ER Co-Repressor Function of SAFB in Breast Cancer

描述（由申请人提供）：支架附着因子/核基质蛋白SAFB定位于人乳腺癌中杂合性丢失极高的基因座。在许多乳腺癌和抗雌激素抗性的异种移植模型中，其表达也减少。最近我们发现SAFB直接与雌激素受体（ER）结合，并作为ER辅阻遏物发挥作用。抗雌激素他莫昔芬可增加SAFB与ER的结合，SAFB可增强他莫昔芬介导的ER抑制。SAFB对ER活性的抑制作用似乎涉及染色质重塑，因为组蛋白去乙酰化酶（HDAC）抑制剂阿司他丁A可缓解抑制作用。支持这一点，我们最近绘制了一个独立的抑制结构域在SAFB结合蛋白质与LIM和RING域已被证明是参与染色质介导的调控基因expression.We因此建议确定的功能SAFB在调节ER功能，利用我们独特的模型系统，将阐明特定的SAFB效应ER在体外和体内，以及SAFB的缺失在抗雌激素抵抗发生中的作用。具体而言，我们将问：1）哪些内源性雌激素调节基因受到SAFB的影响，以及这如何转化为生长效应？我们将在一个独特的模型中研究SAFB水平诱导性变化对生长和基因表达的影响，比较ER阴性MCF-7衍生细胞（C4-12）与ER功能恢复的C4-12细胞（C4-I2 ER-HA）。2)SAFB介导的ER抑制是否涉及染色质重塑？由于SAFB的ER抑制作用中涉及染色质重塑的证据，我们将研究与HDAC和其他参与调节染色质结构的蛋白质的相互作用。3)SAFB的表达对雌激素反应组织的发育是否至关重要，这是否反映在体内雌激素靶基因的表达改变上？我们将在SAFB缺失小鼠中解决这些问题。4)SAFB是否参与乳腺癌细胞抗雌激素抵抗的发展？因为SAFB增强了抗雌激素如他莫昔芬抑制ER介导的转录的能力，并且SAFB在他莫昔芬抗性的异种移植模型中减少，我们将直接测试SAFB水平降低是否改变了该模型中雌激素调节基因的表达并增强抗性的发生。

DESCRIPTION (provided by applicant): The scaffold attachment factor/nuclear matrix protein SAFB maps to a locus with extremely high loss of heterozygosity in human breast cancer. Its expression is also reduced in many breast cancers, and in a xenograft model of antiestrogen resistance. Recently we discovered that SAFB binds directly to the estrogen receptor (ER), and functions as an ER corepressor. SAFB binding to ER is increased by the antiestrogen tamoxifen, and SAFB can enhance tamoxifen-mediated repression of ER. The repressive effect of SAFB on ER activity appears to involve chromatin remodeling, since repression is relieved by the histone deacetylase (HDAC) inhibitor trichostatin A. Supporting this, we have recently mapped an independent repression domain in SAFB that binds proteins with LIM and RING domains which have been shown to be involved in chromatin-mediated regulation of gene expression.We therefore propose to define the function of SAFB in regulating ER function, making use of our unique model systems that will elucidate specific SAFB effects upon ER in vitro and in vivo, and the role of loss of SAFB in the onset of antiestrogens resistance. Specifically, we will ask: 1) Which classes of endogenous estrogen-regulated genes are affected by SAFB, and how does this translate to growth effects? We will investigate the growth and gene expression effects of inducible changes in SAFB levels in a unique model, comparing ER-negative MCF-7-derived cells (C4-12) vs. C4-12 cells with restored functional ER (C4-I2ER-HA). 2) Does SAFB-mediated repression of ER involve chromatin remodeling? Because of the evidence implicating chromatin remodeling in the ER-repressive effects of SAFB, we will investigate the involvement of interaction with HDACs and other proteins implicated in modulating chromatin structure. 3) Is SAFB expression critical for the development of estrogen-responsive tissues, and is this reflected by altered expression of estrogen target genes in vivo? We will address these issues in SAFB-null mice. 4) Is SAFB involved in the development of antiestrogen resistance in breast cancer cells? Because SAFB enhances the ability of antiestrogens like tamoxifen to inhibit ER-mediated transcription, and SAFB is reduced in a xenograft model of tamoxifen resistance, we will test directly whether decreased SAFB levels change expression of estrogen-regulated genes in this model and enhance the onset of resistance.