Inhibitory effect of transforming growth factor-beta on DNA synthesis of adult rat hepatocytes in primary culture

Pathology of recombinant human transforming growth factor-beta 1 in rats and rabbits

The systemic administration of high doses of rHuTGF-beta 1 to rats produced a spectrum of lesions in multiple target tissues, including liver, bone, kidney, heart, thymus, pancreas, stomach, cecum, at the injection vein, and in skeletal muscle at the site of anesthetic injection. The majority of these lesions can be attributed to known biological activities of TGF-beta 1. High-dose dermal application resulted in local effects at the wound sites without systemic toxicity.

Growth stimulation of primary rat hepatocytes by 2,3,7,8-tetrachlorodibenzo-p-dioxin

The modulation of liver growth control by the tumor promoter, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), was investigated in primary hepatocytes of adult rats. Under defined conditions in serum-free cultures, the interaction of TCDD with growth-related hormones was studied. TCDD-treatment of the cultured hepatocytes for two days caused a transient stimulation of both DNA synthesis and mitotic activity. This effect was maximal at the very low nontoxic concentration of 10(-12) M TCDD, i.e., two orders of magnitude below the optimal concentrations for induction of drug metabolizing enzymes. Growth stimulation by TCDD was dependent on the presence of growth-related hormones; in primary rat hepatocytes, TCDD acted synergistically with insulin and epidermal growth factor (EGF) and antagonized the growth inhibition by dexamethasone. Under culture conditions allowing high rates of DNA synthesis, e.g., at low concentrations of dexamethasone, in the presence of EGF plus alpha 1-adrenergic agonists or rat serum, no significant effect of TCDD on cellular growth was observed. Furthermore, TCDD failed to stimulate DNA synthesis in a rat hepatoma cell line, H4IIE, which is less sensitive to growth controlling factors than normal hepatocytes. Therefore, the results suggest that the growth modulation of primary rat hepatocytes by TCDD is the most sensitive parameter of the agent thus far observed. This effect may involve both a release from the growth inhibition caused, for instance, by glucocorticoids, as well as a direct growth-stimulating effect, synergistic to the one induced by insulin.

Differential regulation of glucose transporter 1 and 2 mRNA expression by epidermal growth factor and transforming growth factor-beta in rat hepatocytes

We have examined by Northern blot analysis the expression of two members of the glucose transporter family of genes (GLUT-1 and GLUT-2) in regenerating liver and in hepatocytes cultured under various conditions. GLUT-1, although thought to be a growth-associated gene, is not expressed in normal or regenerating liver, whereas GLUT-2, a liver-specific gene, is abundant in normal liver and gradually up-regulated during liver regeneration. Conversely, in hepatocytes cultured conventionally on dried rat tail collagen (RTC) in the presence of EGF and insulin, which potentiate proliferation, GLUT-1 mRNA is rapidly and abundantly expressed, whereas GLUT-2 is depressed. To investigate the causes of this "switch" in glucose transporter expression seen when hepatocytes are removed from the liver and cultured under the conventional proliferative conditions, we examined the effects of specific growth factors and extracellular matrices on cultured hepatocytes. EGF, a potent liver mitogen, although causing a threefold induction of GLUT-1, was found to have no effect on GLUT-2 expression, suggesting that the increase in GLUT-2 seen in regenerating liver is not due to EGF. Inhibition of protein synthesis by cycloheximide in cultured hepatocytes does not prevent the induction of GLUT-1 mRNA. In addition, treatment of cells with cycloheximide appears to stabilize the GLUT-2 mRNA, preventing the usual down-regulation of this gene in cultured hepatocytes. The expression of the two glucose transporter mRNAs also differed when the hepatocytes were adherent to particular cell matrices. Culture of hepatocytes on a reconstituted basement membrane gel matrix (EHS) is known to restrain their growth and mediate high levels of differentiated hepatocytic functions that are lost under conventional culture conditions. Unlike cells on RTC, hepatocytes on EHS expressed low levels of GLUT-1 mRNA, and decreased GLUT-2 mRNA. TGF-beta, an attenuator of DNA synthesis, when added to cultures on RTC, substantially down-regulated GLUT-2 but had no effect on GLUT-1. We propose that the effectors, EGF, TGF-beta and basement membrane components, play a significant role in the regulation of expression of GLUT-1 and GLUT-2 in hepatocytes.

Transforming growth factor-beta 1 rapidly activates phosphorylase in a calcium-dependent manner in rat hepatocytes

Transforming growth factor-beta 1 (TGF-beta 1) rapidly activated phosphorylase in isolated rat hepatocytes (half-maximal rate of activation with approximately 0.1 ng/ml). Removal of Ca2+ from the external medium just before TGF-beta 1 addition markedly attenuated phosphorylase activation. TGF-beta 1 (1 ng/ml) produced a small increase in [Ca2+]i (approximately 10% increase after 30 s), which appears sufficient to account for phosphorylase activation. These observations indicate that activation of the TGF-beta 1 signal transduction system in hepatocytes is linked with a small increase in [Ca2+]i, and external Ca2+ may contribute in part to this increase.

Effects of epidermal growth factor and transforming growth factor-beta on insulin-induced differentiation in rat dental pulp cells

An established pulp cell line (RPC-C2A) was used to study the regulatory effect of insulin on dentinogenesis. Insulin increased alkaline phosphatase activity and the incorporation of [2,3-3H]-proline into collagenase-digestible protein, whereas [3H]-thymidine incorporation by the cells was inhibited by insulin. The enhancing effect of insulin on alkaline phosphatase activity was inhibited by epidermal growth factor (EGF) or transforming growth factor-beta (TGF-beta). The stimulatory effect of insulin on collagen synthesis was also inhibited when insulin was combined with EGF, but was accelerated by the addition of TGF-beta. Inhibitory effects of insulin on the [3H]-thymidine incorporation were potentiated by EGF, though EGF alone strongly increased the effect; whereas the addition of TGF-beta had no significant effect on the insulin action. These findings suggest that insulin may be concerned with the differentiation of pulp cells in dentinogenesis and that EGF or TGF-beta regulate the insulin effects.

Transforming growth factor (TGF)-beta stimulates hepatic jun-B and fos-B proto-oncogenes and decreases albumin mRNA

Transforming growth factor-beta (TGF-beta) modulates some components of the acute phase response in hepatic cells. The mechanisms for these actions of TGF-beta are largely unknown. The authors recently found that the decrease in albumin mRNA after TGF-beta 1 treatment required de novo RNA and protein synthesis, suggesting that TGF-beta acts through induction of another gene. The purpose of the current study was to determine whether TGF-beta 1 could regulate the expression of both the jun and fos genes that encode transcriptional regulatory proteins that constitute the AP-1 complex, and to determine whether expression of these genes may be coordinated with the decrease in albumin mRNA. Northern blot hybridization was used to determine levels of specific mRNAs. Transforming growth factor-beta 1 increased the levels of both jun-B and fos-B mRNA by 60 minutes after treatment of mouse hepatoma (BWTG3) cells. When TGF-beta 1 was removed from the media after 4 hours, there was a sustained effect of increased jun-B and decreased albumin mRNA (greater than 48 hours), and the subsequent decrease in jun-B levels coincided with the increase in albumin mRNA. The tumor-promoting phorbol ester (phorbol 12-myristate 13-acetate [PMA]), known to induce jun and fos gene expression, caused increases in jun-B and fos-B that preceded the decrease in albumin mRNA levels at 24 hours. These observations are consistent with our hypothesis that jun-B and fos-B induction may participate in downregulation of albumin synthesis as well as other hepatic responses to TGF-beta.

