Requirement of DNMT1 to orchestrate epigenomic reprogramming for NPM-ALK driven lymphomagenesis [RNA-Seq]. Requirement of DNMT1 to orchestrate epigenomic reprogramming for NPM-ALK driven lymphomagenesis [RNA-Seq]

Malignant transformation depends on genetic and epigenetic events that result in a burst of deregulated gene expression and chromatin changes. To dissect the sequence of events in this process, we used a T cell-specific lymphoma model based on the human oncogenic NPM-ALK translocation. We find that transformation of T cells shifts thymic cell populations to an undifferentiated immunophenotype, which occurs only after a period of latency, accompanied by induction of the MYC-NOTCH1 axis and deregulation of key epigenetic enzymes. We discover aberrant DNA methylation patterns, overlapping with regulatory regions, plus a high degree of epigenetic heterogeneity between individual tumors. In addition, ALK positive tumors show a loss of associated methylation patterns of neighboring CpG sites. Notably, deletion of the maintenance DNA methyltransferase DNMT1 completely abrogates lymphomagenesis in this model, despite oncogenic signaling through NPM-ALK, suggesting that faithful maintenance of tumor-specific methylation through DNMT1 is essential for sustained proliferation and tumorigenesis Overall design: Evaluation of gene expression and DNA methylation signatures in a transgenic mouse model of ALCL

恶性转化的发生依赖于遗传与表观遗传事件，此类事件可引发基因表达失调与染色质改变的大规模扰动。为解析该过程中的事件时序，我们构建了基于人类致癌性NPM-ALK（nucleophosmin-anaplastic lymphoma kinase）易位的T细胞特异性淋巴瘤模型。我们发现，T细胞恶性转化可将胸腺细胞群转变为未分化免疫表型，该转变仅在经历一段潜伏期后发生，同时伴随MYC-NOTCH1信号轴的激活与关键表观遗传酶的表达失调。我们还发现异常DNA甲基化模式与调控区域存在重叠，且不同个体肿瘤之间存在高度表观遗传异质性。此外，ALK阳性肿瘤会出现相邻CpG位点的关联甲基化模式缺失现象。值得注意的是，尽管存在通过NPM-ALK介导的致癌信号通路，维持性DNA甲基转移酶DNMT1（DNA methyltransferase 1）的基因敲除可完全抑制该模型中的淋巴瘤发生，这表明通过DNMT1精准维持肿瘤特异性甲基化模式，对于肿瘤细胞持续增殖与肿瘤发生至关重要。整体实验设计：在ALCL（间变性大细胞淋巴瘤，anaplastic large cell lymphoma）转基因小鼠模型中评估基因表达与DNA甲基化特征。