Mixed Lineage Leukemia 5 (MLL5) Protein Stability Is Cooperatively Regulated by O-GlcNac Transferase (OGT) and Ubiquitin Specific Protease 7 (USP7)
Mixed Lineage Leukemia 5 (MLL5) Protein Stability Is Cooperatively Regulated by O-GlcNac Transferase (OGT) and Ubiquitin Specific Protease 7 (USP7)
复制标题
混合谱系白血病 5 (MLL5) 蛋白质稳定性由 O-GlcNac 转移酶 (OGT) 和泛素特异性蛋白酶 7 (USP7) 协同调节
DOI：
10.1371/journal.pone.0145023
复制
发表时间：
2015-12-17
期刊：
影响因子：
3.7
通讯作者：
Zhang, Yan
中科院分区：
文献类型：
--
作者：
Ding, Xiaodan;Jiang, Wei;Zhang, Yan
混合谱系白血病5 （MLL5）蛋白是一种三胸家族组蛋白3赖氨酸4 （H3K4）甲基转移酶，调节多种生物过程，包括细胞周期进程、造血和癌症。迄今为止，MLL5蛋白稳定性调控的机制仍不清楚。在这里，我们发现MLL5蛋白的稳定性是由O-GlcNAc转移酶（OGT）和泛素特异性蛋白酶7 （USP7）共同调节的。细胞中OGT的消耗通过泛素/蛋白酶体依赖的蛋白水解降解导致MLL5蛋白水平降低，而OGT蛋白的异位表达抑制MLL5泛素化。我们进一步使用质谱法鉴定了去泛素酶USP7是一种新的mll5相关蛋白。USP7通过直接结合和去泛素化来稳定MLL5蛋白。USP7缺失诱导MLL5蛋白降解。相反，USP7的过表达，而不是催化失活的USP7突变体，导致泛素化降低和MLL5稳定性增加。共免疫沉淀和共免疫染色实验显示，MLL5、OGT和USP7相互作用形成稳定的三联物，主要位于细胞核内。此外，MLL5表达上调与OGT和USP7在人原发性宫颈腺癌中的表达升高相关。我们的研究结果共同揭示了MLL5蛋白稳定性调控的一种新的分子机制，并为O-GlcNAc转移酶、去泛素酶和组蛋白甲基转移酶之间的功能相互作用提供了新的见解。
Mixed lineage leukemia 5 (MLL5) protein is a trithorax family histone 3 lysine 4 (H3K4) methyltransferase that regulates diverse biological processes, including cell cycle progression, hematopoiesis and cancer. The mechanisms by which MLL5 protein stability is regulated have remained unclear to date. Here, we showed that MLL5 protein stability is cooperatively regulated by O-GlcNAc transferase (OGT) and ubiquitin-specific protease 7 (USP7). Depletion of OGT in cells led to a decrease in the MLL5 protein level through ubiquitin/proteasome-dependent proteolytic degradation, whereas ectopic expression of OGT protein suppressed MLL5 ubiquitylation. We further identified deubiquitinase USP7 as a novel MLL5-associated protein using mass spectrometry. USP7 stabilized the MLL5 protein through direct binding and deubiquitylation. Loss of USP7 induced degradation of MLL5 protein. Conversely, overexpression of USP7, but not a catalytically inactive USP7 mutant, led to decreased ubiquitylation and increased MLL5 stability. Co-immunoprecipitation and co-immunostaining assays revealed that MLL5, OGT and USP7 interact with each other to form a stable ternary complex that is predominantly located in the nucleus. In addition, upregulation of MLL5 expression was correlated with increased expression of OGT and USP7 in human primary cervical adenocarcinomas. Our results collectively reveal a novel molecular mechanism underlying regulation of MLL5 protein stability and provide new insights into the functional interplay among O-GlcNAc transferase, deubiquitinase and histone methyltransferase.