- Email: [email protected]
Growth Factors: A scattering of factors
GROWTH FACTORS
RICHARD WARN
GROWTH FACTORS
RICHARD WARN
A scattering of factors Hepatocyte growth factor/scatter factor isa multifunctional growth factor with varied properties: more and more polypeptide factors are being discovered that share these characteristics. Every so often a single observation creates the impetus for rapid progress in a variety of directions. An example was the discovery and biochemical characterization by Stoker, Gherardi and colleagues of a molecule they named scatter factor [1]. This protein has the property of dispersing or scattering epithelial cell colonies in culture into single isolated cells, rupturing intercellular junctions and desmosomes in the process. The scattered cells have enhanced motility, showing random, non-polarized movement in culture. Scatter factor has generally been found to be secreted by mesenchyme cells - fibroblasts and smooth muscle cells - rather than by epithelial and endothelial cells, although its effects are mainly obvious on the latter two cell types. In view of this, scatter factor is usually described as being a paracrine effector molecule. Recent results show that a variety of signalling molecules have similar properties to scatter factor, properties likely to be involved in a number of important physiological and pathological processes. The discovery of scatter factor was rapidly followed by a series of further findings. The determination of its amino-acid sequence showed that scatter factor is identical to hepatocyte growth factor (HGF), an independently characterized, strong mitogen for hepatocytes and a wide variety of other epithelial cell types [2,3]. This was a surprise, partly because the particular variant of the cell line originally used to characterize scatter factor - a dog kidney line (MDCK) - only responds by scattering. Other growth factors had previously been found to promote cell motility, but it was not suspected that a growth factor might have the further property of causing cells to break loose from colonies. Hepatocyte growth factor/scatter factor (HGF/SF), as it is now named, is a heterodimer with a larger x chain of about 60kD and a smaller 13chain of about 30kD, linked by a single inter-chain disulphide bond (Fig. 1). The protein is glycosylated to a varying but significant extent; it is translated from a single mRNA, and the active form is produced by cleavage of the biologically inert precursor chain. Analysis of the likely structure of the molecule has revealed several features that are not shared with any chain contains four other known growth factor. The 'kringles', an unusual structural motif that occurs also in plasminogen, tissue-type and urokinase-type plasminogen activators, factor XII and prothrombin. The chain consists of a serine protease domain that is inactive because of substitutions of two critical residues in the catalytic site. On its own, the ct chain is capable of
inducing some scattering activity, whereas the 3 chain alone has no biological activity [4]. There is a natural variant of HGF/SF, formed by alternative pre-mRNA splicing, which consists of only the first two kringles of the ao chain [5]. This two-kringle form has no growth-promoting properties, but seems to have some motility-inducing effects. Furthermore, the variant competes with the complete form of HGF/SF for binding to its receptor, and hence may act as a natural blocking agent. The discovery that the receptor for HGF/SF is the product of the proto-oncogene c-met was a further milestone [6,7]. The intracellular portion of the c-met protein contains a tyrosine kinase domain that is likely to have similar properties to the analogous domains of related growth factor receptors, such as those for epidermal growth factor (EGF) and platelet derived growth factor (PDGF). Yet another unexpected finding, originally made by Montesano and colleagues [8], was that HGF/SF can
Fig 1. Postulated primary structure of the mouse HGF/SF precursor. The structure is based on the conservation of critical cysteine residues in HGF/SF and plasminogen. The regions that form the a and chains of HGF/SF are shown as blue and red circles, respectively, except for cysteine residues, which are shown in black, and for the three residues corresponding to important active site residues of serine proteases, which are shown in yellow. A 30-residue-long signal sequence is shown in green. (Reproduced with permission from [24].)
