肿瘤抑制因子p53功能及其抗病毒作用研究进展

肿瘤抑制因子p53 作为基因组的守护者,能通过细胞周期调控和促进细胞凋亡而阻止癌细胞及机体肿瘤的发生,p53还能参与DNA损伤修复、调节机体代谢及调节繁殖生育等功能。除此以外,近年来研究发现,p53能通过促进病毒感染的细胞凋亡而起到抗病毒作用以及p53受IFN的调控和p53作为转录调控因子还能直接转录激活IRF9、IRF5、ISG15和TLR3等抗病毒基因,从而确定了p53在抗病毒反应中起到重要作用。这表明p53可能参与先天性免疫、获得性免疫及炎症反应而起到抗病毒的作用。     

p53蛋白泛素化修饰的研究进展

p53具有抑制肿瘤细胞增殖的作用,但是细胞内p53蛋白的堆积反而加速细胞衰老或凋亡,因此对p53进行严格的调控显得格外重要.泛素化、磷酸化和乙酰化是p53蛋白最主要的几种修饰形式,但近来研究表明泛素化对p53调控发挥着中心作用.MDM2是主要的负调节因子,其具有泛素连接酶的活性,早先的研究认为MDM2的作用主要是特异性结合p53并介导其在蛋白酶作用下降解,但近来的研究发现MDM2还可以介导p53的核-浆交换,这种现象在DNA损伤时尤为明显.推测MDM2介导p53的泛素化在体内可能发挥着多种调控功能.     

线粒体自噬的研究进展

由于线粒体在生物氧化和能量转换过程中会产生活性氧,线粒体DNA又比核DNA更容易发生突变,因此线粒体是一种比较容易受到损伤的细胞器.及时清除细胞内受损的线粒体对细胞维持正常的状态具有重要的作用.细胞主要通过自噬来清除损伤线粒体,维持细胞稳态.越来越多的研究表明,线粒体自噬是一种特异性的过程,线粒体通透性孔道通透性的改变在这个过程中起着重要的作用.线粒体自噬在维持细胞内线粒体的正常功能和基因组稳定性上起着重要作用,但是线粒体发生自噬的信号通路及其调控机制还有待进一步深入研究.     

靶向Rad51与肿瘤治疗的研究进展

DNA损伤反应在维持细胞基因组稳定性和机体存活发挥重要作用。DNA双链断裂(Double strand breaks,DSBs)是DNA损伤最严重的形式。同源重组修复是体内参与DSBs损伤修复的重要机制之一,其中Rad51是体内参与同源重组性DNA修复的关键因子。Rad51在人类的多种肿瘤组织中高表达,如乳腺癌、非小细胞肺癌、前列腺癌等,与肿瘤的转移和恶化相关。如何有效下调肿瘤组织中的Rad51的水平,降低肿瘤细胞的DNA损伤修复能力,从而提高肿瘤治疗的疗效具有潜在的临床应用价值。本文对近年来的一个研究热点靶向Rad51在肿瘤治疗研究中的应用进行综述。     

水生生物体内抗氧化酶及其影响因素研究进展

生物体在新陈代谢过程中,细胞内会产生少量的自由基,参与了机体内多种生理过程,具有重要的生理功能。但是在一些应激因子的作用下,体内产生的活性氧大量积累,将会对细胞产生损伤,抗氧化酶类在清除体内活性氧的过程中具有重要作用。在综述了抗氧化酶的分类、结构特点及相互间作用的基础上,阐述了水生生物体内抗氧化酶及其影响因素的研究进展。     

Gadd45a在抑制细胞转化和肿瘤恶性进展中的作用

Gadd45a,一个受p53和BRCA1调节的生长阻滞和DNA损伤基因,在抑制细胞转化和肿瘤恶性进展中扮演重要的角色.Gadd45a可以通过抑制细胞生长以及促进DNA损伤修复等间接或者直接方式维持基因组稳定性,从而抑制细胞转化和肿瘤的恶性进展.此外,Gadd45a还可通过对一些信号传导通路的调节,参与肿瘤发生发展的抑制.     

未照射条件培养基通过影响活性氧水平引起细胞DNA损伤

转移条件培养基是开展细胞间信号传递研究的常用实验手段。在开展辐射诱导旁效应的研究过程中,我们发现未照射的条件培养基也能够引起细胞DNA损伤,为探索DNA损伤的来源,进行了一系列实验。通过测定细胞活力水平、DNA损伤水平、细胞活性氧水平的变化,发现细胞在接受条件培养基之后,细胞活性氧水平上升,细胞活力下降,细胞内的DNA损伤水平上升。这些结果表明,相对于完全未处理的细胞,源于未进行辐照处理细胞的条件培养基能够影响细胞内的活性氧水平,进而引起受体细胞的DNA损伤。因此,在采用条件培养基转移方法的研究,尤其是涉及活性氧及DNA损伤的研究之中,必须要考虑作为对照的条件培养基对细胞的影响。     

p53基因与DNA修复

DNA的损伤修复是一个多因子参与的、多环节的复杂修复系统。p53基因以多条信号通路,多种调控方式参与DNA修复。它可以通过其下游一系列靶基因p21、gadd45等调控细胞周期,使细胞停滞于G1期、G2期等检测点,从而使受损DNA有足够的时间进行多因子参与的修复过程;也可以与DNA修复因子PRSA、PCNA、XPp48基因等相互作用,直接参与DNA修复;还可以蛋白－蛋白相互作用参与DNA修复。     

