Hepatocyte growth factor is a potent stimulator of human melanocyte DNA synthesis and growth

Hepatocyte growth factor is involved in formation of osteoclast-like cells mediated by clonal stromal cells (MC3T3-G2/PA6)

Osteoclast formation from hemopoietic precursors has been shown to require the support of stromal cells in bone tissue. In this study, we demonstrated that hepatocyte growth factor (HGF) is one of the stromal cell-derived molecules responsible for osteoclast-like cell formation. For our experiments, we used a coculture system for osteoclastic cell formation and activation in which hemopoietic blast cells are cocultured with calvaria-derived stromal MC3T3-G2/PA6 (PA6) cells on dentine slices in the presence of 1,25-dihydroxyvitamin D3 [1,25(OH)2D3]. Addition of anti-HGF neutralizing IgG to the cocultures inhibited the formation of osteoclastic cells and their dentine-resorbing activity. We detected a single 6.0-kb transcript for HGF in PA6 cells, and also recognized immunoreactive M(r) 81,000 and 88,000 forms of HGF in conditioned medium (CM) from PA6 cell cultures, the level of which reached 6 ng/ml. Both the CM and HGF stimulated the proliferation of blast cells synergistically with granulocyte-macrophage colony-stimulating factor, resulting in an increased number of osteoclast precursors that respond to 1,25(OH)2D3 that are tartrate-resistant acid phosphatase-positive multinucleate cells in stromal cell-free blast cell cultures in plastic wells. The effect of the CM was diminished by the addition of anti-HGF IgG. However, neither the CM nor HGF stimulated the formation of osteoclastic cells and pits on dentine slices in the absence of PA6 cells. These results suggest that although HGF cannot completely replace stromal cells, it is one of the paracrine mediators produced by stromal cells that act on proliferation of osteoclastic cell precursors.

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 is the most potent endogenous stimulant of rabbit gastric epithelial cell proliferation and migration in primary culture

Various growth factors are suggested to be involved in gastric mucosal repair. Our previous studies have shown that exogenous hepatocyte growth factor (HGF) has a proliferative effect on gastric epithelial cells. In the present study, comparison of the maximum proliferative effects and the optimum concentrations of several growth factors revealed that HGF was the most potent mitogen for gastric epithelial cells, as is the case for hepatocytes. Restitution of gastric epithelial cell monolayers was assessed using a round wound restitution model. HGF was the most effective agent for facilitating gastric epithelial restitution among those tested. A binding assay revealed specific binding of HGF to its receptor on gastric epithelial cells. Northern blot analysis confirmed the expression of specific HGF receptor mRNA (c-met) by gastric epithelial cells but not by gastric fibroblasts. To investigate endogenous HGF production, we determined the effect of gastric fibroblast-conditioned medium on epithelial proliferation and restitution. The conditioned medium produced similar effects to HGF and its activity was neutralized by an anti-HGF antibody. In addition, expression of HGF mRNA was detected in gastric fibroblasts but not in gastric epithelial cells. Our immunohistochemical study confirmed these in vitro data by means of demonstrating the existence and localization of HGF at human native gastric mucosa. HGF was localized at fibroblasts under the epithelial cell layer around gastric ulcers. These results suggest that HGF may be a potent endogenous promotor of gastric epithelial cell proliferation and migration, and may contribute to gastric mucosal repair through a paracrine mechanism.

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.

Stimulation of cultured melanocytes in medium containing a serum substitute: Ultroser-G

Melanocyte cultures were established and maintained routinely in Ham's F-10 medium containing 12-O-tetradecanoyl-phorbol-13-acetate (TPA), isobutylmethylxanthine (IBMX), cholera toxin (CT) and fetal calf serum (FCS). Three serum substitutes (Ultroser-G, Nutridoma-Hu and Nutricyte-H) were tested in order to obtain a medium without FCS having a more constant composition. Melanocyte proliferation was examined in long-term culture experiments by in situ cell counts at different periods of time. Only with Ultroser-G (1-2%) was the proliferation of melanocytes maintained without both FCS and CT, whereas the addition of the other two serum substitutes resulted in stabilization of melanocyte densities in the cultures up to 28 days. In the medium containing 1% Ultroser-G and IBMX without TPA minimal or no increases in melanocyte density were found. Addition of basic fibroblast growth factor (bFGF, 1 ng/ml) to the medium without TPA resulted in a partial restimulation of growth in different experiments. In this system with 1% Ultroser-G and 1 ng/ml bFGF, IBMX could also be replaced by other factors (dbcAMP, LTC4 and a purified form of alpha-melanocyte stimulating hormone). The culture medium with 1% Ultroser-G containing TPA and IBMX is now used for routine melanocyte culture. In this medium TPA/IBMX can easily be replaced by bFGF/dbcAMP with optimal growth stimulation. The combination bFGF/alpha-MSH and other more physiological stimulators offers an alternative to study responses of melanocytes in culture with respect to proliferation, metabolism, and phenotype.

Abnormal protein tyrosine kinase gene expression during melanoma progression and metastasis

Protein tyrosine kinases have been implicated in tumor initiation and progression. Here we used Northern blotting to study expression of their genes in cultured normal melanocytes and 19 melanoma cell lines from different stages of tumor progression. We detected transcripts for 2 cytoplasmic (ABL and FES) and 6 receptor (ECK, ERB-B2, FGF-R4, IGFI-R, KDR and TIE) kinases but not for receptors RET or TRK-A. Genes for ECK, FGF-R4 and TIE were expressed ectopically in melanomas (not in normal melanocytes). Similarly, ECK protein was detected by immunoblotting in metastatic melanomas but not in normal melanocytes. ECK mRNA levels tended to increase again during late melanoma progression. ECK and TIE mRNAs were also detected in highly metastatic variant cells but not in the corresponding poorly metastatic parental lines. Conversely, FES and KDR gene expression was lost in most advanced primary and metastatic melanomas. These findings suggest positive and negative roles for specific tyrosine kinases during progression.

