Immunolocalization of ras oncogene p21 in human liver diseases

Expression and prognostic role of pan-Ras, Raf-1, pMEK1 and pERK1/2 in patients with hepatocellular carcinoma

AIMS

Ras/Raf/mitogen-activated protein kinase (MEK)/extracellular signal-regulated kinase (ERK) signaling cascades play important roles in the transmission of signals involved in apoptosis. Importantly, components of these pathways are aberrantly expressed in human cancer. However, there is limited data linking clinical outcomes with the aberrant expression of this pathway. The present study analyzed the prognostic values of pan-Ras, Raf-1, phosphorylated MEK1 (pMEK1) and phosphorylated ERK1/2 (pERK1/2) in hepatocellular carcinoma (HCC).

METHODS

Expression of pan-Ras, Raf-1, pMEK1 and pERK1/2 in 81 HCC patients who underwent curative resection was examined by immunohistochemical staining. Long-term survival after resection of patients according to the expression of pan-Ras, Raf-1, pMEK1 and pERK1/2 was assessed using univariate analysis and multiple Cox proportional hazards model.

RESULTS

In univariate analysis, patients with Raf-1 or pMEK1 overexpression had shorter disease-free survival (DFS) (P<0.05) and poorer overall survival (OS) (P<0.05) than groups with weak-expression of Raf-1 or pMEK1, respectively. Patients with pan-Ras overexpression had poorer overall survival (OS) (P<0.05) than the group with weak-expression of pan-Ras. Importantly, Raf-1 overexpression was a promising prognostic marker for poor survival according to multivariate Cox regression analysis (DFS, Hazard Ratio 1.807, P = 0.035; OS, Hazard Ratio 1.959, P = 0.044).

CONCLUSIONS

Raf-1 overexpression could be considered as an independent prognostic biomarker in HCC and may predict early tumor recurrence and death for HCC patients. It can be used to stratify patients at higher risk for poor prognosis and help to select the appropriate therapeutic regime of HCC.

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.

The potential for the use of cell proliferation and oncogene expression as intermediate markers during liver carcinogenesis

Intense research using animal models has indicated that chemically-induced rat liver cancer proceeds through multiple, distinct stages that can be characterised morphologically and biochemically. Primary human liver cancer, with hepatitis B and other environmental factors such as poor nutrition and food contaminating mycotoxins as contributing etiological factors, is one of the major causes of cancer deaths in African, Asian and some Western countries. Recent advances in surgical and diagnostic techniques have also allowed the identification of potential morphological precursors of primary human liver cancer, and suggested a model consistent with the concepts of initiation--promotion--progression as in the rat. The expression of proliferating cell nuclear antigen (PCNA), silver-staining nucleolar organiser regions (AgNOR), oncogenes and the tumor suppressor gene p53 in preneoplastic and neoplastic lesions of rat and human livers is presently reviewed. This undertaking is an attempt to evaluate whether the current knowledge regarding molecular mechanisms of carcinogenesis is sufficient to permit the use of these molecular parameters as 'intermediate' markers in studies of risk assessment and cancer prevention, without having to resort to tumor appearance as an end-point.

Activation of ras oncogene in livers with cirrhosis

Activation of cellular oncogenes and inactivation of anti-oncogenes have been postulated as important mechanisms during hepatocarcinogenesis. This study was conducted to detect abnormal levels of several proto-oncogenes (c-jun, c-fos, c-H-ras) and of the p53 and the alpha-fetoprotein gene in the liver during cirrhosis, a pathological process which predisposes to the development of hepatocarcinoma. Liver tissue from 11 patients with cirrhosis of different etiologies, and seven histologically normal liver fragments taken at the periphery of benign liver tumors of metastases were studied. Transcripts of the various oncogenes and of the alpha-fetoprotein gene were detected by in situ hybridization, and the p53 protein was revealed by immunocytochemistry. No overexpression of any of the mRNA tested or of the p53 protein was found in histologically normal liver in contact with benign or metastatic tumors. In contrast, 10 of the 11 specimens with cirrhosis (90.9%) displayed abnormally high levels of c-H-ras transcripts. Five samples with cirrhosis revealed a moderate increase in the level of c-fos mRNA. Only one case and two cases, respectively, exhibited increased levels of c-jun and alpha-fetoprotein mRNA. No cases were positive for the p53 antigen. Liver-cell proliferation, as assessed by immunocytochemistry with the Ki 67 monoclonal antibody, was low in both the group with cirrhosis and the control groups (0.49% and 0.55% positive cells, respectively). These data demonstrate that activation of c-H-ras mRNA is an almost constant finding in hepatocytes of livers with cirrhosis. This gene overexpression is not linked to hepatocellular proliferation.(ABSTRACT TRUNCATED AT 250 WORDS)