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

The TGF-β/NADPH Oxidases Axis in the Regulation of Liver Cell Biology in Health and Disease

The Transforming Growth Factor-beta (TGF-β) pathway plays essential roles in liver development and homeostasis and become a relevant factor involved in different liver pathologies, particularly fibrosis and cancer. The family of NADPH oxidases (NOXs) has emerged in recent years as targets of the TGF-β pathway mediating many of its effects on hepatocytes, stellate cells and macrophages. This review focuses on how the axis TGF-β/NOXs may regulate the biology of different liver cells and how this influences physiological situations, such as liver regeneration, and pathological circumstances, such as liver fibrosis and cancer. Finally, we discuss whether NOX inhibitors may be considered as potential therapeutic tools in liver diseases.

The dichotomous role of TGF-β in controlling liver cancer cell survival and proliferation

Hepatocellular carcinoma (HCC) is the major form of primary liver cancer and one of the most prevalent and life-threatening malignancies globally. One of the hallmarks in HCC is the sustained cell survival and proliferative signals, which are determined by the balance between oncogenes and tumor suppressors. Transforming growth factor beta (TGF-β) is an effective growth inhibitor of epithelial cells including hepatocytes, through induction of cell cycle arrest, apoptosis, cellular senescence, or autophagy. The antitumorigenic effects of TGF-β are bypassed during liver tumorigenesis via multiple mechanisms. Furthermore, along with malignant progression, TGF-β switches to promote cancer cell survival and proliferation. This dichotomous nature of TGF-β is one of the barriers to therapeutic targeting in liver cancer. Thereafter, understanding the underlying molecular mechanisms is a prerequisite for discovering novel antitumor drugs that may specifically disable the growth-promoting branch of TGF-β signaling or restore its tumor-suppressive arm. This review summarizes how TGF-β inhibits or promotes liver cancer cell survival and proliferation, highlighting the functional switch mechanisms during the process.

Inflammation and repair in viral hepatitis C

Hepatitis C viral infection (HCV) results in liver damage leading to inflammation and fibrosis of the liver and increasing rates of hepatic decompensation and hepatocellular carcinoma (HCC). However, the host's immune response and viral determinants of liver disease progression are poorly understood. This review will address the determinants of liver injury in chronic HCV infection and the risk factors leading to rapid disease progression. We aim to better understand the factors that distinguish a relatively benign course of HCV from one with progression to cirrhosis. We will accomplish this task by discussion of three topics: (1) the role of cytokines in the adaptive immune response against the HCV infection; (2) the progression of fibrosis; and (3) the risk factors of co-morbidity with alcohol and human immunodeficiency virus (HIV) in HCV-infected individuals. Despite recent improvements in treating HCV infection using pegylated interferon alpha (PEGIFN-alpha) and ribavirin, about half of individuals infected with some genotypes, for example genotypes 1 and 4, will not respond to treatment or cannot be treated because of contraindications. This review will also aim to describe the importance of IFN-alpha-based therapies in HCV infection, ways of monitoring them, and associated complications.

Relationship between transforming growth factor β1 and chronic hepatitis B

Transforming growth factor-β (TGF-β) is a family of related proteins that regulate many cellular processes including growth, differentiation, extracellular matrix formation and breaking down and immunosuppression. TGF-β1 is considered to play a pivotal role in hepatic stellate cell activation and a confirmed role in liver fibrosis, and its antiproliferative, proapoptotic, and immunosuppressive activities can play important roles in the pathogenesis of viral hepatitis. There is a marked correlation between the concentration and gene polymorphisms of TGF-β1 and chronic hepatitis B.

Response of porcine hepatocytes in primary culture to plasma from severe viral hepatitis patients

AIM

To observe the effects of plasma from patients with severe viral hepatitis (SVHP) on the growth and metabolism of porcine hepatocytes and the clinical efficiency of bioartificial liver device.

METHODS

Hepatocytes were isolated from male porcines by collagenase perfusion. The synthesis of DNA and total protein, leakages of AST and LDH, changes in glutathione (GSH), catalase and morphology of porcine hepatocytes exposed to SVHP were investigated to indicate the effect of plasma from patients with severe hepatitis on the growth, injury, detoxification, and morphology of porcine hepatocytes.

RESULTS

The synthesis of DNA and protein was inhibited in the medium containing 100% SVHP compared to the controls. The leakages of LDH and AST increased in porcine hepatocytes following exposure to 100% SVHP for 5 h. The difference between 100% SVHP and 10% newborn calf serum (NCS) was significant in t-test (LDH: t = 24.552, P = 0.001; AST: t = 4.169, P = 0.014). After exposure to SVHP for 24 h, alterations in GSH status were significant (F = 2.746, P<0.05) between porcine hepatocytes in 100% SVHP and 10% NCS, but no alteration occurred in the culture medium after 48 h (F = 4.378, P<0.05). A similar profile was observed in catalase activity. Many round vacuoles were observed in porcine hepatocytes cultured in SVHP. The membranes of these cells became indistinct and almost all the cells died on d 5.

