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

Activation of caspase-8 in transforming growth factor-beta-induced apoptosis of human hepatoma cells

Transforming growth factor-beta1 (TGF-beta1) has been shown to induce apoptosis in normal or transformed hepatocytes. To elucidate the biochemical pathways leading to apoptosis induced by TGF-beta1 in human hepatoma cells (HuH-7), we examined the expression of Bcl-2-related proteins and X-chromosome-linked inhibitor of apoptosis (XIAP), and activation of the caspase cascade following TGF-beta1 treatment. Bcl-xL expression began to decline at 12 hours after TGF-beta1 treatment and progressively decreased to very low levels in a time-dependent manner. Bax expression showed a little change throughout the experiment. On the other hand, activation of caspase-8 was clearly observed at 36 hours after TGF-beta1 treatment, followed by activation of caspase-9, and caspase-3 was activated at 48 hours after treatment at which time apoptosis of HuH-7 cells was observed. TGF-beta1 significantly decreased XIAP expression in HuH-7 cells. Addition of an inhibitor of caspase-8 or caspase-3 (IETD-FMK or DEVD-CHO) markedly inhibited TGF-beta1-induced apoptosis of HuH-7 cells. Fas/Fas ligand (FasL) interactions in HuH-7 cells were not involved in the apoptotic process. Furthermore, epidermal growth factor (EGF) also completely inhibited TGF-beta1-induced apoptosis of HuH-7 cells by inhibiting activation of the caspase cascade. Our results suggested that activation of caspase-3 initiated through caspase-8 activation is involved in the apoptotic process induced by TGF-beta1 in HuH-7 cells. Our results also showed that down-regulation of the expression of Bcl-xL and XIAP by TGF-beta1 may facilitate activation of caspase-3 in these cells.

Growth state-dependent regulation of plasminogen activator inhibitor type-1 gene expression during epithelial cell stimulation by serum and transforming growth factor-beta1

Transcription of the plasminogen activator inhibitor type-1 (PAI-1) gene appears to be growth state regulated in several cell types (e.g. , Ryan and Higgins, 1993, J Cell Physiol 155:376-384; Mu et al., 1998, J Cell Physiol 174:90-98). Transit of serum-stimulated normal rat kidney (NRK) epthelial cells through the first division cycle after release from quiescence (G(0)) provided a model system to assess the kinetics and mechanisms underlying PAI-1 expression in a growth "activated" phenotype. PAI-1 mRNA transcripts increased by more than 20-fold during the G(0)-->G(1) transition; induced expression had immediate-early response characteristics and abruptly declined prior to the onset of DNA synthesis. Transcriptional activity of the PAI-1 gene paralleled the steady-state mRNA abundance profile during this first synchronized growth cycle after release from quiescence. Although PAI-1 mRNA levels were up-regulated (approximately threefold) upon exposure to several different growth factors, neutralizing antibodies to transforming growth factor-beta1 (TGF-beta1) effectively attenuated the more than ninefold serum-associated PAI-1 inductive response by more than 70% (at both the mRNA transcript and protein levels). Similar to the metabolic requirements for serum-mediated PAI-1 transcription, PAI-1 induction upon addition of TGF-beta1 to quiescent NRK cell cultures was actinomycin D sensitive and resistant to cyclohexamide and puromycin, suggesting a primary mode of transcript control. The response to protein synthesis inhibitors, however, was complex. While cyclohexamide appeared to stabilize, or at least maintain, fetal bovine serum (FBS)- or TGF-beta1-stimulated PAI-1 mRNA levels, puromycin had no such affect. The amplitude and duration of induced PAI-1 expression were the same in either the presence or absence of puromycin. Cyclohexamide when used alone (i.e., in non-FBS- or TGF-beta1-treated cultures), moreover, effectively stimulated PAI-1 induction whereas puromycin was ineffective. Although TGF-beta1 was not a complete mitogen in the NRK cell system, incubation of quiescent renal cell cultures with TGF-beta1, prior to serum stimulation, resulted in a 10- to 12-fold increase in PAI-1 expression coincident with exit out of G(0). These data support a model in which PAI-1 gene expression is closely associated with creation of the growth-activated state and that cell cycle controls appear to be superimposed on the time course of the serum-induced expression of the PAI-1 gene.

Stimulation of in vitro rat hepatocyte proliferation by conditioned medium obtained from an immortalized macrophage cell line

The hepatomitogenic effect of conditioned medium (CDM), obtained from the N-11 mouse macrophage cell line was analysed in rat hepatocyte primary cultures. CDM concentrations from 0.01% to 100% were used and the stimulating action in terms of mitotic index (MI) was evaluated. A clear mitogenic effect was observed only with concentrations higher than 10% with peak effects around 60%. Further increase in CDM concentrations resulted in an MI decrease, and at 100% CDM the effect was totally abolished. Tests addressed to identify the presence of hepatocyte growth factor (HGF) yielded negative results. In order to identify the mitogenic factor(s) involved, we tested CDM obtained after lipopolysaccharide (LPS) stimulation of N-11 cells. Comparison of the results obtained with untreated or LPS stimulated CDMs suggested that macrophage activation does not affect the release of hepatomitogenic activity. To further characterize this macrophage-derived activity, we checked whether CDM could interact with the mitogenic effects of epidermal growth factor (EGF). CDM (10 or 50%) showed no stimulatory effect to hepatocytes cultured in the presence of a maximally stimulatory concentration of EGF. Conversely, both CDM concentrations were able to increase the MI of hepatocyte cultures treated with a suboptimal dose of EGF. These results suggest that macrophages release factor(s) which interact, in hepatocytes, with the EGF signal transduction mechanisms, or with the EGF receptor itself.

Transforming growth factor beta1 helps maintain differentiated functions in mitogen-treated primary rat hepatocyte cultures

Mechanisms that control function and repair of the injured liver remain unclear. We hypothesized that after liver injury, elevated blood TGF-beta1 levels may reflect an adaptive response to help maintain differentiated functions in surviving hepatocytes affected by excessive amounts of HGF. We thus studied the effect of HGF, EGF, TGF-beta1, HGF + TGF-beta1, or EGF + TGF-beta1 on the expression of liver-enriched transcription factors and genes which remain under their regulatory activity. The peak [3H]thymidine uptake induced by 20 ng/ml of either HGF or EGF was seen after 72 h; however, DNA binding of C/EBP and HNF1 decreased already after 6 h (electrophoretic mobility shift assay). Addition of TGF-beta1 antagonized these effects. Also at the mRNA level, TGF-beta1 counteracted at one point or another the decrease in C/EBPalpha, C/EBPbeta, HNF1beta, and HNF4 expression; HNF1alpha and COUP-TF showed similar responses and, additionally, were downregulated by TGF-beta1 at 24 h (Northern blot). Albumin and apolipoprotein B mRNA levels were decreased after 24-h treatment with HGF, whereas addition of TGF-beta1 increased their levels. The same pattern was found with EGF, but not until 48 h. PEPCK mRNA was dramatically lowered with either EGF or HGF, and TGF-beta1 did not counteract these effects. Id-1 was expressed only in cultures treated for 24 and 48 h with both the mitogen (EGF, HGF) and TGF-beta1 and in those treated for 48 h with TGF-beta1 alone.

Inhibition of rat hepatocyte proliferation by transforming growth factor beta and glucagon is associated with inhibition of ERK2 and p70 S6 kinase

Stimulation of hepatocyte proliferation by epidermal growth factor (EGF) and insulin is inhibited by transforming growth factor beta (TGF-beta) and by glucagon. It is also suppressed by inhibitors of various protein kinases, including rapamycin, which blocks activation of p70 S6 kinase (p70(S6k)), PD98059, which inhibits the activation of extracellular-regulated kinase (ERK), and SB 203580, an inhibitor of the p38 mitogen-activated protein kinase (p38 MAPK). In this study, we investigated whether the inhibition of proliferation by TGF-beta involves these protein kinase cascades. Culture of hepatocytes with TGF-beta for 16 hours decreased the stimulation by EGF of ERK2 and p70(S6k) (by 50% and 35%, respectively), but did not affect the stimulation of either p38 MAPK, c-jun NH2-terminal kinase (JNK), or protein kinase B (PKB). Culture of hepatocytes with glucagon for 16 hours also inhibited the stimulation by EGF of activation of ERK2 and p70(S6k) (by approximately 50%). The inhibitory effects of glucagon were observed when the hormone was added either 10 minutes or 60 minutes before EGF addition, whereas no effects of TGF-beta were observed after 10-minute or 60-minute incubation. These results suggest that the inhibition of hepatocyte proliferation by TGF-beta may be in part mediated by inhibition of ERK2 and p70(S6k), but does not involve PKB, JNK, or p38 MAPK. Unlike glucagon, the effects of TGF-beta are not elicited in response to short-term treatment.

Hepatocyte growth inhibitory factor derived from HTLV-I(+) T-cell line is identical to IL-6

We previously reported that the culture supernatant of the human T-cell leukemia virus (HTLV-I) infected-T-cell line--ATL-2--included factor(s), which had an inhibitory effect on epidermal growth factor (EGF)-stimulated proliferation of primary cultured rat hepatocytes. After crude purification, we arbitrarily named it hepatocyte growth inhibitory factor (HGI). In this study, we further purified HGI and determined its amino acid sequence. For purification, we used 4-steps column chromatography and SDS-PAGE. The purified proteins consisted of two bands of 20 and 27 kDa in SDS-PAGE analysis. Protein extracted from each band had an inhibitory effect on rat hepatocyte growth. Amino acid analysis of the purified 20 kDa band revealed that the 34 amino acids were identical to those of IL-6. The inhibitory effect of the factor was neutralized by an anti IL-6 neutralizing antibody. Using Western blot analysis of HGI, an anti IL-6 antibody recognized both 20 and 27 kDa bands. Consequently HGI was determined to be identical to IL-6, which occurred in higher levels in the sera of adult T-cell leukemia (ATL) patients.

