SAFB1 /2 Factors as Noval Breast Tumor Suppressor Genes

描述（由申请人提供）：我们最近鉴定并表征了两个支架附着因子，称为SAFB1和SAFB2，它们在染色体19p13上显示75%的同源性并在一起（头对头方向）。我们已经发现safb在乳腺癌细胞中起生长抑制剂的作用，并且它们在染色体19p13上的位点在临床乳腺癌中显示出最高的杂合性损失（78%）。SAFB1/2蛋白表达在大约20%的乳腺癌中缺失，低表达与较短的总生存期相关。我们在乳腺肿瘤中发现了SAFB1突变，而这些突变在邻近的正常组织中并不存在。因此，我们假设SAFB1和SAFB2是肿瘤抑制因子，其在乳腺肿瘤中的频繁失活导致致瘤性和转移性表型，我们将使用体内和体外模型对其进行评估。虽然这两种蛋白都具有生长抑制剂和内质网共抑制因子的功能，但它们也具有不同的特性——两者都存在于细胞核中，但只有SAFB1在应激条件下被招募到核体中，只有SAFB2也出现在细胞质中并与vinexin- β结合。因此，我们将评估哪些SAFB功能对肿瘤抑制至关重要，哪些功能在SAFB1和SAFB2之间是相加的、协同的、代偿的或拮抗的。具体来说，我们将问：1)SAFB1/2在人类乳腺肿瘤中是如何失活的？我们将研究乳腺癌进化过程中的失活，并确定失活是否通过突变和/或其他表观遗传事件发生，如基因间双向SAFB1/2启动子的超甲基化。2)中和SAFB1在体外和体内的生物学效应如何？我们将比较和对比（通过RNAi）降低SAFB1和SAFB2、临床乳腺癌标本中发现的SAFB突变体和小鼠模型中基因敲除（SAFB1-/-和SAFB2-/-）的效果。3) SAFB1和SAFB2水平如何与临床乳腺癌预后相关？我们将在排列的乳腺肿瘤库中测量SAFB1和SAFB2水平，并将其与生存和其他已知预后因素相关联。这项结合了分子、细胞和体内遗传方法的研究的成功完成，将为人类乳腺癌中受到严重干扰的调节机制提供重要的见解。

DESCRIPTION (provided by applicant): We have recently identified and characterized two scaffold attachment factors termed SAFB1 and SAFB2, which show 75 percent homology and map together (in head-to-head orientation) on chromosome 19p13. We have discovered that the SAFBs function as growth inhibitors in breast cancer cells, and that their locus on chromosome 19p13 displays one of the highest losses of heterozygosity (78 percent) reported in clinical breast cancer. Protein expression of SAFB1/2 is lost in approximately 20 percent of breast cancers, and low expression is associated with a shorter overall survival. We have found SAFB1 mutations in breast tumors that are not present in adjacent normal tissue. Therefore, we hypothesize that SAFB1 and SAFB2 are tumor suppressors whose frequent inactivation in breast tumors results in tumorigenic and metastatic phenotypes, which we will assess using in vivo and in vitro models. While both proteins function as growth inhibitors and ER co-repressors, they also have distinct properties - both are found in the cell nucleus, but only SAFB1 is recruited to nuclear bodies under stress conditions, and only SAFB2 also appears in the cytoplasm and binds vinexin-beta. We will therefore assess which SAFB functions are essential for tumor suppression, and which functions are additive, synergistic, compensatory, or antagonistic between SAFB1 and SAFB2. Specifically, we will ask: 1) How are SAFB1/2 inactivated in human breast tumors? We will investigate loss during breast cancer evolution, and determine whether inactivation occurs through mutations and/or other epigenetic events such as hypermethylation of the intergenic bidirectional SAFB1/2 promoter. 2) What are the biological effects of neutralizing SAFB1 in vitro and in vivo? We will compare and contrast the effects of lowering (by RNAi) SAFB1 and SAFB2, of SAFB mutants identified in clinical breast cancer specimens, and of gene knockouts in mouse models (SAFB1-/- and SAFB2-/-). 3) How do SAFB1 and SAFB2 levels correlate with clinical breast cancer outcome? We will measure SAFB1 and SAFB2 levels in an arrayed breast tumor bank, and correlate the levels with survival and other known prognostic factors. Successful completion of this study, which incorporates molecular, cellular, and in vivo genetic approaches, will provide important insight into regulatory mechanisms which are critically disturbed in human breast cancer.