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映射到人类乳腺癌中杂合性损失极高的位点。在许多乳腺癌和抗雌激素抵抗的异种移植模型中，它的表达也减少。最近我们发现SAFB直接与雌激素受体（ER）结合，并作为ER的协同抑制因子。抗雌激素的他莫昔芬增加了SAFB与ER的结合，SAFB可以增强他莫昔芬介导的ER抑制。SAFB对内质网活性的抑制作用似乎涉及染色质重塑，因为这种抑制被组蛋白去乙酰化酶（HDAC）抑制剂trichostatin a缓解。为了支持这一点，我们最近在SAFB中绘制了一个独立的抑制结构域，该结构域将蛋白质与LIM和RING结构域结合，这已被证明参与染色质介导的基因表达调节。因此，我们建议定义SAFB在调节内质网功能中的功能，利用我们独特的模型系统来阐明SAFB在体外和体内对内质网的特定作用，以及SAFB缺失在抗雌激素抗性发生中的作用。具体来说，我们将问：1)哪些内源性雌激素调节基因受到SAFB的影响，这如何转化为生长效应？我们将在一个独特的模型中研究诱导SAFB水平变化对生长和基因表达的影响，比较ER阴性mcf -7来源的细胞（C4-12）和恢复功能ER的C4-12细胞（C4-I2ER-HA）。2) safb介导的ER抑制是否涉及染色质重塑？由于有证据表明，染色质重塑参与了SAFB的er抑制作用，我们将研究与HDACs和其他参与调节染色质结构的蛋白质的相互作用。3) SAFB的表达对雌激素应答组织的发育是否至关重要，这是否通过体内雌激素靶基因的表达改变来反映？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耐药的发展？由于SAFB增强了抗雌激素如他莫昔芬抑制er介导的转录的能力，而SAFB在他莫昔芬耐药的异种移植模型中降低，我们将直接测试SAFB水平降低是否会改变该模型中雌激素调节基因的表达并增强耐药的发生。

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.