Sequestration of a hepatocyte growth factor in extracellular matrix in normal adult rat liver

Activation of hepatocyte growth factor by two homologous proteases, blood-coagulation factor XIIa and hepatocyte growth factor activator

Hepatocyte growth factor (HGF) is secreted as an inactive single-chain precursor from the producing cells, and normally remains in this form associated with the extracellular matrix. In response to tissue injury, the single-chain precursor is converted to a biologically active heterodimer by a serine protease, the activity of which is induced in the injured tissue. We have previously identified HGF activator, a serum serine protease that activates single-chain HGF. The sequence of HGF activator cDNA revealed that the HGF activator is homologous to blood-coagulation factor XIIa. In this study, we found that coagulation factor XIIa has an ability to activate single-chain HGF. Factor XIIa exhibited a significant level of HGF-converting activity in the presence of dextran sulfate, although the specific activity of factor XIIa was slightly lower than that of the HGF activator. Since factor XIIa is activated during the initiation of contact activation induced by tissue injury, factor XIIa may function as an HGF-converting enzyme together with HGF activator in the injured tissue. C1-inhibitor, antithrombin III and alpha 2-antiplasmin, that regulate the blood-clotting activity of factor XIIa, were also effective against the HGF-converting activity of factor XIIa. Furthermore, factor XIIa was not active in the HGF-converting activity in serum. Thus, the HGF-converting activity of factor XIIa may be regulated by these serum inhibitors.

Biological activation of pro-HGF (hepatocyte growth factor) by urokinase is controlled by a stoichiometric reaction

Hepatocyte growth factor (HGF) is a paracrine inducer of morphogenesis and invasive growth in epithelial and endothelial cells. HGF is secreted by mesenchymal cells as an inactive precursor (pro-HGF). The crucial step for HGF activation is the extracellular hydrolysis of the Arg494-Val495 bond, which converts pro-HGF into alpha beta-HGF, the high-affinity ligand for the Met receptor. We previously reported that the urokinase-type plasminogen activator (uPA) activates pro-HGF in vitro. We now show that this is a stoichiometric reaction, and provide evidence for its occurrence in tissue culture. Activation involves the formation of a stable complex between pro-HGF and uPA. This complex was isolated from the in vitro reaction of pure uPA with recombinant pro-HGF, as well as from the membrane of target cells, after sequential addition of uPA and pro-HGF. On the cell membrane, the uPA-HGF complex was bound to the Met receptor. Monocytic cell lines, and primary monocytes after adhesion, activated efficiently pro-HGF both on their surface and in the culture medium. This activation was inhibited by anti-catalytic anti-uPA antibodies, and occurred by a stoichiometric reaction. The stoichiometry of the activation reaction suggests that the biological effects of HGF can be titrated in vivo by the level of uPA activity. Adequate amounts of uPA can be locally provided by the macrophages, which would condition the tissue microenvironment by rendering HGF bioavailable to its target cells.

Effects of ethanol feeding on the interaction of rat hepatocytes with laminin peptides

Laminin, a complex glycoprotein of the extracellular matrix, contains a number of biologically active sites. These sites are involved in cell growth, attachment, differentiation, and gene expression. Our previous studies have shown that chronic ethanol consumption by rats impairs hepatocyte attachment to various components of the extracellular matrix including laminin. In this study, three synthetic peptides (PA22-2, YIGSR, and RGD) that correspond to three distinct functional sites on the laminin molecule were used to investigate the effect of ethanol consumption on their cognate receptors. Initially, varying concentrations of each peptide were incubated with isolated hepatocytes from ethanol-fed and pair-fed control rats. These hepatocytes were then assayed for the ability to attach to laminin. The results indicated that all three peptides effectively inhibited laminin-mediated cell adhesion: the degree of inhibition appeared similar between pair-fed controls and ethanol-fed animals. Of the three peptides, PA22-2 showed the most dramatic inhibition of attachment. Therefore, we investigated the ability of hepatocytes to attach directly to PA22-2 itself. Attachment of hepatocytes from ethanol-fed animals to PA22-2 was impaired by 30% after 4 days and 90% by 14 days. Conversely, no significant difference in attachment to the entire laminin molecule was observed in ethanol-fed animals at these early time points. These results indicated that the ethanol-induced impairment of hepatocyte attachment to laminin may be caused by the decreased interaction of hepatocytes with specific functional sites on the laminin molecule and that specific receptors on the hepatocyte may be affected differently.(ABSTRACT TRUNCATED AT 250 WORDS)

