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

Overexpression of the met/HGF receptor in renal cell carcinomas

The c-met oncogene encodes the receptor for hepatocyte growth factor/scatter factor (HGF/SF), a multifunctional cytokine able to mediate morphogenesis as well as mitogenesis, motogenesis and invasiveness of epithelial cells. HGF/SF has been implicated in branching tubulogenesis of the developing kidney and in regeneration after renal injury and nephrectomy. We have examined the expression of the met/HGF receptor in normal human kidney and tissues of the genito-urinary tract, and in 50 kidney neoplasms of different histotypes, using monoclonal antibodies (MAbs) against the met/HGF receptor and immunohistochemistry. In normal kidneys, weak staining restricted to the distal tubules was observed. Transitional cell carcinomas were consistently negative, whereas increased expression at various levels was found in 87% of renal cell carcinomas with different cytological features and histological patterns. Western blot analysis of samples showed that the met/HGF receptor found in the malignant cells exhibits features of the normal receptor. The met/HGF receptor is also overexpressed in a renal cell carcinoma cell line, whose motility is triggered by HGF/SF. Our data suggest that expression of the met/HGF receptor may be involved in the onset and progression of renal cell carcinomas.

Scatter factor/hepatocyte growth factor as a regulator of skeletal muscle and neural crest development

Factors that regulate cellular migration during embryonic development are essential for tissue and organ morphogenesis. Scatter factor/hepatocyte growth factor (SF/HGF) can stimulate motogenic and morphogenetic activities in cultured epithelial cells expressing the Met tyrosine kinase receptor and is essential for development; however, the precise physiological role of SF/HGF is incompletely understood. Here we provide functional evidence that inappropriate expression of SF/HGF in transgenic mice influences the development of two distinct migratory cell lineages, resulting in ectopic skeletal muscle formation and melanosis in the central nervous system, and patterned hyperpigmentation of the skin. Committed TRP-2 positive melanoblasts were found to be situated aberrantly within defined regions of the transgenic embryo, including the neural tube, which overproduced SF/RGF. Our data strongly suggest that SF/HGF possesses physiologically relevant scatter activity, and functions as a true morphogenetic factor by regulating migration and/or differentiation of select populations of premyogenic and neural crest cells during normal mammalian embryogenesis.

Hepatocyte growth factor and its receptor are expressed in cardiac myocytes during early cardiogenesis

In the mouse, the heart primordium arises when mesoderm is set aside during gastrulation, is induced by pharyngeal endoderm, migrates ventrally to the midline of the embryo, forms a tube, and begins beating. Little is known of the molecular mechanisms that mediate the determination, mitosis, differentiation, and migration that lead to the beating heart. Transcripts for hepatocyte growth factor/scatter factor (HGF) and its receptor are coexpressed transiently and dynamically in the premyocardium but not in other heart progenitor cells. Transcripts the HGF ligand and receptor are first detected before cardiac function and looping and persist through the first looping stage, when heart morphology begins to elaborate. HGF ligand and receptor mRNA are detectable after the putative heart transcription factor, Csx/Nkx2-5, and concomitantly with the heart structural gene, cardiac actin. HGF receptor mRNA is detected in the mesoderm of the headfold stage and persists in myocardial precursors of the ventricles and atria (but not in the outflow-tract smooth muscle cells) through the 14-somite stage at approximately 8.75 days after fertilization (day E8.75). At the headfold stage, between E7.5 and E8.0, HGF receptor mRNA was detected in myocardial cells before fusion at the ventral midline. HGF ligand and receptor mRNA transcripts are coexpressed in the embryo, except in the headfold state (when only the HGF receptor can be detected) and in the heart at the 14- to 18-somite stage (when only HGF ligand can be detected). The dynamic pattern of coexpression suggests an autoregulatory role for HGF and its receptor in early heart development.

Motogenic and morphogenic activity of epithelial receptor tyrosine kinases

Receptor tyrosine kinases play essential roles in morphogenesis and differentiation of epithelia. Here we examined various tyrosine kinase receptors, which are preferentially expressed in epithelia (c-met, c-ros, c-neu, and the keratin growth factor [KGF] receptor), for their capacity to induce cell motility and branching morphogenesis of epithelial cells. We exchanged the ligand-binding domain of these receptors by the ectodomain of trkA and could thus control signaling by the new ligand, NGF. We demonstrate here that the tyrosine kinases of c-met, c-ros, c-neu, the KGF receptor, and trkA, but not the insulin receptor, induced scattering and increased motility of kidney epithelial cells in tissue culture. Mutational analysis suggests that SHC binding is essential for scattering and increased cell motility induced by trkA. The induction of motility in epithelial cells is thus an important feature of various receptor tyrosine kinases, which in vivo play a role in embryogenesis and metastasis. In contrast, only the c-met receptor promoted branching morphogenesis of kidney epithelial cells in three-dimensional matrices, which resemble the formation of tubular epithelia in development. Interestingly, the ability of c-met to induce morphogenesis could be transferred to trkA, when in a novel receptor hybrid COOH-terminal sequences of c-met (including Y14 to Y16) were fused to the trkA kinase domain. These data demonstrate that tubulogenesis of epithelia is a restricted activity of tyrosine kinases, as yet only demonstrated for the c-met receptor. We predict the existence of specific substrates that mediate this morphogenesis signal.