Fetal liver development requires a paracrine action of oncostatin M through the gp130 signal transducer

Fetal liver, the major site of hematopoiesis during embryonic development, acquires additional various metabolic functions near birth. Although liver development has been characterized biologically as consisting of several distinct steps, the molecular events accompanying this process are just beginning to be characterized. In this study, we have established a novel culture system of fetal murine hepatocytes and investigated factors required for development of hepatocytes. We found that oncostatin M (OSM), an interleukin-6 family cytokine, in combination with glucocorticoid, induced maturation of hepatocytes as evidenced by morphological changes that closely resemble more differentiated hepatocytes, expression of hepatic differentiation markers and intracellular glycogen accumulation. Consistent with these in vitro observations, livers from mice deficient for gp130, an OSM receptor subunit, display defects in maturation of hepatocytes. Interestingly, OSM is expressed in CD45(+) hematopoietic cells in the developing liver, whereas the OSM receptor is expressed predominantly in hepatocytes. These results suggest a paracrine mechanism of hepatogenesis; blood cells, transiently expanding in the fetal liver, produce OSM to promote development of hepatocytes in vivo.

Ethanol-Induced Macrophage Apoptosis: The Role of TGF-β

Both clinical and laboratory reports indicate that ethanol addicts are prone to recurrent infections. We hypothesize that ethanol promotes macrophage apoptosis, thus compromising the efficiency of the mononuclear phagocyte system in dealing with infection. We studied the effect of ethanol on macrophage apoptosis. Human monocytes isolated from healthy subjects after an alcohol drinking binge showed enhanced apoptosis (before, 1.2 ± 0.3% vs after, 28.4 ± 3.7% apoptotic cells/field). Peritoneal macrophages harvested from ethanol-treated rats also showed increased (p < 0.0001) apoptosis. DNA isolated from peritoneal macrophages of ethanol-treated rats displayed integer multiples of 200 base pairs (ladder pattern). Furthermore, macrophages harvested from ethanol-treated rats had an enhanced expression as well as accumulation of TGF-β. In in vitro studies, ethanol promoted apoptosis of human monocytes as well as rat peritoneal macrophages. In addition, ethanol enhanced apoptosis of murine macrophages (J774) in a time-dependent manner. The ethanol-induced apoptosis was amplified by LPS and partly attenuated (p < 0.001) by anti-TGF-β Ab. TGF-β also promoted macrophage apoptosis in a dose-dependent manner. Moreover, ethanol enhanced TGF-β protein production by macrophages. These results indicate that ethanol promotes macrophage apoptosis. This effect of ethanol seems to be partly mediated through the generation of TGF-β by macrophages.

Expression of matrix metalloproteinase-13 and tissue inhibitor of metalloproteinase-1 in acute liver injury

BACKGROUND/AIMS

Matrix metalloproteinase-13, one of the principal neutral proteinases capable of cleaving native fibrillar collagens, is important in the degradation and remodeling of extracellular matrix. However, its precise expression in liver injury has not been characterized. We examined the kinetics of the expression of matrix metalloproteinase-13 and one of its specific inhibitors, tissue inhibitor of metalloproteinase-1, in acute liver injury in rats.

METHODS

Acute liver injury was induced by administration of carbon tetrachloride or two different doses of D-galactosamine hydrochloride in Wistar rats. Hepatic matrix metalloproteinase-13 and tissue inhibitor of metalloproteinase-1 mRNA levels were then examined by Northern blotting.

RESULTS

All rats survived after liver injury induced by carbon tetrachloride or low doses of D-galactosamine hydrochloride. However, rats died 5 days after induction of liver injury by high doses of D-galactosamine hydrochloride. In carbon tetrachloride-induced liver injury, matrix metalloproteinase-13 mRNA was transiently increased between 6 h and 1 day after injury. Tissue inhibitor of metalloproteinase-1 mRNA expression was increased between 6 h and 3 days after the peak of matrix metalloproteinase-13 expression. Similar patterns of matrix metalloproteinase-13 and tissue inhibitor of metalloproteinase-1 expression were observed in low-dose D-galactosamine hydrochloride-induced liver injury. In contrast, in high-dose D-galactosamine hydrochloride-induced liver injury, tissue inhibitor of metalloproteinase-1 expression peaked before matrix metalloproteinase-13 expression, which was increased 2 days after injury. Both mRNA levels continued to increase until death.

CONCLUSIONS

Transient expression of matrix metalloproteinase-13, followed by that of tissue inhibitor of metalloproteinase-1, was observed during recovery from acute liver injury induced by carbon tetrachloride and low-dose D-galactosamine hydrochloride. In contrast, disordered expression of matrix metalloproteinase-13 was observed in fatal liver injury caused by high-dose D-galactosamine hydrochloride. These results indicate that matrix metalloproteinase13 plays an important role in the early phase of recovery from liver injury.

Hepatocyte proliferative activity in human liver cirrhosis

BACKGROUND/AIMS

The objective of this study was to validate, with an independent prospective cohort of patients, our previous data indicating that the proliferating cell nuclear antigen-labeling index (PCNA-LI) reflects the liver functional reserve in human cirrhosis and might have prognostic significance for patient survival. We also examined how this proliferative index is related to the expression of transforming growth factor beta1 (TGFbeta1) as a possible correlate of hepatocyte proliferative activity.

METHODS

The present group (n=70 patients) was similar in composition to our previous group regarding age, sex and severity of liver cirrhosis. PCNA and TGFbeta1 immunostaining were analyzed on methanol-fixed, paraffin-embedded liver biopsies.

RESULTS

Our data show that PCNA-LI declined significantly with worsening Child class and was negatively correlated with the Pugh score. Twenty-five patients died and 10 underwent liver transplantation during the observation period. Liver function, hepatic venous pressure gradient and hepatocyte PCNA-LI were significantly different in survivors and non-survivors. At a mean follow-up of 356 days, the patients with a PCNA-LI higher than 4.4% (the previously determined best cut-off value) had a significantly higher probability of survival than those with a PCNA-LI < or = 4.4% (0.87 vs 0.48, p=0.0009). TGFbeta1 expression in liver parenchyma correlated negatively with PCNA-LI, suggesting that this cytokine could be involved in the impaired regeneration observed in worsened liver cirrhosis.

CONCLUSIONS

This prospective study strengthens our previous observation that, in cirrhosis, hepatocyte proliferative activity, as evaluated by the PCNA-LI, provides information on liver functional reserve as well as on the patient's prognosis.

Hepatocyte growth factor gene therapy of liver cirrhosis in rats

Liver cirrhosis is the irreversible end result of fibrous scarring and hepatocellular regeneration, characterized by diffuse disorganization of the normal hepatic structure of regenerative nodules and fibrotic tissue. It is associated with prominent morbidity and mortality, and is induced by many factors, including chronic hepatitis virus infections, alcohol drinking and drug abuse. Hepatocyte growth factor (HGF), originally identified and cloned as a potent mitogen for hepatocytes, shows mitogenic, motogenic and morphogenic activities for a wide variety of cells. Moreover, HGF plays an essential part in the development and regeneration of the liver, and shows anti-apoptotic activity in hepatocytes. In a rat model of lethal liver cirrhosis produced by dimethylnitrosamine administrations, repeated transfections of the human HGF gene into skeletal muscles induced a high plasma level of human as well as enodogenous rat HGF, and tyrosine phosphorylation of the c-Met/HGF receptor. Transduction with the HGF gene also suppressed the increase of transforming growth factor-beta1 (TGF-beta1), which plays an essential part in the progression of liver cirrhosis, inhibited fibrogenesis and hepatocyte apoptosis, and produced the complete resolution of fibrosis in the cirrhotic liver, thereby improving the survival rate of rats with this severe illness. Thus, HGF gene therapy may be potentially useful for the treatment of patients with liver cirrhosis, which is otherwise fatal and untreatable by conventional therapy.

Involvement of polyamines in retinoblastoma protein phosphorylation

Hepatocyte growth factor (HGF) increased both levels of phosphorylated and non-phosphorylated forms of retinoblastoma protein (RB) in primary cultured rat hepatocytes. Combined treatment of HGF and a specific inhibitor of ornithine decarboxylase (ODC), alpha-difluoromethylornithine (DFMO), reduced the levels of hyper-phosphorylated and hypo-phosphorylated forms of RB and increased the levels of the non-phosphorylated form, compared to HGF alone, but did not affect the total level of RB. Polyamines added exogenously overcame the effects of DFMO; they increased hyper- and hypo-phosphorylated forms and decreased non-phosphorylated RB. TGF-beta1 inhibited the increases in ODC activity, RB phosphorylation, and DNA synthesis induced by HGF. However, polyamines added exogenously could not overcome the inhibition by RB phosphorylation and DNA synthesis by TGF-beta1. These results suggest that polyamines are involved in the phosphorylation of RB, but the inhibition of polyamine biosynthesis by TGF-beta1 did not result in the inhibition of RB phosphorylation and DNA synthesis.

