Effect of simvastatin, a 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor, on alpha-fetoprotein gene expression through interaction with the ras-mediated pathway.
OBJECTIVE
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.
Mazume
H
H
The First Department of Internal Medicine, Nagasaki University School of Medicine, Japan.
Nakata
K
K
Hida
D
D
Hamasaki
K
K
Tsuruta
S
S
Nakao
K
K
Kato
Y
Y
Eguchi
K
K
D006528:Carcinoma, Hepatocellular; D002455:Cell Division / Q000187:drug effects; D015500:Chloramphenicol O-Acetyltransferase / Q000235:genetics; D005786:Gene Expression Regulation / Q000187:drug effects*; D005822:Genetic Vectors; D006801:Humans; D019161:Hydroxymethylglutaryl-CoA Reductase Inhibitors / Q000494:pharmacology*; D007700:Kinetics; D008113:Liver Neoplasms; D000090063:Proto-Oncogene Mas; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis; D012709:Serum Albumin / Q000235:genetics; D015398:Signal Transduction; D019821:Simvastatin / Q000494:pharmacology*; D014158:Transcription, Genetic / Q000187:drug effects*; D014162:Transfection; D014407:Tumor Cells, Cultured; D000509:alpha-Fetoproteins / Q000235:genetics*; D018631:ras Proteins / Q000235:genetics / Q000378:metabolism*
D019161:Hydroxymethylglutaryl-CoA Reductase Inhibitors; C000715470:MAS1 protein, human; D000090063:Proto-Oncogene Mas; D011993:Recombinant Fusion Proteins; D012709:Serum Albumin; D000509:alpha-Fetoproteins; D019821:Simvastatin; D015500:Chloramphenicol O-Acetyltransferase; D018631:ras Proteins