Molecular cloning of Xenopus HGF cDNA and its expression studies in Xenopus early embryogenesis

We isolated Xenopus HGF cDNA and examined its expression pattern in Xenopus early embryos and their dissected parts. Xenopus HGF consists of 710 amino acids and contains four kringle domains and serine protease-like structure just like mammalian HGF. Northern blot analysis showed that expression of Xenopus HGF mRNA starts at the late gastrula stage and its level increases during the period of later embryogenesis. Dissection experiments revealed that Xenopus HGF mRNA is expressed in the mesoderm region, especially in the ventral mesoderm, which for the most part gives rise to mesenchymal cells. Furthermore, HGF mRNA was expressed in response to activin A and basic FGF in blastula animal cap cells. Interestingly, a stronger activity was observed with bFGF than with activin and this finding corroborates the preferential expression of HGF mRNA in the ventral mesoderm. Based on these results, we conclude that the Xenopus homologue of HGF gene is transcribed during early embryogenesis preferentially in ventral mesodermal tissues, probably in response to the signals that induce ventral mesoderm.

Rapid induction of mRNAs for liver regeneration factor and insulin-like growth factor binding protein-1 in primary cultures of rat hepatocytes by hepatocyte growth factor and epidermal growth factor

Liver regeneration factor belongs to the leucine-zipper family of transcription factors. It was originally cloned and characterized through differential screening of a regenerating rat liver cDNA library. The mRNA for liver regeneration factor-1 is barely detectable in normal rat liver but is dramatically induced after two-thirds hepatectomy, with a peak 1 to 3 hr after surgery. The nature of the signaling molecule(s) for this rapid induction is not known. It has been suggested that the liver regeneration factor-1 protein product, through complex interactions with other transcription factors such as c-Jun and Jun-B, controls expression of genes that are required during the G1 phase of hepatic growth. Hepatocyte growth factor has been shown to be the most potent mitogen for hepatocytes in vitro and in vivo. Plasma levels of hepatocyte growth factor rapidly (within 30 min) increase after loss of hepatic parenchyma induced by partial hepatectomy or carbon tetrachloride treatment. It has been postulated that hepatocyte growth factor plays a crucial role in stimulating the hepatocyte to enter the cell cycle. In this communication, we report that addition of pure hepatocyte growth factor to primary cultures of rat hepatocytes in the absence of serum and insulin results in rapid and transient induction of liver regeneration factor-1 mRNA (more than 20-fold) with a peak of expression 1 hr after treatment. The levels of jun-B and c-fos mRNAs, which are also known to be induced during the early hours of liver regeneration, were also increased after treatment of isolated hepatocytes with hepatocyte growth factor.(ABSTRACT TRUNCATED AT 250 WORDS)

Hepatocyte growth factor/scatter factor stimulates hair growth of mouse vibrissae in organ culture

Hepatocyte growth factor/scatter factor (HGF/SF) is a multifunctional polypeptide that acts as a mitogen, motogen, or morphogen, depending on the biologic context. In this study, we examined the effect of HGF/SF on hair growth using a serum-free organ culture system. Vibrissal hair follicles isolated from newborn mice were cultured at 31 degrees C in 95% O2/5% CO2 for 72 h in the presence of various cytokines or growth factors, and elongation of hair shaft, DNA, and protein synthesis in hair follicles were measured. Among the agents tested, only HGF/SF significantly increased hair follicle length (p < 0.001), 3H-thymidine (p < 0.001), and 35S-cysteine (p < 0.05) incorporation. The effect of HGF/SF was dose dependent, with maximal stimulation obtained at 10 ng/ml. The increase in hair follicle length and thymidine incorporation were specifically inhibited by a neutralizing antibody against HGF/SF. These results indicate that HGF/SF can promote hair growth and may have clinical utility in this regard.

Expression of hepatocyte growth factor mRNA, and c-met mRNA (hepatocyte growth factor receptor) in human liver tumours

We have quantified mRNA for the hepatocyte growth factor and its putative receptor the c-met proto-oncogene protein product, in a series of human primary and secondary liver tumours and adjacent non-neoplastic liver. In all hepatocellular cancers, hepatocyte growth factor 6 kb mRNA expression was less (mean 23.93% +/- 6.33% S.E.M. n = 7) in the tumours than in the adjacent normal liver. Both relative over- and under-expression of c-met transcripts were found in tumour tissue compared to non-neoplastic liver. Thus hepatocellular cancer tissue does not over-express mRNA for hepatocyte growth factor, though this growth factor might play a role in hyperproliferative states leading to liver cancer.

Expression and functional interaction of hepatocyte growth factor-scatter factor and its receptor c-met in mammalian brain

Hepatocyte growth factor-scatter factor (HGF-SF) is a pleiotropic cytokine with mito-, morpho-, and motogenic effects on a variety of epithelial and endothelial cells. HGF-SF activity is mediated by the c-met protooncogene, a membrane-bound tyrosine kinase. Here, we demonstrate that both genes are expressed in developing and adult mammalian brains. HGF-SF mRNA is localized in neurons, primarily in the hippocampus, the cortex, and the granule cell layer of the cerebellum, and it is also present at high levels in ependymal cells, the chorioid plexus, and the pineal body. c-met is expressed in neurons, preferentially in the CA-1 area of the hippocampus, the cortex, and the septum, as well as in the pons. In the embryonic mouse, brain HGF-SF and c-met are expressed as early as days 12 and 13, respectively. Neuronal expression of HGF-SF is evolutionary highly conserved and detectable beyond the mammalian class. Incubation of septal neurons in culture with HGF-SF leads to a rapid increase of c-fos mRNA levels. The results demonstrate the presence of a novel growth factor-tyrosine kinase signaling system in the brain, and they suggest that HGF-SF induces a functional response in a neuronal subpopulation of developing and adult CNS.