Changes in TGF-beta receptors of rat hepatocytes during primary culture and liver regeneration: increased expression of TGF-beta receptors associated with increased sensitivity to TGF-beta-mediated growth inhibition

To clarify the role of transforming growth factor-beta (TGF-beta) and its receptors in hepatocyte growth, we studied the expression of TGF-beta1 and its receptors and the sensitivity to growth inhibition by TGF-beta1 protein in rat hepatocytes derived from resting and regenerating livers. In hepatocytes derived from resting livers, mRNAs for TGF-beta type II receptor (TbetaR-II), insulin-like growth factor-II/mannose 6-phosphate receptor (IGF-II/M-6-PR), and TGF-beta1 increased with time in primary culture. The cell surface TGF-beta receptor proteins (TbetaR-I, II, and III), examined by the receptor affinity-labeling assay using 125I-TGF-beta1, also increased, especially after 48 hr of culture. Hepatocytes were more sensitive to inhibition of DNA synthesis, when the TGF-beta1 protein was added at later times in culture, corresponding to the presence of increased TGF-beta receptors. In hepatocytes from regenerating livers after a partial hepatectomy (PH), an increase of TbetaR-I, TbetaR-II, TbetaR-III, IGF-II/M-6-PR, and TGF-beta1 mRNAs was found, compared with hepatocytes from resting livers. Similarly, using TGF-beta receptor affinity-labeling assay, hepatocytes from PH livers were found to have an increase in TbetaR-I, II, and III proteins, with a peak at 4 days post-PH, compared with hepatocytes from resting livers. When TGF-beta1 protein was added for a short period (6 or 24 hr) after cell attachment to hepatocyte cultures, it inhibited DNA synthesis more effectively in hepatocytes from regenerating compared with resting livers. Our results show that hepatocyte TGF-beta receptors and sensitivity to growth inhibition by TGF-beta1 protein change together and are modulated during liver regeneration, as well as during the conditions of primary culture.

The involvement of aryl hydrocarbon receptor in the activation of transforming growth factor-beta and apoptosis

The aryl hydrocarbon receptor (AHR) is believed to mediate many of the toxic, carcinogenic, and teratogenic effects of environmental contaminants such as dioxins, polycyclic aromatic hydrocarbons, and polyhalogenated biphenyls. Ligands for the AHR have been shown to influence cell proliferation, differentiation, and apoptosis, but the mechanism by which the AHR affects the cell cycle is not known. Increased levels of mature transforming growth factor-beta (TGFbeta) has been correlated with reduced cell proliferation and increased rates of apoptosis and fibrosis. Based on the increase in portal fibrosis and small liver size observed in AHR-null (Ahr-/-) mice, the relationship between TGFbeta expression and apoptosis in this mouse line was analyzed. Livers from Ahr-/- mice had marked increase in active TGFbeta1 and TGFbeta3 proteins and elevated numbers of hepatocytes undergoing apoptosis compared with wild-type mice. Furthermore, increases in TGFbeta and apoptotic cells were found in the portal areas of the liver, where fibrosis is found in the Ahr-/- mice. In vitro, primary hepatocyte cultures from Ahr-/- mice exhibited a high number of cells in later stages of apoptosis and an elevated secretion of active TGFbeta into the media compared with cultures from wild-type mice, which have previously been shown to secrete only latent forms of the molecule. Conditioned media from Ahr-/- hepatocytes stimulated apoptosis in cultured hepatocytes from wild-type mice. Taken together, these findings suggest that the phenotypic abnormalities in Ahr-/- mice could be mediated in part by abnormal levels of active TGFbeta and altered cell cycle control.

Hepatocyte apoptosis and hepatic expression of transforming growth factor-beta1 mRNA during involution of hyperplastic rat liver induced by hepatocyte growth factor

Hepatocyte apoptosis occurs during involution of hyperplastic liver induced by administration of xenobiotic compounds in rats. With this hyperplasia and involution, hepatic transforming growth factor (TGF)-beta1 is reported to be expressed to stimulate hepatocyte apoptosis. In regenerating liver after partial resection showing no hyperplasia, such expression of TGF-beta1 is also seen. However, no hepatocyte apoptosis develops despite the high levels of TGF-beta1. When rats received an intravenous injection of human hepatocyte growth factor at 12 h intervals for 14 days, the hepatic DNA content was increased 12 h after the last injection to 140% of control. This DNA content was significantly decreased at 108 and 180 h after discontinuation of treatment. At 60 h after the last injection, the number of apoptotic bodies positive for nick end-labelling of DNA in hepatocytes was significantly greater in treated rats than in control rats. Hepatocyte apoptosis was also identified electron micrographically. Hepatic TGF-beta1 mRNA levels in treated rats were significantly lower than in control rats at 12 h and then gradually increased towards control levels. We conclude that hyperplastic liver induced in normal rats by hepatocyte growth factor regresses with hepatocyte apoptosis and suppressed hepatic TGF-beta1 mRNA levels.

Effects of lysophosphatidic acid on proliferation of stellate cells and hepatocytes in culture

Lysophosphatidic acid (LPA) is a growth factor-like mediator for fibroblasts or smooth muscle cells produced and released by activated platelets. Platelet activation occurs with hepatic necrosis and subsequent liver regeneration and fibrosis. In the fibrosis, hepatic stellate cells proliferate with phenotypic transformation to myofibroblasts. Thus, effects of LPA on proliferation of hepatocytes and stellate cells were investigated. In cultured rat stellate cells, LPA increased DNA synthesis with enhanced MAP kinase activity. Pertussis toxin (PTX) attenuated this mitogenic action. In contrast, LPA decreased DNA synthesis by cultured rat hepatocytes induced by hepatocyte growth factor (HGF) or epidermal growth factor (EGF) without affecting protein synthesis. Enhanced MAP kinase activity by HGF or EGF was not changed by LPA. This anti-mitogenic action was attenuated by PTX. TGFbeta level in the medium was less than the level effective for inhibiting the DNA synthesis in the presence of LPA. Our results suggest that LPA might affect proliferation of hepatocytes and stellate cells in liver diseases complicating platelet activation.

Transforming growth factor-beta (TGF-beta) and EGF promote cord-like structures that indicate terminal differentiation of fetal hepatocytes in primary culture

When fetal hepatocytes were cultured in the presence of transforming growth factor-beta (TGF-beta 1) and epidermal growth factor (EGF), some morphological changes were observed. Under these conditions, cells migrated, from typical clusters that hepatocytes adopt in culture, to form elongated, cord-like structures similar to the hepatic acinus organization. Immunocytochemical analysis of these cells revealed high levels of albumin and cytokeratin 18, phenotypic markers of parenchymal hepatocytes. Although some of the cells in the cord-like structures presented a cortical ring distribution of F-actin filaments, the cord also presented thick peripheral bundles and cells of the tips showed thin stress fibers oriented to the cell edges, typical of a migratory phenotype. In addition to these morphological effects, flow cytometric analysis of the cells revealed a larger size, granularity and intracellular lipid content (as a parameter related to liver metabolic function), in TGF-beta + EGF-treated hepatocytes. Western blot analysis of the albumin levels revealed that both expression and secretion of albumin were increased in EGF + TGF-beta-treated cells. Finally, all these changes were coincident with an enhancement in the DNA-binding activity for hepatocyte nuclear factors (HNF1, HNF3, and HNF4), as revealed in gel-shift experiments with nuclear extracts. We conclude that a cooperative action between TGF-beta and EGF might modulate terminal maturation of fetal hepatocytes.

Progression through G1 and S phases of adult rat hepatocytes

Regenerating liver, hepatocyte primary cultures and differentiated hepatoma cell lines are widely used to study the proliferation/differentiation/apoptosis equilibrium in liver. In hepatocytes, priming factors (TNF alpha, IL6) target G0/G1 transition while growth factors (HGF, EGF, TGF alpha) control a mid-late G1 restriction point. A characteristic pattern of cdk/cyclin expression is observed in hepatocytes, presumably related to their ability to proliferate a limited number of times and to undergo a reversible differentiation. Interestingly, cell-cell interactions between hepatocytes and liver biliary cells in co-cultures, result in a cell cycle arrest in mid G1 of hepatocytes which are insensitive to mitogens. Apoptosis exists in hepatocytes but is still poorly documented. However, hepatoma cell lines stimulated by TGF beta undergo cell death in a p53-independent pathway. In conclusion, the interplay of growth and apoptosis regulators and cell-cell interactions control the proliferation/differentiation/apoptosis balance which is a specific feature of hepatocytes.

