P53-dependent GSTP1 Gene Regulation and Glioma Drug Resistance

描述（由申请人提供）：胶质母细胞瘤（GBMs）是最致命和对治疗反应最迟钝的人类肿瘤之一。然而，驱动GBM耐药的机制仍然没有得到很好的理解，因此很难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 （Glutathione S-transferase P1, GSTP1）是一种参与II期代谢和细胞信号调节的多功能蛋白，在GBM中经常高表达，大量临床前和临床研究表明，GSTP1是肿瘤耐药、治疗失败和患者生存不良的主要决定因素。P53编码一种转录因子，这种转录因子可被多种细胞压力激活，包括抗癌药物造成的细胞压力。一旦被激活，p53在一个复杂的细胞网络中起作用，触发一系列下游通路，以保护细胞的基因组完整性。p53基因的突变，包括失活和功能获得，是包括GBM在内的人类癌症中最常见的遗传缺陷之一。因此，p53突变状态在临床前和临床研究中都被深入研究，以了解其在肿瘤治疗反应中的作用。然而，这些研究得出了不同的结果，一些研究显示p53突变与耐药性之间存在很强的相关性，而另一些研究表明野生型p53而不是突变型p53与耐药性有关。p53在肿瘤耐药中的这种明显的冲突作用反映了p53网络的复杂性，p53突变的功能异质性以及p53下游靶点的全谱尚未完全表征的事实。最近，我们发现人类GSTP1基因含有一个功能性的典型p53结合基序，并在肿瘤细胞中被p53转录激活。因此，p53和GSTP1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基因毒性化合物（其中许多是GSTP1底物）的侵害方面。更好地理解和表征p53-GSTP1相互作用将为耐药表型的生物学提供重要见解，并为开发改善化疗结果的新策略提供基础。这些发现也可能揭示了p53状态与癌症化疗结果之间明显冲突关系的潜在基础，以及p53在细胞代谢中的关键作用日益得到认可。要验证的假设是，野生型53和功能获得型p53突变体转录激活GSTP1基因会增加GSTP1基因的表达，从而增强GSTP1介导的药物代谢和下游MAP激酶信号的抑制，从而导致胶质母细胞瘤更具侵袭性的生长和耐药表型。验证这一新的肿瘤耐药假说的具体目的有：目的1。确定GBM中p53基因状态与GSTP1基因转录活性的关系；目标2。研究GSTP1基因在GBM细胞和Aim 3中p53依赖性转录调控的功能和机制基础。研究p53-GSTP1串扰对GBM耐药的影响，并探讨是否可以靶向提高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.