Activation of ras oncogene in livers with cirrhosis

Interactions between Myc and Mediators of Inflammation in Chronic Liver Diseases

Most chronic liver diseases (CLDs) are characterized by inflammatory processes with aberrant expressions of various pro- and anti-inflammatory mediators in the liver. These mediators are the driving force of many inflammatory liver disorders, which often result in fibrosis, cirrhosis, and liver tumorigenesis. c-Myc is involved in many cellular events such as cell growth, proliferation, and differentiation. c-Myc upregulates IL-8, IL-10, TNF-α, and TGF-β, while IL-1, IL-2, IL-4, TNF-α, and TGF-β promote c-Myc expression. Their interactions play a central role in fibrosis, cirrhosis, and liver cancer. Molecular interference of their interactions offers possible therapeutic potential for CLDs. In this review, current knowledge of the molecular interactions between c-Myc and various well known inflammatory mediators is discussed.

The effect of Ras inhibition on the proliferation, apoptosis and matrix metalloproteases activity in rat hepatic stellate cells

In vivo inhibition of Ras by its antagonist farnesylthiosalicylic acid (FTS) prevents and reverses liver fibrosis in a rat model. In this study we showed the in vitro effects of Ras inhibition in a rat hepatic stellate cell line, HSC-T6. The IC(50) of FTS that inhibited PDGF-induced proliferation was 15 microM. FTS, by itself or in combination with PDGF, induced a three- to fivefold increase in the number of apoptotic stellate cells but did not induce apoptosis in cells cultured with TGFbeta1. We observed increased activity of MMP-9 and MMP-2 induced by FTS in combination with PDGF or TGFbeta. FTS, alone or in the presence of PDGF and TGFbeta, reduced collagen I mRNA expression. In conclusion, the in vivo amelioration of liver fibrosis by FTS may be explained by its ability to inhibit hepatic stellate cell proliferation, induce apoptosis and MMP-2 and MMP-9 activity, and decrease collagen I expression.

Mechanisms of liver fibrosis

Liver fibrosis represents a significant health problem worldwide of which no acceptable therapy exists. The most characteristic feature of liver fibrosis is excess deposition of type I collagen. A great deal of research has been performed to understand the molecular mechanisms responsible for the development of liver fibrosis. The activated hepatic stellate cell (HSC) is the primary cell type responsible for the excess production of collagen. Following a fibrogenic stimulus, HSCs change from a quiescent to an activated, collagen-producing cell. Numerous changes in gene expression are associated with HSC activation including the induction of several intracellular signaling cascades, which help maintain the activated phenotype and control the fibrogenic and proliferative state of the cell. Detailed analyses in understanding the molecular basis of collagen gene regulation have revealed a complex process offering the opportunity for multiple potential therapeutic strategies. However, further research is still needed to gain a better understanding of HSC activation and how this cell maintains its fibrogenic nature. In this review we describe many of the molecular events that occur following HSC activation and collagen gene regulation that contribute to the fibrogenic nature of these cells and provide a review of therapeutic strategies to treat this disease.

Treatment of thioacetamide-induced liver cirrhosis by the Ras antagonist, farnesylthiosalicylic acid

BACKGROUND/AIMS

Several studies have indicated increased expression of the Ras protooncogenes in liver cirrhosis. In a previous study in rats, we have shown that a synthetic Ras antagonist, S-farnesylthiosalicylic acid (FTS), could inhibit the development of liver cirrhosis. The aim of the current study was to examine whether FTS will accelerate the resolution of liver cirrhosis induced in rats by thioacetamide.

METHODS

Cirrhosis was induced in male Wistar rats by intraperitoneal (i.p.) administration of thioacetamide (200 mg/kg twice weekly for 12 weeks). In the treated group, the Ras antagonist FTS (5 mg/kg, i.p./3 times/week) was administered for 8 weeks after liver cirrhosis has already been established. Control cirrhotic rats received PBS injections for 8 weeks.

RESULTS

Rats treated with FTS for 8 weeks had lower histopathologic score of fibrosis (P = 0.01), lower hepatic hydroxyproline levels (P = 0.0002) and lower spleen weight (P = 0.02) than the cirrhotic rats treated with PBS. Following FTS treatment, the MMP-2 and MMP-9-induced collagenolytic activity and TIMP-2 expression, were increased in FTS-compared to PBS-treated rats. TUNEL assay of liver sections performed 8 weeks after thioacetamide withdrawal showed increased apoptotic figures in both groups (P = NS).

CONCLUSIONS

These results indicate that the Ras antagonist FTS accelerates the regression of experimentally-induced hepatic cirrhosis. The mechanism may involve increased collagenolytic activity.

Activation of NF-kappa B, AP-1 and STAT transcription factors is a frequent and early event in human hepatocellular carcinomas

BACKGROUND/AIMS

Hepatitis B and C viruses, two inducers of hepatocarcinomas, have been shown to activate AP-1, NF-kappa B and STAT in vitro, but no detailed information on the activity of these transcription factors in vivo have been provided.