CD8+ Cells Are Not Necessary for Allograft Rejection or the Induction of Apoptosis in an Experimental Model of Small Intestinal Transplantation

Allospecific CTL can function as cellular effectors of solid organ graft rejection; however, the specific mechanisms of cell damage remain undetermined. In this study we examined the role of CD8+ T cells in apoptosis and rejection of small intestinal allografts. ACI rat intestinal grafts transplanted into Lewis rat recipients showed apoptosis of epithelial crypt cells on day 3 posttransplant as determined by terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end labeling staining. By day 7 numerous apoptotic crypt cells were detected in allografts, but were rarely observed in FK506-treated allograft recipients, isografts, or native intestine of allograft recipients. To further investigate the mechanism of rejection, recipient rats were depleted of CD8+ cells by treatment with OX-8 mAbs the day before and the day after transplantation of rat small intestinal allografts. Depletion of CD8+ cells from allograft recipients did not alter the tempo or the histologic features of rejection compared with those in the control (IgG-treated) group. Moreover, there was no difference in the number of apoptotic crypt epithelial cells in the grafts of control and CD8-depleted rats. Reverse transcriptase-PCR analyses determined there were similar levels of transcripts for Fas, Fas ligand, perforin, and granzyme B in control and CD8-depleted allograft recipients. By Western blot it was determined that the levels of Fas ligand protein were increased in the CD8-depleted group compared with those in control and FK506-treated allograft recipients. These data suggest that CD8 cells are not required for tissue injury or apoptotic cell death in small intestine allograft rejection.

Growth of intraportally transplanted islets under liver regeneration stimulus and restoration of normoglycemia in streptozocin-diabetic rats

BACKGROUND

Limitation of beta-cell growth after intraportal islet transplantation plays an important role in graft failure. To induce transplanted beta-cell proliferation, we studied the effect of compensatory liver growth in diabetic rats that had a subtherapeutic islet mass previously injected into the liver.

METHODS

Syngeneic rats were used as islet donors or recipients; diabetes was induced by streptozocin. Three groups of streptozocin-treated rats were studied. In group 1, 250 islets were selectively transplanted into the posterior liver lobes and 10 days later anterior portal branch ligation (PBL) was performed (n = 18); in group 2, 250 islets were transplanted into the posterior lobes and 10 days later sham PBL was performed (n = 13); in group 3, rats underwent a sham transplantation and PBL (n = 6). Nonfasting blood glucose levels and body weight were monitored. Six rats in groups 1 and 2 were killed 48 hours after PBL, liver sections were stained for proliferating cell nuclear antigen, and islet cell labeling index was calculated. The remaining rats were killed 30 days later. Liver compensatory growth or atrophy was calculated and morphometric determination of beta-cell area was assessed on insulin-immunostained sections of the liver.

RESULTS

In group 1 rats killed 48 hours after PBL, islet cell labeling index was significantly higher than in group 2 (p < 0.0001). After PBL, we observed normalization of nonfasting blood glucose levels in 10 of 12 rats. At 30 days, posterior liver lobes showed compensatory growth (218.5% +/- 18.6%) accompanied by atrophy of the anterior lobes; morphometric study of liver-engrafted islets showed a significant increase of individual beta-cell area, compared with group 2 (p < 0.0001). In groups 2 and 3, normoglycemia was not achieved.

CONCLUSIONS

In streptozocin-diabetic rats, normoglycemia was restored after transplantation of a sub-therapeutic islet mass, followed by PBL-induced liver regeneration. Histologic and morphometric results indicating islet cell proliferation suggest that compensatory liver growth might have induced a hypertrophic/hyperplastic response in the intraportally transplanted beta-cells.

Plasma levels and hepatic mRNA expression of transforming growth factor-beta1 in patients with fulminant hepatic failure

BACKGROUND/AIMS

Transforming growth factor-beta1 is an important cytokine involved in cell growth and inflammation which has been shown to be inhibitory to hepatic DNA synthesis. The aim of this study was to investigate the plasma levels and hepatic mRNA expression of transforming growth factor-beta1 in patients with fulminant hepatic failure in whom liver regeneration may be impaired.

METHODS

Plasma levels of transforming growth factor-beta1 and human hepatocyte growth factor were measured in 57 fulminant hepatic failure patients and 20 healthy volunteers by ELISA. Northern blot analysis of transforming growth factor-beta1 and H3 histone, a marker for liver proliferation, was performed in liver tissue of 14 fulminant hepatic failure patients.

RESULTS

The plasma levels of total transforming growth factor-beta1 in fulminant hepatic failure patients on admission (median 38.8 ng/ml, range 8.4-108 ng/ml) were significantly higher than those in control subjects (23.0 ng/ml, 8.5-34.9 ng/ml, p<0.001). Significantly higher levels were observed in non-A, non-B hepatitis patients (57.9 ng/ml, 38.8-108 ng/ml, n=10, p<0.001) compared to patients with paracetamol overdose (37.1 ng/ml, 8.4-72.5 ng/ml, n=47). In contrast, the plasma levels of free transforming growth factor beta1 were greater in paracetamol overdose (623 pg/ml, 46.7-1241 pg/ml, n=21) than in non-A, non-B hepatitis (131 pg/ml, 77.2-254 pg/ml, n=9), with both being higher than control (72.3 pg/ml, 28.7-108, n=7, p<0.001). The plasma levels of human hepatocyte growth factor in patients with paracetamol overdose (7.04 ng/ml, 1.00-62.4 ng/ml) were significantly higher than those in patients with non-A, non-B hepatitis (4.48 ng/ml, 0.74-9.10 ng/ml, p<0.05). Northern blots showed increased mRNA expression of transforming growth factor-beta1 in paracetamol-overdose patients (n=8, p<0.05), but not in patients with non-A non-B hepatitis (n=6), compared to controls (n=4).

CONCLUSIONS

The increased circulating plasma TGF-beta1 in FHF may be part of the tissue repair process in fulminant hepatic failure. In patients with non-A, non-B hepatitis, the increased total transforming growth factor-beta1 together with a less elevated hepatocyte growth factor could be related to impaired liver regeneration in this group.

Cell cycle-mediated regulation of hepatic regeneration

BACKGROUND

Hepatic regeneration after partial hepatectomy (PH) is characterized by a synchronous induction of normally quiescent hepatocytes to reenter the cell cycle, leading to a complete restoration of hepatic mass. Cell cycle progression requires activation of cyclin-dependent kinases (Cdks) that are regulated by cyclins and Cdk inhibitors.

METHODS

Protein expression of the cyclins (D-type and E), Cdks (Cdk2 and 4), and Cdk inhibitors (p21 and p27) was measured by Western blot after SHAM operation or PH in F344 rats. In addition, Cdk2-associated kinase activity was measured.

RESULTS

Rapid induction of D-type and E cyclins, as well as their catalytic partners, Cdk2 and Cdk4, occurred after PH in rats. Complexes containing cyclin E and Cdk2 assembled in the regenerating liver, leading to increased Cdk2-associated kinase activity. The regenerating liver returned to preresection weight by day 7, at which time the Cdk2 activity also returned to SHAM levels. Biphasic induction of the Cdk inhibitor p21 was observed; the first peak occurred as early as 6 hours after PH, with a subsequent peak in expression occurring at 24 to 72 hours after PH.

CONCLUSIONS

Taken together, these data support the concept that cyclins, Cdks, and Cdk inhibitors regulate cell cycle progression in the regenerating liver. In addition, the induction of p21 at two time points suggests that this protein may regulate both early proliferation and subsequent inhibition of hepatocyte regeneration.

Regulation of cell cycle-related genes in rat hepatocytes by transforming growth factor beta1

Transforming growth factor beta (TGF-beta) is a potent inhibitor of the proliferation of many cell types. We investigated the effects of TGF-beta1 on cyclin D1, cyclin A, p21, p27, and p53 mRNA expressions in primary cultured rat hepatocytes by the reverse-transcription polymerase chain reaction (RT-PCR) method. TGF-beta1 decreased the level of cyclin A mRNA in a dose-dependent manner, while it had little effect on the level of cyclin D1 mRNA. p21 mRNA expression was greatly induced by TGF-beta1 in a p53-independent mechanism, while p27 mRNA expression was not affected by TGF-beta1. These results suggest that TGF-beta1 may inhibit liver cell proliferation by regulating p21 and cyclin A mRNAs.

Transient down-regulation of inhibin-betaC expression following partial hepatectomy

Inhibin-betaC is a recently described TGF-beta family member most homologous to inhibin-betaA and inhibin-betaB. By Northern analysis, inhibin-betaC mRNA was detected exclusively in the liver among a large number of adult mouse tissues surveyed. The expression of inhibin-betaC mRNA in adult liver dropped sharply and transiently following partial hepatectomy. At 6 and 12 hours following partial hepatectomy, the levels of inhibin-betaC mRNA were at least 8-fold lower than in control animals. The liver specificity of inhibin-betaC expression and its down-regulation following partial hepatectomy suggest that inhibin-betaC may function as a negative regulator of liver growth.

Characterization of glycosaminoglycans in regenerating canine liver

BACKGROUND/AIMS

Liver regeneration after partial hepatectomy is accompanied by hepatocyte proliferation and alteration of the extracellular matrix. Glycosaminoglycans, which are components of the extracellular matrix, interact with other matrix components, and are related to hepatocyte growth. The aim of this study was to investigate the relationship between hepatocyte proliferation and changes in glycosaminoglycan.

METHODS

Hepatocyte proliferation and changes in glycosaminoglycan were investigated in dogs after 55% partial hepatectomy. Hepatocyte mitosis was investigated by immunohistochemistry using anti-proliferating cell nuclear antigen antibody. The amount of glycosaminoglycan was determined by the carbazole-sulfuric acid method. We used a new method for analysis of glycosaminoglycan chains, involving endo-beta-xylosidase digestion and fluorescence labelling, to investigate the components of glycosaminoglycan.

