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

描述（由申请人提供）：Wnt/β-连环蛋白信号传导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）中已经报道了该途径的畸变。在HCC中靶向β-连环蛋白是迫在眉睫的。它是全球第三大致命癌症，其发病率和相关死亡率自20世纪80年代以来稳步上升。HCC的细胞和分子基础知之甚少。由于各种原因，Wnt信号传导被认为在17-40%的HCC中是活跃的，并且所有HCC中约20-40%在编码非丝氨酸/苏氨酸可磷酸化的、稳定的和组成型活性蛋白的β-连环蛋白基因（CTNNB 1）的外显子3中具有单等位基因体细胞突变，使其成为有吸引力的治疗靶标。在过去的几年里，我们已经做了几个重要的和一些矛盾的观察，包括鉴定新的相互作用和β-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，要求进行深入分析，这可能不仅在HCC中，而且在β-连环蛋白靶向可能至关重要的其他肝脏病理学中具有广泛的意义，例如肝纤维化、损伤和代谢综合征。该提案的首要假设是β-连环蛋白的治疗靶向必须考虑到与特定信号传导途径的现有冗余和串扰，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。目的一：探讨氧化应激依赖性增强β-catenin条件性基因敲除小鼠肝癌发生的机制 (Hep-β-CatKO）以解决增强的HCC是否是由于β-连环蛋白在鼠肝细胞中维生素C生物合成中的作用而引起的鼠“伪像”。我们确定了β-连环蛋白信号在小鼠肝脏维生素C生物合成中的新作用，维生素C是已知的主要抗氧化剂。与人类和灵长类动物不同，啮齿类动物在肝细胞中合成维生素C，而普通小鼠的食物不含抗坏血酸。我们假设Hep-β-Cat KO中增加的HCC和氧化应激是由于维生素C生物合成受损，其正常化将减轻HCC，并证明β-连环蛋白是HCC的全球治疗靶点。目的2：研究肝癌细胞中β-catenin抑制后PDGFRα上调和激活的机制和生物学意义。我们假设PDGFRα上调沿着其特异性下游信号臂的激活是β-连环蛋白抑制后允许HCC生长的重要机制，并且理解这种现象的作用和调节将对有效的HCC治疗产生重要影响。在目标3中，我们将研究？抑制肝脏中β-连环蛋白表达后的连环蛋白稳定。我们假设？-在HCC中β-连环蛋白抑制过程中连环蛋白的稳定化将防止与细胞-细胞粘附破坏相关的任何不利影响。该补助金中的所有拟议研究将利用体外和体内实验的平衡，预期结果将具有高度相关性和转化性。

DESCRIPTION (provided by applicant): Wnt/ß-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 ß-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 ß-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 ß-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 ß-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 ß-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 ß-catenin conditional knockout mice (Hep-ß-Cat KO) to address if enhanced HCC is a murine 'artifact' due to the role of ß-catenin in vitamin C biosynthesis in murine hepatocytes. We identified a novel role of ß-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-ß-Cat KO is due to compromised vitamin C biosynthesis and its normalization will alleviate HCC and demonstrate ß-catenin to be a global therapeutic target in HCC. In aim 2 we will investigate mechanism and biological implications of PDGFRα upregulation and activation after ß-catenin inhibition in HCC cells. We hypothesize that PDGFRα upregulation along with the activation of its specific downstream signaling arm is an important mechanism that will allow growth of HCC after ß-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 ß-catenin expression in the liver. We hypothesize that ?-catenin stabilization during ß-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.