超氧化物歧化酶(SOD)研究进展

环境胁迫使植物细胞中积累大量的活性氧,从而导致蛋白质、膜脂、DNA及其它细胞组分的严重损伤。植物体内有效清除活性氧的酶类包括超氧化物歧化酶(SOD)、抗坏血酸过氧化物酶(APX)、过氧化氢酶(CAT)等,其中研究最深入的是SOD。利用基因工程策略增加这些物质在植物体内的含量,从而获得抗逆转基因植株。     

导言

线粒体是细胞内具有双层膜结构和独立基因组DNA的重要细胞器,在细胞生命活动中发挥着至关重要的作用。一方面它们是真核细胞的主要能量工厂,通过有氧代谢产生ATP,为细胞生命活动提供能量;另一方面,线粒体是细胞内活性氧产生中心,同时也是细胞内主要钙库之一,调节细胞内钙信号和细胞生长活动。更为重要的是,线粒体还是细胞凋亡和衰老的调控中心。在细胞凋亡过程中,线粒体释放促凋亡因子（如细胞色素C）,对细胞内凋亡信号进行整合和放大。不言而喻,线粒体在细胞生长、衰老和凋亡等生理、病理过程中扮演着重要的角色。     

ATR/ATM targets are phosphorylated by ATR in response to hypoxia and ATM in response to reoxygenation

The ATR kinase phosphorylates both p53 and Chk1 in response to extreme hypoxia (oxygen concentrations of less than 0.02%). In contrast to ATR, loss of ATM does not affect the phosphorylation of these or other targets in response to hypoxia. However, hypoxia within tumors is often transient and is inevitably followed by reoxygenation. We hypothesized that ATR activity is induced under hypoxic conditions because of growth arrest and ATM activity increases in response to the oxidative stress of reoxygenation. Using the comet assay to detect DNA damage, we find that reoxygenation induced significant amounts of DNA damage. Two ATR/ATM targets, p53 serine 15 and histone H2AX, were both phosphorylated in response to hypoxia in an ATR-dependent manner. These phosphorylations were then maintained in response to reoxygenation-induced DNA damage in an ATM-dependent manner. The reoxygenation-induced p53 serine 15 phosphorylation was inhibited by the addition of N-acetyl-l-cysteine (NAC), indicating that free radical-induced DNA damage was mediated by reactive oxygen species. Taken together these data implicate both ATR and ATM as critical roles in the response of hypoxia and reperfusion in solid tumors.     

c-Myc can induce DNA damage,increase reactive oxygen species,and mitigate p53 function: a mechanism for oncogene-induced genetic instability

Oncogene overexpression activates p53 by a mechanism posited to involve uncharacterized hyperproliferative signals. We determined whether such signals produce metabolic perturbations that generate DNA damage, a known p53 inducer. Biochemical, cytological, cell cycle, and global gene expression analyses revealed that brief c-Myc activation can induce DNA damage prior to S phase in normal human fibroblasts. Damage correlated with induction of reactive oxygen species (ROS) without induction of apoptosis. Deregulated c-Myc partially disabled the p53-mediated DNA damage response, enabling cells with damaged genomes to enter the cycle, resulting in poor clonogenic survival. An antioxidant reduced ROS, decreased DNA damage and p53 activation, and improved survival. We propose that oncogene activation can induce DNA damage and override damage controls, thereby accelerating tumor progression via genetic instability.     

Single-stranded DNA induces ataxia telangiectasia mutant (ATM)/p53-dependent DNA damage and apoptotic signals

Single-stranded DNA has been speculated to be the initial signal in the DNA damage signaling pathway. We showed that introduction of single-stranded DNA with diverse sequences into mammalian cells induced DNA damage as well as apoptosis signals. Like DNA damaging agents, single-stranded DNA up-regulated p53 and activated the nuclear kinase ataxia telangiectasia mutant (ATM) as evidenced by phosphorylation of histone 2AX, an endogenous ATM substrate. Single-stranded DNA also triggered apoptosis as evidenced by the formation of caspase-dependent chromosomal DNA strand breaks, cytochrome c release, and increase in reactive oxygen species production. Moreover, single-stranded DNA-induced apoptosis was reduced significantly in p53 null cells and in cells treated with ATM small interfering RNA. These results suggest that single-stranded DNA may act upstream of ATM/p53 in DNA damage signaling.     

