Response of phenobarbital- and ciprofibrate-exposed hepatocytes to growth factors in type I collagen gels

The response of promoter-exposed hepatocytes to the complete hepatic mitogens hepatocyte growth factor (HGF), epidermal growth factor (EGF) and acidic fibroblast growth factor (aFGF) was studied. Male Fisher 344 rats were administered phenobarbital or ciprofibrate. Hepatocytes were isolated at various time points and cultured in type I collagen gels, a 3-dimensional culture system that allows stable long-term hepatocyte differentiation. DNA synthetic activity in response to addition of HGF, aFGF or EGF to the cultures was assayed by incorporation of [3H]thymidine. Administration of ciprofibrate to rats caused an immediate decreased growth response in hepatocytes to all three growth factors. Phenobarbital administration caused a gradual decrease in responsiveness to the growth factors: after 10 days, hepatocytes became insensitive to the mitogenic effects of HGF, EGF and aFGF. However, an early increase in responsiveness to HGF and aFGF occurred in phenobarbital-exposed hepatocytes. The results indicate that phenobarbital and ciprofibrate have similar inhibitory effects on hepatocyte DNA synthesis in culture after long-term in vivo exposure. However, their early effects on hepatocyte growth response differ considerably, suggesting that their effects on cellular proliferation occur via different mechanisms.

Hepatocyte growth factor, blood clearance, organ uptake, and biliary excretion in normal and partially hepatectomized rats

BACKGROUND

Hepatocyte growth factor (HGF) (also known as scatter factor (SF)) is a heterodimeric protein that is the most potent known complete mitogen for hepatocytes in culture. HGF is a mitogen for many epithelial cells including hepatocytes, kidney tubular epithelial cells, mammary epithelial cells, keratinocytes, etc. The protein encoded by the proto-oncogene c-met is the high affinity receptor for HGF. HGF concentration in the plasma dramatically increases after partial hepatectomy and in fulminant hepatic failure. This study describes the pharmacokinetics of HGF in the rat.

EXPERIMENTAL DESIGN

Human recombinant HGF (a gift from Genentech) was radioiodinated and shown to retain biologic activity and structure. Approximately 74 ng of [125I]HGF was injected into the penile vein of male Fisher rats 5 minutes after a complete bile fistula and jugular venous catheterization were performed for blood and bile sampling. Half of the rats were subjected to 70% partial hepatectomy.

RESULTS

The percentage of injected radioactivity present in the liver of control rats was 29.5% +/- 0.5% at 15 minutes and decreased to 8.6% +/- 1.0% at 120 minutes; the kidneys had 6.2% +/- 0.2% at 15 minutes, decreasing to 1.48% +/- 0.3% at 120 minutes. All the other organs examined had less than 1% of the injected radioactivity. The remaining radioactivity was present in low affinity sites in blood, bone, muscle, and skin. In control rats, radioactivity appeared in the bile within 3 minutes, reached a peak between 40 to 50 minutes, and tapered thereafter for a total 2-hour collection of 2.3% +/- 0.5%. In the partially hepatectomized rats, the HGF blood clearance was decreased (partial hepatectomy = 0.27 +/- 0.03 ml/minute; control = 0.53 +/- 0.06 ml/minute, p < 0.006), and the terminal half-life prolonged (partial hepatectomy = 124 +/- 11 minutes; control = 83 +/- 10 minutes, p < 0.03). The initial half-life for HGF, as extrapolated from the chart, was estimated at 3.8 minutes in control rats.

CONCLUSIONS

Liver is the principle organ for initial uptake of [125I]HGF; disappearance from the blood suggests multicompartment kinetics with a rapid phase and a slower phase; only a portion of the hepatic uptake appears in the bile; and partial hepatectomy decreases the blood clearance of [125I]HGF. These results are correlated with previous findings bearing on the role of HGF elevation after partial hepatectomy as a stimulus for transfer of hepatocytes from G0 to G1 early in liver regeneration after partial hepatectomy.