CONCLUSION

Plasma from patients with severe hepatitis inhibits the growth, injures membrane, disturbs GSH homeostasis and induces morphological changes of porcine hepatocytes. It is suggested that SVHP should be pretreated to reduce the toxin load and improve the performance of porcine hepatocytes in extracorporeal liver-support devices.

Transforming growth factor-?1 is not involved in TCDD-dependent release from contact inhibition in WB-F344 cells

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is the most potent tumor promoter ever tested in rodents. Although it is known that most of the effects of TCDD are mediated by binding to the aryl hydrocarbon receptor (AhR), the mechanisms leading to tumor promotion still remain to be elucidated. Loss of contact inhibition is one characteristic hallmark in tumorigenesis. In WB-F344 cells TCDD induces a release from contact inhibition which is manifested by a two- to threefold increase in DNA synthesis when TCDD (1 nM) is applied to confluent cells. Since proliferation of epithelial cells is known to be inhibited by TGF-beta, we investigated whether decreased TGF-beta1 mediates TCDD-dependent release from contact inhibition in WB-F344 cells. Expression of TGF-beta (type II) receptor in WB-F344 cells was analyzed by Western blot analysis. Exposure of 0.1 ng/ml TGF-beta1 to exponentially growing WB-F344 cells resulted in a 40% decrease in DNA synthesis, which was blocked by preincubation with a neutralizing anti-TGF-beta1 antibody, indicating that the TGF-beta receptor in WB-F344 cells is functionally active. Preincubation of confluent, G1-arrested cultures with the neutralizing anti-TGF-beta1-antibody did not lead to an increase in DNA synthesis, ruling out an involvement of TGF-beta1 in mediating contact inhibition in WB-F344 cells. In accord with this, Western blot analysis revealed that protein expression of TGF-beta1 is neither upregulated in confluent cultures nor decreased after TCDD treatment. We conclude that TGF-beta1 is not involved in contact inhibition or in TCDD-dependent release from contact inhibition in WB-F344 cells.

Transforming growth factor beta1 is not involved in 2,3,7,8-tetrachlorodibenzo- p-dioxin-dependent release from contact-inhibition in WB-F344 cells

TCDD (2,3,7,8-tetrachlorodibenzo- p-dioxin) is the most potent tumor promoter ever tested in rodents. Although it is known that most of the effects of TCDD are mediated by binding to the aryl hydrocarbon receptor (AhR), the mechanisms leading to tumor promotion still remain to be elucidated. Loss of contact-inhibition is one characteristic hallmark in tumorigenesis. In WB-F344 cells, TCDD induces a release from contact-inhibition, which is manifested by a two- to three-fold increase in DNA-synthesis when TCDD (1 nM) is given to confluent cells. Since proliferation of epithelial cells is known to be inhibited by transforming growth factor beta (TGF-beta) we investigated whether decreased TGF-beta expression mediates TCDD-dependent release from contact-inhibition in WB-F344 cells. Expression of TGF-beta (type II) receptor in WB-F344 cells was shown by Western blot analysis. Exposure of exponentially growing WB-F344 cells to 0.1 ng/ml TGF-beta1 resulted in a 40% decrease in DNA synthesis, which could be blocked by pre-incubation with a neutralizing anti-TGF-beta1 antibody indicating that the TGF-beta receptor in WB-F344 cells is functionally active. Pre-incubation of confluent, G1-arrested cultures with the neutralizing anti-TGF-beta1 antibody did not lead to an increase in DNA synthesis, ruling out an involvement of TGF-beta1 in mediating contact-inhibition in WB-F344 cells. In accordance with this, Western blot analysis revealed that protein expression of TGF-beta1 was neither upregulated in confluent cultures nor decreased after TCDD treatment. We therefore conclude that TGF-beta1 is not involved in contact-inhibition nor in TCDD-dependent release from contact-inhibition in WB-F344 cells.