The effect of various cytokines on hair growth of mouse vibrissae in organ culture

Hepatocyte growth factor/scatter factor (HGF) is a multifunctional polypeptide which acts as a mitogen, motogen or morphogen depending on the biological context. In this study, we examined the effect of HGF on hair growth using a serum-free organ culture system. Vibrissal hair follicles isolated from newborn mice were cultured at 31 degrees C in 95% O2-5%CO2 for 72 h in the presence of various cytokines or growth factors. DNA, protein synthesis and elongation of the hair shaft in the hair follicles were measured. Among the agents tested, only HGF significantly increased hair follicle length (P < 0.001) and 3H-thymidine (P < 0.001) incorporation. The effect of HGF was dose-dependent, with maximal stimulation obtained at 10 ng/ml. The increase in hair follicle length and thymidine incorporation were specifically inhibited by a neutralizing antibody against HGF. These results indicate that HGF is able to promote hair growth and may have clinical utility in this regard.

Effects of activators (SC-9 and OAG) and inhibitors (staurosporine and H-7) of protein kinase C on the proliferation of mouse epidermal melanoblasts in serum-free culture

Mouse epidermal melanoblasts preferentially proliferated from disaggregated epidermal cell suspensions derived from newborn mouse skin in a serum-free melanoblast proliferation medium containing dibutyryl adenosine 3′:5′-cyclic monophosphate and basic fibroblast growth factor. After 12 days, almost all of the keratinocytes died and pure cultures of melanoblasts (approximately 80%) and melanocytes (approximately 20%) could be obtained. No further proliferation of melanoblasts was observed in the melanoblast proliferation medium. In order to clarify the role of protein kinase C, which is important for the regulation of cellular proliferation, activators or inhibitors of protein kinase C were added to the culture of the quiescent melanoblasts at 12 days. The proliferation of melanoblasts was induced by an activator of protein kinase C, N-(6-phenylhexyl)-5-chloro-1-naphthalene-sulfonamide or 1-oleoyl-2-acetyl-glycerol. It was also induced by an inhibitor of protein kinase C, staurosporine or 1-(5-isoquinolinesulfonyl)-2-methyl-piperazine. However, the melanoblasts failed to proliferate in the melanoblast proliferation medium supplemented with both the activator and the inhibitor. These results suggest that the proliferation of mouse epidermal melanoblasts in culture is regulated by activating or inhibiting the activity of protein kinase C.

Terminal differentiation and senescence in the human melanocyte: repression of tyrosine-phosphorylation of the extracellular signal-regulated kinase 2 selectively defines the two phenotypes

Melanocytes are pigmented cells distributed in humans in several organs like the epidermis, the leptomeninges, the eye, and the inner ear. Epidermal melanocytes, whether derived from adult or neonatal skin, proliferate well in a medium supplemented with phorbol esters and other mitogens before they undergo senescence. Potent cAMP inducers like cholera toxin are also growth promoters for neonatal melanocytes but only transient growth stimulators for cells derived from adults. We used this cellular system to delineate biochemical pathways involved in proliferation and in terminal differentiation. Here we show that after a period of 4-8 wk of sustained proliferation in the presence of cholera toxin, the adult melanocytes became round, flat, and enlarged. These changes were associated with terminal growth and preceded by a five- to sixfold increase in cAMP levels and an 8- to 10-fold increase in melanin content. The simultaneous addition of phorbol esters and cholera toxin did not prevent cells from reaching terminal differentiation. Identified targets for phorbol esters are protein kinase C (PKC) and the mitogen-activated kinases (MAPKs), also called extracellular signal-regulated kinases (ERKs). PKC was found to be similarly regulated in proliferating and in terminally differentiated melanocytes. Proliferating melanocytes in early or late passage showed identical activation of the kinase ERK2. This kinase was rapidly phosphorylated upon phorbol 12-myristate 13-acetate (PMA) addition and specifically accumulated in the nucleus of the cells, whereas in unstimulated cells it had a perinuclear distribution. In contrast, senescent and terminally differentiated cells were unable to phosphorylate tyrosine residues of the ERK2 gene product in spite of presenting normal amounts of ERK2 protein. In addition, ERK2 did not show the nuclear accumulation observed in proliferating melanocytes after PMA activation and remained localized in the perinuclear area. These results demonstrate that senescent and terminally differentiated melanocytes share a common block in a critical pathway thought to integrate multiple intracellular signals transmitted by various second messengers and specifically prevent the continuation of the signal transduction cascade initiated by PMA activation of PKC.

Expression and localization of hepatocyte growth factor in rat submandibular gland

By combination of in situ hybridization and immunohistochemical techniques, the expression of hepatocyte growth factor (HGF) was demonstrated in the submandibular gland of rats. Both the mRNA signal and immunoreactivity for HGF were localized exclusively to the epithelial cells of granular convoluted tubules, whereas they were absent from the other components of the submandibular gland. In the granular convoluted tubule cells, HGF-immunoreactivity was localized to the apical secretory granules, which was further substantiated by immunoelectron microscopy. These results added HGF to the list of many growth factors that are produced in the rat submandibular gland and secreted into the saliva.