Effects of hepatocyte growth factor (HGF) on human glioma cells in vitro: HGF acts as a motility factor in glioma cells

Expression of c-Met, the receptor for hepatocyte growth factor (HGF), and the biological roles of HGF were examined in cultured human glioma cells. All of the 5 glioma cell lines examined expressed c-Met protein as well as the c-met gene. Expression of the c-met gene was also confirmed in a glioblastoma tissue. Three cell lines (MGM-3, U251, KG-1-C) demonstrated chemotactic response to HGF in a dose-dependent manner. The response was not only chemotactic but also chemokinetic as judged by a checkerboard analysis. The amounts of c-Met mRNA and protein were abundant in the cell lines which showed a migratory response to HGF. Moreover, c-Met protein expression was highest in U251 with the highest migratory response to HGF. Among the cell lines, KG-1-C produced notable amounts of HGF protein as well as of c-Met, suggesting that HGF may act in an autocrine fashion in this case. HGF did not act as an apparent growth factor in the glioma cell lines examined. Furthermore, HGF stimulated the production of metalloproteinase, probably gelatinase A, in U251 cells.

Heparin induces dimerization and confers proliferative activity onto the hepatocyte growth factor antagonists NK1 and NK2

Hepatocyte growth factor (HGF) is a potent epithelial mitogen whose actions are mediated through its receptor, the proto-oncogene c-Met. Two truncated variants of HGF known as NK1 and NK2 have been reported to be competitive inhibitors of HGF binding to c-Met, and to function as HGF antagonists (Lokker, N.A., and P.J. Godowski. 1993. J. Biol. Chem. 268: 17145-17150; Chan, A.M., J.S. Rubin, D.P. Bottaro, D.W. Hirschfield, M. Chedid, and S.A. Aaronson. 1991. Science (Wash. DC). 254:1382-1387). We show here, however, that NK1 acts as a partial agonist in mink lung cells. Interestingly, NK1, which is an HGF antagonist in hepatocytes in normal conditions, was converted to a partial agonist by adding heparin to the culture medium. The interaction of NK1 and heparin was further studied in BaF3 cells, which express little or no cell surface heparan sulfate proteoglycans. In BaF3 cells transfected with a plasmid encoding human c-Met, heparin and NK1 synergized to stimulate DNA synthesis and cell proliferation. There was no effect of heparin on the IL-3 sensitivity of BaF3-hMet cells, and no effect of NK1 plus heparin in control BaF3 cells, indicating that the response was specific and mediated through c-Met. The naturally occurring HGF splice variant NK2 also stimulated DNA synthesis in mink lung cells and exerted a heparin-dependent effect on BaF3-hMet cells, but not on BaF3-neo cells. The activating effect of heparin was mimicked by a variety of sulfated glycosaminoglycans. Mechanistic studies revealed that heparin increased the binding of NK1 to BaF3-hMet cells, stabilized NK1, and induced dimerization of NK1. Based on these studies, we propose that the normal agonist activity of NK1 and NK2 in mink lung cells is due to an activating interaction with an endogenous glycosaminoglycan. Consistent with that model, a large portion of the NK1 binding to mink lung cells could be blocked by heparin. Moreover, a preparation of glycosaminoglycans from the surface of mink lung cells induced dimerization of NK1. These data show that the activity of NK1 and NK2 can be modulated by heparin and other related glycosaminoglycans to induce proliferation in cells expressing c-Met.

Pax3 modulates expression of the c-Met receptor during limb muscle development

Pax3 is a transcription factor whose expression has been used as a marker of myogenic precursor cells arising in the lateral somite destined to migrate to and populate the limb musculature. Accruing evidence indicates that the embryologic origins of axial and appendicular muscles are distinct, and limb muscle abnormalities in both mice and humans harboring Pax3 mutations support this distinction. The mechanisms by which Pax3 affects limb muscle development are unknown. The tyrosine kinase receptor for hepatocyte growth factor/scatter factor encoded by the c-met protooncogene is also expressed in limb muscle progenitors and, like Pax-3, is required in the mouse for limb muscle development. Here, we show that c-met expression is markedly reduced in the lateral dermomyotome of Splotch embryos lacking Pax3. We show that Pax3 can stimulate c-met expression in cultured cells, and we identify a potential Pax3 binding site in the human c-MET promoter that may contribute to direct transcriptional regulation. In addition, we have found that several cell lines derived from patients with rhabdomyosarcomas caused by a t(2;13) chromosomal translocation activating PAX3 express c-MET, whereas those rhabdomyosarcoma cell lines examined without the translocation do not. These results are consistent with a model in which Pax3 modulates c-met expression in the lateral dermomyotome, a function that is required for the appropriate migration of these myogenic precursors to the limb where the ligand for c-met (hepatocyte growth factor/scatter factor) is expressed at high levels.

Hepatocyte growth factor is involved in the morphogenesis of tooth germ in murine molars

The patterns of gene expression for hepatocyte growth factor (HGF) and its receptor, c-Met, were revealed in the tooth germ of rat mandibular molars using RT-PCR. In situ hybridization demonstrated that the HGF gene was expressed only in the cells of the dental papilla of the tooth germ in vivo. The characteristic temporospatial distribution of HGF and c-Met during germ development was revealed using immunohistochemical studies in vivo. In order to demonstrate the functional role played by HGF in tooth development, HGF translation arrest by antisense phosphorothioate oligodeoxynucleotide (ODN) was carried out in vitro. In the control experiment, explants of tooth germs from embryonic 14 day mice were cultured in a modification of Trowell's system under serum-free and chemically defined conditions for two weeks. Other explants were cultured with 15mer antisense or sense ODN targeted to the HGF mRNA. Both the control and the sense-treated explants showed normal histological structure, as observed in vivo. On the other hand, antisense-treated explants exhibited an abnormal structure in which the enamel organs were surrounded by a thin layer of dentin and dental papilla, appearing ‘inside-out’ compared to the control and sense-treated explants, although the cytodifferentiation of ameloblasts and odontoblasts was not inhibited. The explants treated with recombinant human HGF combined with antisense ODN showed normal development, indicating that exogenous HGF rescued the explants from the abnormal structure caused by antisense ODN. The findings of a BrdU incorporation experiment suggested that the imbalance between the proliferation activity of the inner enamel epithelium and that of the dental papilla caused by HGF translation arrest results in the abnormal structure of the tooth germ. These results indicate that HGF is involved in the morphogenesis of the murine molar.