Induction of apoptosis in cultured hepatocytes and in regressing liver by transforming growth factor beta 1

In previous studies hepatocytes undergoing cell death by apoptosis but not normal hepatocytes in rat liver showed immunostaining for transforming growth factor beta 1 (TGF-beta 1). Staining was much stronger with antibodies recognizing the pro-region of TGF-beta 1 than the mature peptide itself. Therefore we investigated the ability of both forms of TGF-beta 1 to induce apoptosis in primary cultures of rat hepatocytes. Mature TGF-beta 1 induced rounding up of the cells and fragmentation into multiple vesicles. As revealed by the DNA-specific stain H33258, the chromatin of these cells condensed and segregated into masses at the nuclear membrane; this was obviously followed by fragmentation of the nucleus. Ultrastructurally the cytoplasm was well preserved, as demonstrated by the presence of intact cell organelles. These features strongly suggest the occurrence of apoptosis. Quantification of nuclei with condensed chromatin revealed that mature TGF-beta 1 was 30-fold more effective than the TGF-beta 1 latency-associated protein complex. Finally, we administered TGF-beta 1 in vivo using an experimental model in which regression of rat liver was initiated by a short preceding treatment with the hepatomitogen cyproterone acetate. Two doses of TGF-beta 1, each 1 nM/kg, augmented the incidence of apoptotic hepatocytes 5-fold. Equimolar doses of TGF-beta 1 latency-associated protein complex were ineffective. These studies suggest that TGF-beta 1 is involved in the initiation of apoptosis in the liver and that the mature form of TGF-beta 1 is the active principle.

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.

Inhibition by methylprednisolone acetate suggests an indirect mechanism for TGF-B induced angiogenesis

Angiogenesis induced by transforming growth factor beta (TGFB) implanted in the rabbit cornea is accompanied by an influx of inflammatory cells. To determine if the inflammatory cells are the mediators of the neovascularization, they were depleted by local administration of methylprednisolone acetate (MPA). Subconjunctival injections of 16 mg of MPA immediately following implantation of 50 ng of TGFB in the cornea prevented the inflammation and subsequent formation of capillaries. If the injections of MPA were delayed by 48 hr and the inflammatory cells were allowed to enter the cornea, angiogenesis occurred, demonstrating that MPA had no adverse effects on the ability of endothelial cells to form capillaries. These results confirm the hypothesis that TGFB induces angiogenesis indirectly by recruiting inflammatory cells capable of stimulating direct angiogenesis.

Tumor necrosis factor stimulates DNA synthesis of mouse hepatocytes in primary culture and is suppressed by transforming growth factor beta and interleukin 6

In a previous study, we revealed that tumor necrosis factor (TNF) was secreted in mouse liver at an early phase of liver regeneration after partial hepatectomy. Here, we investigated direct actions of TNF on the in vitro DNA synthesis of adult mouse hepatocytes in primary culture. TNF enhanced both 3H-TdR uptake and the number of 3H-TdR-labeled nuclei of hepatocytes. Their time courses were similar to those by epidermal growth factor (EGF) with about a 15 h lag period and a peak period of 24-48 h. This action of TNF was abrogated by DNA polymerase alpha inhibitor, aphidicolin and blocked specifically by anti-TNF antibody. The actions of rmTNF and rhTNF were not distinguishable; ED50 was about 7.5U/ml (5ng/ml) and 30U/ml (20ng/ml) for maximal response (about 2-fold or more of control). Other inflammatory monokines showed differential effects on in vitro DNA synthesis of hepatocyte. Neither type of interleukin 1 affected hepatocyte DNA synthesis in the range examined (up to 50 ng/ml). IL-6 markedly inhibited the hepatocyte DNA synthesis stimulated by TNF and EGF. The action of TNF was completely suppressed by transforming growth factor beta, which is known as a potent inhibitor of hepatocyte growth. Interferon gamma also blocked this TNF action when added simultaneously. These results indicate that the activation of tissue macrophages and local secretion of TNF in liver after partial hepatectomy is of physiological importance in liver regeneration, in part by a direct stimulation of hepatocyte DNA synthesis. Cytokines induced by TNF may also participate in the later termination of liver regeneration.

Growth of normal human hepatocytes in primary culture: effect of hormones and growth factors on DNA synthesis

Although the ability of hormones and growth factors to stimulate DNA synthesis in rat hepatocytes has been investigated extensively, no such study of human hepatocytes has been reported. Here we describe a series of experiments to identify those factors that regulate human hepatocyte DNA synthesis in vitro and which therefore may play a role in the control of human liver regeneration. Human hepatocytes were isolated from normal liver tissue obtained after graft reduction for transplantation into pediatric recipients. Cells were maintained in culture for up to 5 days, and DNA synthesis was determined. Hydroxyurea reduced [3H]thymidine incorporation into DNA by 95%, indicating replicative DNA synthesis. As previously found with rat hepatocytes, epidermal growth factor and transforming growth factor-alpha stimulated DNA synthesis at low nanomolar concentrations; transforming growth factor-alpha was slightly more potent. Although the overall rate of thymidine incorporation was lower than that for rodent cells, human hepatocytes were sensitive to lower concentrations of these growth factors, and the degree of stimulation was similar. Conversely, transforming growth factor-beta inhibited DNA synthesis at low picomolar levels. By contrast (unlike rat hepatocytes), arginine-vasopressin failed to initiate or potentiate DNA synthesis in human cells. These data indicate that normal human hepatocytes can respond to low concentrations of growth promoters or inhibitors, previously shown to have activity on rat hepatocytes. These factors may then play a role in control of human liver growth. However, important species differences are apparent, highlighting the limitations of extrapolating from animal studies to humans.

