Regulation of p53 activity through lysine methylation

p53 is a tumour suppressor that regulates the cellular response to genotoxic stresses. p53 is a short-lived protein and its activity is regulated mostly by stabilization via different post-translational modifications. Here we report a novel mechanism of p53 regulation through lysine methylation by Set9 methyltransferase. Set9 specifically methylates p53 at one residue within the carboxyl-terminus regulatory region. Methylated p53 is restricted to the nucleus and the modification positively affects its stability. Set9 regulates the expression of p53 target genes in a manner dependent on the p53-methylation site. The crystal structure of a ternary complex of Set9 with a p53 peptide and the cofactor product S-adenosyl-l-homocysteine (AdoHcy) provides the molecular basis for recognition of p53 by this lysine methyltransferase.     

PML regulates p53 acetylation and premature senescence induced by oncogenic Ras

The tumour suppressor p53 induces cellular senescence in response to oncogenic signals. p53 activity is modulated by protein stability and post-translational modification, including phosphorylation and acetylation. The mechanism of p53 activation by oncogenes remains largely unknown. Here we report that the tumour suppressor PML regulates the p53 response to oncogenic signals. We found that oncogenic Ras upregulates PML expression, and overexpression of PML induces senescence in a p53-dependent manner. p53 is acetylated at lysine 382 upon Ras expression, an event that is essential for its biological function. Ras induces re-localization of p53 and the CBP acetyltransferase within the PML nuclear bodies and induces the formation of a trimeric p53-PML-CBP complex. Lastly, Ras-induced p53 acetylation, p53-CBP complex stabilization and senescence are lost in PML-/- fibroblasts. Our data establish a link between PML and p53 and indicate that integrity of the PML bodies is required for p53 acetylation and senescence upon oncogene expression.     

Delayed ageing through damage protection by the Arf/p53 pathway

The tumour-suppressor pathway formed by the alternative reading frame protein of the Cdkn2a locus (Arf) and by p53 (also called Trp53) plays a central part in the detection and elimination of cellular damage, and this constitutes the basis of its potent cancer protection activity. Similar to cancer, ageing also results from the accumulation of damage and, therefore, we have reasoned that Arf/p53 could have anti-ageing activity by alleviating the load of age-associated damage. Here we show that genetically manipulated mice with increased, but otherwise normally regulated, levels of Arf and p53 present strong cancer resistance and have decreased levels of ageing-associated damage. These observations extend the protective role of Arf/p53 to ageing, revealing a previously unknown anti-ageing mechanism and providing a rationale for the co-evolution of cancer resistance and longevity.     

Fission yeast mod5p regulates polarized growth through anchoring of tea1p at cell tips

Microtubules have a central role in eukaryotic cell polarity, in part through interactions between microtubule end-binding proteins and the cell cortex. In the fission yeast Schizosaccharomyces pombe, microtubules and the polarity modulator tea1p maintain cylindrical cell shape and strictly antipodal cell growth. The tea1p protein is transported to cell tips by association with growing microtubule plus ends; once at cell tips, tea1p releases from microtubule ends and associates with the cell cortex, where it coordinates polarized growth. Here we describe a cortical protein, mod5p, that regulates the dynamic behaviour of tea1p. In mod5Delta cells, tea1p is efficiently transported on microtubules to cell tips but fails to anchor properly at the cortex and thus fails to accumulate to normal levels. mod5p contains a signal for carboxy-terminal prenylation and in wild-type cells is associated with the plasma membrane at cell tips. However, in tea1Delta cells, although mod5p remains localized to the plasma membrane, mod5p is no longer restricted to the cell tips. We propose that tea1p and mod5p act in a positive-feedback loop in the microtubule-mediated regulation of cell polarity.     

p53振子的形成机制及microRNA对p53目标基因表达的精细调控

肿瘤抑制因子p53调控着大量的基因,在肿瘤抑制中起着关键作用.实验结果表明,当DNA受损后,p53的表达呈现周期性振荡.已有的一些p53振子的理论模型,其振子产生机制通常依赖于p53和Mdm2之间相互作用的时滞因素.考虑基因表达的转录和翻译过程,运用动力学方程建模的方法,给出一种新模型,并利用Hopf分叉理论,给出p53振子产生的条件.数值模拟结果表明,与已有的时滞模型相比,该模型对参数具有更好的鲁棒性,较好地解释了p53振子的产生机制.最近的许多实验表明,p53调控着miR-34家族中大量microRNA的表达,这些microRNA又在后转录水平上对p53的下游目标基因起着调控作用.在这一模型基础上,研究microRNA加入p53调控网络后所起的调控作用,数值模拟结果初步表明,microRNA对p53下游目标基因表达起到了精细调控作用.     

Deubiquitination of p53 by HAUSP is an important pathway for p53 stabilization

The p53 tumour suppressor is a short-lived protein that is maintained at low levels in normal cells by Mdm2-mediated ubiquitination and subsequent proteolysis. Stabilization of p53 is crucial for its tumour suppressor function. However, the precise mechanism by which ubiquitinated p53 levels are regulated in vivo is not completely understood. By mass spectrometry of affinity-purified p53-associated factors, we have identified herpesvirus-associated ubiquitin-specific protease (HAUSP) as a novel p53-interacting protein. HAUSP strongly stabilizes p53 even in the presence of excess Mdm2, and also induces p53-dependent cell growth repression and apoptosis. Significantly, HAUSP has an intrinsic enzymatic activity that specifically deubiquitinates p53 both in vitro and in vivo. In contrast, expression of a catalytically inactive point mutant of HAUSP in cells increases the levels of p53 ubiquitination and destabilizes p53. These findings reveal an important mechanism by which p53 can be stabilized by direct deubiquitination and also imply that HAUSP might function as a tumour suppressor in vivo through the stabilization of p53.     

