Anti-pancreatic tumorigenesis by inactivation of SAG/RBX2 E3 ubiquitin ligase

描述（由申请方提供）：凋亡敏感基因（SAG，人；SAG，小鼠）也称为RBX2/ROC2，是SCF （SKP1, Cullins， F-box蛋白）E3泛素连接酶的重要环组分，通过促进各种关键调控蛋白的泛素化和降解，控制几个重要的生物过程，包括细胞周期进程、信号转导、转录和DNA复制。我们已发表和未发表的数据显示，SAG与胰腺癌的直接关联如下：a) SAG在胰腺癌组织中过表达，且SAG核表达与胰腺癌患者预后不良相关；b)敲低SAG siRNA可引起肿瘤抑制蛋白的积累，抑制胰腺癌细胞的存活和非锚定生长；c)敲低SAG siRNA可显著抑制胰腺癌细胞原位生长和基质侵袭。这些研究表明，在胰腺肿瘤发生过程中，SAG的过表达可能具有致癌作用。本申请的目的是使用胰腺特异性Sag转基因或KO小鼠模型来机制研究Sag在Kras激活（KrasG12D）和p53突变（p53R172H）引发的胰腺肿瘤发生中的作用。核心假设是，SAG通过促进肿瘤抑制底物（如detor、I¿B和p21/p27）的降解，导致mTOR和NF¿B途径的激活，从而促进肿瘤发生。因此，Sag -pancreatic的转基因表达会促进由KrasG12D引发的胰腺肿瘤的发生，而Sag -pancreatic的缺失会通过肿瘤抑制蛋白的积累消除致癌信号，从而抑制由KrasG12D和p53R172H引发的胰腺肿瘤的发生。我们提出了两个具体目标：1)确定Sag在KrasG12D/ p53r172h诱导的胰腺肿瘤发生中的作用；2)阐明Sag调控胰腺肿瘤发生的机制。影响：我们的研究使用再现胰腺导管腺癌（PDAC）发展的小鼠模型来研究Sag E3连接酶在PDAC的发生和发展中的作用，并阐明其作用机制。我们的研究将从机制上验证SAG E3泛素连接酶作为一种新的抗胰腺癌靶点，并为未来发现特异性的SAG E3连接酶抑制剂作为一类新的抗胰腺癌药物提供概念验证证据。因此，我们的工作是高度创新的，具有重要的翻译价值。

DESCRIPTION (provided by applicant): Sensitive to Apoptosis Gene (SAG, human; Sag, mouse) also known as RBX2/ROC2, is an essential RING component of SCF (SKP1, Cullins, F-box proteins) E3 ubiquitin ligase which, by promoting ubiquitination and degradation of various key regulatory proteins, controls several important biological processes including cell cycle progression, signal transduction, transcription, and DNA replication. Our published and unpublished data showed a direct association of SAG with pancreatic cancer as follows: a) SAG is overexpressed in pancreatic cancer tissues, and SAG nuclear expression is associated with poor prognosis of pancreatic cancer patients; b) SAG siRNA knockdown caused accumulation of tumor suppressive proteins and inhibited survival and anchorage-independent growth of pancreatic cancer cells, and c) orthotopic in vivo growth and matrigel invasion of pancreatic cancer cells were significantly inhibited, respectively, by SAG siRNA knockdown. All these studies suggested that SAG overexpression could be oncogenic during pancreatic tumorigenesis. The objectives of this application are to use pancreatic specific Sag transgenic or KO mouse models to mechanistically study the role of Sag in pancreatic tumorigenesis triggered by Kras activation (KrasG12D) and p53 mutation (p53R172H). The central hypothesis is that SAG promotes tumorigenesis by promoting the degradation of tumor suppressive substrates such as DEPTOR, I¿B, and p21/p27, leading to activation of the mTOR and NF¿B pathways. Thus, SAG-pancreatic transgenic expression would promote pancreatic tumorigenesis, initiated by KrasG12D, whereas Sag pancreatic deletion would abrogate oncogenic signals by accumulation of tumor suppressive proteins, thus suppressing pancreatic tumorigenesis triggered by KrasG12D and p53R172H. Two specific aims are proposed to 1) determine the role of Sag in KrasG12D/p53R172H-induced pancreatic tumorigenesis and 2) elucidate mechanism(s) by which Sag regulates pancreatic tumorigenesis. IMPACT: Our study uses mouse models that recapitulate the development of pancreatic ductal adenocarcinoma (PDAC) to investigate the role of Sag E3 ligase in the initiation and progression of PDAC and to elucidate its mechanism of action. Our study will mechanistically validate SAG E3 ubiquitin ligase as a novel anti-pancreatic cancer target and provide proof-of-concept evidence for future discovery of specific inhibitor of SAG E3 ligase as a novel class of anti-pancreatic cancer drugs. Our work is, therefore, highly innovative and of significant impact with translational value.