The Role of post-translational activation of Myc in pancreatic cancer

 描述(申请人提供)：胰腺癌患者的5年生存率仅为6%，是所有主要癌症中最低的，这表明迫切需要从机制上加深对胰腺癌发展的了解，以确定新的治疗靶点。C-Myc(Myc)癌蛋白在包括胰腺导管腺癌(PDA)在内的多种癌症中过度表达，通常与不良预后相关。Myc通过其对基因转录的全球调控，帮助调节多种致癌过程，包括癌细胞的内在增殖、存活和黏附/迁移，以及外部肿瘤微环境的重建，包括血管生成和免疫细胞重新编程。Myc的表达和活性在正常细胞中受到严格调控。我们已经确定丝氨酸62(S62)是一个关键的磷酸化位点，它增加了Myc的稳定性和DNA结合活性。S62在RAS信号下游被磷酸化；KRAS中的激活突变几乎是PDA中普遍存在的驱动突变。然而，Myc在胰腺癌中的作用目前还知之甚少。我们观察到胰腺癌细胞系和原发胰腺肿瘤标本中S62磷酸化Myc(pS62-Myc)水平升高。此外，对肿瘤周围的早期前体病变(Panin)的分析也显示，与邻近的正常导管相比，pS62-Myc升高。我们已经建立了一个新的小鼠模型，LSL-KrasG12D；ROSA-LSL-MycWT；Pdx1-或P48-Cre(KMC)小鼠，这表明在生理水平上Myc的非调控表达能够与突变的KRAS协同作用，加速腺泡到导管的化生(ADM)、Panin进展和向转移性PDA的转化。重要的是，我们的初步数据表明，KMC肿瘤发生了人类疾病演变过程中常见的突变，启动了明显的间质反应，对标准化疗表现出耐药性，并可进展为侵袭性、低分化的PDA，转移率高。此外，我们已经在实验室中建立了两种翻译后针对Myc的治疗方法，这两种方法在体外和体内都显示出了良好的抗胰腺癌活性。这一提议的总体假设是，KRAS介导的丝氨酸62位Myc的磷酸化是胰腺癌细胞转化的重要驱动因素，这种激活Myc的机制显著促进了转移性PDA的演变，靶向Myc的翻译后激活对胰腺癌具有治疗效果。目标1：阐明Myc和KRAS介导的丝氨酸62磷酸化在胰腺癌发生发展中的作用；目标2：研究KRAS/Myc驱动的胰腺肿瘤的演变、间质扩张、异质性和治疗耐药性；目标3：建立靶向翻译后激活的治疗效果。 治疗胰腺癌的MYC。这项工作将揭示KRAS下游Myc的磷酸化是否在胰腺癌的发生和发展中发挥关键作用，以及针对这种翻译后激活的Myc是否在治疗这种毁灭性疾病方面具有治疗价值。

 DESCRIPTION (provided by applicant): The 5-year survival rate for pancreatic cancer patients is only 6%, the lowest of all major cancers, indicating a critical need for increased mechanistic understanding of pancreatic cancer development in order to identify new therapeutic targets. The c-Myc (Myc) oncoprotein is overexpressed in a variety of cancers, including pancreatic ductal adenocarcinoma (PDA), and generally correlates with poor prognosis. Through its global regulation of gene transcription, Myc helps regulate multiple oncogenic processes, including cancer cell intrinsic proliferation, survival, and adhesion/migration, as well as extrinsic tumor microenvironment remodeling including angiogenesis and immune cell reprogramming. The expression and activity of Myc is tightly regulated in normal cells. We have identified Serine 62 (S62) as a critical phosphorylation site, which increases the stability and DNA binding activity of Myc. S62 is phosphorylated downstream of RAS signaling; and activating mutations in KRAS are near universal driver mutations in PDA. The role of Myc in pancreatic cancer, however, is currently poorly understood. We have observed elevated levels of S62 phosphorylated Myc (pS62-Myc) in pancreatic cancer cell lines and primary pancreatic tumor samples. Furthermore, analysis of early precursor lesions (PanIN) peripheral to tumors also shows elevated pS62-Myc as compared to adjacent normal ducts. We have generated a novel mouse model, LSL-KRASG12D;ROSA-LSL-MycWT;Pdx1- or p48-Cre (KMC) mice, which shows that deregulated expression of Myc at physiologic levels is able to cooperate with mutant KRAS to accelerate acinar to ductal metaplasia (ADM), PanIN progression, and conversion to metastatic PDA. Importantly, our preliminary data indicate that KMC tumors develop common mutations seen in the evolution of the human disease, initiate a pronounced stromal reaction, show resistance to standard chemotherapy, and can progress to an aggressive, poorly differentiated PDA with a high metastatic rate. Further, we have established two therapeutics in the lab that target Myc post-translationally, both of which have shown promising activity against pancreatic cancer in vitro and in vivo. The overall hypothesis of this proposal is that KRAS-mediated phosphorylation of Myc at Serine 62 is an important driver of pancreatic cancer cell transformation, that this mechanism of activating Myc significantly contributes to the evolution of metastatic PDA, and that targeting post-translational activation of Myc has therapeutic efficacy in pancreatic cancer. The following aims are proposed: Aim 1: Elucidate the role of Myc and KRAS-mediated Serine 62 phosphorylation in the development of pancreatic cancer; Aim 2: Characterize KRAS/Myc-driven pancreatic tumor evolution, stromal expansion, heterogeneity, and therapeutic resistance; Aim 3: Establish the therapeutic efficacy of targeting post-translational activation of Myc for the treatment of pancreatic cancer. This work will reveal if phosphorylation of Myc downstream of KRAS plays a critical role in pancreatic cancer development and progression, and whether targeting this post-translational activation of Myc could have therapeutic value in the treatment of this devastating disease.