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

Measurement of hepatocyte growth factor in serum and plasma

To investigate whether serum or plasma should be used for the measurement of blood hepatocyte growth factor, the levels were compared in 28 normal subjects and 30 patients who had undergone surgery. The serum level was significantly higher than the plasma level. The serum and plasma hepatocyte growth factor levels differed markedly depending on the subjects, although overall there was a significant correlation between levels (r=0.862, P=0.0001). In serum obtained by the clotting of platelet- or leukocyte-containing plasma with thrombin, hepatocyte growth factor increased in proportion to the number of leukocytes. The difference between serum and plasma hepatocyte growth factor levels also correlated with the number of leukocytes in the patients (r=0.642, P=0.0004). Such a correlation was not observed for platelets. These findings suggest that the serum hepatocyte growth factor level does not strictly reflect the in vivo blood level, due to the release from leukocytes during sample preparation (i.e., blood clotting ) and that plasma is more suitable for assay of blood hepatocyte growth factor.

Enhancement by hepatocyte growth factor of bone and cartilage formation during embryonic mouse mandibular development in vitro

To elucidate the possible roles of hepatocyte growth factor (HGF) in the early development of mouse mandible, HGF was applied to an organ-culture system with chemically defined media. Mandibular arches microdissected from mouse embryos at the 10th day of gestation were cultured for 10 days with or without HGF, HGF plus HGF-receptor (c-met) antisense oligodeoxyribonucleotide, or HGF plus c-met sense oligodeoxyribonucleotide in the media. The cultured mandibles were then analysed, histologically in serial paraffin sections. In the absence of HGF, the tooth organs of bud stage, Meckel's cartilage and the tongue were formed, whereas only a slight amount of bone tissue was formed in the cultured mandible. The expression of intrinsic HGF and c-met in the cultured mandibles was confirmed by reverse transcriptase-polymerase chain reaction. Furthermore, immunohistochemistry demonstrated that both HGF and c-met were localized in areas of the mesenchymal tissue forming bone and cartilage. With HGF in the medium, the volume of both bone and cartilage increased significantly and dose-dependently. HGF also increased the rate of proliferation of osteogenic cells and chondrocytes. Addition of c-met antisense oligodeoxyribonucleotide partially inhibited the HGF-induced enhancement of bone and cartilage formation, whereas addition of c-met sense oligodeoxyribonucleotide had no effect. These results revealed that exogenous HGF enhances bone and cartilage morphogenesis in the cultured mandibles, suggesting physiological roles for intrinsic HGF in the early development of mouse mandible.

Stimulation of DNA synthesis in trophoblasts and human umbilical vein endothelial cells by hepatocyte growth factor bound to extracellular matrix

Hepatocyte growth factor (HGF) promotes the growth not only of hepatocytes but also of several other types of cells such as cytotrophoblasts and endothelial cells. Recent studies have revealed that HGF is trapped in the extracellular (ECM) matrix through heparan sulphate in vivo, thereby acting as a mitogen for hepatocytes in cooperation with heparan sulphate. In this study, we detected HGF protein in chorionic tissue and placental tissue extracts, and found that HGF and heparan sulphate were co-distributed in the endothelial basement membrane and trophoblast basement membrane on immunohistochemical examination. The rates of DNA synthesis in primary cultured cytotrophoblasts and human umbilical vein endothelial cells (HUVEC) cultured on HGF-bound Matrigeltrade mark were 6-8 times those of control cytotrophoblasts and HUVEC. When Matrigeltrade mark dishes were pretreated with heparinase and heparitinase prior to binding of HGF, stimulation of DNA synthesis was markedly decreased. A considerable decrease in stimulation of DNA synthesis was observed following washing of HGF-bound Matrigeltrade mark with 1 m acetic acid, 1 m NaCl and 0.1 per cent trypsin, but not following treatment with chondroitinase ABC. These observations suggest that HGF can be trapped in ECM in vivo, thereby acting as a mitogen for cytotrophoblasts and placental vein endothelial cells in cooperation with heparan sulphate.

Hepatocyte growth factor in human osteoarthritic cartilage

OBJECTIVE

Hepatocyte growth factor/scatter factor is a potent mitogen, morphogen and motogen for a variety of mainly epithelial cells. Hepatocyte growth factor is synthesized by mesenchymal cells and can be found in various tissues. The objective of this study was to investigate the expression and distribution patterns of this pleiotropic growth factor and its receptor, the product of the proto-oncogene c-met in normal and osteoarthritic human knee cartilage.

METHODS

Five normal and 14 osteoarthritic human cartilage samples graded histomorphologically by Mankin Score, were studied by radioactive in-situ hybridization and immunohistochemistry for the expression of Hepatocyte growth factor and the c-met receptor.

RESULTS

Hepatocyte growth factor could be found by immunohistochemistry in the territorial matrix surrounding the chondrocytes of calcified cartilage and within the deep zone of normal cartilage. Chondrocytes of these cartilage zones showed also positive c-met receptor-staining. Moreover, a small number of chondrocytes in the superficial and intermediate zone showed c-met staining. In accordance with the increased hepatocyte growth factor staining of osteoarthritic cartilage, an enhanced expression of hepatocyte growth factor-RNA by chondrocytes of the deep zone as well as the deeper mid zone was observed. Contrary to normal cartilage, c-met was identified immunohistochemically in osteoarthritic chondrocytes of all cartilage zones.

CONCLUSION

These results indicate that hepatocyte growth factor seems to be acting in an autocrine/paracrine manner in normal and osteoarthritic cartilage. The ubiquitous presence of the HGF/HGF-receptor complex in osteoarthritic chondrocytes suggests that hepatocyte growth factor may contribute to the altered metabolism in osteoarthritic cartilage.

An in vitro tubule assay identifies HGF as a morphogen for the formation of seminiferous tubules in the postnatal mouse testis

We have been working with a recently immortalized Sertoli cell line, SF7, that appears to produce sleeves, or hollow tubules, when cultivated on a layer of growth factor-reduced Matrigel (GFR-Matrigel) in medium supplemented with serum. We tried to determine which components of GFR-Matrigel and serum provide the environment needed for tubule formation. While laminin and collagen IV were essential for the formation of flat cords, none of the basement membrane constituents, when taken alone or in combination, would support the formation of tubules in minimal culture medium. Moreover, none of the growth factors present in GFR-Matrigel could induce tubulogenesis. Recently, much attention has been focused upon the role of hepatocyte growth factor (HGF) and its receptor c-met in the induction of tubulogenesis by epithelial cells. Therefore, we investigated the expression of HGF/c-met in the mouse testis at different postnatal stages and in the adult and evaluated the contribution of HGF/c-met in the production of Sertoli cell tubules by SF7 and primary Sertoli cells in vitro. Our results confirm that laminin and collagen IV are essential for the formation of testicular cords and reveal that HGF/c-met are necessary for the further remodeling of these cords into tubules.

A peptide representing the carboxyl-terminal tail of the met receptor inhibits kinase activity and invasive growth

Interaction of the hepatocyte growth factor (HGF) with its receptor, the Met tyrosine kinase, results in invasive growth, a genetic program essential to embryonic development and implicated in tumor metastasis. Met-mediated invasive growth requires autophosphorylation of the receptor on tyrosines located in the kinase activation loop (Tyr(1234)-Tyr(1235)) and in the carboxyl-terminal tail (Tyr(1349)-Tyr(1356)). We report that peptides derived from the Met receptor tail, but not from the activation loop, bind the receptor and inhibit the kinase activity in vitro. Cell delivery of the tail receptor peptide impairs HGF-dependent Met phosphorylation and downstream signaling. In normal and transformed epithelial cells, the tail receptor peptide inhibits HGF-mediated invasive growth, as measured by cell migration, invasiveness, and branched morphogenesis. The Met tail peptide inhibits the closely related Ron receptor but does not significantly affect the epidermal growth factor, platelet-derived growth factor, or vascular endothelial growth factor receptor activities. These experiments show that carboxyl-terminal sequences impair the catalytic properties of the Met receptor, thus suggesting that in the resting state the nonphosphorylated tail acts as an intramolecular modulator. Furthermore, they provide a strategy to selectively target the MET proto-oncogene by using small, cell-permeable, peptide derivatives.

