Activation of hepatocyte growth factor (HGF) by endogenous HGF activator is required for metanephric kidney morphogenesis in vitro

A distinct cardiopharyngeal mesoderm genetic hierarchy establishes antero-posterior patterning of esophagus striated muscle

In most vertebrates, the upper digestive tract is composed of muscularized jaws linked to the esophagus that permits food ingestion and swallowing. Masticatory and esophagus striated muscles (ESM) share a common cardiopharyngeal mesoderm (CPM) origin, however ESM are unusual among striated muscles as they are established in the absence of a primary skeletal muscle scaffold. Using mouse chimeras, we show that the transcription factors Tbx1 and Isl1 are required cell-autonomously for myogenic specification of ESM progenitors. Further, genetic loss-of-function and pharmacological studies point to MET/HGF signaling for antero-posterior migration of esophagus muscle progenitors, where Hgf ligand is expressed in adjacent smooth muscle cells. These observations highlight the functional relevance of a smooth and striated muscle progenitor dialogue for ESM patterning. Our findings establish a Tbx1-Isl1-Met genetic hierarchy that uniquely regulates esophagus myogenesis and identify distinct genetic signatures that can be used as framework to interpret pathologies arising within CPM derivatives.

Investigating proteins and proteases composing amniotic and allantoic fluids during chicken embryonic development

In amniotes, the amniotic fluid is a significant contributor to fetal development and health. While numerous studies have been conducted in mammalian amniotic fluid, the composition of amniotic and other extraembryonic fluids in avian egg along with their physiological functions remain largely unexplored. In such a context, our objective was to characterize the chicken amniotic fluid (AmF) and allantoic fluid (AlF) properties, protein composition, and some associated functions from day 8 to day 16 of incubation. SDS-PAGE combined to mass spectrometry analysis revealed common and specific proteins to each fluid, suggesting distinct properties and functions. Indeed, major AlF proteins are mostly "egg yolk" proteins involved in lipid, vitamin metabolisms, and metal ion transport, while major AmF proteins resemble those of albumen. Drastic changes in the AmF protein profiles were observed during incubation, when the albumen transfers from day 12 onwards, while few changes were detected for the AlF protein profile. The decreases in osmolality (from 231 to 183 mOsm/kg) and pH (from 8.26 to 7.26) observed in the AlF during incubation are associated with water and electrolytes reallocation for the embryo needs. In contrast, AmF pH value remained stable (≈7.5). Active proteolytic enzymes have been identified in the 2 fluids using gelatin zymography, followed by mass spectrometry analysis for protease identification. A total of 12 proteases was detected in the AlF, compared to 5 in the AmF. We have shown that AlF concentrates proteolytic enzymes assumed to participate in digestive processes: aminopeptidase N, dipeptidyl peptidase-4, meprin A, and 72 kDa type IV collagenase preproprotein. The other proteases identified in both fluids also could have a role in morphogenesis (hepatocyte growth factor activator, suppressor of tumorigenicity 14, astacin-like metalloendopeptidase) and hemostasis (prothrombin and coagulation factor X). Altogether, these data suggest that the roles of chicken AlF and AmF are not merely associated with protection of the embryo and regulation of metabolic disposable wastes, but also they could have more sophisticated roles during embryonic development.

Regulating temporospatial dynamics of morphogen for structure formation of the lacrimal gland by chitosan biomaterials

The lacrimal gland is an important organ responsible for regulating tear synthesis and secretion. The major work of lacrimal gland (LG) is to lubricate the ocular surface and maintain the health of eyes. Functional deterioration of the lacrimal gland happens because of aging, diseases, or therapeutic complications, but without effective treatments till now. The LG originates from the epithelium of ocular surface and develops by branching morphogenesis. To regenerate functional LGs, it is required to explore the way of recapitulating and facilitating the organ to establish the intricate and ramified structure. In this study, we proposed an approach using chitosan biomaterials to create a biomimetic environment beneficial to the branching structure formation of developing LG. The morphogenetic effect of chitosan was specific and optimized to promote LG branching. With chitosan, increase in temporal expression and local concentration of endogenous HGF-related molecules creates an environment around the emerging tip of LG epithelia. By efficiently enhancing downstream signaling of HGF pathways, the cellular activities and behaviors were activated to contribute to LG branching morphogenesis. The morphogenetic effect of chitosan was abolished by either ligand or receptor deprivation, or inhibition of downstream signaling transduction. Our results elucidated the underlying mechanism accounting for chitosan morphogenetic effects on LG, and also proposed promising approaches with chitosan to assist tissue structure formation of the LG.

Synergistic signaling of tumor cell invasiveness by hepatocyte growth factor and hypoxia

Hepatocyte growth factor (HGF) signaling promotes tumor invasiveness in renal cell carcinoma (RCC) and other cancers. In clear cell RCC, VHL loss generates pseudohypoxia that exacerbates HGF-driven invasion through β-catenin deregulation. Hypoxia also enhances HGF-driven invasiveness by papillary RCC cells, but in the absence of VHL, loss signaling integration involves three parallel routes: 1) hypoxia-induced reactive oxygen species production and decreased DUSP2 expression, leading to enhanced mitogen-activated protein kinase (MAPK) cascade activation; 2) reactive oxygen species-induced diacylglycerol production by phospholipase Cγ, leading to protein kinase C activation and increased protein phosphatase- 2A activity, thereby suppressing HGF-induced Akt activation; and 3) a profound shift from HGF-enhanced, proliferation- oriented metabolism to autophagy-dependent invasion and suppression of proliferation. This tripartite signaling integration was not unique to RCC or HGF; in RCC cells, invasive synergy induced by the combination of hypoxia and epidermal growth factor occurred through the same mechanism, and in estrogen receptor-positive breast cancer cells, this mechanism was suppressed in the absence of estrogen. These results define the molecular basis of growth factor and hypoxia invasive synergy in VHL-competent papillary RCC cells, illustrate the plasticity of invasive and proliferative tumor cell states, and provide signaling profiles by which they may be predicted.