Cooperative roles of hepatocyte growth factor and plasminogen activator in tubular morphogenesis by human microvascular endothelial cells

Epidermal growth factor (EGF) or transforming growth factor-alpha (TGF-alpha) stimulated cell migration, chemotaxis, and the expression of tissue-type plasminogen activator (t-PA) in human omental microvascular endothelial (HOME) cells. Hepatocyte growth factor (HGF) stimulated cell proliferation, but had a negligible stimulatory effect on cell migration, the expression of t-PA and tube-like formation into collagen gel in HOME cells. Basic fibroblast growth factor stimulated cell proliferation, cell migration, tubulogenesis and the expression of urokinase-type plasminogen activator (u-PA) in bovine aortic endothelial (BAE) cells. HOME and BAE cells had both high- and low-affinity receptors for HGF. In BAE cells, u-PA activity and tube-like structures in collagen gel were induced in the presence of HGF alone. In contrast, in HOME cells, t-PA activity and tube-like structures were induced in the presence of TGF-alpha alone, but not in the presence of HGF alone. However, we observed a marked induction of tube formation by HOME cells when both t-PA and HGF were added simultaneously. In the model system for tumor angiogenesis, when HOME cells were co-cultured with a renal cancer cell line, KPK13, tube-like structures were induced in the presence of HGF:KPK13 cells expressed large amounts of t-PA mRNA. Our present study suggested that HGF in concert with active t-PA could be angiogenic in HOME cells.

Hepatocyte growth factor/scatter factor, liver regeneration and cancer metastasis

Hepatocyte growth factor (HGF) is the most potent stimulator of hepatocyte growth and DNA synthesis identified; it is now known to be the same molecule as scatter factor, which increases the motility of a variety of cell types. HGF is becoming recognized as one of the most important factors in the regulation of liver regeneration after surgical resection or chemical damage. HGF is produced by several tissues, including neoplasms; it can therefore provide a stimulus for increased motility of malignant cells by both a paracrine and autocrine mechanism. The receptor for HGF has been identified as the product of the oncogene c-met, raising the possibility that this gene plays a key role in facilitating cellular invasion. HGF may therefore be important not only for liver cell growth but also in metastasis. This article summarizes the current position of research on HGF, and presents both clinical and scientific evidence that strongly implicates this factor in liver regeneration and cancer invasion and metastasis.

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

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

Macrophages release melanocyte dendrite extension factor in response to ultra-violet ray

Mammalian melanocytes in epidermis extend their dendrites in response to UV ray in vivo in addition to proliferation and pigmentation. We found that cultured macrophages exert a factor in response to UV irradiation and that this factor induces the extension of dendrites of melanocyte. We designated this factor as dendrite extension factor (DEF) and characterized it as a protein. Our results indicate that the molecular weight of DEF is 30,000-100,000 and that it is heat-labile. Macrophages release DEF through transcription and translation. DEF seems to be a novel factor that enhances melanogenesis by UV irradiation.

Regulation of spreading and growth of colon cancer cells by hepatocyte growth factor

Hepatocyte growth factor (HGF), also known as scatter factor, regulates both cell motility and the growth of some cell types. We have determined the effects of HGF on the motility and growth of human colon cancer cell lines (HT115, HT29, HRT18 and HT55). Cell motility, as measured by dissociation from carrier beads or by scattering of cell colonies, was greatly increased in all cell lines. The effects were completely blocked by anti-HGF antibody. In contrast, cell growth of HT115, HT29 and HRT18 cells was inhibited by a wide range of concentrations of HGF. HT55 cell growth was also inhibited but needed a prolonged culture period (> 5 days). The HGF receptor/Met protein is highly expressed in the membrane fraction of these cells as determined by Western blotting. It is concluded that HGF has an effect on both colon cancer cell motility and growth, which may be important in the control of the spread of colon cancer.

Cell-specific expression of hepatocyte growth factor in liver. Upregulation in sinusoidal endothelial cells after carbon tetrachloride

The cellular origin of hepatocyte growth factor (HGF), a polypeptide implicated in liver regeneration, was examined in normal liver and in hepatic regeneration induced by carbon tetrachloride. In normal liver, HGF and its mRNA were abundant in lipocytes, with smaller amounts present also in sinusoidal endothelial and Kupffer cells. In regenerating liver, HGF gene expression increased exclusively in endothelial cells. HGF mRNA levels rose sixfold in these cells, peaking at 6 h after toxin administration and returning to near normal by 24 h. The rise in HGF mRNA was accompanied by a 5.4-fold increase in HGF secretion. CCl4 did not alter HGF expression by either Kupffer cells or lipocytes; nor did it induce HGF expression by hepatocytes. Nonparenchymal liver cells contained two HGF transcripts: one predicting a full-length molecule of 728 amino acids; and the other encoding a functional five-amino acid deletion variant of HGF. The variant was less abundant than the full-length transcript, but increased in parallel with native HGF mRNA in response to CCl4. The response of nonparenchymal cells to HGF was examined by plating endothelial cells and lipocytes in the presence of recombinant human HGF. Under the conditions examined, the growth factor exerted neither mitogenic nor scatter factor activity on these cells.

Immunohistochemical localization of hepatocyte growth factor protein in pancreas islet A-cells of man and rats

Hepatocyte growth factor (HGF), a potent mitogen for adult rat hepatocytes in primary culture, has previously been shown to be primarily expressed in the nonparenchymal cells of the liver. Using polyclonal antisera against human and rat HGFs we studied the tissue distribution of HGF immunohistochemically and found the most intense staining in the pancreas islet cells in both man (autopsy cases) and the rat. Differential localization of 4 pancreas islet hormones, glucagon, insulin, somatostatin and pancreatic polypeptide, revealed HGF to be preferentially expressed within the glucagon‐positive cells. The results indicate that HGF is primarily produced or stored in A‐cells and may act as a growth factor in a paracrine and an endocrine fashion, like various other hormones.