© Current Biology 1994, Vol 4 No 11
1043
1044
Current Biology 1994, Vol 4 No 11 lung and intestine, whereas HGF/SF mRNA is simultaneously expressed by the adjacent mesenchyme. The implication is that HGF/SF and its receptor together act as a morphogen signalling mechanism in a variety of organ differentiation events. Studies of gene 'knockout' mice should provide data that bear directly on this hypothesis. The properties of HGF/SF suggest that it might also have some involvement in tumour growth and dissemination, and there is now some supporting evidence for such a view. Various tumour cell lines are dissociated in vitro by HGF/SF; furthermore, their migration into collagen gels is enhanced, a behaviour which mimics that of more highly invasive tumour lines [11]. Pleural effusion fluids containing metastatic tumours have significant levels of HGF/SF [12], so the tumours are in an environment in which enhanced expression of the HGF/SF receptor would stimulate a more rapid proliferation and spread. Furthermore, a wide range of tumours, including lung tumours, have been found to express elevated levels of the HGF/SF receptor [13] - the highest levels have been recorded in human thyroid cancers, where they were found to be 100 times higher than in normal thyroid tissue.
Fig 2. HGF/SF can have a number of different effects on the cells of an epithelial cell colony. More than one of these effects may occur at the same time.
-induce tubule-formation by MDCK cells grown in suspension within a collagen gel. In these conditions, HGF/SF acts to promote differentiation in association with increased cell division. Expression of the HGF/SF receptor has been detected by immunostaining in regions bordering the duct lumen in several tissues, including normal mammary glands [9]. Furthermore, there is a cultured human mammary line (T47D) that is capable of spontaneous tubule formation in culture - the lumens of these tubules express high levels of the HGF/SF receptor, and the tubules become much more uniform and ordered after HGF/SF treatment. Similar results were obtained with several colon lines. The ability of HGF/SF to induce tubule formation, particularly the branching tubules produced by MDCK cells, strongly suggests that HGF/SF has polarized effects on its target cells, presumably reflecting the polarized expression of the HGF/SF receptor on the target cells. HGF/SF is likely to have a number of important functions in development, one of which is, very probably, a role in generating the complex patterns of tubulogenesis that occur during organ formation and growth. A very careful in situ hybridization study [10] has elegantly demonstrated that HGF/SF and HGF/SF-receptor mRNAs are both expressed in complex, changing patterns during early mouse development. HGF/SF-receptor mRNA is expressed by the epithelial cells of a number of developing tubular organs, including kidney,
There is now some direct evidence that autocrine secretion of HGF/SF can promote tumorigenesis in nude mice. If a human bladder cell line is transfected with the HGF/SF gene before being introduced into nude mice, it generates tumours significantly more quickly than appropriate controls [14]. The tumours formed by transfected cell populations produce HGF/SF, as demonstrated by Western blot analysis. It will be of interest to determine whether cell-cell cooperation occurs in this system - that is, whether injected cell populations containing only a small proportion of HGF/SF transfectants also show more rapid tumour growth and spread. One must, however, be extremely careful before drawing any general conclusions about HGF/SF and tumours. For some tumour cell lines in culture, HGF/SF inhibits, rather than promotes, cell proliferation (see [15], for example), and one might also expect HGF/SF to induce terminal cell differentiation and perhaps also apoptosis. Proof of HGF/SF's role in tumorigenesis will only come from a clear-cut demonstration that specifically blocking HGF/SF inhibits tumour growth and spread, but circumstantial evidence has come from the recent report [16] that the level of HGF/SF associated with primary human breast tumours is a good prognostic indicator of tumour recurrence and survival. Further confirmation of this work may prove to be of clinical value. HGF/SF emerges as a multifunctional factor with a surprising repertoire of properties (Fig. 2). It is to be expected that these properties will turn out to be modulated by external influences, in particular the extracellular matrix. Indeed, another MDCK cell line has been identified that cannot scatter on serum- or vitronectin-coated glass surfaces but can on fibronectin-coated surfaces [17].
