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.     

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。     

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.     

Selective activation of p53-mediated tumour suppression in high-grade tumours

Non-small cell lung carcinoma (NSCLC) is the leading cause of cancer-related death worldwide, with an overall 5-year survival rate of only 10-15%. Deregulation of the Ras pathway is a frequent hallmark of NSCLC, often through mutations that directly activate Kras. p53 is also frequently inactivated in NSCLC and, because oncogenic Ras can be a potent trigger of p53 (ref. 3), it seems likely that oncogenic Ras signalling has a major and persistent role in driving the selection against p53. Hence, pharmacological restoration of p53 is an appealing therapeutic strategy for treating this disease. Here we model the probable therapeutic impact of p53 restoration in a spontaneously evolving mouse model of NSCLC initiated by sporadic oncogenic activation of endogenous Kras. Surprisingly, p53 restoration failed to induce significant regression of established tumours, although it did result in a significant decrease in the relative proportion of high-grade tumours. This is due to selective activation of p53 only in the more aggressive tumour cells within each tumour. Such selective activation of p53 correlates with marked upregulation in Ras signal intensity and induction of the oncogenic signalling sensor p19(ARF)( )(ref. 6). Our data indicate that p53-mediated tumour suppression is triggered only when oncogenic Ras signal flux exceeds a critical threshold. Importantly, the failure of low-level oncogenic Kras to engage p53 reveals inherent limits in the capacity of p53 to restrain early tumour evolution and in the efficacy of therapeutic p53 restoration to eradicate cancers.     

p53基因调控网络研究进展

肿瘤抑制基因p53表达的p53蛋白是一个通用转录因子,与其上、下游功能相关基因组成了一个复杂的基因调控网络,在这个基因网络中p53基因起着关键作用;DNA损伤、缺氧、原癌基因的激活等均能刺激p53基因表达;p53表达升高后,可通过p53-MDM2反馈环路与泛素系统等对p53表达水平进行精确调节;p53通过调控多种下游/靶基因表达完成多种生物学功能,主要包括阻滞细胞周期、促进细胞凋亡、维持基因组稳定性等;认识p53基因调控网络的功能有助于理解p53及其下游/靶基因间的具体作用机制。     

GCK2软件在p53基因克隆过程中的应用

p53基因是迄今发现与人类肿瘤相关性最高的押癌基因，通过克隆p53基因对其表达调控进行研究。利用分子生物学软件GCK2．0对整个克隆过程进行分析，制定克隆策略，通过测序鉴定结果，得到了舍目的基因p53cDNA全序列的pTRE—p53重组质粒。通过GCK2．0分析，减少了基因克隆的盲目性，提高了工作效率。     

GCK2软件在p53基因克隆过程中的应用

p53基因是迄今发现与人类肿瘤相关性最高的抑癌基因,通过克隆p53基因对其表达调控进行研究。利用 分子生物学软件GCK2.0对整个克隆过程进行分析,制定克隆策略,通过测序鉴定结果,得到了含目的基因 p53cDNA全序列的pTRE-p53重组质粒,通过GCK2.0分析,减少了基因克隆的盲目性,提高了工作效率。     

Localization of gene for human p53 tumour antigen to band 17p13

Recently the gene for the cellular tumour antigen p53, a phosphoprotein found in increased concentration in a variety of human cells, had been mapped to region 17q22 by in situ hybridization techniques and has been shown to translocate to the chromosome carrying the translocation [t(15; 17)] associated with acute promyelocytic leukaemia (APL). Based on this finding it has been postulated that this gene has a role in the pathogenesis of APL. Here we present evidence that the gene for p53 is not located on the long arm of chromosome 17, but maps to band 17p13. We therefore suggest that this gene is not directly involved in the chromosome translocation observed in APL.     

Human p53 gene localized to short arm of chromosome 17

The p53 gene codes for a nuclear protein that has an important role in normal cellular replication. The concentration of p53 protein is frequently elevated in transformed cells. Transfection studies show that the p53 gene, in collaboration with the activated ras oncogene, can transform cells. Chromosomal localization may provide a better understanding of the relationship of p53 to other human cellular genes and of its possible role in malignancies associated with specific chromosomal rearrangements. A recent study mapped the human p53 gene to the long arm of chromosome 17 (17q21-q22) using in situ chromosomal hybridization. Here, by Southern filter hybridization of DNAs from human-rodent hybrids, we have localized the p53 gene to the short arm of human chromosome 17.     

The pathological response to DNA damage does not contribute to p53-mediated tumour suppression

The p53 protein has a highly evolutionarily conserved role in metazoans as 'guardian of the genome', mediating cell-cycle arrest and apoptosis in response to genotoxic injury. In large, long-lived animals with substantial somatic regenerative capacity, such as vertebrates, p53 is an important tumour suppressor--an attribute thought to stem directly from its induction of death or arrest in mutant cells with damaged or unstable genomes. Chemotherapy and radiation exposure both induce widespread p53-dependent DNA damage. This triggers potentially lethal pathologies that are generally deemed an unfortunate but unavoidable consequence of the role p53 has in tumour suppression. Here we show, using a mouse model in which p53 status can be reversibly switched in vivo between functional and inactive states, that the p53-mediated pathological response to whole-body irradiation, a prototypical genotoxic carcinogen, is irrelevant for suppression of radiation-induced lymphoma. In contrast, delaying the restoration of p53 function until the acute radiation response has subsided abrogates all of the radiation-induced pathology yet preserves much of the protection from lymphoma. Such protection is absolutely dependent on p19(ARF)--a tumour suppressor induced not by DNA damage, but by oncogenic disruption of the cell cycle.     

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.     

Mutations in the p53 gene occur in diverse human tumour types

The p53 gene has been a constant source of fascination since its discovery nearly a decade ago. Originally considered to be an oncogene, several convergent lines of research have indicated that the wild-type gene product actually functions as a tumour suppressor gene. For example, expression of the neoplastic phenotype is inhibited, rather than promoted, when rat cells are transfected with the murine wild-type p53 gene together with mutant p53 genes and/or other oncogenes. Moreover, in human tumours, the short arm of chromosome 17 is often deleted. In colorectal cancers, the smallest common region of deletion is centred at 17p13.1; this region harbours the p53 gene, and in two tumours examined in detail, the remaining (non-deleted) p53 alleles were found to contain mutations. This result was provocative because allelic deletion coupled with mutation of the remaining allele is a theoretical hallmark of tumour-suppressor genes. In the present report, we have attempted to determine the generality of this observation; that is, whether tumours with allelic deletions of chromosome 17p contain mutant p53 genes in the allele that is retained. Our results suggest that (1) most tumours with such allelic deletions contain p53 point mutations resulting in amino-acid substitutions, (2) such mutations are not confined to tumours with allelic deletion, but also occur in at least some tumours that have retained both parental 17p alleles, and (3) p53 gene mutations are clustered in four 'hot-spots' which exactly coincide with the four most highly conserved regions of the gene. These results suggest that p53 mutations play a role in the development of many common human malignancies.