Regulation of Mutant P53 Expression and Oncogenic Activity

描述（由申请人提供）：p53突变是人类癌症中最常见的遗传改变。大多数肿瘤源性p53突变是错义突变，并且聚集在中心DNA结合结构域内。突变型p53在序列特异性DNA结合和生长抑制方面有缺陷，这定义了经典的功能缺失突变。此外，具有完整的四聚化结构域的突变体p53是显性负性的，因为突变体可以与野生型p53形成异源四聚体。此外，突变型p53获得额外的活性，称为功能获得。在携带p53基因的一个无效等位基因和一个突变等位基因（R172 H或R270 H）的敲除小鼠中重现突变p53功能的获得。与p53缺失小鼠相比，这些敲入小鼠发展出侵袭性肿瘤。最近，我们和其他人发现，携带突变p53的肿瘤细胞依赖突变体生存和抵抗DNA损伤。因此，突变型p53的致癌特性提供了靶向突变型p53用于癌症治疗的基本原理，包括将突变体重新激活为野生型样的突变体。然而，大量的p53突变（> 2，314种突变类型;：www-p53.iarc.fr）对开发通用的p53再活化药物提出了重大挑战，特别是考虑到需要修饰和/或物理相互作用来将突变体转化为野生型样。此外，许多p53突变体在稳定时与其他p53家族肿瘤抑制因子（即，p63和p73），这将增强这些p53突变体的功能获得。因此，我们假设靶向突变型p53表达是一种可行的治疗策略，肿瘤成瘾突变型p53。为了进一步解决这个问题，提出了三个具体的目标：（1）确定组蛋白脱乙酰酶（HDAC），特别是HDAC 8如何转录调控突变型p53表达以及HDAC 8调控突变型p53表达的生物学意义;（二）为了确定RNPC 1调节突变型p53表达的生物学意义，以及RNPC 1表达在携带突变型p53的人肿瘤中是否受到抑制，突变型p53;以及（3）确定砷如何调节突变型p53蛋白的稳定性以及砷是否能够抑制突变型p53诱导的细胞转化和肿瘤进展。 公共卫生相关性：突变型p53是人类癌症中的主要致癌基因，因为超过50%的肿瘤携带突变型p53。最近，我们和其他人发现，携带突变p53的肿瘤细胞依赖突变体生存和抵抗DNA损伤。这些特性为靶向突变型p53用于癌症治疗提供了理论基础。为了解决这一问题，提出了三个具体的目标，以探讨如何在转录，翻译和蛋白质稳定性的水平上调节突变型p53的表达。因此，拟议的研究与公共卫生高度相关。首先，目的1中提出的研究将揭示突变型p53在HDAC介导的生长抑制中的作用，这可能进一步探索用于癌症治疗。第二，RNPC 1突变型p53通路可能是癌症治疗的靶点。第三，砷是一种治疗急性早幼粒细胞白血病的药物，至少部分原因是PML-RAR？降解，这促使我们研究砷对突变型p53的潜在影响。因此，目标3中的拟议研究将为扩大砷作为药物（或佐剂）用于对突变型p53上瘾的肿瘤提供见解。

DESCRIPTION (provided by applicant): Mutation of p53 is the most frequent genetic alteration in human cancer. The majority of tumor- derived p53 mutations is missense mutation and clustered within the central DNA-binding domain. Mutant p53 is defective in sequence-specific DNA binding and growth suppression, which defines the classical loss of function mutation. In addition, mutant p53 with an intact domain for tetramerization is dominant negative since the mutant can form a heterotetramer with wild-type p53. Moreover, mutant p53 acquires additional activity, called gain of function. Mutant p53 gain of function is recapitulated in knockn mice that carry one null allele and one mutant allele (R172H or R270H) of the p53 gene. These knockin mice develop aggressive tumors compared to p53-null mice. Recently, we and others showed that tumor cells carrying a mutant p53 are addicted to the mutant for survival and resistance to DNA damage. Thus, the oncogenic properties of mutant p53 provide a rationale to target mutant p53 for cancer therapy, including the ones reactivating a mutant into wild-type-like. However, the large number of p53 mutations (> 2,314 types of mutations; ://www-p53.iarc.fr) poses a major challenge to develop versatile p53-reactivating drugs, especially considering that a modification and/or physical interaction is needed to convert a mutant into wild-type-like. Furthermore, a number of p53 mutants, when stabilized, associate with and inhibit other p53 family tumor suppressors (i.e., p63 and p73), which would then enhance gain of function for these p53 mutants. Thus, we hypothesize that targeting mutant p53 expression is a viable therapeutic strategy for tumors addicted to mutant p53. To further address this, three specific aims are proposed: (1) to determine how mutant p53 expression is transcriptionally regulated by histone deacetylases (HDACs), particularly HDAC8 and the biological significance of HDAC8 regulation of mutant p53 expression; (2) to determine the biological significance of RNPC1 regulation of mutant p53 expression and whether RNPC1 expression is suppressed in human tumors carrying a mutant p53; and (3) to determine how mutant p53 protein stability is regulated by arsenic and whether arsenic can suppress mutant p53-induced cell transformation and tumor progression. PUBLIC HEALTH RELEVANCE: Mutant p53 is a leading oncogene in human cancer since more than 50% of tumors carry mutant p53. Recently, we and others showed that tumor cells carrying a mutant p53 are addicted to the mutant for survival and resistance to DNA damage. These properties provide a rationale to target mutant p53 for cancer therapy. To address this, three specific aims are proposed to explore how mutant p53 expression is regulated at the level of transcription, translation, and protein stability. Thus, the proposed study is highly relevant t public health. First, the proposed study in aim 1 will reveal the role of mutant p53 in HDAC inhibitor-mediated growth suppression, which might be further explored for cancer therapy. Second, the RNPC1-mutant p53 pathway might be targeted for cancer therapy. Third, arsenic is a drug to treat acute promyelocytic leukemia at least in part due to degradation of PML-RAR?, which prompts us to examine the potential effect of arsenic on mutant p53. Thus, the proposed study in aim 3 will provide an insight into expanding the use of arsenic as a drug (or an adjuvant) for tumors addicted to mutant p53.