Hepatocyte growth factor and macrophage inflammatory protein 1 beta: structurally distinct cytokines that induce rapid cytoskeletal changes and subset-preferential migration in T cells

T-cell migration into tissue depends on a cascade of rapid and selective adhesive interactions with endothelium. "Triggering" is a step in that cascade required to activate T-cell integrins. Hepatocyte growth factor (HGF) may be a physiologically relevant trigger, since we demonstrate that HGF can induce both adhesion and migration of human T-cell subsets and can be detected immunohistochemically on inflamed endothelium. HGF preferentially induces responses from T cells of memory phenotype, in contrast to macrophage inflammatory protein 1 beta (MIP-1 beta), a chemokine which acts preferentially on naive cells. HGF, like the chemokines, binds to heparin, and HGF retained in extracellular matrix is efficient in promoting migration. Further, both MIP-1 beta and HGF induce actin polymerization within seconds, kinetics that approach those required to contribute to physiologic triggering. HGF is a member of a structural family distinct from the chemokines, whose only known receptor is the tyrosine kinase c-Met. HGF induces tyrosine phosphorylation on T cells apparently via a distinct receptor, since no c-Met is detectable by surface staining, PCR, or anti-phosphotyrosine immunoprecipitation. Thus, promotion of T-cell adhesion and migration are previously undescribed functions of HGF that we propose are relevant to selective T-cell recruitment.

High glucose and hyperosmolality stimulate hepatocyte growth factor secretion from cultured human mesangial cells

Hepatocyte growth factor is a recently cloned potent mitogen to hepatocytes, but its extrahepatic roles are not completely defined. It causes proliferation of endothelial and epithelial cells implicating potential action in the glomerulus. We aimed to determine whether cultured human mesangial cells secrete hepatocyte growth factor and the effect of high glucose conditions. Mesangial cells were isolated from the normal cortex of a child's kidney. After differential glomerular sieving and trypsin digestion of glomeruli, mesangial cells were cultured in 20% fetal calf serum/RPMI. Glucose concentration in the medium was adjusted to 5 mmol/l, 11 mmol/l, 25 mmol/l or 5 mmol/l/20 mmol/l mannitol to correct for osmolality. After 0, 24, 48, 72 h incubation, hepatocyte growth factor was measured in the supernatant by enzyme immuno assay using recombinant hepatocyte growth factor and monoclonal antibodies to human hepatocyte growth factor. Hepatocyte growth factor was secreted by cultured mesangial cells. High glucose and hyperosmolar conditions caused a 100-200% increase in hepatocyte growth factor secretion at 48-72 h (p = 0.001). Hepatocyte growth factor secretion at 48 h in 5 mmol/l glucose was 16.46 +/- 1.09 ng/ml (mean +/- SEM), 11 mmol/l glucose: 32.98 +/- 4.54, 25 mmol/l glucose: 33.32 +/- 7.89, 5 mmol/l glucose/20 mmol/l mannitol: 34.05 +/- 3.64; at 72 h in 5 mmol/l glucose: 23.92 +/- 2.85 ng/ml, 11 mmol/l glucose: 28.26 +/- 2.03, 25 mmol/l glucose: 62.04 +/- 12.2, 5 mmol/l glucose/20 mmol/l mannitol: 45.76 +/- 6.25. Trypan blue exclusion demonstrated membrane integrity.(ABSTRACT TRUNCATED AT 250 WORDS)

Targeting of the SF/HGF receptor to the basolateral domain of polarized epithelial cells