Significance of tumor necrosis factor (TNF) and interleukin-1 (IL-1) in the pathogenesis of fulminant hepatitis: possible involvement of serine protease in TNF-mediated liver injury

The effect of tumor necrosis factor (TNF)-alpha and interleukin-1 (IL-1) alpha, which are thought to be principal mediators inducing homeostatic abnormalities during endotoxemia, were investigated on cultured hepatocytes in an attempt to understand their role in the pathogenesis of fulminant hepatitis. Both TNF and IL-1 had no direct cytotoxicity on cultured adult rat hepatocytes as assessed by their effects on protein synthesis and also cytosolic enzyme activity released into the culture medium in the presence of 5 mM D-galactosamine (Ga1N). However, IL-1 caused a dose-dependent inhibition of DNA synthesis in cultured adult rat hepatocytes. Moreover, the serum from TNF-treated rats, prepared after intravenous administration of TNF (5 X 10(4) U per rat), caused a significant increase of enzyme release into culture medium in contrast to control rat serum. The cytotoxicity disappeared when the serum from TNF-treated rats was pretreated by heating at 56 degrees C for 30 min, and was decreased by the addition of the protease inhibitor, aprotinin. In vivo, gabexate mesilate, a serine-type protease inhibitor, prevented GalN/TNF-induced fulminant hepatitis, whereas MX-1, an anti-complement agent, had no such effect. These results strongly suggest that IL-1 has a inhibitory effect on hepatocytes in terms of DNA synthesis and that TNF indirectly induces hepatocellular damage through the serine proteases which are possibly activated by the cytokine in vivo.

Transforming growth factor-beta (TGF-beta) isoforms in rat liver regeneration: messenger RNA expression and activation of latent TGF-beta

Expression of transforming growth factor-beta s (TGF-beta s) 1-3 was studied in normal liver and during liver regeneration after partial hepatectomy in the rat to determine whether each of these isoforms might be involved in hepatocyte growth in vivo. Expression of the mRNAs for all three TGF-beta isoforms increases in the regenerating liver. In addition, the levels of expression of the mRNAs for several extracellular matrix proteins, including fibronectin, vitronectin, laminin, and collagen, also increase in the regenerating liver. Immunohistochemical staining analysis shows a similar distribution of all three TGF-beta s in normal and regenerating liver; however, in both tissues, the level of expression of TGF-beta 1 is 8- to 10-fold higher than that of TGF-beta 2 as determined by sandwich enzyme-linked immunosorbent assay. Expression of all three TGF-beta mRNAs is restricted to liver nonparenchymal cells. Although hepatocytes from normal and regenerating livers do not synthesize TGF-beta, they are sensitive to inhibition of growth by all three TGF-beta isoforms. Hepatocytes from regenerating livers are capable of activating latent TGF-beta 1 complexes in vitro, whereas normal hepatocytes are not. The different TGF-beta isoforms may function in an inhibitory paracrine mechanism that is activated during liver regeneration and may also regulate the synthesis of extracellular matrix components in the regenerating liver.

Characterization of trans-immortalized hepatic cell lines established from transgenic mice

Hepato-specific regulatory (promoter/enhancer) DNA sequences were used for targeting the expression of onc genes, such as murine c-myc and Simian Virus 40 T Antigen, to hepatocytes of transgenic mice which subsequently developed hepatocellular carcinomas after a variable period of time (depending on the type of onc gene employed). Several trans-immortalized cell lines were established and compared with respect to the expression of adult hepatic markers and response to growth factors. Despite the morphological differences observed between trans-hepatomas, owing to the expression of the two different onc genes, all tumor-derived cell lines behaved in a comparable fashion during long-term culture displaying an adult hepatic phenotype for at least 40 passages. They differed, however, in response to epidermal growth factor. When the gene coding for human alpha 1-antitrypsin was placed under the control of the same hepato-specific promoter/enhancer, high levels of the human recombinant protein could be harvested from the supernatants of trans-hepatoma-derived cell lines.

Effects of transforming growth factor-beta 1 on growth of aortic smooth muscle cells. Influences of interaction with growth factors, cell state, cell phenotype, and cell cycle

Transforming growth factor (TGF)-beta 1 may have different effects on cell proliferation depending on many conditions. This paper clarifies the effects of various conditions on the effect of TGF-beta 1 on proliferation of cultured rabbit aortic smooth muscle cells (SMC) and also the time of its action during the cell cycle. TGF-beta 1 at 10-10,000 pg/ml inhibited DNA synthesis of SMC in the G0 stage derived from normal media or atheromatous intima stimulated by either platelet-derived growth factor (PDGF), fibroblast growth factor, SMC-derived growth factor, or fetal bovine serum (FBS). TGF-beta 1 also inhibited the growth of SMC in the growing state stimulated by either PDGF or FBS. TGF-beta 1 was effective only when added to the culture within 2 h after stimulation of the G0 state SMC with PDGF. It also inhibited increase in transcription of the c-myc protooncogene on stimulation of SMC with PDGF. These data suggest that TGF-beta 1 inhibited proliferation of SMC irrespective of the cell phenotype, growth conditions, and growth factors present and that it exerted this inhibitory effect during the time of the G0/G1 transition.

Protooncogenes and growth factors associated with normal and abnormal liver growth

Hepatocyte replication during liver regeneration depends on extrinsic (circulating) and intrinsic (intrahepatic) factors. Two important growth factors produced in the regenerating liver are discussed, TGF alpha, an autocrine, stimulatory growth factor, and TGF beta, a paracrine inhibitory factor. The balance between the activities of these factors is likely to play an important role in regulating hepatocyte proliferation. The expression of some protooncogenes occurs sequentially during the first few hours after partial hepatectomy and is a marker for the entry of hepatocytes into the cell cycle (proliferative competence). As hepatocytes become competent to proliferate, they respond to TGF alpha and other growth factors and enter a proliferative phase. It is possible that TGF beta 1 serves as a stop signal for liver regeneration but the mechanisms by which TGF beta inhibits hepatocyte DNA synthesis are still unknown.

Transforming growth factors beta 1 and alpha in chronic liver disease. Effects of interferon alfa therapy

BACKGROUND

Cirrhosis is a diffuse process of hepatic fibrosis and regenerative nodule formation of unknown pathogenesis. Transforming growth factor (TGF) beta 1 induces the production of extracellular matrix proteins by liver cells and has been implicated in the pathogenesis of hepatic fibrosis in laboratory animals. TGF alpha is a hepatocyte mitogen that participates in liver regeneration.

METHODS

Using Northern blot analysis, we studied the expression of TGF beta 1 messenger RNA (mRNA) in liver specimens from 42 patients with chronic hepatitis and cirrhosis and 12 subjects with either normal or fatty livers. The results were correlated with measurements of procollagen Type I mRNA in liver tissue, procollagen Type III peptide in serum, and the degree of histologic injury. We also investigated whether TGF alpha mRNA would be detectable in biopsy specimens of livers with proliferative activity.

RESULTS

TGF beta 1 mRNA expression correlated closely with the expression of procollagen Type I mRNA (r = 0.94) and serum procollagen Type III peptide (r = 0.89) and with the histologic activity index (r = 0.73). All patients with increased fibrogenic activity (serum procollagen Type III peptide level, greater than 11.9 micrograms per liter) had increased levels of TGF beta 1 mRNA (2 to 14 times the levels in the control group or in patients with normal fibrogenic activity), and both TGF alpha and H3 histone (a marker of DNA synthesis) mRNAs were detectable in patients with regenerative nodules. Six of eight patients with hepatitis C treated with interferon alfa for one year had sustained clinical responses with normalization of serum procollagen Type III peptide and aminotransferase activity. All these patients had normal levels of TGF beta 1 mRNA in liver specimens obtained at the end of the year.

