factor is a protein growth factor with a strong mitogenic effect on hepatocytes. Recently, hepatocyte growth factor and hepatocyte growth factor messenger RNA have been extracted from several organs of humans, rats and rabbits. This study was undertaken to comprehensively define and compare the cellular localization of hepatocyte growth factor in human and rat tissues in detail. Paraffin-embedded sections and frozen sections were examined by immunohistochemistry using a polyclonal antiserum to hepatocyte growth factor. The distribution of hepatocyte growth factor was almost identical in humans and rats. Strong or moderate cytoplasmic immunoreactivity for hepatocyte growth factor was present in most surface epithelia, distal tubules and collecting ducts of the kidneys, large neurons, megakaryocytes, granulocytes, exocrine pancreas, salivary glands, prostate, epididymis and trophoblast. Varying degrees of immunoreactivity were observed in endothelial cells, chondrocytes and macrophages. We conclude that hepatocyte growth factor is widely distributed in numerous tissues and cell types independent of their regenerative activity. This suggests that hepatocyte growth factor may have mitogenic and/or trophic effects on multiple cell types in addition to hepatocytes.

Induction of epithelial tubular morphogenesis in vitro by fibroblast-derived soluble factors

We have designed an in vitro system in which Madin-Darby canine kidney (MDCK) epithelial cells are cocultured in collagen gels with fibroblasts under conditions precluding heterocellular contact. Using this experimental approach, we have obtained evidence that fibroblast-derived soluble factors play a crucial role in the control of epithelial morphogenesis. First, MDCK cells suspended alone in collagen gels form spherical cysts, whereas in the presence of fibroblasts they form branching tubules. Second, MDCK cells grown as a monolayer on fibroblast-containing collagen gels invade the underlying matrix, within which they form a network of tubules. Third, fibroblast-conditioned medium mimics the effects of coculture by eliciting tubulogenesis by MDCK cells. These results demonstrate the involvement of diffusible paracrine factors in morphogenetic epithelial-mesenchymal interactions and provide a strategy for their molecular characterization.

The proliferative and morphologic responses of a colon carcinoma cell line (LIM 1215) require the production of two autocrine factors

The role of autocrine growth factors in tumor cell growth has been difficult to prove. Our results indicate that more than one autocrine factor is required for the autonomous growth of the LIM 1215 colonic carcinoma cell line. Furthermore, the morphologic changes induced by epidermal growth factor (EGF) are also density dependent and appear to require a synergistic autocrine factor. The serum-free proliferation of the colonic carcinoma cell line LIM 1215 depends on cell density and the presence of EGF (A. Sizeland, S. Bol, and A.W. Burgess, Growth Factors 4:129-143, 1991). At cell densities below 10(4)/cm2, conditioned medium (from cells at a density of 10(5)/cm2) was required for the cells to elicit a mitogenic response to exogenous EGF. At higher cell densities (10(5)/cm2), the cells were independent of both exogenous EGF and conditioned medium. In addition, the EGF receptor was found to be phosphorylated on tyrosine in LIM 1215 cells proliferating at high density, suggesting that the autocrine production of transforming growth factor alpha (TGF alpha) and subsequent ligation to the EGF receptor was occurring. The proliferation of cells at high density was partly inhibited by TGF alpha antibodies but was almost completely inhibited by an antisense oligonucleotide to TGF alpha. The antisense inhibition could be overcome by the addition of EGF, indicating that the effect of the antisense TGF alpha oligonucleotide was on the production of autocrine TGF alpha. LIM 1215 cells were also observed to undergo morphologic changes (spreading and actin cable organization) in response to EGF. These changes were density dependent, but they occurred with a cell density dependence different from that of the proliferative response. These results suggest two possibilities: that the morphologic changes and proliferative responses have different sensitivities to the autocrine factors or that the actions of the autocrine factors are mediated through different signal transduction pathways.

