Plakophilin-3 Catenin Associates with the ETV1/ER81 Transcription Factor to Positively Modulate Gene Activity

Members of the plakophilin-catenin sub-family (Pkp-1, -2, and -3) facilitate the linkage of desmosome junctional components to each other (e.g. desmosomal cadherins to desmoplakin) and the intermediate-filament cytoskeleton. Pkps also contribute to desmosomal stabilization and the trafficking of its components. The functions of Pkps outside of the desmosome are less well studied, despite evidence suggesting their roles in mRNA regulation, small-GTPase modulation (e.g. mid-body scission) during cell division, and cell survival following DNA damage. Pkp-catenins are further believed to have roles in the nucleus given their nuclear localization in some contexts and the known nuclear roles of structurally related catenins, such as beta-catenin and p120-catenin. Further, Pkp-catenin activities in the nuclear compartment have become of increased interest with the identification of interactions between Pkp2-catenin and RNA Pol III and Pkp1 with single-stranded DNA. Consistent with earlier reports suggesting possible nuclear roles in development, we previously demonstrated prominent nuclear localization of Pkp3 in Xenopus naïve ectoderm (“animal cap”) cells and recently resolved a similar localization in mouse embryonic stem cells. Here, we report the association and positive functional interaction of Pkp3 with a transcription factor, Ets variant gene 1 (ETV1), which has critical roles in neural development and prominent roles in human genetic disease. Our results are the first to report the interaction of a sequence-specific transcription factor with any Pkp. Using Xenopus laevis embryos and mammalian cells, we provide evidence for the Pkp3:ETV1 complex on both biochemical and functional levels.斑珠蛋白-连环蛋白（plakophilin-catenin）亚家族成员（涵盖Pkp1、Pkp2与Pkp3）可介导桥粒（desmosome）连接组分之间的相互连接（例如将桥粒钙粘蛋白与桥粒斑蛋白（desmoplakin）相连），并将桥粒锚定至中间丝细胞骨架（intermediate-filament cytoskeleton）。Pkp同时还参与桥粒的稳定化过程及其组分的转运。尽管已有证据表明Pkp在mRNA调控、细胞分裂过程中的小GTP酶调控（如中体断裂）以及DNA损伤后的细胞存活中发挥作用，但针对其在桥粒之外的功能的研究尚未得到充分开展。鉴于部分场景下Pkp-连环蛋白可定位于细胞核，且结构相关的连环蛋白（如β-连环蛋白（beta-catenin）与p120连环蛋白（p120-catenin））已被证实具有核内功能，因此Pkp-连环蛋白在细胞核内的活性也日益受到学界关注。进一步而言，随着研究发现Pkp2-连环蛋白与RNA聚合酶III（RNA polymerase III，简称RNA Pol III）、Pkp1与单链DNA（single-stranded DNA）之间存在相互作用，学界对其核内功能的研究兴趣进一步提升。与早期报道提出的Pkp可能在发育过程中发挥核内功能的观点相符，我们此前的研究证实了Pkp3在爪蟾原始外胚层（"动物帽"，animal cap）细胞中具有显著的核定位特征，且近期在小鼠胚胎干细胞中也观察到了类似的定位模式。本研究报道了Pkp3与转录因子Ets变异基因1（Ets variant gene 1，简称ETV1）之间的相互关联与正向功能调控作用；ETV1在神经发育中发挥关键作用，且与人类遗传性疾病密切相关。本研究首次报道了序列特异性转录因子与任意Pkp家族成员之间的相互作用。我们通过非洲爪蟾（Xenopus laevis）胚胎与哺乳动物细胞，从生物化学与功能层面证实了Pkp3与ETV1复合物的存在。