Interferon-gamma upregulates the c-Met/hepatocyte growth factor receptor expression in alveolar epithelial cells

In the repair process after lung injury, the regeneration of alveolar epithelial cells plays an important role by covering the damaged alveolar wall and preventing the activated fibroblasts from invading the intra- alveolar spaces. Hepatocyte growth factor (HGF) is a potent mitogen for alveolar epithelial cells and has been reported to be capable of repressing the fibrosing process by connecting to the c-Met/HGF receptor on alveolar epithelial cells. However, it has been reported that the c-Met expression was downregulated in an acute phase of lung injury, which may limit the effect of HGF for therapeutic use. In the present study we observed that interferon (IFN)-gamma upregulates the c-Met messenger RNA (mRNA) and protein expression in A549 alveolar epithelial cells. We analyzed the mechanism of this upregulation and found that IFN-gamma enhances the transcription of the c-met proto-oncogene, and that it does not prolong the stability of the c-Met mRNA. HGF is known to act as a motogen as well as a mitogen for epithelial cells. We also found that the migratory activity of A549 cells induced by HGF is strongly enhanced by preincubation with IFN-gamma. Finally, we administered recombinant IFN-gamma to C57BL/6 mice and confirmed that this upregulation is also observed in vivo. These results suggest that the combination of HGF and IFN-gamma could be a new therapeutic approach for fibrosing pulmonary diseases.

Mutant Met-mediated transformation is ligand-dependent and can be inhibited by HGF antagonists

Mutations in the genes encoding for Met, Ret and Kit receptor tyrosine kinases invariably result in increased kinase activity and in the acquisition of transforming potential. However, the requirement of receptor ligands for the transformation process is still unclear. We have investigated the role of hepatocyte growth factor (HGF), the high-affinity ligand for Met, in mutant Met-mediated cell transformation. We provide evidence that the transforming potential displayed by mutant forms of Met found in human cancer is not only sensitive but entirely dependent on the presence of HGF, by showing that mutant Met transforms NIH3T3 fibroblasts, which produce endogenous HGF, but is not able to transform epithelial cells, unless exogenous HGF is supplied. Accordingly, mutant Met-induced transformation of NIH3T3 cells can be inhibited by HGF antagonists and increased by HGF stimulation. We also show that an engineered Met receptor which contains an oncogenic mutation but is impaired in its ability to bind HGF completely loses its transforming activity, which can be rescued by causing receptor dimerization using a monoclonal antibody. These results indicate that point mutations resulting in Met kinase activation are necessary but not sufficient to cause cell transformation, the latter being dependent on ligand-induced receptor dimerization. They also suggest that mutant Met-driven tumour growth depends on the availability and tissue distribution of active HGF, and provide proof-of-concept for the treatment of mutant-Met related pathologies by HGF-antagonizing drugs.

The von Hippel-Lindau tumor suppressor gene inhibits hepatocyte growth factor/scatter factor-induced invasion and branching morphogenesis in renal carcinoma cells

Loss of function in the von Hippel-Lindau (VHL) tumor suppressor gene occurs in familial and most sporadic renal cell carcinomas (RCCs). VHL has been linked to the regulation of cell cycle cessation (G(0)) and to control of expression of various mRNAs such as for vascular endothelial growth factor. RCC cells express the Met receptor tyrosine kinase, and Met mediates invasion and branching morphogenesis in many cell types in response to hepatocyte growth factor/scatter factor (HGF/SF). We examined the HGF/SF responsiveness of RCC cells containing endogenous mutated (mut) forms of the VHL protein (VHL-negative RCC) with that of isogenic cells expressing exogenous wild-type (wt) VHL (VHL-positive RCC). We found that VHL-negative 786-0 and UOK-101 RCC cells were highly invasive through growth factor-reduced (GFR) Matrigel-coated filters and exhibited an extensive branching morphogenesis phenotype in response to HGF/SF in the three-dimensional (3D) GFR Matrigel cultures. In contrast, the phenotypes of A498 VHL-negative RCC cells were weaker, and isogenic RCC cells ectopically expressing wt VHL did not respond at all. We found that all VHL-negative RCC cells expressed reduced levels of tissue inhibitor of metalloproteinase 2 (TIMP-2) relative to the wt VHL-positive cells, implicating VHL in the regulation of this molecule. However, consistent with the more invasive phenotype of the 786-0 and UOK-101 VHL-negative RCC cells, the levels of TIMP-1 and TIMP-2 were reduced and levels of the matrix metalloproteinases 2 and 9 were elevated compared to the noninvasive VHL-positive RCC cells. Moreover, recombinant TIMPs completely blocked HGF/SF-mediated branching morphogenesis, while neutralizing antibodies to the TIMPs stimulated HGF/SF-mediated invasion in vitro. Thus, the loss of the VHL tumor suppressor gene is central to changes that control tissue invasiveness, and a more invasive phenotype requires additional genetic changes seen in some but not all RCC lines. These studies also demonstrate a synergy between the loss of VHL function and Met signaling.

Dynamics of E-cadherin and gamma-catenin complexes during dedifferentiation of polarized MDCK cells

BACKGROUND

E-cadherin mediated cell-cell adhesion and hepatocyte growth factor (HGF) are important for renal epithelial morphogenesis. We previously showed that HGF dedifferentiates previously well polarized Madin-Darby canine kidney (MDCK) cell monolayers grown on filters. The regulation of E-cadherin during epithelial dedifferentiation is not known. We hypothesized that E-cadherin mediated cell-cell adhesion is modulated during HGF induced dedifferentiation of MDCK cell monolayers.

METHODS

We analyzed E-cadherin/gamma-catenin interaction and distribution during epithelial dedifferentiation in vitro using a model of polarized MDCK cell monolayers treated with HGF.

RESULTS

Surface immunoprecipitation experiments showed that HGF increased the amount of cell surface E-cadherin associated with gamma-catenin. Biochemical and morphological examination of the TX-100 solubility of junctional E-cadherin and gamma-catenin in control and HGF treated cells showed an increase in solubility of only E-cadherin during loss of cell polarity. Metabolic labeling of control and HGF treated cells showed that HGF stimulated the synthetic rate of E-cadherin and gamma-catenin molecules. Inulin flux across MDCK cell monolayers increases with HGF treatment.

CONCLUSION

These data provide evidence for both the dissociation of E-cadherin molecules from the actin cytoskeleton and an increase in the total number of E-cadherin/gamma-catenin complexes on the cell surface during HGF-induced dedifferentiation of polarized renal epithelium. These data support the hypothesis that E-cadherin function is inhibited by a mechanism of detachment from the actin based cytoskeleton during HGF induced dedifferentiation of polarized renal epithelia.

Prostaglandin production in mouse mammary tumour cells confers invasive growth potential by inducing hepatocyte growth factor in stromal fibroblasts

Interactions between stromal and mammary tumour cells play a crucial role in determining the malignant behaviour of tumour cells. Although MMT mouse mammary tumour cells do not produce hepatocyte growth factor (HGF), addition of conditioned medium (CM) from MMT cells to cultures of human fibroblasts derived from skin and breast tissues stimulated the production of HGF, thereby indicating that MMT cells secrete an inducing factor for HGF. This HGF-inducing factor, purified from MMT-derived CM, proved to be prostaglandin E2 (PGE2). Consistently, treatment of MMT cells with indomethacin, an inhibitor of cyclooxygenase, abolished this HGF-inducing activity in MMT-derived CM, while treatment of MMT cells with HGF stimulated cell growth and cell motility. Likewise, HGF strongly enhanced urokinase-type plasminogen activator activity and invasion of MMT cells through Matrigel: a 15-fold stimulation in the invasion of MMT cells was seen by HGF. Finally, MMT cells in the upper compartment were co-cultivated with fibroblasts in the lower compartment of the Matrigel chamber, HGF levels in the co-culture system exceeded the level in fibroblasts alone and suppression occurred with exposure to indomethacin. Together with increase in the HGF level, the invasion of MMT cells was enhanced by co-cultivation with fibroblasts, whereas the increased invasion of MMT cells was significantly inhibited by an anti-HGF antibody and by indomethacin. These results indicate mutual interactions between MMT cells and fibroblasts: MMT-derived PGE2 plays a role in up-regulating HGF production in fibroblasts, while fibroblast-derived HGF leads to invasive growth in MMT cells. The mutual interactions mediated by HGF and prostaglandins may possibly be a mechanism regulating malignant behaviour of mammary tumour cells, through tumour-stromal interactions.