The effect of octreotide on hepatic regeneration in rats

The effect of the long-acting somatostatin analog octreotide on liver regeneration was studied in rats in vitro and in vivo. The effect of continuous subcutaneous octreotide infusion on regenerative liver weight and relative DNA synthesis was examined in rats that had undergone 70% hepatectomy. Administration of octreotide resulted in a 33% reduction of regenerating liver weight at 72 hours and a 67% reduction of regenerative hepatocellular hyperplasia at 24 hours. This effect was reversed within 12 hours after withdrawal of the drug. The mechanism for the inhibitory effect of octreotide appears to be indirect, because experiments in hepatocyte cultures did not demonstrate a direct inhibitory effect on serum-free or epidermal growth factor-induced regenerative hepatocyte proliferation. Because insulin levels were suppressed by octreotide in the in vivo experiments, suppression of hepatotrophs may be the mechanism by which octreotide inhibits liver regeneration.

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

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

The presence of hepatocyte growth factor in the developing rat

Hepatocyte growth factor (HGF), a heparin-binding polypeptide mitogen, stimulates DNA synthesis in adult rat and human hepatocytes and in several other cells of epithelial origin. Recently, it was determined that scatter factor (SF), a protein that has been shown to cause the dispersion and migration of epithelial cells in culture, is identical to HGF. Moreover, the receptor for HGF was identified as the product of the proto-oncogene, c-MET, a tyrosine kinase-containing transmembrane protein. c-MET expression has been reported in a variety of adult and embryonic mouse tissues. Similarly, we and others have demonstrated that HGF is expressed in various adult rat and human tissues. In the present study, the tissue distribution of HGF during rat development was determined by immunohistochemistry using an HGF-specific polyclonal antiserum. Between day 12 and day 19, immunoreactivity for HGF was present in various locations such as hematopoietic cells, somites, squamous epithelium of the esophagus and skin, periventricular germinal matrix of the brain, bronchial epithelium, renal collecting tubules and chondrocytes. After day 19, HGF immunoreactivity was also present in the pancreas, submaxillary glands and neural tissues. In addition to immunolocalizing HGF in tissue sections, bioreactive and immunoreactive HGF was extracted and purified from rat fetuses. Other studies demonstrated the presence of HGF and c-MET mRNA in total fetal rat, and in fetal and neonatal rat liver. Addition of purified HGF to fetal and neonatal rat liver cultures enriched for hepatocytes stimulated DNA synthesis up to six-fold over controls. These findings strongly suggest a pivotal role for this potent regulator of growth and development.

Proliferating cell nuclear antigen in human placenta and trophoblastic disease

Expression of proliferating cell nuclear antigen (PCNA), an auxiliary factor for the DNA polymerase delta, is closely related to cell proliferation. Using the monoclonal anti-PCNA antibody 19F4, we examined the distribution of PCNA in formalin-fixed, paraffin-embedded sections of mature and first-trimester placentas, 8 hydatidiform moles, and 7 choriocarcinomas. In normal placentas there was strong expression of PCNA in cytotrophoblastic nuclei, while the syncytium and the amnionic epithelium were PCNA unreactive. Staining of stromal cells was variable. These results are in complete agreement with the autoradiographic localization of [3H]thymidine incorporation and demonstrate that immunoreactivity for PCNA accurately defines areas of proliferative activity in routinely processed placental tissues. In choriocarcinomas and hydatidiform moles PCNA was predominantly expressed in the cytotrophoblast and intermediate trophoblast. Again, the syncytium was largely unreactive for PCNA. These findings indicate that even after neoplastic transformation the syncytium has comparatively little proliferative activity whereas the mononuclear trophoblastic cells divide actively.