Hepatocyte Growth Factor Isoforms in Tissue Repair, Cancer, and Fibrotic Remodeling

Hepatocyte growth factor (HGF), also known as scatter factor (SF), is a pleotropic factor required for normal organ development during embryogenesis. In the adult, basal expression of HGF maintains tissue homeostasis and is up-regulated in response to tissue injury. HGF expression is necessary for the proliferation, migration, and survival of epithelial and endothelial cells involved in tissue repair in a variety of organs, including heart, lung, kidney, liver, brain, and skin. The administration of full length HGF, either as a protein or using exogenous expression methodologies, increases tissue repair in animal models of tissue injury and increases angiogenesis. Full length HGF is comprised of an N-terminal hairpin turn, four kringle domains, and a serine protease-like domain. Several naturally occurring alternatively spliced isoforms of HGF were also identified. The NK1 variant contains the N-terminal hairpin and the first kringle domain, and the NK2 variant extends through the second kringle domain. These alternatively spliced forms of HGF activate the same receptor, MET, but they differ from the full length protein in their cellular activities and their biological functions. Here, we review the species-specific expression of the HGF isoforms, their regulation, the signal transduction pathways they activate, and their biological activities.

Concise review: can the intrinsic power of branching morphogenesis be used for engineering epithelial tissues and organs?

Branching morphogenesis is critical to the development of organs such as kidney, lung, mammary gland, prostate, pancreas, and salivary gland. Essentially, an epithelial bud becomes an iterative tip-stalk generator (ITSG) able to form a tree of branching ducts and/or tubules. In different organs, branching morphogenesis is governed by similar sets of genes. Epithelial branching has been recapitulated in vitro (or ex vivo) using three-dimensional cell culture and partial organ culture systems, and several such systems relevant to kidney tissue engineering are discussed here. By adapting systems like these it may be possible to harness the power inherent in the ITSG program to propagate and engineer epithelial tissues and organs. It is also possible to conceive of a universal ITSG capable of propagation that may, by recombination with organ-specific mesenchymal cells, be used for engineering many organ-like tissues similar to the organ from which the mesenchyme cells were derived, or toward which they are differentiated (from stem cells). The three-dimensional (3D) branched epithelial structure could act as a dynamic branching cellular scaffold to establish the architecture for the rest of the tissue. Another strategy-that of recombining propagated organ-specific ITSGs in 3D culture with undifferentiated mesenchymal stem cells-is also worth exploring. If feasible, such engineered tissues may be useful for the ex vivo study of drug toxicity, developmental biology, and physiology in the laboratory. Over the long term, they have potential clinical applications in the general fields of transplantation, regenerative medicine, and bioartificial medical devices to aid in the treatment of chronic kidney disease, diabetes, and other diseases.

Systemic administration of naked plasmid encoding HGF attenuates puromycin aminonucleoside-induced damage of murine glomerular podocytes

Podocyte injury is considered to play important roles in the pathogenesis of human glomerular disease. There is accumulating evidence suggesting that hepatocyte growth factor (HGF) elicits preventive activity for glomerular cells in animal models of chronic renal diseases. In this study, we demonstrated that delivery of a naked plasmid vector encoding the human HGF gene into mice by a hydrodynamic-based in vivo gene transfection approach markedly reduced proteinuria and attenuated podocyte injury in a mouse model induced by puromycin aminonucleoside (PAN) injection. Systemic administration by rapid injection via the tail vein of a naked plasmid containing HGF cDNA driven under a cytomegalovirus promoter (pCMV-HGF) produced a remarkable level of human HGF protein in the circulation. Tissue distribution studies suggested that the kidney expressed a high level of the HGF transgene. Meanwhile, compared with tubules and interstitium, a higher level of exogenous HGF protein was detected in the glomeruli. Administration of pCMV-HGF dramatically abated the urine albumin excretion and podocyte injury in PAN nephropathy in mice. Exogenous expression of HGF produced evidently beneficial effects, leading to restoration of Wilms' tumor-1 (WT1) and α-actinin-4 expression and attenuation of ultrastructural damage of the podocytes. In vitro, HGF not only restored WT1 and α-actinin-4 expression but also inhibited albumin leakage of podocytes incubated with PAN in a Transwell culture chamber. These results suggest that HGF might provide a novel strategy for amelioration of podocyte injury.

Hepatocyte growth factor activator (HGFA): pathophysiological functions in vivo

Hepatocyte growth factor activator (HGFA) is a serine protease initially identified as a potent activator of hepatocyte growth factor/scatter factor. Hepatocyte growth factor/scatter factor is known to be critically involved in tissue morphogenesis, regeneration, and tumor progression, via its receptor, MET. In vivo, HGFA also activates macrophage-stimulating protein, which has roles in macrophage recruitment and inflammatory processes, cellular survival and wound healing through its receptor, RON. Therefore, the pericellular activity of HGFA might be an important factor regulating the activities of these multifunctional cytokines in vivo. HGFA is secreted mainly by the liver, circulates in the plasma as a zymogen (pro-HGFA), and is activated in response to tissue injury, including tumor growth. In addition, local production of pro-HGFA by epithelial, stromal or tumor cells has been reported. Although the generation of HGFA-knockout mice revealed that the role played by HGFA in normal development and physiological settings can be compensated for by other protease systems, HGFA has important roles in regeneration and initial macrophage recruitment in injured tissue in vivo. Insufficient activity of HGFA results in impaired regeneration of severely damaged mucosal epithelium, and may contribute to the progression of fibrotic lung diseases. On the other hand, deregulated excess activity of HGFA may be involved in the progression of some types of cancer.

