Investigating multifactorial beta-catenin activation in hepatocellular cancers

摘要 肝细胞癌是一种致命的恶性肿瘤，治疗选择有限，而且缺乏分子- 有针对性的治疗。Wnt/β-catenin通路的激活在肝细胞癌的发生中起着重要作用 发病机制。编码β-连环蛋白的基因CTNNB1的突变干扰了它的降解，导致 它的功能增强(GOF)和激活，并涉及20-35%的所有肝癌。相互排斥的群体 另外约8%的肝癌是AXIN1功能丧失(LOF)突变的肝癌，它编码 对于一种对β-连环蛋白降解至关重要的支架蛋白AXIN1。我们之前的研究也表明，β- 单靠连接素的激活不足以促进肝细胞癌的发展。基于CTNNB1的伴随存在 ~11%的人肝细胞癌中存在突变和c-met激活，AXIN1和c-Met中存在LOF突变 在~4%的人肝癌中，MET被激活，我们建立了c-Met/β-catenin和c-Met/Met-catenin两种小鼠肝癌模型。 C-Met/sgAxin1，采用睡美人转座子/转座子+尾静脉注射(SB-HDTVI)。 这些模型基于基因表达研究概括了各自的人类肝细胞癌亚型。有趣的是， 使用这些小鼠模型和人类肝癌样本，我们发现AXIN1 LOF突变的肝癌没有 显示典型的肝脏特异性β-连环蛋白靶基因激活，如谷氨酰胺合成酶(Gs)和Tbx3， 这在CTNNB1突变的肝癌中很明显。相比之下，河马级联在LOF突变中被灭活 AXIN1突变，但不存在CTNNB1突变的肝癌细胞。基于上述观察，我们的总体假设 尽管β-连环蛋白是常见的下游效应器，但CTNNB1和AXIN1的突变导致 不同分子亚型的肝细胞癌，这两类肿瘤的发生需要不同的参与 信号通路。我们提出以下三个具体目标来解决我们高度相关的假设。在……里面 目的1，我们计划确定c-Met/sgAxin1是否需要配体依赖的Wnt/β-连环蛋白的激活 诱导小鼠肝癌的形成。在目标2中，我们将研究Gs依赖和独立的代谢和 小鼠肝细胞癌发生过程中的信号级联。在目标3中，我们将描述 河马在CTNNB1GOF和Axin1LOF突变的肝癌细胞中级联。总之，我们的研究将阐明不同的 由于两种不同的机制，β-连环蛋白激活所诱导的信号通路，以及我们如何有效地 根据基因变异来定位这些肿瘤。该提案代表了一种持续且富有成效的协作 加州大学旧金山分校的陈欣博士和匹兹堡大学的保罗·蒙加博士。这一结果可能会为 肝癌的精准医学之路。

Abstract Hepatocellular carcinoma (HCC) is a deadly malignancy with limited treatment options, and lacks molecular- targeted therapies. Activation of Wnt/β-catenin cascade has been shown to play a major role during HCC pathogenesis. Mutations in CTNNB1, the gene encoding for β-catenin, interfere with its degradation leading to its gain-of function (GOF) and activation, and are implicated in 20-35% of all HCCs. A mutually exclusive group of additional around 8% of HCCs is the one with the loss-of-function (LOF) mutations in AXIN1, which encodes for a scaffolding protein AXIN1, essential for β-catenin degradation. Our previous studies also showed that β- catenin activation alone is insufficient for HCC development. Based on the concomitant presence of CTNNB1 mutations and c-MET activation in ~11% of human HCC, and the presence of LOF mutations in AXIN1 and c- MET activation together in ~4% of human HCC, we established two murine HCC models, c-Met/β-catenin and c-Met/sgAxin1, using sleeping beauty transposon/transposase and hydrodynamic tail vein injection (SB-HDTVI). These models recapitulate the respective human HCC subsets based on gene expression studies. Intriguingly, using these mouse models and human HCC samples, we discovered that AXIN1 LOF mutant HCC does not show activation of canonical liver-specific β-catenin target genes such as glutamine synthetase (Gs) and Tbx3, which was evident in CTNNB1-mutant HCCs. In contrast, Hippo cascade is inactivated in LOF mutations in AXIN1 mutant, but not in CTNNB1-mutant HCCs. Based on the above observations, our overarching hypothesis is that despite β-catenin being the common downstream effector, mutations in CTNNB1 and AXIN1 lead to distinct molecular subtypes of HCC, and tumor development in these two classes requires participation of distinct signaling pathways. We propose the following three specific aims to address our highly relevant hypothesis. In Aim 1, we plan to define whether ligand dependent activation of Wnt/β-catenin is required for c-Met/sgAxin1 induced HCC formation in mice. In Aim 2, we will investigate Gs dependent and independent metabolic and signaling cascades in mouse HCC development. And in Aim 3, we will characterize the functional contribution of Hippo cascade in Ctnnb1 GOF and Axin1 LOF mutant HCCs. Altogether, our studies will elucidate the distinct signaling pathways induced by β-catenin activation due to two distinct mechanisms, and how we may effectively target these tumors based on genetic variations. The proposal represents an ongoing & productive collaboration between Dr. Xin Chen from UCSF and Dr. Paul Monga from University of Pittsburgh. The results may pave a way for precision medicine in HCC.