Cdc42, Rac1, and their effector IQGAP1 as molecular switches for cadherin-mediated cell-cell adhesion

Cell-cell adhesion is a dynamic process in various cellular and developmental situations. Cadherins, well-known Ca(2+)-dependent adhesion molecules, are thought to play a major role in the regulation of cell-cell adhesion. However, the molecular mechanism underlying the rearrangement of cadherin-mediated cell-cell adhesion is largely unknown. Cdc42 and Rac1, belonging to the Rho small GTPase family, have recently been shown to be involved in the regulation of cell-cell adhesion. In addition, IQGAP1, an effector for Cdc42 and Rac1, has been shown to regulate the cadherin function through interaction with beta-catenin, a molecule associated with cadherin. In this review, we will summarize the mode of action of Cdc42 and Rac1 as well as IQGAP1 as molecular switches for the cadherin function, and then discuss physiological processes in which the Cdc42/Rac1/IQGAP1 system may be involved.

Characterization of a functional relationship between hepatocyte growth factor and mouse bone marrow-derived mast cells

During the early stage (at 4 weeks) of interleukin-3 (IL-3)-induced development, mouse bone marrow-derived mast cells (BMMC) express alpha 4, alpha 5 and alpha 6 integrins, whereas with further maturation beyond 10 weeks, only alpha 5 integrin remains stably expressed. Hepatocyte growth factor (HGF) modulates the growth and movement of diverse cell types upon binding to its receptor, encoded by the proto-oncogene c-met. We report here the expression of c-met by BMMC throughout the course of their development. In addition, HGF stimulated migration of early week-4 BMMC, but not of the later stage week-10 BMMC, on fibronectin and laminin substrates. The developmental stage-dependent effect of HGF on BMMC was due to specific stimulation of the migratory function of alpha 4 and alpha 6, but not alpha 5 integrins. In addition, HGF had no effect on BMMC growth, either alone or in combination with IL-3. While HGF is stimulatory of the migratory function of BMMC, our results show that BMMC in turn can modulate HGF function. Thus, upon activation via the IgE receptors, BMMC released proteases that abolished HGF activities. Analyses of the degradation products by two-dimensional sodium dodecyl sulfate polyacrylamide gel electrophoresis and Western blot using antisera prepared against recombinant HGF and the kringle 3 domain of HGF revealed specific degradation of HGF alpha but not beta/beta' subunits. Therefore, our results suggest that: 1) the motogenic effect of HGF on BMMC varies according to the stage of their development, 2) HGF stimulation of BMMC migration is due to selective activation of alpha 4 and alpha 6, but not alpha 5 integrin function, and 3) there exists a two-way relationship between BMMC and HGF such that HGF stimulates the beta 1 integrin-mediated migratory function of BMMC, which can, in turn, modulate HGF function by release of serine proteases.

Hepatocyte growth factor induces tubulogenesis of primary renal proximal tubular epithelial cells

Hepatocyte growth factor (HGF)-induced tubulogenesis has been demonstrated with renal epithelial cell lines grown in collagen gels but not with primary cultured renal proximal tubular epithelial cells (RPTEs). We show that HGF selectively induces proliferation and branching morphogenesis of primary cultured rat RPTEs. Additional growth factors including fibroblast growth factor (FGF)-1, epidermal growth factor (EGF), FGF-7, or insulin-like growth factor-1 (IGF-1) did not selectively induce tubulogenesis. However, when administered in combination, these factors initiated branching morphogenesis comparable to HGF alone and greatly augmented HGF-induced proliferation and branching. Microscopic analysis revealed that branching RPTEs were undergoing tubulogenesis and formed a polarized epithelium. TGF-beta1 blocked HGF- or growth factor cocktail (GFC; HGF, FGF-1, EGF, IGF-1)-induced proliferation and branching morphogenesis. Adding TGF-beta1 after GFC-induced tubulogenesis had occurred caused a progressive regression of the tubular structures, a response associated with an increase in apoptosis of the RPTEs. Primary cultured RPTEs are capable of undergoing HGF-induced tubulogenesis. Unlike cell lines, combinations of growth factors differentially augment the response.

Hepatocyte growth factor and c-MET are expressed in rat prepuberal testis

The hepatocyte growth factor (HGF) receptor (c-MET) is present in different mammalian tissues and transduces multiple biological effects. The HGF is known to regulate many fundamental cellular functions, such as cell growth, movement and differentiation, and is involved in embryonal morphogenesis. We have studied HGF and c-MET expression in prepuberal rat testis. c-MET gene expression was found in total testis and in homogeneous cell populations, as demonstrated by Northern blotting. In the seminiferous tubules, c-MET gene was only expressed in the myoid cells. In these cells, c-MET was detectable and constantly expressed for at least six days of culture. The interstitial tissue was also c-MET positive. The protein encoded by the MET proto-oncogene was detected in myoid cells, and HGF administration to these cells induced morphological changes in the cells. HGF expression was not detected by Northern blotting using RNA extracted from total testis. By contrast, when homogenous cell populations were used, HGF expression was detectable and exclusively localized in myoid cells. Myoid cell-conditioned medium was able to induce scattering of canine kidney epithelial (MDCK) cells, and the scatter effect of a 3-days conditioned medium was evident even after 7-fold dilution of the medium. Our findings demonstrate that HGF and its receptor are present in rat prepuberal testis. The coexpression of factor and receptor in the myoid cells suggests a new role for HGF as autocrine regulator of myoid cell function and, possibly, as regulator of mammalian testicular function.

Progression-linked overexpression of c-Met in prostatic intraepithelial neoplasia and latent as well as clinical prostate cancers

The c-met proto-oncogene encoding the receptor for the hepatocyte growth factor is expressed in several cancers. In the present study, c-met protein (c-Met) was detected in eight of 22 (36%) cases of prostatic intraepithelial neoplasia (PIN), five of 15 (33%) latent and 17 of 21 (81%) clinical prostate cancers, including seven metastatic lesions, using an immunohistochemical method. All seven (100%) metastatic lesions investigated demonstrated strong staining, and a correlation between c-Met expression and histology was observed. These results suggest a significant relationship between c-Met expression and progression of prostate neoplasms, including latent cancers.

Gene transfection of hepatocyte growth factor attenuates reperfusion injury in the heart

BACKGROUND

Hepatocyte growth factor (HGF), a ligand for the c-Met receptor tyrosine kinase, plays a role as organotrophic factor for regeneration of various organs. HGF has an angiogenic activity and exhibits a potent antiapoptotic activity in several types of cells. Although HGF and the c-Met/HGF receptor are expressed in the heart, the role of HGF in the heart has remained unknown.

METHODS

After we analyzed changes in expression of endogenous HGF and c-Met mRNA levels in the rat left ventricle after myocardial infarction, the human HGF gene in hemagglutinating virus of Japan (HVJ)-liposome was transfected into the normal whole rat heart. Three days after transfection, the heart was subjected to global warm ischemia and subsequent reperfusion, followed by assessment of its cardiac functions.

RESULTS

Both HGF and c-Met/HGF receptor mRNAs were expressed in adult rat heart, and c-Met/HGF receptor mRNA was upregulated in response to myocardial infarction. HGF-transfected heart showed significant increase of human HGF protein level in the heart. Cardiac functions in terms of the left ventricular developed pressure, maximum dp/dt, and pressure rate product in hearts with HGF gene transfection were significantly superior to those in control hearts. In addition, leakage of creatine phosphokinase in the coronary artery effluent in hearts with HGF gene transfection was significantly lower than that in control hearts.

CONCLUSIONS

These data indicated that both HGF and c-Met/HGF receptor mRNAs were upregulated in response to myocardial ischemic injury, and that HGF is likely to have a cytoprotective effect on cardiac tissue, presumably through the c-Met/HGF receptor.

Evidence that hepatocyte growth factor abrogates contact inhibition of mitosis in Madin-Darby canine kidney cell monolayers

It is becoming increasingly apparent that hepatocyte growth factor (HGF) plays an important role in kidney development, regeneration, and transformation to carcinoma. Previous in vitro studies have shown that HGF stimulates cell scattering, but not proliferation, in the renal epithelial cell line Madin-Darby canine kidney (MDCK) when grown on plastic at low density. This communication demonstrates that HGF treatment of confluent monolayers of MDCK also stimulates DNA synthesis and cell division. HGF stimulated thymidine incorporation in confluent MDCK cell monolayers grown on plastic in a dose dependent fashion, but did not stimulate thymidine incorporation in MDCK cells at 10-20% confluency on plastic. Additionally, basolaterally, but not apically, applied HGF stimulated thymidine incorporation in confluent MDCK cell monolayers grown on filters. Immunofluorescent labeling of nuclei in control and HGF treated MDCK cell monolayers grown on filters demonstrated an increase in mitotic figures. Confocal X-Z section views and direct cell counts of MDCK cell monolayers grown on filters demonstrated an increase in cell number after HGF treatment compared to controls. This is the first report of HGF stimulating cell proliferation in previously quiescent renal epithelial cell monolayers. This model will be useful for studying the mechanisms controlling cell proliferation rates in epithelial tissue.

