Vitamin D, Metabolic Flux and Breast Cancer

描述（由申请人提供）：大多数癌细胞依靠改变的代谢来维持快速增殖。发生在癌细胞中的“代谢开关”与特定的癌基因和肿瘤抑制因子（myc, p53）有关。表达p53的正常细胞具有高GLS2（磷酸盐活化谷氨酰胺酶）活性，通过TCA循环分流谷氨酸，并提供谷胱甘肽（GSH）合成和抗氧化防御。这些数据表明，谷氨酸通量的调节有助于p53的肿瘤抑制作用，并提出了一种可能性，即模仿p53对代谢的影响的膳食制剂可能有效预防癌症。通过基因组分析，我们确定了SLC1A1（谷氨酸转运蛋白）和GLUL（谷氨酰胺合成酶）是维生素D调节基因，这表明维生素D可能像p53一样通过调节谷氨酸代谢来降低转化风险。假设和目的：我们假设维生素D对SLC1A1和GLUL的调节改变了谷氨酸/谷氨酰胺池，并抑制了与肿瘤发生相关的代谢开关。这一假说预测，维生素D维持高细胞内谷氨酸，以增强线粒体呼吸和TCA循环，促进谷胱甘肽合成。在Aim 1中，25-羟基维生素D （25D）的生理浓度对非转化乳腺细胞中代谢基因表达和谷氨酸/谷氨酰胺代谢的影响将被评估与谷胱甘肽合成和增殖有关。我们还将进行代谢组学分析，以确定维生素D的反应途径。在Aim 2中，我们将开发模拟癌症相关代谢紊乱的细胞模型，以测试25D是否可以预防代谢变化。在Aim 3中，我们将使用动物模型来确定膳食维生素D是否会改变正常乳腺或“高危”乳腺组织中SLC1A1和GLUL的表达/活性，从而与肿瘤预防有关。相关性：虽然一些流行病学研究支持维生素D在乳腺癌预防中的作用，但关于维生素D的具体目标和机制、组织特异性和最佳摄入量以最大限度地降低癌症风险的问题仍然存在。医学研究所最近评估了已发表的关于维生素D和癌症的文献，并确定需要进一步的研究来建立维生素D摄入与癌症预防相关的指导方针。在拟议的项目中，我们将研究乳腺癌小鼠模型中维生素D状态与代谢之间的关系，通过饮食操纵来诱导广泛的血清25D水平，代表人类维生素D缺乏、充足和过剩。虽然我们的饮食研究将在小鼠中进行，但膳食维生素D和血清25D之间的保守关系将为人类人群的外推提供一个起点。

DESCRIPTION (provided by applicant): Most cancer cells rely on altered metabolism to sustain rapid proliferation. The "metabolic switch" that occurs in cancer cells has been linked to specific oncogenes and tumor suppressors (myc, p53). Normal cells expressing p53 have high GLS2 (phosphate-activated glutaminase) activity that shunts glutamate through the TCA cycle and provides for glutathione (GSH) synthesis and antioxidant defense. These data suggest that regulation of glutamate flux contributes to the tumor suppressive actions of p53, and raise the possibility that dietary agents that mimic the effects of p53 on metabolism might be effective in cancer prevention. Through genomic profiling, we identified SLC1A1 (a glutamate transporter) and GLUL (glutamine synthetase) as vitamin D regulated genes suggesting that, like p53, vitamin D might act to reduce risk of transformation by regulation of glutamate metabolism. Hypothesis and Objectives: We hypothesize that regulation of SLC1A1 and GLUL by vitamin D alters glutamate/glutamine pools and suppresses the metabolic switch associated with tumorigenesis. This hypothesis predicts that vitamin D maintains high intracellular glutamate to enhance mitochondrial respiration and the TCA cycle and promote GSH synthesis. In Aim 1, the effects of physiological concentrations of 25- hydroxyvitamin D (25D) on metabolic gene expression and glutamate/glutamine metabolism in non- transformed mammary cells will be assessed in relation to GSH synthesis and proliferation. We will also conduct metabolomics analysis to identify vitamin D responsive pathways. In Aim 2, we will develop cellular models that mimic cancer-associated metabolic disturbances to test whether 25D can prevent changes in metabolism. In Aim 3, we will use animal models to determine whether dietary vitamin D alters SLC1A1 and GLUL expression/activity in normal mammary gland or in "at-risk" mammary tissue in relation to tumor prevention. Relevance: While some epidemiologic studies support a role for vitamin D in breast cancer prevention, questions remain regarding specific targets and mechanisms, tissue specificity, and optimal intakes of vitamin D to maximize potential benefits on cancer risk. The Institute of Medicine recently evaluated published literature on vitamin D and cancer and determined that additional research is needed to establish guidelines for vitamin D intake with respect to cancer prevention. In the proposed project, we will examine the relationship between vitamin D status and metabolism in mouse models of breast cancer using dietary manipulation to induce a wide range of serum 25D levels representative of human vitamin D deficiency, sufficiency and excess. Although our dietary studies will be conducted in mice, the conserved relationship between dietary vitamin D and serum 25D will provide a starting point for extrapolation to human populations.