Destruxin E, a Cyclodepsipeptide Antibiotic, Reduces Cyclin D1 Levels and Inhibits Anchorage-Independent Growth of v-Ki-ras-Expressed pMAM-ras-REF Cells

Destruxin E (DE), a cyclodepsipeptide isolated from fermentation broths of Metarhizium sp. MA324, inhibited the growth of v-Ki-ras-expressed pMAM-ras-REF (rasREF) cells in the suspension (anchorage-independent) culture (a) more strongly than that in the substratum-attached (anchorage-dependent) culture (b) or that of v-Ki-ras-unexpressed pMAM-ras-REF (REF) cells in the substratum-attached culture (c); the IC(50) values of DE were 0.07 microM (a), 0.4 microM (b), and 1.2 microM (c). DE arrested G1 phase cell cycle progression of rasREF cells in the substratum-attached culture (b). In rasREF cells treated with DE for 72 h in suspension culture (a), the levels of cyclin D1, cyclin A, p27(Kip1), and hyperphosphorylated Rb were decreased, but the levels of cdk4, cdk6, cdk2, p16(INK4a), and p21(Cip1) were not affected. Among these effects, the decrease in cyclin D1 was prominent. DE decreased the level of cyclin D1 in rasREF cells in the suspension culture (a) at 0.1 microM and in the substratum-attached culture (b) at 1 microM, while the level of cyclin D1 in REF cells in the substratum-attached culture (c) was not decreased at 1 microM. The extent of growth inhibition correlated with the decrease in cyclin D1. The level of cyclin D1 mRNA of rasREF cells in the suspension culture (a) was also decreased by DE. DE decreased cyclin D1 mRNA, resulting in inhibition of anchorage-independent growth of rasREF cells.

The immunosuppressive agent tacrolimus induces p21WAF/CIP1WAF1/CIP1 via TGF-beta secretion

Tacrolimus (Tac) is more immunosuppressive drug compared to cyclosporine (CsA). Our previous studies have demonstrated that CsA induces the expression of p21WAF/CIP1 expression. In this study we explored if like CsA, Tac also induces expression of p21WAF/CIP1. We also determined if induction of p21WAF/CIP1 by Tac is dependent on TGF-beta. Using RT-PCR and Western blot analysis, we studied the induction of p21WAF/CIP1 mRNA and protein in human T cells and A-549 cells (human lung adenocarcinoma cells) by Tac. The stimulation of p21WAF/CIP1 promoter activity was studied by luciferase assay using p21WAF/CIP1-luc, chimeric plasmid DNA containing a p21WAF/CIP1 promoter segment and luciferase reporter gene. Using anti-TGF-beta antibody, we studied if induction of p21WAF/CIP1 by tacrolimus is dependent on TGF-beta. The results demonstrate that Tac induced p21WAF/CIP1 mRNA and protein expression as well as stimulated its promoter activity in T cells and A-549 cells. The induction of p21WAF/CIP1 expression by tacrolimus was dependent on TGF-beta since a neutralizing anti-TGF-beta antibody inhibited induction of p21WAF/CIP1in A-549 cells. These data support the hypothesis that cyclin inhibitor p21WAF/CIP1 might represent a unified mediator of the anti-proliferative effects of Tac and other immunosuppressive agents. Strategies involving p21WAF/CIP1 induction should be considered a viable alternative strategy to achieve immunosuppression possibly with reduced toxicity associated with current immunosuppression.

Smad4 overexpression in hepatocellular carcinoma is strongly associated with transforming growth factor beta II receptor immunolabeling

In the normal liver, the transforming growth factor beta (TGF-beta) signaling pathway plays an important role in inhibiting hepatocyte growth. This effect is mediated through Smad4 (or Dpc4), a tumor-suppressor gene that affects gene transcription and controls cell growth. A loss of Smad4 is associated with carcinoma in a number of other organs, including the pancreas and colon. Despite these facts, several recent studies using cDNA microarrays have surprisingly shown overexpression of Smad4 in hepatocellular carcinoma (HCC). Because Smad4 plays a central role in the TGF-beta signaling pathway, we hypothesized that activation of the TGF-beta signaling pathway may explain Smad4 overexpression. To investigate this, 21 surgically resected HCCs were immunostained with antibodies to Smad4 and TGF-beta receptor II. Tumor and normal liver tissues were stained in all cases, and expression in the tumor was scored in comparison to the nonneoplastic liver. Thirteen hepatic adenomas were also immunostained as a control group. The average age at resection was 58 +/- 16 years for the 17 men and 4 women with HCC. TGF-beta receptor II was weakly expressed in the hepatocyte cytoplasm of all normal livers and was overexpressed in 10 of 21 HCCs. Of these 10 HCCs increased Smad4 immunolabeling was also present in 10 of 10 cases. In contrast, of the 11 of HCCs that did not show TGF-beta overexpression, only 1 showed increased Smad4 immunolabeling. Increased TGF-beta receptor II and Smad4 labeling was associated with a worse nuclear grade and increased mitotic activity. For the hepatic adenomas, the 13 women had an average age at resection of 36 +/- 10 years. Whereas 2 adenomas showed over expression of TGF-beta receptor II, there was no Smad4 overexpression in any case. In conclusion, increased Smad4 protein expression in HCC is tightly linked to overexpression of TGF-beta II receptors and is associated with increased mitoses and a worse nuclear grade. Hepatic adenomas only rarely show overexpression of TGF-beta II receptors and did not show increased Smad4 labeling. The results from this study indicate that Smad4 protein overexpression is present in a subset of HCCs and is strongly correlated with immunostaining for TGF-beta II receptor, findings that may represent activation or dysregulation of the TGF-beta signaling pathway.