Scatter Factor, also known as Hepatocyte Growth Factor (SF/HGF), has pleiotropic functions including direct control of cell-cell and cell-substrate adhesion in epithelia. The subcellular localization of the SF/HGF receptor is controversial. In this work, the cell surface distribution of the SF/HGF receptor was studied in vivo in epithelial tissues and in vitro in polarized MDCK monolayers. A panel of monoclonal antibodies against the beta chain of the SF/HGF receptor stained the basolateral but not the apical surface of epithelia lining the lumen of human organs. Radiolabeled or fluorescent-tagged anti-receptor antibodies selectively bound the basolateral cell surface of MDCK cells, which form a polarized monolayer sealed by intercellular junctions, when grown on polycarbonate filters in a two-chamber culture system. The receptor was concentrated around the cell-cell contact zone, showing a distribution pattern overlapping with that of the cell adhesion molecule E-cadherin. The basolateral localization of the SF/HGF receptor was confirmed by immunoprecipitation after domain selective cell surface biotinylation. When cells were fully polarized the SF/HGF receptor became resistant to non-ionic detergents, indicating interaction with insoluble component(s). In pulse-chase labeling and surface biotinylation experiments, the newly synthesized receptor was found exclusively at the basolateral surface. We conclude that the SF/HGF receptor is selectively exposed at the basolateral plasma membrane domain of polarized epithelial cells and is targeted after synthesis to that surface by direct delivery from the trans-Golgi network.

Long-term ethanol feeding selectively impairs the attachment of rat perivenous hepatocytes to extracellular matrix substrates

BACKGROUND/AIMS

We have previously shown that long-term ethanol consumption by rats results in a profound decrease in hepatocyte attachment to various extracellular matrix substrates. The present study investigated whether differences in attachment exist between cells isolated from either the periportal or perivenous regions of the liver.

METHODS

Rats received long-term ethanol, and hepatocytes were selectively isolated by the digitonin-collagenase perfusion method. The ability of periportal and perivenous cells isolated from ethanol-fed and pair-fed control rats to attach to plates coated with either laminin, fibronectin, or type I collagen was then assayed.

RESULTS

With all substrates, the attachment of perivenous hepatocytes isolated from ethanol-fed animals was significantly impaired. Time-course studies showed that although the rate of attachment of perivenous cells from ethanol-fed animals was only slightly reduced, a dramatic decrease in absolute attachment was observed. Furthermore, the perivenous cells isolated from ethanol-fed animals detached more readily from the substrate-coated plates than the corresponding periportal cells or either periportal or perivenous cells from pair-fed controls.

CONCLUSIONS

Long-term ethanol consumption impairs hepatocyte-extracellular matrix interactions more severely in the perivenous region of the liver. This finding could be relevant to the pathological changes observed in alcoholic liver injury.

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

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

Decrease in the hepatic clearance of hepatocyte growth factor in carbon tetrachloride-intoxicated rats

To examine whether a decrease in hepatic uptake, clearance or both of hepatocyte growth factor contributes to increased plasma hepatocyte growth factor levels, we kinetically analyzed hepatic hepatocyte growth factor handling using rats with carbon tetrachloride-induced liver injury in both in vivo and perfused liver systems. After the intravenous administration of tracer 125I-hepatocyte growth factor, the time profile of trichloroacetic acid-precipitable 125I-hepatocyte growth factor was analyzed, and tissue clearance and total body plasma clearance were determined. For the tissues examined (liver, kidney, lung, spleen and adrenal), liver and adrenal clearance of 125I-hepatocyte growth factor decreased significantly. It was found that the hepatic clearance explains the bulk of the total body plasma clearance. The hepatic clearance and the total body clearance decreased to minimums (approximately 40% of control) 24 hr after carbon tetrachloride administration and recovered to near-control values over a 6-day period. At 24 hr after carbon tetrachloride administration, a single-pass liver perfusion of 125I-hepatocyte growth factor was performed, and its results were compared with the control results. After a 15-min perfusion of 125I-hepatocyte growth factor, we washed the liver sequentially with heparin and then with acid buffer to separately determine the cell-surface-bound and internalized 125I-hepatocyte growth factor. In carbon tetrachloride-intoxicated rats, both the acid-washable binding and the internalized 125I-hepatocyte growth factor dropped to almost half of the control values, but the decrease in heparin-washable binding was minimal. In contrast, when 125I-hepatocyte growth factor was perfused with excess unlabeled hepatocyte growth factor (135 pmol/L), mostly saturating the cell-surface receptors, the change in cell-surface-bound 125I-hepatocyte growth factor and internalized 125I-hepatocyte growth factor in carbon tetrachloride-intoxicated rats was minimal. This finding, along with our previous finding that the cell-surface hepatocyte growth factor receptors are greatly down-regulated in carbon tetrachloride-intoxicated rats, suggests that the hepatic clearance of hepatocyte growth factor through receptor-mediated endocytosis decreases in carbon tetrachloride-intoxicated rats. The decrease in the hepatic clearance of hepatocyte growth factor could be one of the causes of the elevated hepatocyte growth factor level in the circulating blood in liver diseases.