Involvement of oxidative stress in tumor cytotoxic activity of hepatocyte growth factor/scatter factor

In this study, we show that N-acetylcysteine (NAC), a precursor of glutathione and an intracellular free radical scavenger, almost completely prevented hepatocyte growth factor (HGF)-suppressed growth of Sarcoma 180 and Meth A cells, and HGF-induced apoptosis, assessed by DNA fragmentation, and increase in caspase-3 activity, in Sarcoma 180 cells. The reduced form of glutathione also prevented HGF-suppressed growth of the cells as effective as NAC. Ascorbic acid partially prevented the effect of HGF, but other antioxidants such as superoxide dismutase, catalase, and vitamin E, and the free radical spin traps N-t-butyl-alpha-phenylnitrone and 3,3,5, 5-tetramethyl-1-pyrroline-1-oxide did not have protective effects. HGF caused morphological changes of the cells, many cells showing condensation and rounding, and enhanced the generation of intracellular reactive oxygen species (ROS) as judged by flow cytometric analysis using 2',7'-dichlorofluorescein diacetate. NAC completely prevented both HGF-induced morphological changes and the enhancement of ROS generation in the cells. However, NAC did not prevent the HGF-induced scattering of Madin-Darby canine kidney cells. To our knowledge, this is the first report that HGF stimulates the production of ROS, and our results suggest the involvement of oxidative stress in the mechanism by which HGF induces growth suppression of tumor cells.

Mitogen-activated protein kinase activation regulates intestinal epithelial differentiation

BACKGROUND & AIMS

The human colon cancer-derived cell line HT29 displays a multipotent phenotype. A subclone of HT29 cells containing numerous mucous granules and termed HT29-18-N2 was studied to determine the cellular mechanisms underlying a switch to the differentiated phenotype.

METHODS

Northern (RNA) blotting, immunoblotting, and immunocytochemistry of HT29-N2 cells, grown under glucose-containing and glucose-free conditions with or without the use of the mitogen-activated protein (MAP) kinase kinase (MEK) inhibitor PD98059, were performed.

RESULTS

Loss of activation of the MAP kinases ERK 1 and ERK 2 in HT29-N2 cells upon a change to glucose-free growth medium preceded the change in phenotype and up-regulation of the goblet cell gene product intestinal trefoil factor (ITF). Long-term pharmacological MAP kinase inhibition with the MEK inhibitor PD98059 induced expression of the terminal differentiation markers ITF, sucrase-isomaltase, and the mucin gene MUC2. This was accompanied by morphological evidence of gland formation and mucin secretion and the appearance of discrete goblet cell and enterocyte populations. Induction of ITF and sucrase-isomaltase after MEK inhibition in HT29-N2 cells did not involve loss of MAP kinase responsiveness and was not mediated by receptor tyrosine kinases.

CONCLUSIONS

Regulation of ERK activation may be a key biochemical switch responsible for terminal differentiation of components of the crypt-villus unit.

HP33: hepatocellular carcinoma-enriched 33-kDa protein with similarity to mitochondrial N-acyltransferase but localized in a microtubule-dependent manner at the centrosome

Using a new subtraction method and chemically induced rat hepatocellular carcinomas, we identified a hepatocellular carcinogenesis and hepatocyte proliferation-related gene designated hp33 that encoded a 33-kDa protein. The predicted protein was similar to the bovine aralkyl N-acyltransferase and arylacetyl N-acyltransferase. HP33 was restrictively expressed in the liver and kidney, and its gene expression was stimulated in the regenerating liver as well as in hepatocellular carcinoma. Interestingly, it was demonstrated in various hepatic cells that HP33 was localized in regions surrounding the centrosome, where mitochondria were not concentrated. Moreover, its centrosomal localization was evident in the interphase but not in the mitotic phase of the cell cycle. The centrosomal localization of HP33 was dependent on microtubules, and ectopically expressed HP33 was seen at centrosomes even in fibroblasts, which do not exhibit a typical staining pattern of HP33. The centrosomal localization of HP33 became invisible by nocodazole treatment, whereas the mitochondrial staining pattern was not affected by it. In vitro cosedimentation experiments using purified microtubules indicated that HP33 bound to MTs directly and that its MT-binding ability was dependent on the C-terminal basic domain of the protein. These results suggest that, different from early predictions based on its primary structure, HP33 has a growth- and carcinogenesis-related function that may be independent of mitochondrial function.

Hepatocyte growth factor releases mink epithelial cells from transforming growth factor beta1-induced growth arrest by restoring Cdk6 expression and cyclin E-associated Cdk2 activity

Transforming growth factor beta (TGF-beta) potently suppresses Mv1Lu mink epithelial cell growth, whereas hepatocyte growth factor (HGF) counteracts TGF-beta-mediated growth inhibition and induces Mv1Lu cell proliferation (J. Taipale and J. Keski-Oja, J. Biol. Chem. 271:4342-4348, 1996). By addressing the cell cycle regulatory mechanisms involved in HGF-mediated release of Mv1Lu cells from TGF-beta inhibition, we show that increased DNA replication is accompanied by phosphorylation of the retinoblastoma protein and alternative regulation of cyclin-Cdk-inhibitor complexes. While TGF-beta treatment decreased the expression of Cdk6, this effect was counteracted by HGF, followed by partial restoration of cyclin D2-associated kinase activity. Notably, HGF failed to prevent TGF-beta induction of p15 and its association with Cdk6. However, HGF reversed the TGF-beta-mediated decrease in Cdk6-associated p27 and cyclin D2-associated Cdk6, suggesting that HGF modifies the TGF-beta response at the level of G1 cyclin complex formation. Counteraction of TGF-beta regulation of Cdk6 by HGF may in turn affect the association of p27 with Cdk2-cyclin E complexes. Though HGF did not differentially regulate the total levels of p27 in TGF-beta-treated cells, p27 immunodepletion experiments suggested that upon treatment with both growth factors, less p27 is associated with Cdk2-cyclin E complexes, in parallel with restoration of the active form of Cdk2 and the associated kinase activity. The results demonstrate that HGF intercepts TGF-beta cell cycle regulation at multiple points, affecting both G1 and G1-S cyclin kinase activities.

Tubular morphogenesis and mesenchymal interactions affect renin expression and secretion in SIMS mouse submandibular cells

We have previously immortalized a mouse submandibular gland (SMG) ductal epithelial cell line, SIMS, from pubertal male mice transgenic for the SV40 large T antigen under the control of the adenovirus 5 E1A promoter. Here we demonstrate the role of the extracellular environment in directing not only the morphogenetic behavior of the cells, but also their functional differentiation in terms of renin expression and secretion. First, we measured renin activity of polarized SIMS cells. Low levels of renin are secreted from both the apical and the basolateral domains; the mechanism appears to be direct as no renin was found to be transcytosed across the cell. Second, we studied homotypic and heterotypic mesenchymal cell interactions with SIMS cells. We found that epithelial-mesenchymal coculture in collagen I gels results in branching tubular morphogenesis of SIMS cells and that significant amounts of renin are secreted, probably into the lumen, as the precursor form, prorenin. Third, we investigated the effects of the basement membrane on SIMS cell morphology and function and found that this structure alone is sufficient to allow expression and secretion of both prorenin and active renin. Finally, we established that SIMS cells can express androgen-regulated genes in a transient transfection assay. In addition, in Matrigel cultures androgen receptor expression appears to be induced, suggesting that the SIMS cell line will be useful for further studies on the molecular basis of the observed high-level expression of SMG-specific genes in male mice.