CONCLUSIONS

TGF beta 1 may have an important role in the pathogenesis of fibrosis in patients with chronic liver disease, and TGF alpha expression may be associated with liver regeneration in these patients.

Mechanisms controlling growth of hepatocytes in primary culture

Mature hepatocytes in primary culture express most of the functions and hormonal responsiveness seen in normal liver studied in vivo. The growth of hepatocytes in culture is regulated by various growth factors. We have identified a hepatocyte growth factor that is isolated from rat platelets. We found that rat platelets also contain a growth inhibitor, transforming growth factor-beta which is secreted as a latent molecule. Its latency is due to its binding with a masking protein. Growth of hepatocytes is also suppressed by interleukin-1 (IL-1) and IL-6. Moreover, the growth and functions of liver cells in culture are regulated reciprocally by cell density: at higher cell density liver-specific functions are expressed and growth is suppressed, whereas the opposite situation is observed at lower cell density. In contrast, neonatal hepatocytes in culture grow autonomously without a requirement for added hormones. This autonomous growth is due to an autocrine mechanism in which the cells secrete one or more growth factors into the culture medium. However, this autonomous growth ceases one week after birth at a time when the cells begin to express differentiated characteristics. Based upon these data, the mechanisms of liver regeneration, differentiation, and hepatocarcinogenesis are discussed.

Transforming growth factor beta 1 differentially regulates alpha-fetoprotein and albumin in HuH-7 human hepatoma cells

Transforming growth factor beta 1 (TGF-beta 1) is known to inhibit hepatocyte growth in vitro and in vivo. In this study, we analyzed the effect of TGF-beta 1 on alpha-fetoprotein (AFP) and albumin gene expression in HuH-7 human hepatoma cells. TGF-beta 1 inhibited cell growth in a dose dependent manner. The cellular secretion rate of AFP but not albumin was suppressed significantly by TGF-beta 1. TGF-beta 1 caused a significant reduction in the level of AFP mRNA. In contrast, the levels of albumin mRNA or beta-actin mRNA were not changed by TGF-beta 1. In transient transfection experiments, TGF-beta 1 resulted in selective repression of AFP promoter activity. These results suggest that TGF-beta 1 is one of the key factors involved in the differential regulation of the AFP gene and the albumin gene.

Hepatocyte growth factor is a potent mitogen for cultured rabbit renal tubular epithelial cells

Hepatocyte growth factor (HGF), which is a potent growth factor of adult rat hepatocytes in primary culture, also strongly stimulated DNA synthesis of rabbit renal tubular epithelial cells in secondary culture. Its mitogenic activity was dose-dependent, being detectable at 3 ng/ml and maximal at 30 ng/ml. Over 20% of the cells were shifted to the S-phase by HGF alone, judging by the labeling index. HGF had additive effects with EGF, acidic fibroblast growth factor (a-FGF), and insulin. Transforming growth factor-beta 1 (TGF-beta 1) strongly inhibited DNA synthesis of renal tubular cells stimulated by HGF. The growth of renal tubular epithelial cells was also regulated by cell density: DNA synthesis stimulated by HGF was high at lower cell density and was strongly suppressed at high cell density. These results suggest that HGF may act as a renotropic factor in compensatory renal growth or renal regeneration in vivo.

Counteracting effects of dexamethasone and alpha 2-macroglobulin on inhibition of proliferation of normal and neoplastic rat hepatocytes by transforming growth factors-beta type 1 and type 2

Primary cultures of hepatocytes isolated from normal F-344 rats or from F-344 rats with hepatocellular carcinomas generated by a 2-step model of chemical carcinogenesis were used to determine if dexamethasone (DEX) or alpha 2-macroglobulin (alpha 2M) modify the ability of transforming growth factors-beta type I (TGF-beta I) and type 2 (TGF-beta 2) to inhibit labelling index of hepatocytes cultured continuously with or without epidermal growth factor (EGF). Both TGF-beta 1 and beta 2 were equivalently potent inhibitors of S-phase DNA synthesis in normal and neoplastic hepatocytes as determined by 3H-thymidine autoradiography. Both DEX (1 to 100 microM) and alpha 2M (50-200 microM) partially counteracted the mito-inhibitory effect of both TGF-betas on the proliferation of normal and surrounding hepatocytes. In contrast, neoplastic hepatocytes cultured with DEX released much less immunoreactive alpha 2M and were less able to overcome the inhibitory effect of TGF-beta than normal or surrounding hepatocytes. Purified bovine alpha 2M partially counteracted the inhibition of TGF-beta 1 or beta 2 of both surrounding and neoplastic hepatocytes. Both DEX and alpha 2M were more effective against the mito-inhibitory activity of TGF-beta 2. Our data suggest that alpha 2M released by DEX-treated normal hepatocytes contributes to the counteraction of the TGF-beta effect by DEX. Our results support the hypothesis that glucocorticoids and growth-factor-binding proteins may have important roles in modulating the effects of TGF-beta on normal hepatocyte proliferation and suggest that under some conditions hepatocellular neoplasms can be more sensitive than normal hepatocytes to inhibition of proliferation by TGF-beta.

Immediate early gene responses of NIH 3T3 fibroblasts and NMuMG epithelial cells to TGF beta-1

Transforming growth factor beta has a wide range of physiological effects on cell growth and metabolism. We have previously reported on the rapid induction of jun transcription factors in TGF beta-treated cells. Here we show that the early genomic response to TGF beta-1 includes activation of a broad spectrum of serum-inducible genes both in NIH 3T3 fibroblasts and in NMuMG epithelial cells, which are growth-stimulated and growth-inhibited by TGF beta, respectively. Of particular interest is the presence of a putative nuclear DNA-binding receptor (N10) and zinc finger transcription factors (Krox 20 and Krox 24) among the TGF beta-induced genes. In addition to the stimulatory effects of TGF beta, expression of a few genes including c-myc is decreased in both types of cells. In cells transformed by neu or ras oncogenes the immediate early mRNA responses to TGF beta are deregulated. Our results suggest that certain transcription factors are required for both positive and negative regulation of cell proliferation by TGF beta, and that their relative concentrations may determine the subsequent cellular responses.

Cell cycle arrest and cellular differentiation mediated by a cell surface sialoglycopeptide

Cell cycling by a relatively wide variety of cell lines was shown to be reversibly inhibited by a cell surface sialoglycopeptide (SGP) isolated and purified from intact bovine cerebral cortex cells. Cell cycle arrest, mediated by the bovine SGP inhibitor, was shown to be completely reversible with mouse Swiss 3T3, mouse 1316 fibrosarcoma, mouse N2a neuroblastoma, bovine MDBK and monkey BSC-1 cells. These cell lines represented both fibroblast and epithelial-like cells, transformed and nontransformed cells, as well as their being derived from a broad array of species. In contrast to the others tested, human HL-60 leukemic cells were sensitive to the inhibitory effects of the SGP but did not reenter the mitotic cycle after the removal of the inhibitor. Instead, the mitotic arrest of HL-60 cells appeared to enhance entry into a terminal and irreversible state of cellular differentiation.