Enhanced tumorigenicity and invasion-metastasis by hepatocyte growth factor/scatter factor-met signalling in human cells concomitant with induction of the urokinase proteolysis network

Hepatocyte growth factor/scatter factor (HGF/SF) is a pleiotropic effector of cells expressing the Met tyrosine kinase receptor. Although HGF/SF is synthesized by mesenchymal cells and acts predominantly on epithelial cells, we have recently demonstrated that human sarcoma cell lines often inappropriately express high levels of Met and respond mitogenically to HGF/SF. In the present report we show that HGF/SF-Met signalling in the human leiomyosarcoma cell line SK-LMS-1 enhances its in vivo tumorigenicity, an effect for which the mitogenicity of this signalling pathway is likely to play a role. In addition, we found that HGF/SF-Met signalling dramatically induces the in vitro invasiveness and in vivo metastatic potential of these cells. We have studied the molecular basis by which HGFSF-Met signalling mediates the invasive phenotype. A strong correlation has previously been demonstrated between the activation of the urokinase plasminogen activator (uPA) proteolysis network and the acquisition of the invasive-metastatic phenotype, and we show here that HGF/SF-Met signalling significantly increases the protein levels of both uPA and its cellular receptor in SK-LMS-1 cells. This results in elevated levels of cell-associated uPA and enhanced plasmin-generating ability by these cells. These studies couple HGF/SF-Met signalling to the activation of proteases that mediate dissolution of the extracellular matrix-basement membrane, and important property for cellular invasion-metastasis.

Relationship of hepatocyte growth factor in human umbilical vein serum to gestational age in normal pregnancies

Hepatocyte growth factor (HGF) is expressed in placental syncitium and fetal organs and acts as a mitogen, motogen, and morphogen in vitro, suggesting a role in fetal growth and development. We aimed to examine the correlates of serum HGF in human cord blood. HGF was measured by ELISA using recombinant human HGF and mouse MAb to recombinant human HGF (Immunology Institute, Tokyo). Umbilical vein blood was collected prospectively at 148 deliveries including 94 normal pregnancies and 54 pregnancies complicated by medical conditions, primarily diabetes mellitus and pregnancy-induced hypertension. Growth parameters, gestation, pregnancy history, and perinatal events were recorded. Sera from 54 adolescents and 32 adult controls were also analyzed. Cord HGF [0.97 (0.66-1.33) ng/mL] [median (25-75 percentile)] was higher than HGF levels in adolescent sera [0.28 (0.21-0.35) ng/mL, p < 0.0001] and adult control sera [0.23 (0.14-0.31) ng/mL, p < 0.0001]. Cord HGF correlated with gestational age (r = 0.42, p = 0.0001) in normal pregnancies, with term babies (n = 69) having higher cord HGF than babies less than 37 wk of gestation (n = 25) [1.11 (0.78-1.45), 0.78 (0.46-1.03) ng/mL, p = 0.0007]. However, there was no relationship between gestation and cord HGF in complicated pregnancies. Cord HGF did not differ at term between appropriate for gestational age babies and small for gestational age babies. There were no independent correlations between cord HGF and birth weight, birth length and placental weight. We provide evidence for the first time that cord HGF levels are high and relate to gestation in normal pregnancies. HGF may have a significant role in fetal development during pregnancy.

Pax-3 is necessary for migration but not differentiation of limb muscle precursors in the mouse

The limb muscles of vertebrates are derived from precursor cells that migrate from the lateral edge of the dermomyotome into the limb bud. Previous studies have shown that the paired domain-containing transcription factor Pax-3 is expressed in the limb in cells that are precursors for limb muscles (Williams, B. and Ordahl, C.P. (1994) Development 120, 785–796). In splotch (Pax-3-) embryos, the limb muscles fail to develop and cells expressing Pax-3 are no longer found in the limb. In this paper we have analyzed the role of Pax-3 in the migration and subsequent differentiation of limb muscle precursors. By labeling somites adjacent to the prospective forelimb with the lipophilic dye DiI, we have shown that cells derived from these somites do not migrate into the limbs of splotch mice. The failure of limb muscle precursors to invade the limb in splotch mice is associated with the absence of c-met expression in premigratory cells, together with a change in the morphology of the ventral dermomyotome. In addition, we have shown the lateral half of somites derived from day E9.25 splotch embryos can undergo muscle differentiation when grafted into the limb bud stage 20 chick host embryos. Our results indicate that Pax-3 regulates the migration of limb muscle precursors into the limb and is not required for cells in the lateral somite to differentiate into muscle.

