Laganière Josée, Deblois Geneviève, Lefebvre Céline, Bataille Alain R, Robert François, Giguère Vincent
Molecular Oncology Group, Department of Medicine, McGill University Health Centre, Montreal, QC, Canada H3A 1A1.
Proc Natl Acad Sci U S A. 2005 Aug 16;102(33):11651-6. doi: 10.1073/pnas.0505575102. Epub 2005 Aug 8.
Nuclear receptors can activate diverse biological pathways within a target cell in response to their cognate ligands, but how this compartmentalization is achieved at the level of gene regulation is poorly understood. We used a genome-wide analysis of promoter occupancy by the estrogen receptor alpha (ERalpha) in MCF-7 cells to investigate the molecular mechanisms underlying the action of 17beta-estradiol (E2) in controlling the growth of breast cancer cells. We identified 153 promoters bound by ERalpha in the presence of E2. Motif-finding algorithms demonstrated that the estrogen response element (ERE) is the most common motif present in these promoters whereas conventional chromatin immunoprecipitation assays showed E2-modulated recruitment of coactivator AIB1 and RNA polymerase II at these loci. The promoters were linked to known ERalpha targets but also to many genes not directly associated with the estrogenic response, including the transcriptional factor FOXA1, whose expression correlates with the presence of ERalpha in breast tumors. We found that ablation of FOXA1 expression in MCF-7 cells suppressed ERalpha binding to the prototypic TFF1 promoter (which contains a FOXA1 binding site), hindered the induction of TFF1 expression by E2, and prevented hormone-induced reentry into the cell cycle. Taken together, these results define a paradigm for estrogen action in breast cancer cells and suggest that regulation of gene expression by nuclear receptors can be compartmentalized into unique transcriptional domains by means of licensing of their activity to cofactors such as FOXA1.
核受体可响应其同源配体激活靶细胞内多种生物学途径，但在基因调控水平上如何实现这种区室化却知之甚少。我们利用全基因组分析雌激素受体α（ERα）在MCF-7细胞中的启动子占据情况，来研究17β-雌二醇（E2）在控制乳腺癌细胞生长中作用的分子机制。我们鉴定出在E2存在下被ERα结合的153个启动子。基序查找算法表明雌激素反应元件（ERE）是这些启动子中最常见的基序，而传统的染色质免疫沉淀分析显示在这些位点E2调节共激活因子AIB1和RNA聚合酶II的募集。这些启动子与已知的ERα靶标相关，但也与许多与雌激素反应无直接关联的基因相关，包括转录因子FOXA1，其表达与乳腺肿瘤中ERα的存在相关。我们发现MCF-7细胞中FOXA1表达的缺失抑制了ERα与原型TFF1启动子（其含有一个FOXA1结合位点）的结合，阻碍了E2对TFF1表达的诱导，并阻止了激素诱导的细胞周期重新进入。综上所述，这些结果定义了乳腺癌细胞中雌激素作用的模式，并表明核受体对基因表达的调控可通过将其活性许可给诸如FOXA1等辅因子而被区室化为独特的转录结构域。