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

Scatter factor (SF), a secretory protein of fibroblasts, dissociates and increases the motility of epithelial cells and may be involved in cell migration processes during embryogenesis and tumor progression. Hepatocyte growth factor (HGF), a protein isolated from serum of patients with liver failure, is a potent mitogen for hepatocytes and is thought to play a role in liver regeneration. Here we present structural and functional evidence that human SF and human HGF (and also the human lung fibroblast-derived mitogen) are identical proteins encoded by a single gene, since (i) no major difference could be found by protein sequencing, by cDNA analysis, and by immunological comparison and (ii) SF in fact acts as a hepatocyte growth factor--i.e., stimulates DNA synthesis of activity--i.e., dissociates and induces invasiveness of various epithelial cells. The human SF/HGF gene was localized to chromosome bands 7q11.2-21. These results have important consequences for further studies on the involvement of SF/HGF as a modulator of cellular growth and motility in embryonal, malignant, and regenerative processes.

Purification and characterization of biologically active scatter factor from ras-transformed NIH 3T3 conditioned medium

Scatter factor (SF), a glycoprotein produced by cultured fibroblasts, acts in vitro on epithelial cells causing separation and increased local motility. In this study, the polypeptide was purified to apparent homogeneity in high yields with conserved biological activity from medium conditioned by ras-transformed NIH 3T3 cells, by a three-step procedure involving ammonium sulphate fractionation, cation-exchange and hydroxyapatite chromatography. After purification, SF specific activity increased from approximately 0.3 units/microgram in unprocessed conditioned medium to approximately 5 units/ng, and cumulative recovery of biological activity was approximately 38%. Treatment of pure SF with N-glycanase resulted in a decreased Mr, but no concomitant effect was observed on biological activity. Proteolytic activity was absent from samples of both partially purified and pure SF. Our biochemical studies showed that SF, which is highly aggregated in low-ionic-strength media, is not aggregated in 0.4 M-salt. Under non-reducing conditions, pure SF migrated as a single stained band at Mr 67,000 on SDS/PAGE, and biological activity was eluted from unstained gels with an identical Mr. SF was electrofocused sharply at pI 8.5 with no degradation of activity. From ultracentrifugation studies (under non-aggregating conditions), the sedimentation coefficient of active SF was 3.7 S and f.p.l.c. molecular sieve chromatography indicated a Stokes' radius of 2.95 nm. The calculated Mr from these data was 61,400. The appearance of three stained polypeptides of Mr 82,000, 57,000 and 32,000 derived from the Mr-67,000 constituent after reduction with mercaptoethanol suggests that SF may be a heterodimer of Mr-57,000 and -32,000 subunits. Data from protein sequence analysis of the hydroxyapatite-purified protein confirms that SF has sequence identity with both rat hepatocyte growth factor and human fibroblast tumour cytotoxic factor.

The proliferative and morphologic responses of a colon carcinoma cell line (LIM 1215) require the production of two autocrine factors

The role of autocrine growth factors in tumor cell growth has been difficult to prove. Our results indicate that more than one autocrine factor is required for the autonomous growth of the LIM 1215 colonic carcinoma cell line. Furthermore, the morphologic changes induced by epidermal growth factor (EGF) are also density dependent and appear to require a synergistic autocrine factor. The serum-free proliferation of the colonic carcinoma cell line LIM 1215 depends on cell density and the presence of EGF (A. Sizeland, S. Bol, and A.W. Burgess, Growth Factors 4:129-143, 1991). At cell densities below 10(4)/cm2, conditioned medium (from cells at a density of 10(5)/cm2) was required for the cells to elicit a mitogenic response to exogenous EGF. At higher cell densities (10(5)/cm2), the cells were independent of both exogenous EGF and conditioned medium. In addition, the EGF receptor was found to be phosphorylated on tyrosine in LIM 1215 cells proliferating at high density, suggesting that the autocrine production of transforming growth factor alpha (TGF alpha) and subsequent ligation to the EGF receptor was occurring. The proliferation of cells at high density was partly inhibited by TGF alpha antibodies but was almost completely inhibited by an antisense oligonucleotide to TGF alpha. The antisense inhibition could be overcome by the addition of EGF, indicating that the effect of the antisense TGF alpha oligonucleotide was on the production of autocrine TGF alpha. LIM 1215 cells were also observed to undergo morphologic changes (spreading and actin cable organization) in response to EGF. These changes were density dependent, but they occurred with a cell density dependence different from that of the proliferative response. These results suggest two possibilities: that the morphologic changes and proliferative responses have different sensitivities to the autocrine factors or that the actions of the autocrine factors are mediated through different signal transduction pathways.