Neurotrophic effect of hepatocyte growth factor on central nervous system neurons in vitro

Although the expression of hepatocyte growth factor (HGF) and its receptor, proto-oncogene c-met, has been demonstrated in the central nervous system (CNS), the function of HGF in the CNS was not fully understood. In the present studies, we determined the effects of HGF on neuronal development in neocortical explant and mesencephalic neurons obtained from embryonic rat brain. HGF clearly enhanced neurite outgrowth in neocortical explants. In the mesencephalic culture, the number of tyrosine hydroxylase (TH)-positive neurons was significantly higher in the HGF-treated wells and the neurites of the TH-positive neurons appear to be more developed. Moreover, the dopamine uptake into mesencephalic neurons was also enhanced by HGF treatment, indicating that HGF promotes the survival and/or maturation of mesencephalic dopaminergic neurons. In both neocortical explants and mesencephalic neurons, c-met autophosphorylation was induced by HGF and MAP kinase activation was also detected in the neocortical explant. Furthermore, Western blot analysis of the cultured CNS cells revealed that HGF was expressed mainly in microglia. These results suggest that HGF from microglia has neurotrophic activity on the CNS neurons and plays significant roles in the development of the CNS.

Hepatocyte growth factor releases epithelial and endothelial cells from growth arrest induced by transforming growth factor-beta1

Human lung fibroblasts and Mv1Lu mink lung epithelial cells were used as a model to study the role of extracellular matrix in epithelial-mesenchymal interactions. Extracellular matrices of fibroblasts were found to contain growth promoting activity that reduced the sensitivity of Mv1Lu cells to the growth inhibitory effects of transforming growth factor-beta (TGF-beta). The majority of the activity was identified as hepatocyte growth factor/scatter factor (HGF) by inhibition with specific antibodies and by reconstitution of the effect by recombinant HGF. HGF induced cell proliferation when contact-inhibited Mv1Lu cells were trypsinized and plated in the presence of TGF-beta1. The effect was valid also in assays where Madin-Darby canine kidney epithelial cells or bovine capillary endothelial cells were used. The multiplication of chronically TGF-beta1 inhibited Mv1Lu cells was also induced by HGF. In addition, HGF induced anchorage independent growth of Mv1Lu cells that was refractory to TGF-beta1 growth inhibition. Immunoprecipitation analysis indicated that HGF prevented the suppression of Cdk4 and Cdk2, but not the induction of p21, by TGF-beta1. Since both TGF-beta1 and HGF require proteolysis for activation, the results imply that proteolytic activity of epithelial and endothelial cells directs their responses to signals from mesenchymal-type extracellular matrices, and that during development, matrix-bound growth and invasion promoting and suppressing factors are activated in a coordinated manner.

Hepatocyte growth factor/scatter factor expression and c-met in primary breast cancer

Hepatocyte growth factor/scatter factor (HGF/SF) is a fibroblast-derived cytokine whose receptor is encoded by c-met. Activation of c-met promotes tumour cell proliferation, dissociation, invasiveness and angiogenesis. Aberrant expression of HGF/SF or c-met may play a role in tumour progression. HGF/SF and c-met were determined in 73 breast cancers (median follow up: 61 months) and 10 samples of tumour-free breast tissue. HGF/SF was detected at significantly higher concentrations in breast cancers (median 350, range 58-1604 ng per 100 mg total protein) when compared with normal breast tissue (median 108, range 66-213 ng per 100 mg total protein) (P < 0.001). C-met was detected in all 10 samples of tumour-free breast tissue and in 26 breast cancers. HGF/SF concentrations correlated with disease relapse (P < 0.001) and reduced overall survival (P < 0.001). Tumours with detectable c-met correlated significantly with disease-relapse (P = 0.012). Multivariate analysis demonstrated a significant interaction between HGF/SF and c-met in relation to disease-relapse (P = 0.014). These results suggest a biological interaction involving HGF/SF and c-met in promoting tumour progression in breast cancer.

Hepatocyte growth factor/scatter factor is present in most pleural effusion fluids from cancer patients

Pleural effusion samples were obtained from 55 patients with malignant disease, including patients with primary lung cancers and those with a variety of other tumours metastatic to the pleura. The effusions were assayed for the presence of hepatocyte growth factor/scatter factor (HGF/SF), by both ELISA and bioassay. The presence of malignant cells in the effusions was also assessed. Detectable amounts of the factor, as judged by both criteria, were found in over 90% of all the effusions, including those from patients with a wide variety of carcinomas and also lymphomas. A wide range of HGF/SF levels were found for all tumour classes, some effusions containing high levels above 4 ng ml-1. It is concluded that tumours within the pleura and adjacent lung tissue are usually exposed to biologically significant levels of HGF/SF.

Anti-invasion drugs

Most of the pharmaceuticals in clinical practice today for treatment of breast and other cancers are cytotoxic or cytostatic inhibitors of tumor growth. While this type of drug has found its place, along with surgery and radiotherapy, in treatment of disease, the breast cancer death rate has not decreased. This appears to be the result of rising incidence, resistance to therapy, and metastasis of the disease. Since distant metastasis (usually indicated by lymph node involvement) of breast cancer is related only indirectly to tumor size, it would appear that a concerted effort should be made to discover drugs which directly interfere with this complex process. Metastasis appears to depend upon tumor cell motility, dedifferentiation, local invasion, and angiogenesis. Significant progress has been recently made in the creation of new animal models of metastasis and in identifying several new drugs which may be suitable for clinical inhibition of this process. This article reviews current findings on anti-invasion/metastasis drugs with a focus on breast cancer.

