1alpha,25-Dihydroxyvitamin D3 down-regulates estrogen receptor abundance and suppresses estrogen actions in MCF-7 human breast cancer cells

Clin Cancer Res. 2000 Aug;6(8):3371-9.

Abstract

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.

Publication types

  • Comparative Study
  • Research Support, U.S. Gov't, Non-P.H.S.
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Breast Neoplasms / drug therapy
  • Breast Neoplasms / metabolism*
  • Breast Neoplasms / pathology
  • Calcitriol / analogs & derivatives
  • Calcitriol / pharmacology*
  • Cell Division / drug effects
  • Dose-Response Relationship, Drug
  • Down-Regulation / drug effects
  • Drug Interactions
  • Estradiol / metabolism
  • Estradiol / pharmacology*
  • Estradiol / physiology
  • Estrogen Antagonists / pharmacology*
  • Estrogen Receptor alpha
  • Humans
  • Receptors, Estrogen / biosynthesis
  • Receptors, Estrogen / genetics
  • Receptors, Estrogen / metabolism*
  • Transcription, Genetic / drug effects
  • Tumor Cells, Cultured

Substances

  • Estrogen Antagonists
  • Estrogen Receptor alpha
  • Receptors, Estrogen
  • Estradiol
  • Calcitriol