DISPATCH
Responses to HGF/SF will also depend on cell type for example, transfection of murine 3T3 fibroblasts with the human c-met gene followed by exposure to HGF/SF caused an increase in motility, but no increase in cell growth [18]. This may reflect a more general inability of fibroblasts as a cell class to trigger a mitogenic response to HGF/SFE When scatter factor was first isolated, it was characterized by its ability to disperse epithelial cell colonies. However, as indicated by the title of this article, an increasing number of cytokines have been found to share this ability, along with the ability to stimulate or inhibit cell growth. Acidic fibroblast growth factor (aFGF) was the second scattering agent to be identified [19], closely followed by tumour necrosis factor (TNF) [20]. A scatter factor-like factor (SFL) has recently been identified [21], and also a novel scattering agent produced by monocytes [22]. EGF is the latest factor found to have scattering activity [23]. All these scattering factors act on epithelial cell colonies, but different factors act on different cell types. SFL, like HGF/SF, also scatters MDCK cells, but aFGF, TNF, EGF and the monocyte factor do not. To complicate the picture further, EGF is known to stimulate DNA synthesis in MDCK cells, so the precise effects of the factor will depend on the type of cell as well as its extracellular environment. The biological functions of scattering are unknown at present. The loosening of cell contacts by factors is beginning to seem much more than simply an in vitro phenomenon, and may well prove to be a major effector of cellular changes of several kinds. A very complex picture of this fascinating group of molecules is thus beginning to emerge: one might be tempted to describe the current picture as scattered pieces of a jigsaw. References 1. Stoker M, Gherardi E, Perryman M, Gray J: Scatter factor is a fibroblast-derived modulator of epithelial cell mobility. Nature 1987, 327:239-242. 2. Matsumoto K, Nakamura T: Roles of HGF as a pleiotropic factor in organ regeneration. In Hepatocyte Growth Factor - Scatter Factor and the c-met Receptor. Edited by Goldberg I and Rosen EM. Birkhiuser; 1993:225-250. 3. Tsubouchi H, Gohda E, Strain AJ, Daikuhara Y: The role of HGF/SF in animal and human hepatic physiology and pathology. In Hepatocyte Growth Factor - Scatter Factor and the c-met Receptor. Edited by Goldberg I, Rosen EM. Birkauser; 1993:251-274. 4. Hartmann G, Naldini L, Weidner KM, Sachs M, Vigna E, Comoglio PM, Birchmeier W: A functional domain in the heavy chain of scatter factor/hepatocyte growth factor binds the c-met receptor, induces cell dissociation but not mitogenesis. Proc Natl Acad Sci USA 1992, 89:11574-11578. 5. Chan AM, Rubin JS, Bottaro DP, Hirschfield DW, Chedid MM, Aaronson SA: Identification of a competitive HGF antagonist encoded by an alternative transcript. Science 1991, 254:1382-1385. 6. Naldini L, Vigna E, Narsimhan R, Gaudino G, Zarnegar R, Michalopoulos GK, Comoglio PM: Hepatocyte growth factor (HGF) stimulates the tyrosine kinase activity of the receptor encoded by the proto-oncogene c-met. Oncogene 1991, 6:501-504.
