p53信号网络的非线性动力学研究

p53蛋白作为细胞内重要的肿瘤抑制因子,通过复杂的信号转导网络调节细胞生理活动,维护基因组的稳定性与完整性.p53网络能对细胞遭遇的一系列应激信号(如DNA损伤、致癌基因激活和端粒受损等)做出响应,启动DNA修复、细胞周期阻滞、细胞衰老或凋亡等来避免基因组缺陷的复制和遗传.p53蛋白浓度在细胞应激响应过程中呈现脉冲、开关等动力学行为,具有丰富的非线性特征.本文旨在综述p53网络动力学领域的最新进展,揭示细胞DNA损伤响应过程中p53动力学与功能之间的潜在联系.     

启动变异细胞凋亡的酶被发现

细胞中的DNA发生变异，细胞就会癌变。在以往的研究中，科学家们发现，细胞中抑制癌变的基因“p53”会判断DNA变异的程度，如果变异较小，这种基因就促使细胞自我修复，若DNA变异较大，“p53”就诱导细胞凋亡。“p53”能在某种酶的作用下被激活，但科学家一直未确定是哪种酶。     

铀矿冶低剂量γ射线辐照对淋巴细胞凋亡的影响

淋巴细胞凋亡在其发育中起着重要的作用,淋巴细胞凋亡率升高可能会引起免疫缺陷,抑制淋巴细胞凋亡率可能会促进淋巴瘤的发展。铀矿冶低剂量γ射线辐照会诱导淋巴细胞的凋亡,流式细胞术检测结果表明,淋巴细胞在接受剂量率为14 μGy/h的低剂量率γ射线辐照的21 d内凋亡率逐渐增高,并基本呈线性增加趋势。全转录组测序结果表明,低剂量γ射线辐照后,淋巴细胞内共有1 677个表达差异显著(任意两组间p值<0.05)的基因,主要与细胞对压力的反应、细胞周期、DNA构象变化、DNA修复、细胞蛋白分解代谢过程、病毒致癌机理、染色体分离、p53的转录调控相关。低剂量γ辐射会激活肿瘤抑制蛋白p53,最终使细胞凋亡率升高。     

KLF4沉默与阿霉素诱导的DNA损伤协同抑制肝癌HepG2细胞的生长

探究KLF4沉默与经不同作用浓度阿霉素处理诱导的DNA损伤对肝癌HepG2细胞增殖凋亡的影响及其作用机制.应用RNA干扰技术,采用siRNA转染HepG2细胞以沉默KLF4基因.采用MTT法检测KLF4沉默前后对HepG2细胞增殖的影响,使用流式细胞术检测KLF4沉默前后对HepG2细胞周期变化影响,应用Western blot法检测转染前后HepG2细胞中KLF4蛋白及细胞周期相关蛋白表达变化.Western blot检测到高浓度的阿霉素促进KLF4的表达,并且低浓度的阿霉素可使得细胞停滞在G2/M期,高浓度的阿霉素则使部分细胞凋亡(19.31%).将KLF4沉默后,发现细胞生长变缓,低浓度的阿霉素处理后,细胞随时间增加而出现更多的细胞凋亡;高浓度的阿霉素处理后,细胞数明显减少,更多的细胞发生凋亡(28.89%),且在KLF4沉默前后均发现低浓度阿霉素促进p53与p21表达,高浓度阿霉素抑制其表达.阿霉素诱导的DNA损伤可提高KLF4的表达,KLF4依赖于DNA损伤激活的p53促进p21的表达,进而引起G1/S期细胞周期阻滞.沉默KLF4与阿霉素诱导的DNA损伤可协同抑制肝癌细胞的增殖、促进凋亡,其在肝癌细胞 HepG2中扮演十分重要的角色.     