SIRT3 deregulation is linked to mitochondrial dysfunction in Alzheimer's disease

Alzheimer's disease (AD) is the leading cause of dementia in the elderly. Despite decades of study, effective treatments for AD are lacking. Mitochondrial dysfunction has been closely linked to the pathogenesis of AD, but the relationship between mitochondrial pathology and neuronal damage is poorly understood. Sirtuins (SIRT, silent mating type information regulation 2 homolog in yeast) are NAD‐dependent histone deacetylases involved in aging and longevity. The objective of this study was to investigate the relationship between SIRT3 and mitochondrial function and neuronal activity in AD. SIRT3 mRNA and protein levels were significantly decreased in AD cerebral cortex, and Ac‐p53 K320 was significantly increased in AD mitochondria. SIRT3 prevented p53‐induced mitochondrial dysfunction and neuronal damage in a deacetylase activity‐dependent manner. Notably, mitochondrially targeted p53 (mito‐p53) directly reduced mitochondria DNA‐encoded ND2 and ND4 gene expression resulting in increased reactive oxygen species (ROS) and reduced mitochondrial oxygen consumption. ND2 and ND4 gene expressions were significantly decreased in patients with AD. p53‐ChIP analysis verified the presence of p53‐binding elements in the human mitochondrial genome and increased p53 occupancy of mitochondrial DNA in AD. SIRT3 overexpression restored the expression of ND2 and ND4 and improved mitochondrial oxygen consumption by repressing mito‐p53 activity. Our results indicate that SIRT3 dysfunction leads to p53‐mediated mitochondrial and neuronal damage in AD. Therapeutic modulation of SIRT3 activity may ameliorate mitochondrial pathology and neurodegeneration in AD.     

Novel role of p53 in maintaining mitochondrial genetic stability through interaction with DNA Pol gamma

Mitochondrial DNA (mtDNA) mutations and deletions are frequently observed in cancer, and contribute to altered energy metabolism, increased reactive oxygen species (ROS), and attenuated apoptotic response to anticancer agents. The mechanisms by which cells maintain mitochondrial genomic integrity and the reason why cancer cells exhibit more frequent mtDNA mutations remain unclear. Here, we report that the tumor suppressor molecule p53 has a novel role in maintaining mitochondrial genetic stability through its ability to translocate to mitochondria and interact with mtDNA polymerase gamma (pol gamma) in response to mtDNA damage induced by exogenous and endogenous insults including ROS. The p53 protein physically interacts with mtDNA and pol gamma, and enhances the DNA replication function of pol gamma. Loss of p53 results in a significant increase in mtDNA vulnerability to damage, leading to increased frequency of in vivo mtDNA mutations, which are reversed by stable transfection of wild-type p53. This study provides a mechanistic explanation for the accelerating genetic instability and increased ROS stress in cancer cells associated with loss of p53.     

Mechanisms of sulfur mustard analog 2-chloroethyl ethyl sulfide-induced DNA damage in skin epidermal cells and fibroblasts

Employing mouse skin epidermal JB6 cells and dermal fibroblasts, here we examined the mechanisms of DNA damage by 2-chloroethyl ethyl sulfide (CEES), a monofunctional analog of sulfur mustard (SM). CEES exposure caused H2A.X and p53 phosphorylation as well as p53 accumulation in both cell types, starting at 1 h, that was sustained for 24 h, indicating a DNA-damaging effect of CEES, which was also confirmed and quantified by alkaline comet assay. CEES exposure also induced oxidative stress and oxidative DNA damage in both cell types, measured by an increase in mitochondrial and cellular reactive oxygen species and 8-hydroxydeoxyguanosine levels, respectively. In the studies distinguishing between oxidative and direct DNA damage, 1 h pretreatment with glutathione (GSH) or the antioxidant Trolox showed a decrease in CEES-induced oxidative stress and oxidative DNA damage. However, only GSH pretreatment decreased CEES-induced total DNA damage measured by comet assay, H2A.X and p53 phosphorylation, and total p53 levels. This was possibly due to the formation of GSH–CEES conjugates detected by LC-MS analysis. Together, our results show that CEES causes both direct and oxidative DNA damage, suggesting that to rescue SM-caused skin injuries, pleiotropic agents (or cocktails) are needed that could target multiple pathways of mustard skin toxicities.     

The antioxidant function of the p53 tumor suppressor

It is widely accepted that the p53 tumor suppressor restricts abnormal cells by induction of growth arrest or by triggering apoptosis. Here we show that, in addition, p53 protects the genome from oxidation by reactive oxygen species (ROS), a major cause of DNA damage and genetic instability. In the absence of severe stresses, relatively low levels of p53 are sufficient for upregulation of several genes with antioxidant products, which is associated with a decrease in intracellular ROS. Downregulation of p53 results in excessive oxidation of DNA, increased mutation rate and karyotype instability, which are prevented by incubation with the antioxidant N-acetylcysteine (NAC). Dietary supplementation with NAC prevented frequent lymphomas characteristic of Trp53-knockout mice, and slowed the growth of lung cancer xenografts deficient in p53. Our results provide a new paradigm for a nonrestrictive tumor suppressor function of p53 and highlight the potential importance of antioxidants in the prophylaxis and treatment of cancer.