Hepatocyte growth factor system in the mouse uterus: variation across the estrous cycle and regulation by 17-beta-estradiol and progesterone

Hepatocyte growth factor (HGF) and its receptor MET have been implicated in uterine development, pregnancy, and endometrial disorders, such as endometriosis and carcinoma. In vitro studies have shown that HGF acts as a mitogen, motogen, and morphogen on endometrial epithelial cells. However, the expression and regulation of HGF and MET in the uteri of different species remain obscure. The present study aimed to investigate the changes of HGF, MET, and HGF activator (HGFA) expression in the uterine endometrium during the estrous cycle in mice and to explore estrogen and progesterone regulation of their expression. MKI67 immunostaining was conducted to examine the association between HGF/MET expression and endometrial cell proliferation. Endometrial epithelial and stromal cells both expressed HGF, HGFA, and MET, but the cell type-specific patterns changed during the cycle. Estrogen and progesterone differentially regulated HGF, MET, and HGFA expression. Progesterone up-regulated their expression in the stroma and down-regulated their expression in the luminal epithelium, whereas 17-beta-estradiol down-regulated their expression in the glandular epithelium. The pattern of HGF/MET overall correlated with that of MKI67. In conclusion, HGF, HGFA, and MET expression in mouse uterus changes during the estrous cycle in a stage-, cell type-, and compartment-specific manner under the influence of estrogen and progesterone. HGF likely plays a role in cyclic endometrial remodeling, such as cell proliferation via autocrine/paracrine mechanisms in mouse uterus.

Plasma level of soluble c-Met is tightly associated with the clinical risk of preeclampsia

OBJECTIVE

The objective of the study was to examine the relevance of the soluble form c-Met (sMet) with the clinical risk for severe preeclampsia.

STUDY DESIGN

This prospective case-control study was performed by using plasma derived from 44 preeclamptic and 51 uncomplicated pregnant women. Plasma concentration of sMet was measured with specific enzyme-linked immunosorbent assay, and the predictive values were determined based on the receiver-operating characteristic (ROC) curves analysis.

RESULTS

Plasma s-Met level in normal pregnant women changed in a gestation-dependent manner, peaking at weeks 19-24. In women with severe preeclampsia, the circulating sMet level was significantly lower than that in the gestational stage-matched controls during gestational weeks 15-30. The ROC curve analysis revealed a significant correlation between plasma sMet level and the risk of developing severe preeclampsia.

CONCLUSION

Plasma sMet could serve as a potential biomarker for predicting severe preeclampia at early second trimester of pregnancy.

Targeting the Met signaling pathway in renal cancer

Renal cell carcinoma (RCC), the most common form of kidney cancer, accounts for 3% of all adult malignancies and its incidence has significantly increased over the last 20 years. RCC claims 13,000 lives annually in the USA and more than 100,000 worldwide. A better understanding of the molecular basis of RCC has facilitated the development of novel and more selective therapeutic approaches. An important role in RCC oncogenesis is played by the receptor for HGF, Met, which has attracted considerable attention, more recently as a molecular target for cancer therapy, and several drugs selectively targeting this pathway are now in clinical trials. This review will focus on efforts to understand the role of the Met signaling pathway in renal cancer and how this has contributed to the development of potent and selective drug candidates.

VHL loss of function and its impact on oncogenic signaling networks in clear cell renal cell carcinoma

Loss of von Hippel-Lindau tumor suppressor gene function occurs in familial and most sporadic clear cell renal cell carcinoma, resulting in the aberrant expression of genes that control cell proliferation, metabolism, invasion and angiogenesis. The molecular mechanisms by which loss of function leads to tumorigenesis are not yet fully defined. The von Hippel-Lindau gene product is part of an ubiquitin ligase complex that targets hypoxia inducible factors for polyubiquitination and proteasomal degradation, linking hypoxia response genes to renal cell carcinoma oncogenesis. Loss von Hippel-Lindau gene function also promotes cell invasiveness in response to hepatocyte growth factor, an important regulator of kidney development and renal homeostasis. Increased cell invasiveness is mediated by another ubiquitin ligase target with relevance to the molecular pathogenesis of renal cell carcinoma: beta-catenin. This discovery and other recent insights into kidney cancer oncogenesis implicate convergent developmental and homeostatic signaling pathways in tumorigenesis, tumor invasiveness and metastasis.

Distribution of attenuated salmonellae carrying hepatocyte growth factor genes in murine gastric ulcers

AIM: To highlight tissue distribution of attenuated salmonellae carrying hepatocyte growth factor (HGF) genes in murine gastric ulcers and thereby to provide a basis for HGF application in gene therapy for gastric ulcers.

METHODS: Eighty acetic acid-induced gastric ulcer rats were randomly divided into two groups: HGF treatment group (n = 40 rats) and green fluorescent protein (GFP) treatment group (n = 40 rats). Intragastric administration of attenuated salmonellae carrying HGF and GFP was performed on rats, each one with 0.2 mL, and once every two days for totally 3 times. Three rats in GFP group were killed each time on day 1, 3, 5, 7, 9 and frozen sections were made from stomach, liver, intestines, spleen and kidney to observe tissue distribution of target genes under fluorescence microscopy; 3 rats in HCF group were killed each time on day 1, 3, 5, 7, 9, 11, 13, 15, 17, 19 and 21 to obverse tissue expression using ELISA and to detect tissue distribution of eukaryotic expression vector using PCR.

