以任何方法剪接:Mdm2位于肿瘤监视的十字路口

鼠双微基因2(Mdm2)是p53最重要的调节基因,同时也是对各种类型细胞应激(包DNA损害和致癌损伤)的主要应答者.尽管已有文章描述了Mdm2基因的替代产物的异常拼接产物,但是关于该变异体的起源、功能和影响,现在尚不清楚.最近发现了一种新的mdm2基因的剪接形式.在该剪接体中,108bp的基因内序列合并到成熟的Mdm2 mRNA中.编码框内终止密码子的额外序列可使Mdm2蛋白明显缩短.最有趣的现象是,阿霉素和放线菌素D能诱导产生一种交替剪接形式,即成熟的Mdm2 108,而其他的DNA损伤剂没有这种诱导作用.Mdm2 108基因可诱导p53的大量快速聚集,证明该交替剪接事件的作用是形成p53的肿瘤监视途径,同时抑制细胞的增殖(该细胞为被有效的遗传毒性化合物所破坏的细胞).     

核糖体蛋白与肿瘤

核糖体由核糖体蛋白和核糖体RNA组成,是蛋白质生物合成的重要场所.核糖体蛋白参与蛋白质的翻译过程,核糖体蛋白和核糖体RNA的表达紊乱将激活核糖体蛋白的核糖体外功能,该功能在肿瘤的发生发展过程中发挥重要作用.核糖体蛋白有望作为生物标志物或治疗靶点用于肿瘤的早期诊断和治疗中.     

Expression of DNA damage response proteins and complete remission after radiotherapy of stage IB-IIA of cervical cancer

The primary aim of this study was to investigate if the expression of the DNA damage identifying protein DNA-PKcs known to be involved in DNA repair after treatment with ionising radiation can be used as a predictive marker for radiotherapy (RT) response in cervical cancer. Formalin-fixed primary tumour biopsies from 109 patients with cervical cancer, FIGO-stage IB-IIA, treated with preoperative brachytherapy followed by radical surgery were analysed by immunohistochemistry. In addition, correlation studies between early pathological tumour response to radiation and expression of Ku86, Ku70, Mdm-2, p53 and p21 in primary tumours were also performed. We found that tumour-transformed tissue shows positive immunostaining of DNA-PKcs, Ku86 and Ku70, while non-neoplastic squamous epithelium and tumour-free cervix glands show negative immunoreactivity. Expression of DNA-PKcs positively correlated with both Ku86 and Ku70, and a statistically significant correlation between the Ku subunits was also found. After RT, 85 patients demonstrated pathologic complete remission (pCR), whereas 24 patients had residual tumour in the surgical specimen (non-pCR). The main finding of our study is that there was no correlation between the outcome of RT and the expression of DNA-PK subunits. Positive p53 tumours were significantly more common among non-pCR cases than in patients with pCR (P=0.031). Expression of p21 and Mdm-2 did not correlate with the outcome of RT.     

Mdm2: Open questions

The Mdm2 oncoprotein and its association with p53 were discovered 30 years ago, and a cornucopia of activities and regulatory pathways have been associated with it. In this review, we will raise questions about Mdm2 and its cousin Mdm4 that we consider worth pursuing in future research, reaching from molecular structures and intracellular activities all the way to development, evolution, and cancer therapy. We anticipate that such research will not only close a few gaps in our knowledge but could add new dimensions to our current view. This compilation of questions contributes to the preparation for the 10th Mdm2 Workshop in Tokyo.     

ARF-BP1 as a potential therapeutic target

In this review, we discuss the recent identification of ARF-BP1 (also known as Mule, UREB1, E3(histone), LASU1, and HectH9). ARF-BP1, a HECT domain-containing E3 ubiquitin ligase, interacts with ARF and p53. Its ubiquitin ligase activity is inhibited by ARF. Inactivation of ARF-BP1 stabilised p53 and induced apoptosis. Notably, inactivation of ARF-BP1 also caused cell growth repression in p53-null cells and breast cancer cells with mutant p53. Thus, ARF-BP1 emerges as a novel therapeutic target against cancer regardless of p53 status.     