Co-expression of the HGF/SF and c-met genes during early mouse embryogenesis precedes reciprocal expression in adjacent tissues during organogenesis

Early experiments with cells in culture and recent targeting experiments have confirmed that the mesenchyme-derived growth factor hepatocyte growth factor/scatter factor (HGF/SF) is a paracrine agent that regulates the development of several epithelial and myogenic precursor cells during organogenesis. Here, we report the expression pattern of HGF/SF and its receptor, the product of the proto-oncogene c-met, during gastrulation and early organogenesis in mouse embryo. During gastrulation, the expression of HGF/SF and c-met overlaps. Initially the two genes are expressed in the endoderm and in the mesoderm along the rostro-intermediate part of the primitive streak and, later, in the node and in the notochord. Neither HGF/SF nor c-met is expressed in the ectodermal layer throughout gastrulation. During early organogenesis, overlapping expression of HGF/SF and c-met is found in heart, condensing somites and neural crest cells. However, a second and distinct pattern of expression, characterized by the presence of the ligand in mesenchymal tissues and the receptor in the surrounding ectoderm, is seen in the bronchial arches and in the limb buds. At 13 days postcoitum (d.p.c.), only this second pattern of expression is observed in differentiated somites and several major organs (i.e., lungs, liver, and gut). The expression of the HGF/SF and c-met genes throughout embryogenesis suggests a shift from an autocrine to a paracrine signaling system. The shift takes place in early organogenesis and implies different roles of HGF/SF in development. During gastrulation, HGF/SF may affect the fate of migrating mesodermal cells and may play a role in axis determination, whereas during organogenesis, the expression patterns of HGF/SF and its receptor reflect the recently established roles in the growth of certain epithelia and the migration of specific myogenic precursor cells.

Analysis of the structure and expression of the augmenter of liver regeneration (ALR) gene

BACKGROUND

The gene encoding the hepatotrophic factor Augmenter of Liver Regeneration (ALR) has recently been cloned in the rat. The availability of the mouse form of ALR would allow the analysis of the role of this factor in the physiology of liver and other organs, while the identification of the human homolog would allow the transfer of the great wealth of information that has been generated in animal models to clinically oriented pilot trials, and eventually the therapeutic application of this information.

MATERIALS AND METHODS

Standard molecular biology approaches have been used to determine the genomic structure of the ALR gene in the mouse, and to characterize the ALR transcript and its protein product. The human ALR cDNA was also isolated and the amino acid sequence of the human gene product deduced. The mapping of mouse and human ALR genes on mouse and human chromosomes was then completed.

RESULTS

The protein coding portion of the mouse ALR gene is comprised of three exons, the first containing the 5' untranslated sequence and the initial 18 bases after the ATG translation initiation codon, the second exon encompasses 198 bases, and the third exon contains the remaining portion of the protein coding sequence. Rat, mouse, and human ALR genes (and protein products) were found to be highly conserved and preferentially expressed in the testis and in the liver. The ALR gene maps to the mouse chromosome 17, in a region syntenic with human chromosome 16, where the T/t region has also been mapped.

CONCLUSIONS

ALR appears to be a protein with important physiologic properties, not exclusively limited to liver regeneration, with roles that are involved in the synthesis or stability of the nuclear and mitochondrial transcripts that are present in actively regenerating cells, particularly the germ cells of the testes.

Microtubule dynamic turnover is suppressed during polarization and stimulated in hepatocyte growth factor scattered Madin-Darby canine kidney epithelial cells

The dynamic behavior of microtubules has been measured in non-polarized, polarized, and hepatocyte growth factor treated Madin-Darby canine kidney epithelial cells. In a nocodazole disassembly assay, microtubules in polarized cells were more resistant to depolymerization than microtubules in non-polarized cells; microtubules in scattered cells were nearly completely disassembled. Analysis of fluorescent microtubules in living cells further revealed that individual microtubules in polarized cells were kinetically stabilized and microtubules in scattered cells were highly dynamic. Individual microtubule behavior in polarized cells was characterized by a suppression of the average rate of shortening, an increase in the average duration of pause, a decrease in the frequency of catastrophe transitions, and an increase in the frequency of rescue transitions, when compared with microtubules in non-polarized cells. In contrast, microtubule behavior in epithelial cells treated with hepatocyte growth factor was characterized by increase in the average rates of microtubule growth and shortening, a decrease in the frequency of rescue transitions, and an increase in the frequency of catastrophe transitions, when compared with polarized cells. Dynamicity, a measure of the gain and loss of subunits from microtubule plus ends, was 2.7 microns/min in polarized cells and 11.1 microns/min in scattered cells. These results demonstrate that individual microtubule dynamic behavior is markedly suppressed in polarized epithelial cells. Our results further demonstrate that in addition to its previously characterized effects on cell locomotion, hepatocyte growth factor stimulates microtubule dynamic turnover in lamellar regions of living cells.

Regulation and clinical implications of corneal epithelial stem cells

The corneal epithelium is known to have a rapid self-renewing capacity. The major advance in the field of corneal epithelial cell biology in the last decade is the establishment of the location of corneal epithelial stem cells at the limbus, i.e., the junctional zone between the cornea and the conjunctiva. This concept has helped explain several experimental and clinical paradoxes, produced a number of important clinical applications, and spawned many other research studies. This unique enrichment of epithelial stem cells at a site anatomically separated from their transient amplifying cells makes the ocular surface an ideal model to study the regulation of epithelial stem cells. The present review includes data from more recent studies and lays out other areas for future investigation, especially with respect to the role of apoptosis and cytokine dialogue between limbal epithelial stem cells and their stromal microenvironment.