Scatter factor affects major changes in the cytoskeletal organization of epithelial cells

The effects of scatter factor on the cytoskeleton of MDCK and PtK2 cells are described. During the first 6 h after the addition of scatter factor, MDCK cells were found to increase their projected areas twofold, as well as the number and size of their F-actin stress fibers. In contrast PtK2 cells showed no change in their projected areas or in their stress fiber content. However, when both MDCK and PtK2 cells began to separate and scatter after approximately 6 h, the size and number of stress fibers was found to decrease considerably. Unscattered PtK2 cells and cells treated with scatter factor which had yet to scatter showed focal contacts present over the whole ventral surface, as judged by staining for both vinculin and talin. After treated cells separated, both vinculin and talin staining were mainly present in focal contacts on the ventral surfaces of the cell bodies and the distal ends of the processes. However, the cell processes showed few focal contacts along their lengths. The distribution of microtubules and vimentin and keratin intermediate filaments also did not change significantly until scattering had occurred. After cell separation, the processes were always packed with microtubules which were often, but not always, rich in detyrosinated alpha-tubulin and often, but not always, packed with intermediate filaments. All these changes in cytoskeletal organization are consistent with the adoption of a much more motile phenotype. The changes found are compared with those brought about by transformation.

Modulation of fibroblast motility by a cytosolic extract of Cyanobacteria

Proliferation and migratory behavior of L929 murine fibroblasts were shown to be modified in the presence of a cytosolic extract of Phormidium sp. (Cyanobacteria). The addition of Phormidium extract to the growth medium (Dulbecco's modified Eagle's medium) supplemented with 0.5% newborn calf serum increased cell proliferation. The effect was shown to be cell line specific. A quantitative analysis performed according to De Laat, Tertoolen, and Bluemink (1981, Eur. J. Cell Biol., 23, 273-279), showed that Phormidium extract was a potential aggregative effector for fibroblasts. Heating (100 degrees C, 4 min) inactivated the clustering effect of the extract, but the effect on cell proliferation was retained. A video analysis of cells after divisions showed that the extract activated cell migration in the same way as 5% serum did during the first 24 h of treatment. Between 24 and 48 h of treatment, cell migration in the presence of the extract was inhibited when compared to migration in 0.5 or 5% serum. We have shown that Phormidium extract may contain two or three kinds of effectors which acted as exogenous growth factors (allowing attachment and proliferation) and as modulator(s) of the cell migratory behavior (activator of migration in early times of the growth and inhibitor later).

Secreted or nonsecreted forms of acidic fibroblast growth factor produced by transfected epithelial cells influence cell morphology, motility, and invasive potential

Addition of exogenous acidic fibroblast growth factor (aFGF) to NBT-II epithelial carcinoma cells results in fibroblastic transformation and cell motility. We have generated aFGF-producing NBT-II cells by transfection with recombinant expression vectors containing human aFGF cDNA, or the human aFGF cDNA coupled to a signal peptide (SP) sequence. The effects of the nonsecreted and the secreted 16-kDa growth factor on the morphology, motility, and cell invasive potential (gelatinase activity) were compared. aFGF coupled to a SP was actively secreted out of the producing cells. The secretion of aFGF was not necessary for induction of gelatinase activity, as this was observed in NBT-II cells producing aFGF with or without SP. Production of aFGF, whether secreted or not secreted, resulted in increased in vitro motility of most isolated clones; however, there was no correlation between aFGF level and motility rate. The data suggest that expression of aFGF in NBT-II cells induces metastatic potential through an autocrine or intracrine mechanism.