RESULTS: In GFP group, some strong fluorescence was observed in the stomach and intestines under fluorescence microscopy, and weak fluorescence in liver, spleen and kidneys. The intensity of fluorescence reached its peak on day 5 and day 7. In HGF group, high-level HGF gene expression by ELISA was detected in stomach, liver, spleen, kidney and intestines with higher expression in the intestines and stomach. CMV promoter fragment of eukaryotic expression vectors was detected in stomach, liver, spleen, kidney, large intestine and small intestine.

CONCLUSION: As a cellular vector, orally-administrated attenuated salmonellae could transfer target genes eukaryotic expression vector into stomach and intestinal tissues for gastric ulcer treatment in rats.

Enhanced Analysis of the Mouse Plasma Proteome Using Cysteine-Containing Tryptic Glycopeptides

A comprehensive understanding of the mouse plasma proteome is important for studies using mouse models to identify protein markers of human disease. To enhance our analysis of the mouse plasma proteome, we have developed a method for isolating low-abundance proteins using a cysteine-containing glycopeptide strategy. This method involves two orthogonal affinity capture steps. First, glycoproteins are coupled to an azlactone copolymer gel using hydrazide chemistry and cysteine residues are then biotinylated. After trypsinization and extensive washing, tethered N-glycosylated tryptic peptides are released from the gel using PNGase F. Biotinylated cysteinyl-containing glycopeptides are then affinity selected using a monomeric avidin gel and analyzed by LC-MS/MS. We have applied the method to a proteome analysis of mouse plasma. In two independent analyses using 200 muL each of C57BL mouse plasma, 51 proteins were detected. Only 42 proteins were seen when the same plasma sample was analyzed by glycopeptides only. A total of 104 N-glycosylation sites were identified. Of these, 17 sites have hitherto not been annotated in the Swiss-Prot database whereas 48 were considered probable, potential, or by similarity - i.e., based on little or no experimental evidence. We show that analysis by cysteine-containing glycopeptides allows detection of low-abundance proteins such as the epidermal growth factor receptor, the Vitamin K-dependent protein Z, the hepatocyte growth factor activator, and the lymphatic endothelium-specific hyaluronan receptor as these proteins were not detected in the glycopeptide control analysis.

The von Hippel-Lindau tumor suppressor gene product represses oncogenic beta-catenin signaling in renal carcinoma cells

Loss of von Hippel-Lindau (VHL) tumor suppressor gene function occurs in familial and most sporadic clear cell renal cell carcinoma (RCC), resulting in the aberrant expression of genes that control cell proliferation, invasion, and angiogenesis. The molecular mechanisms by which VHL loss leads to tumorigenesis are not yet fully defined. VHL loss has been shown to allow robust RCC cell motility, invasiveness, and morphogenesis in response to hepatocyte growth factor (HGF) stimulation, processes that are known to contribute to tumor invasiveness and metastatic potential. Among the most likely intracellular mediators of these HGF-driven activities is beta-catenin, a structural link between cadherens and the actin cytoskeleton, as well as a gene transactivator. We show that reconstitution of VHL expression in RCC cells repressed HGF-stimulated beta-catenin tyrosyl phosphorylation, adherens junction disruption, cytoplasmic beta-catenin accumulation, and reporter gene transactivation in RCC cells. Ectopic expression of a ubiquitination-resistant beta-catenin mutant specifically restored HGF-stimulated invasion and morphogenesis in VHL-transfected RCC cells. VHL gene silencing in non-RCC renal epithelial cells phenotypically mimicked VHL loss in RCC, and HGF-driven invasiveness was blocked by the expression of a dominant-negative mutant of Tcf. We conclude that, unlike many other cancers, where HGF pathway activation contributes to malignancy through the acquisition of autocrine signaling, receptor overexpression, or mutation, in RCC cells VHL loss enables HGF-driven oncogenic beta-catenin signaling. These findings identify beta-catenin as a potential target in biomarker and drug development for RCC.

Hepatocyte growth factor activation inhibitors (HAI-1 and HAI-2) regulate HGF-induced invasion of human breast cancer cells

Hepatocyte growth factor (HGF) plays a plethora of roles in cancer metastasis and tumour growth. The interaction between tumour cells and their surrounding stromal environment is a crucial factor regulating tumour invasion and metastasis. Stromal fibroblasts are the main source of HGF in the body, and release HGF as an inactive precursor (pro-HGF). HGF activator (HGFA), matriptase, urokinase-type plasminogen activator and hepsin are the main factors responsible for converting pro-HGF into active HGF. HAI-1 and HAI-2 are 2 novel Kunitz-type serine protease inhibitors that regulate HGF activity through inhibition of HGFA, matriptase and hepsin action. Recent studies demonstrate that HAI-1 and HAI-2 may also potently inhibit a number of other pro-metastatic serine proteases and therefore have direct bearing on the spread of tumours. Our study examined the potential of these HAI's to suppress the influence of HGF and regulate cancer metastasis. We generated a retroviral expression system that induced HAI expression in a human fibroblast cell line. Forced expression of either HAI-1 or HAI-2 in these fibroblasts resulted in a dramatic decrease in the production of bioactive hepatocyte growth factor (HGF). This reduction in HGF activity subsequently suppressed HGF's metastatic influence on breast cancer cells. To further assess the anti-cancer properties of HAI-1 and HAI-2 we generated recombinant HAI proteins. These recombinant HAI proteins possessed the ability to potently quench HGF activity. We also demonstrate that these recombinant HAI's suppressed fibroblast-mediated breast cancer invasion. An additional ribozyme transgenes study revealed that elimination of HAI-1 and HAI-2 expression, in an MDA-MB-231 breast cancer cell line, significantly enhanced the migratory, proliferative and invasive nature of these breast cancer cells. Overall, our data demonstrates the important roles of HAI-1 and HAI-2 in cancer metastasis, and reveals that these serine protease inhibitors display strong therapeutic potential.

