Supplementary Materials from Estrogen-Related Receptor α Expression and Function Is Associated with the Transcriptional Coregulator AIB1 in Breast Carcinoma
ARTICLE ABSTRACT
The significance of the estrogen-related receptor α (ERRα) as prognostic marker for poor clinical outcome in breast carcinoma has recently been reported. Transcriptional activity of nuclear receptors such as ERRα depends on coregulatory proteins. Thus, we compared the expression of different receptors, coregulators, and target genes on RNA and protein level in identical primary breast tumor samples (n = 48). We found a positive correlation between the transcripts of ERRα and AIB1 (amplified in breast cancer-1), a coactivator overexpressed in breast cancers and associated with resistance to antihormone treatment. These data were confirmed on protein level, studying an independent patient collection (n = 257). Expression of the estrogen-regulated gene pS2 was associated with ERRα only in tumors, where estrogen receptor (ERα) expression was low or absent. In ERα high expressing tumors, no correlation of ERRα and pS2 was observed. AIB1 interacts directly with ERRα as shown by fluorescence-resonance energy transfer, mammalian two-hybrid, and coimmunoprecipitation assays with endogenous proteins. It enhances ERRα transcriptional activity in ERα-negative breast cancer cell lines as shown in functional reporter gene assays. Blocking ERRα with an inverse agonist abolished interaction and coactivation by AIB1. Recruitment of both proteins to ERRα target gene promoters further supports the significance of their interaction. Our findings identify AIB1 as functionally relevant cofactor for ERRα in breast carcinoma. ERRα/AIB1 complexes may control estradiol-regulated genes in a hormone-independent manner. Accordingly, ERRα might be a rewarding target for treatment of endocrine-resistant tumors. [Cancer Res 2009;69(12):5186–93]
