Defining USP22 Functions During Mammalian Development

描述(由申请人提供)：高度保守的SAGA复合体在酵母、苍蝇、小鼠和人类细胞的基因调控中发挥重要作用。SAGA中的乙酰转移酶活性是由GCN5提供的，但该复合体也包含由USP22(人和小鼠)或其同源物、NONSTOP(苍蝇)和UBP8(酵母)提供的泛素特异性蛋白酶活性。在高度转移性、耐药的人类肿瘤中，USP22被确认为11基因‘癌症死亡’干细胞信号的一部分，但USP22的过度表达如何导致癌症干细胞表型，或者这些功能是否与SAGA复合体的整体功能相关尚不清楚。我们以前创造了Gcn5的几个突变等位基因来探索SAGA在哺乳动物发育过程中的功能，我们的研究表明SAGA复合体在早期发育中具有重要的帽子无关功能。这些功能中至少有一些可能与USP22有关，因为我们发现Gcn5缺失会导致USP22活性降低(Atanassov等人，2009年)。我们推测，USP22在胚胎干细胞和胚胎发育中具有重要功能，这可能与其在肿瘤发生中的作用直接相关。我们最近利用USP22基因陷阱等位基因进行的研究证实，USP22功能对于正常胚胎发育和存活是重要的。我们将通过以下途径进一步确定USP22的发育作用：1)通过创建携带USP22的漂浮等位基因或催化死亡等位基因的小鼠来定义SAGA依赖和独立的USP22功能；2)通过功能缺失和过度表达的方式定义小鼠ES细胞分化前后的USP22功能；3)确定USP22在ES细胞中的基因组位置、基因靶点和蛋白底物。从长远来看，这些研究将为USP22过度表达如何有助于癌症干细胞的形成或维持以及高侵袭性肿瘤的发展提供重要的见解。

DESCRIPTION (provided by applicant): The highly conserved SAGA complex plays important roles in gene regulation in yeast, fly, mouse, and human cells. Acetyltransferase activity in SAGA is provided by Gcn5, but the complex also contains a ubiquitin specific protease activity provided by USP22 (humans and mice) or its orthologs, nonstop (flies) and Ubp8 (yeast). USP22 was identified as part of an 11 gene 'death from cancer' stem cell signature in highly metastatic, therapy-resistant human tumors, but how over expression of USP22 contributes to a cancer stem cell phenotype, or whether these functions are related to the overall functions of the SAGA complex is not yet clear. We previously created several mutant alleles of Gcn5 to probe SAGA functions during mammalian development, and our studies indicate that the SAGA complex has important HAT-independent functions during early development. At least some of these functions are likely related to USP22, since we discovered that Gcn5 deletion results in diminished USP22 activity (Atanassov et al, 2009). We hypothesize that USP22 has important functions in embryonic stem cells and in embryo development that may be directly related to its roles in tumorigenesis. Our recent studies using USP22 gene trap alleles confirm that USP22 functions are important for normal embryo development and survival. We will further define the developmental roles of USP22 through: 1) Definition of SAGA dependent and independent USP22 functions by creating mice bearing either a floxed allele or a catalytically dead allele of USP22 2) Definition of USP22 functions in mouse ES cells before and after differentiation through both loss of function and over expression approaches and 3) Determination of genomic locations, gene targets and protein substrates of USP22 in ES cells. In the long term, these studies will provide important insights into how USP22 over expression contributes to the formation or maintenance of cancer stem cells and the development of highly aggressive tumors.