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基因改变。大多数肿瘤来源的p53突变是错义突变，聚集在中心dna结合域内。突变型p53在序列特异性DNA结合和生长抑制方面存在缺陷，这是典型的功能缺失突变。此外，具有完整四聚结构域的突变型p53是显性阴性的，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，称为功能增益。突变型p53的功能获得在携带p53基因的一个空等位基因和一个突变等位基因（R172H或R270H）的敲除小鼠中重现。与p53缺失小鼠相比，这些敲入基因小鼠会产生侵袭性肿瘤。最近，我们和其他人发现携带p53突变体的肿瘤细胞依赖于突变体来生存和抵抗DNA损伤。因此，p53突变体的致癌特性为靶向p53突变体进行癌症治疗提供了理论依据，包括将突变体重新激活为野生型。然而，大量的p53突变（bb0 2,314种突变；：// www.p53.iarc.fr）给开发多功能p53再激活药物带来了重大挑战，特别是考虑到需要修饰和/或物理相互作用才能将突变体转化为野生型。此外，许多p53突变体在稳定后，与其他p53家族肿瘤抑制因子（即p63和p73）结合并抑制，从而增强这些p53突变体的功能增益。因此，我们假设靶向突变型p53的表达对于依赖突变型p53的肿瘤是一种可行的治疗策略。为了进一步解决这一问题，提出了三个具体目标：(1)确定组蛋白去乙酰化酶（hdac），特别是HDAC8如何转录调节突变型p53的表达，以及HDAC8调节突变型p53表达的生物学意义；(2)确定RNPC1调控突变体p53表达的生物学意义，以及在携带突变体p53的人类肿瘤中RNPC1的表达是否受到抑制；(3)确定砷如何调节突变体p53蛋白的稳定性，砷是否能抑制突变体p53诱导的细胞转化和肿瘤进展。

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.