Department of Pediatrics and Communicable Diseases, University of Michigan Medical School, Ann Arbor, Michigan, USA.
Department of Molecular and Integrative Physiology, University of Michigan Medical School, Ann Arbor, Michigan, USA.
J Pathol. 2018 Jul;245(3):324-336. doi: 10.1002/path.5085. Epub 2018 May 28.
Developmental transcription programs are epigenetically regulated by multi-protein complexes, including the menin- and MLL-containing trithorax (TrxG) complexes, which promote gene transcription by depositing the H3K4me3 activating mark at target gene promoters. We recently reported that in Ewing sarcoma, MLL1 (lysine methyltransferase 2A, KMT2A) and menin are overexpressed and function as oncogenes. Small molecule inhibition of the menin-MLL interaction leads to loss of menin and MLL1 protein expression, and to inhibition of growth and tumorigenicity. Here, we have investigated the mechanistic basis of menin-MLL-mediated oncogenic activity in Ewing sarcoma. Bromouridine sequencing (Bru-seq) was performed to identify changes in nascent gene transcription in Ewing sarcoma cells, following exposure to the menin-MLL interaction inhibitor MI-503. Menin-MLL inhibition resulted in early and widespread reprogramming of metabolic processes. In particular, the serine biosynthetic pathway (SSP) was the pathway most significantly affected by MI-503 treatment. Baseline expression of SSP genes and proteins (PHGDH, PSAT1, and PSPH), and metabolic flux through the SSP were confirmed to be high in Ewing sarcoma. In addition, inhibition of PHGDH resulted in reduced cell proliferation, viability, and tumor growth in vivo, revealing a key dependency of Ewing sarcoma on the SSP. Loss of function studies validated a mechanistic link between menin and the SSP. Specifically, inhibition of menin resulted in diminished expression of SSP genes, reduced H3K4me3 enrichment at the PHGDH promoter, and complete abrogation of de novo serine and glycine biosynthesis, as demonstrated by metabolic tracing studies with C-labeled glucose. These data demonstrate that the SSP is highly active in Ewing sarcoma and that its oncogenic activation is maintained, at least in part, by menin-dependent epigenetic mechanisms involving trithorax complexes. Copyright © 2018 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.
发育转录程序受多蛋白复合物的表观遗传调控，包括含有 menin 和 MLL 的 trithorax（TrxG）复合物，该复合物通过在靶基因启动子处沉积 H3K4me3 激活标记来促进基因转录。我们最近报道，在尤文肉瘤中，MLL1（赖氨酸甲基转移酶 2A，KMT2A）和 menin 过表达，并作为癌基因发挥作用。menin-MLL 相互作用的小分子抑制导致 menin 和 MLL1 蛋白表达的丧失，并抑制生长和致瘤性。在这里，我们研究了 menin-MLL 在尤文肉瘤中介导致癌活性的机制基础。溴尿嘧啶测序（Bru-seq）用于鉴定尤文肉瘤细胞暴露于 menin-MLL 相互作用抑制剂 MI-503 后新生基因转录的变化。menin-MLL 抑制导致代谢过程的早期和广泛重编程。特别是，丝氨酸生物合成途径（SSP）是受 MI-503 处理影响最大的途径。SSP 基因和蛋白质（PHGDH、PSAT1 和 PSPH）的基线表达以及 SSP 的代谢通量在尤文肉瘤中被证实很高。此外，PHGDH 的抑制导致体内细胞增殖、活力和肿瘤生长减少，揭示了尤文肉瘤对 SSP 的关键依赖性。功能丧失研究验证了 menin 和 SSP 之间的机制联系。具体而言，menin 的抑制导致 SSP 基因表达减少，PHGDH 启动子处 H3K4me3 富集减少，以及从头丝氨酸和甘氨酸生物合成完全被阻断，如通过用 C 标记的葡萄糖进行代谢追踪研究所示。这些数据表明 SSP 在尤文肉瘤中高度活跃，其致癌激活至少部分通过涉及 trithorax 复合物的 menin 依赖性表观遗传机制维持。版权所有©2018 英国和爱尔兰病理学学会。由 John Wiley & Sons，Ltd. 出版
