Accumulation of class I mutant p53 and apoptosis induced by carboplatin in a human glioma cell line

Following DNA damage, wild-type p53 increases and mediates the multiple cellular responses for the repair of DNA damage or apoptosis. Inactivation of p53 by single-amino-acid substitutions contributes to the malignant phenotype and confers resistance to therapy. Among tumor-derived p53 mutants, class I mutants still retain a native-like three-dimensional structure, whereas class II mutants have unfolded DNA-binding domains. Sequencing analysis demonstrated that a human glioma cell line (U-373MG) had only a class I mutant form of p53 of His273, which targets an Arg273 that contacts DNA but retains the native structure. In this study, we investigated the metabolic alteration of the class I mutant p53 in apoptosis of U-373MG. The cell cycle progression of U-373MG cells was affected by the addition of carboplatin, while the amount of mutant p53 also increased in their nuclei. The treated cells underwent apoptosis 48h after exposure to 50 μg/ml carboplatin. Although the exact mechanism of the class I mutant p53 in the process of apoptosis has not yet been clarified, the fact that accumulation of the activated mutant p53 in the nucleus of U-373MG is concomitant with apoptosis, just as wild-type p53 does, implies that the class I mutant p53 might retain the ability to participate in apoptosis.     

p53凋亡刺激蛋白在肿瘤中的研究进展

p53凋亡刺激蛋白(ASPP)是p53的重要调节蛋白,其成员有ASPP1、ASPP2、iASPP.它们与p53形成复合物后,ASPP1和ASPP2特异性促进p53的细胞凋亡功能,而iASPP则同ASPP1和ASPP2竞争性地与p53结合位点结合,从而抑制p53的抑癌功能.ASPP家族尤其是iASPP有望成为肿瘤治疗的新靶点.     

Targeting p53 as a therapeutic strategy in sensitizing TRAIL-induced apoptosis in cancer cells

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) has been intensively studied as a cancer therapeutic agent due to its unique ability to induce apoptosis in malignant cells but not in normal cells. However, as more human cancer cells are reported to be resistant to TRAIL treatment, it is important to develop new therapeutic strategies to overcome this resistance. p53 is an important tumor suppressor that is widely involved in cellular responses to various stresses. In this mini-review, we aim to provide an overview of the intricate relationship between p53 and the TRAIL-mediated apoptosis pathway, and to summarize the current approaches of targeting p53 as a therapeutic strategy to sensitize TRAIL-induced apoptosis in human cancer cells. Although in some cases TRAIL kills cancer cells in a p53-independent manner, it is believed that in cancers with wild-type and functional p53, targeting p53 may be an important strategy for overcoming TRAIL-resistance in cancer therapy.     

Effects of p53 overexpression on neoplastic cell mitosis and apoptosis in nasopharyngeal carcinoma

p53 gene alteration is an important molecular event in tumourigenesis of many malignancies.[1] However, the mutation rate of p53 gene in nasopharyngeal carcinoma (NPC) is lower.[2] The PCR-SSCP performed by FU Mao-fu et al. in the authors' lab in 1994 demonstrated that there were only 4 specimens showing aberrant shift in 18 NPCs (22.2%)--one in exon 5, three in exon 8.[3] On another aspect, the p53 overexpression rate almost reached about 80%.[4,5] It is well known that because the half…     

鼻咽癌中p53蛋白积聚对瘤细胞有丝分裂和凋亡的影响

目的：观察疗前鼻咽癌组织中Ｐ５３蛋白的积聚及其对瘤细胞有丝分裂和凋亡的影响。方法随机收集１９９７年疗前鼻咽癌活检标本４３例,采用免疫组化ＬＳＡＢ法ＤＯ－７一抗检测Ｐ５３蛋白的表达。在Ｈ＆Ｅ染色切片上位细胞死亡试剂盒检测瘤细胞凋亡,平均每个高倍视野下的凋亡瘤细胞数为凋亡指数（ＴＵＮＥＬ ｉｎｄｅｘ,Ｔ１）。比较高于位细胞死亡试剂盒检测瘤细胞凋亡,平均每个高倍视野下的细胞瘤细胞数为凋亡指数（ＴＵＮＥＬ     

The role of p53 in gemcitabine-mediated cytotoxicity and radiosensitization

Purpose: We compared the cytotoxic and radiosensitizing effects of gemcitabine (2′,2′-difluoro-2′-deoxycytidine, dFdCyd), a clinically valuable radiosensitizer, in colon cancer RKO cells which differed in their p53 status. The parental RKO cells, RKO-P, contain wild-type p53 protein. In RKO-E6 cells, the p53 function has been disrupted by transfection of the cells with the human papillomavirus type-16 E6 gene. Results: We found that the RKO-P cells were significantly more sensitive to dFdCyd-mediated cytotoxicity and apoptosis than RKO-E6 cells (IC₁₀ 39.3 ± 5.3 nM and 62.0 ± 6.9 nM, respectively). The cytotoxic effect of dFdCyd in RKO-P cells was accompanied by induction of the proapoptotic protein Bax at the time when p53 was induced. In contrast, similar treatment of RKO-E6 cells with dFdCyd resulted in only limited expression of Bax, suggesting that the cytotoxic effect of dFdCyd was mediated, in part, by a p53-dependent apoptosis pathway. We also studied the effect of dFdCyd on radiation sensitivity. We found that at minimally cytotoxic concentrations dFdCyd failed to radiosensitize either RKO-P or RKO-E6 cells, whereas at cytotoxic concentrations equal sensitization was produced. Finally, we assessed the influence of dFdCyd on cell cycle distribution. We found that dFdCyd synchronized RKO-P cells, whereas synchrony was not produced in p53-disrupted RKO-E6 cells. Conclusion: These results suggest that p53 status may influence dFdCyd-mediated apoptosis, cytotoxicity, and cell cycle progression but do not support an important role for p53 in radiosensitization. Received: 4 May 1999 / Accepted: 19 November 1999     

