Integration of S-adenosylmethionine Metabolism with Epigenetics and Cell Cycle

描述（由申请人提供）：主要甲基供体S-腺苷甲硫氨酸（SAM）由甲硫氨酸和ATP合成，与ATP以外的任何其他分子相比，SAM参与更多的细胞反应。作为所有染色质甲基化事件的辅助因子，SAM对于表观遗传信息的维持和传递至关重要。合理的预测是，细胞系统监测细胞内SAM浓度并防止细胞内SAM的起始。 当SAM水平太低而不能确保S期期间染色质甲基化的忠实复制时，细胞分裂。这个概念让人想起细胞周期检查点的想法，因此我们将其称为SAM检查点。对于我的论文工作，我建议产生一个分子的理解，细胞如何监测细胞内SAM浓度，以及如何将这些信息传递到细胞周期机制，以诱导SAM检查点。我将研究细胞如何监测细胞内SAM水平，以及当SAM水平低于临界阈值浓度时DNA复制如何被阻断。我的假设是，SAM传感与少量“感觉”蛋白质的翻译控制有关。我认为，选择这些感觉蛋白的mRNA在mRNA帽甲基化的水平进行调节。这种调节的机制将通过从经历SAM限制的细胞中纯化N7甲基加帽的mRNA来解决。此外，模型已经开发，这将使我能够解决表观遗传稳定性和饮食限制对表观遗传学的影响的基本问题。为了评估表观遗传稳定性，我将使用经修饰以逃避SAM检查点的酵母报告菌株，并在SAM限制条件下监测酵母细胞的组蛋白甲基化。类似的实验，使用诱导敲低蛋氨酸腺苷转移酶，负责SAM合成的酶，将解决相关的问题，在哺乳动物系统。对于我的论文工作，我建议产生一个分子的理解细胞如何监测细胞内SAM浓度，以及如何将这些信息传递到细胞周期机制，以诱导SAM检查点。这项研究可能会产生一个代谢物调节细胞周期检查点的范例，并将接近表观遗传学的基本问题。我提出的研究将产生第一个洞察代谢途径是如何连接到细胞功能， 分子水平。我的建议特别针对代谢途径的相互作用和表观遗传信息的稳定性。结果可能对我们理解饮食因素和补充剂（如SAMe，叶酸或维生素B12）产生重要影响。我的论文建议将只是开始解决营养不平衡作为一个因素的表观遗传变化。然而，我将开发工具，让其他人扩大对营养素和表观遗传学之间的相互作用的研究。

DESCRIPTION (provided by applicant): The principal methyl-donor S-adenosylmethionine (SAM) is synthesized from methionine and ATP, and participates in more cellular reactions than any other molecule except for ATP. As the co-factor for all chromatin methylation events, SAM is critical for the maintenance and transmission of epigenetic information. It is reasonable to predict a cellular system that monitors intracellular SAM concentrations and prevents initiation of cell division when SAM levels are too low to ensure faithful duplication of chromatin methylation during S-phase. This concept is reminiscent of the cell cycle checkpoint idea and we thus refer to it as the SAM-checkpoint. For my thesis work I propose to generate a molecular understanding for how cells monitor intracellular SAM concentrations and how this information is transmitted to the cell cycle machinery to induce the SAM-checkpoint. I will examine how cells monitor intracellular SAM levels and how DNA replication is blocked when SAM levels fall below a critical threshold concentration. My hypothesis is that SAM sensing is linked to translational control of a small number of "sensory" proteins. I suggest that select mRNAs of these sensory proteins are regulated at the level of mRNA cap methylation. The mechanism of this regulation will be addressed via purification of N7 methyl-capped mRNAs from cells experiencing SAM limitation. Furthermore, models have been developed that will allow me to address fundamental questions about epigenetic stability and the effect of dietary limitations on epigenetics. To assess epigenetic stability I will use yeast reporter strains modified to evade the SAM-checkpoint and monitor histone methylation of yeast cells in SAM limiting conditions. Similar experiments using inducible knock-down of methionine adenosyltransferase, the enzyme responsible for SAM synthesis, will address related questions in the mammalian system. For my thesis work I propose to generate a molecular understanding for how cells monitor intracellular SAM concentrations and how this information is transmitted to the cell cycle machinery to induce the SAM-checkpoint. This research may generate a paradigm for metabolite-regulated cell cycle checkpoints and will approach fundamental questions about epigenetics. My proposed studies will generate a first insight into how metabolic pathways are connected to cell function at the molecular level. My proposal specifically addresses the interaction of metabolic pathways and stability of epigenetic information. Results may have important consequences for our understanding of dietary factors and supplements such as SAMe, folates, or vitamin B12. My thesis proposal will only begin to address nutrient imbalance as a factor of epigenetic changes. However, I will develop tools to allow others to expand research on the interaction between nutrients and epigenetics.