Vitamin K2 inhibits the proliferation of HepG2 cells by up-regulating the transcription of p21 gene.
OBJECTIVE
Vitamin K2 has been reported to inhibit the growth of human hepatocellular carcinoma (HCC) in vitro and suppress hepatocarcinogenesis in vivo. However, its inhibitory mechanism has not yet been clarified.


METHODS
Different concentrations of vitamin K2 (30, 10, 1, 0.1 and 0.01 muM) were added to the HCC cell line HepG2 to assess effects on cell growth. The effect of vitamin K2 on cell cycle progression was determined by flow-cytometric analysis. The expression of cell cycle regulatory proteins p21 and p27 was then examined by Western blot. Whether vitamin K2 regulates the gene expression through action on the p21 promoter region was investigated by luciferase assay.


RESULTS
Vitamin K2 inhibited the growth of HepG2 cells dose-dependently, and its inhibitory rate reached approximately 50% at the dose of 30 muM after 96 h treatment. After treatment with vitamin K2, the proportion of cells in G0-G1 phase increased, and in S phase decreased. Apoptotic cells were not detected. The expression of cell cycle regulatory protein p21 was induced by vitamin K2 treatment, but p27 was not. By the luciferase assay, vitamin K2 significantly activated the promoter of p21. Knock-down of p21 by siRNA reversed the growth inhibition of HepG2 cells by vitamin K2.


CONCLUSIONS
The findings suggest that vitamin K2 suppresses the proliferation of HCC cells by blocking the cell cycle G1/S progression through the transcriptional induction of p21.
Liu
Weidong
W
Division of Hepatobiliary and Pancreatic Medicine, Department of Internal Medicine, Hyogo College of Medicine, Hyogo, Japan.
Nakamura
Hideji
H
Yamamoto
Teruhisa
T
Ikeda
Naoto
N
Saito
Masaki
M
Ohno
Masao
M
Hara
Naoki
N
Imanishi
Hiroyasu
H
Shimomura
Soji
S
Yamamoto
Tetsuo
T
Sakai
Toshiyuki
T
Nishiguchi
Shuhei
S
Hada
Toshikazu
T