Defining USP22 Functions During Mammalian Development

描述（由申请人提供）：高度保守的佐贺复合物在酵母、苍蝇、小鼠和人类细胞的基因调控中起重要作用。佐贺中的乙酰转移酶活性由Gcn 5提供，但复合物还含有由USP 22（人和小鼠）或其直系同源物、nonstop（苍蝇）和Ubp8（酵母）提供的泛素特异性蛋白酶活性。USP22被鉴定为高转移性、治疗抗性人类肿瘤中11个基因“癌症死亡”干细胞特征的一部分，但USP22的过度表达如何促成癌症干细胞表型，或者这些功能是否与佐贺复合物的整体功能相关尚不清楚。我们以前创建了几个突变等位基因的Gcn 5探针佐贺功能在哺乳动物的发展，我们的研究表明，佐贺复合物具有重要的HAT独立的功能在早期发展。这些功能中至少有一些可能与USP 22相关，因为我们发现Gcn5缺失导致USP 22活性降低（Atanassov et al，2009）。我们推测USP22在胚胎干细胞和胚胎发育中具有重要功能，可能与其在肿瘤发生中的作用直接相关。我们最近使用USP22基因陷阱等位基因的研究证实，USP22功能对正常胚胎发育和存活很重要。我们将通过以下方式进一步确定USP22的发展作用：1）通过产生携带USP 22的floxed等位基因或催化死亡等位基因的小鼠来定义佐贺依赖性和独立性USP 22功能2）通过功能丧失和过表达方法来定义分化前后小鼠ES细胞中的USP 22功能和3）确定基因组位置，ES细胞中USP22的基因靶点和蛋白底物。从长远来看，这些研究将为USP22过度表达如何促进癌症干细胞的形成或维持以及高度侵袭性肿瘤的发展提供重要见解。

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.