揭秘癌细胞拒绝凋亡

细胞产生不可修复的DNA损伤后通常会程序性死亡，或称凋亡。然而在肿瘤细胞中这一机制失去作用，所以它能够肆意增殖，拒绝接受凋亡的命令。德国科学家最近研究发现，严重DNA损伤后触发细胞凋亡的其中一类蛋白是HIPK2分子。HIPK2分子不断地在健康细胞中产生，不断积累，触发健康细胞凋亡。     

MdmX在Axin-p53信号通路中的调控机制

鼠双微体基因X(MdmX)是肿瘤抑制因子p53信号通路中重要的负调控蛋白,它能与p53直接结合,抑制p53的转录活性.体轴发育抑制因子Axin作为构架蛋白与p53及同源结构域互作蛋白激酶2(HIPK2)等相互作用形成复合物,诱导p53的转录活化,共同促进细胞的凋亡.本研究将MdmX引入Axin-p53信号通路的调控中,发现MdmX通过竞争Axin与p53的结合,抑制Axin诱导p53的转录激活.p53结合区域缺失的MdmX突变体MdmXΔp53则不能抑制Axin对p53的激活.这些实验结果为进一步深入研究Axin-p53信号通路在细胞凋亡及肿瘤发生发展中的作用提供了重要的理论依据.     

Killin介导p53信号通路的机理与其在细胞周期不同时期特异性分布的相关性研究

本研究中,通过检测killin在其它p53下游相关基因缺失的情况下能否激活细胞凋亡,证明了p53通过killin介导的S期抑制以及细胞凋亡与p21、puma和bax通路没有直接关系.另外通过将EGFP-PCNA和RFP-killin表达质粒共同转染到cosE5细胞中,并观察细胞处于不同时期时Killin蛋白的分布情况,发现在细胞S期中Killin与PCNA的核定位呈现相互排斥的点状分布,与先前BrdU标记结果吻合.这一结果再次印证了Killin在S期可能抑制DNA复制.同时Killin被观察到在非S期时聚集于核仁内,从而可能影响核糖体RNA的合成.这些发现意味着killin作为主要的p53靶基因之一,可能在细胞周期不同检查点进行调控.     

I3C在p53网络中对细胞命运的影响

研究发现天然化合物I3C对癌症治疗很有帮助。在此,将I3C抑制PTEN泛素化降解过程加入p53网络,研究I3C在DNA损伤反应网络中如何促进细胞凋亡机制。通过数值模拟,发现I3C对细胞凋亡的促进作用存在特定阈值,这一机制可能是一种有效可靠的控制模式,模拟电离辐射下I3C调控细胞凋亡情况,发现在低于阈值时,细胞对I3C更为敏感,强调了I3C调控细胞凋亡在DNA损伤反应中的重要性。     

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。     

增殖细胞核抗原（PCNA）的分子结构及其生物学功能研究进展

增殖细胞核抗原（PCNA）是真核生物复制复合体的核心成分，具有特殊的环状三级结构. 作为真核细胞DNA聚合酶δ的推动因子，与不同复制相关蛋白结合，协调DNA复制过程. 同时PCNA还作为功能转换因子，通过不同调控方式与多种细胞因子作用，参与了DNA损伤修复、细胞周期调控及凋亡等许多重要的细胞事件. 另外作为细胞增殖的指标，PCNA与肿瘤等细胞增殖性疾病的发生和发展存在相关性，因此在临床上对PCNA的深入研究有重要意义. 文中就PCNA的“功能性”结构及其在不同细胞事件中的功能转换（Function Switch）进行简要综述.     

DNA damage stress induces the dissociation of Smurf1/2 from MDM2 in a slow manner

The tumor suppressor p53 locates at the key point of cell growth or apoptosis balance, and the expression level of p53 is tightly controlled by ubiquitin ligases including MDM2. Upon DNA damage stresses, p53 was accumulated and activated, leading to cell cycle arrest or apoptosis. We previously showed that Smad ubiquitylation regulatory factor 1/2 (Smurf1/2) promotes p53 degradation by interacting with and stabilizing MDM2, and consequently enhancing MDM2-mediated ubiquitylation of p53. However, it is unclear how the Smurf1-MDM2 interaction is regulated in response to DNA damage stress. Here, we show that in response to etoposide treatment Smurf1 dissociates from MDM2, resulting in MDM2 destabilization and p53 accumulation. The negative regulation of Smurf1 on apoptosis is released. Notably, this dissociation is a slow process rather than a rapid response, implicating high expression of Smurf1 might confer the resistance against p53 activation. Consistent with this notion, we observed that Smurf1/2 ligases are highly expressed in colon cancer, esophageal squamous cell carcinoma and pancreatic cancer tissues, suggesting the oncogenic tendency of Smurf1/2.     