Up-regulated transcriptional repressors SnoN and Ski bind Smad proteins to antagonize transforming growth factor-beta signals during liver regeneration

Transforming growth factor-beta (TGF-beta) functions as an antiproliferative factor for hepatocytes. However, for unexplained reasons, hepatocytes become resistant to TGF-beta signals and can proliferate despite the presence of TGF-beta during liver regeneration. TGF-beta is up-regulated during liver regeneration, although it is not known whether it is active or latent. TGF-beta activity may be examined by assessing Smad activation, a downstream signaling pathway. Smad pathway activation during liver regeneration induced by partial hepatectomy or CC4 injury was examined by assessing the levels of phospho-Smad2 and Smad2-Smad4 complexes. We found that Smad proteins were slightly activated in quiescent liver, but that their activation was further enhanced in regenerating liver. Interestingly, TGF-beta/Smad pathway inhibitors (SnoN and Ski) were up-regulated during regeneration, and notably, SnoN was induced mainly in hepatocytes. SnoN and Ski are transcriptional repressors that may render some cells resistant to TGF-beta via binding Smad proteins. Complexes between SnoN, Ski, and the activated Smad proteins were detected from 2 to 120 h during the major proliferative phase in regenerating liver. Inhibitory complexes decreased after liver mass restitution (5-15 days), suggesting that persistently activated Smad proteins might participate in returning the liver to a quiescent state. Our data show that active TGF-beta/Smad signals are present during regeneration and suggest that SnoN/Ski induction might explain hepatocyte resistance to TGF-beta during the proliferative phase.

dally, a Drosophila member of the glypican family of integral membrane proteoglycans, affects cell cycle progression and morphogenesis via a Cyclin A-mediated process

division abnormally delayed (dally) encodes an integral membrane proteoglycan of the glypican family that affects a number of patterning events during both embryonic and larval development. Earlier studies demonstrated that Dally regulates cellular responses to Wingless (Wg) and Decapentaplegic (Dpp) in a tissue-specific manner, consistent with its proposed role as a growth factor co-receptor. dally mutants also display cell cycle progression defects in specific sets of dividing cells in the developing optic lobe and retina. The affected cells in the retina and lamina show delays in completion of the G2-M segment of the cell cycle. We have investigated the molecular basis of dally-mediated cell division defects by examining the genetic interactions between dally and known cell cycle regulators.

Reductions in cyclin A but not cyclin B or string expression, suppress dally cell division defects in the optic lobe. cycA mutations also dominantly rescue many dally adult morphological defects including lethality, phenotypes that are unaffected by reducing cycB function. dally mutants show abnormal Cyclin A expression in the dividing cells affected, with appreciable levels of Cyclin A remaining in late prophase and metaphase, stages where Cyclin A is normally absent. Given that Dally is known to regulate the activity of secreted growth factors our findings suggest that extracellular cues influence the degradation of Cyclin A in a manner that controls cell cycle progression and ultimately, cell division patterning.

Dominant-negative TAK1 induces c-Myc and G(0) exit in liver

Transforming growth factor-beta (TGF-beta)-activated kinase 1 (TAK1), a serine/threonine kinase, is reported to function in the signaling pathways of TGF-beta, interleukin 1, and ceramide. However, the physiological role of TAK1 in vivo is largely unknown. To assess the function of TAK1 in vivo, dominant-negative TAK1 (dnTAK1) was expressed in the rat liver by adenoviral gene transfer. dnTAK1 expression abrogated c-Jun NH(2)-terminal kinase and c-Jun but not nuclear factor (NF)-kappaB or SMAD activation after partial hepatectomy (PH). Expression of dnTAK1 or TAM-67, a dominant-negative c-Jun, induced G(0) exit in quiescent liver and accelerated cell cycle progression after PH. Finally, dnTAK1 and TAM-67 induced c-myc expression in the liver before and after PH, suggesting that G(0) exit induced by dnTAK1 and TAM-67 is mediated by c-myc induction.