METHODS

We have measured the DNA binding activity of these transcription factors in the peri-tumoral and the tumoral parts of 15 primary liver cancers, of viral or non-viral etiologies, and in five hepatic metastases using electrophoretic mobility shift assays.

RESULTS

AP-1, NF-kappa B and STAT binding activities were increased in the peritumoral tissue, compared with histologically normal livers in 73, 87 and 70%, respectively, of the cases. A further activation of AP-1, NF-kappa B, but not STAT binding in the tumoral parts was detected in 40 and 80%, respectively, of the cases. A close correlation was found between JunD and c-Jun levels and AP-1 binding activity at the tumoral stage. By contrast, AP-1 and NF-kappa B binding activities were low or only slightly elevated in the peri-tumoral and the tumoral tissue of metastases.

CONCLUSIONS

Early activation of AP-1, NF-kappa B and STAT contributes probably to the acquisition of a transformed phenotype during hepatocarcinogenesis, whatever the etiology.

The Ras antagonist, farnesylthiosalicylic acid (FTS), inhibits experimentally-induced liver cirrhosis in rats

BACKGROUND/AIMS

Protooncogenes may play an important role, not only in carcinogenesis, but also in the regulation of normal cellular proliferation and differentiation. Several studies have indicated increased expression of the Ras protooncogenes in the liver in animal models and in patients with liver cirrhosis. The aim of the present study was to examine whether a synthetic Ras antagonist, S-farnesylthiosalicylic acid (FTS), which specifically dislodges Ras from the membrane of Ras-transformed fibroblasts (EJ cells), can prevent experimentally-induced liver cirrhosis in rats.

METHODS

Cirrhosis was induced in male Wistar rats by intraperitoneal administration of thioacetamide (200 mg/kg twice weekly for 12 weeks). The Ras antagonist, farnesylthiosalicylic acid (FTS, 5 mg/kg), was administered during the study period 3 times a week. Ras expression in the liver was determined by Western blot analysis with pan anti-Ras antibodies and by immunohistochemistry.

RESULTS

Rats treated with thioacetamide and the Ras antagonist, farnesylthiosalicylic acid (FTS), for 12 weeks had lower histopathologic scores of fibrosis and inflammation (p-values of 0.003 and 0.008, respectively) than those treated with thioacetamide only. There were no differences between the histopathologic scores in vehicle (control) and in Ras-antagonist (FTS) only treatments. Analysis of hepatic hydroxyproline levels from the two thioacetamide-treated groups and controls confirmed the histopathologic scores (7.7+/-0.9 mg/g protein in the TAA-treated vs. 3.8+/-0.5 mg/g protein in the TAA+FTS treated group, p = 0.007). Ras levels, determined by Western blot analysis, were markedly increased in the livers treated with TAA (17-fold over control) and significantly decreased (by about 70%) in the livers of rats treated with TAA and FTS. Studies in isolated human hepatic stellate cells demonstrated that FTS inhibited both DNA synthesis and migration of those cells (p<0.05).

CONCLUSION

These results indicate that inhibition of Ras expression in the liver during fibrogenesis, prevents the development of experimentally-induced hepatic cirrhosis.

Effect of simvastatin, a 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor, on alpha-fetoprotein gene expression through interaction with the ras-mediated pathway

BACKGROUND/AIMS

The ras proto-oncogene encodes a small GTP-binding protein (Ras) which regulates cell growth and differentiation by relaying signals from the cell surface to the nucleus. In the present study, the role of Ras signal transduction pathway in alpha-fetoprotein (AFP) gene expression was evaluated in HuH-7 human hepatoma cells using simvastatin, a 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor, which blocks Ras function through inhibition of farnesylation, and the ras(val-12) expression vector.

METHODS

The HuH-7 cells were treated with simvastatin (10 micromol/l), or both simvastatin and mevalonate (300 micromol/l), and numbers of viable cells were counted after treatment. To elucidate the effects of simvastatin on AFP gene expression and the interactive effect of simvastatin on Ras signal transduction pathway, Northern blotting and transient chloramphenicol acetyltransferase plasmid transfection assays were performed.

RESULTS

Cell growth was inhibited by simvastatin, and this growth inhibition was restored by addition of mevalonate. Levels of AFP mRNA but not albumin mRNA were elevated by simvastatin in a dose-dependent manner (1-10 micromol/l). AFP promoter and enhancer activities were stimulated by simvastatin. In contrast, both activities were repressed by transfection with the ras(val-12) expression vector. The ras(val-12)-mediated repression was restored by simvastatin and returned to the repressed level by simvastatin plus mevalonate.

CONCLUSIONS

These results indicate that the Ras signal transduction pathway functions to down-regulate the AFP gene transcription in human hepatoma cells.