Transfer of motogenic and invasive response to scatter factor/hepatocyte growth factor by transfection of human MET protooncogene

The MET protooncogene encodes p190MET, a tyrosine kinase which is the receptor for a molecule known as scatter factor or hepatocyte growth factor (SF/HGF). This molecule has different biological activities, including stimulation of cell motility, promotion of matrix invasion and, in some cells, mitogenesis. We have cloned the full-length MET cDNA and transfected it into NIH 3T3 fibroblasts. Stable transfectants expressed the p190MET receptor together with two previously described truncated forms of 140 and 130 kDa lacking the tyrosine kinase domain. All three forms bound radiolabeled SF/HGF. The factor stimulated tyrosine kinase activity of the transfected p190MET and induced changes in cell shape, migration in Boyden chambers, and invasion of collagen matrices in vitro. The motile and invasive phenotype was transient and strictly dependent on the presence of SF/HGF. The factor did not stimulate either cell growth or thymidine incorporation in transfected cells, while it promoted colony formation in soft agar in the presence of 5% fetal calf serum. These data show that, in the presence of its ligand, the MET receptor expressed in fibroblasts induces cells to pursue a motogenic-invasive rather than a proliferative program.

Hepatocyte growth factor stimulates phosphoinositide hydrolysis and mitogenesis in cultured renal epithelial cells

Hepatocyte growth factor (HGF), a novel heparin-binding peptide growth factor of MW 97-kDa, is a potent mitogen for parenchymal hepatocytes. HGF is present in normal serum and increases following liver injury or partial hepatectomy. In addition to liver, HGF mRNA has been detected in kidney. In cultured rabbit proximal tubule cells, recombinant human HGF (10(-10) M) increased DNA synthesis, measured as [3H] thymidine incorporation, from 1345 +/- 213 to 2931 +/- 636 cpm/10(6) cells; n = 9; p < 0.005). HGF was found to exert mitogenic effects at lower concentrations than epidermal growth factor (EGF), with half maximal effects seen at 6 x 10(-11) M compared to 7 x 10(-10) M for EGF. HGF was additive with EGF in stimulating [3H] thymidine incorporation. In addition to rabbit proximal tubule cells, HGF increased proliferation in a cultured mouse proximal tubule cell line, MCT, and in rat glomerular epithelial cells. In contrast, HGF did not stimulate proliferation of either rat mesangial cells or a rat aortic smooth muscle cell line, A7r5. The HGF receptor is the product of the c-met proto-oncogene. C-met mRNA was detected in total kidney and in cultured proximal tubule cells but was not detected in cultured mesangial cells. In contrast, HGF mRNA was detected in mesangial cells but not in cultured proximal tubule cells. Preincubation of rabbit proximal tubule cells with the tyrosine kinase inhibitor, genistein (50 microM), prevented HGF-stimulation of [3H] thymidine incorporation. In LiCl pretreated rabbit proximal tubule cells loaded with [3H] myoinositol, HGF increased total inositol phosphate release, measured by anion exchange chromatography (control: 2181 +/- 414 vs HGF: 2609 +/- 478 cpm/10(6) cells; n = 6; p < 0.05). Although genistein did not affect baseline phosphoinositide hydrolysis, it inhibited the HGF stimulation. Thus, HGF is mitogenic for cultured proximal tubule cells as well as glomerular epithelial cells. Inhibition of proliferation and PI turnover by genistein suggests that HGF's actions are mediated in part by tyrosine kinase activity. In mammalian kidney, HGF released from mesangial cells may serve as a paracrine activator of the adjacent epithelial cells.

Hepatocyte growth factor is linked by O-glycosylated oligosaccharide on the alpha chain

The glycosylation site and the structure of O-glycosylated oligosaccharide of recombinant human HGF were investigated. N-acetylgalactosamine (GalNAc) in the alpha chain suggested the presence of O-glycosylated oligosaccharide. Sugar analysis and amino acid sequence analysis of peptide fragments produced by limited degradation revealed that O-glycosylated oligosaccharide linked to Thr445 of the alpha chain. The molecular weight of the oligosaccharide was determined with ion spray mass spectrometry. From these studies, the structure of the O-glycosylated oligosaccharide on the alpha chain of HGF was concluded as [formula: see text].

Hepatocyte growth factor down-regulates the alpha-fetoprotein gene expression in PLC/PRF/5 human hepatoma cells

Hepatocyte growth factor (HGF) is a potent mitogen for hepatocytes; however, in certain human hepatoma cell lines, the growth is inhibited by HGF. In the present study, the effect of HGF on the alpha-fetoprotein (AFP) gene expression was analyzed in PLC/PRF/5 human hepatoma cells. HGF did not inhibit cell proliferation, but dose-dependently suppressed AFP secretion at the concentrations of 10 ng/ml or less. By Northern blot analysis, the levels of AFP mRNA were suppressed by HGF, whereas the levels of beta-actin mRNA used as a control did not show any significant changes. In the transient chloramphenicol acetyltransferase plasmid transfection assays, the AFP promoter activity was repressed by HGF, in contrast, the AFP enhancer activity was not affected by HGF. These results suggest that the AFP gene expression is down-regulated by HGF through the suppression of its promoter activity in human hepatoma cells.