Significant role of laminin-1 in branching morphogenesis of mouse salivary epithelium cultured in basement membrane matrix

Mouse submandibular epithelium shows branching morphogenesis in mesenchyme-free conditions when covered with a basement membrane matrix (Matrigel) in medium supplemented with epidermal growth factor. In the present study, the role of laminin-1 (LN1), a major glycoprotein of Matrigel, in this culture system was defined. When the epithelium was cultured in a LN1-nidogen gel, the epithelium showed much branching, comparable to that observed with Matrigel. By electron microscopy, only a felt-like matrix was formed on the epithelial surface in the LN1-nidogen gel cultures, while an organized basal lamina structure was formed on the epithelial surface in direct or transfilter recombination cultures with mesenchyme. Next, the epithelium covered with Matrigel was cultured in medium containing either biologically active peptides from LN1, IKVAV-including peptide (2097-2108), AG10 (2183-2194), AG32 (2370-2381) or AG73 (2719-2730) from the alpha1 chain, or YIGSR-including peptide (926-933) from the beta1 chain. Only AG73 (RKRLQVQLSIRT from the alpha1 chain carboxyl-terminal globular domain) inhibited the epithelial branching in Matrigel. These results suggest that LN1-nidogen can support the branching morphogenesis of submandibular epithelium even if LN1-nidogen is not assembled into an intact basal lamina, and that the AG73 sequence is an important site on LN1, which interacts with submandibular epithelial cells.

Molecular regulation of nephron endowment

Recent data suggests that the number of nephrons in normal adult human kidneys ranges from approximately 300,000 to more than 1 million. There is increasing evidence that reduced nephron number, either inherited or acquired, is associated with the development of essential hypertension, chronic renal failure, renal disease in transitional indigenous populations, and possibly the long-term success of renal allografts. Three processes ultimately govern the number of nephrons formed during the development of the permanent kidney (metanephros): branching of the ureteric duct in the metanephric mesenchyme; condensation of mesenchymal cells at the tips of the ureteric branches; and conversion of the mesenchymal condensates into epithelium. This epithelium then grows and differentiates to form nephrons. In recent years, we have learned a great deal about the molecular regulation of these three central processes and hence the molecular regulation of nephron endowment. Data has come from studies on cell lines, isolated ureteric duct epithelial cells, isolated metanephric mesenchyme, and whole metanephric organ culture, as well as from studies of heterozygous and homozygous null mutant mice. With accurate and precise methods now available for estimating the total number of nephrons in kidneys, more advances in our understanding of the molecular regulation of nephron endowment can be expected in the near future.

Expression of c-ret promotes morphogenesis and cell survival in mIMCD-3 cells

c-Ret, a protein tyrosine kinase receptor, and its ligand glial-derived neurotropic factor (GDNF) are critical for early regulation of ureteric bud development and nephrogenesis. To address whether c-ret directly initiates epithelial cell morphogenesis, the c-ret receptor was expressed in murine inner medullary collecting duct cells (mIMCD-3, a cell line of ureteric bud origin, which has no detectable endogenous c-ret expression). Stable expression of wild-type c-ret was found to yield a constitutively tyrosine-phosphorylated receptor, with no change after the addition of GDNF. Examination of mRNA from these cells demonstrated the message for endogenous GDNF, suggesting that c-ret was potentially being constitutively activated by an autocrine mechanism. When mIMCD-3 cells stably expressing the phosphorylated c-ret receptor were cultured in a type I collagen matrix, they exhibited little GDNF-independent or -dependent branching process formation at early time points compared with the known morphogen hepatocyte growth factor (HGF) (48 h; control, 0.33 +/- 0.33; GDNF, 1.0 +/- 0.58, P = nonsignificant; and HGF, 6.33 +/- 0.33 processes/20 cell clusters, P < 0.001), whereas extended culture (7 days) under serum-free conditions revealed a marked increase in cell survival and the spontaneous development of rudimentary branching process formation. Extended culture (7 days) of c-ret-expressing clones in type I collagen with the epithelial morphogens HGF and/or epidermal growth factor (EGF) resulted in the development of complex three-dimensional spiny cysts, whereas parental mIMCD-3 cells died under these conditions. We conclude that activated c-ret appears to mediate epithelial morphogenesis by prolonging cell survival and, in conjunction with activation of the morphogenic receptors c-met and the EGF receptor, initiates the events required for very early branching morphogenesis.

Overexpression of a kinase-deficient transforming growth factor-beta type II receptor in mouse mammary stroma results in increased epithelial branching

Members of the transforming growth factor-beta (TGF-beta) superfamily signal through heteromeric type I and type II serine/threonine kinase receptors. Transgenic mice that overexpress a dominant-negative mutation of the TGF-beta type II receptor (DNIIR) under the control of a metallothionein-derived promoter (MT-DNIIR) were used to determine the role of endogenous TGF-betas in the developing mammary gland. The expression of the dominant-negative receptor was induced with zinc and was primarily localized to the stroma underlying the ductal epithelium in the mammary glands of virgin transgenic mice from two separate mouse lines. In MT-DNIIR virgin females treated with zinc, there was an increase in lateral branching of the ductal epithelium. We tested the hypothesis that expression of the dominant-negative receptor may alter expression of genes that are expressed in the stroma and regulated by TGF-betas, potentially resulting in the increased lateral branching seen in the MT-DNIIR mammary glands. The expression of hepatocyte growth factor mRNA was increased in mammary glands from transgenic animals relative to the wild-type controls, suggesting that this factor may play a role in TGF-beta-mediated regulation of lateral branching. Loss of responsiveness to TGF-betas in the mammary stroma resulted in increased branching in mammary epithelium, suggesting that TGF-betas play an important role in the stromal-epithelial interactions required for branching morphogenesis.

The multisubstrate docking site of the MET receptor is dispensable for MET-mediated RAS signaling and cell scattering

The scatter factor/hepatocyte growth factor regulates scattering and morphogenesis of epithelial cells through activation of the MET tyrosine kinase receptor. In particular, the noncatalytic C-terminal tail of MET contains two autophosphorylation tyrosine residues, which form a multisubstrate-binding site for several cytoplasmic effectors and are thought to be essential for signal transduction. We show here that a MET receptor mutated on the four C-terminal tyrosine residues, Y1311F, Y1347F, Y1354F, and Y1363F, can induce efficiently a transcriptional response and cell scattering, whereas it cannot induce cell morphogenesis. Although the mutated receptor had lost its ability to recruit and/or activate known signaling molecules, such as GRB2, SHC, GAB1, and PI3K, by using a sensitive association-kinase assay we found that the mutated receptor can still associate and phosphorylate a approximately 250-kDa protein. By further examining signal transduction mediated by the mutated MET receptor, we established that it can transmit efficient RAS signaling and that cell scattering by the mutated MET receptor could be inhibited by a pharmacological inhibitor of the MEK-ERK (MAP kinase kinase-extracellular signal-regulated kinase) pathway. We propose that signal transduction by autophosphorylation of the C-terminal tyrosine residues is not the sole mechanism by which the activated MET receptor can transmit RAS signaling and cell scattering.

Aberrant expression of gastrin-releasing peptide and its receptor by well-differentiated colon cancers in humans

Epithelial cells lining the adult human colon do not normally express gastrin-releasing peptide (GRP) or its receptor (GRPR). In contrast, approximately one-third of human colon cancers and cancer cell lines have been shown to express GRP-binding sites. Because GRPR activation causes the proliferation of many cancer cell lines, GRP has been presumed to act as a clinically significant growth factor. Yet GRP has not been shown to be expressed by colon cancers in humans nor has the effect of GRP and/or GRPR coexpression on tumor behavior been investigated. We therefore determined GRP and GRPR expression by immunohistochemistry in 50 randomly selected colon cancers resected between 1980 and 1997, all 37 associated lymph node and liver metastases, and 20 polyps. Tumor sections studied were those that contained the margin and adjacent nonmalignant epithelium. Overall, 84% of cancers aberrantly expressed GRP or GRPR, with 62% expressing both ligand and receptor, whereas expression was not observed in adjacent normal epithelium. Consistent with the previously established mitogenic capabilities of GRP, tissues coexpressing GRP and GRPR were more likely to express proliferating cell nuclear antigen than tissues not expressing both ligand and receptor. Yet GRP/GRPR coexpression was seen with equal frequency in stage A as in stage D cancers and was only detected in 1 in 37 metastases. Furthermore, Kaplan-Meier analysis did not reveal any difference in patient survival between those whose tumors did or did not express GRP/GRPR. In contrast, GRP/GRPR coexpression was found in all well-differentiated tumor regions, whereas poorly differentiated tissues never coexpressed GRP/GRPR. Overall, these data indicate that, although GRP is a mitogen, it is not a clinically significant growth factor in human colon cancers. Rather, the strong association of GRP/GRPR coexpression with tumor differentiation raises the possibility that these proteins primarily act in vivo as morphogens.