Transforming growth factor-beta 1 stimulates proliferation of Morris hepatoma cells in serum-free soft agar culture system supplemented with EGF and insulin

The anchorage-independent growth of Morris hepatoma 7777 (MH) cells in serum-free medium was examined. The influence of insulin, epidermal growth factor and transforming growth factor beta 1 (TGF-beta 1) on [3H]thymidine incorporation and colony formation of the investigated cells was described. Contrary to normal rat hepatocytes TGF-beta 1 plus EGF and insulin were found to stimulate MH cells proliferation in presented conditions. A simple, chemically-defined culture system suitable for research on mitogenic peptides was proposed.

Changes in sensitivity of hepatocytes isolated from regenerating rat liver to the growth inhibitory action of transforming growth factor beta

Transforming growth factor beta (TGFB) is a potent inhibitor of DNA synthesis in adult rat hepatocytes in vitro. In the present study, the response of hepatocytes from normal or regenerating rat liver to TGFB was determined. TGFB inhibited DNA synthesis uniformly in hepatocytes from both groups in the absence of EGF. However, hepatocytes from 3 h regenerating liver maintained for 3 days in the presence of EGF were less sensitive to the growth-inhibitory action of TGFB. [3H]-thymidine incorporation was inhibited at 20 pM TGFB by only 7% in hepatocytes from 3 h regenerating liver compared with 70% in normal hepatocytes. By increasing the dose of TGFB to 100 pM, however, the full inhibitory response was restored. Reduced sensitivity was also found when the nuclear labelling index was determined, but no change was observed in cells from rats 3 h following sham hepatectomy. The change in sensitivity to TGFB required the presence of 5 ng/ml EGF or greater. Within a further 24-48 h in culture, the response to lower doses of TGFB was at least partially restored. While the present experimental design cannot directly confirm the role of TGFB as a paracrine inhibitor of liver growth in vivo, the data are compatible with this hypothesis.

Sensitivity of the cell cycle to TGF beta 1 does not correlate with transformation of a rat liver epithelial cell line

The effects of TGF beta 1 on cell cycle events in a rat liver derived epithelial cell line (BL9) and in two in vitro transformants of this line were studied by flow cytometry. Using either ethidium bromide staining or the incorporation of bromodeoxyuridine to evaluate DNA synthesis it was shown that TGF beta 1 prevented the entry of G0/G1 phase BL9 cells into S phase. TGF beta 1 did not exert its inhibitory effect(s) on DNA synthesis by the modulation of early events in the cell cycle. The tumorigenic transformed BL9 cell lines gave contrasting responses to the effects of TGF beta 1. DNA synthesis in a BL9 cell line derived by transfection with an active N-ras oncogene was unaffected by TFG beta 1 and thus appeared refractory to its growth controlling effects. On the other hand cells from a BL9 cell line derived by in vitro transformation with activated aflatoxin B1 retained their sensitivity to the effects of TGF beta 1. Thus the loss of the inhibitory effect of TGF beta 1 on DNA synthesis is not obligatory for the malignant transformation of rat liver epithelial cells.

Transforming growth-factor-beta (TGF-beta) inhibits albumin synthesis in normal human hepatocytes and in hepatoma HepG2 cells

We explored the effect of transforming growth factor beta (TGF-beta), a cytokine that appears to play a central role in inflammatory events, on albumin expression by normal adult human hepatocytes and hepatoma cells. Addition of TGF-beta to primary human hepatocyte cultures resulted in a dramatic decrease in albumin accumulation and synthesis. This effect was dose-dependent, took place after a 48h incubation period and was maintained over 96h. TGF-beta-decreased albumin protein levels were associated with reduced albumin mRNA content. Actin mRNA levels were concomittantly increased. Comparable qualitative effects of TGF-beta were observed on human hepatoma HepG2 cells.

Serum changes the response of cultured Morris hepatoma 7777 cells to autocrine growth factors

The addition of calf serum to culture medium alters the biological response of Morris hepatoma 7777 (MH) cells to autocrine growth factors isolated from conditioned medium of the investigated cells. Acetic acid (AA) extract obtained from conditioned medium of MH cells showed a change in anchorage-independent growth-regulatory activity from stimulation (serum-free) to inhibition (10% calf serum). Two protein fractions of apparent molecular weight 15 and 7.5 kDa isolated from AA-extract by Bio-Gel P-60 filtration also changed their growth-regulatory activity after supplementation of culture medium with calf serum. The contradictory effect of autocrine regulators estimated in soft agar using the 3H-thymidine (3H-TdR) incorporation test and colony formation assay gave generally comparable results, except in the case of the 15-kDa fraction. The most active 7.5-kDa fraction stimulated 3H-TdR incorporation and colony formation in serum-free medium up to about 300 and 500% respectively, while in the presence of 10% calf serum inhibition of about 20 and 50% has been observed. Our results suggest that the fraction contains an autocrine growth factor(s), whose activity is inverted in the presence of serum.

Transformed fat storing cells inhibit the proliferation of cultured hepatocytes by secretion of transforming growth factor beta

Conditioned medium from secondary cultures of fat storing cells (transformed fat storing cells) inhibits replicative (hydroxyurea-sensitive) DNA synthesis dose-dependently in primary cultures of hepatocytes stimulated in vitro by transforming growth factor (TGF) alpha. Similarly, [3H]thymidine incorporation into the DNA of hepatocytes from the regenerating rat liver is reduced by about 70% by fat storing, cell conditioned medium. Medium which had been transiently acidified was more potent than native medium. It displaced [125I]TGF-beta from binding sites on the hepatocyte surface and the inhibitory activity was completely blocked by anti-TGF-beta antibodies. From binding studies, a TGF-beta concentration of 1.8 +/- 0.4 ng/ml conditioned medium produced by 2 X 10(5) cells per 24 h was estimated. Transformed, but not primary, cultures of fat storing cells at an early state produce and secrete TGF-beta, which reduces hepatocellular proliferation significantly.

Transforming growth factor beta-like activity in human hydrocele fluid

In this study transforming growth factor beta (TGF-beta)-like activity in human hydrocele fluid was investigated. Inhibition of DNA synthesis of adult rat hepatocytes in primary culture and stimulation of colony formation of normal rat kidney (NRK) fibroblasts, clone 49F in soft agar were observed in all acidified hydrocele fluids and these activities were neutralized by the specific antibody raised against human native TGF-beta. In samples obtained from recurrent cases of hydrocele, TGF beta-like activity was observed in its active form (without acidification). These results suggest that human hydrocele fluid contains TGF beta-like activity and that the active form of TGF-beta in recurrent hydrocele fluid may be responsible for the recurrence of the disease even after repeated aspiration.

