P53-dependent GSTP1 Gene Regulation and Glioma Drug Resistance

描述（由申请人提供）：胶质母细胞瘤（GBM）是人类肿瘤中最致命和对治疗反应最小的肿瘤之一。然而，驱动GBM耐药性的机制仍然没有得到很好的理解，因此难以设计更有效的策略和/或开发新的治疗方法来克服这种耐药性。谷胱甘肽S-转移酶P1（GSTP 1）是一种参与II相代谢和调节细胞信号传导的多功能蛋白质，其在GBM中频繁高表达，大量临床前和临床研究表明其是肿瘤耐药性、治疗失败和患者生存不良的主要决定因素。p53编码一种由多种细胞应激激活的转录因子，所述应激包括由抗癌剂引起的应激。一旦被激活，p53在复杂的细胞网络中起作用，触发下游通路的级联反应，以保护细胞的基因组完整性。p53基因的失活突变和功能获得突变是人类癌症（包括GBM）中最常见的遗传缺陷之一。因此，p53突变状态已被深入研究，无论是在临床前和临床研究中，其在肿瘤对治疗的反应中的作用。然而，这些研究产生了混合的结果，一些研究显示p53突变的存在与耐药性之间存在很强的相关性，而另一些研究则表明野生型p53而不是突变形式与耐药性相关。p53在肿瘤耐药性中的这种明显的相互冲突的作用反映了p53网络的复杂性、p53突变的功能异质性以及下游p53靶点的全谱尚未完全表征的事实。最近，我们提出了挑衅性的发现，人GSTP 1基因包含一个典型的p53结合基序的功能和转录激活的p53在肿瘤细胞中。因此，p53和GSTP 1之间的串扰可能是这两个基因及其编码蛋白的细胞功能的主要组成部分，特别是在保护细胞基因组免受遗传毒性化合物的侵害方面，其中许多是GSTP 1底物。更好地理解和表征p53-GSTP 1相互作用将提供重要的见解，耐药表型的生物学和开发新的策略，以改善化疗的结果的基础。这些发现也可能揭示p53状态和癌症化疗结果之间明显矛盾关系的潜在基础，以及越来越多的人认识到p53在细胞代谢中的关键作用。待检验的假设是，野生型53和功能获得性p53突变体对GSTP 1基因的转录激活将增加GSTP 1基因表达，导致GSTP 1介导的药物代谢增强和MAP激酶信号传导的下游抑制，从而导致胶质母细胞瘤中更具侵袭性的生长和耐药表型。检验这一肿瘤耐药新假说的具体目的是：目的1。确定GBM中p53基因状态和GSTP 1基因转录活性之间的关系;目的2。研究GBM细胞和Aim 3中GST P1基因的p53依赖性转录调控的功能和机制基础。研究p53-GSTP 1串扰对GBM耐药性的影响，并检查这是否可以靶向改善胶质母细胞瘤的治疗效果。

DESCRIPTION (provided by applicant): Glioblastomas (GBMs) are among the deadliest and least responsive of human tumors to therapy. The mechanisms driving GBM drug resistance are, however, still not well understood, thus making it difficult to design more effective strategies and/or to develop novel therapeutics to overcome this resistance. Glutathione S-transferase P1, GSTP1, a multifunctional protein involved in phase II metabolism and in the regulation of cell signaling is frequently highly expressed in GBM and a large number of preclinical and clinical studies have shown it to be a major determinant of tumor drug resistance, treatment failure and poor patient survival. p53 encodes a transcription factor activated by a variety of cellular stresses, including, those inflicted by anti-cancer agents. Once activated, p53 acts in a complex cellular network triggering a cascade of downstream pathways to protect genomic integrity of the cell. Mutations in the p53 gene, both inactivating and gain-of-function, are among the most common genetic defects in human cancer, including, GBM. Consequently, p53 mutational status has been intensively investigated, both preclinically and in clinical studies, for its role in tumor response to therapy. These studies, however, have yielded mixed results, with some showing a strong correlation between the presence of p53 mutations and drug resistance while others have shown that wild-type p53, rather than the mutated form, is associated with drug resistance. This apparent conflicting role of p53 in tumor drug resistance reflects the complexity of the p53 network, the functional heterogeneity of p53 mutations and the fact that the full spectrum of downstream p53 targets has not been fully characterized. Recently, we made the provocative finding that the human GSTP1 gene contains a functional canonical p53 binding motif and is transcriptionally activated by p53 in tumor cells. The crosstalk between p53 and GSTP1 could thus be a major component of the cellular function of these two genes and their encoded proteins, particularly, in the protection of the cellular genome against genotoxic compounds, many of which are GSTP1 substrates. A better understanding and characterization of the p53-GSTP1 interaction will provide important insights into the biology of the resistance phenotype and a basis for developing novel strategies to improve the outcome of chemotherapy. The findings might also shed light on the underlying basis of the apparent conflicting relationship between p53 status and outcome of cancer chemotherapy and the increasing recognition of a critical role for p53 in cellular metabolism. The hypothesis to be tested is that transcriptional activation of the GSTP1 gene by wild-type 53 and gain-of-function p53 mutants will increase GSTP1 gene expression, resulting in enhanced GSTP1-mediated drug metabolism and downstream inhibition of MAP kinase signaling leading to more aggressive growth and a drug resistant phenotype in glioblastomas. The Specific Aims to test this novel hypothesis of tumor drug resistance are: Aim 1. Determine the relationship between p53 gene status and transcriptional activity of the GSTP1 gene in GBM; Aim 2. Investigate the functional and mechanistic basis for the p53-dependent transcriptional regulation of the GSTP1 gene in GBM cells and Aim 3. Investigate the impact of the p53-GSTP1 crosstalk on drug resistance in GBM and examine whether this can be targeted to improve therapeutic efficacy in glioblastoma.