7. Bottaro DP, Rubin JS, Faletto DL, Chan AML, Kmiecik TE, Vande Woude GF, Aaronson SA: Identification of the hepatocyte growth factor receptor as the c-met proto-oncogene product. Science 1991, 251:802-804. 8. Montesano R,Matsumoto K, Nakamura T, Orci : Identification of a fibroblast derived epithelial morphogen as hepatocyte growth factor. Cell 1991, 67:901-908. 9. Tsarfaty I, Resau JH, Rulong S, Keydar I, Faletto D, Vande Woude G: The met proto-oncogene receptor and lumen formation. Science 1992, 257:1258-1261. 10. Sonnenberg E, Meyer D, Weidner KM, Birchmeier C: Scatter factor/hepatocyte growth factor and its receptor the c-met tyrosine kinase can mediate a signal exchange between mesenchyme and epithelia during mouse development. J Cell Biol 1993, 123:223-235. 11. Weidner KM, Behrens J, Vanderkerckhove J, Birchmeier W: Scatter factor: molecular characteristics and effect on the invasiveness of epithelial cells. J Cell Biol 1990, 111:2097-2108. 12. Kenworthy P, Dowrick P, Baillie-Johnson H, McCann B, Tsubouchi H, Arakaki N, Daikuhara Y, Warn RM: The presence of scatter factor in patients with metastatic spread to the pleura. BrJ Cancer 1992, 66:243-247. 13. Di Renzo MF, Narsimham RP, Olivero M, Bretti S, Giordano S, Medico E, Gaglia P, Zara P, Comoglio PM: Expression of the met/HGF receptor in normal and neoplastic human tissues. Oncogene 1991, 6:1997-2003. 14. Bellusci S, Moens G, Gaudino G, Comoglio P, Nakamura T, Thiery JP, Jouanneau J: Creation of an hepatocyte growth factor/scatter factor autocrine loop in carcinoma cells induces invasive properties associated with increased tumorigenicity. Oncogene 1994, 9:1091-1099. 15. Jiang WG, Lloyds D, Puntis M, Nakamura T, Hallet M: Regulation of spreading and growth of colon cancer cells by the hepatocyte growth factor. Clin Exp Metastasis 1993, 11:235-242. 16. Yamashita J, Ogawa M, Yamashita S, Nomura K, Kuramoto M, Saishoji T, Shin S: Immunoreactive hepatocyte growth factor is a strong and independent predictor of recurrence and survival in human breast cancer. Cancer Res 1994, 54:1630-1633. 17. Clark P: Modulation of scatter factor/hepatocyte growth factor activity by cell-substratum adhesion. J Cell Sci 1994, 107:1265-1276. 18. Giordano S, Zhen Z, Medico E, Gaudino G, Galimi F, Comoglio PM: Transfer of motogenic and invasive response to scatter factor/hepatocyte growth factor by transfection of human met proto-oncogene. Proc Natl Acad Sci USA 1993, 90:649-653. 19. Valles AM, Buyer B, Badet J, Tucker GC, Barritault D, Theiry JP: Acidic fibroblast growth factor is a modulator of epithelial plasticity in a rat bladder carcinoma line. Proc Natl Acad Sci USA 1990, 87:1124-1128. 20. Rosen E,Goldberg I, Liu D, Setter E, Donovan M, Bhargava M, Reiss M, Kacinski B: Tumrnour necrosis factor stimulates epithelial tumour cell motility. Cancer Res 1991, 51:5315-5321. 21. Bellusci S, Moens G, Thiery JP, Jouanneau J: A scatter factor-like factor is produced by a metastatic variant of a rat bladder carcinoma line. J Cell Sci 1994, 107:1277-1287. 22. Jiang WG, Puntis MCA, Hallett M: Monocyte-conditioned media possess a novel factor which increases motility of cancer cells. IntJ Cancer 1993, 53:426-431. 23. Shibamoto S, Hayakawa M, Takeuchi K, Hori T, Oku N, Miyazawa K, Kitamura K, Takeichi M, Ito F: Tyrosine phosphorylation of p-catenin and plakoglobin enhanced by hepatocyte growth factor and epidermal growth factor in human carcinoma cells. Cell Adh and Commn 1994, 1:295-305. 24. Gherardi E, Sharpe M, Lane K, Sirulnik A, Stoker M: Hepatocyte growth factor/scatter factor (HGF/SF), the c-met receptor and the behaviour of epithelial cells. In Cell Behaviour, Adhesion and Motility. Edited by Jones G, Wigley C, Warn RM. S.E.B. Symp 47, 1993:163-181.
Richard Warn, School of Biological Sciences, University of East Anglia, Norwich NR4 7TJ, UK.
