Ginsenoside Rb1 inhibits tube-like structure formation of endothelial cells by regulating pigment epithelium-derived factor through the oestrogen beta receptor.
OBJECTIVE
Angiogenesis is a crucial step in tumour growth and metastasis. Ginsenoside-Rb1 (Rb1), the major active constituent of ginseng, potently inhibits angiogenesis in vivo and in vitro. However, the underlying mechanism remains unknown. We hypothesized that the potent anti-angiogenic protein, pigment epithelium-derived factor (PEDF), is involved in regulating the anti-angiogenic effects of Rb1.


METHODS
Rb1-induced PEDF was determined by real-time PCR and western blot analysis. The anti-angiogenic effects of Rb1 were demonstrated using endothelial cell tube formation assay. Competitive ligand-binding and reporter gene assays were employed to indicate the interaction between Rb1 and the oestrogen receptor (ER).


RESULTS
Rb1 significantly increased the transcription, protein expression and secretion of PEDF. Targeted inhibition of PEDF completely prevented Rb1-induced inhibition of endothelial tube formation, suggesting that the anti-angiogenic effect of Rb1 was PEDF specific. Interestingly, the activation of PEDF occurred via a genomic pathway of ERbeta. Competitive ligand-binding assays indicated that Rb1 is a specific agonist of ERbeta, but not ERalpha. Rb1 effectively recruited transcriptional activators and activated an oestrogen-responsive reporter gene. Furthermore, Rb1-mediated PEDF activation and the subsequent inhibition of tube formation were blocked by the ER antagonist ICI 182,780 or transfection of ERbeta siRNA, indicating ERbeta dependence.


CONCLUSIONS
Here we show for the first time that the Rb1 suppressed the formation of endothelial tube-like structures through modulation of PEDF via ERbeta. These findings demonstrate a novel mechanism of the action of this ginsenoside that may have value in anti-cancer and anti-angiogenesis therapy.
Leung
K W
KW
Department of Biology, Hong Kong Baptist University, Kowloon Tong, Hong Kong, China.
Cheung
L W T
LW
Pon
Y L
YL
Wong
R N S
RN
Mak
N K
NK
Fan
T-P D
TP
Au
S C L
SC
Tombran-Tink
J
J
Wong
A S T
AS
D020533:Angiogenesis Inhibitors / Q000494:pharmacology*; D002460:Cell Line; D042783:Endothelial Cells / Q000187:drug effects* / Q000502:physiology; D004958:Estradiol / Q000031:analogs & derivatives / Q000494:pharmacology; D004965:Estrogen Antagonists / Q000494:pharmacology; D047629:Estrogen Receptor beta / Q000819:agonists* / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D005136:Eye Proteins / Q000378:metabolism*; D000077267:Fulvestrant; D036145:Ginsenosides / Q000494:pharmacology*; D006801:Humans; D009414:Nerve Growth Factors / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D015843:Serpins / Q000378:metabolism*; D000099174:Pigment Epithelium-Derived Factor
D020533:Angiogenesis Inhibitors; D004958:Estradiol; D004965:Estrogen Antagonists; D047629:Estrogen Receptor beta; D005136:Eye Proteins; D000077267:Fulvestrant; D036145:Ginsenosides; D009414:Nerve Growth Factors; D012333:RNA, Messenger; D015843:Serpins; D000099174:Pigment Epithelium-Derived Factor; C442759:ginsenoside Rb1