RESULTS

Hepatocyte mitosis was increased after hepatectomy, reaching a peak at postoperative day 7. The total amount of hepatic glycosaminoglycan reached a maximum at 1 to 2 weeks afer hepatectomy, and the ratio of the components showed a concomitant change, the amount of heparan sulfate increasing, and that of chondroitin sulfate/dermatan sulfate decreasing. Increased heparan sulfate has shorter chains at 1 to 2 weeks after hepatectomy.

CONCLUSIONS

These results suggest that the transient changes in heparan sulfate with a decreased chain length and chondroitin sulfate/dermatan sulfate and observed during liver regeneration are associated with hepatocyte proliferation.

Synergistic enhancement of EGF, but not HGF, stimulated hepatocyte motility by TGF-beta 1 in vitro

The ability of TGF-beta 1 (transforming growth factor-beta 1) to suppress growth factor induced proliferation of many cell types in vitro is well documented; however, TGF-beta 1 increases within a similar time frame as the hepatocyte mitogens HGF (hepatocyte growth factor), EGF (epidermal growth factor), and TGF-alpha (transforming growth factor-alpha) prior to hepatocyte proliferation during liver regeneration. This has raised the issue that TGF-beta 1 may have effects on hepatocytes additional to mito-inhibition and that these effects may be relevant to the regenerative process. To this end, we examined the effect of TGF-beta 1 on both the mitogenesis and the motility of growth factor stimulated primary rat hepatocytes and the hepatoblastoma cell line HepG2 in vitro. TGF-beta 1 significantly enhanced the chemotactic motility of EGF or TGF-alpha, and not HGF, stimulated hepatocytes on a collagen I substratum. TGF-beta 1 was not chemotactic when added alone and decreased the DNA synthesis of all hepatocyte cultures to near control levels. HepG2 cells were chemotactic toward HGF, EGF, and TGF-beta 1 alone and displayed an additive chemotactic response when TGF-beta 1 was added to either HGF or EGF. Additionally, HepG2 cells were refractory to the growth stimulatory effects of HGF or EGF and the growth inhibitory effects of TGF-beta 1. Hepatocytes plated onto other collagen-containing substrates (collagen IV, Matrigel, or ECL, an entactin-collagen IV-laminin matrix), but not on fibronectin or laminin alone, also displayed enhanced EGF stimulated motility by TGF-beta 1. The data indicate that an additional, novel role for TGF-beta 1 during liver tissue remodeling following PHx may include the synergistic enhancement EGF stimulated hepatocyte motility responses, and this enhancement is observed only on collagen-containing extracellular matrices.

Inhibition of Fas antigen-mediated apoptosis of rheumatoid synovial cells in vitro by transforming growth factor beta 1

OBJECTIVE

To investigate the mitogenic and anti-apoptotic effects of transforming growth factor beta 1 (TGF beta 1) on rheumatoid synovial cells in vitro.

METHODS

Synovial cells were cultured with or without TGF beta 1. After incubation, the proliferative response of synovial cells and the expression of Fas antigen and bcl-2 on synovial cells were examined. Finally, Fas antigen-mediated apoptosis of synovial cells was investigated by the addition of anti-Fas antibody.

RESULTS

TGF beta 1 enhanced the proliferation of synovial cells in a dose-dependent manner. In addition, Fas antigen expression on synovial cells was inhibited by the addition of TGF beta 1 with up-regulation of bcl-2 expression. The addition of anti-Fas antibody induced synovial cell apoptosis. However, stimulation of synovial cells with TGF beta 1 became markedly resistant to Fas antigen-mediated apoptosis. The results were not affected by the addition of a neutralizing antibody to platelet-derived growth factor type AA (PDGF-AA), which suggests that the effect of TGF beta 1 on synovial cells was promoted via PDGF-AA-independent mechanisms.

CONCLUSION

Our results suggest that TGF beta 1 promotes synovial cell proliferation through its mitogenic effect on synovial cells and interference with the apoptotic process mediated by the Fas antigen, resulting in the perpetuation of the synovial hyperplasia in patients with rheumatoid arthritis.

Hepatocyte growth factor and transforming growth factor beta regulate 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase gene expression in rat hepatocyte primary cultures

Hepatocyte growth factor (HGF) and transforming growth factor beta (TGF-beta) are believed to be of major importance for hepatic regeneration after liver damage. We have studied the effect of these growth factors on fructose 2,6-bisphosphate (Fru-2,6-P2) levels and the expression of 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase (6PF2K/Fru-2,6-BPase) in rat hepatocyte primary cultures. Our results demonstrate that HGF activates the expression of the 6PF2K/Fru-2,6-BPase gene by increasing the levels of its mRNA. As a consequence of this activation, the amount of 6PF2K/Fru-2,6-BPase protein and 6-phosphofructo-2-kinase activity increased, which was reflected by a rise in Fru-2,6-P2 levels. In contrast, TGF-beta decreased the levels of 6PF2K/Fru-2,6-BPase mRNA, which led to a decrease in the amount of 6PF2K/Fru-2,6-BPase protein and Fru-2,6-P2. The different actions of HGF and TGF-beta on 6PF2K/Fru-2,6-BPase gene expression are concomitant with their effect on cell proliferation. Here we show that, in the absence of hormones, primary cultures of hepatocytes express the F-type isoenzyme. In addition, HGF increases the expression of this isoenzyme, and dexamethasone activates the L-type isoform. HGF and TGF-beta were able to inhibit this activation.

Regulation of transforming growth factor-beta 1 expression by the hepatitis B virus (HBV) X transactivator. Role in HBV pathogenesis

TGF-beta 1 has been implicated in the pathogenesis of liver disease. The high frequency of detection of the hepatitis B virus X (HBx) antigen in liver cells from patients with chronic hepatitis, cirrhosis, and liver cancer suggested that expression of HBx and TGF-beta 1 may be associated. To test this possibility, we examined the expression of TGF-beta 1 in the liver of transgenic mice expressing the HBx gene. We show that the patterns of expression of TGF-beta 1 and Hbx protein are similar in these mice and that HBx activates transcription of the TGF-beta 1 gene in transfected hepatoma cells. The cis-acting element within the TGF-beta 1 gene that is responsive to regulation by Hbx is the binding site for the Egr family of transcription factors. We further show that the Egr-1 protein associates with the HBx protein, allowing HBx to participate in the transcriptional regulation of immediate-early genes. Our results suggest that expression of Hbx might induce expression of TGF-beta 1 in the early stages of infection and raise the possibility that TGF-beta 1 may play a role in hepatitis B virus pathogenesis.

Distortion in TGF beta 1 peptide immunolocalization in biliary atresia: comparison with the normal pattern in the developing human intrahepatic bile duct system

Biliary atresia is an important cause of neonatal obstructive jaundice in which there is inflammation, sclerosis and eventual obliteration of the bile duct system. Its onset may be antenatal, affecting the normal development of the biliary system. The intrahepatic biliary system is derived from the ductal plate, a sheath of cuboidal epithelium that appears at the hepatocyte-mesenchymal junction around the portal vein branches at 6 weeks gestation. This epithelial structure is moulded into a network of tubular bile ducts by the proliferating mesenchyme. Certain portions of the ductal plate are selected to become definitive bile ducts, while redundant biliary epithelium is deleted. The molecular dynamics controlling the intra-uterine development of the biliary system in humans are not yet clearly understood. Transforming growth factor-beta 1 is a cytokine that stimulates mesenchymal proliferation and inhibits epithelial growth, and has been shown to be important in organogenesis. In the present study, the pattern of TGF beta 1 peptide immunolocalization was investigated with the aid of computerized image analysis, in normal human bile duct development and in biliary atresia. TGF beta 1 peptide was detected within hepatocytes and ductal plate epithelium from 7 weeks gestation; increased TGF beta 1 immunoreactivity was present within the epithelium of developing bile ducts at 13 weeks gestation, and apical polarization of the cytokine was observed from 16 weeks gestation. In biliary atresia, the TGF beta 1 immunoreactivity pattern within the bile duct structures at the porta hepatis and within intrahepatic portal tracts resembled that of the primitive ductal plate, and there was no significant apical polarization. This may indicate a developmental arrest in the normal ductal plate remodelling process in biliary atresia, and suggests an underlying epithelial-mesenchymal interactive disorder.

Transforming growth factor beta modulates growth and differentiation of fetal hepatocytes in primary culture

Fetal hepatocytes in primary culture are cells capable to carry out both proliferation and differentiation processes simultaneously. Previous studies have shown that these cells respond to mitogens, such as hepatocyte growth factor (HGF) or epidermal growth factor (EGF), inducing the expression of early genes, such as fos and myc. The transforming growth factor-beta (TGF-beta) family is one of the most influential groups of growth and differentiation factors. In this report, we show that TGF-beta 1 inhibits fetal hepatocyte proliferation, arresting these cells at G1 phase of the cell cycle. In addition, TGF-beta down-regulates the mitogen-induced myc early expression. However, TGF-beta has no effect on the expression of other protooncogenes, such as fos and H-ras. In addition to its inhibitory role on fetal hepatocyte growth, TGF-beta increases the mRNA levels of fibronectin, an extracellular matrix protein, and maintains the expression of some liver specific genes, such as albumin and alfafetoprotein, above control values. The analysis of the expression of some hepatocyte transcriptional factors has shown that TGF-beta increases HNF1 alpha and HNF1 beta mRNA levels. We conclude that TGF-beta may modulate liver growth and differentiation throughout fetal development.