1045
RICHARD WARN
GROWTH FACTORS
RICHARD WARN
A scattering of factors Hepatocyte growth factor/scatter factor isa multifunctional growth factor with varied properties: more and more polypeptide factors are being discovered that share these characteristics. Every so often a single observation creates the impetus for rapid progress in a variety of directions. An example was the discovery and biochemical characterization by Stoker, Gherardi and colleagues of a molecule they named scatter factor [1]. This protein has the property of dispersing or scattering epithelial cell colonies in culture into single isolated cells, rupturing intercellular junctions and desmosomes in the process. The scattered cells have enhanced motility, showing random, non-polarized movement in culture. Scatter factor has generally been found to be secreted by mesenchyme cells - fibroblasts and smooth muscle cells - rather than by epithelial and endothelial cells, although its effects are mainly obvious on the latter two cell types. In view of this, scatter factor is usually described as being a paracrine effector molecule. Recent results show that a variety of signalling molecules have similar properties to scatter factor, properties likely to be involved in a number of important physiological and pathological processes. The discovery of scatter factor was rapidly followed by a series of further findings. The determination of its amino-acid sequence showed that scatter factor is identical to hepatocyte growth factor (HGF), an independently characterized, strong mitogen for hepatocytes and a wide variety of other epithelial cell types [2,3]. This was a surprise, partly because the particular variant of the cell line originally used to characterize scatter factor - a dog kidney line (MDCK) - only responds by scattering. Other growth factors had previously been found to promote cell motility, but it was not suspected that a growth factor might have the further property of causing cells to break loose from colonies. Hepatocyte growth factor/scatter factor (HGF/SF), as it is now named, is a heterodimer with a larger x chain of about 60kD and a smaller 13chain of about 30kD, linked by a single inter-chain disulphide bond (Fig. 1). The protein is glycosylated to a varying but significant extent; it is translated from a single mRNA, and the active form is produced by cleavage of the biologically inert precursor chain. Analysis of the likely structure of the molecule has revealed several features that are not shared with any chain contains four other known growth factor. The 'kringles', an unusual structural motif that occurs also in plasminogen, tissue-type and urokinase-type plasminogen activators, factor XII and prothrombin. The chain consists of a serine protease domain that is inactive because of substitutions of two critical residues in the catalytic site. On its own, the ct chain is capable of
inducing some scattering activity, whereas the 3 chain alone has no biological activity [4]. There is a natural variant of HGF/SF, formed by alternative pre-mRNA splicing, which consists of only the first two kringles of the ao chain [5]. This two-kringle form has no growth-promoting properties, but seems to have some motility-inducing effects. Furthermore, the variant competes with the complete form of HGF/SF for binding to its receptor, and hence may act as a natural blocking agent. The discovery that the receptor for HGF/SF is the product of the proto-oncogene c-met was a further milestone [6,7]. The intracellular portion of the c-met protein contains a tyrosine kinase domain that is likely to have similar properties to the analogous domains of related growth factor receptors, such as those for epidermal growth factor (EGF) and platelet derived growth factor (PDGF). Yet another unexpected finding, originally made by Montesano and colleagues [8], was that HGF/SF can
Fig 1. Postulated primary structure of the mouse HGF/SF precursor. The structure is based on the conservation of critical cysteine residues in HGF/SF and plasminogen. The regions that form the a and chains of HGF/SF are shown as blue and red circles, respectively, except for cysteine residues, which are shown in black, and for the three residues corresponding to important active site residues of serine proteases, which are shown in yellow. A 30-residue-long signal sequence is shown in green. (Reproduced with permission from [24].)