Chemically induced rat mammary tumor treated with tamoxifen showed decreased expression of cyclin D1, cyclin E, and p21(Cip1)

We studied the effects of tamoxifen (TAM) on the growth of 7,12-dimethylbenz(a)anthracene (DMBA)-induced rat mammary tumor and the expression of cyclin D1, cyclin E, p21(Cip1), and estrogen receptors (ER) by performing immunohistochemistry and Western blot analysis. When tumor size reached between 10 and 15mm in the largest dimension, the rats were divided into a DMBA-control group and a DMBA-TAM group. The administration of TAM markedly decreased the tumor development and showed decreased expression of bromodeoxyuridine, cyclin D1, cyclin E, and p21(Cip1) when compared with those of the DMBA-control group; however, a few tumors showed progressive growth in spite of TAM treatment. These tumors had decreased expression of ER. This study suggests that TAM suppresses tumor development through the down-expression of cyclin D1 and cyclin E.

Hepatocellular expression of a dominant-negative mutant TGF-beta type II receptor accelerates chemically induced hepatocarcinogenesis

The potent growth-inhibitory activity of cytokines of the transforming growth factor-beta (TGF-beta) superfamily and their widespread expression in epithelia suggest that they may play an important role in the maintenance of epithelial homeostasis. To analyse TGF-beta mediated tumor suppressor activity in the liver, we generated transgenic mice overexpressing a dominant negative type II TGF-beta receptor in hepatocytes under control of the regulatory elements of the human C-reactive protein gene promoter. Transgenic animals exhibited constitutive and liver-specific transgene expression. The functional inactivation of the TGF-beta signaling pathway in transgenic hepatocytes was shown by reduced TGF-beta induced inhibition of DNA synthesis in primary hepatocyte cultures. Liver morphology and spontaneous tumorigenesis were unchanged in transgenic mice suggesting that interruption of the signaling of all three isoforms of TGF-beta in hepatocytes does not disturb tissue homeostasis in the liver under physiological conditions. However, following initiation with the carcinogen diethylnitrosamine and tumor-promotion with phenobarbital transgenic mice exhibited a moderate albeit significant increase in the incidence, size and multiplicity of both preneoplastic tissue lesions in the liver and of hepatocellular carcinomas. These results give in vivo evidence for a tumor suppressor activity of the endogenous TGF-beta system in the liver during chemical hepatocarcinogenesis.

Regulation of c-met expression in rats with acute hepatic failure

BACKGROUND

Earlier we described a model of fulminant hepatic failure (FHF) in the rat where partial hepatectomy is combined with induction of right liver lobe necrosis. In FHF rats, lack of hepatocyte proliferation was associated with delayed expression of HGF and HGF receptor c-met. Since the c-met promoter region has Sp1 binding sites, we decided to examine whether in FHF rats down-regulation of c-met is associated with decreased Sp1 function and whether changes in blood HGF, IL-6, and TGFbeta1 levels might be responsible for these effects.

MATERIALS AND METHODS

Induction of FHF, partial (2/3) hepatectomy (PH), and sham hepatectomy (SH) was performed in adult Sprague-Dawley rats. The levels of c-met mRNA and Sp1 DNA binding activity were studied in rat liver remnants at different time points after surgery. Blood levels of HGF, IL-6, and TGFbeta1 were also measured in these rats. Additionally, the effects of treatment with TGF-beta1, IL-6, or a combination of both on c-met expression and Sp1 DNA binding were studied in HGF-induced rat hepatocyte cultures.

RESULTS

Compared to SH rats, in PH rat livers c-met was up-regulated after 6 h and Sp1 DNA binding was at or only slightly lower than levels at all time points studied. In FHF rat livers, c-met expression was markedly reduced after 2 and 6 h, moderate after 12 h, and undetectable after 24 h. At the same time, Sp1 DNA binding was detected at 2 h postinduction only. In FHF rats, blood levels of all three cytokines showed early and sustained elevation. In vitro, IL-6 had no effect on c-met expression, whereas TGFbeta1 up-regulated c-met. When used alone, none of the cytokines affected Sp1 DNA binding activity. In contrast, a combination of IL-6 and TGFbeta1 down-regulated c-met expression as well as Sp1 DNA binding activity. These effects were dependent on the IL-6 concentration used. This study suggests that following massive loss of hepatocyte mass in rats, early increase in blood IL-6 and TGFbeta1 levels may weaken the expression of HGF receptor c-met in surviving hepatocytes through suppression of Sp1 DNA binding.

Biology of transforming growth factor beta in hepatocarcinogenesis

TGF-beta is an important factor in the regulation of liver growth. It is an inhibitor of hepatocyte DNA synthesis and may induce active cell death, e.g., to remove excessive tissue mass. Studies using transgenic mice suggest that expression in the resting liver has to be well balanced; either under- or overexpression appear to cause an increased turnover of hepatocytes and to predispose to hepatocarcinogenesis. TGF-beta overexpression is frequently observed in human hepatocellular carcinomas, probably as a late event in tumor development. In men and mice, TGF-beta overexpression appears to be associated with loss of TGF-beta responsiveness often by disruption of TGF-beta signaling. However, mechanisms as mutations in TGF-beta receptor II or Smad2 and 4 genes, frequently observed in other human cancers, have only rarely been observed in hepatocellular carcinomas. Further studies may clarify the mechanisms by which hepatocellular tumors escape TGF-beta growth control, as well as analyze possible roles of TGF-beta overexpression in immunosuppression and angiogenesis.