Modulation of c-myc expression by transforming growth factor beta 1 in human hepatoma cell lines

The effects of transforming growth factor beta 1 (TGF-beta 1) on cell proliferation of human hepatoma cell lines, PLC/PRF/5 and Mahlavu, were investigated under serum-free conditions. DNA synthesis was strongly inhibited in the PLC/PRF/5 cells by addition of TGF-beta 1 (0.5 to 4.0 ng/ml), but remained unchanged in the Mahlavu cells. Also the expression of c-myc mRNA was suppressed by the addition of TGF-beta 1 in the PLC/PRF/5 cells but not in the Mahlavu cells. These results indicate that TGF-beta 1 might regulate cell growth, in part, by modulating c-myc expression, although there is no direct proof that c-myc expression is really relevant to DNA synthesis mediated by TGF-beta 1.

Heparin-binding growth factor type 1 (acidic fibroblast growth factor): a potential biphasic autocrine and paracrine regulator of hepatocyte regeneration

Heparin-binding growth factor type 1 (HBGF-1; sometimes termed acidic fibroblast growth factor) is potentially an important factor in liver regeneration. HBGF-1 alone (half-maximal effect at 60 pM) stimulated hepatocyte DNA synthesis and bound to a high-affinity receptor (Kd = 62 pM; 5000 per cell). Epidermal growth factor (EGF) neutralized or masked the mitogenic effect of HBGF-1 concurrent with appearance of low-affinity HBGF-1 binding sites. HBGF-1 reduced the inhibitory effect of transforming growth factor type beta (TGF-beta) on the EGF stimulus. Nanomolar levels of HBGF-1 decreased the EGF stimulus. An increase in hepatic HBGF-1 gene expression after partial hepatectomy precedes increases in expression of the EGF homolog, TGF-alpha, and nonparenchymal-cell-derived TGF-beta in the regenerating liver. Expression of HBGF-1 mRNA occurs in both hepatocytes and nonparenchymal cells and persists for 7 days in liver tissue after partial hepatectomy. HBGF-1 acting through a high-affinity receptor is a candidate for the early autocrine stimulus that drives hepatocyte DNA synthesis prior to or concurrent with the EGF/TGF-alpha stimulus. It may allow hepatocyte proliferation to proceed in the presence of low levels of TGF-beta. An EGF/TGF-alpha-dependent change in HBGF-1 receptor phenotype and increasing levels of nonparenchymal-cell-derived HBGF-1 and TGF-beta may serve to limit hepatocyte proliferation.

Promotion of murine hepatocarcinogenesis by testosterone is androgen receptor-dependent but not cell autonomous

Tfm (testicular feminization) mutant mice lack functional androgen receptors. By studying liver tumor development in Tfm mice, we have shown that the greater susceptibility of male mice relative to female mice for liver tumor induction by N,N-diethylnitrosamine is androgen receptor-dependent. C57BL/6J normal and Tfm mutant mice were injected at 12 days of age with N,N-diethylnitrosamine (0.2 mumol/g, i.p.), and liver tumors were enumerated in 50-week-old animals. Normal males averaged 20 liver tumors per animal; Tfm males, 0.7; normal females, 0.6; and Tfm/+ heterozygous females, 1.5. The androgen receptor gene and the Tfm mutation are X chromosome linked. Because of random X chromosome inactivation, hepatocytes from Tfm/+ heterozygous female mice are mosaic with respect to the expression of mutant or wild-type receptors. To determine if testosterone acts directly as a liver tumor promoter, through the androgen receptor in preneoplastic hepatocytes, or by an indirect mechanism, we chronically treated these mosaic female mice with testosterone and measured the androgen receptor content of the resulting tumors. B6C3F1 Tfm/+ mosaic and +/+ wild-type female mice were injected i.p. at 12 days of age with N,N-diethylnitrosamine (0.1 mumol/g) and ovariectomized at 8 weeks of age. Half of the mice of each group subsequently received biweekly s.c. injections of testosterone (0.15 mg per mouse) for 30 weeks. Tumor multiplicity was the same for wild-type and Tfm/+ mosaic females treated with testosterone (31-32 tumors per animal at 38 weeks of age) and was increased relative to females not treated with testosterone (13-17 tumors per animal at 50 weeks of age). Testosterone treatment did not significantly increase the percentage of androgen receptor-positive tumors in Tfm/+ mosaic females: 58% of the tumors from Tfm/+ mosaic females treated with testosterone were receptor positive compared to 48% in Tfm/+ females not treated with testosterone and 92% in wild-type females treated with testosterone. Finally, the number of androgen receptors in the majority of liver tumors examined was greatly decreased relative to the surrounding normal liver tissue. We conclude that liver tumor promotion by testosterone requires a functional androgen receptor in the intact animal. However, this promotion is not cell autonomous; that is, the response of the preneoplastic hepatocyte is not dependent on the expression of functional receptor in the target cell.

Growth-inhibitory effect of TGF-B on human fetal adrenal cells in primary monolayer culture

We examined the effects of transforming-growth factor-B (TGF-B) on growth ([3H]-thymidine uptake) and function (dehydroepiandrosterone sulfate [DHAS] and cortisol production) of human fetal zone adrenal cells. Results indicate that TGF-B significantly inhibits, in a dose-related manner, both basal and epidermal growth factor (EGF)-stimulated cell growth: IC50 = 0.1-0.25 ng/ml. EGF is ineffective in overcoming the inhibitory effect of TGF-B, suggesting a noncompetitive antagonism between the two factors. Also, the inhibitory effect of TGF-B is additive to that of adrenocorticotropic hormone (ACTH). On the other hand, TGF-B (1 ng/ml) does not significantly change basal or ACTH-stimulated DHAS or cortisol secretion. We conclude that, unlike its effect on other steroid-producing cells, TGF-B inhibits growth of fetal zone cells and does not appear to have a significant inhibitory effect on steroidogenesis.

Characterization of transforming growth factors produced by the insulin-independent teratoma-derived cell line 1246-3A

The 1246-3A cell line is an insulin-independent variant derived from the adipogenic cell line 1246. Data presented in this paper indicate that the 1246-3A cell line releases in its culture medium two types of transforming growth factors, TGF-alpha- and TGF-beta-like polypeptides, and a growth inhibitor. TGF-alpha like polypeptide eluted from Biogel P60 column into two fractions with an apparent molecular weight of 50 kDa and 13 kDa. These high-molecular-weight TGF-alpha-like factors competed with 125I-EGF for binding to epidermal growth factor (EGF) receptors and were specifically immunoprecipitated by incubation with antirat TGF-alpha antibody, not by incubation with anti-EGF antibody. Both fractions promoted anchorage-independent growth of normal rat kidney NRK cells in the absence of EGF and stimulated DNA synthesis in quiescent Balb/c-3T3 cells in a fashion similar to EGF and synthetic TGF-alpha. In addition to secreting TGF-alpha-like polypeptides, 1246-3A cells produce TGF-beta. This polypeptide, eluted from Biogel P60 chromatography with an apparent molecular weight of 25 kDa, promoted anchorage-independent growth of NRK cells in the presence of EGF and was growth inhibitory for Chinese hamster lung fibroblasts CCL 39 cells. Interestingly, another growth inhibitory activity was detected in Biogel P60 fractions and eluted with an apparent molecular weight of between 9.5-11 kDa. This fraction was different from TGF-beta and TGF-alpha as determined by specific radioreceptor competition assays. TGF-alpha and TGF-beta-like polypeptides could represent autocrine growth stimulators for the insulin-independent 1246-3A cells and act in synergy with insulin-related factor (IRF) for an optimal stimulation of 1246-3A cell proliferation in serum-free medium.