Developmental changes in hepatocyte growth factor mRNA and its receptor in rat liver, kidney and lung

Hepatocyte growth factor (HGF) is a mesenchymal-derived factor which induces mitosis, cell movement and morphogenesis of tissue-like structure. We analyzed changes in HGF mRNA and its receptor, the c-met proto-oncogene product, in the liver, kidney and lung during late fetal and postnatal development in rats. In the liver, the HGF-mRNA level was very low during late gestation and in neonates, it increased remarkably and reached a maximum two weeks postnatally, to be followed by a decrease to 33% of the maximum. HGF mRNA in the kidney and lung was either undetectable or very low during late gestation and the neonatal period and increased markedly to reach a maximum, respectively, 3-4 weeks postnatally. HGF-mRNA level in the adult rat lung was fivefold higher than that in the liver and kidney. The number of HGF receptors on plasma membranes of these tissues was low in neonates but there was a rapid increase after birth and a maximum was reached within three weeks. The number of HGF receptors/ng plasma membrane protein at the maximal level was highest in the liver and lowest in the lung. c-met/HGF-receptor mRNA in the liver was also low during late-gestation or in early neonatal periods and increased postnatally. Since HGF-mRNA and HGF-receptor levels changed differently in liver, kidney and lung, the expression of HGF and its receptor may be independently regulated in each organ. However, in these organs, HGF mRNA and the HGF receptor increased within a few weeks of birth, HGF may play roles in organ growth, organ maturation and the maintenance of tissue homeostasis during the postnatal period, presumably through its potential to act as mitogen, motogen and morphogen.

Differential expression of hepatocyte growth factor, transforming growth factor-alpha and transforming growth factor-beta 1 messenger RNAs in two experimental models of liver cell proliferation

Hepatocyte growth factor, a potent hepatocyte mitogen in vitro, appears to trigger hepatocyte regeneration after partial hepatectomy and after acute liver cell necrosis. Transforming growth factor-alpha and transforming growth factor-beta 1 may also be involved in the control of liver regeneration. In this study we assessed possible roles of hepatocyte growth factor, transforming growth factor-alpha and transforming growth factor-beta 1 on liver cell proliferation in vivo, using a model of choline deficiency that is associated with liver cell necrosis and a model of a hypolipidemic agent (4-chloro-6-(2,3 xylidino)-2-pyrimidinylthio (N-beta-hydroxyethyl) acetamide) without liver necrosis. Male F344 rats were fed a choline-deficient diet or 0.16% 4-chloro-6-(2,3 xylidino)-2-pyrimidinylthio (N-beta-hydroxyethyl) acetamide diet for 6 and 4 wk, respectively. Rats were killed periodically, and the expression of hepatocyte growth factor messenger RNA in the liver, lung and kidney was determined by Northern-blot analysis. The levels of transforming growth factor-alpha and transforming growth factor-beta 1 messenger RNAs in the liver were also determined. Feeding a choline-deficient diet for 1 to 6 wk led to gradual increases in the levels of hepatocyte growth factor, transforming growth factor-alpha and transforming growth factor-beta 1 messenger RNAs in the liver. Feeding a 4-chloro-6-(2,3 xylidino)-2-pyrimidinylthio (N-beta-hydroxyethyl) acetamide diet for 3 days and 2 wk induced marked enhancement of liver cell proliferation as judged by hepatocyte 5-bromo-2-deoxyuridine incorporation.(ABSTRACT TRUNCATED AT 250 WORDS)

Hepatocyte growth factor induces calcium mobilization and inositol phosphate production in rat hepatocytes

The effects of hepatocyte growth factor (HGF) on intracellular Ca2+ mobilization were studied using fura-2-loaded single rat hepatocytes. Hepatocytes microperfused with different amounts of HGF responded with a rapid concentration-dependent rise in the cytosolic free Ca2+ concentration with a maximum increase of 142% at 80 ng/ml of HGF. The lag period of the Ca2+ response was decreased with increasing HGF concentrations, being 64 +/- 12 s, 42 +/- 6 s, and 14 +/- 2 s, respectively, with 8, 20, and 80 ng/ml of HGF. The detailed pattern of Ca2+ transients, however, was variable. Out of 16 cells tested using 20 ng/ml of HGF, 68% showed sustained oscillatory responses, whereas other cells showed a sustained increase in the cytosolic-free Ca2+ upon exposure to HGF, which was dependent on the presence of extracellular Ca2+. HGF also induced Ca2+ entry across the plasma membrane. Mobilization of Ca2+ by HGF was accompanied by a rapid accumulation of inositol 1,4,5-trisphosphate (Ins 1,4,5-P3). The effects of HGF and epidermal growth factor (EGF) were comparable and partly additive for Ins 1,4,5-P3 production and for the sustained phase of Ca2+ mobilization. Preincubation of cells with 10 microM of genistein to inhibit protein tyrosine kinases abolished the HGF-induced Ca2+ response and also inhibited HGF-induced Ins 1,4,5-P3 production in rat liver cells. These data indicate that early events in the signal transduction pathways mediated by HGF and EGF have in common the requirements for tyrosine kinase activity, Ins 1,4,5-P3 production, and Ca2+ mobilization.

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

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

Allergic contact dermatitis releases soluble factors that stimulate melanogenesis through activation of protein kinase C-related signal-transduction pathway