Functional analysis of HGF/MET signaling and aberrant HGF-activator expression in diffuse large B-cell lymphoma

Inappropriate activation of MET, the receptor tyrosine kinase for hepatocyte growth factor (HGF), has been implicated in tumorigenesis. Although we have previously shown that HGF/MET signaling controls survival and proliferation of multiple myeloma (MM), its role in the pathogenesis of other B-cell malignancies has remained largely unexplored. Here, we have examined a panel of 110 B-cell malignancies for MET expression, which, apart from MM (48%), was found to be largely confined to diffuse large B-cell lymphomas (DLBCLs) (30%). No amplification of the MET gene was found; however, mutational analysis revealed 2 germ-line missense mutations: R1166Q in the tyrosine kinase domain in 1 patient, and R988C in the juxtamembrane domain in 4 patients. The R988C mutation has recently been shown to enhance tumorigenesis. In MET-positive DLBCL cells, HGF induces MEK-dependent activation of ERK and PI3K-dependent phosphorylation of PKB, GSK3, and FOXO3a. Furthermore, HGF induces PI3K-dependent α4β1 integrin-mediated adhesion to VCAM-1 and fibronectin. Within the tumor microenvironment of DLBCL, HGF is provided by macrophages, whereas DLBCL cells themselves produce the serine protease HGF activator (HGFA), which autocatalyzes HGF activation. Taken together, these data indicate that HGF/MET signaling, and secretion of HGFA by DLBCL cells, contributes to lymphomagenesis in DLBCL. (Blood. 2006;107:760-768)

Branching ducts similar to mesonephric ducts or ureteric buds in teratomas originating from mouse embryonic stem cells

Ureteric bud epithelial cells and metanephric mesenchymal cells that comprise the metanephric kidney primordium are capable of producing nephrons and collecting ducts through reciprocal inductive interaction. Once these cells are induced from pluripotent embryonic stem (ES) cells, they have the potential to become powerful tools in the regeneration of kidney tissues. In this study, we investigated these renal primordial cells and structures in mouse ES cell outgrowths and their transplants. Gene expression essential for early kidney development was examined by RT-PCR in embryoid body (EB) outgrowths and their transplants in adult mice. Histochemical detection of kidney primordial structures and gene expression analysis coupled with laser microdissection were performed in transplant tissues. RT-PCR analysis detected gene expression of Pax-2, Lim-1, c-Ret, Emx2, Sall1, WT-1, Eya-1, GDNF, and Wnt-4 in the EB outgrowths from days 6–9 of expansion onward, and also in the teratoma tissues 14 and 28 days after transplantation. Histochemical analysis 14 days after transplantation showed that some ducts were positive for Pax-2, endo A cytokeratin, kidney-specific cadherin, and Dolichos biflorus agglutinin and that dichotomous branching of these ducts had occurred. These staining patterns and morphological features are intrinsic for mesonephric ducts and ureteric buds. In long-term survival of 28 days, Pax-2-immunoreactivity disappeared in some renal primordia-like structures, indicating their differentiation. Some ducts were accompanied by mesonephric nephron-like convoluted tubules. RT-PCR analysis of those structures collected by microdissection confirmed that they expressed kidney development-related genes. In conclusion, these data suggest the potential of ES cells to produce renal primordial duct structures and provides an insight into the regeneration of kidney tissues.

Follicular dendritic cells catalyze hepatocyte growth factor (HGF) activation in the germinal center microenvironment by secreting the serine protease HGF activator

Ag-specific B cell differentiation, the process that gives rise to plasma cells and memory B cells, involves the formation of germinal centers (GC). Within the GC microenvironment, multiple steps of B cell proliferation, selection, and maturation take place, which are controlled by the BCR in concert with cytokines and contact-dependent signals from follicular dendritic cells (FDCs) and T cells. Signaling by the multifunctional cytokine hepatocyte growth factor (HGF) and its receptor MET has been shown to induce integrin-mediated adhesion of B cells to VCAM-1, which is expressed by FDCs. In the present study we have examined the expression of regulatory components of the HGF/MET pathway, including HGF activator (HGFA), within the secondary lymphoid organ microenvironment. We show that MET is expressed by both centroblasts and plasma cells, and that HGFA is expressed by plasma cells. Because we have shown that HGF is a potent growth and survival factor for malignant plasma cells, HGF may also serve as a survival factor for normal plasma cells. Furthermore, we demonstrate that FDCs are the major source for HGF and its activator within the GC microenvironment. Both HGF and HGFA are expressed by FDCs in the GC dark zone (CD21high/CD23low), but not in the light zone (CD21high/CD23high). These findings suggest that HGF and HGFA provided by dark zone FDCs help to regulate the proliferation, survival, and/or adhesion of MET-positive centroblasts.