Fibroblast growth factor-2 induces hepatocyte growth factor/scatter factor expression in osteoblasts

Hepatocyte growth factor/scatter factor (HGF/SF) is a multifunctional growth factor with a major role in tissue morphogenesis and repair. It stimulates the proliferation of cells of the osteoblast and osteoclast lineages. Mitogenic factors playing a role in fracture repair may act by regulating HGF/SF expression or activity in bone-forming cells. We investigated the effect of fibroblast growth factor-2 (FGF-2) on the expression of HGF/SF and its receptor, encoded by c-met, in the MC3T3-E1 osteoblastic cell line. MC3T3-E1 cells expressed low levels of HGF/SF messenger RNA (mRNA), which were markedly increased by FGF-2 in a dose- and time-dependent manner. FGF-2 also induced HGF/SF polypeptide synthesis. The stimulation of HGF/SF mRNA expression by FGF-2 was blocked by cycloheximide, a protein synthesis inhibitor, but not by DNA or prostaglandin synthesis inhibitors. FGF-2 increased the rate of HGF/SF gene transcription by approximately 2-fold, as determined by nuclear run-on assays, and did not modify the decay of HGF/SF mRNA in transcriptionally arrested cells. FGF-2 also caused a dose- and time-dependent stimulation of c-met mRNA. In conclusion, FGF-2 induces HGF/SF expression in osteoblasts and may promote HGF/SF activity by increasing the expression of its receptor. Through these mechanisms, HGF/SF could mediate FGF actions on bone repair.

Direct evidence that hepatocyte growth factor-induced invasion of hepatocellular carcinoma cells is mediated by urokinase

BACKGROUND/AIMS

We have shown that hepatocyte growth factor secreted by human hepatic myofibroblasts increased the in vitro invasion of the hepatocarcinoma cell line HepG2 through Matrigel. Our aim in this study was to evaluate the role of urokinase in this process.

METHODS

Expression of urokinase in HepG2 cells was measured by Northern blot and zymography, and plasminogen activation was shown by a chromogenic substrate assay. Cell invasion was assayed on Matrigel-coated filters. Urokinase and urokinase receptor transcripts in hepatocarcinoma were detected by reverse transcription-polymerase chain reaction. Activated hepatocyte growth factor was detected by Western blot with a hepatocyte growth factor-beta chain-specific antibody.

RESULTS

HepG2 cells expressed urokinase mRNA and secreted active urokinase. Urokinase expression was enhanced by hepatocyte growth factor at the protein and mRNA level. Notably, cell-surface-associated urokinase was increased 22-fold by hepatocyte growth factor. Hepatocyte growth factor also increased urokinase receptor mRNA expression. B428, a urokinase inhibitor, decreased by up to 70% HepG2 invasion induced by myofibroblasts and by 90% that induced by recombinant hepatocyte growth factor. This was not due to a decrease in the generation of activated hepatocyte growth factor by myofibroblasts. Finally, all 17 hepatocarcinoma samples tested expressed urokinase and urokinase receptor transcripts.

CONCLUSION

Hepatocyte growth factor-dependent, myofibroblasts-induced invasion of HepG2 cells is secondary to the induction of urokinase expression on tumor cells.

Regulation of the c-met proto-oncogene promoter by p53

In the present study, we have investigated the possible involvement of p53 in the transcriptional regulation of the c-met gene. Cotransfection of various c-met promoter reporter vectors with p53 expression plasmids demonstrated that only wild-type p53 but not tumor-derived mutant forms of p53 resulted in a significant enhancement of c-met promoter activity. Functional assays revealed that the p53 responsive element in the c-met promoter region is located at position -278 to -216 and confers p53 responsiveness not only in the context of the c-met promoter but also in the context of a heterologous promoter. Electrophoretic mobility shift assays using purified recombinant p53 protein showed that the p53 binding element identified within the c-met promoter specifically binds to p53 protein. Induction of p53 by UV irradiation in RKO cells that express wild-type p53 increased the level of the endogenous c-met gene product and p21(WAF1/CIP1), a known target of p53 regulation. On the other hand, in RKO cells in which the function of p53 is impaired either by stable transfection of a dominant negative form of p53 or by HPV-E6 viral protein, no induction of the endogenous c-met gene or p21(WAF1/CIP1) was noted by UV irradiation. These results suggest that the c-met gene is also a target of p53 gene regulation.

Hepatocyte growth factor is a major mediator in heparin-induced angiogenesis

Heparin has a potent angiogenic effect in experimental animals and patients with ischemic diseases; however, the precise mechanism behind this angiogenesis remains to be clarified. The aim of this study was to determine whether the administration of heparin affects the levels of heparin-binding angiogenic factors in human plasma, and to identify the molecule responsible for heparin-induced angiogenesis. Plasma levels of hepatocyte growth factor (HGF), basic fibroblast growth factor (bFGF), and vascular endothelial growth factor (VEGF) were measured before and after administration of 100 U, 3,000 U or 10,000 U of heparin in patients with coronary artery disease. Administration of 3,000 U or 10,000 U of heparin caused significant increases in plasma HGF (40- and 54-fold, respectively), in absence of obvious increases in bFGF and VEGF levels. Furthermore, compared with the serum collected before heparin administration, the serum collected after heparin administration had more prominent growth-promoting and vascular tube-inducing properties on endothelial cells, and these increased activities were completely inhibited by neutralization of HGF, whereas neutralization of bFGF and VEGF had no effect. These findings suggest that HGF plays a significant role in heparin-induced angiogenesis.

Up-regulation of hepatocyte growth factor receptor: an amplification and targeting mechanism for hepatocyte growth factor action in acute renal failure

BACKGROUND

Hepatocyte growth factor (HGF) and its c-met receptor comprise a signaling system that has been implicated in tissue repair and regeneration. HGF action is specifically targeted to the damaged organ following injury; however, the mechanism underlying this important targeting process remains to be elucidated. We reasoned that induction of c-met expression might be a critical factor in determining the site specificity of this receptor-ligand system. To test this hypothesis, we examined changes in activity of the HGF/c-met system in the folic acid model of acute tubular injury and repair.

METHODS

Tissue HGF and c-met mRNA levels were detected by RNase protection assay and Northern blot analysis following acute renal injury induced by a single injection of folic acid. HGF and c-met proteins were examined by a specific enzyme immunoassay and Western blotting, respectively. C-met expression and trans-activation were investigated by exposing renal epithelial mIMCD-3 cells to various cytokines in vitro.

RESULTS

Extremely rapid induction of renal HGF and c-met mRNA was observed beginning one hour following injection of folic acid. Circulating plasma HGF protein level rose dramatically (approximately 16-fold), peaking first at two hours and again at 24 hours following injection. Despite elevated HGF mRNA in the kidney, total kidney HGF protein actually decreased significantly at 24 hours following injury. On the other hand, both c-met mRNA and c-met protein were markedly increased in the kidney, where active renal tubule repair and regeneration take place. In vitro studies suggested that increased levels of HGF, as well as other cytokines, might account for enhanced c-met expression in renal tubular epithelial cells. Pretreatment of the cells with actinomycin D totally blocked c-met induction, suggesting that induced c-met expression occurs primarily at the transcriptional level. Using a cloned region of the c-met promoter coupled to a reporter gene, we demonstrated that HGF directly stimulated c-met promoter transactivation in renal epithelial cells.

CONCLUSION

These results suggest that local up-regulation of c-met transcription in the kidney is crucial to renal tubule repair and regeneration, not only because it increases overall activity of this receptor-ligand system, but also as a mechanism targeting HGF action specifically to renal epithelia.