Mouse models of Mdm2 and Mdm4 and their clinical implications

Mdm2 and Mdm4 are two key negative regulators of the tumor suppressor p53. Deletion of either Mdm2 or Mdm4 induces p53-dependent early embryonic lethality in knockout mouse models. The tissue-specific ...     

Updates on p53: modulation of p53 degradation as a therapeutic approach

The p53 pathway is aberrant in most human tumours with over 50% expressing mutant p53 proteins. The pathway is critically controlled by protein degradation. Here, we discuss the latest developments in the search for small molecules that can modulate p53 pathway protein stability and restore p53 activity for cancer therapy.     

星形细胞瘤中Mdm2、p53的表达及调控机制探讨

 目的　探讨不同组织病理分级的星形细胞瘤中Mdm2、p5 3的表达水平 ,并从蛋白质水平分析在肿瘤细胞中p5 3/Mdm2负反馈调节机制紊乱的原因。方法　采用免疫组织化学方法检测 6 8例星形细胞瘤标本中Mdm2和 p5 3的表达水平。 结果　星形细胞瘤中Mdm2和 p5 3的表达率分别是4 1.2 %( 2 8/ 6 8)和 4 5 .6 % ( 31/ 6 8) ,随着肿瘤恶性程度的增加 ,Mdm2、p5 3的表达率呈上升趋势 ,Spearman等级相关分析显示 ,Mdm2、p5 3的表达与肿瘤分级呈正相关。Mdm2表达和p5 3一致表达符合率达6 6 .2 %( 4 5 / 6 8) ,两者的表达密切相关 (P <0 .0 5 ) ,Spearman等级相关分析Mdm2表达与 p5 3表达呈正相关 (P<0 .0 1)。结论　Mdm2、p5 3的表达与星形细胞瘤组织病理分级呈正相关。Mdm2的表达与 p5 3的表达存在一致性 ,两者的联合表达是肿瘤高度恶性的生物学标志。     

HCV C蛋白、p53、Mdm2、p14和p21在原发性肝癌中的表达及相关性

目的:研究原发性肝癌(HCC)组织中核心蛋白、突变p53、Mdm2、p14和p21的表达及其相关性,探讨HCV核心蛋白对突变p53、Mdm2、p14和p21表达影响及临床意义。方法:收集42例HCC石蜡组织,采用免疫组织化学EnVision法检测HCC组织中核心蛋白、突变p53、Mdm2、p14和p21的表达,用统计学方法及临床联系分析它们之间的关系。结果:核心蛋白、突变p53、Mdm2、p14和p21的阳性表达主要定位于细胞核中;HCC组织中核心蛋白、突变p53、Mdm2、p14和p21阳性率分别为40.5%、47.62%、75.57%、45.24%、19.05%;5组间的Kruskal-Wallis检验P=0.000,差异显著,核心蛋白与突变p53、Mdm2、p14和p21间的Mann-WhitneyU秩和检验P值分别为0.043、0.009、1.0、0.023;HCVC蛋白与突变p53、p14、p21阳性强度两者间相关性Spearman检验P值分别为0.000、0.000、0.43,相关系数rs分别为0.67、0.64、-0.29;p53和Mdm2、p21阳性强度间相关性Spearman检验p值为0.000、0.174,rs分别为0.72、-0.45。结论:在HCV感染的HCC中HCVC蛋白可能促进野生p53突变和表达,p14的表达与C蛋白有关联;突变p53和p14很可能促进Mdm2的表达;HCC中p21表达缺陷是十分常见的,HCV相关的HCC主要与p53通路改变有关,C蛋白可能下调p21的表达。因此,HCV相关的HCC中C蛋白、突变p53、Mdm2很可能促进肝细胞增生或恶性生长。     

Mdm2-SNP309 polymorphism in prostate cancer: no evidence for association with increased risk or histopathological tumour characteristics