Localisation of hepatocyte growth factor and its receptor (c-met) protein and mRNA in human term placenta

Successful pregnancy depends upon placental growth and development, which follows a specific spatial and temporal sequence. Hepatocyte Growth Factor (HGF) is a potent mitogen, morphogen and motogen to both endothelial and epithelial cell types and is linked to a tyrosine kinase, proto-oncogene, c-met receptor. In 'normal' third trimester placentae (n = 5) full thickness biopsies (obtained at Caesarean section), immunolocalisation and in situ hybridisation studies were performed for HGF and c-met., respectively. HGF immunoreactive protein was present in mesenchymal core, the vaculosyncytial membrane (syncytotrophoblast) and the vascular endothelial cells of villous trophoblast. The HGF mRNA was present particularly strongly in the perivascular stromal cells surrounding the villous vasculature and the amnion/chorionic membranes. Immunoreactive c-met protein was strongly localised to the endothelial cells lining the villous vasculature and the vasculosyncytial membrane. A relatively weak and diffuse hybridisation signal for c-met mRNA was present throughout the villous trophoblast, most pronounced in the vasculosyncytial membrane. These results indicate that HGF may serve as a paracrine mediator to control placental development and growth.

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

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

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

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

Restricted expression of the ron gene encoding the macrophage stimulating protein receptor during mouse development

The human ron gene codes for a transmembrane protein tyrosine kinase which is a receptor for the macrophage stimulating protein. The ron receptor, together with the hepatocyte growth factor/scatter factor receptor encoded by the proto-oncogene met, and the product of the c-sea proto-oncogene, make up a family of structurally related receptors. We have cloned murine ron cDNA sequences and used them as probes for in situ hybridization and Northern blot experiments. We show that ron gene expression occurs relatively late in development, and is much more restricted than that of the met gene. ron gene expression is detected in specific areas of the central and the peripheric nervous system, as well as in discrete cells in developing bones, and in the glandular epithelia along the digestive tract.

Hepatocyte growth factor activates quiescent skeletal muscle satellite cells in vitro

The effect of hepatocyte growth factor (HGF) on the activation of quiescent rat skeletal muscle satellite cells was evaluated in vitro. Satellite cells from 9-month-old adult rats are quiescent in vivo and when cultured, display a protracted lag phase prior to division that is not present in satellite cells from neonatal or regenerating muscle. Under normal growth conditions, satellite cells divide for the first time between 42 and 60 hr. Hepatocyte growth factor increased proliferation in a dose-dependent fashion prior to 48 hr with half-maximal stimulation at approximately 3 ng/ml; in addition, heparin enhanced this activity. The time course of cyclin-D1 and proliferating cell nuclear antigen (PCNA) expression was accelerated in HGF-treated satellite cells, indicating that cells entered the cell cycle earlier. No significant effects on muscle-derived fibroblast proliferation was observed. The signalling receptor for HGF is the product of the c-met protooncogene, and rtPCR analysis of satellite cells 0-72 hr in culture demonstrated the presence of this message throughout this time period. The presence of c-met in quiescent satellite cells, the ability of HGF to stimulate precocious entry into the cell cycle, and the previously described localization of HGF message in regenerating muscle (Jennische et al., 1993) indicate that HGF could act as an activator of quiescent satellite cells in vivo.

Cloning of mouse c-ros renal cDNA, its role in development and relationship to extracellular matrix glycoproteins

Renal organogenesis ensues following reciprocal interactions between the uninduced metanephric mesenchyme and the ureteric bud. Conceivably, the presence of ligands or growth factors on a given cell type, and expression of receptors, including receptor proto-oncogenes, on the other cell type of different lineage would facilitate such epithelial-mesenchymal interactions. During these interactions, other macromolecules, such as extracellular matrix (ECM) proteins, present at the epithelial-mesenchymal surface, also play a role in the kidney morphogenesis. In this study the proto-oncogene, c-ros, was cloned and sequenced; its role in the metanephric development was examined, and correlated with the changes in the expression of ECM proteins. The mouse c-ros renal cDNA, belonging to phosphotyrosine kinase (PTK) receptor family, had a translation product of 2340 amino acids. The extracellular domain had 32 N-linked glycosylation sites and 30 cysteine residues. The transmembrane segment had a hydrophobicity approaching approximately 3.5. Multiple phosphorylation sites, typical of a PTK catalytic unit, were present in the cytoplasmic domain. The 3' noncoding region did not contain any A(U)nA mRNA instability motifs. The c-ros mRNA was highly expressed on the ureteric bud branches and their tips and on the developing glomeruli. Competitive RT-PCR analyses revealed the c-ros expression was the highest at 13th day of gestation, and it declined to very low levels during the neonatal period. Exposure of metanephric kidneys to c-ros antisense-oligonucleotide, derived from the PTK domain, caused dysmorphogenesis of the kidney and loss of c-ros expression on the ureteric bud branches. Concomitant with the reduced c-ros gene expression, a decreased expression of ECM glycoproteins, in particular the proteoglycans, was observed. These findings suggest that the c-ros plays a role in the metanephric development, and its effects may be modulated by the ECM macromolecules present at the epithelial-mesenchymal interface.

