H3K4 Methyltransferase Activity Is Required for MLL4 Protein Stability.
H3K4 Methyltransferase Activity Is Required for MLL4 Protein Stability.
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DOI：
10.1016/j.jmb.2016.12.016
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发表时间：
2017-06-30
影响因子：
5.6
通讯作者：
Ge K
中科院分区：
文献类型：
--
作者：
Jang Y;Wang C;Zhuang L;Liu C;Ge K
转录增强子在细胞类型特异性基因表达和细胞命运转变中起关键作用。增强子由组蛋白H3 K4单甲基化和二甲基化（H3 K4 me 1/2）标记。肿瘤抑制因子MLL 4（KMT 2D）是一种主要的增强子H3 K4单甲基转移酶和二甲基转移酶，与MLL 3（KMT 2C）具有部分功能冗余。然而，MLL 4酶活性的功能作用仍然难以捉摸。为了解决这个问题，我们已经产生了MLL 4酶死敲入（KI）胚胎干（ES）细胞和小鼠，它们在MLL 4蛋白的酶促SET结构域中携带Y 5477 A/Y5523 A/Y5563 A突变。纯合子MLL 4酶死亡KI（M114 KI/KI）小鼠是胚胎致死的，并且在E10.5左右死亡，其表型复制M114敲除（KO）小鼠。有趣的是，ES细胞中的酶死MLL 4蛋白是高度不稳定的。与M114 KO ES细胞一样，M114 KI/KI ES细胞显示降低的H3 K4 me 1/2水平。此外，我们表明，异位表达组蛋白H3.3赖氨酸4甲硫氨酸（K4 M）突变体，这降低了内源性H3 K4甲基化水平在ES细胞中，降低MLL 3和MLL 4的蛋白质稳定性，但不是H3 K4甲基转移酶SET 1A（KMT 2F）和SET 1B（KMT 2G）。总之，我们的研究结果表明，MLL 4蛋白的稳定性受到其H3 K4甲基转移酶活性的严格调控。
Transcriptional enhancers play a key role in cell type-specific gene expression and cell fate transition. Enhancers are marked by histone H3K4 mono- and di-methylation (H3K4me1/2). The tumor suppressor MLL4 (KMT2D) is a major enhancer H3K4 mono- and di-methyltransferase with a partial functional redundancy with MLL3 (KMT2C). However, the functional role of MLL4 enzymatic activity remains elusive. To address this issue, we have generated MLL4 enzyme-dead knock-in (KI) embryonic stem (ES) cells and mice, which carry Y5477A/Y5523A/Y5563A mutations in the enzymatic SET domain of the MLL4 protein. Homozygous MLL4 enzyme-dead KI (Mll4KI/KI) mice are embryonic lethal and die around E10.5, which pheno-copies Mll4 knockout (KO) mice. Interestingly, enzyme-dead MLL4 protein in ES cells is highly unstable. Like Mll4 KO ES cells, Mll4KI/KI ES cells show reduced levels of H3K4me1/2. Further, we show that ectopic expression of histone H3.3 lysine 4 to methionine (K4M) mutant, which reduces endogenous H3K4 methylation levels in ES cells, decreases protein stability of MLL3 and MLL4 but not that of H3K4 methyltransferases SET1A (KMT2F) and SET1B (KMT2G). Taken together, our findings indicate that MLL4 protein stability is tightly regulated by its H3K4 methyltransferase activity.