Orotic acid, nucleotide-pool imbalance, and liver-tumor promotion: a possible mechanism for the mitoinhibitory effects of orotic acid in isolated rat hepatocytes

This study was designed to determine the possible mechanism by which orotic acid exerts its mitoinhibitory effect on rat hepatocytes in primary culture. Orotic acid inhibited, dose-dependently DNA synthesis in hepatocytes induced by epidermal growth factor, transforming growth factor alpha, hepatocyte growth factor, acidic fibroblast growth factor, or plasma from rats exposed to various liver cell-proliferative stimuli, such as two-thirds partial hepatectomy, lead nitrate, cyproterone acetate, ethylene dibromide, or a diet deficient in choline. Further, orotic acid inhibited DNA synthesis even when added 24 h after the hepatocytes were primed with transforming growth factor alpha. Taken together, these results suggested that the target site may not be at the level of the growth-factor receptor and receptor-mediated early events. In a preliminary experiment, orotic acid inhibited the expression of the ribonucleoside diphosphate reductase gene. Exposure to orotic acid results in an imbalance in nucleotide pools characterized by an increase in uridine nucleotides and a decrease in adenosine nucleotides. It is hypothesized that this imbalance in nucleotide pools inhibits the expression of the ribonucleoside diphosphate reductase gene and, therefore, is a likely target for the mitoinhibitory effect of orotic acid.

Hepatocyte regeneration in acute fulminant and nonfulminant hepatitis: a study of proliferating cell nuclear antigen expression

It has been suggested that in fulminant hepatitis it is the lack of hepatocyte regeneration that in the presence of an ongoing loss of hepatocytes leads to hepatic failure and ultimately determines the grim prognosis of this disease. However, little data are available concerning hepatocyte regeneration in human acute hepatitis. We compared the nuclear expression of proliferating cell nuclear antigen with the incorporation of bromodeoxyuridine in formalin-fixed, paraffin-embedded liver tissues of rats at different stages of regeneration after two-thirds partial hepatectomy. Immunohistochemical staining for proliferating cell nuclear antigen was performed using the monoclonal antibody 19F4. A good correlation was seen between nuclear labeling for bromodeoxyuridine and proliferating cell nuclear antigen, which indicates that the immunoreactivity for proliferating cell nuclear antigen accurately reflects hepatocyte proliferation. Subsequently, we determined the nuclear expression of proliferating cell nuclear antigen on archival paraffin-embedded samples of the normal human liver (8 cases), acute nonfulminant hepatitis (10 cases) and fulminant hepatitis (4 cases). The mean proliferating cell nuclear antigen labeling indices were the following: normal liver = 0.4%; acute nonfulminant hepatitis = 43.0%; and fulminant hepatitis = 45.9%. The indices for proliferating cell nuclear antigen were significantly greater in acute hepatitis than in the normal liver, reflecting the high cell turnover in hepatitis. However, no significant difference was seen between the expression of proliferating cell nuclear antigen in nonfulminant and fulminant acute hepatitis. These data suggest that the net loss of hepatocytes in fulminant hepatitis may not be caused by a lack of hepatocyte regeneration but rather results from overwhelming hepatocyte injury with subsequent cell death.

Plasma levels of HGF in rats treated with tumor promoters

Hepatocyte growth factor (HGF), mol. wt 105,000 is a potent mitogen for hepatocytes. HGF is strongly associated with compensatory regeneration in the liver after two-thirds partial hepatectomy and carbon tetrachloride administration. Plasma levels of HGF increase markedly during early stages of compensatory hyperplasia caused by these treatments. This is followed by an increase in HGF mRNA in the liver. This is in contrast to other growth factors for liver (epidermal growth factor, transforming growth factor alpha and acidic fibroblast growth factor) whose levels in plasma remain virtually undetectable during compensatory hyperplasia. We have shown that during augmentative hyperplasia caused by the tumor promoters alpha-hexachlorocyclohexane, phenobarbital and ciprofibrate, plasma levels of HGF also increase. This increase of HGF occurs during the transient wave of DNA synthesis caused by administration of these xenobiotics, providing further support for HGF as being the stimulator of DNA synthesis during both augmentative and compensatory hyperplasia.

