title: Equol, a metabolite of the soybean isoflavone daidzein, inhibits neoplastic cell transformation by targeting the MEK/ERK/p90RSK/activator protein-1 pathway.
abstract: Daidzein and genistein are isoflavones found in soybean. Genistein is known to exhibit anticarcinogenic activities and inhibit tyrosine kinase activity. However, the underlying molecular mechanisms of the chemopreventive activities of daidzein and its metabolite, equol, are not understood. Here we report that equol inhibits 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced neoplastic transformation of JB6 P+ mouse epidermal cells by targeting the MEK/ERK/p90RSK/activator protein-1 signaling pathway. TPA-induced neoplastic cell transformation was inhibited by equol, but not daidzein, at noncytotoxic concentrations in a dose-dependent manner. Equol dose-dependently attenuated TPA-induced activation of activator protein-1 and c-fos, whereas daidzein did not exert any effect when tested at the same concentrations. The TPA-induced phosphorylation of ERK1/2, p90RSK, and Elk, but not MEK or c-Jun N-terminal kinase, was inhibited by equol but not by daidzein. In vitro kinase assays revealed that equol greatly inhibited MEK1, but not Raf1, kinase activity, and an ex vivo kinase assay also demonstrated that equol suppressed TPA-induced MEK1 kinase activity in JB6 P+ cell lysates. Equol dose-dependently inhibited neoplastic transformation of JB6 P+ cells induced by epidermal growth factor or H-Ras. Both in vitro and ex vivo pull-down assays revealed that equol directly bound with glutathione S-transferase-MEK1 to inhibit MEK1 activity without competing with ATP. These results suggested that the antitumor-promoting effect of equol is due to the inhibition of cell transformation mainly by targeting a MEK signaling pathway. These findings are the first to reveal a molecular basis for the anticancer action of equol and may partially account for the reported chemopreventive effects of soybean.
authors.affiliation: Hormel Institute, University of Minnesota, 801 16th Avenue NE, Austin, MN 55912, USA.
authors.forename: Nam Joo
authors.initials: NJ
authors.lastname: Kang
authors.forename: Ki Won
authors.initials: KW
authors.lastname: Lee
authors.forename: Evgeny A
authors.initials: EA
authors.lastname: Rogozin
authors.forename: Yong-Yeon
authors.initials: YY
authors.lastname: Cho
authors.forename: Yong-Seok
authors.initials: YS
authors.lastname: Heo
authors.forename: Ann M
authors.initials: AM
authors.lastname: Bode
authors.forename: Hyong Joo
authors.initials: HJ
authors.lastname: Lee
authors.forename: Zigang
authors.initials: Z
authors.lastname: Dong
mesh_terms: D000818:Animals; D001665:Binding Sites; D002460:Cell Line; D004815:Epidermal Growth Factor / Q000494:pharmacology; D060754:Equol; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism*; D007529:Isoflavones / Q000737:chemistry* / Q000378:metabolism / Q000494:pharmacology*; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism; D048369:MAP Kinase Kinase 1 / Q000737:chemistry / Q000378:metabolism*; D020935:MAP Kinase Signaling System / Q000187:drug effects; D051379:Mice; D008958:Models, Molecular; D015394:Molecular Structure; D009369:Neoplasms / Q000378:metabolism / Q000473:pathology; D010766:Phosphorylation; D016760:Proto-Oncogene Proteins c-fos / Q000378:metabolism; D051818:Replication Protein C / Q000378:metabolism*; D038744:Ribosomal Protein S6 Kinases, 90-kDa / Q000378:metabolism*; D013025:Glycine max / Q000737:chemistry*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D018631:ras Proteins / Q000378:metabolism
chemical_list: C007610:4',7-dihydroxy-3,4-dihydroisoflavone; D007529:Isoflavones; D016760:Proto-Oncogene Proteins c-fos; D060754:Equol; D004815:Epidermal Growth Factor; C004742:daidzein; D038744:Ribosomal Protein S6 Kinases, 90-kDa; D048049:Extracellular Signal-Regulated MAP Kinases; D048031:JNK Mitogen-Activated Protein Kinases; D048369:MAP Kinase Kinase 1; D051818:Replication Protein C; D018631:ras Proteins; D013755:Tetradecanoylphorbol Acetate