Adenovirus-mediated gene transfer of dominant-negative Smad4 blocks TGF-beta signaling in pancreatic acinar cells

Transforming growth factor-beta (TGF-beta) is a potent inhibitor of pancreatic acinar cell growth. Smad4 is a central mediator in the TGF-beta signaling pathway. To study the effect of Smad4 on pancreatic growth, cell cycle protein expression, and the expression of a TGF-beta-responsive promoter in vitro, we constructed an adenovirus containing dominant-negative COOH terminal truncated Smad4 (AddnSmad4) downstream of the rat elastase promoter. Acinar cells expressed dominant-negative Smad4 within 8 h after infection, and expression persisted for 72 h. Mouse pancreatic acini were infected with either AddnSmad4 or control adenovirus expressing green fluorescent protein, and TGF-beta was added 8 h after infection. Acinar cells were then incubated for 1, 2, or 3 days, and [(3)H]thymidine incorporation was determined. AddnSmad4 significantly reduced TGF-beta inhibition of [(3)H]thymidine incorporation, with maximal effects on day 3. AddnSmad4 also completely blocked TGF-beta-mediated growth inhibition in the presence of basic fibroblast growth factor. We next examined the effects of AddnSmad4 on TGF-beta-induced expression of the cell cycle regulatory proteins p21(Cip1) and p27(Kip1). TGF-beta induced upregulation of p21(Cip1), which was completely blocked by AddnSmad4. AddnSmad4 also inhibited TGF-beta-induced expression of the TGF-beta-responsive luciferase reporter 3TP-Lux. These results show that Smad4 is essential in TGF-beta-mediated signaling in pancreatic acinar cells.

Replicative senescence of biliary epithelial cells precedes bile duct loss in chronic liver allograft rejection: increased expression of p21(WAF1/Cip1) as a disease marker and the influence of immunosuppressive drugs

Early chronic liver allograft rejection (CR) is characterized by distinctive cytological changes in biliary epithelial cells (BECs) that resemble cellular senescence, in vitro, and precede bile duct loss. If patients suffering from early CR are treated aggressively, the clinical and histopathological manifestations of CR can be completely reversed and bile duct loss can be prevented. We first tested whether the senescence-related p21(WAF1/Cip1) protein is increased in BECs during early CR, and whether treatment reversed the expression. The percentage of p21+ BECs and the number of p21+ BECs per portal tract is significantly increased in early CR (26 +/- 17% and 3.6 +/- 3.1) compared to BECs in normal liver allograft biopsies or those with nonspecific changes (1 +/- 1% and 0.1 +/- 0.3; P: < 0.0001 and P: < 0.02), chronic hepatitis C (2 +/- 3% and 0.7 +/- 1; P: < 0.0001 and P: < 0.04) or obstructive cholangiopathy (7 +/- 7% and 0.7 +/- 0.6; P: < 0.006 and P: = 0.04). Successful treatment of early CR is associated with a decrease in the percentage of p21+ BECs and the number of p21+ BECs per portal tract. In vitro, nuclear p21(WAF1/Cip1) expression is increased in large and multinucleated BECs, and is induced by transforming growth factor (TGF)-beta. TGF-beta1 also increases expression of TGF-beta receptor II, causes phosphorylation of SMAD-2 and nuclear translocation of p21(WAF1/Cip1), which inhibits BEC growth. Because conversion from cyclosporine to tacrolimus is an effective treatment for early CR, we next tested whether these two immunosuppressive drugs directly influenced BEC growth in vitro. The results show that cyclosporine, but not tacrolimus, stimulates BEC TGF-beta1 production, which in turn, causes BEC mito-inhibition and up-regulation of nuclear p21(WAF1/Cip1). In conclusion, expression of the senescence-related p21(WAF1/Cip1) protein is increased in BECs during early CR and decreases with successful recovery. Replicative senescence accounts for the characteristic BEC cytological alterations used for the diagnosis of early CR and lack of a proliferative response to injury. The ability of cyclosporine to inhibit the growth of damaged BECs likely accounts for the relative duct sparing properties of tacrolimus.