Characterization of the effects of human placental HGF on rat hepatocytes

Hepatocyte growth factor (HGF) also known as hepatopoietin A (HPTA) (Michalopoulos, FASEB J., 4:176-187, 1990) is a heparin-binding growth factor whose characterization and tissue distribution have been reported elsewhere. This growth factor was recently cloned and its amino acid sequence determined under the name of hepatocyte growth factor (HGF) (Miyazawa et al., Biochem. Biophys. Res. Commun., 163:967-973, 1989; Zarnegar et al., Biochem. Biophys. Res. Commun., 163:1370-1376, 1989; Nakamura et al., Nature, 342:440-443, 1989). Human placenta is one of the tissues that contains significant amounts of HGF. We isolated HGF from human placenta and characterized its biologic effect on rat hepatocytes. Human placenta HGF was isolated in high purity as a single chain molecule. Single chain HGF stimulated DNA synthesis in primary rat hepatocyte cultures in serum-free medium. The maximal effect was seen at 5-10 ng/ml. The maximal response occurred at 25-48 hours after plating of the hepatocytes. Protein synthesis was also stimulated by HGF in primary rat hepatocyte cultures. There were peak responses at 19-24 and 37-42 hours after plating of the hepatocytes. TGF beta 1 inhibited more than 95% of HGF-induced DNA synthesis but only 25% of HGF-induced protein synthesis. HGF interacted in an additive manner with EGF, a well-known hepatocyte mitogen. There was not an additive interaction between HGF and aFGF. Regenerating liver hepatocytes obtained from rats which underwent two-thirds partial hepatectomies (PHX) also responded to HGF in a dose-dependent manner as the hepatocytes from normal liver.

Patterns of alpha-1-adrenergic receptor expression in regenerating and neoplastic hepatic tissue

As norepinephrine is a potent hepatocyte comitogen through binding to the alpha 1-adrenergic receptor, we have examined mRNA levels of the alpha 1a- and alpha 1b-adrenergic receptor subtypes in normal and regenerating rat hepatocytes as well as in several different rat hepatoma cell lines. All rat hepatomas examined lacked both alpha 1a- and alpha 1b-receptor message and receptor binding in radioligand binding experiments, suggesting that the growth of dedifferentiated neoplastic rat hepatocytes is not regulated by the alpha 1-adrenergic receptor. Interestingly, unlike the rat hepatomas analyzed, the human hepatocellular carcinoma cell line, HepG2, was positive for both alpha 1a and alpha 1b message at 4.5 kb, yet this cell line lacked receptor binding in radioligand binding assays. While normal and regenerating liver is negative for alpha 1a-receptor expression, it is positive for alpha 1b expression and is characterized by the presence of two bands at approximately 4.0 and 3.2 kb which peaked between 20 and 48 h after partial hepatectomy. A dramatic decrease in message level of the lower band and the continued presence of the upper band between 6 and 12 h after partial hepatectomy, and before the peak in DNA synthesis in regenerating rat liver, may correspond with observed differences in alpha 1-receptor function during liver regeneration.

Localization of hepatocyte growth factor (HGF) gene on human chromosome 7

Hepatocyte growth factor (HGF) is a potent mitogen for hepatocytes and a variety of epithelial cells in culture. The cDNAs for human and rat HGF have been cloned by different researchers, including ourselves; however, no information on the genomic structure and chromosome localization of the HGF gene is yet available. To investigate HGF's chromosomal localization, DNA from a battery of human-hamster somatic cell hybrids was digested with BglII and analyzed by Southern blot using a 2.3-kb human HGF cDNA as a hybridization probe. The gene encoding the human HGF was assigned to human chromosome 7. Restriction enzyme and Southern blot analyses using the HGF cDNA and HGF-specific oligonucleotides as probes suggest that the human HGF gene exists as a single-copy gene and is composed of several exons.

Synthesis and phosphorylation of an extracellular polypeptide reacting with anti-MYC antisera in primary rat hepatocyte cultures

Primary hepatocytes stimulated with appropriate growth factors enter into S phase and it is believed that c-myc and other cell cycle-related genes play an important role in the G0-G1/S phase transition. Four polypeptides reacting with anti-MYC antisera were detected in normal primary rat hepatocyte lysates, showing a pattern of 55-67 KDa on SDS-PAGE. A 67 KDa polypeptide was detected in the extracellular medium of the hepatocyte culture capable of undergoing phosphorylation. Both extracellular and intracellular polypeptides reacting with MYC-specific antisera exhibited an unusually long half life. It is believed that the intracellular MYC polypeptides may represent degradation products or species undergoing at present unknown post-transcriptional modification(s). We suggest that the extracellular MYC polypeptide(s) may be involved in the regulation of cell growth and differentiation.

