Lee Jeong-Heon, Skalnik David G
Herman B Wells Center for Pediatric Research, Section of Pediatric Hematology/Oncology, Department of Pediatrics, Indiana University School of Medicine, Indianapolis, Indiana 46202, USA.
J Biol Chem. 2005 Dec 16;280(50):41725-31. doi: 10.1074/jbc.M508312200. Epub 2005 Oct 26.
CpG-binding protein (CXXC finger protein 1 (CFP1)) binds to DNA containing unmethylated CpG motifs and is required for mammalian embryogenesis, normal cytosine methylation, and cellular differentiation. Studies were performed to identify proteins that interact with CFP1 to gain insight into the molecular function of this protein. Immunoprecipitation and mass spectrometry reveal that human CFP1 associates with a approximately 450-kDa complex that contains the mammalian homologues of six of the seven components of the Set1/COMPASS complex, the sole histone H3-Lys4 methyltransferase in yeast. In vitro assays demonstrate that the human Set1/CFP1 complex is a histone methyltransferase that produces mono-, di-, and trimethylated histone H3 at Lys4. Confocal microscopy reveals that CFP1 and Set1 co-localize to nuclear speckles associated with euchromatin. A Set1 complex of reduced mass persists in murine embryonic stem cells lacking CFP1. These cells carry elevated levels of methylated histone H3-Lys4 and reduced levels of methylated histone H3-Lys9. Together with the previous finding of reduced levels of cytosine methylation, these data indicate that cells lacking CFP1 contain reduced levels of heterochromatin. Furthermore, ES cells lacking CFP1 exhibit a 4-fold excess of histone H3-Lys4 methylation following induction of differentiation, indicating that CFP1 restricts the activity of the Set1 histone methyltransferase complex. These results reveal a mammalian counterpart to the yeast Set1/COMPASS complex. The presence of CFP1 in this complex implicates this protein as a critical epigenetic regulator of histone modification in addition to cytosine methylation and reveals one mechanism by which this protein intersects with the epigenetic machinery.
CpG结合蛋白（CXXC指蛋白1，CFP1）与含有未甲基化CpG基序的DNA结合，是哺乳动物胚胎发生、正常胞嘧啶甲基化和细胞分化所必需的。本研究旨在鉴定与CFP1相互作用的蛋白质，以深入了解该蛋白的分子功能。免疫沉淀和质谱分析表明，人CFP1与一个约450 kDa的复合物相关联，该复合物包含Set1/COMPASS复合物七个组分中六个组分的哺乳动物同源物，Set1/COMPASS复合物是酵母中唯一的组蛋白H3赖氨酸4甲基转移酶。体外实验表明，人Set1/CFP1复合物是一种组蛋白甲基转移酶，可在赖氨酸4位点产生单甲基化、二甲基化和三甲基化的组蛋白H3。共聚焦显微镜显示，CFP1和Set1共定位于与常染色质相关的核斑点。在缺乏CFP1的小鼠胚胎干细胞中，质量降低的Set1复合物持续存在。这些细胞中甲基化组蛋白H3赖氨酸4的水平升高，而甲基化组蛋白H3赖氨酸9的水平降低。结合之前胞嘧啶甲基化水平降低的发现，这些数据表明缺乏CFP1的细胞中异染色质水平降低。此外，缺乏CFP1的胚胎干细胞在诱导分化后，组蛋白H3赖氨酸4甲基化水平增加了4倍，这表明CFP1限制了Set1组蛋白甲基转移酶复合物的活性。这些结果揭示了酵母Set1/COMPASS复合物在哺乳动物中的对应物。CFP1存在于该复合物中，这表明该蛋白除了参与胞嘧啶甲基化外，还是组蛋白修饰的关键表观遗传调节因子，并揭示了该蛋白与表观遗传机制相互作用的一种机制。
