Notch Ankyrin Repeat Domain Variation Influences Leukemogenesis and Myc Transactivation

BackgroundThe functional interchangeability of mammalian Notch receptors (Notch1-4) in normal and pathophysiologic contexts such as cancer is unsettled. We used complementary in vivo, cell-based and structural analyses to compare the abilities of activated Notch1-4 to support T cell development, induce T cell acute lymphoblastic leukemia/lymphoma (T-ALL), and maintain T-ALL cell growth and survival. Principal FindingsWe find that the activated intracellular domains of Notch1-4 (ICN1-4) all support T cell development in mice and thymic organ culture. However, unlike ICN1-3, ICN4 fails to induce T-cell acute lymphoblastic leukemia/lymphoma (T-ALL) and is unable to rescue the growth of Notch1-dependent T-ALL cell lines. The ICN4 phenotype is mimicked by weak gain-of-function forms of Notch1, suggesting that it stems from a failure to transactivate one or more critical target genes above a necessary threshold. Experiments with chimeric receptors demonstrate that the Notch ankyrin repeat domains differ in their leukemogenic potential, and that this difference correlates with activation of Myc, a direct Notch target that has an important role in Notch-associated T-ALL. Conclusions/SignificanceWe conclude that the leukemogenic potentials of Notch receptors vary, and that this functional difference stems in part from divergence among the highly conserved ankyrin repeats, which influence the transactivation of specific target genes involved in leukemogenesis.

研究背景 哺乳动物Notch受体（Notch receptors）在正常状态及癌症等病理生理情境中的功能互换性尚未明确。我们结合互补的体内实验、细胞实验与结构分析手段，对比了激活型Notch1-4支持T细胞发育、诱导T细胞急性淋巴细胞白血病/淋巴瘤（T-cell acute lymphoblastic leukemia/lymphoma, T-ALL），以及维持T-ALL细胞生长与存活的能力。
主要研究结果 我们发现，Notch1-4的激活型细胞内结构域（intracellular domains of Notch1-4, ICN1-4）均可在小鼠及胸腺器官培养体系中支持T细胞发育。然而，与ICN1-3不同，ICN4无法诱导T-ALL，也无法挽救依赖Notch1的T-ALL细胞系的生长。ICN4的表型可被弱功能获得型Notch1所模拟，这提示其机制在于无法将一个或多个关键靶基因的转录激活水平提升至必要阈值以上。嵌合受体实验表明，Notch锚蛋白重复序列结构域的致白血病潜能存在差异，且该差异与Myc的激活相关——Myc作为Notch的直接靶标，在Notch相关T-ALL中发挥重要作用。
结论与意义 我们认为，不同Notch受体的致白血病潜能存在差异，这种功能差异部分源于高度保守的锚蛋白重复序列之间的序列分歧，后者可影响致白血病相关特定靶基因的转录激活。