The search for inherited cancer susceptibility factors is a major focus of epidemiologic cancer studies. Analyses of single-nucleotide polymorphisms (SNP) in a variety of genes revealed a correlation between a specific allele variant and cancer predisposition. Human mouse double-minute 2 protein (Mdm2) is a cellular E3 ligase capable of ubiquitination and degradation of p53. Therefore, Mdm2 is a crucial factor of cell cycle control and cell survival. The Mdm2 promoter SNP309 was shown to increase Mdm2 expression and can, thereby, inhibit the p53 pathway. This SNP was found to be associated with increased risk and early onset of various malignancies. For prostate cancer no studies are reported to date. In a case-control study we determined the distribution of the Mdm2 SNP309 in 145 male subjects with prostate cancer and in 124 male controls without any malignancy using RFLP analysis. Cases and controls showed a similar distribution of the SNP (P=0.299). Genotype distribution showed neither an association with histopathological characteristics of the tumours nor with prognosis. Age at disease onset was also not modified by the SNP. This first study of the Mdm2 SNP309 in prostate cancer patients suggests no correlation between a certain allelic variant and an increased cancer risk.     

Selective inhibition of histone deacetylase 2 induces p53-dependent survivin downregulation through MDM2 proteasomal degradation

In the present study, we found that selective inhibition of histone deacetylase 2 (HDAC2) with small inhibitory RNA (siRNA) induced survivin downregulation in a p53-dependent manner. Interestingly, suberoylanilide hydroxamic acid (SAHA) or knockdown of HDAC2 induced downregulation of Mdm2, a negative regulator of p53, at the protein level. SAHA and/or HDAC2 siRNA increased Mdm2 ubiquitination, and MG132, an inhibitor of proteosome function, prevented HDAC2 inhibition-induced degradation of Mdm2. Clinically, the mRNA levels of HDAC2 and survivin were prominently overexpressed in lung cancer patients compared to normal lung tissues. Silencing of HDAC2 enhanced the cell death caused by ionizing radiation in lung cancer cells. Collectively, our results indicate that selective inhibition of HDAC2 causes survivin downregulation through activation of p53, which is mediated by downregulation of Mdm2. They further suggest that HDAC2 may exert a dominant effect on lung cancer cell survival by sustaining Mdm2-survivin levels.     

Anti-diol epoxide of benzo[a]pyrene induces transient Mdm2 and p53 Ser15 phosphorylation, while anti-diol epoxide of dibenzo[a,l]pyrene induces a nontransient p53 Ser15 phosphorylation

The polycyclic aromatic hydrocarbons (PAHs) dibenzo[a,l]pyrene (DBP) and benzo[a]pyrene (BP) are environmental contaminants and potent carcinogens. DBP is several orders of magnitude more mutagenic/carcinogenic than BP. This can be ascribed to differences in DNA binding efficiency of their ultimate carcinogenic bay- and fjord-region diol epoxide (DE) intermediates, differences in structural features of the DNA adducts and differences in DNA adduct recognition and the subsequent downstream signaling. In this study, we have characterized the effect of the ultimate carcinogenic DEs, (+)-anti-BPDE and (-)-anti-DBPDE following short exposure times, on Mdm2 and p53 pathway in A549 human lung epithelial carcinoma cells. In contrast to (-)-anti-DBPDE, (+)-anti-BPDE induces stabilization of phosphorylated Mdm2. (+)-anti-BPDE-induced effects on Mdm2 were transient and correlated with transient p53 Ser15 phosphorylation. DNA adducts of (-)-anti-DBPDE are more refractory to removal by nucleotide excision repair (NER) than adducts of (+)-anti-BPDE and do not induce Mdm2 phosphorylation. This suggests a role of phosphorylated Mdm2 in the repair process. In addition, (-)-anti-DBPDE, in contrast to (+)-anti-BPDE, induced prolonged p53 Ser15 phosphorylation as well as phosphorylation of p53 at Ser46, a phosphorylation site associated with apoptosis. It is also concluded that p53 Ser15 phosphorylation and antibody 2A10-site specific Mdm2 alterations are induced by nonidentical signaling pathways by the bay- and fjord-region DE. These differences may reflect the different carcinogenic potential of these compounds.     

