ABSTRACT
Estrogen-related receptor alpha (ERRalpha) is an orphan member of the nuclear receptor family of transcription factors. In addition to its function as a metabolic regulator, ERRalpha has been implicated in the growth and progression of several malignancies. In the setting of breast cancer, not only is ERRalpha a putative negative prognostic factor, but we have recently found that knock-down of its expression retards tumor growth in a xenograft model of this disease. The specific aspects of ERRalpha function that are responsible for its actions in breast cancer, however, remain unclear. Using the coactivator PGC-1alpha as a protein ligand to regulate ERRalpha activity, we analyzed the effects of this receptor on gene expression in the ERalpha-positive MCF-7 cell line. This analysis led to the identification of a large number of potential ERRalpha target genes, many of which were subsequently validated in other breast cancer cell lines. Importantly, we demonstrate in this study that activation of ERRalpha in several different breast cancer cell lines leads to a significant increase in VEGF mRNA expression, an activity that translates into an increase in VEGF protein secretion. The induction of VEGF results from the interaction of ERRalpha with specific ERR-responsive elements within the VEGF promoter. These findings suggest that ERRalpha-dependent induction of VEGF may contribute to the overall negative phenotype observed in tumors in which ERRalpha is expressed and provide validation for its use as a therapeutic target in cancer.
Subject(s)
Breast Neoplasms/metabolism , Estrogen Receptor alpha/metabolism , Receptors, Estrogen/metabolism , Vascular Endothelial Growth Factor A/metabolism , Animals , Breast Neoplasms/pathology , Cell Line, Tumor , Estrogen Receptor alpha/genetics , Female , Gene Expression Regulation, Neoplastic , Heat-Shock Proteins/genetics , Heat-Shock Proteins/metabolism , Humans , Peroxisome Proliferator-Activated Receptor Gamma Coactivator 1-alpha , Promoter Regions, Genetic , Receptors, Estrogen/genetics , Transcription Factors/genetics , Transcription Factors/metabolism , Vascular Endothelial Growth Factor A/genetics , ERRalpha Estrogen-Related ReceptorABSTRACT
Expression of estrogen-related receptor alpha (ERRalpha) has recently been shown to carry negative prognostic significance in breast and ovarian cancers. The specific role of this orphan nuclear receptor in tumor growth and progression, however, is yet to be fully understood. The significant homology between estrogen receptor alpha (ERalpha) and ERRalpha initially suggested that these receptors may have similar transcriptional targets. Using the well-characterized ERalpha-positive MCF-7 breast cancer cell line, we sought to gain a genome-wide picture of ERalpha-ERRalpha cross-talk using an unbiased microarray approach. In addition to generating a host of novel ERRalpha target genes, this study yielded the surprising result that most ERRalpha-regulated genes are unrelated to estrogen signaling. The relatively small number of genes regulated by both ERalpha and ERRalpha led us to expand our study to the more aggressive and less clinically treatable ERalpha-negative class of breast cancers. In this setting, we found that ERRalpha expression is required for the basal level of expression of many known and novel ERRalpha target genes. Introduction of a small interfering RNA directed to ERRalpha into the highly aggressive breast carcinoma MDA-MB-231 cell line dramatically reduced the migratory potential of these cells. Although stable knockdown of ERRalpha expression in MDA-MB-231 cells had no effect on in vitro cell proliferation, a significant reduction of tumor growth rate was observed when these cells were implanted as xenografts. Our results confirm a role for ERRalpha in breast cancer growth and highlight it as a potential therapeutic target for estrogen receptor-negative breast cancer.
Subject(s)
Breast Neoplasms/pathology , Cell Proliferation , Estrogen Receptor alpha/physiology , Breast Neoplasms/metabolism , Cell Line, Tumor , Cell Movement , Estrogen Receptor alpha/metabolism , Humans , Signal TransductionABSTRACT
The estrogen-related receptor alpha (ERRalpha) is a potential target for activation in the treatment of metabolic disease. To date, no small-molecule agonists of ERRalpha have been identified despite several high-throughput screening campaigns. We describe the synthesis and profiling of a small array of compounds designed on the basis of a previously reported agonist-bound crystal structure of the closely related receptor ERRgamma. The results suggest that ERRalpha may be intractable as a direct target for pharmacologic activation.