Properties and functions of scatter factor/hepatocyte growth factor and its receptor c-Met

Scatter factor (SF), a cell motility factor with a multimodular structure, is identical to hepatocyte growth factor (HGF), a potent mitogen of various cell types. The receptor for SF/HGF has recently been identified as the c-Met proto-oncogene product, a transmembrane receptor tyrosine kinase. Depending on the target cells and culture conditions, SF/HGF has several distinct activities in vitro, i.e., it induces cell motility, proliferation, invasiveness, tubular morphogenesis, angiogenesis, or cytotoxicity. In vivo, SF/HGF might be involved in tissue regeneration, tumor progression, and embryological processes.

Tyrosine kinase receptors in the control of epithelial growth and morphogenesis during development

The c-ros, c-met and c-neu genes encode receptor-type tyrosine kinases and were originally identified because of their oncogenic potential. However, recent progress in the analysis of these receptors and their respective ligands indicate that they do not mediate exclusively mitogenic signals. Rather, they can induce cell movement, differentiation or morphogenesis of epithelial cells in culture. Interestingly, the discussed receptors are expressed in embryonal epithelia, whereas direct and indirect evidence shows that the corresponding ligands are produced in mesenchymal cells. In development, signals given by mesenchymal cells are major driving forces for differentiation and morphogenesis of epithelia; embryonal epithelia are generally unable to differentiate without the appropriate mesenchymal factors. The observed activities of these receptor/ligand systems in cultured cells and their expression patterns indicate that they regulate epithelial differentiation and morphogenesis also during embryogenesis and suggest thus a molecular basis for mesenchymal epithelial interactions.

Increase in portal flow induces c-myc expression in isolated perfused rat liver

We examined expression of the c-myc oncogene in isolated perfused livers to elucidate the mechanisms involved in triggering the proliferation of hepatocytes after partial hepatectomy (PH). During perfusion with a 1:1 mixture of Dulbecco's modified Eagle's medium and the oxygen transport fluid FC-43, rat livers were two-thirds resected (PH), and further perfused for 1 1/2 hours at the physiological portal flow throughout the perfusion. Expression of c-myc in the perfused livers with PH(+) was ten times higher than in those with PH(-). Furthermore, expression of c-myc in the PH(-) livers perfused with a threefold volume of the physiological portal flow was 5-10 times higher than that in the livers perfused with the physiological portal flow. The perfusates that passed through the livers did not induce DNA synthesis of primary cultured hepatocytes. These results suggest that an increase in the portal flow volume may act as a trigger for hepatocyte proliferation after PH.