Screening for candidate hepatic growth factors by selective portal infusion after canine Eck's fistula

Completely diverting portacaval shunt (Eck's fistula) in dogs causes hepatocyte atrophy, disruption of hepatocyte organelles, fatty infiltration and low-grade hyperplasia. The effect of hepatic growth regulatory substances on these changes was assessed by constantly infusing test substances for four postoperative days after Eck's fistula into the detached left protal vein above the shunt. The directly infused left lobes were compared histopathologically with the untreated right lobes. In what has been called an hepatotrophic effect, stimulatory substances prevented the atrophy and increased hepatocyte mitoses. Of the hormones tested, only insulin was strongly hepatotrophic; T3 had a minor effect, and glucagon, prolactin, angiotensin II, vasopressin, norepinephrine and estradiol were inert. Insulin-like growth factor, hepatic stimulatory substance, transforming growth factor-alpha and hepatocyte growth factor (also known as hematopoietin A) were powerfully hepatotrophic, but epidermal growth factor had a barely discernible effect. Transforming growth factor-beta was inhibitory, but tamoxifen, interleukin-1 and interleukin-2 had no effect. The hepatotrophic action of insulin was not altered when the insulin infusate was mixed with transforming growth factor-beta or tamoxifen. These experiments show the importance of in vivo in addition to in vitro testing of putative growth control factors. They illustrate how Eck's fistula model can be used to screen for such substances and possibly to help delineate their mechanisms of action.

Scatter factor and hepatocyte growth factor are indistinguishable ligands for the MET receptor

Scatter Factor (SF) is a fibroblast-secreted protein which promotes motility and matrix invasion of epithelial cells. Hepatocyte Growth Factor (HGF) is a powerful mitogen for hepatocytes and other epithelial tissues. SF and HGF, purified according to their respective biological activities, were interchangeable and equally effective in assays for cell growth, motility and invasion. Both bound with identical affinities to the same sites in target cells. The receptor for SF and HGF was identified as the product of the MET oncogene by: (i) ligand binding and coprecipitation in immunocomplexes; (ii) chemical crosslinking to the Met beta subunit; (iii) transfer of binding activity in insect cells by a baculovirus carrying the MET cDNA; (iv) ligand-induced tyrosine phosphorylation of the Met beta subunit. SF and HGF cDNA clones from human fibroblasts, placenta and liver had virtually identical sequences. We conclude that the same molecule (SF/HGF) acts as a growth or motility factor through a single receptor in different target cells.

Localization of hepatocyte growth factor in human and rat tissues: an immunohistochemical study

Hepatocyte growth factor is a protein growth factor with a strong mitogenic effect on hepatocytes. Recently, hepatocyte growth factor and hepatocyte growth factor messenger RNA have been extracted from several organs of humans, rats and rabbits. This study was undertaken to comprehensively define and compare the cellular localization of hepatocyte growth factor in human and rat tissues in detail. Paraffin-embedded sections and frozen sections were examined by immunohistochemistry using a polyclonal antiserum to hepatocyte growth factor. The distribution of hepatocyte growth factor was almost identical in humans and rats. Strong or moderate cytoplasmic immunoreactivity for hepatocyte growth factor was present in most surface epithelia, distal tubules and collecting ducts of the kidneys, large neurons, megakaryocytes, granulocytes, exocrine pancreas, salivary glands, prostate, epididymis and trophoblast. Varying degrees of immunoreactivity were observed in endothelial cells, chondrocytes and macrophages. We conclude that hepatocyte growth factor is widely distributed in numerous tissues and cell types independent of their regenerative activity. This suggests that hepatocyte growth factor may have mitogenic and/or trophic effects on multiple cell types in addition to hepatocytes.