Conformational lability in serine protease active sites: structures of hepatocyte growth factor activator (HGFA) alone and with the inhibitory domain from HGFA inhibitor-1B

Hepatocyte growth factor activator (HGFA) is a serine protease that converts hepatocyte growth factor (HGF) into its active form. When activated HGF binds its cognate receptor Met, cellular signals lead to cell growth, differentiation, and migration, activities which promote tissue regeneration in liver, kidney and skin. Intervention in the conversion of HGF to its active form has the potential to provide therapeutic benefit where HGF/Met activity is associated with tumorigenesis. To help identify ways to moderate HGF/Met effects, we have determined the molecular structure of the protease domain of HGFA. The structure we determined, at 2.7 A resolution, with no pseudo-substrate or inhibitor bound is characterized by an unconventional conformation of key residues in the enzyme active site. In order to find whether this apparently non-enzymatically competent arrangement would persist in the presence of a strongly-interacting inhibitor, we also have determined, at 2.6 A resolution, the X-ray structure of HGFA complexed with the first Kunitz domain (KD1) from the physiological inhibitor hepatocyte growth factor activator inhibitor 1B (HAI-1B). In this complex we observe a rearranged substrate binding cleft that closely mirrors the cleft of other serine proteases, suggesting an extreme conformational dynamism. We also characterize the inhibition of 16 serine proteases by KD1, finding that the previously reported enzyme specificity of the intact extracellular region of HAI-1B resides in KD1 alone. We find that HGFA, matriptase, hepsin, plasma kallikrein and trypsin are potently inhibited, and use the complex structure to rationalize the structural basis of these results.

Implications of gene networks for understanding resilience and vulnerability in the kidney branching program

Branching morphogenesis in the kidney is tightly regulated. Whereas disruption of certain pathways produces catastrophic effects, numerous instances exist in which mutation of ostensibly key molecules has minimal apparent phenotypic consequence. We suggest how the network structure of gene interactions in the branching program might explain these findings as well as apparant discrepancies between in vivo and in vitro studies. Emerging genetic, cell-biological, and microarray data should help test and/or clarify these ideas.

Multiple myeloma cells catalyze hepatocyte growth factor (HGF) activation by secreting the serine protease HGF-activator

Multiple myeloma (MM) is a common hematologic neoplasm consisting of malignant plasma cells, which expand in the bone marrow. A potential key signal in the evolution of MM is hepatocyte growth factor (HGF), which acts as a potent paracrine and/or autocrine growth factor and survival factor for MM cells. Proteolytic conversion of HGF into its active form is a critical limiting step in HGF/MET signaling. Here, we show that malignant MM plasma cells convert HGF into its active form and secrete HGF-activator (HGFA), a serine protease specific for HGF activation. By using serine protease inhibitors and neutralizing antibodies, we demonstrate that HGFA produced by the MM cells is responsible for their ability to catalyze HGF activation. We, therefore, suggest that autocatalyzation of HGF conversion by MM cells is an important step in HGF/MET-induced myeloma growth and survival, which may have implications for the management of this incurable form of cancer. (Blood. 2004;104:2172-2175)

Hepatocyte growth factor activator inhibitor types 1 and 2 are expressed by tubular epithelium in kidney and down-regulated in renal cell carcinoma

PURPOSE

Hepatocyte growth factor (HGF) and its receptor MET have been implicated in kidney development and renal cell carcinoma (RCC) progression. HGF is secreted as an inactive proform and it must be activated to initiate MET signaling. HGF activator (HGFA) activates pro-HGF in injured tissue. We evaluated the expression of HGFA and its endogenous inhibitors HAI-1 and HAI-2 in normal kidney and RCC.

MATERIALS AND METHODS

We examined the gene expression of HGFA, HAI-1, HAI-2, HGF and MET in a normal kidney by laser captured microdissection, followed by reverse transcriptase-polymerase chain reaction. We also quantified the mRNA levels of these proteins in 14 RCC cases by real-time reverse transcriptase-polymerase chain reaction.

RESULTS

HAI-1 and HAI-2 were abundant in the normal kidney. The uriniferous tubules showed the highest levels of HAI-1 and HAI-2 mRNA. HGFA was hardly detectable in the normal kidney. However, in the kidney with RCC a low but distinct level of HGFA mRNA became detectable in the tumor and adjacent renal tissue. The HAI-1 mRNA level was significantly and consistently down-regulated in RCC relative to normal tissue. HAI-2 mRNA was also significantly low in the advanced stage of RCC. MET was up-regulated in most cases of RCC.

CONCLUSIONS

HAI-1 and HAI-2 were expressed in renal tubular epithelial cells. The expression of the 2 HAIs was significantly down-regulated in RCC, whereas HGFA expression was enhanced in the diseased kidney, suggesting an imbalance between HAI and its target proteinases, including HGFA, in favor of proteinase activities in RCC.

Immunohistochemical localization of hepatocyte growth factor activator (HGFA) in developing mouse liver tissues. Heterogeneous distribution of HGFA protein

Hepatocyte growth factor activator (HGFA) can activate the single-chain hepatocyte growth factor (HGF) required for embryonic development. We studied the immunohistochemical (IHC) localization of HGFA in adult mouse liver and its developmental changes from embryonic day 12 to postnatal day 30. A heterogeneous distribution of HGFA was observed in adult liver tissues. The hepatocytes around the hepatic veins were preferentially positive for HGFA, whereas those in other areas were negative. Depending on the vascular diameter, the hepatic veins were bordered by a one- to three-cell-thick layer of hepatocytes positive for HGFA, which showed evidence of cell-cell heterogeneity in staining intensity. Immunoelectron microscopy detected ubiquitous distribution of the gold particle reaction product for HGFA in the cytoplasm of these hepatocytes, especially in the rough endoplasmic reticulum. Developmental analysis indicated that there was hardly any staining of HGFA until postnatal day 0 and that noticeable staining was initially detected in the pericentral hepatocytes on postnatal day 3. Subsequently, immunoreactivity increased and the distinct staining pattern had been established by postnatal day 30. These results suggest that HGFA proteins are produced in the hepatocytes surrounding the efferent hepatic veins in the mouse and that development of the unique distributing pattern takes place postnatally.