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

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

Hepatocyte growth factor is a potent angiogenic factor which stimulates endothelial cell motility and growth

Hepatocyte Growth Factor (HGF, also known as Scatter Factor) is a powerful mitogen or motility factor in different cells, acting through the tyrosine kinase receptor encoded by the MET protooncogene. Endothelial cells express the MET gene and expose at the cell surface the mature protein (p190MET) made of a 50 kD (alpha) subunit disulfide linked to a 145-kD (beta) subunit. HGF binding to endothelial cells identifies two sites with different affinities. The higher affinity binding site (Kd = 0.35 nM) corresponds to the p190MET receptor. Sub-nanomolar concentrations of HGF, but not of a recombinant inactive precursor, stimulate the receptor kinase activity, cell proliferation and motility. HGF induces repairs of a wound in endothelial cell monolayer. HGF stimulates the scatter of endothelial cells grown on three-dimensional collagen gels, inducing an elongated phenotype. In the rabbit cornea, highly purified HGF promotes neovascularization at sub-nanomolar concentrations. HGF lacks activities related to hemostasis-thrombosis, inflammation and endothelial cells accessory functions. These data show that HGF is an in vivo potent angiogenic factor and in vitro induces endothelial cells to proliferate and migrate.

Alteration of rat liver proteoglycans during regeneration

Sepharose CL-6B column chromatography of crude extracts from the slices of regenerating rat livers after partial hepatectomy and sham-operated controls labeled with [35S]sulfuric acid revealed an enhancement of [35S]sulfate incorporation into proteoglycan fractions during regeneration. The 35S-labeled proteoglycans contained heparan sulfate (more than 80% of the total) and chondroitin/dermatan sulfate. The 35S-incorporation into both glycosaminoglycans increased to maxima 3-5 days after partial hepatectomy and decreased thereafter toward the respective control levels. When [35S]sulfuric acid was replaced by [3H]glucosamine, similar results were obtained. These results suggest that the maximal stimulation of proteoglycan synthesis in regenerating rat liver follows the maximal mitosis of hepatic cells 1-2 days after partial hepatectomy. The 35S-labeled proteoglycans from regenerating liver 3 days after partial hepatectomy and control were analyzed further. They were similar in chromatographic behavior on a gel filtration or an anion-exchange column and in glycosaminoglycan composition. Their glycosaminoglycans were indistinguishable in electrophoretic mobility. However, these proteoglycans were slightly but significantly different in their affinity to octyl-Sepharose and in the molecular-weight distribution of their glycosaminoglycans.

Hepatocyte growth factor modulates migration and proliferation of human microvascular endothelial cells in culture

Epidermal growth factor (EGF) induces tubular formation of cultured human omental microvascular endothelial (HOME) cells and EGF also stimulates cell migration as well as expression of tissue type plasminogen activator (t-PA). Here we studied the effects of hepatocyte growth factor (HGF) on cell proliferation, cell migration and expression of t-PA and other related genes. Migration of confluent HOME cells into the denuded space was stimulated by HGF after being wounded with razor blade, but at a reduced rate in comparison with EGF. HOME cells could be proliferated in response to exogenous 100 ng/ml of HGF at rates comparable to that of 20 ng/ml EGF. The chemotactic activity of HOME cells was significantly stimulated by HGF in a dose-dependent manner when assayed by Boyden chamber. HGF did not efficiently enhance expression of both the t-PA gene and a tissue inhibitor of metalloproteinase gene whereas it stimulated expression of plasminogen activator inhibitor-1. Our present study provides a new evidence that some of the biological effects of HGF on HOME cells in culture are similar to those of EGF.

Expression of hepatocyte growth factor mRNA in regenerating rat liver after partial hepatectomy

Hepatocyte Growth Factor (HGF) is a potent complete mitogen for primary cultures of hepatocytes in vitro. There is strong evidence that this novel growth factor may mediate hepatocyte regeneration after liver damage. We have shown previously that the amount of immunoreactive HGF markedly increases in the serum of rats soon after partial hepatectomy or CCl4 administration. In the present paper, we demonstrate that the level of HGF mRNA in rat liver also dramatically increases from 3 to 6 hours post hepatectomy, peaks at 12 hr and gradually returns to undetectable levels by 72 to 96 hours post hepatectomy. In separate experiments, DNA synthesis (in vivo) was determined in rat liver remnants after partial hepatectomy. DNA synthesis peaked 24 hr after hepatectomy, 12 hr after the peak of HGF mRNA expression. These results suggest that HGF may be one of the major early signals that triggers hepatocyte proliferation during liver regeneration.