Abstract
Vascular endothelial growth factor (VEGF) is a potent stimulator of angiogenesis and a prognostic factor for many tumors including those of endocrine-responsive tissues such as the breast and uterus. We and others have previously shown that VEGF is regulated by estradiol and tamoxifen in the uterus and by estradiol in human breast cancer cells, and pharmacological evidence has suggested that this regulation was mediated by transcriptional activation of the estrogen receptor (ER). This prompted us to investigate whether the VEGF gene contains sequences that bind the ER and confer hormonal inducibility to reporter constructs in the presence of the two ER subtypes. These studies identified two sequences homologous to the consensus estrogen response element, GGTCAnnnTGACC, which bind both ER-alpha and ER-beta. One of these elements is located in the 5'-untranslated region of the VEGF gene (GGGCAaagTGACT), and the other is located in the 3'-untranslated region (GAGCAcccTGCCC). Competition with excess unlabeled oligonucleotides indicates that these two elements bind both ERs specifically, mutations in either half-site of the two elements abolish receptor binding, and ER-alpha- and ER-beta-specific antibodies interact with complexes formed with the corresponding receptor subtypes. In cells containing either ER-alpha or ER-beta, the 3'-element behaves as a traditional enhancer that confers hormone inducibility to reporter constructs in an orientation-independent manner, and transcriptional activity is blocked by the pure antiestrogen ICI 182,780. The pattern of transcriptional activity of the element located in the 5'-flanking region is more complex. In the orientation found in the endogenous gene, this element is nonresponsive to ER-beta but confers estrogen-dependent inhibition of transcription with ER-alpha that is blunted by ICI 182,780. In the opposite orientation, the 5'-element confers hormone inducibility with either ER-alpha or -beta, and ICI 182,780 blocks activation by ER-alpha but not by ER-beta. These findings support the hypotheses that estrogens directly regulate VEGF transcription in target tissues and tumors, although such regulation appears likely to involve a complex interplay of cis- and trans-acting elements not previously observed for other hormone-responsive genes.