Epithelial polarity and tubulogenesis in vitro

The most fundamental type of organization of cells in metazoa is that of epithelia, which comprise sheets of adherent cells that divide the organism into topologically and physiologically distinct spaces. Some epithelial cells cover the outside of the organism; these often form multiple layers, such as in skin. Other epithelial cells form monolayers that line internal organs, and yet others form tubes that infiltrate the whole organism, carrying liquids and gases containing nutrients, waste and other materials. These tubes can form elaborate networks in the lung, kidney, reproductive passages and vasculature tree, as well as the many glands branching from the digestive system such as the liver, pancreas and salivary glands. In vitro systems can be used to study tube formation and might help to define common principles underlying the formation of diverse types of tubular organ.

Role of cancer cell-stroma interaction in invasive growth of cancer cells

Invasive growth is one of the hallmarks of cancer malignancy. To date, a significant body of evidence is accumulating in favor of the notion that invasive growth results from the cross-talk between cancer cells and the host stromal cells, comprising fibroblasts (myofibroblasts), endothelial cells, and leukocytes, all of which are themselves invasive. In this review we describe cross-talk between invasive cancer cells and host stromal fibroblasts and an impact of pericellular microenvironment on the invasive phenotype of cancer cells, focusing on two molecules, extracellular matrix metalloproteinase inducer (EMMPRIN, also known as tumor cell-derived collagenase stimulatory factor, basigin, CD147) and hepatocyte growth factor (HGF, also known as scatter factor). Both molecules are deeply involved in the regulation of invasion-associated cellular activities, such as pericellular proteolysis, migration and ectopic survival of cancer cells.

Unusual proteolytic activation of pro-hepatocyte growth factor by plasma kallikrein and coagulation factor XIa

Hepatocyte growth factor (HGF), the ligand for the receptor tyrosine kinase c-Met, is composed of an alpha-chain containing four Kringle domains (K1-K4) and a serine protease domain-like beta-chain. Receptor activation by HGF is contingent upon prior proteolytic conversion of the secreted inactive single chain form (pro-HGF) into the biologically active two chain form by a single cleavage at the Arg(494)-Val(495) bond. By screening a panel of serine proteases we identified two new HGF activators, plasma kallikrein and coagulation factor XIa (FXIa). The concentrations of kallikrein and FXIa to cleave 50% (EC(50)) of (125)I-labeled pro-HGF during a 4-h period were 10 and 17 nm. Unlike other known activators, both FXIa and kallikrein processed pro-HGF by cleavage at two sites. Using N-terminal sequencing they were identified as the normal cleavage site Arg(494)-Val(495) and the novel site Arg(424)-His(425) located in the K4 domain of the alpha-chain. The identity of this unusual second cleavage site was firmly established by use of the double mutant HGF(R424A/R494E), which was completely resistant to cleavage by kallikrein and FXIa. Experiments with another mutant form, HGF(Arg(494) --> Glu), indicated that cleavage at the K4 site was independent of a prior cleavage at the primary, kinetically preferred Arg(494)-Val(495) site. The cleavage at the K4 site had no obvious consequences on HGF function, because it was fully capable of phosphorylating the c-Met receptor of A549 cells. This may be explained by the disulfide bond network in K4, which holds the cleaved alpha-chain together. In conclusion, the ability of plasma kallikrein and FXIa to activate pro-HGF in vitro raises the possibility that mediators of inflammation and blood coagulation may also regulate processes that involve the HGF/c-Met pathway, such as tissue repair and angiogenesis.

Differentiative potential of human metanephric mesenchymal cells

OBJECTIVE

To evaluate the ability of mesenchymal cells derived from nonhematopoietic organs to form blood and other tissues in vitro and in vivo.

MATERIALS AND METHODS

Because of its mesodermic derivation, human fetal kidney was used as a source of mesenchymal cells. Two populations of kidney cells were studied at a nonclonal level: a crude preparation, and an adherent fraction that was derived from the first by propagation in vitro (MNMC). Both populations were transplanted into sheep fetuses and analyzed at intervals for the presence of human cells in different organs by flow cytometry, PCR, immunohistochemistry, and in situ hybridization. Secondary transplantation studies were performed using human hematopoietic cells obtained from the bone marrow (BM) of primary recipients.

RESULTS

MNMC were Thy-1(+), CD51(+), CD44(+), CD45(-), and vimentin(+), a phenotype consistent with that of metanephric mesenchyme. The crude population displayed the same phenotype but was contaminated with 0.4% CD34(+)CD45(+) cells. Cells with hepatocyte-like morphology and phenotype were obtained from the MNMC after culture in specific inducing media. After transplantation, both populations of cells produced multilineage hematopoietic engraftment and gave rise to CD34(+) cells. Successful hematopoietic engraftment in secondary recipients demonstrated the generation of long-term engrafting hematopoietic stem cells from MNMC. PCR analysis confirmed human hematopoietic engraftment and revealed that human cells were also present within other organs. Liver sections of transplanted animals contained human albumin-producing hepatocyte-like cells.

CONCLUSION

A human metanephric mesenchymal cell population simultaneously gave rise to human blood and liver-like cells, suggesting that mesenchymal cells may represent a broad population of putative stem cells in multiple adult organs.