Proliferation- and Apoptosis-related Proteins in Intracranial Ependymomas: An Immunohistochemical Analysis

As the value of grading of ependymomas is currently debated we studied the expression of proliferation- and apoptosis-related proteins in these tumors as these mechanisms both are suggested to be important in tumor growth. We characterized the immunohistochemical expression of p53, Mdm2, Bcl-2, and Bax in 51 intracranial ependymomas. We also assessed the apoptosis- and proliferation-index, measured by MIB-1, PCNA-immunohistochemistry, and analyzed the clinical parameters. Of all used antibodies, the correlation with survival and the correlation among ordered categories was assessed. None of the analyzed immunohistochemical variables were significantly correlated with tumor grade. On the other hand, PCNA, MIB-1, and p53 were significantly related to the survival of the patient. In multivariate analysis, p53 was the only independent predictive variable (p = 0.0132). Conclusion: The strongest predictors of survival in univariate analysis were the expression of PCNA, MIB-1 and p53. In multivariate analysis a p53 expression >1% showed to be significantly related with a worse survival. The predicting value of p53 expression has to be confirmed by others before solid conclusions can be made. Apoptosis seems not to be an important mechanism in tumor growth in ependymomas. The expression of Mdm2, Bcl-2, and Bax were not related to survival.     

Mutant p53 accumulates in cycling and proliferating cells in the normal tissues of p53 R172H mutant mice

The tumour suppressor p53 is regulated primarily at the protein level. In normal tissues its levels are maintained at a very low level by the action of specific E3 ligases and the ubiquitin proteosome pathway. The mutant p53 protein contributes to transformation, metastasis and drug resistance. High levels of mutant p53 can be found in tumours and the accumulation of mutant p53 has previously been reported in pathologically normal cells in human skin. We show for the first time that similarly elevated levels of mutant p53 can be detected in apparently normal cells in a mutant p53 knock-in mouse model. In fact, in the small intestine, mutant p53 spontaneously accumulates in a manner dependent on gene dosage and cell type. Mutant p53 protein is regulated similarly to wild type p53, which can accumulate rapidly after induction by ionising radiation or Mdm2 inhibitors, however, the clearance of mutant p53 protein is much slower than wild type p53. The accumulation of the protein in the murine small intestine is limited to the cycling, crypt base columnar cells and proliferative zone and is lost as the cells differentiate and exit the cell cycle. Loss of Mdm2 results in even higher levels of p53 expression but p53 is still restricted to proliferating cells in the small intestine. Therefore, the small intestine of these p53 mutant mice is an experimental system in which we can dissect the molecular pathways leading to p53 accumulation, which has important implications for cancer prevention and therapy.     

Pharmacological inhibition of Mdm2 triggers growth arrest and promotes DNA breakage in mouse colon tumors and human colon cancer cells

The p53 tumor suppressor protein performs a number of cellular functions, ranging from the induction of cell cycle arrest and apoptosis to effects on DNA repair. Modulating p53 activity with Mdm2 inhibitors is a promising approach for treating cancer; however, it is presently unclear how the in vivo application of Mdm2 inhibitors impact the myriad processes orchestrated by p53. Since approximately half of all colon cancers (predominately cancers with microsatellite instability) are p53-normal, we assessed the anticancer activity of the Mdm2 inhibitor Nutlin-3 in the mouse azoxymethane (AOM) colon cancer model, in which p53 remains wild type. Using a cell line derived from an AOM-induced tumor, we found that four daily exposures to Nutlin-3 induced persistent p53 stabilization and cell cycle arrest without significant apoptosis. A 4-day dosing schedule in vivo generated a similar response in colon tumors; growth arrest without significantly increased apoptosis. In adjacent normal colon tissue, Nutlin-3 treatment reduced both cell proliferation and apoptosis. Surprisingly, Nutlin-3 induced a transient DNA damage response in tumors but not in adjacent normal tissue. Nutlin-3 likewise induced a transient DNA damage response in human colon cancer cells in a p53-dependent manner, and enhanced DNA strand breakage and cell death induced by doxorubicin. Our findings indicate that Mdm2 inhibitors not only trigger growth arrest, but may also stimulate p53's reported ability to slow homologous recombination repair. The potential impact of Nutlin-3 on DNA repair in tumors suggests that Mdm2 inhibitors may significantly accentuate the tumoricidal actions of certain therapeutic modalities.     