Expression of hepatocyte growth factor receptor (c-met) mRNA in primary cultures of human hepatocytes

Aim-To investigate the regulation of hepatocyte growth factor (HGF) receptor (c-met) gene expression in isolated primary human hepatocytes.Methods-Primary hepatocytes were maintained in monolayer culture for up to 72 hours in serum-free medium. They were treated with growth factors and the level of HGF, c-met and reduced glyceraldehyde-phosphate dehydrogenase mRNA expression determined by northern blot analysis.Results-Hepatocytes expressed a single 9 kilobase c-met gene transcript whilst HGF mRNA analysis was negative. Addition of HGF and epidermal growth factor, both potent mitogens for human hepatocytes, enhanced c-met mRNA expression approximately twofold within 24 hours, after which levels returned to normal. In non-growth factor treated cells, transforming growth factor-beta (TGFbeta) had little effect upon c-met mRNA levels. However, TGFbeta inhibited the HGF induced increase in c-met mRNA levels.Conclusions-These results indicate that hepatocytes which proliferate in response to HGF demonstrate levels of c-met mRNA which are subject to growth factor modulation and suggest an important means of growth regulatory control.

Cell-specific expression of transforming growth factor-beta in rat liver. Evidence for autocrine regulation of hepatocyte proliferation

Expression of the group of cytokines known as transforming growth factor-beta (TGF-beta 1, -beta 2 and -beta 3) is increased during liver regeneration induced by a 70% partial hepatectomy. The origin of these changes was examined in purified isolates of hepatocytes, sinusoidal endothelial cells, Kupffer cells (liver macrophages), and lipocytes (Ito or stellate cells) from normal and regenerating liver. In normal liver, TGF-beta 1 and -beta 2 levels were relatively high in sinusoidal endothelial cells and Kupffer cells. After partial hepatectomy, an early peak of TGF-beta 2 and -beta 3 was present in all four cell types, followed by a sustained increase in mRNA for TGF-beta 1, -beta 2, and -beta 3 primarily in the hepatocyte population. The specificity of these changes was established by examining a mechanistically different injury model, fibrosis induced by ligation of the biliary duct. In this model, TGF beta mRNA was increased only in lipocytes and the increase was progressive over a 7-d period of observation. Secretion of TGF beta protein was examined in cell isolates placed in short-term primary culture and generally reflected the corresponding mRNA level. The TGF beta released by hepatocytes was entirely in the latent form, whereas the individual nonparenchymal cell isolates released 50-90% active TGF beta. Hepatocyte-conditioned culture medium, after treatment to activate latent TGF beta, inhibited hepatocellular DNA synthesis as did the authentic factor. The data indicate that after injury TGF beta increases selectively in the cells that are the target of the factor, i.e., in hepatocytes after partial hepatectomy and in lipocytes in inflammation and fibrosis. We conclude that the effects of TGF beta in liver regeneration and fibrogenesis are predominantly, if not exclusively, autocrine.

Dexamethasone inversely regulates DNA synthesis and phosphoenolpyruvate carboxykinase mRNA levels in cultured rat hepatocytes: interactions with insulin, glucagon, and transforming growth factor beta 1

In hepatocytes, glucocorticoids control the expression of several genes and exert significant, but complex, regulation of the proliferation. To shed more light on the growth responses to glucocorticoids in these cells, we treated adult rat hepatocytes in primary culture with dexamethasone, in various combinations with other hormones (insulin, glucagon, transforming growth factor beta 1 (TGF beta 1)), and examined the relationship between the effects on the DNA synthesis and the mRNA level of phosphoenolpyruvate carboxykinase, a gene typically expressed in differentiated hepatocytes. Insulin exhibited the previously observed suppressing effect on the glucocorticoid-induced phosphoenolpyruvate carboxykinase mRNA level, and also reversed growth-inhibitory effects of the glucocorticoid. Dexamethasone and glucagon (via cAMP) acted strongly synergistically both in enhancing the phosphoenolpyruvate carboxykinase expression and inhibiting the growth, the inhibitory effect of glucagon on DNA synthesis being totally dependent on dexamethasone. The effects of dexamethasone plus glucagon on both the phosphoenolpyruvate carboxykinase mRNA abundance and the DNA synthesis were partially counteracted by insulin. Dexamethasone is permissive for a promoting effect of TGF beta 1 on phosphoenolpyruvate carboxykinase expression, and was found to increase the maximal inhibitory effect of (but reduced the sensitivity to) TGF beta 1 on the DNA synthesis. The results indicate that there is an inverse glucocorticoid-induced regulation of the DNA synthesis and the expression of a liver-typical gene.

Expression of HGF and TGF-beta 1 mRNA after partial hepatectomy in rats with liver cirrhosis

Hepatocyte growth factor (HGF) is a potent mitogen for the maturation of hepatocytes in vitro which plays a role in liver regeneration in vivo. In addition, transforming growth factor-beta 1 (TGF-beta 1) is also a potent regulator of liver regeneration. In attempting to clarify the mechanisms related to liver regeneration after partial hepatectomy, we investigated the expression of HGF and TGF-beta 1 in rats with liver cirrhosis (LC). A rat model of LC was prepared using carbon tetrachloride (CCl4). The expression of HGF mRNA in both the LC and control groups showed a similar time-course with the highest expression seen at 18h after a 70% hepatectomy. The expression of TGF-beta 1 mRNA peaked at 18h after partial hepatectomy in the LC group and at 48h in the control group. The 5-bromo-2'-deoxyuridine (BrdU) labeling index for the LC group at 24, 48, and 72 h after partial hepatectomy was 9.2%, 5.9%, and 1.8%, while for the control group it was 7.0%, 11.7%, and 6.8%, respectively. The BrdU labeling index in the LC group was thus suppressed earlier than that in the control group. We therefore postulate that regeneration of the remnant liver in the presence of LC accelerates immediately after partial hepatectomy, but the extent of regeneration is insufficient because of an early cessation due to an early expression of TGF-beta 1.

Expression of hepatocyte growth factor and transforming growth factor beta 1 mRNA in P. acnes and lipopolysaccharide-treated rats

Hepatocyte growth factor (HGF), a potent hepatocyte mitogen in vitro, triggers hepatocyte regeneration after partial hepatectomy and acute liver cell necrosis induced by chemicals. In contrast, transforming growth factor beta 1 inhibits hepatocyte proliferation in vitro and suppresses liver regeneration in vivo. We assessed the expression of HGF and TGF beta 1 mRNA in an endotoxin-related hepatic cell necrosis model. Intravenous injection of Gram-negative lipopolysaccharide (LPS) into rats previously given heat-killed Propionibacterium acnes induced endotoxin-related hepatic cell necrosis. In this model, serum ALT began to rise to more than 100IU as early as 3 h after LPS injection, reaching 300IU 12h after injection. HGF mRNA levels in the liver did not increase significantly until 5h after LPS injection; at 12h, they had increased about threefold compared with controls. TGF beta 1 mRNA expression increased threefold after P. acnes treatment alone and increased further after LPS injection. In the spleen, HGF mRNA levels increased within 3h, but in the lung no increase in HGF mRNA was observed. Early elevation of liver TGF beta 1 mRNA levels and delayed elevation of HGF mRNA levels, with low expression of HGF in the lung, may play a role in the pathogenesis of endotoxin-related hepatic necrosis.

Receptor-mediated regulation of differentiation and proliferation of hepatocytes by synthetic polymer model of asialoglycoprotein

Morphology and responses of hepatocytes are investigated using an artificial asialoglycoprotein model polymer--lactose-carrying polystyrene (PVLA) as a culture substratum, especially in focusing on the effect of the surface density of the PVLA substratum. The surface density of PVLA on polystyrene dishes was determined using fluorescein-labeled PVLA as a probe under a fluorescence laser microscope. PVLA-coated surfaces were observed by scanning electron microscope and atomic force microscopies under air and water, which showed that PVLA molecules were adsorbed patchily on low density surfaces and uniformly concentrated all over the dish on high density surfaces. It is suggested from the requirement of the Ca2+ ion, inhibition of galactosyl substances, and localization of receptors that the adhesion of hepatocytes to both low and high PVLA-density surfaces is mediated by galactose-specific interactions between PVLA and asialoglycoprotein receptors. At low PVLA densities (0.07 micrograms cm-2), the hepatocytes were flat and expressed high levels of 3H-thymidine uptake and low levels of bile acid secretion. Contrastingly, at high PVLA densities (1.08 micrograms cm-2), they were round and expressed a low level of 3H-thymidine uptake and a high level of bile acid secretion. The shapes, proliferation, and differentiation of hepatocytes could be regulated by varying the densities of PVLA adsorbed to polystyrene dishes. We assume that there are two recognition mechanisms operating between PVLA and hepatocytes: (1) adhesion through highly concentrated or clustered galactose-specific interaction; and (2) responses in shape, proliferation, and differentiation by PVLA-coating densities.

Differing distribution of hepatocyte growth factor-positive cells in the liver of LEC rats with acute hepatitis, chronic hepatitis and hepatoma

Using anti-rat hepatocyte growth factor (HGF) antibody, we investigated the distribution of HGF-positive cells in the liver tissues of LEC rats at various phases of liver diseases. During the phase of fulminant hepatitis, HGF-positive cells increased remarkably, and many of them were localized at the portal triads; these cells were identified from their shape as non-epithelial cells. A reduced number of HGF-positive cells was observed during the phase of chronic hepatitis, while no HGF-positive cells were seen in the tissue of cholangiofibrosis. During the phase of carcinoma, staining revealed that both the hepatocellular carcinoma cells and the non-epithelial cells in cancerous liver tissue were HGF-positive. These results suggest that, in LEC rats, HGF may play an important role in the regeneration of hepatocytes as well as in the development of hepatocellular carcinoma.