Regulation of motility in bovine brain endothelial cells

Scatter factor (SF) is a fibroblast-derived cytokine which stimulates motility of epithelial and vascular endothelial cells. We used a quantitative assay based on migration of cells from microcarrier beads to flat surfaces to study the regulation of motility in bovine brain endothelial cells (BBEC). Peptide growth factors (EGF, ECGF, basic FGF) did not stimulate migration. Tumor promoting phorbol esters (PMA, PDD) markedly stimulated migration, while inactive phorbol esters (4a-PDD, phorbol-13,20-diacetate) did not affect migration. Both SF- and PMA-stimulated migration were inhibited by 1) TGF-beta; 2) protein kinase inhibitors (e.g., staurosporine, K-252a); 3) activators of the adenylate cyclase signaling pathway (e.g., dibutyryl cyclic AMP, theophylline); 4) cycloheximide; and 5) anti-cytoskeleton agents (e.g., cytochalasin B, colcemid). However, PMA and SF pathways were distinguishable: 1) PMA induced additional migration at saturating SF concentrations; 2) the onset of migration-stimulation was immediate for PMA and delayed for SF; and 3) down-modulation of protein kinase C (PKC) ablated PMA but not SF responsiveness. Assessment of PKC by (3H)-phorbol ester (PDBu) binding and by immunoblot showed 1) scatter factor does not cause significant redistribution or down-modulation of PDBu binding or alpha-PKC; and 2) PDBu mediates redistribution and down-modulation of both binding and alpha-PKC. These findings suggest two pathways for BBEC motility: a PKC-dependent pathway and an SF-stimulated/PKC-independent pathway.

Purification, characterization and mechanism of action of scatter factor from human placenta

Scatter factor (SF) causes contiguous sheets of epithelium to spread and cells to separate from each other. SF also increases the velocity, area, and reduces the circularity of individual cells. These changes are mediated in part by alterations in protein synthesis, protein phosphorylation, cytoskeletal reorganization, and cell surface components. SF has been purified from the conditioned medium of ras transformed 3T3 cells and human placenta. Sequence information suggests that SF from 3T3 cells is closely related to hepatocyte growth factor. SF is a glycoprotein, but glycosylation is not necessary for its activity. Glycosylation of target cell proteins, however, is required for SF action.

Scatter factor stimulates migration of vascular endothelium and capillary-like tube formation

Scatter factors (SFs) are heat- and trypsin-sensitive cytokines secreted by fibroblastic and vascular smooth muscle cell lines which stimulate motility of normal epithelium, carcinoma cells, and vascular endothelium. Human and mouse SFs have been purified and identified as 90 kD heterodimeric proteins consisting of heavy (58 kD) and light (31 kD) disulfide-bonded subunits. Partial amino acid sequence data from SF-derived tryptic peptides indicate marked sequence homology with hepatocyte growth factors, suggesting a common multigene family. In this chapter we describe the regulation by SF of vascular endothelial cell chemotaxis and chemokinesis; migration from microcarrier beads to flat surfaces; invasion through porous filters coated with reconstituted basement membrane; secretion of plasminogen activator; and in vitro capillary-like tube formation on a basement membrane surface.

Interleukin-6 stimulates motility of vascular endothelium

Interleukin-6 (IL-6) is a cytokine which regulates host response to injury. Various preparations of recombinant human IL-6 stimulated migration of bovine brain and bovine aortic endothelial cells, with maximal responses at 100-600 ng/ml. The migration response was inhibited by anti-IL-6 monoclonal antibody. IL-6 also inhibited endothelial cell proliferation in a dose-dependent fashion. Combinations of IL-6 and tumor necrosis factor induced additive stimulation of migration. Studies with inhibitors and stimulators of various metabolic processes suggest that IL-6-induced motility: 1) does not require a pertussis toxin-sensitive G-protein, protein kinase C, or DNA synthesis; and 2) is regulated differently from the motility induced by scatter factor. A possible role for IL-6 in the regulation of physiologic angiogenesis is discussed.

