CHROMATIN ACTIVATION IN RETINOID-INDUCED APOPTOSIS

类维生素A是维生素A的代谢物，对正常细胞和肿瘤细胞的生长、分化和死亡（凋亡）有深远的影响。虽然我们对类维甲酸调节细胞增殖和分化的机制了解甚多，但对类维甲酸诱导细胞凋亡的分子机制了解甚少。为了解决这个问题，我们最近获得了一项RO1拨款（CA76088）来研究类视黄酮诱导细胞凋亡的信号通路。这些研究旨在确定体内细胞凋亡中参与组织转谷氨酰胺酶诱导的类视黄酮受体和信号通路（直接与间接作用）。在提交申请时，尚不可能研究这些作用的分子机制，因为对配体结合与转录激活之间的受体后机制知之甚少。然而，在此期间，这一领域取得了重要进展，发现（部分基于合作研究者的发现）视黄醇受体的配体激活将具有组蛋白乙酰转移酶活性的蛋白质招募到靶基因的启动子上。据推测，继发于组蛋白乙酰化的染色质结构改变可能是配体依赖性转录激活的重要因素。支持这一假设的实验证据主要是在模型系统中收集的。本研究的目标是确定类视黄酮依赖性的染色质乙酰化是否有助于激活类视黄酮诱导的细胞凋亡的基因表达。拟议的研究将涉及两个具体目标。第一个将是表征类维甲酸诱导的髓系白血病细胞染色质结构的变化，在体外进行类维甲酸诱导的细胞凋亡。第二个目的是研究类维生素a对体内指间网退化过程中细胞凋亡中染色质结构的影响。这两项研究的结果应该为体外和体内细胞凋亡中历史性乙酰化和去乙酰化的作用提供新的信息。

Retinoids are metabolites of vitamin A that have profound effects on the growth, differentiation and death (apoptosis) of normal and neoplastic cells. While a lot has been learned of the mechanisms by which retinoids regulate cellular proliferation and differentiation remarkably little is known about the molecular mechanisms involved in retinoid - induced apoptosis. To address this problem, we were recently awarded an RO1 grant (CA76088) to investigate the signaling pathways involved in retinoid-induced apoptosis. These studies were designed to identify the retinoid receptors and signaling pathways (direct versus indirect effects) involved in the induction of the enzyme tissue transglutaminase in cells undergoing apoptosis in vivo. At the time this application was submitted it was not possible to investigate the molecular mechanism of these effects because little was known of the post-receptor mechanisms that linked ligand binding to transcriptional activation. In the interim however important progress has been made in this field with the discovery (based in part on the collaborating investigators findings) that ligand activation of retinoid receptors recruits proteins with histone acetyl transferase activity to the promoter of target genes. It has been hypothesized that alterations in chromatin structure secondary to histone acetylation may be an important contributor to the ligand - dependent activation of transcription. The experimental evidence in support of this hypothesis have been largely gathered in model systems. The goal of the studies included in this proposal will be to determine whether retinoid - dependent acetylation of chromatin contributes to the activation of gene expression in cells undergoing retinoid-induced apoptosis. The proposed studies will address two specific aims. The first will be to characterize retinoid -induced changes in chromatin structure in myeloid leukemia cells undergoing retinoid-induced apoptosis in vitro. The second aim will be to examine the effects of retinoids on chromatin structure in cells undergoing apoptosis during regression of the interdigital webs in vivo. The results of both of these studies should provide novel information on the role of historic acetylation and de-acetylation in cells undergoing apoptosis in vitro and in vivo.