A continuous culture of pluripotent fetal hepatocytes derived from the 8-day epiblast of the pig

Continuous cultures of pluripotent parenchymal hepatocytes were derived from the epiblasts of 8-day-old pig blastocysts. The cells were polygonal and had phase-contrast dark, granular cytoplasm with prominent nuclei and nucleoli. These feeder-dependent cell cultures differentiated into large, multicellular, secretory, duct-like structures or formed small canaliculi between individual cells. Alternatively, the cells accumulated droplets that stained intensely with Oil Red O, a lipid-specific stain. Alpha-fetoprotein (AFP), albumin, and beta-fibrinogen mRNAs were expressed as the cells differentiated in culture. Serum-free medium that was conditioned by the cells contained transferrin, AFP, and albumin. The growth and viability of the cells were inhibited by transforming growth factor beta 1 (TGF beta 1) at concentrations > or = 1 ng/ml. The cell cultures grew slowly with doubling times of 2 to 3 d. One of the cultures, pig inner cell mass-19 (PICM-19), was passaged continuously for over 2 yr [> 100 population doublings (PD)] and appears to be an infinitely self-renewing cell population. The stem cell characteristics of the epiblast-derived fetal hepatocytes indicate that the cells may be unique for investigations of liver differentiation and organogenesis.

TGF beta 1 suppresses EGF-induced increase in nuclear type 1 protein phosphatase activity at the G1/S transition of hepatocyte proliferation

Nuclear type 1 protein phosphatase (PP1) activity in primary culture of EGF-stimulated hepatocytes was significantly and transiently increased at the G1/S transition, being about 2.5-fold, while that in non-stimulated hepatocytes showed almost no change. On the other hand, non-nuclear PP1 activity was gradually increased until the G1/S transition, but the activity showed no difference between EGF-stimulated and non-stimulated hepatocytes. Under growth-inhibited conditions in the presence of TGF beta 1, the increase in nuclear PP1 activity was completely suppressed, whereas non-nuclear PP1 activity was little affected. Such close correlation between nuclear PP1 activity and growth factor-induced positive or negative growth signaling strongly suggests an involvement of PP1 in progression from G1 to S phase of hepatocytes. On Western immunoblotting using antisera for PP1 alpha, PP1 gamma 1, and PP1 delta, no isoform showed any change in amount under these conditions. Mechanism(s) of growth-associated alterations in nuclear PP1 activity is discussed.

Cell-extracellular matrix interactions can regulate the switch between growth and differentiation in rat hepatocytes: reciprocal expression of C/EBP alpha and immediate-early growth response transcription factors

Previous investigations have shown that culture of freshly isolated hepatocytes under conventional conditions, i.e., on dried rat tail collagen in the presence of growth factors, facilitates cell growth but also causes an extensive down-regulation of most liver-specific functions. This dedifferentiation process can be prevented if the cells are cultured on a reconstituted basement membrane gel matrix derived from the Englebreth-Holm-Swarm mouse sarcoma tumor (EHS gel). To gain insight into the mechanisms regulating this response to extracellular matrix, we are analyzing the activities of two families of transcription factors, C/EBP and AP-1, which control the transcription of hepatic and growth-responsive genes, respectively. We demonstrate that isolation of hepatocytes from the normal quiescent rat liver by collagenase perfusion activates the immediate-early growth response program, as indicated by increased expression of c-jun, junB, c-fos, and c-myc mRNAs. Adhesion of these activated cells to dried rat tail collagen augments the elevated levels of these mRNAs for the initial 1 to 2 h postplating; junB and c-myc mRNA levels then drop steeply, with junB returning to normal quiescence and the c-myc level remaining slightly elevated during the 3-day culture period. Levels of c-jun mRNA and AP-1 DNA binding activity, however, remain elevated from the outset, while C/EBP alpha mRNA expression is down-regulated, resulting in a decrease in the steady-state levels of the 42- and 30-kDa C/EBP alpha polypeptides and C/EBP alpha DNA binding activity. In contrast, C/EBP beta mRNA production remains at near-normal hepatic levels for 5 to 8 days of culture, although its DNA binding activity decreases severalfold during this time. Adhesion of hepatocytes to the EHS gel for the same period of time dramatically alters this program: it arrests growth and inhibits AP-1 DNA binding activity and the expression of c-jun, junB, and c-myc mRNAs, but, in addition, it restores C/EBP alpha mRNA and protein as well as C/EBP alpha and C/EBP beta DNA binding activities to the abundant levels present in freshly isolated hepatocytes. These changes are not due merely to growth inhibition, because suppression of hepatocyte proliferation on collagen by epidermal growth factor starvation or addition of transforming growth factor beta does not inhibit AP-1 activity or restore C/EBP alpha DNA binding activity to normal hepatic levels. These data suggest that expression of the normal hepatic phenotype requires that hepatocytes exist in a G0 state of growth arrest, facilitated here by adhesion of cells to the EHS gel, in order to express high levels of hepatic transcription factors such as C/EBP alpha.

Cell-extracellular matrix interactions can regulate the switch between growth and differentiation in rat hepatocytes: reciprocal expression of C/EBP alpha and immediate-early growth response transcription factors

Previous investigations have shown that culture of freshly isolated hepatocytes under conventional conditions, i.e., on dried rat tail collagen in the presence of growth factors, facilitates cell growth but also causes an extensive down-regulation of most liver-specific functions. This dedifferentiation process can be prevented if the cells are cultured on a reconstituted basement membrane gel matrix derived from the Englebreth-Holm-Swarm mouse sarcoma tumor (EHS gel). To gain insight into the mechanisms regulating this response to extracellular matrix, we are analyzing the activities of two families of transcription factors, C/EBP and AP-1, which control the transcription of hepatic and growth-responsive genes, respectively. We demonstrate that isolation of hepatocytes from the normal quiescent rat liver by collagenase perfusion activates the immediate-early growth response program, as indicated by increased expression of c-jun, junB, c-fos, and c-myc mRNAs. Adhesion of these activated cells to dried rat tail collagen augments the elevated levels of these mRNAs for the initial 1 to 2 h postplating; junB and c-myc mRNA levels then drop steeply, with junB returning to normal quiescence and the c-myc level remaining slightly elevated during the 3-day culture period. Levels of c-jun mRNA and AP-1 DNA binding activity, however, remain elevated from the outset, while C/EBP alpha mRNA expression is down-regulated, resulting in a decrease in the steady-state levels of the 42- and 30-kDa C/EBP alpha polypeptides and C/EBP alpha DNA binding activity. In contrast, C/EBP beta mRNA production remains at near-normal hepatic levels for 5 to 8 days of culture, although its DNA binding activity decreases severalfold during this time. Adhesion of hepatocytes to the EHS gel for the same period of time dramatically alters this program: it arrests growth and inhibits AP-1 DNA binding activity and the expression of c-jun, junB, and c-myc mRNAs, but, in addition, it restores C/EBP alpha mRNA and protein as well as C/EBP alpha and C/EBP beta DNA binding activities to the abundant levels present in freshly isolated hepatocytes. These changes are not due merely to growth inhibition, because suppression of hepatocyte proliferation on collagen by epidermal growth factor starvation or addition of transforming growth factor beta does not inhibit AP-1 activity or restore C/EBP alpha DNA binding activity to normal hepatic levels. These data suggest that expression of the normal hepatic phenotype requires that hepatocytes exist in a G0 state of growth arrest, facilitated here by adhesion of cells to the EHS gel, in order to express high levels of hepatic transcription factors such as C/EBP alpha.

Plasma transforming growth factor-beta 1 in patients with hepatocellular carcinoma. Comparison with chronic liver diseases

BACKGROUND

Many kinds of human malignant tissue, including hepatocellular carcinoma (HCC), were reported to overexpress transforming growth factor-beta 1 (TGF-beta 1) gene. However, little work has been done on the circulating TGF-beta 1 in patients with malignant tumors.

METHODS

Plasma TGF-beta 1 levels in patients with HCC (n = 26) were compared with those in patients with chronic hepatitis (CH) (n = 12) and cirrhosis (n = 11) and in normal subjects (n = 20) using an enzyme-linked immunosorbent assay system after acid/ethanol extraction.

RESULTS

The patients with HCC had significantly higher plasma TGF-beta 1 levels (19.3 +/- 19.5 ng/ml; mean +/- standard deviation [SD]) than those in normal subjects (1.4 +/- 0.8 ng/ml) and in patients with CH (3.0 +/- 3.1 ng/ml) and cirrhosis (3.7 +/- 2.1 ng/ml) (P < 0.01). Plasma TGF-beta 1 concentrations in the patients with cirrhosis were also significantly higher than those in the normal subjects (P < 0.05). The extracted plasma TGF-beta 1 from the patients with HCC had biologic activity according to a growth inhibitory assay using mink lung epithelial cells. No significant correlation was found between the plasma TGF-beta 1 levels in the patients with HCC and serum alpha-fetoprotein levels. After successful treatment for HCC, the amount of plasma TGF-beta 1 significantly decreased from 22.6 plus or minus 16.7 ng/ml (mean +/- SD) to 10.2 plus or minus 6.5 ng/ml (P < 0.05).