In vitro reconstitution of the tracheal epithelium

We have developed a unique in vitro reconstitution system for tracheal epithelia of guinea pigs. In the system, a human amnion membrane was used as a basement membrane and the tracheal epithelial cells were cultured on the epithelial side of the membrane. Three weeks later, the tracheal fibroblasts were co-cultured on the serosal side of the amnion membrane and the culturing was continued for an additional 10 d. The morphology of the cultured epithelial cells consisted of a pseudostratified columnar ciliated epithelium from cuboidal ciliated epithelium during the last 10 d of the culture period. Epithelial cells included both goblet-like and basal cells. In addition, the frequency of each type of differentiated cells was almost identical to that of in vivo tracheas. Interestingly, the same results were obtained when the conditioned medium of the tracheal fibroblasts was used instead of the fibroblasts themselves. These results suggest that epithelial-mesenchymal interaction is likely involved in growth and differentiation of epithelial cells in vivo in a soluble factor(s)-mediated manner. As well as the epithelial cells, the fibroblasts also formed a multilayer during the last 10 d of co-culturing. This indicates that in vitro reconstitution of tracheal epithelia is achieved without addition of any exogenous growth or differentiation factors. The reconstitution system is shown to be useful for investigating the cellular and molecular interaction of epithelial and mesenchymal cells. Possible applications of the culture system and possible factors involved in growth and differentiation of epithelial cells are discussed.

Role of cyclooxygenase 2 in hepatocyte growth factor-mediated gastric epithelial restitution

Migration of epithelial cells (restitution) is an essential step in the repair of gastric mucosal lesions. Although a variety of growth factors are reported to facilitate gastric epithelial restitution, the intracellular mechanisms of this process are not fully understood. In this study we investigated the effects of hepatocyte growth factor (HGF) on restitution of normal rat gastric epithelial RGM-1 cell monolayers after injury and examined whether cyclooxygenase-2 (COX-2) is involved in HGF-mediated epithelial restitution. Restitution of RGM-1 monolayers was assessed using a round wound restitution model. Application of HGF (5 ng/ml) significantly facilitated the restitution of RGM-1 monolayers after artificial wounding. HGF also induced expression of COX-2 protein in RGM-1 cells, and wounding itself induced COX-2 expression in the cells located at the edge of the wound. Inhibition of COX-2 activity by NS-398, a specific COX-2 inhibitor, significantly delayed the HGF-mediated restitution. These results suggest the involvement of COX-2 in the action of HGF on gastric epithelial restitution.

Bcl-2 overexpression prevents apoptosis-induced Madin-Darby canine kidney simple epithelial cyst formation

BACKGROUND

Madin-Darby canine kidney (MDCK) cells develop into simple epithelial cell cysts when cultured in type I collagen gel. We found that MDCK cells initially grow into multilayer cell aggregates and subsequently develop central lumen that contain apoptotic cells. We hypothesized that apoptosis might be essential for the formation of MDCK cysts.

METHODS

Using MDCK cells cultured in collagen gel as the experimental model, we investigated how renal cells organize to form cysts. To delineate the role of apoptosis in the process of cyst formation, MDCK cells were transfected with the bcl-2 gene. Characterization of apoptosis was studied by morphological and biochemical methods.

RESULTS

Bcl-2 overexpression conferred resistance to apoptosis. Cultured in collagen gel, Bcl-2 transfectants rarely formed a simple epithelial cyst, but instead remained as a multilayer cell aggregate containing central or multiple lumens, or even developing into branching structures.

CONCLUSIONS

Because Bcl-2 overexpression averts cyst cavitation, these data clearly indicate that apoptosis is an essential initial event for renal cyst formation.

Hepatocyte growth factor activator: a possible regulator of morphogenesis during fetal development of the rat gastrointestinal tract

The role played by the hepatocyte growth factor activator (HGFA) during morphogenesis of the gastrointestinal tract was investigated in fetal rats between days 16 and 21 of gestation. By our recently established method using chelation and dissecting microscope, samples could be separated into epithelium and mesenchyme, essentially without cross-contamination. The expression of the gene for HGFA together with those for hepatocyte growth factor (HGF) and its receptor, c-met, was investigated in each tissue element by RT-PCR. In the fetal rat gastrointestinal tract, mRNA signals for the HGFA gene were observed only in epithelia expressing c-met mRNA. In contrast, expression of HGF mRNA was limited to the mesenchymal elements, indicating the presence of a local HGF system in the gastrointestinal tract; an inactive form of HGF (proHGF) is secreted from the mesenchyme and then cleaved into the active form by HGFA secreted by the target epithelia. During the period of morphogenesis and histodifferentiation in the gastrointestinal tract, enhanced expression of the genes for HGF and its receptor/c-met was evident, with elevated HGFA mRNA level observed throughout the gastrointestinal tract except in the forestomach, where mRNA expression was barely detectable. These results strongly suggest the possibility that morphogenesis of the gastrointestinal tract is regulated not only by a local increase in production of HGF, but also by enhanced proteolytic activation of proHGF. Thus, it is probable that locally synthesized HGFA plays a significant role as a regulator of the morphogenic action of HGF during gastrointestinal tract development.

Hepatocyte growth factor and Madin-Darby canine kidney cells: in vitro models of epithelial cell movement and morphogenesis

It is becoming increasingly apparent that epithelial cell movement and changes in morphology are central to both development and regeneration of epithelial organs and are involved with pathological processes such as transformation of epithelia to carcinoma and metastasis. Hepatocyte growth factor (HGF) is a mesenchymally derived growth factor with pleiotrophic effects on epithelia depending on culture conditions. In vivo, HGF plays a role in mesenchymal-epithelial interactions. Madin-Darby canine kidney (MDCK) cells, which share many properties with polarized epithelia in vivo, are remarkably sensitive to HGF. In vitro models of HGF-treated MDCK cells have proven to be useful for the study of epithelial cell movement and changes in morphology. When cultured on plastic at low density, MDCK cells scatter in response to HGF. MDCK cells grown as cell suspensions in collagen gels form complex branching tubular structures in response to HGF. When cultivated as a monolayer on permeant supports, MDCK cells are well polarized with established E-cadherin mediated cell-cell junctions and dedifferentiate in response to HGF. Some of the mechanisms responsible for changes in cell movement and morphology that have been characterized using these models are summarized in this review. Models of MDCK cells exposed to HGF will continue to be useful in the study of epithelial cell movement and morphogenesis in vitro and will provide important clues into the cellular mechanisms important during in vivo epithelial processes such as organ development, regeneration, and transformation to carcinoma.

Morphogenetic mechanisms of epithelial tubulogenesis: MDCK cell polarity is transiently rearranged without loss of cell-cell contact during scatter factor/hepatocyte growth factor-induced tubulogenesis

Many organ systems are composed of networks of epithelial tubes. Recently, molecules that induce development of epithelial tubules and regulate sites of branching have been identified. However, little is known about the mechanisms regulating cell rearrangements that are necessary for tubule formation. In this study we have used a scatter factor/hepatocyte growth factor-induced model system of MDCK epithelial cell tubulogenesis to analyze the mechanisms of cell rearrangement during tubule development. We examined the dynamics of cell polarity and cell-cell junctions during tubule formation and present evidence for a multistep model of tubulogenesis in which cells rearrange without loss of cell-cell contacts and tubule lumens form de novo. A three-dimensional analysis of markers for apical and basolateral membrane subdomains shows that epithelial cell polarity is transiently lost and subsequently regained during tubulogenesis. Furthermore, components of cell-cell junctional complexes undergo profound rearrangements: E-cadherin is randomly distributed around the cell surface, desmoplakins I/II accumulate intracellularly, and the tight junction protein ZO-1 remains localized at sites of cell-cell contact. This suggests that differential regulation of cell-cell junctions is important for the formation of tubules. Therefore, during tubulogenesis, cell-cell adhesive contacts are differentially regulated while the polarity and specialization of plasma membrane subdomains reorganize, enabling cells to remain in contact as they rearrange into new structures.

Architectural patterns in branching morphogenesis in the kidney

During kidney development, several discrete steps generate its three-dimensional pattern including specific branch types, regional differential growth of stems, the specific axes of growth and temporal progression of the pattern. The ureteric bud undergoes three different types of branching. In the first, terminal bifid type, a lateral branch arises and immediately bifurcates to form two terminal branches whose tips induce the formation of nephrons. After 15 such divisions (in humans) of this specifically renal type of branching, several nephrons are induced whose connecting tubules fuse and elongate to form the arcades. Finally, the last generations undergo strictly lateral branching to form the cortical system. The stems of these branches elongate in a highly regulated pattern. The molecular basis of these processes is unknown and we briefly review their potential mediators. Differential growth in three different axes of the kidney (cortico-medullary, dorsoventral and rostro-caudal) generate the characteristic shape of the kidney. Rapid advances in molecular genetics highlight the need for development of specific assays for each of these discrete steps, a prerequisite for identification of the involved pathways. The identification of molecules that control branching (the ultimate determinant of the number of nephrons) has acquired new urgency with the recent suggestion that a reduced nephron number predisposes humans to hypertension and to progression of renal failure.

