Department of Chemistry and Biochemistry, The University of Texas at Arlington, Arlington, TX 76019, USA.
Br J Cancer. 2012 Jul 10;107(2):315-24. doi: 10.1038/bjc.2012.263. Epub 2012 Jun 19.
Mixed lineage leukaemia-4 (MLL4) is one of the MLL family of histone H3 lysine-4 (H3K4)-specific methyl transferases that have critical roles in gene expression and epigenetics in human. Though MLLs are well recognised as crucial players in histone methylation and gene regulation; little is known about the biochemical functions of MLL4 and its roles in cancer.
Herein, we have investigated the roles of MLL4 in cell viability, cell-cycle progression and explored its potential roles in tumour growth using antisense-mediated knockdown experiments, flow-cytometry analysis, chromatin immunoprecipitation, immunofluorescence staining and animal models.
Our studies demonstrated that knockdown of MLL4 severely affects cell-cycle progression and induces apoptotic cell death in cultured tumour cells. Knockdown of MLL4 induced nuclear condensation, fragmentation, cytochrome-c release from mitochondria to cytosol and activated caspase-3/7 indicating apoptotic cell death. The MLL4 regulates expression of various critical cell-cycle regulatory genes such as cyclin D, cyclin E, p27, HOXA5 and HOXB7 via histone H3K4 trimethylation and recruitment of RNA polymerase II. Interestingly, application of MLL4 antisense suppressed tumour growth in vivo in colon cancer xenograft implanted in nude mouse. The MLL4 antisense specifically knocked down MLL4 in tumour tissue and also downregulated the expression of various growth and angiogenic factors resulting in tumour suppression.
Our results demonstrated that MLL4 is a crucial player in cell viability, cell-cycle progression and is critical for tumour growth in vivo.
混合谱系白血病-4（MLL4）是组蛋白 H3 赖氨酸-4（H3K4）特异性甲基转移酶 MLL 家族的一员，在人类基因表达和表观遗传学中具有关键作用。尽管 MLL 被认为是组蛋白甲基化和基因调控的关键因子，但对 MLL4 的生化功能及其在癌症中的作用知之甚少。
本文通过反义介导的敲低实验、流式细胞术分析、染色质免疫沉淀、免疫荧光染色和动物模型，研究了 MLL4 在细胞活力、细胞周期进展中的作用，并探索了其在肿瘤生长中的潜在作用。
我们的研究表明，MLL4 的敲低严重影响细胞周期进展，并诱导培养肿瘤细胞中的细胞凋亡。MLL4 的敲低诱导核浓缩、碎裂、线粒体细胞色素-c 释放到细胞质中，并激活 caspase-3/7，表明细胞凋亡。MLL4 通过组蛋白 H3K4 三甲基化和 RNA 聚合酶 II 的募集，调节各种关键细胞周期调节基因的表达，如细胞周期蛋白 D、细胞周期蛋白 E、p27、HOXA5 和 HOXB7。有趣的是，MLL4 反义的应用抑制了裸鼠植入结肠癌异种移植瘤的体内肿瘤生长。MLL4 反义物特异性敲低肿瘤组织中的 MLL4，并下调各种生长和血管生成因子的表达，从而抑制肿瘤。
我们的研究结果表明，MLL4 是细胞活力、细胞周期进展的关键调控因子，也是体内肿瘤生长所必需的。