Phenylazo-naphthol (PAN) allergy induces visibly well-defined and late-appearing hyperpigmentation of brownish yellow guinea pig skin in clear contrast to dinitrochlorobenzene (DNCB) allergy, which has very low incidence of hyperpigmentation. Skin extract from PAN allergy at 20-29 d post-challenge exhibited marked melanogenic stimulatory effects (3H2O release and 14C-thiouracil incorporation) when added to cultured guinea pig melanocytes. The time course in the appearance of melanogenic factor was definitely consistent with the induction pattern of visible pigmentation. By contrast, the addition of DNCB-challenged skin extract demonstrated no significant stimulating effect on melanogenesis in either assay system on any of the post-challenge days tested. Assay of intracellular inositol 1,4,5-trisphosphate formed through incubation with the melanocytes demonstrated that the PAN-allergy skin extract at day 28, which contains definite melanogenic factors, stimulated the formation of inositol 1,4,5-trisphosphate that occurs around 50 seconds in contrast to no or little increase with extracts obtained at days 0 and 1 post-challenge. Gel chromatographic analysis revealed that the PAN-allergy skin extract at day 28 contained a newly generated melanogenic fraction with a molecular weight of approximately 9000 Da which was also capable of stimulating DNA synthesis and activating the signal-transduction process (inositol trisphosphate formation) when added to guinea pig melanocytes. Both stimulations of melanogenesis and DNA synthesis by the 9000 Da fraction were completely abolished by the prior and simultaneous addition of protein kinase C (PKC) inhibitor (H-7) or its down-regulatory agent, phorbol 12,13-dibutyrate (PdBu). Taken together, these results suggest that PAN allergy provides a new mechanism of hypermelanization in which endogenous factors synthesized within skin induce the activation of signal-transduction pathways such as phosphoinositide turnover through ligands-receptor binding, resulting in the stimulation of melanocytes possibly through the activation of PKC.

Regulation of cell growth and motility by hepatocyte growth factor and receptor expression in various cell species

Hepatocyte growth factor (HGF), a humoral mediator for regeneration of liver and kidney, possesses multiple biological activities. To investigate target cell specificity and to examine whether multiple actions of HGF are related to properties of the HGF receptor on target cells, we examined the effects of HGF on cell growth and motility and analyzed the HGF receptor in various species of cells. HGF stimulated growth and DNA synthesis of PAM212 (naturally immortalized mouse keratinocytes), Mv1Lu (mink lung epithelia), and A431 (human epidermoid carcinoma) cells, as well as mature hepatocytes, but inhibited those of IM-9 (human B-lymphoblasts). Conversely, HGF had a marked stimulatory effect on cell motility of MDCK (Mardin-Darby canine kidney epithelia) cells, but not on their growth. Also, HGF enhanced the motility of various species of cells, including A431, PAM212, HepG2 (human hepatoma), KB (human epidermoid carcinoma), and J-111 (human monocytes) cells. Scatchard analysis of 125I-HGF binding to hepatocytes indicated that the cells expressed both high- and low-affinity binding sites for HGF with Kd values of 23 and 260 pM, respectively. High-affinity HGF receptor with Kd values of 20-25 pM was detected at 40-720 sites/cell in MDCK, A431, PAM212, Lu99, and IM-9 cells, but not in fibroblasts and hematopoietic cells. In contrast, low-affinity binding sites were detected in all cell lines examined, even in those not responsive to HGF. Northern blots revealed that cells possessing a high-affinity HGF receptor expressed c-MET/HGF receptor mRNA. Therefore, HGF probably regulates both cell growth and motility of various types of epithelial cells and some types of mesenchymal cells. The multiple biological activities of HGF may be exerted through a high-affinity HGF receptor linked to multiple distinct intracellular signaling pathways.

Marked induction of hepatocyte growth factor mRNA in intact kidney and spleen in response to injury of distant organs

Hepatocyte growth factor (HGF) is a potent mitogen for various epithelial cells, including mature hepatocytes and renal tubular cells. Here, HGF mRNA was found to be markedly increased in non-injured kidney and spleen, when the liver or kidney in rats was injured by 70% partial hepatectomy or unilateral nephrectomy. HGF mRNA increased to 3-4 fold higher level than the normal in the kidney and spleen as well as in the remnant liver after partial hepatectomy. Similarly, HGF mRNA markedly increased in the spleen as well as in the remnant kidney after unilateral nephrectomy. These results suggest that the onset of injury to the liver or kidney may be recognized by distal non-injured organs by the signalling of a humoral factor and that HGF derived from these organs may be involved in the regeneration of liver or kidney, through an endocrine mechanism.

Identification and characterization of "injurin," an inducer of expression of the gene for hepatocyte growth factor

The marked and rapid increase of hepatocyte growth factor (HGF) mRNA in the intact lung of rats after partial hepatectomy or unilateral nephrectomy suggests the existence of a humoral factor mediating a signal of injury to distal organs and may induce the expression of HGF gene in these organs. We have now identified a proteinous factor in the sera of rats with injury of liver or kidney that increases HGF mRNA in the intact lung. When the serum of rats with liver insult caused by partial hepatectomy or ischemic treatment was injected i.p. into normal noninjured rats, it induced a marked HGF mRNA expression in the lung of the recipient rats. The addition of serum from rats with various hepatic or renal injuries to MRC-5 human embryonic lung fibroblasts in culture also led to the induction of HGF mRNA expression, so that the production of HGF by MRC-5 cells after treatment with the sera was remarkably increased in the culture medium. However, serum from the normal intact rat induced no HGF production and no HGF mRNA in the lung in vivo and lung fibroblasts in vitro. This factor, which increases HGF production, was purified greater than 200-fold from sera of CCl4-treated rats. The factor proved to be an acid- and heat-stable protein with an apparent molecular mass of 10-20 kDa in SDS/PAGE. Its activity markedly increased within 3-6 hr in the plasma of rats after various treatments that injured the liver or kidney. These results suggest that the factor specifically appears in the blood of rats with organ injury and may be involved in organ regeneration through the potential to increase the synthesis of HGF. Since the factor seems to mediate various organ injuries, we named it "injurin."

c-Kit-kinase induces a cascade of protein tyrosine phosphorylation in normal human melanocytes in response to mast cell growth factor and stimulates mitogen-activated protein kinase but is down-regulated in melanomas