Biology of transforming growth factor beta in hepatocarcinogenesis

TGF-beta is an important factor in the regulation of liver growth. It is an inhibitor of hepatocyte DNA synthesis and may induce active cell death, e.g., to remove excessive tissue mass. Studies using transgenic mice suggest that expression in the resting liver has to be well balanced; either under- or overexpression appear to cause an increased turnover of hepatocytes and to predispose to hepatocarcinogenesis. TGF-beta overexpression is frequently observed in human hepatocellular carcinomas, probably as a late event in tumor development. In men and mice, TGF-beta overexpression appears to be associated with loss of TGF-beta responsiveness often by disruption of TGF-beta signaling. However, mechanisms as mutations in TGF-beta receptor II or Smad2 and 4 genes, frequently observed in other human cancers, have only rarely been observed in hepatocellular carcinomas. Further studies may clarify the mechanisms by which hepatocellular tumors escape TGF-beta growth control, as well as analyze possible roles of TGF-beta overexpression in immunosuppression and angiogenesis.

Suppression of cell cycle progression by a fungal lectin: activation of cyclin-dependent kinase inhibitors

The antiproliferative activity of a fungal lectin (VVL) isolated from the mushroom, Volvariella volvacea, was studied using a battery of cultured tumor cell lines. It was revealed that [(3)H]thymidine incorporation into the cell lines was markedly reduced at 0.32 microM VVL. When S180 mouse sarcoma cells were incubated for 48 hr with doses of VVL ranging from 0.32 to 0.8 microM, prominent blebs on the cell surface and large vacuoles in the cytoplasm, but not apoptotic bodies, were observed under a fluorescence microscopy. VVL did not exert ribosome-inactivating activity or induce any changes in the expression of cyclins A, D1, and E. However, it did activate the expression of cyclin kinase inhibitors, namely p21, p27, p53, and Rb, in a dose-dependent manner. Flow cytometric analysis demonstrated an accumulation of cells in the G2/M phase in a time- and dose-dependent manner, indicating that VVL arrested cell proliferation by blocking cell cycle progression in the G2/M phase.

The effects of acute ethanol exposure on inhibitors of hepatic regenerative activity in the rat

The purpose of this study was to identify the mechanism(s) whereby acute ethanol exposure inhibits hepatic regenerative activity in the rat. Adult, male, Sprague-Dawley rats (200-250 g) were randomized to receive either ethanol (1 g/kg i.p. q 4 h) or an equal volume of saline (controls) for 24 h beginning 1 h prior to a 70% partial hepatectomy (PHx). At 0, 3, 6, 12 and 24 h post-PHx, rats were sacrificed (N = 4-6/group), and the expression of the following genes associated with inhibition of hepatocyte proliferation were documented; p53, p21, transforming growth factor-beta1 (TGF-beta1) and gamma aminobutyric acid transport protein (GABA-TP). Inhibition of hepatic regenerative activity was confirmed by 3H-thymidine incorporation into hepatic DNA at 24 h post-PHx. The results of the study revealed that in ethanol-treated rats, DNA synthesis was inhibited by 37% when compared to saline-treated controls (p < 0.01). Regarding suppressor gene expression, both p21 and TGF-beta1 mRNA expression in ethanol-treated rats were similar to those obtained in saline-treated controls. Although p53 mRNA expression differed in the two groups, in the ethanol-treated group, p53 mRNA expression was decreased rather than increased (relative to controls) at 24 h post-PHx, a finding not in keeping with inhibition of DNA synthesis. GABA-TP mRNA was strongly expressed prior to PHx in both ethanol- and saline-treated rats. Following PHx, GABA-TP mRNA expression decreased in both groups but remained low in the saline-treated group while returning to pre-PHx values in ethanol-treated rats. In summary, the results of this study indicate that the inhibitory effects of ethanol on hepatic regeneration are not associated with significant or the appropriate changes in mRNA expression of the p53, p21 or TGF-beta1 suppressor genes. On the other hand, transcriptional changes in GABA-TP gene expression post-PHx are in keeping with an inhibitory effect of GABA on hepatic regeneration.

Control of cyclins, cyclin-dependent kinase inhibitors, p21 and p27, and cell cycle progression in rat hepatocytes by extracellular matrix

BACKGROUND/AIMS

The extracellular matrix plays an essential role in the regulation of cell proliferation in different cell types. However, the regulation of cell cycle control in hepatocytes in response to growth factors and extracellular matrix signals is not well understood. The aims of this study were to investigate the expression of key cell cycle control elements, including cyclins, A and D1, and cyclin-dependent kinase inhibitors, p21 and p27, in rat hepatocytes in primary culture on dried collagen or Engelbreth-Holm-Swarm in the presence of epidermal growth factor.

METHODS

Hepatocytes prepared from Wistar rats were cultured on various extracellular matrix in Williams medium E in the presence or absence of 20 ng/ ml epidermal growth factor. DNA synthesis was measured by [3H]thymidine uptake and mRNA expression of cell cycle-related genes was determined by reverse transcription polymerase chain reaction.

