Department of Gastroenterology and Hepatology, Erasmus MC Cancer Institute, University Medical Center, Rotterdam, the Netherlands.
Cancer Biology Program, University of Hawaii Cancer Center, Honolulu, Hawaii.
Cancer Res. 2024 May 2;84(9):1443-1459. doi: 10.1158/0008-5472.CAN-23-2268.
AXIN1 is a major component of the β-catenin destruction complex and is frequently mutated in various cancer types, particularly liver cancers. Truncating AXIN1 mutations are recognized to encode a defective protein that leads to β-catenin stabilization, but the functional consequences of missense mutations are not well characterized. Here, we first identified the GSK3β, β-catenin, and RGS/APC interaction domains of AXIN1 that are the most critical for proper β-catenin regulation. Analysis of 80 tumor-associated variants in these domains identified 18 that significantly affected β-catenin signaling. Coimmunoprecipitation experiments revealed that most of them lost binding to the binding partner corresponding to the mutated domain. A comprehensive protein structure analysis predicted the consequences of these mutations, which largely overlapped with the observed effects on β-catenin signaling in functional experiments. The structure analysis also predicted that loss-of-function mutations within the RGS/APC interaction domain either directly affected the interface for APC binding or were located within the hydrophobic core and destabilized the entire structure. In addition, truncated AXIN1 length inversely correlated with the β-catenin regulatory function, with longer proteins retaining more functionality. These analyses suggest that all AXIN1-truncating mutations at least partially affect β-catenin regulation, whereas this is only the case for a subset of missense mutations. Consistently, most colorectal and liver cancers carrying missense variants acquire mutations in other β-catenin regulatory genes such as APC and CTNNB1. These results will aid the functional annotation of AXIN1 mutations identified in large-scale sequencing efforts or in individual patients.
Characterization of 80 tumor-associated missense variants of AXIN1 reveals a subset of 18 mutations that disrupt its β-catenin regulatory function, whereas the majority are passenger mutations.
AXIN1 是 β-连环蛋白破坏复合物的主要组成部分，在各种癌症类型中经常发生突变，特别是肝癌。截断的 AXIN1 突变被认为编码一种有缺陷的蛋白质，导致 β-连环蛋白稳定，但错义突变的功能后果尚未很好地描述。在这里，我们首先确定了 AXIN1 的 GSK3β、β-连环蛋白和 RGS/APC 相互作用域，这些域对正确的 β-连环蛋白调节最为关键。对这些域中 80 个与肿瘤相关的变异进行分析，确定了 18 个显著影响 β-连环蛋白信号的变异。共免疫沉淀实验表明，它们中的大多数失去了与相应突变域结合伴侣的结合。全面的蛋白质结构分析预测了这些突变的后果，这些后果在功能实验中很大程度上与对 β-连环蛋白信号的观察影响重叠。结构分析还预测，RGS/APC 相互作用域内的功能丧失突变要么直接影响 APC 结合的界面，要么位于疏水区内并使整个结构不稳定。此外，AXIN1 截短长度与 β-连环蛋白调节功能呈反比，较长的蛋白质保留更多的功能。这些分析表明，AXIN1 截断突变中的所有突变至少部分影响 β-连环蛋白的调节，而这仅适用于错义突变的一部分。一致地，携带错义变异的大多数结直肠癌和肝癌获得了其他 β-连环蛋白调节基因如 APC 和 CTNNB1 的突变。这些结果将有助于对大规模测序工作或个别患者中鉴定的 AXIN1 突变进行功能注释。
AXIN1 肿瘤相关错义变异的 80 个的特征揭示了一组 18 个突变，这些突变破坏了其 β-连环蛋白调节功能，而大多数则是过客突变。
