Role of Akt-regulated acetyl-CoA metabolism in altering the cancer cell epigenome

 描述(申请人提供)：组蛋白乙酰化改变在许多人类恶性肿瘤中很明显。在胶质母细胞瘤和其他癌症中，组蛋白乙酰化增加被报道与较差的患者预后相关。一般说来，肿瘤细胞组蛋白的乙酰化是通过依赖于三磷酸腺苷柠檬酸裂解酶(ACLY)将葡萄糖衍生的柠檬酸转化为乙酰辅酶A来调节的，而乙酰辅酶A是蛋白质乙酰化的供体。在低糖条件下，乙酰辅酶A水平降低，成为组蛋白乙酰化的限制物。伴随而来的促生长基因表达的减少反映了全局和启动子特异性组蛋白乙酰化的减少。重要的是，补充醋酸盐可以挽救细胞内乙酰辅酶A、组蛋白乙酰化的池，并恢复促生长基因的表达。这些发现表明，乙酰辅酶A在肿瘤中作为基因表达的直接调节因子发挥作用。然而，这一监管的确切机制尚不清楚。蛋白激酶B(Akt/PKB)通常在癌细胞中被激活，通过磷酸化增加ACLY酶的活性，促进更高的葡萄糖摄取和乙酰辅酶A的产生(S455)。事实上，Akt的激活在体外和体内都会导致ACLY组蛋白乙酰化和磷酸化增加。值得注意的是，在几种癌症类型中，Akt的激活导致持续的组蛋白乙酰化，而与细胞外葡萄糖浓度无关。我们的发现表明，通过Akt激活的肿瘤代谢重新编程通过调节乙酰辅酶A浓度来改变细胞表型。广泛地说，癌基因诱导的乙酰辅酶A依赖的组蛋白乙酰化的改变可能会潜在地影响一些染色质依赖的过程，如基因表达，并在波动的微环境中影响癌细胞的生长和存活。该项目的目标是研究乙酰辅酶A在Akt激活的癌细胞中的作用。线粒体外乙酰辅酶A被用于脂质合成和蛋白质乙酰化。目前尚不清楚在波动的营养条件下，乙酰辅酶A在脂质合成和组蛋白乙酰化之间的分配是否会影响细胞的生长或存活。目标1中的实验将确定乙酰辅酶A是否用于组蛋白乙酰化或脂类 合成是Akt生存计划的贡献者。目标2中的实验将研究乙酰辅酶A浓度调节基因表达的机制。从RNA测序确定的乙酰辅酶A调节基因的列表中，我将确定这些基因的表达是否受乙酰辅酶A的调节，通过基因启动子上的乙酰化和/或通过乙酰化依赖的转录因子招募到染色质来调节。越来越明显的是，乙酰辅酶A位于细胞内代谢和信号过程的中枢，因为它的浓度受到细胞外营养供应和生长因子信号的调节。该项目概述的目标将阐明这些过程对肿瘤生长和生存的贡献。

 DESCRIPTION (provided by applicant): Altered histone acetylation is evident in many human malignancies. In glioblastoma and other cancers, increased histone acetylation is reported to correlate with poorer patient prognosis. Generally, tumor cell histone acetylation is regulated in a glucose-dependent manner, through ATP-citrate-lyase (ACLY)-dependent conversion of glucose-derived citrate into acetyl-CoA, the acetyl-donor for protein acetylation. In low glucose conditions, acetyl-CoA levels decrease and become limiting for histone acetylation. Concomitant decreases in expression of pro-growth genes mirror the reduction in global and promoter-specific histone acetylation. Importantly, supplementation of acetate can rescue intracellular pools of acetyl-CoA, histone acetylation, and restore growth promoting gene expression. These findings suggest that acetyl-CoA functions as a direct regulator of gene expression in tumors. However, the precise mechanisms for this regulation are not clear. Protein kinase B (Akt/PKB) is commonly activated in cancer cells, promoting higher glucose uptake and acetyl-CoA production by increasing ACLY enzymatic activity through phosphorylation (S455). Indeed, Akt activation leads to increased histone acetylation and phosphorylation of ACLY in vitro and in vivo. Notably, Akt activation leads to sustained histone acetylation in several cancer types, regardless of extracellular glucose concentrations. Our findings suggest that tumor metabolic reprogramming via Akt activation alters cellular phenotypes via modulation of acetyl-CoA concentrations. Broadly speaking, oncogene-induced alterations in acetyl-CoA-dependent histone acetylation could potentially impact several chromatin-dependent processes, such as gene expression, and influence cancer cell growth and survival in fluctuating microenvironments. The goals of this project are to examine the role of acetyl-CoA in cancer cells with Akt activation. Extra-mitochondrial acetyl-CoA is utilized in lipid synthesis and protei acetylation. It is unclear whether partitioning of acetyl-CoA between lipid synthesis and histone acetylation in the setting of fluctuating nutrient conditions impacts cell growth or survival. Experiments in aim 1 will determine whether acetyl-CoA utilization for histone acetylation or lipid synthesis is a contributor to Akt's survival program. Experiments in aim 2 will investigate the mechanisms by which acetyl-CoA concentrations modulate gene expression. From a list of top acetyl-CoA regulated genes identified by RNA-sequencing, I will determine whether the expression of these genes are regulated by acetyl-CoA, through acetylation at gene promoters and/or via acetylation-dependent regulation of transcription factor recruitment to chromatin. It i becoming increasingly apparent that acetyl-CoA sits at the hub of both metabolic and signaling processes within the cell, as its concentrations are modulated by both extracellular nutrient availability and growth factor signaling. The aims outlined in this project will shed light on the contribution of these processes to tumor growth and survival.