Dynamics of Histone Acetylation in Cancer Cell Physiology

描述(由申请人提供)：我们的实验室发现，全球组蛋白乙酰化水平较低的癌症组织显示出显著的肿瘤复发率或癌症相关死亡率，这一发现已被多个其他实验室独立验证。然而，组蛋白乙酰化的全球变化在正常生物学中的作用及其对癌症表型的影响一直是完全未知的。我们提出的证据表明，全局组蛋白的乙酰化和去乙酰化与醋酸盐和质子进出细胞的共同运输相耦合，有效地使染色质成为细胞内质子负载的调节器，从而调节细胞内的pH(Phi)。在酸性条件下， 组蛋白被整体去乙酰化，由此产生的醋酸酯分子与质子通过单羧酸转运体(MCT)共同运输出细胞，从而降低细胞内的质子负荷。在碱性pH下，组蛋白被全局乙酰化，用来储存醋酸盐分子，并抵抗phi的进一步增加。组蛋白在低pH下的脱乙酰化需要持续的组蛋白脱乙酰酶(HDAC)活性，而不是由于HAT活性的降低。抑制HDAC或MCTs以分别降低醋酸盐的利用率或输出，会降低phi，特别是在酸性微环境中损害phi的维持。因此，组蛋白乙酰化起到了调节phi的变阻器的作用。我们的数据表明了HDAC抑制剂的一种新的作用机制，并提高了组蛋白乙酰化水平较低的癌症组织可能正在分泌醋酸盐和质子以维持相对于细胞外环境的碱性phi的可能性--这是细胞快速分裂的标志。在这项应用中，我们的目标是确定组蛋白乙酰化的全球变化如何映射到基因组的特定区域，以及对基因表达的影响。我们将确定pH诱导组蛋白去乙酰化的机制，并确定主要的MCTs运输由HDACs从染色质中释放的醋酸酯分子。我们还将确定组蛋白乙酰化对pH的响应如何影响癌细胞的致瘤特性。最后，我们将联系MCTs的表达、HDACs的定位和全局组蛋白乙酰化水平，以确定MCTs的临床相关性。 我们的发现。我们的工作将为细胞的染色质和组蛋白乙酰化功能增加一个新的维度。

DESCRIPTION (provided by applicant): Our laboratory has discovered that cancer tissues with lower global levels of histone acetylation display significantly increased rate of tumor recurrence or cancer-related mortality, findings that have been validated independently by multiple other laboratories. However, the function of global changes in histone acetylation in normal biology and how it might contribute to the cancer phenotype have been completely unknown. We present evidence that global histone acetylation and deacetylation is coupled to the co-transport of acetate and protons in and out of the cell, effectively making chromatin a regulator of intracellular proton load, and hence, of intracellular pH (pHi). In acidic conditions, histones are globally deacetylated and the resulting acetate molecules are co-transported with protons out of the cell through the monocarboxylate transporters (MCTs), thereby decreasing the intracellular proton load. At alkaline pH, histones are globally acetylated, serving to store acetate molecules and resisting further increases in pHi. Deacetylation of histones at low pH requires continuous histone deacetylase (HDAC) activity and is not due to compromised HAT activity. Inhibition of HDACs or MCTs to decrease acetate availability or export, respectively, lowers pHi and particularly compromises pHi maintenance in acidic microenvironments. Thus histone acetylation functions as a rheostat to regulate pHi. Our data suggest a novel mechanism of action for HDAC inhibitors and raise the possibility that cancer tissues displaying low levels o histone acetylation may be secreting acetate and protons to maintain an alkaline pHi relative to the extracellular environment-a hallmark of rapidly dividing cells. In this application, we aim to determine how global changes in histone acetylation in response to pH map to specific regions of the genome and the consequences for gene expression. We will determine the mechanism of pH- induced histone deacetylation and identify the main MCTs that transport the acetate molecules that are released from chromatin by HDACs. We will also determine how global changes in histone acetylation in response to pH affect the tumorigenic properties of cancer cells. Finally, we will relate the expression of MCTs, localization of HDACs and global histone acetylation levels in fully-annotated primary cancer tissues to determine the clinical relevance of our findings. Our work will add a novel dimension to the functions chromatin and histone acetylation serve for the cell.