© Current Biology 1994, Vol 4 No 11
1043
1044
Current Biology 1994, Vol 4 No 11 lung and intestine, whereas HGF/SF mRNA is simultaneously expressed by the adjacent mesenchyme. The implication is that HGF/SF and its receptor together act as a morphogen signalling mechanism in a variety of organ differentiation events. Studies of gene 'knockout' mice should provide data that bear directly on this hypothesis. The properties of HGF/SF suggest that it might also have some involvement in tumour growth and dissemination, and there is now some supporting evidence for such a view. Various tumour cell lines are dissociated in vitro by HGF/SF; furthermore, their migration into collagen gels is enhanced, a behaviour which mimics that of more highly invasive tumour lines [11]. Pleural effusion fluids containing metastatic tumours have significant levels of HGF/SF [12], so the tumours are in an environment in which enhanced expression of the HGF/SF receptor would stimulate a more rapid proliferation and spread. Furthermore, a wide range of tumours, including lung tumours, have been found to express elevated levels of the HGF/SF receptor [13] - the highest levels have been recorded in human thyroid cancers, where they were found to be 100 times higher than in normal thyroid tissue.
Fig 2. HGF/SF can have a number of different effects on the cells of an epithelial cell colony. More than one of these effects may occur at the same time.
-induce tubule-formation by MDCK cells grown in suspension within a collagen gel. In these conditions, HGF/SF acts to promote differentiation in association with increased cell division. Expression of the HGF/SF receptor has been detected by immunostaining in regions bordering the duct lumen in several tissues, including normal mammary glands [9]. Furthermore, there is a cultured human mammary line (T47D) that is capable of spontaneous tubule formation in culture - the lumens of these tubules express high levels of the HGF/SF receptor, and the tubules become much more uniform and ordered after HGF/SF treatment. Similar results were obtained with several colon lines. The ability of HGF/SF to induce tubule formation, particularly the branching tubules produced by MDCK cells, strongly suggests that HGF/SF has polarized effects on its target cells, presumably reflecting the polarized expression of the HGF/SF receptor on the target cells. HGF/SF is likely to have a number of important functions in development, one of which is, very probably, a role in generating the complex patterns of tubulogenesis that occur during organ formation and growth. A very careful in situ hybridization study [10] has elegantly demonstrated that HGF/SF and HGF/SF-receptor mRNAs are both expressed in complex, changing patterns during early mouse development. HGF/SF-receptor mRNA is expressed by the epithelial cells of a number of developing tubular organs, including kidney,
There is now some direct evidence that autocrine secretion of HGF/SF can promote tumorigenesis in nude mice. If a human bladder cell line is transfected with the HGF/SF gene before being introduced into nude mice, it generates tumours significantly more quickly than appropriate controls [14]. The tumours formed by transfected cell populations produce HGF/SF, as demonstrated by Western blot analysis. It will be of interest to determine whether cell-cell cooperation occurs in this system - that is, whether injected cell populations containing only a small proportion of HGF/SF transfectants also show more rapid tumour growth and spread. One must, however, be extremely careful before drawing any general conclusions about HGF/SF and tumours. For some tumour cell lines in culture, HGF/SF inhibits, rather than promotes, cell proliferation (see [15], for example), and one might also expect HGF/SF to induce terminal cell differentiation and perhaps also apoptosis. Proof of HGF/SF's role in tumorigenesis will only come from a clear-cut demonstration that specifically blocking HGF/SF inhibits tumour growth and spread, but circumstantial evidence has come from the recent report [16] that the level of HGF/SF associated with primary human breast tumours is a good prognostic indicator of tumour recurrence and survival. Further confirmation of this work may prove to be of clinical value. HGF/SF emerges as a multifunctional factor with a surprising repertoire of properties (Fig. 2). It is to be expected that these properties will turn out to be modulated by external influences, in particular the extracellular matrix. Indeed, another MDCK cell line has been identified that cannot scatter on serum- or vitronectin-coated glass surfaces but can on fibronectin-coated surfaces [17].
