Role of p53-mediated unconventional functions in tumor suppression

描述（由申请人提供）：越来越多的证据表明，在正常生理条件下，p53在糖酵解、活性氧（ROS）产生和氧化应激反应的调控中起着关键作用。许多研究表明，p53的缺失导致线粒体呼吸减少和糖酵解增强，从而导致Warburg效应。p53还诱导多种抗氧化基因，包括TIGAR和GLS2，以降低活性氧（ROS）的水平。值得注意的是，ROS的产生通过增加8-羟基-22-脱氧鸟苷（8-OH-dG）水平而氧化核苷酸碱基导致DNA损伤。因此，p53的抗氧化活性通过降低ROS水平参与限制DNA损伤。然而，目前尚不清楚p53的这部分功能是否直接促成了p53作为肿瘤抑制因子的作用。我们最近证明了p53的乙酰化是激活细胞周期阻滞和细胞凋亡所必需的。在我们的初步研究中，我们培养了在p53关键乙酰化位点的一个（p53K117R）或三个（p533KR; K117R+K161R+K162R）发生赖氨酸到精氨酸突变的小鼠。虽然p53K117R/K117R细胞具有p53介导的细胞周期阻滞和衰老能力，但不具有凋亡能力，但这三个过程在p533KR/3KR细胞中均被消除。令人惊讶的是，不像p53缺失的小鼠会迅速死于自发性胸腺淋巴瘤，p53K117R/K117R或p533KR/3KR动物中不会发生早发性肿瘤形成。由于小鼠缺乏p533KR/3KR

DESCRIPTION (provided by applicant): There is accumulating evidence indicating that p53 is critical in regulation of glycolysis, reactive oxygen species (ROS) production and oxidative stress responses under normal physiological conditions. A number of studies showed that loss of p53 results in decreased mitochondrial respiration and enhanced glycolysis, leading to the Warburg effect. p53 also induces several antioxidant genes, including TIGAR and GLS2, to reduce the levels of reactive oxygen species (ROS). Notably, ROS production causes DNA damage through oxidation of nucleotide bases by increasing 8-hydroxy-22-deoxyguanosine (8-OH-dG) levels. Thus, antioxidant activities of p53 are involved in limiting DNA damage through reducing ROS levels. Nevertheless, it remains unclear whether this part of p53 functions directly contributes to the role of p53 as a tumor suppressor. We have recently demonstrated that acetylation of p53 is required for its activation of cell cycle arrest and apoptosis. In our preliminary studies, we have generated mice bearing lysine to arginine mutations at one (p53K117R) or three (p533KR; K117R+K161R+K162R) of the critical p53 acetylation sites. While p53K117R/K117R cells are competent for p53-mediated cell-cycle arrest and senescence, but not apoptosis, all three of these processes are ablated in p533KR/3KR cells. Surprisingly, unlike p53-null mice, which rapidly succumb to spontaneous thymic lymphomas, early-onset tumor formation does not occur in either p53K117R/K117R or p533KR/3KR animals. Since p533KR/3KR mice lack p53-mediated cell cycle arrest, apoptosis, and senescence, this observation suggests that other aspects of p53 function are sufficient for suppression of early-onset tumorigenesis. Notably, p533KR retains the ability to transactivate metabolic target genes, such as TIGAR and GLS2, and subsequently suppresses glycolysis and reactive oxygen species (ROS) production. The central hypothesis to be tested here is whether p53-mediated effects in glycolysis, ROS production and oxidative stress responses act as an independent mechanism in tumor suppression in the absence of cell-cycle arrest, apoptosis and senescence. The proposed studies include the following two specific aims. In Aim 1, we will dissect the role of p53 in regulating reactive oxyge species (ROS) production, oxidative stress responses and glycolysis, in the absence of cell cycle arrest, apoptosis and senescence. In Aim 2, we will examine whether p53 mediated effects on reactive oxygen species (ROS) production, DNA oxidation damage and glycolysis are critical in suppressing oncogene-mediated tumorigenesis. PUBLIC HEALTH RELEVANCE: There is accumulating evidence indicating that p53 is critical in regulation of glycolysis, reactive oxygen species (ROS) production and oxidative stress responses under normal physiological conditions. Nevertheless, it remains unclear whether this part of p53 functions directly contributes to the role of p53 as a tumor suppressor. We have recently demonstrated that cell cycle arrest, senescence and apoptosis are not absolutely required for tumor suppression. Furthermore, we found that p53-mutant mice lack p53-mediated cell cycle arrest, apoptosis, and senescence but retain the ability to regulate glycolysis and reactive oxygen species (ROS) production. By using these p53-mutant mice, we will test whether p53-mediated effects in glycolysis, ROS production and oxidative stress responses act as an independent mechanism in tumor suppression in the absence of cell-cycle arrest, apoptosis and senescence.