Inhibition of DNA synthesis and cell division by a cell surface sialoglycopeptide

We have isolated and purified a cell surface sialoglycopeptide (SGP) from bovine cerebral cortex cells that previously was shown to be a potent inhibitor of cellular protein synthesis. The following studies were carried out to characterize the potential ability of the SGP to inhibit DNA synthesis and to arrest cell division. Treatment of exponentially proliferating Swiss 3T3 cells with the SGP inhibitor resulted in a marked inhibition of thymidine incorporation within 24 h. When the SGP was removed from inhibited cultures, a sharp rise in 3H-thymidine incorporation followed within 3-4 h that peaked well above that measured in exponentially growing cultures, suggesting that the inhibitory action of the SGP was reversible and that a significant proportion of the arrested cells was synchronized in the mitotic cycle. In addition to DNA synthesis, the inhibitory action of the SGP was monitored by direct measurement of cell number. Consistent with the thymidine incorporation data, the SGP completely inhibited 3T3 cell division 20 h after its addition to exponentially growing cultures. Upon reversal there was a delay of 15 h before cell division resumed, when the arrested cells quickly doubled. Most, if not all, of the growth-arrested cells appeared to have been synchronized by the SGP. The SGP inhibited DNA synthesis in a surprisingly wide variety of target cells, and the relative degree of their sensitivity to the inhibitor was remarkably similar. Cells sensitive to the SGP ranged from vertebrate to invertebrate cells, fibroblast and epitheliallike cells, primary cells and established cell cultures, as well as a wide range of transformed cell lines.

Transforming growth factor alpha may be a physiological regulator of liver regeneration by means of an autocrine mechanism

We investigated whether transforming growth factor alpha (TGF-alpha) is involved in hepatocyte growth responses both in vivo and in culture. During liver regeneration after partial hepatectomy in rats, TGF-alpha mRNA increased; it reached a maximum (approximately 9-fold higher than normal) at the peak of DNA synthesis. The message and the peptide were localized in hepatocytes and found in higher amounts in hepatocytes obtained from regenerating liver. TGF-alpha caused a 13-fold elevation of DNA synthesis in hepatocytes in primary culture and was slightly more effective than epidermal growth factor. TGF-beta blocked TGF-alpha stimulation when added either simultaneously with TGF-alpha or a day later. TGF-alpha message increased in hepatocytes stimulated to undergo DNA synthesis by TGF-alpha or epidermal growth factor, and the peptide was detected in the culture medium by RIA. In the regenerating liver, the increase in TGF-alpha mRNA during the first day after partial hepatectomy coincided with an increase in epidermal growth factor/TGF-alpha receptor mRNA and a decrease (already reported) in the number of these receptors. We conclude that TGF-alpha may function as a physiological inducer of hepatocyte DNA synthesis during liver regeneration by means of an autocrine mechanism and that its stimulatory effects in this growth process are balanced by the inhibitory action of TGF-beta 1.

Correlations between heparan sulfate metabolism and hepatoma growth

A rat hepatoma cell line (Gershenson et al., Science, 170:859-861, 1970) contains a dynamic steady-state pool of free heparan sulfate (HS) chains in the nucleus that increases in amount when growing cells reach confluence (Fedarko and Conrad, J. Cell Biol., 102:587-599, 1986). In logarithmically growing cells labeled with 35SO4(2-) steady-state levels of [35SO4]HS in the nucleus are altered by a variety of culture conditions. Rapidly dividing cells (doubling time = 18-22 h) growing under optimized conditions had steady-state levels of nuclear HS within the range of 40-50 pmol 35SO4 in nuclear HS/10(6) cells. The steady-state levels of nuclear HS were lowered by several changes in culture conditions, including 1) additions of 1 mM p-nitrophenyl-beta-D-xyloside, 0.25-0.5 mM (+)-catechin, 0.5 ng/ml transforming growth factor beta, 20 ng/ml phorbol-12-myristate-13-acetate, 1 mM dibutyryl cAMP, or 1 mM inositol-2-PO4; 2) decreased levels of D-glucose; or 3) deletions of serum, insulin, or inositol. In all cases lowering of the nuclear HS level was accompanied by an increase in the cell doubling times, suggesting a correlation in which nuclear HS levels must be optimized for maximal growth rates. When cells cultured under optimal growth conditions reached confluence, the level of nuclear HS increased threefold and the cells stopped dividing. The same culture conditions that lowered the steady-state levels of HS in the logarithmically growing cells prevented this rise in the nuclear HS as the cells reached confluence and resulted in loss of contact inhibition and overgrowth of the confluent cultures. These observations suggest a second correlation in which elevated nuclear HS levels are found when cell growth is inhibited at confluence; prevention of this rise results in continued growth. Consistent with this correlation between elevated nuclear HS and reduced growth rates, it was observed that addition of either 0.5 microgram/ml hydrocortisone or 0.05 microgram/ml retinoic acid to the culture medium of logarithmically growing cultures resulted in increases in steady-state levels of nuclear HS that were accompanied by increased cell doubling times. The two agents that increased the levels of nuclear HS in logarithmically growing cultures had little effect on levels of nuclear HS in confluent cells or on contact inhibition.(ABSTRACT TRUNCATED AT 400 WORDS)

DNA synthesis in cultured adult rat hepatocytes: effect of serum and calcium

We have investigated the influence of serum and of varying Ca2+ concentrations on the DNA synthesis in primary monolayer cultures of adult rat hepatocytes, using a defined basic medium. Supplementation of the medium with 10% horse serum did not significantly affect the time course of the DNA synthesis induced by insulin and epidermal growth factor. Dose effect curves showed that serum moderately sensitized the cells to low concentrations of insulin and slightly sensitized them to epidermal growth factor, but was not required for full responses to maximal concentrations of the hormones. In the serum-free cultures a wide range of Ca2+ concentrations (0.4 - 1.8 mmol/l) yielded maximal DNA synthesis, suggesting a broad Ca2+ optimum of the S phase entry in the hepatocyte monolayers.

One of two subunits of masking protein in latent TGF-beta is a part of pro-TGF-beta

A high molecular mass latent form of transforming growth factor type-beta (TGF-beta) was purified to homogeneity from rat platelets by a seven-step procedure involving group-specific affinity chromatographies on Red-Toyopearl and zinc chelating-Sepharose. The purified latent TGF-beta was a complex of TGF-beta (25 kDa) and the binding protein previously named masking protein (approximately 400 kDa) [(1986) Biochem. Biophys. Res. Commun. 141, 176-184]. Analysis of the peptide structure by gel electrophoresis showed that the masking protein consisted of two subunits of 39 kDa and 105-120 kDa linked by disulfide bonds. N-terminal amino-acid sequencing of the 39 kDa subunit indicated that this subunit was identical to the N-terminal part of the TGF-beta precursor.

