title: Green tea polyphenol epigallocatechin gallate reduces endothelin-1 expression and secretion in vascular endothelial cells: roles for AMP-activated protein kinase, Akt, and FOXO1.
abstract: Epigallocatechin gallate (EGCG), a green tea polyphenol, promotes vasodilation by phosphatidylinositol 3-kinase-dependent activation of Akt and endothelial nitric oxide synthase to stimulate production of nitric oxide. Reduction in endothelin-1 (ET-1) synthesis may also increase bioavailability of nitric oxide. We hypothesized that the phosphatidylinositol 3-kinase-dependent transcription factor FOXO1 may mediate effects of EGCG to regulate expression of ET-1 in endothelial cells. EGCG treatment (10 microm, 8 h) of human aortic endothelial cells reduced expression of ET-1 mRNA, protein, and ET-1 secretion. We identified a putative FOXO binding domain in the human ET-1 promoter 51 bp upstream from the transcription start site. Trans-activation of a human ET-1 (hET-1) promoter luciferase reporter was enhanced by coexpression of a constitutively nuclear FOXO1 mutant, whereas expression of a mutant FOXO1 with disrupted DNA binding domain did not trans-activate the hET-1 promoter. Disrupting the hET-1 putative FOXO binding domain by site-directed mutagenesis ablated promoter activity in response to overexpression of wild-type FOXO1. EGCG stimulated time-dependent phosphorylation of Akt (S(473)), FOXO1 (at Akt phosphorylation site T(24)), and AMP-activated protein kinase alpha (AMPK alpha) (T(172)). EGCG-induced nuclear exclusion of FOXO1, FOXO1 binding to the hET-1 promoter, and reduction of ET-1 expression was partially inhibited by the AMPK inhibitor Compound C. Basal ET-1 protein expression was enhanced by short interfering RNA knock-down of Akt and reduced by short interfering RNA knock-down of FOXO1 or adenovirus-mediated expression of dominant-negative Foxo1. We conclude that EGCG decreases ET-1 expression and secretion from endothelial cells, in part, via Akt- and AMPK-stimulated FOXO1 regulation of the ET-1 promoter. These findings may be relevant to beneficial cardiovascular actions of green tea.
authors.affiliation: Diabetes Unit, National Center for Complementary and Alternative Medicine, National Institutes of Health, 9 Memorial Drive, Bethesda, Maryland 20892-0920, USA.
authors.forename: Chad E N
authors.initials: CE
authors.lastname: Reiter
authors.forename: Jeong-a
authors.initials: JA
authors.lastname: Kim
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Quon
mesh_terms: D055372:AMP-Activated Protein Kinases / Q000378:metabolism / Q000502:physiology*; D000818:Animals; D001665:Binding Sites / Q000235:genetics; D002392:Catechin / Q000031:analogs & derivatives* / Q000494:pharmacology; D002417:Cattle; D002478:Cells, Cultured; D015536:Down-Regulation / Q000187:drug effects / Q000235:genetics; D042783:Endothelial Cells / Q000187:drug effects* / Q000378:metabolism; D019332:Endothelin-1 / Q000235:genetics / Q000378:metabolism; D005419:Flavonoids / Q000494:pharmacology; D000071161:Forkhead Box Protein O1; D051858:Forkhead Transcription Factors / Q000378:metabolism / Q000502:physiology*; D015870:Gene Expression / Q000187:drug effects; D006801:Humans; D051379:Mice; D041681:NIH 3T3 Cells; D051058:Oncogene Protein v-akt / Q000378:metabolism / Q000502:physiology*; D010636:Phenols / Q000494:pharmacology; D059808:Polyphenols; D011401:Promoter Regions, Genetic / Q000187:drug effects; D013662:Tea / Q000737:chemistry
chemical_list: D019332:Endothelin-1; C085126:FOXO1 protein, human; D005419:Flavonoids; D000071161:Forkhead Box Protein O1; D051858:Forkhead Transcription Factors; D010636:Phenols; D059808:Polyphenols; D013662:Tea; D002392:Catechin; C045651:epigallocatechin gallate; D051058:Oncogene Protein v-akt; D055372:AMP-Activated Protein Kinases