Increased nuclear expression and transactivation of vitamin D receptor by the cardiotonic steroid bufalin in human myeloid leukemia cells.
The active form of vitamin D(3), 1alpha,25-dihydroxyvitamin D(3) [1,25(OH)(2)D(3)], is a potent ligand for the nuclear receptor vitamin D receptor (VDR) and induces myeloid leukemia cell differentiation. The cardiotonic steroid bufalin enhances vitamin D-induced differentiation of leukemia cells and VDR transactivation activity. In this study, we examined the combined effects of 1,25(OH)(2)D(3) and bufalin on differentiation and VDR target gene expression in human leukemia cells. Bufalin in combination with 1,25(OH)(2)D(3) enhanced the expression of VDR target genes, such as CYP24A1 and cathelicidin antimicrobial peptide, and effectively induced differentiation phenotypes. An inhibitor of the Erk mitogen-activated protein (MAP) kinase pathway partially inhibited bufalin induction of VDR target gene expression. 1,25(OH)(2)D(3) treatment induced transient nuclear expression of VDR in HL60 cells. Interestingly, bufalin enhanced 1,25(OH)(2)D(3)-induced nuclear VDR expression. The MAP kinase pathway inhibitor increased nuclear VDR expression induced by 1,25(OH)(2)D(3) and did not change that by 1,25(OH)(2)D(3) plus bufalin. A proteasome inhibitor also enhanced 1,25(OH)(2)D(3)-induced CYP24A1 expression and nuclear VDR expression. Bufalin-induced nuclear VDR expression was associated with histone acetylation and VDR recruitment to the CYP24A1 promoter in HL60 cells. Thus, the Na(+),K(+)-ATPase inhibitor bufalin modulates VDR function through several mechanisms, including Erk MAP kinase activation and increased nuclear VDR expression.
Division of Biochemistry, Department of Biomedical Sciences, Nihon University School of Medicine, Itabashi-ku, Tokyo, Japan.
Yusuke
Y
Amano
Yoshitake
Y
Cho
Manabu
M
Matsunawa
Kazuo
K
Komiyama
Makoto
M
Makishima
D000971:Antineoplastic Combined Chemotherapy Protocols / Q000494:pharmacology; D002018:Bufanolides / Q000494:pharmacology*; D002301:Cardiac Glycosides / Q000494:pharmacology; D002454:Cell Differentiation / Q000187:drug effects; D002467:Cell Nucleus / Q000378:metabolism; D002762:Cholecalciferol / Q000494:pharmacology*; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D018922:HL-60 Cells; D006801:Humans; D007951:Leukemia, Myeloid / Q000188:drug therapy* / Q000473:pathology; D018167:Receptors, Calcitriol / Q000235:genetics*; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors; D013250:Steroid Hydroxylases / Q000235:genetics; D015533:Transcriptional Activation / Q000187:drug effects*; D065668:Vitamin D3 24-Hydroxylase
D002018:Bufanolides; D002301:Cardiac Glycosides; D018167:Receptors, Calcitriol; D002762:Cholecalciferol; D013250:Steroid Hydroxylases; C585549:CYP24A1 protein, human; D065668:Vitamin D3 24-Hydroxylase; D048049:Extracellular Signal-Regulated MAP Kinases; D000254:Sodium-Potassium-Exchanging ATPase; C022777:bufalin