The role of E-cadherin and scatter factor in tumor invasion and cell motility

The acquisition of invasive properties by transformed epithelial cells constitutes an essential step in the progression of carcinomas. We have defined 2 types of interferences leading to enhanced motility and invasiveness of epithelial cells: (i) disturbances of intercellular adhesion, and (ii) treatment with "scatter factor", a secretory protein of mesenchymal cells. Invasive properties (invasion of collagen gels or embryonal heart tissue) are acquired by epithelial cells in vitro when intercellular adhesion is inhibited by antibodies that are specific for the cell-cell adhesion molecule E-cadherin. Furthermore, we found that differentiated human carcinoma cell lines are noninvasive and express E-cadherin, whereas dedifferentiated carcinoma lines are invasive and have lost E-cadherin expression. Invasiveness of these latter cells could be prevented by transfection with E-cadherin cDNA and was again induced by treatment of the transfected cells with anti-E-cadherin antibodies. A correlation between the degree of tumor differentiation and the amount of E-cadherin expression was also visualized on frozen sections of ovarian carcinomas, lobular breast carcinomas, and squamous carcinomas of head and neck. Thus, loss of E-cadherin appears to be a critical step in the establishment of an invasive, i.e. fully malignant phenotype. Scatter factor, which is also capable of dissociating epithelial cell colonies in vitro, was isolated from conditional medium of human fibroblasts; it is a 92,000 mol.wt glycoprotein, which is proteolytically cleaved into 62,000 and 34/32,000 mol.wt subunits. The purified glycoprotein induces invasion of MDCK cells into collagen matrices, and induces or enhances the invasive properties of various human carcinoma cell lines. Sequencing of tryptic peptides of scatter factor revealed strong similarity with hepatocyte growth factor. Furthermore, both factors exhibit identical activities, i.e. scatter factor stimulates DNA synthesis of primary hepatocytes and hepatocyte growth factor dissociates and increases the motility of various epithelial cells. Thus scatter factor and hepatocyte growth factor represent identical or closely similar proteins.

Tumor cell autocrine motility factor receptor

The ability to locomote and migrate is fundamental to the acquisition of invasive and metastatic properties by tumor cells. Autocrine motility factor (AMF) is a cytokine produced by various tumor cells which stimulates their in vitro motility and in vivo lung-colonizing ability. AMF stimulates cell motility via a receptor-mediated signalling pathway. Signal transduction following binding of AMF to its receptor, a cell surface glycoprotein of 78 kD (gp78), is mediated by a pertussis toxin sensitive G protein, inositol phosphate production and the phosphorylation of gp78. AMF induces gp78 internalization to intracellular tubulovesicles and transport to the leading edge stimulating pseudopodial protrusion and cell motility.

Stromal regulation of epithelial function

Stromal influences upon epithelia are part of a continuum of cellular interactions that begins at fertilization and extends into adulthood. In parenchymal organs, the most thoroughly characterized interactions have been those that occur during development between mesenchyme, embryonic stroma, and epithelium. Mesenchyme is essential for epithelial proliferation, morphogenesis, and differentiation. Hormones affect stromal-epithelial interactions, and in some cases, steroid hormones may produce their effects on the epithelium indirectly, acting via the mesenchyme. In many adult organs the epithelia continually proliferate and differentiate and consequently may be considered developing systems within the mature organism. This is especially true in organs with a rapidly renewing epithelium, such as the intestine, and in organs that have cycles of functional activity, such as those of the female reproductive system. The mechanisms by which stroma affects epithelial structure and function are not well understood. Current models of how signaling may be accomplished include transmission via diffusible substances, via the extracellular matrix (ECM), and via direct cell-cell contact. Growth factors and organ-specific paracrine factors are candidates for stromal cues that affect the epithelium in some systems. Components of the ECM appear to play a role in permissive interactions and may affect epithelial function by changing cell shape or by binding ECM to the cell surface integrin receptors. Signaling via direct stromal-epithelial contact may be accomplished via interactions between complimentary cell surface adhesion molecules. The importance of stromal-epithelial interactions is reemphasized by several models of carcinogenesis that suggest that perturbations in these interactions may be involved in tumor progression.

Purification and characterization of scatter factor

Scatter factor is a fibroblast-derived protein which disrupts and scatters epithelial colonies and enhances the local movement of individual epithelial and endothelial cells. The factor purified from mouse fibroblasts by cation-exchange and reverse phase chromatography is a dimer of 57 kD and 30 kD protein subunits (A and B subunits), is active at picomolar concentrations and requires intact intra- and/or inter-chain disulphide bonds for activity. In serum-free conditioned medium the factor is highly aggregated but in the presence of high-salt buffers or protein denaturants elutes from gel filtration columns with an apparent Mr of approximately 50 kD. From a combination of molecular sieving and ultracentrifugation studies, a calculated Mr of 61.4 kD is obtained for native mouse scatter factor, a value which agrees well with the Mr estimates obtained by SDS-PAGE (62-67 kD). Mouse fibroblast scatter factor is a heparin-binding, basic protein (pI 8.5-9.5) which contains N-linked carbohydrates which are not, however, essential for activity. The factor has no metallo- or serine protease activity and there is no evidence so far that its junctional-breaking activity involves proteolytic cleavage of surface molecules on target cells. Scatter factor is either identical or closely related to hepatocyte growth factor/hepatopoietin A (a potent mitogen for rat hepatocytes recently purified from human and rabbit serum and rat platelets). The factor is thus an effector of mesenchymal-epithelial interactions which affects the movement or the growth of different epithelia.

