Homeostatic Regulation of Folate Metabolism

本研究的目的是阐明铁调节叶酸代谢的细胞机制，从而促进细胞内稳态。叶酸是合成核苷酸和s-腺苷甲硫氨酸所必需的。这些产物是许多反应的关键代谢物，包括DNA合成、DNA甲基化、蛋白质合成和细胞信号传导。尽管所有细胞都需要这些产物，但每种细胞类型的叶酸代谢都是根据单碳单位的来源、叶酸进口的机制和个体叶酸相关基因的调节而量身定制的。维生素缺乏、遗传易感性或药物治疗导致叶酸代谢中断，导致血清同型半胱氨酸升高和DNA中尿嘧啶含量增加；导致组织和细胞特异性病理的条件。虽然我们对与叶酸代谢相关的个体生物合成反应了解很多，但对叶酸代谢的调节机制却知之甚少，从而影响细胞过程。本文将阐明铁代谢调节叶酸代谢的生化机制。我们提供的证据表明，丝氨酸羟甲基转移酶（cSHMT）在铁代谢中表现出强大的营养调节作用，并在调节dUMP和同型半胱氨酸的甲基化中发挥关键作用。待验证的主要假设是：(1)cSHMT表达受铁代谢的强烈营养调节。(2)细胞铁通过改变cSHMT表达调节叶酸代谢。(3). cSHMT表达的变化影响人MCF-7细胞中许多基因的表达。该项目的长期目标是：(1)确定细胞调节叶酸代谢的稳态机制。(2)阐明cSHMT表达在叶酸代谢稳态控制中的作用。

The goal of this research is to elucidate the cellular mechanisms whereby iron regulates folate metabolism and thereby facilitates cellular homeostasis. Folate is necessary for the synthesis of nucleotides and s-adenosylmethionine. These products are key metabolites for numerous reactions including DNA synthesis, DNA methylation, protein synthesis, and cell signaling. Although these products are required for all cells, folate metabolism is uniquely tailored in each cell type with respect to the source of single carbon units, the mechanisms of folate import, and the regulation of individual folate-related genes. Disruption of folate metabolism by vitamin deficiency, genetic predisposition or medical therapies leads to elevated serum homocysteine and increased uracil content in DNA; conditions that lead to tissue- and cell-specific pathologies. While we understand much about the individual biosynthetic reactions associated with folate metabolism, less characterized are the mechanisms that regulate folate metabolism, and thereby influence cellular processes. In this proposal, the biochemical mechanisms whereby iron metabolism regulates folate metabolism will be elucidated. We provide evidence that the enzyme serine hydroxymethyltransferase (cSHMT) displays robust nutrient regulation by iron metabolism and plays a key role in regulating the methylation of dUMP and homocysteine. The principle hypotheses to be tested are that: (1). cSHMT expression displays robust nutrient regulation by iron metabolism. (2). cellular iron regulates folate metabolism by altering cSHMT expression. (3). changes in cSHMT expression influence the expression of many genes in human MCF-7 cells. The long-term goals of this project are: (1). to define homeostatic mechanisms used by cells to regulate folate metabolism. (2). to elucidate the role(s) of cSHMT expression in the homeostatic control of folate metabolism.