Mechanism of novel vitamin K analog induced growth inhibition in human hepatoma cell line.
OBJECTIVE
To understand the mechanisms of liver regeneration or hepatoma apoptosis, it is important to estimate the turning point of the signal transduction by growth factor receptor. Since 2-(2-hydroxyethylsulfaryl) 3-methyl-1,4-naphthoquinone or CPD 5 has been shown to mediate the phosphorylation of epidermal growth factor (EGF) receptor in Hep3B hepatoma cells, the differences between EGF and CPD 5-mediated signal transduction were studied.


METHODS
DNA content was measured by Hoechst fluorescent assay. Phosphorylated proteins were described with Western blots or two-dimensional electrophoresis.


RESULTS
CPD 5-induced EGFR phosphorylation was functional to stimulate Ras pathway. However, CPD 5-mediated extracellular signal-regulated kinase (ERK) phosphorylation was not antagonized by inhibition of upstream activation with PD153035. CPD 5 inhibited ERK dephosphorylation in cell lysate, suggesting that ERK phosphorylation by CPD 5 was depending on kinase activity and phosphatase inhibition. Two-dimensional electrophoresis showed extra phospho ERK spot, which was indicated to have close association with CPD 5-induced growth inhibition, since U0126 antagonized growth inhibition and appearance of this spot.


CONCLUSIONS
The turning point of EGFR pathway was proved to have close association with the expressed level of phosphorylated ERK. ERK phosphorylation was suggested to play a critical role in growth factor-induced signal transduction.
Osada
S
S
Second Department of Surgery, Gifu University School of Medicine, Gifu City, Japan. sting@cc.gifu-u.ac.jp
Carr
B I
BI
D000970:Antineoplastic Agents / Q000494:pharmacology*; D000975:Antioxidants / Q000494:pharmacology; D006528:Carcinoma, Hepatocellular / Q000473:pathology*; D002455:Cell Division / Q000187:drug effects; D006801:Humans; D048031:JNK Mitogen-Activated Protein Kinases; D008113:Liver Neoplasms / Q000473:pathology*; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D009285:Naphthoquinones / Q000494:pharmacology*; D010766:Phosphorylation / Q000187:drug effects; D015398:Signal Transduction / Q000187:drug effects; D013438:Sulfhydryl Compounds / Q000494:pharmacology; D014407:Tumor Cells, Cultured; D014812:Vitamin K / Q000031:analogs & derivatives*; D048051:p38 Mitogen-Activated Protein Kinases; D018631:ras Proteins / Q000502:physiology
C420442:2-(2-hydroxyethylsulfaryl)-3-methyl-1,4-naphthoquinone; D000970:Antineoplastic Agents; D000975:Antioxidants; D009285:Naphthoquinones; D013438:Sulfhydryl Compounds; D014812:Vitamin K; D048031:JNK Mitogen-Activated Protein Kinases; D020928:Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D018631:ras Proteins