Role of TGF-beta in normal differentiation and oncogenesis in rat liver

Transforming growth factor-beta 1 (TGF-beta 1) is capable of eliciting a myriad of biological responses associated with cellular proliferation, as well as effects unrelated to the control of cell growth. We examined the possible role of TGF-beta 1 in the differentiation of rat liver epithelial (RLE) cells in vitro and studied the cellular distribution of TGF-beta 1 transcripts and protein during in vivo differentiation of oval cells. Furthermore, we followed the cellular distribution of TGF-beta 1 transcripts and protein during chemical hepatocarcinogenesis. By using in situ hybridization and immunohistochemical techniques, we showed that both TGF-beta 1 transcripts and protein are localized in nonparenchymal cells in normal liver, are expressed in oval cells during very early stages of hepatocytic differentiation in vivo, and are exclusively expressed in the nontumorous mesenchymal cell compartment during hepatocarcinogenesis. Furthermore, we showed that TGF-beta 1 is capable of inducing differentiation of RLE cells in vitro consistent with early stages of hepatocytic lineage differentiation. Our data indicate that the RLE cells similar to the oval cells in vivo may be an epithelial progenitor cell for hepatocytic cell lineage in adult mammalian liver.

Interleukin-1 beta is a potent growth inhibitor of adult rat hepatocytes in primary culture

Interleukin-1 beta (IL-1 beta) strongly inhibited DNA synthesis of adult rat hepatocytes in primary culture stimulated by insulin and epidermal growth factor (EGF). Its effect was dose-dependent and was maximal at 2 ng/ml. IL-1 beta had no cytotoxic effect but changed the cells from a flat to a spindle shape as shown by phase-contrast microscopy. The inhibition of DNA synthesis by IL-1 beta was closely correlated with a decrease in the labeling index. This inhibitory effect was observed only when IL-1 beta was added for 10 h to cultured hepatocytes in the G1 phase within 12 h after addition of insulin and EGF: it was not observed in the S phase, which starts about 24 h after addition of the mitogens. Exposure of the hepatocytes to IL-1 beta for two 1-h periods, one at an early stage (0-6 h) and one at a late stage (6-12 h) of the G1 phase, resulted in the same marked inhibition of DNA synthesis as exposure to IL-1 beta for 10 h in the G1 phase. This requirement of IL-1 beta at two stages in the G1 phase for inhibition of DNA synthesis of hepatocytes is different from that with transforming growth factor-beta, which is required for only 1 h in the early G1 phase for a similar inhibition. These findings suggest that IL-1 beta acts at two distinct stages in the G1 phase and that its cooperative actions are necessary to inhibit growth of adult rat hepatocytes in primary culture. Other cytokines, such as IL-6/B-cell stimulating factor-2, were less potent, but caused significant inhibition of DNA synthesis of adult rat hepatocytes at 2 ng/ml, whereas IL-2 and tumor necrosis factor did not affect hepatocyte growth. From these results it is suggested that Kupffer cells in liver lobules and macrophages in the blood may play important roles, mainly via IL-1, in repair of liver damage and regeneration.

Inhibitory effect of transforming growth factor-beta on epidermal growth factor-induced proliferation of cultured rat aortic smooth muscle cells

This study was conducted to investigate the effect of transforming growth factor-beta (TGF-beta) on the proliferation of cultured rat aortic smooth muscle cells (SMCs). DNA synthesis, measured by the incorporation of [3H] thymidine, and the cell number of monolayered SMCs were measured after incubation with TGF-beta (1-100 ng/ml) in the presence or absence of epidermal growth factor (EGF; 100 ng/ml). TGF-beta alone did not affect DNA synthesis of SMCs. EGF significantly increased both DNA synthesis and cell number, while TGF-beta inhibited the increase in both in a dose-dependent manner without accompanying the significant cellular damage. These results indicate that TGF-beta exerts an inhibitory effect on the proliferation of cultured SMCs provoked by EGF.

Type beta transforming growth factor reversibly inhibits the early proliferative response to partial hepatectomy in the rat

Type beta transforming growth factor (TGF-beta), a factor produced by many cell types, is a potent inhibitor of hepatocyte DNA synthesis in vitro. To determine whether TGF-beta can influence hepatocyte proliferation in vivo, its effects were examined on the regenerative response of liver to partial hepatectomy (PH) in the rat. Porcine platelet-derived TGF-beta 1 (0.5 micrograms), administered intravenously at the time of PH and 11 hr later, reduced the fraction of hepatocytes engaged in DNA synthesis 22 hr after PH by 67% and inhibited the rate of hepatic [3H]thymidine incorporation by 50%. TGF-beta 2 produced a similar effect. A single dose of 0.5 micrograms of TGF-beta 1 given 11 hr after PH reduced liver [3H]thymidine incorporation by 32%; 4.5 micrograms of TGF-beta 1 or TGF-beta 2 inhibited DNA synthesis by 88% and the labeling index by 86%. Although sensitive to TGF-beta administered 11 hr after PH, late in the G1 phase of the cell cycle, a single dose of 0.5 micrograms given at the time of PH did not significantly influence DNA synthesis 22 hr after PH. The inhibitory effects of TGF-beta were transient; rats treated with two 0.5-microgram doses of TGF-beta at 0 and 11 hr had completely restored their original liver DNA mass 8 days after PH. Administration of 0.5 microgram of either TGF-beta 1 or TGF-beta 2 every 12 hr for 5 days failed to suppress the recovery of hepatic DNA mass. However, the nuclear labeling index of the TGF-beta-treated animals was significantly higher than that of the controls. There was no evidence of cytotoxicity from TGF-beta, as determined by liver histology and plasma concentrations of glucose, insulin-like growth factor I, and two hepatic enzymes. Thus, TGF-beta 1 and TGF-beta 2 reversibly inhibit the proliferative response of liver to PH and may be important in the modulation of normal liver growth and repair.

Norepinephrine modulates the growth-inhibitory effect of transforming growth factor-beta in primary rat hepatocyte cultures

TGF-beta is a potent inhibitor of EGF-induced DNA synthesis in primary rat hepatocyte cultures. Norepinephrine (NE) was shown to modulate this inhibition of DNA synthesis. It produced a five-fold increase, from 2.8 pM to 14.4 pM, in the ID50 for TGF-beta. The effect was dose-dependent and was significant at concentrations of 10(-6)M NE and greater. The modulation by NE was mediated by the alpha 1-adrenergic receptor as shown by the ability of the alpha 1 antagonist prazosin to block the activity. This effect might be important during liver regeneration in allowing escape of hepatocytes from negative growth control exerted by TGF-beta.