胰腺癌中P53通路相关蛋白的表达及其临床意义

背景与目的:P53通路在胰腺癌的发生发展中发挥重要作用,然而关于此通路是如何启动、如何作用的研究较少,故本研究探讨P53通路相关基因(ATM/P53/Mdm2/P21WAF/CIP1)蛋白在167例胰腺癌发生、发展中及与预后的关系。方法:应用组织芯片和免疫组化法研究ATM、P53、Mdm2和P21WAF/CIP1在167例胰腺外分泌恶性肿瘤和101例癌旁组织以及11例胰腺良性病变中的表达情况。结果:ATM、P53、Mdm2和P21WAF/CIP1在癌组织中的阳性率分别为67.7%、57.5%、64.1%和39.5%,在非癌组织中阳性率分别为82.1%、6.3%、5.4%和71.4%。与非癌组织相比,癌组织中P53和Mdm2表达明显升高(P<0.01),而ATM和P21WAF/CIP1的表达明显降低(P<0.05)。P21WAF/CIP1的阳性表达与发病年龄、神经受累显著相关(P<0.05);P53的阳性表达与肿瘤的分化、淋巴结转移和神经受累均显著相关(P<0.05);Mdm2的阳性表达与肿瘤的分化显著相关(P<0.05);ATM的阳性表达与年龄相关(P<0.05);四者阳性表达两两之间统计学上具有关联性(P<0.05)。44例获1年以上随访者中ATM /Mdm2 /P53 P21WAF/CIP1 、ATM-/Mdm2-/P53-/P21WAF/CIP1-、ATM Mdm2 /P53 分别为9、11、5例,平均生存期依次为9.3、26.1、20月。Kaplan-Meier分析显示全阳性组预后较全阴性组和P21阴性组预后差。结论:P53和Mdm2的过表达以及ATM和P21WAF/CIP1的缺失表达可能会导致胰腺癌的形成和进展;4种蛋白可能以ATM-P53-Mdm2-P21WAF/CIP1通路的方式作用于细胞的转化和肿瘤的形成;联合检测P53和Mdm2的表达可用于评定胰腺癌的恶性程度。     

星形细胞瘤中PTEN、Mdm2和p53表达的相关性研究

目的　探讨不同组织病理分级的星形细胞瘤中PTEN、Mdm2和p5 3的表达水平 ,并分析PTEN影响Mdm2和p5 3表达的信号转导机制。方法　采用免疫组织化学方法检测 6 8例星形细胞瘤标本中 ,PTEN、Mdm2和p5 3的表达水平。结果　星形细胞瘤中 ,PTEN、Mdm2和p5 3的表达水平分别为 5 4 .4 % (37/ 6 8)、4 1.2 % (2 8/ 6 8)和 4 5 .6 % (31/ 6 8)。PTEN阳性标本中 ,Mdm2的表达率 (2 4 .3% ,9/ 37)与PTEN阴性标本中该蛋白的表达率 (6 1.3% ,19/ 31)相比 ,差异有显著性 ,统计学分析显示 ,PTEN表达与Mdm2表达呈负相关 (P <0 .0 1)。Mdm2表达和p5 3表达一致 ,符合率为 6 6 .2 % (45 / 6 8) ,两者的表达密切相关 (P <0 .0 5 )。结论　PTEN、Mdm2和p5 3表达与星形细胞瘤的组织病理分级相关 ;抑癌基因PTEN可以下调癌基因Mdm2的表达水平 ;Mdm2和p5 3的表达存在一致性。