DISPATCH
Responses to HGF/SF will also depend on cell type for example, transfection of murine 3T3 fibroblasts with the human c-met gene followed by exposure to HGF/SF caused an increase in motility, but no increase in cell growth [18]. This may reflect a more general inability of fibroblasts as a cell class to trigger a mitogenic response to HGF/SFE When scatter factor was first isolated, it was characterized by its ability to disperse epithelial cell colonies. However, as indicated by the title of this article, an increasing number of cytokines have been found to share this ability, along with the ability to stimulate or inhibit cell growth. Acidic fibroblast growth factor (aFGF) was the second scattering agent to be identified [19], closely followed by tumour necrosis factor (TNF) [20]. A scatter factor-like factor (SFL) has recently been identified [21], and also a novel scattering agent produced by monocytes [22]. EGF is the latest factor found to have scattering activity [23]. All these scattering factors act on epithelial cell colonies, but different factors act on different cell types. SFL, like HGF/SF, also scatters MDCK cells, but aFGF, TNF, EGF and the monocyte factor do not. To complicate the picture further, EGF is known to stimulate DNA synthesis in MDCK cells, so the precise effects of the factor will depend on the type of cell as well as its extracellular environment. The biological functions of scattering are unknown at present. The loosening of cell contacts by factors is beginning to seem much more than simply an in vitro phenomenon, and may well prove to be a major effector of cellular changes of several kinds. A very complex picture of this fascinating group of molecules is thus beginning to emerge: one might be tempted to describe the current picture as scattered pieces of a jigsaw. References 1. Stoker M, Gherardi E, Perryman M, Gray J: Scatter factor is a fibroblast-derived modulator of epithelial cell mobility. Nature 1987, 327:239-242. 2. Matsumoto K, Nakamura T: Roles of HGF as a pleiotropic factor in organ regeneration. In Hepatocyte Growth Factor - Scatter Factor and the c-met Receptor. Edited by Goldberg I and Rosen EM. Birkhiuser; 1993:225-250. 3. Tsubouchi H, Gohda E, Strain AJ, Daikuhara Y: The role of HGF/SF in animal and human hepatic physiology and pathology. In Hepatocyte Growth Factor - Scatter Factor and the c-met Receptor. Edited by Goldberg I, Rosen EM. Birkauser; 1993:251-274. 4. Hartmann G, Naldini L, Weidner KM, Sachs M, Vigna E, Comoglio PM, Birchmeier W: A functional domain in the heavy chain of scatter factor/hepatocyte growth factor binds the c-met receptor, induces cell dissociation but not mitogenesis. Proc Natl Acad Sci USA 1992, 89:11574-11578. 5. Chan AM, Rubin JS, Bottaro DP, Hirschfield DW, Chedid MM, Aaronson SA: Identification of a competitive HGF antagonist encoded by an alternative transcript. Science 1991, 254:1382-1385. 6. Naldini L, Vigna E, Narsimhan R, Gaudino G, Zarnegar R, Michalopoulos GK, Comoglio PM: Hepatocyte growth factor (HGF) stimulates the tyrosine kinase activity of the receptor encoded by the proto-oncogene c-met. Oncogene 1991, 6:501-504.