RESULTS

Cyclins D1 and A mRNA levels were high at the G1/S boundary in epidermal growth factor-stimulated hepatocytes cultured on dried collagen. In contrast to spread cells, hepatocytes cultured on an Engelbreth-Holm-Swarm gel that were prevented from spreading failed to progress through the G1 phase and enter the S phase. This shape-dependent blockage of cell cycle progression correlated with the up-regulation of the cell cycle inhibitors p21 and p27.

CONCLUSIONS

Changes in hepatocyte-extracellular matrix interactions may control hepatocyte growth within the local microenvironment by modulating cell shape and regulating cyclins and the cyclin-dependent kinase inhibitors p21 and p27.

Acceleration of c-myc-induced hepatocarcinogenesis by Co-expression of transforming growth factor (TGF)-alpha in transgenic mice is associated with TGF-beta1 signaling disruption

We have previously shown in transgenic mice that transforming growth factor (TGF)-alpha dramatically enhances c-myc-induced hepatocarcinogenesis by promoting proliferation and survival of hepatocellular carcinoma (HCC) cells. As transgenic livers display increased levels of mature TGF-beta1 from the early stages of hepatocarcinogenesis, we have now assessed whether impairment of TGF-beta1 signaling contributes to the deregulation of cell cycle progression and apoptosis observed during this process. Focal preneoplastic lesions lacking expression of TGF-beta receptor type II (TbetaRII) were detected in c-myc/TGF-alpha but not in c-myc livers. In c-myc/TGF-alpha mice, 40% (2/5) of adenomas and 90% (27/30) of HCCs showed down-regulation of TbetaRII expression in comparison with 11% (2/18) of adenomas and 47% (14/30) of HCCs in c-myc mice. Down-regulation of the TGF-beta1-inducible p15(INK4B) mRNA and reduced apoptotic rates in TbetaRII-negative HCCs further indicated the disruption of TGF-beta1 signaling. Furthermore, both TbetaRII-negative and -positive c-myc TGF-alpha HCCs, but not c-myc HCCs, were characterized by decreased levels of the cell cycle inhibitor p27. These results suggest 1) an inverse correlation of decreased p27 expression with the particularly strong expression of TGF-alpha in these lesions, consistent with the capacity of TGF-alpha signaling to post-transcriptionally regulate p27, and 2) the presence of alternative, downstream defects of TGF-beta1 signaling in c-myc/TGF-alpha HCCs that may impair the growth-inhibitory response to TGF-beta1. Thus, the accelerated neoplastic development in c-myc/TGF-alpha mice is associated with an early and frequent occurrence of TbetaRII-negative lesions and with reduced levels of p27 in HCC cells, indicating that disruption of TGF-beta1 responsiveness may play a crucial role in the enhancement of c-myc-induced hepatocarcinogenesis by TGF-alpha.

Cyclosporine induces the expression of the cyclin inhibitor p21

BACKGROUND

Current immunosuppression strategies involve inhibition of T cell activation and/or lymphocyte proliferation. During T cell cycle progression/activation, the expression of cyclins and cyclin dependent kinases is increased. In this study, we examined whether cyclosporine A (CsA) suppresses the cell cycle progression through the induction of the cell cycle inhibitor p21. Because CsA induces the expression of transforming growth factor (TGF)-beta, and TGF-beta induces p21 expression, we also determined whether CsA's induction of p21 is dependent on or independent of TGF-beta.

METHOD

Using reverse transcription assisted polymerase chain reaction and western blot analysis, we studied the induction of p21 mRNA and protein in human T cells and A-549 cells (human lung adenocarcinoma cells) by CsA. The stimulation of p21 promoter activity was studied by luciferase assay using p21-luc, chimeric plasmid DNA containing a p21 promoter segment, and luciferase reporter gene. The dependence of CsA's induction of p21 was studied using anti-TGF-beta antibody and TGF-beta altered A-549 cells.

RESULTS

CsA induced p21 mRNA protein expression and stimulated its promoter activity in lymphoid (T cells) and nonlymphoid (human lung adenocarcinoma, A-549 cells).CsA's induction of p21 was inhibited both by a neutralizing anti-TGF-beta antibody and in TGF-beta-altered A-549 cells, consistent with its effects on p21 requiring TGF-beta.

CONCLUSION

These data support the hypothesis that at least one component of CsA's antiproliferative effects may occur through the induction of p21 and that this induction is dependent on TGF-beta. Should p21 induction be a viable immunosuppressive strategy, inducing this molecule independent from the fibrogenic cytokine TGF-beta might reduce the toxicity associated with current immunosuppression.