Yashiro-Ohtani Yumi, Wang Hongfang, Zang Chongzhi, Arnett Kelly L, Bailis Will, Ho Yugong, Knoechel Birgit, Lanauze Claudia, Louis Lumena, Forsyth Katherine S, Chen Sujun, Chung Yoonjie, Schug Jonathan, Blobel Gerd A, Liebhaber Stephen A, Bernstein Bradley E, Blacklow Stephen C, Liu Xiaole Shirley, Aster Jon C, Pear Warren S
Abramson Family Cancer Research Institute, Department of Pathology and Laboratory Medicine, and.
Department of Pathology, Brigham and Women's Hospital, Harvard Medical School, Boston, MA 02115;
Proc Natl Acad Sci U S A. 2014 Nov 18;111(46):E4946-53. doi: 10.1073/pnas.1407079111. Epub 2014 Nov 4.
Notch is needed for T-cell development and is a common oncogenic driver in T-cell acute lymphoblastic leukemia. The protooncogene c-Myc (Myc) is a critical target of Notch in normal and malignant pre-T cells, but how Notch regulates Myc is unknown. Here, we identify a distal enhancer located >1 Mb 3' of human and murine Myc that binds Notch transcription complexes and physically interacts with the Myc proximal promoter. The Notch1 binding element in this region activates reporter genes in a Notch-dependent, cell-context-specific fashion that requires a conserved Notch complex binding site. Acute changes in Notch activation produce rapid changes in H3K27 acetylation across the entire enhancer (a region spanning >600 kb) that correlate with Myc expression. This broad Notch-influenced region comprises an enhancer region containing multiple domains, recognizable as discrete H3K27 acetylation peaks. Leukemia cells selected for resistance to Notch inhibitors express Myc despite epigenetic silencing of enhancer domains near the Notch transcription complex binding sites. Notch-independent expression of Myc in resistant cells is highly sensitive to inhibitors of bromodomain containing 4 (Brd4), a change in drug sensitivity that is accompanied by preferential association of the Myc promoter with more 3' enhancer domains that are strongly dependent on Brd4 for function. These findings indicate that altered long-range enhancer activity can mediate resistance to targeted therapies and provide a mechanistic rationale for combined targeting of Notch and Brd4 in leukemia.
Notch对于T细胞发育是必需的，并且是T细胞急性淋巴细胞白血病中常见的致癌驱动因素。原癌基因c-Myc（Myc）是正常和恶性前T细胞中Notch的关键靶点，但Notch如何调节Myc尚不清楚。在这里，我们鉴定出一个位于人类和小鼠Myc基因3'端>1 Mb处的远端增强子，它与Notch转录复合物结合并与Myc近端启动子发生物理相互作用。该区域中的Notch1结合元件以Notch依赖性、细胞背景特异性的方式激活报告基因，这需要一个保守的Notch复合物结合位点。Notch激活的急性变化会导致整个增强子（一个跨越>600 kb的区域）上H3K27乙酰化的快速变化，这与Myc表达相关。这个受Notch广泛影响的区域包含一个增强子区域，该区域包含多个结构域，可识别为离散的H3K27乙酰化峰。尽管在Notch转录复合物结合位点附近的增强子结构域发生了表观遗传沉默，但选择对Notch抑制剂耐药的白血病细胞仍表达Myc。耐药细胞中Myc的非Notch依赖性表达对含溴结构域4（Brd4）的抑制剂高度敏感，这种药物敏感性的变化伴随着Myc启动子与更多3'增强子结构域的优先结合，这些增强子结构域的功能强烈依赖于Brd4。这些发现表明，改变的远程增强子活性可以介导对靶向治疗的耐药性，并为白血病中Notch和Brd4的联合靶向提供了机制依据。