Genes and proteins in renal development

Metanephric kidney development begins with the formation of the metanephrogenic mesenchyme; this event depends on the prior action in the intermediate mesoderm of transcription factors such as Lim-1, Pax-2, Eya-1, and Foxc-1. Once it has formed, the mesenchyme secretes GDNF; this induces the nearby wolffian duct to produce a ureteric bud which invades the metanephrogenic mesenchyme and begins to arborize. Ureteric bud development and branching depends on the transcription factor Emx-2, the GDNF-cRet and probably the HGF/cMet, signalling systems, and the intracellular regulatory molecules formin IV and timeless. Proteins of the BMP family modulate ureteric bud branching and keep bud development in step with that of other tissue types. Proteins and glycosaminoglycans of the matrix, and their receptors, and also required. The metanephrogenic mesenchyme has a default fate of apoptosis and is dissuaded from suicide by factors secreted from the bud such as TGF-alpha, TIMP-2, EGF, and FGF-2. Other factors such as LIF and TGFbeta2 cooperate with these to induce clumps of mesenchyme cells to differentiate into nephrons, while BMP-7 appears to lead them instead to form stroma. As nephrons form, they express critical transcription factors such as WT-1, Pax-2, and Hoxa11 and d11, condense, and secrete Wnt-4. Wnt-4 acts in an autocrine loop to stimulate its own synthesis and is required for cells to differentiate into epithelia; its action is antagonized by sFRP-1, secreted by stroma, but this antagonism is itself inhibited by sFRP-2 made by the developing nephron. This system probably acts both to limit the spread of Wnt-4's influence and also to commit responding cells to their epithelial fate. As nephrons mature, regions of them differentiate to perform specific physiological functions, a process that requires the proteins WT-1, Lmx-1b, Notch-2, Jagged-1, and Hnf-1.

Expression of a hepatocyte growth-factor activator protein in turkey (Meleagris gallopavo) deferent duct epithelial cells

In previous research, we discovered that turkey deferent duct epithelial cells express a serine protease. Our experimental objective was to identify the gene that encodes this protein. A lambda phage cDNA library from duct cell mRNA was constructed. The library was screened using monoclonal antibodies previously produced against the turkey deferent-duct serine protease. Phage containing the protease cDNA was excised and re-circularized into plasmids. E. coli were transformed with plasmids containing protease cDNA, which was then isolated for sequencing. NCBI BLAST searches within the GenBank database returned 63.5 and 61.7% identity with murine and human hepatocyte growth-factor activator (HGFA) precursor, respectively. The turkey protease cDNA was then cloned into the pQE-32 expression vector and transformed into M15 cells for HIS-tagged expression of the recombinant protein, which was then purified using nickel-chelated Sepharose spin columns. Afterwards, Western blot analysis of the purified recombinant turkey protein revealed recognition by a monoclonal antibody specific to the proteolytic subunit of the turkey deferent duct protease. Therefore, these findings indicate that the recombinant HGFA precursor isolated from the deferent duct is the turkey seminal plasma protease that is secreted from the deferent duct. HGFA, a member of the Kringle-serine proteinase superfamily, can initiate diverse mitogenic, morphogenic and motogenic effects through its substrate hepatocyte growth factor. Although the presence of hepatocyte growth factor and its c-MET receptor have been reported in male mammalian reproductive tracts, our novel findings on the secretion of HGFA precursor from turkeys may help to elucidate the regulation of activated hepatocyte growth factor.

Opinion: Building epithelial architecture: insights from three-dimensional culture models

How do individual cells organize into multicellular tissues? Here, we propose that the morphogenetic behaviour of epithelial cells is guided by two distinct elements: an intrinsic differentiation programme that drives formation of a lumen-enclosing monolayer, and a growth factor-induced, transient de-differentiation that allows this monolayer to be remodelled.

Hepatocyte growth factor and the kidney

Hepatocyte growth factor (HGF) and its specific c-met receptor constitute a paired signaling system that plays an important role in renal development and in the maintenance of normal adult kidney structure and functions. HGF elicits potent mitogenic, motogenic, morphogenic, and antiapoptotic activities in renal tubular epithelial cells. The nature of these pleiotropic actions renders it to be specifically suited to preserve and to reconstitute the structural and functional integrity of renal tubules after acute renal injury. Emerging evidence also indicates that both endogenous and exogenous HGF are beneficial by inhibiting the onset and progression of chronic renal diseases in various animal models. Administration of exogenous HGF protein, or its gene, effectively inhibits the activation of matrix-producing myofibroblasts, attenuates extracellular matrix deposition and interstitial fibrosis, and suppresses profibrogenic cytokine transforming growth factor-beta1 and its type I receptor expression in vivo. Hence, although more studies are warranted to further clarify its role in various chronic renal fibrosis models, delivery of either HGF or its gene may hold promise as a novel therapeutic strategy for promoting initial protection and subsequently regenerative repair after acute insult, and for ameliorating renal fibrosis and kidney dysfunction in chronically diseased conditions.

Multiple roles of neurotrypsin in tissue morphogenesis and nervous system development suggested by the mRNA expression pattern

We have mapped the spatio-temporal expression of the multidomain serine protease neurotrypsin in the developing mouse by in situ hybridization. On embryonic day (E) 8, mRNA is detected in giant trophoblast cells, later in embryonic mesenchymal tissues. On E11, expression begins in Schwann cell precursors, olfactory epithelium, trigeminal ganglion, and midbrain. The floor plate shows strong expression on E12. Further prenatal development is characterized by rising neurotrypsin mRNA in sensory ganglia and motor neurons. Staining in cerebral cortex emerges around birth and culminates toward the end of the first week with a complex laminar and areal pattern. Expression in peripheral nerves and nonneural tissues vanishes soon after birth and the adult neuronal distribution is gradually established until weaning age. This developmental expression pattern suggests roles of neurotrypsin in morphogenesis of nonneural tissues, as well as in neural development, in particular in axonal target invasion, synaptogenesis, and Schwann cell differentiation.