Transcriptional regulation of vascular endothelial growth factor by estradiol and tamoxifen in breast cancer cells: a complex interplay between estrogen receptors alpha and beta.

Vascular endothelial growth factor (VEGF) is a potent angiogenic and prognostic factor for many tumors, including those of endocrine-responsive tissues such as the breast and uterus. Recent studies indicate that 17beta-estradiol (E(2)) modulates VEGF expression in breast and uterine cells, involving transcriptional activation through estrogen receptor (ER) alpha. However, molecular mechanisms of VEGF regulation mediated by the two ER subtypes and the potential role of ERbeta in the control of breast cancer angiogenesis have not yet been investigated. In transient transfection assays using the VEGF(-2275/+54) promoter-luciferase construct, E(2) (1 nM) increased transcription activity in MCF-7 cells (either untransfected or cotransfected with ERalpha) and it increased transcription activity in MDA-MB-231 cells cotransfected with ERalpha or ERbeta (1.8- and 2-fold induction, respectively). The positive effect was abolished when MCF-7 cells were treated with pure antiestrogen ICI 182,780 or the agonist/antagonist tamoxifen (1 micro M). To identify response elements involved in this transcriptional regulation, MCF-7 or MDA-MB-231 cells were transfected with several deletion constructs of the VEGF promoter. Deletion of 1.2-2.3 kb upstream to the transcription start in the VEGF promoter abrogated E(2)-dependent transcription in these cells. This region contains an imperfect estrogen-responsive element (ERE), ERE1520, and one activator protein 1 site. Transfection of MCF-7 cells (ERalpha) with the ERE1520-luciferase construct conferred transcriptional activity with 1 nM E(2) (1.9-fold induction). Also, the imperfect ERE formed a complex with ERalpha or ERbeta proteins in gel shift assay using MCF-7 or MDA-MB-231 nuclear extracts. In contrast to ERalpha, ERbeta could transactivate VEGF reporter construct in MDA-MB-231 cells, in the presence of E(2) or tamoxifen, suggesting different transactivational mechanisms between ERalpha and ERbeta in the presence of tamoxifen. Interestingly, E(2) inhibited VEGF transcription in MCF-7 cells transfected with ERbeta or MDA-MB-231 cells cotransfected with ERalpha and ERbeta, suggesting that heterodimerization of ERalpha/ERbeta has the ability to inhibit E(2)-induced VEGF expression in breast cancer cells. These results demonstrate that VEGF is a target gene for ERalpha and ERbeta in breast cancer cells; it remains to be determined whether ERalpha and ERbeta expression in breast biopsies correlates with VEGF expression and vascular density.