Lipid Regulation of Hypoxia-inducible Factors

人类拥有复杂的机制来维持器官的营养供应，尽管间歇性的能量消耗。血管向组织输送关键的营养物质，如葡萄糖、氧气和脂质。此外，细胞调节其代谢以匹配营养供应，以维持体内平衡。在实体瘤中，癌细胞也必须适应环境以维持生长；在这种情况下，由于肿瘤扩张超过血液供应，导致缺氧，低营养环境。缺氧诱导因子（HIF）转录因子是正常细胞和癌细胞对低氧适应性反应的中心调节因子。hif在低氧条件下上调，并通过改变细胞增殖、代谢和刺激血管生成对肿瘤缺氧做出反应；所有这些都支持肿瘤的生长和转移。因此，HIF是开发抗癌疗法的主要靶点。脂质如胆固醇和脂肪酸是肿瘤细胞生长所必需的细胞构建块。细胞通过摄取细胞外循环的脂蛋白或通过重新合成获得脂质。与氧一样，由于血清脂蛋白供应减少，以及胆固醇和不饱和脂肪酸的合成需要氧，脂质在血管化不良、缺氧的实体瘤中也受到限制。如何维持脂质供应以支持缺氧肿瘤的生长尚不清楚。在研究人类胰腺导管腺癌肿瘤细胞如何维持脂质供应的过程中，我们发现在氧气存在的情况下，去除血清脂蛋白激活HIF1a和HIF2a。基于这些发现，我们假设脂蛋白通过不同于氧的途径调节HIF转录因子的活性来控制脂质稳态。为了了解脂蛋白如何调节HIF以及HIF激活如何影响细胞稳态，我们提出以下具体目标：鉴定调节HIF信号的脂蛋白成分。目标2。明确脂蛋白调节HIFa的机制。目标3。定义hif依赖性转录和代谢程序对脂蛋白耗竭的响应。目标4。确定脂蛋白信号传导至HIF所需的基因。这些实验将确定脂蛋白是独立于氧的HIF的独特调节剂，支持脂蛋白和氧协调控制葡萄糖代谢、红细胞生成、血管生成和癌症代谢的新模型。此外，这些研究将确定HIF在脂质稳态中的功能，为癌细胞在实体瘤的营养剥夺环境中如何获得脂质提供见解。在本研究中，我们将重点放在培养的胰腺癌细胞上，并首次分析了hif依赖性基因在胰腺中的表达。未来的研究将探讨HIF在其他癌细胞类型、原代细胞和动物中的脂蛋白调节作用。

Humans possess elaborate mechanisms to maintain a supply of nutrients to organs despite intermittent energy consumption. Blood vessels deliver key nutrients to tissues, such as glucose, oxygen, and lipids. Further, cells regulate their metabolism to match nutrient availability in order to maintain homeostasis. In solid tumors, cancer cells must also adapt to maintain growth; in this case, to a hypoxic, low nutrient environment because tumor expansion outpaces blood supply. Hypoxia-inducible factor (HIF) transcription factors are central regulators of the adaptive response to low oxygen in both normal and cancer cells. HIFs are upregulated by low oxygen and respond to tumor hypoxia by altering cell proliferation, metabolism, and stimulating angiogenesis; all of which support tumor growth and metastasis. Consequently, HIF is a primary target for the development of anti-cancer therapeutics. Lipids such as cholesterol and fatty acids are essential cell building blocks required for tumor cell growth. Cells obtain lipid either by uptake from circulating lipoproteins outside the cell or through de novo synthesis. Like oxygen, lipid is limiting in poorly vascularized, hypoxic solid tumors due to the reduced supply of serum lipoprotein and because synthesis of cholesterol and unsaturated fatty acids requires oxygen. How lipid supply is maintained to support growth in hypoxic tumors is not understood. During studies of how human pancreatic ductal adenocarcinoma tumor cells maintain lipid supply, we discovered that removal of serum lipoprotein activates both HIF1a and HIF2a in the presence of oxygen. Based on these findings, we hypothesize that lipoprotein regulates activity of HIF transcription factors through a pathway distinct from oxygen to control lipid homeostasis. To understand how lipoprotein regulates HIF and how HIF activation affects cell homeostasis, we propose the following specific aims: Aim 1. To identify the lipoprotein component that regulates HIF signaling. Aim 2. To define the mechanism of lipoprotein regulation of HIFa. Aim 3. To define HIF-dependent transcriptional and metabolic programs in response to lipoprotein depletion. Aim 4. To identify genes required for lipoprotein signaling to HIF. These experiments will define lipoprotein as a distinct regulator of HIF that is independent from oxygen, supporting a new model in which lipoprotein and oxygen coordinately control glucose metabolism, erythropoiesis, angiogenesis, and cancer metabolism. Furthermore, these studies will define functions for HIF in lipid homeostasis, providing insight into how cancer cells acquire lipid in the nutrient-deprived environment of a solid tumor. In this proposal, we focus on cultured pancreas cancer cells and perform the first analysis of HIF-dependent gene expression in the pancreas. Future studies will investigate lipoprotein regulation of HIF in other cancer cell types, primary cells, and animals.