Long-term treatment with hepatic tumor promoters inhibits mitogenic responses of hepatocytes to acidic fibroblast growth factor and hepatocyte growth factor

Studies with hepatocyte cultures have defined four hepatocyte mitogens which can transmit a complete mitogenic signal in cultures kept in completely defined conditions. These four mitogens are epidermal growth factor (EGF), acidic fibroblast growth factor (aFGF), hepatopoietin A/hepatocyte growth factor (HPTA/HGF) and hepatopoietin B (HPTB). In this study, we investigated the effect of aFGF, HGF and the mito-inhibitor transforming growth factor beta (TGF-beta) on cultured hepatocytes isolated from livers of rats treated with the xenobiotic hepatic tumor promoters phenobarbital (PB) and alpha-hexachlorocyclohexane (alpha-HCH). Male F344 rats were treated with each of these two xenobiotics to stimulate hepatic DNA synthesis and augmentative hepatomegaly. At different times on the regimens with tumor promoters, hepatocytes were isolated and placed in primary culture. DNA synthesis of hepatocytes in culture stimulated by these two growth factors and the suppression of DNA synthesis affected by TGF-beta were examined as a function of time of treatment in vivo with these two promoters. Following day 10, hepatocytes from both promoter regimens became unresponsive to these two growth factors for the rest of the duration of the treatment (day 90). TGF-beta suppressed DNA synthesis stimulated by growth factors but did not affect the high background DNA synthesis stimulated by xenobiotics themselves.

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.

Effect of 2% dimethyl sulfoxide on the mitogenic properties of epidermal growth factor and hepatocyte growth factor in primary hepatocyte culture

Two percent dimethyl sulfoxide (DMSO) reversibly inhibited DNA synthesis in primary rat hepatocyte cultures maintained with epidermal growth factor (EGF) or hepatocyte growth factor (HGF). These data suggest that, in vitro, DMSO is a non-specific inhibitor of hepatocyte proliferation, regardless of the stimulating mitogen. In addition, removal of DMSO from mitogen-free cultures resulted in an increase in DNA synthesis. Protein synthesis gradually but irreversibly declined in all cultures after DMSO removal. The relevance of these findings to regulation of hepatocyte growth is discussed.

Hepatopoietins A and B and hepatocyte growth

Serum from control or partially hepatectomized rats contains only two substances associated with stimulation of DNA synthesis in primary cultures of hepatocytes in serum free conditions. Hepatopoietin A is a large (105,000 kDa in monomeric form) heparin binding growth factor that is a heterodimer of two polypeptide chains (70,000 and 35,000 kDa). Another heparin binding growth factor, acidic FGF, also stimulates hepatocyte DNA synthesis but at a level comparable to half that of HPTA. These findings, along with recent observations of stimulation of liver growth and hepatoma formation in mice transgenic for the tat gene of the AIDS virus and overproducers of the heparin binding factor hst/KS3, raise the issue of the overall importance of different heparin binding growth factors in the control of hepatic growth regulation. Hepatopoietin B is a glycolipid that also acts as a complete hepatocytic mitogen. The role of the above substances as well as the role of norepinephrine, acting as a mitogenic trigger for stimulation of the rapid early phenomena associated with liver regeneration, is discussed.

Hepatocyte growth factor in human placenta and trophoblastic disease

The hepatocyte growth factor (HGF) is an acidic protein with a strong mitogenic effect on hepatocytes. Hepatocyte growth factor mRNA recently was cloned from a placental cDNA library. Here we demonstrate the purification of HGF from human placenta with heparin-agarose chromatography and TSK-heparin high-pressure liquid chromatography and describe the distribution of placental HGF by immunohistochemistry using a polyclonal antibody to HGF. The yield of HGF from the placenta was approximately 100 to 200 times greater than that previously obtained from human plasma. Placental HGF was expressed strongly in the villous syncytium, extravillous trophoblast, and amnionic epithelium, and, to a lesser degree in endothelial cells and villous mesenchyme. Hepatocyte growth factor also was identified in the trophoblast of complete hydatidiform moles, choriocarcinomas, and a case of blighted ovum. The presence of HGF in an organ characterized by rapid cell proliferation during gestation and in trophoblastic tumors strongly suggests that the growth-regulating effect of HGF is not limited to hepatocytes.