7. Bottaro DP, Rubin JS, Faletto DL, Chan AML, Kmiecik TE, Vande Woude GF, Aaronson SA: Identification of the hepatocyte growth factor receptor as the c-met proto-oncogene product. Science 1991, 251:802-804. 8. Montesano R,Matsumoto K, Nakamura T, Orci : Identification of a fibroblast derived epithelial morphogen as hepatocyte growth factor. Cell 1991, 67:901-908. 9. Tsarfaty I, Resau JH, Rulong S, Keydar I, Faletto D, Vande Woude G: The met proto-oncogene receptor and lumen formation. Science 1992, 257:1258-1261. 10. Sonnenberg E, Meyer D, Weidner KM, Birchmeier C: Scatter factor/hepatocyte growth factor and its receptor the c-met tyrosine kinase can mediate a signal exchange between mesenchyme and epithelia during mouse development. J Cell Biol 1993, 123:223-235. 11. Weidner KM, Behrens J, Vanderkerckhove J, Birchmeier W: Scatter factor: molecular characteristics and effect on the invasiveness of epithelial cells. J Cell Biol 1990, 111:2097-2108. 12. Kenworthy P, Dowrick P, Baillie-Johnson H, McCann B, Tsubouchi H, Arakaki N, Daikuhara Y, Warn RM: The presence of scatter factor in patients with metastatic spread to the pleura. BrJ Cancer 1992, 66:243-247. 13. Di Renzo MF, Narsimham RP, Olivero M, Bretti S, Giordano S, Medico E, Gaglia P, Zara P, Comoglio PM: Expression of the met/HGF receptor in normal and neoplastic human tissues. Oncogene 1991, 6:1997-2003. 14. Bellusci S, Moens G, Gaudino G, Comoglio P, Nakamura T, Thiery JP, Jouanneau J: Creation of an hepatocyte growth factor/scatter factor autocrine loop in carcinoma cells induces invasive properties associated with increased tumorigenicity. Oncogene 1994, 9:1091-1099. 15. Jiang WG, Lloyds D, Puntis M, Nakamura T, Hallet M: Regulation of spreading and growth of colon cancer cells by the hepatocyte growth factor. Clin Exp Metastasis 1993, 11:235-242. 16. Yamashita J, Ogawa M, Yamashita S, Nomura K, Kuramoto M, Saishoji T, Shin S: Immunoreactive hepatocyte growth factor is a strong and independent predictor of recurrence and survival in human breast cancer. Cancer Res 1994, 54:1630-1633. 17. Clark P: Modulation of scatter factor/hepatocyte growth factor activity by cell-substratum adhesion. J Cell Sci 1994, 107:1265-1276. 18. Giordano S, Zhen Z, Medico E, Gaudino G, Galimi F, Comoglio PM: Transfer of motogenic and invasive response to scatter factor/hepatocyte growth factor by transfection of human met proto-oncogene. Proc Natl Acad Sci USA 1993, 90:649-653. 19. Valles AM, Buyer B, Badet J, Tucker GC, Barritault D, Theiry JP: Acidic fibroblast growth factor is a modulator of epithelial plasticity in a rat bladder carcinoma line. Proc Natl Acad Sci USA 1990, 87:1124-1128. 20. Rosen E,Goldberg I, Liu D, Setter E, Donovan M, Bhargava M, Reiss M, Kacinski B: Tumrnour necrosis factor stimulates epithelial tumour cell motility. Cancer Res 1991, 51:5315-5321. 21. Bellusci S, Moens G, Thiery JP, Jouanneau J: A scatter factor-like factor is produced by a metastatic variant of a rat bladder carcinoma line. J Cell Sci 1994, 107:1277-1287. 22. Jiang WG, Puntis MCA, Hallett M: Monocyte-conditioned media possess a novel factor which increases motility of cancer cells. IntJ Cancer 1993, 53:426-431. 23. Shibamoto S, Hayakawa M, Takeuchi K, Hori T, Oku N, Miyazawa K, Kitamura K, Takeichi M, Ito F: Tyrosine phosphorylation of p-catenin and plakoglobin enhanced by hepatocyte growth factor and epidermal growth factor in human carcinoma cells. Cell Adh and Commn 1994, 1:295-305. 24. Gherardi E, Sharpe M, Lane K, Sirulnik A, Stoker M: Hepatocyte growth factor/scatter factor (HGF/SF), the c-met receptor and the behaviour of epithelial cells. In Cell Behaviour, Adhesion and Motility. Edited by Jones G, Wigley C, Warn RM. S.E.B. Symp 47, 1993:163-181.
Richard Warn, School of Biological Sciences, University of East Anglia, Norwich NR4 7TJ, UK.
1045