1] Laboratory of Biochemistry and Molecular Biology, Rockefeller University, New York, New York, USA. [2] Department of Biochemistry and Molecular Genetics, University of Alabama at Birmingham, Birmingham, Alabama, USA. [3] UAB Stem Cell Institute, University of Alabama at Birmingham, Birmingham, Alabama, USA. [4].
Nat Struct Mol Biol. 2013 Oct;20(10):1156-63. doi: 10.1038/nsmb.2656. Epub 2013 Sep 1.
Although histone H3 Lys4 (H3K4) methylation is widely associated with gene activation, direct evidence for its causal role in transcription, through specific MLL family members, is scarce. Here we have purified a human MLL2 (Kmt2b) complex that is highly active in H3K4 methylation and chromatin transcription in a cell-free system. This effect requires S-adenosyl methionine and intact H3K4, thus establishing a direct and causal role for MLL2-mediated H3K4 methylation in transcription. We also show that human AKAP95, a chromatin-associated protein, physically and functionally associates with MLL complexes and directly enhances their methyltransferase activity. Ectopic AKAP95 stimulates expression of a chromosomal reporter gene in synergy with MLL1 or MLL2, whereas AKAP95 depletion impairs retinoic acid-mediated gene induction in embryonic stem cells. These results demonstrate an important role for AKAP95 in regulating histone methylation and gene expression, particularly during cell-fate transitions.
尽管组蛋白 H3 赖氨酸 4（H3K4）甲基化与基因激活广泛相关，但通过特定的 MLL 家族成员直接证明其在转录中的因果作用仍然很少。在这里，我们纯化了一种人 MLL2（Kmt2b）复合物，该复合物在无细胞系统中具有高度的 H3K4 甲基化和染色质转录活性。这种效应需要 S-腺苷甲硫氨酸和完整的 H3K4，从而确立了 MLL2 介导的 H3K4 甲基化在转录中的直接和因果作用。我们还表明，人 AKAP95，一种染色质相关蛋白，与 MLL 复合物在物理和功能上相互作用，并直接增强其甲基转移酶活性。异位 AKAP95 与 MLL1 或 MLL2 协同刺激染色体报告基因的表达，而 AKAP95 耗尽则会损害胚胎干细胞中视黄酸介导的基因诱导。这些结果表明 AKAP95 在调节组蛋白甲基化和基因表达，特别是在细胞命运转变过程中具有重要作用。
