1alpha,25-Dihydroxyvitamin D3 down-regulates estrogen receptor abundance and suppresses estrogen actions in MCF-7 human breast cancer cells.
1alpha,25-Dihydroxyvitamin D3 [1,25(OH)2D3], the active metabolite of vitamin D, is a potent inhibitor of breast cancer cell growth. Because the estrogen receptor (ER) plays a key role in breast cancer progression, we have studied the effects of 1,25(OH)2D3 on the regulation of ER in the estrogen-responsive MCF-7 human breast cancer cell line, which is known to predominantly express ERalpha. 1,25(OH)2D3 causes significant inhibition of MCF-7 cell growth, and it also decreases the growth-stimulatory effect of 17beta-estradiol (E2). Treatment of MCF-7 cells with 1,25(OH)2D3 reduces ER levels in a dose-dependent manner, as shown by ligand binding assays and Western blot analysis. The 1,25(OH)2D3 analogues EB-1089, KH-1060, Ro 27-0574, and Ro 23-7553 are more potent than 1,25(OH)2D3 in both their antiproliferative actions as well as ER down-regulation. There is a striking correlation (R2 = 0.98) between the growth-inhibitory actions of 1,25(OH)2D3 or analogues and their ability to down-regulate ER levels. Treatment with 1,25(OH)2D3 shows that the reduction in ER is accompanied by a significant decrease in the steady-state levels of ER mRNA. The decrease in ER mRNA is not abolished by the protein synthesis inhibitor cycloheximide. Inhibition of mRNA synthesis with actinomycin D reveals no significant differences between ER mRNA half-life in control and 1,25(OH)2D3-treated cells. Nuclear run-on experiments demonstrate significant decreases in ER gene transcription at the end of 17 h of treatment with 1,25(OH)2D3. These findings indicate that 1,25(OH)2D3 exerts a direct negative effect on ER gene transcription. Coincident with the decrease in ER levels there is an attenuation of E2-mediated bioresponses after 1,25(OH)2D3 treatment. Induction of progesterone receptor by E2 is suppressed by 1,25(OH)2D3, and the E2-mediated increase in breast cancer susceptibility gene (BRCA1) protein is reduced by 1,25(OH)2D3 treatment. Overall, these results suggest that the antiproliferative effects of 1,25(OH)2D3 and its analogues on MCF-7 cells could partially be mediated through their action to down-regulate ER levels and thereby attenuate estrogenic bioresponses, including breast cancer cell growth.
Swami
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Department of Medicine, Stanford University School of Medicine, California 94305, USA.
Krishnan
A V
AV
Feldman
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D001943:Breast Neoplasms / Q000188:drug therapy / Q000378:metabolism* / Q000473:pathology; D002117:Calcitriol / Q000031:analogs & derivatives / Q000494:pharmacology*; D002455:Cell Division / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation / Q000187:drug effects; D004347:Drug Interactions; D004958:Estradiol / Q000378:metabolism / Q000494:pharmacology* / Q000502:physiology; D004965:Estrogen Antagonists / Q000494:pharmacology*; D047628:Estrogen Receptor alpha; D006801:Humans; D011960:Receptors, Estrogen / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic / Q000187:drug effects; D014407:Tumor Cells, Cultured
D004965:Estrogen Antagonists; D047628:Estrogen Receptor alpha; D011960:Receptors, Estrogen; D004958:Estradiol; D002117:Calcitriol