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

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

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

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

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

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

Growth factor regulation of integrin-mediated cell motility

Cell motility, a primary component of tumor cell invasion, is a continuum of sequential events in which the cell extends pseudopodia, forms nascent attachments, assembles and contracts the cytoskeleton, and finally, as it translocates forward, disengages distal adhesions. What triggers cells to move? Substratum contact mediated by integrin adhesion receptors is important, but other signals such as chemokinetic factors appear to be required for continued crawling. It is now apparent that integrins do not simply bind cells to matrix in a Velcro-like fashion, but also are potent signaling molecules. Initial engagement of integrins induces their condensation into focal contacts, forming anchors to the extracellular matrix and discrete signal-transducing complexes on the cytoplasmic surface. A number of growth factors, through either autocrine or paracrine pathways, can activate the cellular machinery that mobilizes the cell. Thus, these two classes of receptors--the integrin receptors that bind specific extracellular adhesion molecules, and growth factor receptors that bind their respective ligands--can regulate cell locomotion. Not surprisingly, there is 'cross-talk' between integrin and growth factor receptors that occurs through their common intracellular signaling pathways. In this way, each receptor type can either amplify or attenuate the other's signal and downstream response. An example of growth factor-induced motility is the epithelial-mesenchymal transition induced by hepatocyte growth factor/scatter factor (HGF/SF). When bound to its receptor, the c-met proto-oncogene product, HGF/SF induces a phenotypic conversion that appears to be an important aspect of tumor progression in malignant carcinomas. The motogenic response produced by HGF/SF in carcinoma cells occurs in discrete steps in which integrins and focal adhesion kinase (p125FAK) are first recruited to focal contacts. This is rapidly followed by cell spreading, disruption of focal adhesions and cell-cell contacts, and, finally, cell crawling. The precise mechanism by which growth factors such as HGF/SF and its receptor induce this motogenic response and modulate integrin function has not been clearly defined but appears to involve several signaling pathways. Understanding the process by which growth factor and integrin receptors interact and regulate motility may suggest novel targets for therapeutic intervention.

Levels of hepatocyte growth factor in maternal serum and amniotic fluid

OBJECTIVE

The purpose of our study was to investigate hepatocyte growth factor levels in maternal serum and amniotic fluid during pregnancy. We also demonstrated production and secretion of hepatocyte growth factor by placenta and amnion at different stages of gestation.

STUDY DESIGN

Hepatocyte growth factor levels in maternal serum (n = 219), cord blood (n = 20), and amniotic fluid samples (n = 90) were measured by an enzyme-linked immunosorbent assay. The secretion of hepatocyte growth factor by placenta and amnion was evaluated by measuring the amount released into the culture supernatant.

RESULTS

Most hepatocyte growth factor levels in maternal serum were below the detection limit before 10 weeks of pregnancy. Levels increased significantly thereafter and continued to increase until term. On the other hand, levels in amniotic fluid were significantly higher between 20 and 29 weeks of gestation than after 30 weeks. Hepatocyte growth factor secretion from the placental tissue per weight seemed unchanged throughout pregnancy. Its secretion from amnion was, however, approximately 300 to 400-fold higher in the second trimester compared with that at term.

CONCLUSION

Both placenta and amnion produce and secrete hepatocyte growth factor, suggesting its role in fetal growth and the growth and differentiation of placenta.

Epithelial-mesenchymal conversion of dermatome progenitors requires neural tube-derived signals: characterization of the role of Neurotrophin-3

Development of the somite-derived dermatome involves conversion of the epithelial dermatome progenitors into mesenchymal cells of the dermis. In chick embryos, neural tube-derived signals are required for this conversion, as the interposition of a membrane between neural tube and somites results in a failure of the dermatome to lose its epithelial arrangement. However, dermis formation can be completely rescued by coating the membranes with Neurotrophin-3, but not with the related molecule Nerve growth factor. Neurotrophin-3 was also found to be necessary for dermatome dissociation using in vitro explants or partially dissociated dermomyotomes. The functional relevance of these observations was investigated by neutralizing endogenous Neurotrophin-3 using a specific blocking antibody. Antibody-treated embryos revealed the presence of tightly aggregated cells between myotome and ectoderm instead of the loose dermal mesenchyme observed in embryos treated with control antibodies. As previous studies have demonstrated the presence of Neurotrophin-3 in the neural tube, these results suggest that it may be a necessary neural tube-derived signal required for early stages of dermis formation.

Evidence for a role of protein phosphatases 1 and 2A during early nephrogenesis

Although most transcriptional events appear to be modulated by reversible protein phosphorylation, little is known about the role of this regulatory system during the development of mammalian organs. Here we have studied the serine/threonine protein phosphatases (PP) 1 and 2A in the early embryonic rat kidney with regard to expression and effects on growth and differentiation. All isoforms of PP-1 and PP-2A were ubiquitously expressed in 15-day embryonic (E15) kidneys (in situ hybridization studies). In contrast, mRNA for inhibitor-1 (I-1), an endogenous inhibitor of PP-1, was detected only in undifferentiated stem cells in the outer cortical area. I-1 is a novel marker for these cells. The abundance of the PP-1 protein, confirmed with immunoblotting, was high in the embryonic kidney. In organ culture of E13 kidneys, okadaic acid (OA), an exogenous inhibitor of PP-1 and PP-2A, dose-dependently inhibited growth and nephron formation (apparent half-maximal effect at 6 nM). OA 10 nM had little effect on the growth of cultured E15 kidneys, whereas nephron formation was disturbed and morphological evidence of apoptosis was seen. In summary, this study points towards important roles for protein phosphatases 1 and/or 2A in regulation of mitogenic activity in the early embryonic kidney.

