title: Enhancement of ligand-dependent vitamin D receptor transactivation by the cardiotonic steroid bufalin.
abstract: Bufalin, a bufadienolide type cardiotonic steroid that is one of the major components of the toad venom-prepared traditional Chinese medicine called Ch'an Su or Senso, exhibits a cardiotonic action by inhibiting the membranous Na(+),K(+)-ATPase. Bufalin also induces differentiation of leukemia cells alone or in combination with other differentiation inducers including 1alpha,25-dihydroxyvitamin D(3) [1,25(OH)(2)D(3)]. In this study, we performed a transient cotransfection assay using a vitamin D receptor (VDR) expression vector and a luciferase reporter and found that although bufalin did not transactivate the VDR, it effectively enhanced VDR activity induced by 1,25(OH)(2)D(3). Bufalin also augmented VDR activation by bile acid ligands, such as lithocholic acid and 3-ketocholanic acid. Other cardiotonic steroids including ouabain, digitoxigenin and cinobufagin did not enhance VDR activation. Bufalin did not bind directly to VDR but did modulate the interaction of VDR and cofactors, such as steroid receptor coactivator-1 and nuclear receptor corepressor. Bufalin treatment significantly increased the expression of an endogenous VDR target gene, CYP24, in kidney- and monocyte-derived cell lines treated with 1,25(OH)(2)D(3). The data indicate that bufalin-mediated cellular mechanisms such as interaction with Na(+), K(+)-ATPase may affect VDR transcriptional activity. Bufalin may be a useful tool in the investigation of VDR regulation by membrane-originating cellular signals and of pathophysiological mechanisms linking VDR to cardiovascular dysfunction.
authors.affiliation: Graduate School of Frontier Biosciences, Osaka University, Osaka 565-0871, Japan.
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Nakano
authors.forename: Manabu
authors.initials: M
authors.lastname: Matsunawa
authors.forename: Atsutaka
authors.initials: A
authors.lastname: Yasui
authors.forename: Ryutaro
authors.initials: R
authors.lastname: Adachi
authors.forename: Katsuyoshi
authors.initials: K
authors.lastname: Kawana
authors.forename: Iichiro
authors.initials: I
authors.lastname: Shimomura
authors.forename: Makoto
authors.initials: M
authors.lastname: Makishima
mesh_terms: D000664:Amphibian Venoms / Q000737:chemistry / Q000302:isolation & purification; D000818:Animals; D001001:Anura; D002018:Bufanolides / Q000737:chemistry / Q000302:isolation & purification / Q000494:pharmacology*; D002117:Calcitriol / Q000494:pharmacology; D002301:Cardiac Glycosides / Q000737:chemistry / Q000302:isolation & purification / Q000494:pharmacology*; D002460:Cell Line; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D004357:Drug Synergism; D004359:Drug Therapy, Combination; D005668:Furylfuramide / Q000737:chemistry / Q000494:pharmacology; D015870:Gene Expression / Q000187:drug effects; D006801:Humans; D007553:Isotope Labeling / Q000379:methods; D008024:Ligands; D008156:Luciferases / Q000187:drug effects / Q000494:pharmacology; D008516:Medicine, Chinese Traditional; D018167:Receptors, Calcitriol / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism; D013250:Steroid Hydroxylases / Q000096:biosynthesis / Q000737:chemistry / Q000235:genetics; D015533:Transcriptional Activation / Q000187:drug effects* / Q000502:physiology; D065668:Vitamin D3 24-Hydroxylase
chemical_list: D000664:Amphibian Venoms; D002018:Bufanolides; D002301:Cardiac Glycosides; D008024:Ligands; D018167:Receptors, Calcitriol; D005668:Furylfuramide; D008156:Luciferases; D013250:Steroid Hydroxylases; D065668:Vitamin D3 24-Hydroxylase; D002117:Calcitriol; C022777:bufalin