The proto-oncogene c-Kit, a transmembrane receptor tyrosine kinase, is an important regulator of cell growth whose constitutively active oncogenic counterpart, v-kit, induces sarcomas in cats. Mutations in murine c-kit that reduce the receptor tyrosine kinase activity cause deficiencies in the migration and proliferation of melanoblasts, hematopoietic stem cells, and primordial germ cells. We therefore investigated whether c-Kit regulates normal human melanocyte proliferation and plays a role in melanomas. We show that normal human melanocytes respond to mast cell growth factor (MGF), the Kit-ligand that stimulates phosphorylation of tyrosyl residues in c-Kit and induces sequential phosphorylation of tyrosyl residues in several other proteins. One of the phosphorylated intermediates in the signal transduction pathway was identified as an early response kinase (mitogen-activated protein [MAP] kinase). Dephosphorylation of a prominent 180-kDa protein suggests that MGF also activates a phosphotyrosine phosphatase. In contrast, MGF did not induce proliferation, the cascade of protein phosphorylations, or MAP kinase activation in the majority of cells cultured from primary nodular and metastatic melanomas that grow independently of exogenous factors. In the five out of eight human melanoma lines expressing c-kit mRNAs, c-Kit was not constitutively activated. Therefore, although c-Kit-kinase is a potent growth regulator of normal human melanocytes, its activity is not positively associated with malignant transformation.

Characterization of hepatocyte-growth-factor receptors on Meth A cells

Hepatocyte growth factor (HGF) is a heparin-binding polypeptide mitogen for a variety of cell types including hepatocytes. HGF also has cytotoxic activity on some tumor cell lines as well as scattering activity on epithelial cells. In this study, recombinant human HGF was used to identify HGF-binding cell surface receptors on Meth A cells, whose growth is inhibited by HGF. Scatchard analysis of binding data indicated that there were two classes of binding sites with high affinity (Kd = 17 pM) and low affinity (Kd = 6.7 nM) and the average numbers were 6600 and 2,600,000 per cell, respectively. Affinity cross-linking of 125I-HGF to Meth A cells resulted in a major and a minor specifically labeled complex. Competition analysis followed by cross-linking indicated that the HGF-binding proteins were involved in the formation of the high-affinity binding. The existence of the two HGF-binding surface proteins was confirmed by HGF-dependent immunoprecipitation of the binding proteins with an anti-HGF polyclonal antibody. The molecular masses of the major and the minor surface proteins were 160 kDa and 130 kDa, respectively. The 160-kDa protein was autophosphorylated in vitro on tyrosine residue and was immunoprecipitated with an antiserum against the c-met proto-oncogene product. These results indicate that the 160-kDa HGF-binding surface protein on Meth A cells is the c-met protein. Furthermore, tyrosine phosphorylation of the c-met protein was stimulated by HGF treatment of Meth A cells, suggesting that it may be involved in the signal transduction of the growth inhibition of Meth A cells by HGF.

Hepatocyte growth factor (HGF) mediates the sustained formation of 1,2-diacylglycerol via phosphatidylcholine-phospholipase C in cultured rat hepatocytes

The addition of hepatocyte growth factor (HGF) to rat hepatocytes in primary culture resulted in the formation of inositol 1,4,5-trisphosphate (Ins(1,4,5)P3) and 1,2-diacylglycerol (DG) by a phosphoinositide-specific phospholipase C (PI-PLC). DG showed a biphasic increase; the first phase, corresponding with the peak of Ins(1,4,5)P3 and a second larger and prolonged phase. The HGF stimulates the phosphatidylcholine (PC)-derived prolonged DG formation by a phospholipase C pathway (PC-PLC) but not by a phospholipase D pathway. HGF also was found to elicit [Ca2+] oscillations which may be associated with the prolonged DG production from PC via the PC-PLC phospholipase C pathway.

Lung may have an endocrine function producing hepatocyte growth factor in response to injury of distal organs

Hepatocyte growth factor (HGF) is a potent growth factor for various epithelial cells including mature hepatocytes and renal tubular cells. When 70% of the rat liver was excised, HGF mRNA in the intact lung markedly increased at 6 h later, then decrease to normal levels at 24 h. A similar marked increase of HGF mRNA was found in the lung of rats with hepatitis induced by CCl4. Moreover HGF mRNA in the intact lung also increased to about a 5 times higher level than the normal, within 12 h after unilateral nephrectomy. Isolated alveolar macrophages significantly expressed HGF mRNA, yet the amount remained unchanged after injury of the liver. The marked increase of HGF mRNA in lungs of partially hepatectomized rats remained even after removal of alveolar macrophages. In situ hybridization showed a marked increase of HGF mRNA signal found in endothelial cells in the lung after partial hepatectomy. We postulate that endothelial cells in the lung recognize damage of distal organs through a mediator and that lung-derived HGF may contribute to tissue repair or regeneration of injured organs, through endocrine-related mechanisms.

Hepatocyte growth factor is a paracrine factor for renal epithelial cells: Stimulation of DNA synthesis and Na,K-ATPase activity

The expressions of mRNAs of hepatocyte growth factor (HGF) and its receptor (c-met) and its effects were examined in cultured renal epithelial cell lines (OK, LLCPK1, and MDCK cells) and rat mesangial cells in primary culture. Northern blot analysis revealed the presence of HGF mRNA in mesangial cells, but not in epithelial cells. c-met mRNA was detected in epithelial cells, but not in mesangial cells. HGF stimulated [3H]-thymidine incorporation (DNA synthesis) dose-dependently in OK and LLCPK1 cells, but not in MDCK and mesangial cells. Ouabaine sensitive rubidium uptake (Na,K-ATPase activity) was stimulated by 63% with HGF (10 ng/ml) treatment for 16hr in MDCK cells. The results suggest that HGF is produced in the kidney, at least in mesangial cells and works on epithelial cells to stimulate the proliferation and/or to modify cell functions in a paracrine manner.