title: Ginsenoside-Rg1 mediates a hypoxia-independent upregulation of hypoxia-inducible factor-1α to promote angiogenesis.
abstract: Hypoxia-inducible factor (HIF-1) is the key transcription regulator for multiple angiogenic factors and is an appealing target. Ginsenoside-Rg1, a nontoxic saponin isolated from the rhizome of Panax ginseng, exhibits potent proangiogenic activity and has the potential to be developed as a new angiotherapeutic agent. However, the mechanisms by which Rg1 promotes angiogenesis are not fully understood. Here, we show that Rg1 is an effective stimulator of HIF-1α under normal cellular oxygen conditions in human umbilical vein endothelial cells. HIF-1α steady-state mRNA was not affected by Rg1. Rather, HIF-1α protein synthesis was stimulated by Rg1. This effect was associated with constitutive activation of phosphatidylinositol 3-kinase (PI3K)/Akt and its effector p70 S6 kinase (p70(S6K)), but not extracellular-signal regulated kinase 1/2. We further revealed that HIF-1α induction triggered the expression of target genes, including vascular endothelial growth factor (VEGF). The use of small molecule inhibitors LY294002 or rapamycin to inhibit PI3K/Akt and p70(S6K) activities, respectively, resulted in diminished HIF-1α activation and subsequent VEGF expression. RNA interference-mediated knockdown of HIF-1α suppressed Rg1-induced VEGF synthesis and angiogenic tube formation, confirming that the effect was HIF-1α specific. Similarly, the angiogenic phenotype could be reversed by inhibition of PI3K/Akt and p70(S6K). These results define a hypoxia-independent activation of HIF-1α, uncovering a novel mechanism for Rg1 that could play a major role in angiogenesis and vascular remodeling.
authors.affiliation: School of Biological Sciences, University of Hong Kong, 4S-14 Kadoorie Biological Sciences Building, Pokfulam Road, Pokfulam, Hong Kong.
authors.forename: Kar-Wah
authors.initials: KW
authors.lastname: Leung
authors.forename: Hoi-Man
authors.initials: HM
authors.lastname: Ng
authors.forename: Maggie K S
authors.initials: MK
authors.lastname: Tang
authors.forename: Chris C K
authors.initials: CC
authors.lastname: Wong
authors.forename: Ricky N S
authors.initials: RN
authors.lastname: Wong
authors.forename: Alice S T
authors.initials: AS
authors.lastname: Wong
mesh_terms: D015153:Blotting, Western; D002478:Cells, Cultured; D002867:Chromones / Q000494:pharmacology; D017931:DNA Primers / Q000235:genetics; D042783:Endothelial Cells / Q000378:metabolism*; D005786:Gene Expression Regulation / Q000187:drug effects*; D036145:Ginsenosides / Q000302:isolation & purification / Q000494:pharmacology*; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000235:genetics / Q000378:metabolism*; D009025:Morpholines / Q000494:pharmacology; D018919:Neovascularization, Physiologic / Q000502:physiology*; D005894:Panax / Q000737:chemistry*; D058539:Phosphatidylinositol 3-Kinase / Q000378:metabolism; D034622:RNA Interference; D020133:Reverse Transcriptase Polymerase Chain Reaction; D027343:Rhizome / Q000737:chemistry; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000378:metabolism; D014471:Umbilical Veins / Q000166:cytology; D042461:Vascular Endothelial Growth Factor A / Q000378:metabolism
chemical_list: D002867:Chromones; D017931:DNA Primers; D036145:Ginsenosides; C497442:HIF1A protein, human; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D009025:Morpholines; D042461:Vascular Endothelial Growth Factor A; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; D058539:Phosphatidylinositol 3-Kinase; D038762:Ribosomal Protein S6 Kinases, 70-kDa; C035054:ginsenoside Rg1