CONCLUSIONS

We demonstrated higher levels of plasma TGF-beta 1 in the patients with HCC than those in patients with chronic hepatitis and cirrhosis. Plasma TGF-beta 1 might be a candidate for a novel tumor marker for hepatocellular carcinoma.

Isolation and characterization of a growth inhibitory factor from hamster liver

Among lysates from various organs and tissues of adult hamsters only lysates from liver demonstrated an inhibitory effect on the cell growth of SV40-transformed hamster fibroblasts in culture. Lysates from the liver of fetal hamsters and those from 7-day-old hamsters did not demonstrate any inhibitory effect on the cell growth. Lysates from the remnant liver 3 days after partial hepatectomy did not show any inhibitory effect on the cell growth but lysates from the remnant liver 14 days after the operation came to show an appreciable inhibitory effect on the cell growth. An inhibitor of the cell growth was purified from adult hamster liver by ammonium sulfate precipitation, DEAE-, hydroxyl apatite-, phenyl Sepharose- and Sephadex G75 column chromatography. The cell growth inhibitor thus prepared was shown to be pure by an ion-exchange chromatography, SDS-PAGE and analytical isoelectric focusing. The inhibitor was found to have a molecular mass of 37 kDa and an isoelectric point of approx. 7.5 and to cause reversible arrest of the transformed fibroblasts predominantly in the G0/G1 phase of the cell cycle at the concentration of approx. 0.9 microgram per ml.

Differential regulation of tissue transglutaminase in rat hepatoma cell lines McA-RH7777 and McA-RH8994: relation to growth rate and cell death

Close correlation between tissue transglutaminase (tTG) induction and growth regulation and/or cell death processes has been suggested in many cell lineages. In this study, the regulation of the tTG levels by various growth and differentiation factors and its relation to growth rate and cell death processes were investigated in two rat hepatoma cell lines, McA-RH7777 and McA-RH8994, using a monoclonal antibody against liver tTG. Transforming growth factor-beta 1 (TGF-beta 1) and retinoic acid (RA) each increased tTG to the level of 8- to 32-fold above that of control cultures in both cell lines after 72-h treatment. Dexamethasone (DEX) induced a 16- to 32-fold of tTG in McA-RH8994 cells while it did not change the enzyme level in McA-RH7777 cells. Simultaneous addition of DEX and RA increased the tTG level to more than 50-fold in McA-RH7777 cells as well as McA-RH8994 cells. Other factors, such as TGF-alpha, hepatocyte growth factor, dimethyl sulfoxide, and protein kinase C activator, did not show significant increases of the tTG levels. Although tTG induction by TGF-beta 1 or DEX appeared to be correlated with their growth suppressive effects, RA increased the tTG level without suppressing the growth rate of hepatoma cells. TGF-beta 1 was also shown to induce cell death in both cell lines. Our results demonstrate that RA and DEX are capable of modulating the TGF-beta 1-induced cell death processes independent of the tTG levels. We present evidence here that tTG induction by itself is not the direct cause of growth suppression and cell death in these hepatoma cells.

Activin A: an autocrine inhibitor of initiation of DNA synthesis in rat hepatocytes

The present study was conducted to examine the effect of activin A on growth of rat hepatocytes. EGF induced a 10-fold increase in DNA synthesis as assessed by [3H]thymidine incorporation in cultured hepatocytes. When activin A was added together with EGF, DNA synthesis induced by EGF was markedly inhibited. Inhibition was detected at a concentration of 10(-10) M, and 5 x 10(-9) M activin A almost completely blocked EGF-mediated DNA synthesis. Similarly, activin A completely blocked DNA synthesis induced by hepatocyte growth factor/scatter factor. Activin A was capable of inhibiting EGF-mediated DNA synthesis, even when added 36 h after the addition of EGF. With the same time interval, TGF-beta also blocked EGF-induced DNA synthesis. Although both activin A and TGF-beta inhibited growth of hepatocytes in a similar manner, either activin A or TGF-beta did not compete with each other in their binding when assessed by competitive binding using an iodinated ligand. When hepatocytes were incubated with EGF, release of bioactivity of activin A into culture medium was detected after 48 h or later. Activity of activin A was released from parenchymal cells but not from nonparenchymal cells. mRNA for beta A subunit of activin was detected only slightly in unstimulated hepatocytes, but markedly increased at 48 h after the addition of EGF. To determine whether endogenously produced activin A affects DNA synthesis, we examined the effect of follistatin, an activin-binding protein that blocks the action of activin A. An addition of follistatin significantly enhanced EGF-induced DNA synthesis. Finally, in partial hepatectomized rat, expression of mRNA for beta A subunit in liver was markedly increased 24 h after the partial hepatectomy. These results indicate that activin A inhibits initiation of DNA synthesis in hepatocytes by acting on its own receptor and that activin A acts as an autocrine inhibitor of DNA synthesis in rat hepatocytes.

Induction of apoptosis by transforming growth factor-beta 1 in the rat hepatoma cell line McA-RH7777: a possible association with tissue transglutaminase expression

We report here that transforming growth factor-beta 1 induces cell death in the Morris hepatoma cell line McA-RH7777. We assessed the type of cell death induced by transforming growth factor-beta 1 in this hepatoma cell line on the basis of morphological and biochemical characteristics. Dying cells, which detached from the cell monolayer, showed morphological characteristics of apoptosis (programmed cell death) such as chromatin condensation, nuclear disintegration and cellular fragmentation into clusters of eosinophilic globules. DNA isolated from these cells showed a ladder pattern consisting of multimers of 180 to 190 bp, indicating extensive DNA cleavage into oligonucleosomal units by an endogenous endonuclease. Treatment of the dead cells with detergents and chaotropic agents resulted in formation of insoluble shells, so-called apoptotic bodies, suggesting extensive cross-linking of cell proteins by tissue transglutaminase. Furthermore, increased amounts of cytosolic tissue transglutaminase, which has been recognized as a possible marker of apoptosis, and extensive cross-linking of cytokeratin polypeptides was demonstrated in TGF-beta 1-treated hepatoma cells on immunoblot analysis. These results provide strong evidence that the cell death induced by TGF-beta 1 in McA-RH7777 hepatoma cells is mainly apoptotic. It also suggests that a specific induction of the cytosolic tissue transglutaminase may be involved in the TGF-beta 1-induced pathways of apoptotic cell death in McA-RH7777 hepatoma cells.

Activin A: an autocrine inhibitor of initiation of DNA synthesis in rat hepatocytes

The present study was conducted to examine the effect of activin A on growth of rat hepatocytes. EGF induced a 10-fold increase in DNA synthesis as assessed by [3H]thymidine incorporation in cultured hepatocytes. When activin A was added together with EGF, DNA synthesis induced by EGF was markedly inhibited. Inhibition was detected at a concentration of 10(-10) M, and 5 x 10(-9) M activin A almost completely blocked EGF-mediated DNA synthesis. Similarly, activin A completely blocked DNA synthesis induced by hepatocyte growth factor/scatter factor. Activin A was capable of inhibiting EGF-mediated DNA synthesis, even when added 36 h after the addition of EGF. With the same time interval, TGF-beta also blocked EGF-induced DNA synthesis. Although both activin A and TGF-beta inhibited growth of hepatocytes in a similar manner, either activin A or TGF-beta did not compete with each other in their binding when assessed by competitive binding using an iodinated ligand. When hepatocytes were incubated with EGF, release of bioactivity of activin A into culture medium was detected after 48 h or later. Activity of activin A was released from parenchymal cells but not from nonparenchymal cells. mRNA for beta A subunit of activin was detected only slightly in unstimulated hepatocytes, but markedly increased at 48 h after the addition of EGF. To determine whether endogenously produced activin A affects DNA synthesis, we examined the effect of follistatin, an activin-binding protein that blocks the action of activin A. An addition of follistatin significantly enhanced EGF-induced DNA synthesis. Finally, in partial hepatectomized rat, expression of mRNA for beta A subunit in liver was markedly increased 24 h after the partial hepatectomy. These results indicate that activin A inhibits initiation of DNA synthesis in hepatocytes by acting on its own receptor and that activin A acts as an autocrine inhibitor of DNA synthesis in rat hepatocytes.

Characterization of the promoter region of the rat hepatocyte-growth-factor/scatter-factor gene

Hepatocyte growth factor/scatter factor (HGF/SF) is a potent mitogen for hepatocytes in primary culture. In response to liver damage, the levels of HGF/SF mRNA change in various tissues. In this study, we isolated a genomic DNA fragment containing the promoter region of the rat HGF/SF gene and analyzed transcription-initiation sites and their utilization in response to acute liver injury. Rat HGF/SF-mRNA synthesis starts from at least three sites in the liver, spleen and kidney. One of these sites is preferentially utilized in the liver and spleen in response to acute liver injury. In the 5' flanking region, several cytokine-related sequence elements that might be involved in the regulation of HGF/SF-gene expression are located near the transcription-initiation sites. The effects of cytokines related to these sequence elements on the production of HGF/SF mRNA were examined using a cell culture system. Transforming growth factor-beta 1 (TGF-beta 1) inhibits the production of HGF/SF mRNA by Shay granulocytic sarcoma-derived cells. The TGF-beta 1-inhibitory element, one of the sequence elements present in the promoter sequence, may mediate the inhibition of HGF/SF-gene expression by TGF-beta 1.