DNA damage stress induces the dissociation of Smurf1/2 from MDM2 in a slow manner

The tumor suppressor p53 locates at the key point of cell growth or apoptosis balance, and the expression level of p53 is tightly controlled by ubiquitin ligases including MDM2. Upon DNA damage stresses, p53 was accumulated and activated, leading to cell cycle arrest or apoptosis. We previously showed that Smad ubiquitylation regulatory factor 1/2 (Smurf1/2) promotes p53 degradation by interacting with and stabilizing MDM2, and consequently enhancing MDM2-mediated ubiquitylation of p53. However, it is uncle...     

肿瘤抑制基因p53的研究进展

综述了p53基因的特性、认识阶段、作用机理主其在癌症研究中的进展。     

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.     

Senescence and tumour clearance is triggered by p53 restoration in murine liver carcinomas

Although cancer arises from a combination of mutations in oncogenes and tumour suppressor genes, the extent to which tumour suppressor gene loss is required for maintaining established tumours is poorly understood. p53 is an important tumour suppressor that acts to restrict proliferation in response to DNA damage or deregulation of mitogenic oncogenes, by leading to the induction of various cell cycle checkpoints, apoptosis or cellular senescence. Consequently, p53 mutations increase cell proliferation and survival, and in some settings promote genomic instability and resistance to certain chemotherapies. To determine the consequences of reactivating the p53 pathway in tumours, we used RNA interference (RNAi) to conditionally regulate endogenous p53 expression in a mosaic mouse model of liver carcinoma. We show that even brief reactivation of endogenous p53 in p53-deficient tumours can produce complete tumour regressions. The primary response to p53 was not apoptosis, but instead involved the induction of a cellular senescence program that was associated with differentiation and the upregulation of inflammatory cytokines. This program, although producing only cell cycle arrest in vitro, also triggered an innate immune response that targeted the tumour cells in vivo, thereby contributing to tumour clearance. Our study indicates that p53 loss can be required for the maintenance of aggressive carcinomas, and illustrates how the cellular senescence program can act together with the innate immune system to potently limit tumour growth.     

早期肺癌病人血液中P53的克隆及其pEGFP-N1-p53的构建

首先用RT-PCR方法从早期肺癌病人的外周血中克隆出人抗癌基因p53,经测序确认为野生型后,通过酶切、连接、转化构建出扩增质粒pMD18-T-p53,然后构建出含增强型绿色荧光蛋白(EGFP)基因的真核表达质粒pEGFP-N1-p53.pEGFP-N1-P53经限制性内切酶Hind Ⅲ和BamH Ⅰ酶切,酶切产物电泳结...     

RECQL4与肿瘤发生的关系

RECQL4属于人类RECQ解旋酶家族,广泛参与DNA的复制和损伤修复.早期研究证实,RECQL4突变会导致RTS,BGS和RAPA 3种综合症,其中RTS和BGS患者都有很高的骨肉瘤和淋巴瘤发生倾向,此外,RECQL4还可通过维持线粒体和端粒的基因稳定避免多种肿瘤发生,RECQL4也被认为与血液恶性肿瘤爆发相关.最新实验结果提示,RECQL4缺陷的大部分骨肉瘤患者9号外显子缺失,RECQL4维持线粒体稳定的重要结合蛋白是p53,RECQL4是与生存素结合在一起避免乳腺癌细胞凋亡的,RECQL4过量表达通过增强MCM复制起始复合物活性而促进宫颈癌细胞等的增殖.但目前有关RECQL4与肿瘤关系的机制仍有许多不明之处,需进一步深入探讨.本文对RECQL4与肿瘤发生的关系作一综述,以期为癌症研究和治疗提供思路.