Scatter factor: molecular characteristics and effect on the invasiveness of epithelial cells

The generation of invasiveness in transformed cells represents an essential step of tumor progression. We have previously shown that MDCK epithelial cells, which are deprived of intracellular adhesion by the addition of anti-Arc-1/uvomorulin antibodies, become invasive for collagen gels and embryonal heart tissue (Behrens, J., M. M. Mareel, F. M. Van Roy, and W. Birchmeier. 1989. J. Cell Biol. 108: 2435-2447.). Here we examined whether invasiveness is also induced by scatter factor, which is known to dissociate epithelial cells (Stoker, M., E. Gherardi, M. Perryman, and J. Gray. 1987. Nature (Lond.). 327:239-242.). Scatter factor was purified to homogeneity from conditioned medium of human fibroblasts by heparin-Sepharose chromatography, followed by cation exchange chromatography, gel filtration, or preparative SDS gel electrophoresis. We found that scatter factor represents a 92,000 mol wt glycoprotein which, apparently, is converted by limited proteolysis into disulfide-linked 62,000 and 34/32,000 mol wt subunits. Reversed phase HPLC and sequence analysis of tryptic peptides confirmed the suggested molecular structure, and revealed further that scatter factor exhibits sequence similarities to hepatocyte growth factor and to plasminogen. Purified scatter factor in fact induces the invasiveness into collagen matrices of MDCK epithelial cells, and induces or promotes the invasiveness of a number of human carcinoma cell lines. Apparently, the effect on the human cells depends on their respective degree of differentiation, i.e., cell lines with a less pronounced epithelial phenotype were more susceptible to the factor. Scatter factor does not seem to influence synthesis, steady-state level, and phosphorylation of the cell adhesion molecule Arc-1/uvomorulin. Thus, scatter factor represents a clearly defined molecular species which induces, in vitro, the progression of epithelial cells to a more motile, i.e., invasive phenotype.

The invasive phenotypes

The expression of the invasive (I+ or I-) phenotypes determines cancer metastasis (M+ or M- phenotype). The invasive (I+ or I-) phenotypes can be divided according to time and site of expression into subphenotypes, which can be assessed separately. At various sites along the metastatic pathway the expression of the I phenotypes can be accompanied by the presence of uncontrolled growth (G+ phenotype) or its absence (G- phenotype). Various combinations of the I and G phenotypes determine the behaviour of metazoan or parasitic cells under normal, pathological non-neoplastic and neoplastic conditions. Although the G+I+M+ combination correlates with full malignancy, the sequence of events leading to the acquisition of these phenotypes during tumor development is not clear. Conditional invasion in experimental systems indicates that a tumor may be invasive and metastatic when part of its population temporarily expresses the I+ phenotype. These experiments further stress the importance of the tumor-host ecosystem for the regulation of the I phenotypes. As distinct from some parasites, the invasive morphotype of vertebrate cells cannot be simply identified. Nevertheless, within the tumor-host ecosystem morphological correlates of the activities of invasive cells may be recognized. They reflect one or more of the I+ functions, namely: motility; loss of homotypic cell-cell adhesion; establishment of alternative cell-substrate and heterotypic cell-cell adhesion; breakdown of extracellular matrices. These functions are not exclusive for I+ tumor cells, and neither are the molecular markers investigated so far. Oncogene activation leads mainly to G+ expression, and in this way serves as a signal amplifier for the I and M phenotypes. Attractive candidate molecular markers of I phenotypes are: regulators of hydrolase activities; cell-cell adhesion molecules; cell surface receptors. From data presently available, we hypothesize that invasion depends upon the balance between and I+ and an I- pathway, with both pathways being sensitive to stimulation inhibition.