The p53 tumour suppressor gene

The cell cycle is composed of a series of steps which can be negatively or positively regulated by various factors. Chief among the negative regulators is the p53 protein. Alteration or inactivation of p53 by mutation, or by its interactions with oncogene products of DNA tumour viruses, can lead to cancer. These mutations seem to be the most common genetic change in human cancers.     

p53抗体与恶性肿瘤

p53基因是人类肿瘤中突变频率最高的抑癌基因,几乎发生于所有的恶性肿瘤.突变基因编码的p53蛋白释放入血,可诱发机体自身免疫应答,产生p53自身抗体.在肿瘤病人和高危人群中检测血清p53抗体可以反映早期p53基因突变,作为一种新的肿瘤生物学指标,p53抗体有望在恶性肿瘤的早期诊断、治疗、预后、监测、复发等方面发挥重要作用.     

肿瘤抑制基因P53综述

本文从Ｐ５３研究的历史，Ｐ５３的基本分子生物学，Ｐ５３与细胞周期调控，Ｐ５３与肿瘤发生以臁Ｐ５３参与转泉调控来实现其生物学功能等诸方面概述Ｐ５３研究的进展。     

胃癌中p53基因失活及其蛋白产物的免疫组化分析

应用ＰＣＲ－ＳＳＣＰ银染，Ｓｏｕｔｈｅｒｎ杂我及免疫组化等方法同步研究２５例胃癌标本的ｐ５３基因突变，杂合性丢失及蛋白持表达，在２２例胃癌中同时获得有关ｐ５３基因突变和杂合性丢失的检测结果，被检出ｐ５３基因突变的５例胃癌中，２例伴有杂合性丢失，３例仅有ｐ５３基因突变。     

携带p53和p21基因腺病毒转移载体的构建

构建携带p53和p21基因的重组腺病毒转移载体以研究p53和p21联合基因治疗效果.将p53cDNA克隆到转移载体pCMV5GFP替代gfp,得到pCMVp53,使其受到CMV启动子的调控;同时将p21基因克隆到pCMVp53,得到重组腺病毒转移载体pCMVp53/p21.得到携带p53和p21基因的重组腺病毒转移载体.     

NUMB controls p53 tumour suppressor activity

NUMB is a cell fate determinant, which, by asymmetrically partitioning at mitosis, controls cell fate choices by antagonising the activity of the plasma membrane receptor of the NOTCH family. NUMB is also an endocytic protein, and the NOTCH-NUMB counteraction has been linked to this function. There might be, however, additional functions of NUMB, as witnessed by its proposed role as a tumour suppressor in breast cancer. Here we describe a previously unknown function for human NUMB as a regulator of tumour protein p53 (also known as TP53). NUMB enters in a tricomplex with p53 and the E3 ubiquitin ligase HDM2 (also known as MDM2), thereby preventing ubiquitination and degradation of p53. This results in increased p53 protein levels and activity, and in regulation of p53-dependent phenotypes. In breast cancers there is frequent loss of NUMB expression. We show that, in primary breast tumour cells, this event causes decreased p53 levels and increased chemoresistance. In breast cancers, loss of NUMB expression causes increased activity of the receptor NOTCH. Thus, in these cancers, a single event-loss of NUMB expression-determines activation of an oncogene (NOTCH) and attenuation of the p53 tumour suppressor pathway. Biologically, this results in an aggressive tumour phenotype, as witnessed by findings that NUMB-defective breast tumours display poor prognosis. Our results uncover a previously unknown tumour suppressor circuitry.     

携带p53基因重组腺病毒载体的构建

将pCMVp53重组转移载体经BamHI和NheI酶切,得到p53基因cDNA,然后将cDNA片段克隆到转移载体pCMV5GFP,使其受CMV5启动子的调控,获得pCMV5p53重组转移载体.用该线状重组转移载体与腺病毒右臂DNA经磷酸钙共转染293细胞获得重组腺病毒,经酶联免疫吸附法(ELISA)测定p53蛋白含量,证明外源p53基因在含重组腺病毒的293细胞中得到表达.     

Association of p53 codon 72 polymorphism with liver metastases of colorectal cancers positive for p53 overexpression

Objective： To evaluate the association between p53 codon 72 polymorphism （R72P） and the risk ofcolorectal liver metastases. Methods： The p53 R72P genotype was identified by polymerase chain reaction-restriction fragment length polymorphism （PCR-RFLP） method in 78 consecutive colorectal cancer patients with liver metastases and 214 age- and sex-matched cases with nonmetastatic colorectal cancer. Results： The R allele of the p53 R72P polymorphism was more frequently found in metastatic cases than in nonmetastatic cases （P=0.075）. Carriers of the 72R allele had a 2.25-fold （95% CI （confidence interval）=1.05-4.83） increased risk of liver metastases. On the stratification analysis, 72R-carrying genotype conferred a 3.46-fold （95% CI=1.02-11.72） and a 1.05-fold （95% CI=0.36-3.08） increased risk of liver metastases for p53 overexpression-positive and negative colorectal cancers, respectively. Conclusion： These results demonstrate for the first time that the 72R allele of the p53 polymorphism has an increased risk for liver metastases in colorectal cancers positive for p53 overexpression.