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

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

Basic fibroblast growth factor can mediate the early inductive events in renal development

The earliest characterized events during induction of tubulogenesis in renal anlage include the condensation or compaction of metanephrogenic mesenchyme with the concurrent upregulation of WT1, the gene encoding the Wilms tumor transcriptional activator/suppressor. We report that basic fibroblast growth factor (FGF2) can mimic the early effects of an inductor tissue by promoting the condensation of mesenchyme and inhibiting the tissue degeneration associated with the absence of an inductor tissue. By in situ hybridization, FGF2 was also found to mediate the transcriptional activation of WT1 and of the hepatocyte growth factor receptor gene, c-met. Although FGF2 can induce these early events of renal tubulogenesis, it cannot promote the epithelial conversion associated with tubule formation in metanephrogenic mesenchyme. For this, an undefined factor(s) from pituitary extract in combination with FGF2 can cause tubule formation in uninduced mesenchyme. These findings support the concept that induction in kidney is a multiphasic process that is mediated by more than a single comprehensive inductive factor and that soluble molecules can mimic these inductive activities in isolated uninduced metanephrogenic mesenchyme.

Differential tubulogenic and branching morphogenetic activities of growth factors: implications for epithelial tissue development

At least two kidney epithelial cell lines, the Madin-Darby canine kidney (MDCK) and the murine inner medullary collecting duct line mIMCD-3, can be induced to form branching tubular structures when cultured with hepatocyte growth factor (HGF) plus serum in collagen I gels. In our studies, whereas MDCK cells remained unable to form tubules in the presence of serum alone, mIMCD-3 cells formed impressive branching tubular structures with apparent lumens, suggesting the existence of specific factors in serum that are tubulogenic for mIMCD-3 cells but not for MDCK cells. Since normal serum does not contain enough HGF to induce tubulogenesis, these factors appeared to be substances other than HGF. This was also suggested by another observation: when MDCK cells or mIMCD-3 cells were cocultured under serum-free conditions with the embryonic kidney, both cell types formed branching tubular structures similar to those induced by HGF; however, only in the case of MDCK cells could this be inhibited by neutralizing antibodies against HGF. Thus, the embryonic kidney produces growth factors other than HGF capable of inducing tubule formation in the mIMCD-3 cells. Of a number of growth factors examined, transforming growth factor alpha (TGF-alpha) and epidermal growth factor (EGF) were found to be tubulogenic for mIMCD-3 cells. Whereas only HGF was a potent tubulogenic factor for MDCK cells, HGF, TGF-alpha, and EGF were potent tubulogenic factors for mIMCD-3 cells. Nevertheless, there were marked differences in the capacity of these tubulogenic factors to induce tubulation as well as branching events in those tubules that did form (HGF >> TGF-alpha > EGF). Thus, at least three different growth factors can induce tubulogenesis and branching in a specific epithelial cell in vitro (though to different degrees), and different epithelial cells that are capable of forming branching tubular structures demonstrate vastly different responses to tubulogenic growth factors. The results are discussed in the context of branching morphogenesis during epithelial tissue development.

Keratinocyte growth factor is a bifunctional regulator of HPV16 DNA-immortalized cervical epithelial cells

Various factors are known to regulate cell growth and differentiation in epithelial-mesenchymal interactions. Keratinocyte growth factor (KGF), an epithelial-specific cytokine produced by dermal fibroblasts and other mesenchymal cells, appears to affect growth, migration, and differentiation in epithelial-mesenchymal interactions. We have previously shown that human embryonic skin fibroblasts induce anchorage-independent growth of HPV16 DNA-immortalized human uterine exocervical epithelial cells (HCE16/3 cell line) in cocultures of HCE16/3 cells and fibroblasts. Here we report that KGF may be a major factor influencing growth and behavior of HCE16/3 cells in the coculture system. KGF stimulated both DNA synthesis and proliferation of normal human cervical epithelial (HCE) cells and HCE16/3 cells and the increase was stronger in HCE16/3 cells than in HCE cells. SiHa cells, a cervical carcinoma cell line with integrated HPV16 DNA, did not respond to the KGF mitogen signal. KGF receptor (KGFR) studies suggested that the different responses to the KGF mitogen signal may be correlated with KGFR. In addition, KGF alone was able to induce anchorage-independent growth of HCE16/3 cells, suggesting a potential role for KGF in the transformation process of epithelial cells. However, the transcription of HPV16 early genes was suppressed by KGF in the immortalized HCE16/3 cells, and this appeared to be due to transcriptional repression rather than a posttranscriptional process according to nuclear run-on analysis. In contrast, viral gene expression was not affected by KGF in SiHa cells. Our results suggest that KGF is a bifunctional growth factor in the HPV-immortalized cells, a positive regulator of cell growth and negative regulator of HPV16 early gene expression.

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

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

Hepatocyte growth factor remains as an inactive single chain after partial hepatectomy or unilateral nephrectomy

Hepatocyte growth factor (HGF) is a potent mitogen for hepatocytes and renal tubular epithelial cells. HGF is proteolytically activated in the tissue injured by hepatotoxin or nephrotoxin, suggesting that HGF functions as a crucial growth factor for tissue regeneration following hepatotoxin- or nephrotoxin-induced injury. In this study, we analyzed the molecular form of HGF after partial hepatectomy or after unilateral nephrectomy. The active form of HGF was not detected under our experimental conditions after these operations. Thus, HGF may play little role in liver regeneration after partial hepatectomy and in compensatory renal enlargement after unilateral nephrectomy.