Abstract：
The β-catenin has two intrinsically disordered regions in both C- and N-terminal domains that trigger the formation of phase-separated condensates. Variants in its C-terminus are associated with familial exudative vitreoretinopathy (FEVR), yet the pathogenesis and the role of these variants in inducing abnormal condensates, are unclear. In this study, we identified a novel heterozygous frameshift variant, c.2104-2105insCC (p.Gln703ProfsTer33), in CTNNB1 from a FEVR-affected family. This variant encodes an unstable truncated protein that was unable to activate Wnt signal transduction, which could be rescued by the inhibition of proteasome or phosphorylation. Further functional experiments revealed the propensity of the Gln703ProfsTer33 variant to form cytoplasmic condensates, exhibiting a lower turnover rate after fluorescent bleaching due to enhanced interaction with AXIN1. LiCl, which specifically blocks GSK3β-mediated phosphorylation, restored signal transduction, cell proliferation, and junctional integrity in primary human retinal microvascular endothelial cells over-expressed with Gln703ProfsTer33. Finally, experiments on two reported FEVR-associated mutations in the C-terminal domain of β-catenin exhibited several functional defects similar to the Gln703ProfsTer33. Together, our findings unravel that the C-terminal region of β-catenin is pivotal for the regulation of AXIN1/β-catenin interaction, acting as a switch to mediate nucleic and cytosolic condensates formation that is implicated in the pathogenesis of FEVR.
摘要：
β-连环蛋白在C-和N-末端结构域中具有两个固有无序的区域,其触发相分离缩合物的形成。其C端变异与家族性渗出性玻璃体视网膜病变（FEVR）相关，然而，这些变异在诱导异常凝聚物中的发病机理和作用，不清楚。在这项研究中,我们发现了一个新的杂合移码变体，c.2104-2105insCC（p。Gln703ProfsTer33),来自FEVR感染家庭的CTNNB1。该变体编码一种不稳定的截短蛋白，该蛋白不能激活Wnt信号转导，可以通过抑制蛋白酶体或磷酸化来挽救。进一步的功能实验揭示了Gln703ProfsTer33变体形成细胞质缩合物的倾向，由于与AXIN1的相互作用增强，荧光漂白后表现出较低的转换率。LiCl,特异性阻断GSK3β介导的磷酸化，恢复信号转导，细胞增殖，用Gln703ProfsTer33过表达的原代人视网膜微血管内皮细胞的连接完整性。最后,对β-cateninC端结构域中两个报道的FEVR相关突变的实验显示出与Gln703ProfsTer33相似的几个功能缺陷。一起,我们的发现揭示了β-连环蛋白的C末端区域是调节AXIN1/β-连环蛋白相互作用的关键，充当介导与FEVR发病机理有关的核酸和胞质缩合物形成的开关。
