Involvement of c-Myc in growth inhibition of Hep 3B human hepatoma cells by a vitamin K analog.
OBJECTIVE
A synthetic vitamin K analog, compound 5 (Cpd 5), is a potent inhibitor of cell growth. The aim was to investigate whether c-Myc was involved in Cpd 5-induced cell growth inhibition.


METHODS
Human hepotoma cells (Hep 3B) were cultured and treated with Cpd 5, and c-Myc protein expression and phosphorylation were investigated using Western blot analysis.


RESULTS
Cpd 5 was found to inhibit c-Myc protein expression and induce c-Myc phosphorylation in Hep 3B cells. The phosphorylation of c-Myc was induced by both Cpd 5-mediated persistent extracellular signal-regulated kinase (ERK) phosphorylation and Cpd 5 increased glycogen synthase kinase-3 (GSK-3) activity. When using GSK-3 inhibitor, SB216763, c-Myc phosphorylation was significantly decreased and c-Myc levels were restored in Cpd 5 treated cells, suggesting that Cpd 5-mediated increase of GSK-3 activity enhanced c-Myc degradation and resulted in reduction of c-Myc levels. The lower c-Myc levels were found to cause altered expression of two c-Myc target genes, growth arrest gene gadd45 and ornithine decarboxylase (ODC).


CONCLUSIONS
The results suggest that Cpd 5-mediated c-Myc phosphorylation resulted in enhanced c-Myc protein degradation and reduced c-Myc protein levels, which may contribute to cell growth inhibition by Cpd 5.
Ge
Lisheng
L
Department of Surgery, Liver Cancer Center, Starzl Transplant Institute, School of Medicine, University of Pittsburgh, E1552 Biomedical Science Tower, 200 Lothrop Street, Pittsburgh, PA 15213, USA.
Wang
Ziqiu
Z
Wang
Meifang
M
Kar
Siddhartha
S
Carr
Brian I
BI
D006528:Carcinoma, Hepatocellular; D018797:Cell Cycle Proteins / Q000378:metabolism; D045744:Cell Line, Tumor; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D038362:Glycogen Synthase Kinase 3 / Q000378:metabolism; D006131:Growth Inhibitors / Q000494:pharmacology*; D006801:Humans; D008113:Liver Neoplasms; D009687:Nuclear Proteins / Q000378:metabolism; D009955:Ornithine Decarboxylase / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D016271:Proto-Oncogene Proteins c-myc / Q000378:metabolism*; D014812:Vitamin K / Q000031:analogs & derivatives* / Q000494:pharmacology*; D000097642:GADD45 Proteins
D018797:Cell Cycle Proteins; D048049:Extracellular Signal-Regulated MAP Kinases; D038362:Glycogen Synthase Kinase 3; D006131:Growth Inhibitors; D009687:Nuclear Proteins; D009955:Ornithine Decarboxylase; D016271:Proto-Oncogene Proteins c-myc; D014812:Vitamin K; C446520:2-(2-hydroxyethylsulfanyl)-3-methyl-1,4-naphthoquinone; C439070:GADD45A protein, human; D000097642:GADD45 Proteins