Targeting beta-catenin in liver pathology: Novel Interactions, Novel Paradigms

描述（由申请人提供）：Wnt/¿-catenin信号在肝脏生物学中与调节分区、再生、发育和代谢有关。然而，在肝纤维化、肝损伤、肝母细胞瘤和肝细胞癌（HCC）中已经报道了该通路的异常。靶向-catenin治疗HCC迫在眉睫。它是世界上第三大致命癌症，自20世纪80年代以来，其发病率和相关死亡率稳步上升。HCC的细胞和分子基础尚不清楚。由于各种原因，Wnt信号在17-40%的hcc中被认为是活跃的，并且大约20-40%的hcc在-catenin基因（CTNNB1）的外显子3中含有单等位体细胞突变，该基因编码非丝氨酸/苏氨酸磷酸化，稳定且构成活性的蛋白质，使其成为一个有吸引力的治疗靶点。在过去的几年里，我们已经做了一些重要的和矛盾的观察，包括确定新的相互作用和连环蛋白和其他分子之间的交叉调节。这些可能具有重要的生物学和翻译意义，需要进行深入的分析，这可能不仅对HCC有广泛的影响，而且对肝纤维化、损伤和代谢综合征等其他以¿-catenin为靶向的肝脏疾病也有广泛的影响。该提案的首要假设是，治疗靶向的¿-catenin必须考虑到现有的冗余和串扰与特定的信号通路，这需要全面阐明。我们将在三个不同但主题相关的目标中测试这些假设。在目的1中，我们将研究氧化应激依赖的-catenin条件敲除小鼠（Hep- -cat KO）肝癌发生的机制，以确定-catenin在小鼠肝细胞中维生素C生物合成中的作用是否导致了肝癌的增强。我们在小鼠肝脏维生素C生物合成中发现了一个新的作用-catenin信号，它是一种已知的主要抗氧化剂。与人类和灵长类动物不同，啮齿动物在肝细胞中合成维生素C，而普通小鼠的食物缺乏抗坏血酸。我们假设Hep-¿-cat KO中HCC和氧化应激的增加是由于维生素C生物合成受损，其正常化将减轻HCC，并证明¿-catenin是HCC的全球治疗靶点。在目标2中，我们将研究HCC细胞中-catenin抑制后PDGFR的上调和激活的机制和生物学意义。我们推测PDGFR的上调及其下游特定信号臂的激活是在-catenin抑制后允许HCC生长的重要机制，了解这一现象的作用和调节将对有效的HCC治疗具有重要意义。在目标3中，我们将研究？-catenin在肝脏中表达抑制后的稳定性。我们假设？在HCC中-catenin抑制期间-catenin的稳定将防止任何与细胞-细胞粘附破坏相关的不良影响。所有在拨款中提出的研究将利用体外和体内实验的平衡，预期的结果将高度相关和转化。

DESCRIPTION (provided by applicant): Wnt/¿-catenin signaling is pertinent in liver biology in regulating zonation, regeneration, development and metabolism. However aberrations in this pathway have been reported in hepatic fibrosis, hepatic injury, hepatoblastomas and hepatocellular cancer (HCC). Targeting ¿ -catenin in HCC is imminent. It is the 3rd fatal cancer worldwide and its incidence and associated death rates have steadily increased since the 1980s. Cellular & molecular basis of HCC is poorly understood. Wnt signaling has been deemed active in 17-40% of HCCs due to various reasons and around 20-40% of all HCCs harbor monoallelic somatic mutations in the exon-3 of the ¿-catenin gene (CTNNB1) that encodes for a non-serine/threonine phosphorylatable, stable and constitutively active protein, making it an attractive therapeutic target. We have made several important and some paradoxical observations over the last few years including identification of novel interactions and cross-regulations between ¿ -catenin and other molecules. These may have significant biological and translational implications mandating an in-depth analysis that may have widespread implications in not just HCC but other hepatic pathologies where ¿ -catenin targeting may be of essence such as hepatic fibrosis, injury and metabolic syndrome. The overarching hypothesis of the proposal is that therapeutic targeting of ¿ -catenin must take into account existing redundancies and crosstalk with specific signaling pathways, which need to be comprehensively elucidated. We will test these hypotheses in three distinct but thematically related aims. In aim 1, we will investigate the mechanism of oxidative stress dependent enhanced hepatocarcinogenesis in ¿ -catenin conditional knockout mice (Hep- ¿ -Cat KO) to address if enhanced HCC is a murine 'artifact' due to the role of - ¿ catenin in vitamin C biosynthesis in murine hepatocytes. We identified a novel role of ¿ -catenin signaling in vitamin C biosynthesis in the murine liver, whic is a known major antioxidant. Unlike humans and primates, rodents synthesize vitamin C in the hepatocytes and regular mouse chow is devoid of ascorbic acid. We hypothesize that increased HCC and oxidative stress in Hep- ¿ -Cat KO is due to compromised vitamin C biosynthesis and its normalization will alleviate HCC and demonstrate ¿ -catenin to be a global therapeutic target in HCC. In aim 2 we will investigate mechanism and biological implications of PDGFR¿ upregulation and activation after ¿-catenin inhibition in HCC cells. We hypothesize that PDGFR¿ upregulation along with the activation of its specific downstream signaling arm is an important mechanism that will allow growth of HCC after ¿-catenin inhibition and that understanding the role and regulation of this phenomena will bear significantly on efficacious HCC treatment. In aim 3, we will investigate the role and regulation of ?-catenin stabilization following inhibition of ¿-catenin expression in the liver. We hypothesize that ?-catenin stabilization during ¿-catenin inhibition in HCC will prevent any untoward effect related to disruption of cell-cell adhesion. All the proposed studies in the grant will utilize a balance of i vitro and in vivo set of experiments and the expected outcomes will be highly relevant and translational.