Cellular interactions in metastasis

The metastatic cascade is a sequence of events that must be completed for metastases to be established. The realization that tumors are heterogeneous, consisting of many different subpopulations differing in many characteristics, and the belief that there are selective events in the metastatic process have led several laboratories to isolate and characterize variants with both high and low metastatic potential. Typically, the highly metastatic variants have been able to form distant metastases when implanted into the subcutis. Such lines have been popular for studies of metastatic mechanisms and anti-metastatic therapy, but they may be atypical examples, and thus not the best experimental models. Recent studies indicate that normal tissue influences metastasis such that many tumors metastasize only if placed in the orthotopic site. Furthermore, some cells that do not metastasize individually are able to do so in conjunction with other variant subpopulations. Thus, mixtures of tumor cells in the tissue of origin can express a more malignant character. We review possible mechanisms for such influential interactions, as well as the role of cellular interactions in generating heterogeneity and stabilizing tumor characteristics.

Human placenta contains an epithelial scatter protein

Scatter factor (SF) is a protein produced by cultured fibroblasts which causes epithelia to "scatter" into isolated cells. We found significant scatter activity in vivo in second trimester (but not term) human amniotic fluid and in human placenta. Placental SF was purified 500,000-fold and identified as a protein with Mr 78 kd. Factor scattered Madin-Darby canine kidney and human squamous carcinoma cells at 15 pM. Amino acid sequences from tryptic peptides did not match any known protein. Human placental fibroblasts produced high titers of scatter activity. SF may be involved in development and may enhance carcinoma invasion.

Induction of distinct phenotypes in clonal and variant GH4 pituitary cells

GH cells are a widely used cell strain for the investigation of mechanisms regulating hormone release and synthesis. This report identifies two inducible phenotypes of the GH4 clone (epithelioid and motile) which may extend studies of this well-characterized cell line to different stages of pituitary cell development. GH4C1 cells treated in suspension with epidermal growth factor plus tetradecanoylphorbol acetate aggregate to form large epithelioid colonies with extensive cell-to-cell and cell-to-substratum adhesion. These cells cease replicating within 48 h, increase 50% in cell volume, and synthesize 40-fold more prolactin. A GH4C1 variant with enhanced substratum adhesion and little or no cell-to-cell adhesion (GH4S1), responds differently to this treatment. These cells cease replicating immediately, show increased cell separation, develop leading lamellae, and display locomotory activity. Each phenotype coexists in mixed cultures of GH4C1 and GH4S1 cells. This indicates that the different inducible response of the variant does not result from autocrine secretion. A molecular basis for cell-to-cell adhesion in GH4 cells was investigated. GH4C1, but not the variant cells, express a 180 kDa immunoreactive protein indistinguishable from an isoform of the neural cell adhesion molecule. Therefore the absence of cell-to-cell adhesion and inability to develop extensive cell-to-cell adhesion characteristic of the epithelioid phenotype may result from altered expression of the neural cell adhesion molecule. These findings are important because they have defined an in vitro approach to investigate genetic and cellular changes associated with the development and progression of pituitary cell phenotype.

Acidic fibroblast growth factor is a modulator of epithelial plasticity in a rat bladder carcinoma cell line

During normal embryogenesis and neoplastic transformation epithelia change their state of differentiation and degree of cohesiveness. It is thus essential to identify the signals modulating these transitions. We report here that acidic fibroblast growth factor (FGF) induces cells derived from a rat bladder carcinoma to lose their epithelial character and to acquire some properties typical of mesenchymal cells. The structurally related basic FGF did not have such an effect; both factors, however, had a mitogenic activity for these cells. Two distinct populations of receptors for acidic FGF and basic FGF were distinguished by their ligand-binding characteristics. The observations that both acidic and basic FGFs had a mitogenic effect on NBT-II cells and that only acidic FGF caused cell dissociation and dispersion strongly suggest that these two biological activities could be medicated through distinct signaling pathways.

Scatter factor regulates vascular endothelial cell motility

Scatter factors (SFs) are mesenchymal cell-derived cytokines which stimulate epithelial motility. SF purified from ras-transformed 3T3 cell supernatants markedly stimulated vascular endothelial cell migration at less than 100 pM. Preliminary studies suggest endothelial lines with cobblestone (epithelioid) morphology respond to SF, while those lines with elongated cells do not respond. SFs may play roles in development and tissue repair.