Regulation of adhesion and migration in the germinal center microenvironment

T cell dependent humoral immune responses are initiated by the activation of naive B cells in the T cell areas of the secondary lymphoid tissues. This primary B cell activation leads to migration of germinal center (GC) cell precursors into B cell follicles where they engage follicular dendritic cells (FDC) and T cells, and differentiate into memory B cells or plasma cells. Both B cell homing to the GC and interaction with FDC critically depend on integrin-mediated adhesion. We have recently indentified the c-met-encoded receptor tyrosine kinase and its ligand, the growth and motility factor hepatocyte growth factor/scatter factor (HGF/SF), as a novel paracrine signalling pathway regulating B cell adhesion (van der Voort et al., 1997, J. Exp. Med. 185, 2121-2131). The c-Met protein is expressed on B cells localized in the dark zone of the GC (centroblasts) and is induced by CD40 plus BCR ligation. Stimulation of c-Met with HGF/SF, which is produced at high levels by tonsillar stromal cells and FDC, leads to receptor phosphorylation and to enhanced integrin-mediated adhesion of B cells to both VCAM-1 and fibronectin. Interestingly, these responses to HGF/SF are promoted by heparan-sulfate proteoglycan forms of CD44 (CD44-HS). Like c-Met, CD44-HS is induced on B cells by CD40 ligation. It efficiently binds HGF/SF and strongly promotes signalling through c-Met. We conclude that integrin regulation during antigen specific B cell differentiation involves cross-talk between the HGF/SF-c-Met pathway and CD44-HS.

Hepatocyte growth factor (HGF) in patients with pneumonia: a comparison between survivors and non-survivors

Hepatocyte growth factor (HGF) is a multifunctional growth factor. After lung injury HGF is secreted in the lung and promotes reconstruction of the damaged organ. We measured, retrospectively, the serum HGF concentrations collected on admission in 55 patients with bacterial pneumonia, using an enzyme-linked immunosorbent assay (ELISA). The patients were divided into 3 groups: Group 1 was survivors with normal liver function (n = 14), Group 2 was survivors with abnormal liver function (n = 31) and Group 3 was non-survivors (n = 10). Median concentrations of HGF were elevated in Groups 1 and 2; and no statistically significant difference between these 2 groups was found. Group 3 had a median HGF concentration within the reference range, significantly lower than both Group 1 and Group 2. In addition LDH was significantly higher in non-survivors as compared with survivors. The combination of LDH and HGF concentrations discriminated between survivors and non-survivors (sensitivity 0.90 and specificity 0.96). The results support the hypothesis that increased levels of HGF might be a natural part of the healing process of lung injury, irrespective of liver involvement, and that patients without increased HGF levels, especially those with concomitant liver function impairment, may have a poor prognosis.

Crystal structure of the NK1 fragment of human hepatocyte growth factor at 2.0 A resolution

BACKGROUND

Hepatocyte growth factor (HGF) is a mitogen for hepatocytes and has also been implicated as an epithelial morphogen in tumor invasion. HGF activates its specific cellular receptor, c-met, through an aggregation mechanism potentiated by heparan sulfate glycosaminoglycans. HGF consists of an N-terminal (N) domain, four kringle domains (the first of which carries receptor-binding determinants), and an inactive serine-protease-like domain. NK1, a naturally occurring fragment of HGF, acts as an antagonist of HGF in the absence of heparin.

RESULTS

The N domain of NK1 consists of a central five-stranded antiparallel beta sheet flanked by an alpha helix and a two-stranded beta ribbon. The overall N domain structure in the context of the NK1 fragment is similar to the structure of the isolated domain; two lysines and an arginine residue coordinate a bound sulfate ion. The NK1 kringle domain is homologous to kringle 4 from plasminogen, except that the lysine-binding pocket is altered by the insertion of a glycine residue. Here, a HEPES molecule is bound in the pocket. The asymmetric unit of the crystal contains a 'head-to-tail' NK1 dimer. We use this dimer to propose a model of the NK2 fragment of HGF.

CONCLUSIONS

A cluster of exposed lysine and arginine residues in or near the hairpin-loop region of the N domain might form part of the NK1 heparin-binding site. In our NK2 model, both kringle domains pack loosely against the N domain, and a long, positively charged groove lines the interface. This groove might be involved in glycosaminoglycan binding. The HGF receptor-binding determinants are clustered near the binding pocket of the first kringle domain, opposite the N domain.

Mammary fibroblast-derived hepatocyte growth factor stimulates growth and morphogenesis of mouse mammary tumor cells in primary culture

We have recently isolated a mammary growth factor from the conditioned medium of mouse mammary stromal fibroblasts and identified it as a mouse homologue of human HGF (hepatocyte growth factor). To elucidate the role of HGF in mouse mammary tumorigenesis, we produced recombinant mouse HGF and examined its effects on primary cultures of mouse mammary tumor cells in this study. HGF at concentrations above 20 ng/ml maximally stimulated the growth of mammary tumor cells in primary monolayer culture. HGF also stimulated the three-dimensional growth and branching morphogenesis of mammary tumor cells cultured inside collagen gels. A comparison of the growth-stimulating activity of HGF with that of EGF (epidermal growth factor) and KGF (keratinocyte growth factor) revealed that HGF is the most potent growth factor among the three. Immunological studies using an antibody against mouse HGF demonstrated that 74% of the growth-stimulating activity present in the mammary fibroblast-conditioned medium was abolished by the antibody, indicating that HGF is the major growth factor produced by the fibroblasts. These observations thus suggest a role for HGF as a mammary stromal fibroblast-derived factor which stimulates growth and morphogenesis of adjacent mammary tumor cells in vivo.

Selective and organotypic culture of intrahepatic bile duct cells from adult pig liver

Secondary culture of nontransformed bile duct epithelium has been difficult to achieve. STO feeder cell-dependent secondary cultures of adult pig bile duct cells were established from primary cultures of adult pig liver cells. Adult pig hepatocytes exhibited limited or no replication and were lost from the secondary culture at Passage 3 or 4. In contrast, adult pig bile duct cells replicated and were carried for 4-8 passages in secondary culture. A simple method to produce nearly pure pig intrahepatic bile duct cultures was first to freeze a relatively crude liver cell preparation. Upon subsequent thawing, all hepatocytes and most macrophages were lysed. Bile duct cells composed 95% of the surviving cells after the freeze/thaw, and they grew out rapidly. The bile duct cells grew on top of the STO feeder cells as closely knit epithelial, colonial outgrowths. Histocytochemical and biochemical analyses demonstrated high levels of gamma-glutamyltranspeptidase activity and low levels of P450 activity in the bile duct cultures. The bile duct cells spontaneously adopted a multicellular ductal morphology after 7-10 d in static culture which was similar to that found in in vivo pig liver. Transmission electron microscopic examination revealed complex junctions and desmosomes typical of epithelium, and lumenally projecting cilia typical of in vivo intrahepatic bile ductules. This simple method for the coculture of pig intrahepatic bile duct cells which adopt in vivo-like structure may facilitate biological studies of this important, but difficult to culture, cell type.

Morphogenetic effects of neuregulin (neu differentiation factor) in cultured epithelial cells

Neuregulin, or neu differentiation factor, induces cell proliferation or differentiation through interaction with members of the ErbB family of receptor tyrosine kinases. We report that neuregulin can also induce profound morphogenic responses in cultured epithelial cells of different origins. These effects include scattering of small epithelial islands and rearrangement of larger cell islands into ordered ring-shaped arrays with internal lumens. The ring-forming cells are interconnected by cadherin- and beta-catenin-containing adherens junctions. In confluent cultures, neuregulin treatment induces formation of circular lumenlike gaps in the monolayer. Both cell scattering and ring formation are accompanied by a marked increase in cell motility that is independent of hepatocyte growth factor/scatter factor and its receptor (c-Met). Affinity-labeling experiments implied that a combination of ErbB-2 with ErbB-3 mediates the morphogenic signal of neuregulin in gastric cells. Indeed, a similar morphogenic effect could be reconstituted in nonresponsive cells by coexpression of ErbB-2 and -3. We conclude that a heterodimer between the kinase-defective neuregulin receptor, ErbB-3, and the coreceptor, ErbB-2, mediates the morphogenetic action of neuregulin.