Gemin3基因通过抑制p53表达阻碍细胞凋亡

目的 探讨Gemin3基因表达在细胞凋亡中的作用及途径.方法 采用免疫共沉淀、谷胱甘肽-S转移酶共沉淀实验确定Gemin3与p53两种蛋白在体内、体外相互结合及相瓦作用的结构域.荧光素酶报告基因检测转染Gemin3基因对p53基因的影响,依靠慢病毒载体介导小干扰RNA敲低Gemin3基因的表达,并经嘌呤霉素筛选获得稳定的Gemin3低表达细胞系,实时定量PCR检测Gemin3敲低对p53及其下游基因在转录水平的影响,流式细胞术检测Gemin3敲低对细胞凋亡的影响.结果 Gemin3的C端与p53的中部DNA部位相互结合.将p53报告基因、p53蛋白基因以及逐渐增量的Gemin3基因共转染Saos-2细胞,随着Gemin3质粒转染浓度的增高,p53介导的报告基因表达水平逐渐降低,Gemin3在转录水平抑制p53基因的表达.实时定量PCR结果显示,与对照细胞比较,Gemin3敲低细胞中,p53、p21和Bax mRNA的表达水平明显增高.Western blot检测结果显示,Gemin3敲低细胞中,p53的表达明显升高.流式细胞术检测结果显示,敲低Gemin3基因的表达导致细胞凋亡的增加.结论 Gemin3与p53相互结合并通过抑制p53的表达阻碍细胞凋亡.     

Involvement of p53 in oroxylin A‐induced apoptosis in cancer cells

Oroxylin A, a naturally occurring monoflavonoid extracted from Scutellariae radix, exhibits anticancer activity and induces apoptosis in human hepatocellular carcinoma HepG2 cells according to our previous data. In this study, we investigate whether p53 is involved in oroxylin A‐triggered viability inhibition and apoptosis induction in cancer cells. In a panel of different cancer cell lines, more potent inhibitory effects of oroxylin A were observed in wtp53 cells than those in mtp53 or p53‐null cells. Moreover, p53‐siRNA‐transfected HepG2 cells showed lower levels of apoptosis induced by oroxylin A than control‐siRNA‐transfected cells. Likewise, after oroxylin A treatment, p53‐null K‐562 cells displayed promoted apoptosis rate when transfected with wtp53 plasmid. Western blot and real‐time RT‐PCR assay revealed that oroxylin A markedly upregulated p53 protein expression in HepG2 and p53‐overexpressing K‐562 cells, but had no influence on p53 mRNA synthesis. Furthermore, after co‐treatment with cycloheximide, oroxylin A still exerted a little effect on p53 expression. The negative regulator of p53, MDM2 protein was detected, and downregulated expression was observed. In the presence of MG132, an inhibitor of proteasome‐mediated proteolysis, no change in p53 expression was obtained. Additionally, the antioxidant N‐acetyl‐L‐cysteine could obviously abrogate p53 stabilization triggered by oroxylin A. Therefore, it is summarized that oroxylin A stabilized p53 expression and induced apoptosis at the posttranslational level via downregulating MDM2 expression and interfering MDM2‐modulated proteasome‐related p53 degradation. This indicated that oroxylin A could be served as a potential, novel agent candidate for cancer therapy. © 2009 Wiley‐Liss, Inc.     

Curcumin causes superoxide anion production and p53-independent apoptosis in human colon cancer cells

Curcumin from the rhizome of the Curcuma longa plant has chemopreventative activity and inhibits the growth of neoplastic cells. Since p53 has been suggested to be important for anticancer activity by curcumin, we investigated curcumin-induced cytotoxicity in cultures of p53^+/+ and p53^−/− HCT-116 colon cancer cells, as well as mutant p53 HT-29 colon cancer cells. Curcumin killed wild-type p53 HCT-116 cells and mutant p53 HT-29 cells in a dose- and time-dependent manner. In addition, curcumin-treated p53^+/+ HCT-116 cells and mutant p53 HT-29 cells showed upregulation of total and activated p53, as well as increased expression of p53-regulated p21, PUMA (p53 upregulated modulator of apoptosis), and Bax; however, an equivalent cytotoxic effect by curcumin was observed in p53^+/+ and p53^−/− HCT-116 cells, demonstrating that curcumin-induced cytotoxicity was independent of p53 status. Similar results were obtained when the cytotoxic effect of curcumin was assessed in wild-type p53 HCT-116 cells after siRNA-mediated p53 knockdown. Chromatin condensation, poly (ADP-ribose) polymerase-1 cleavage and reduced pro-caspase-3 levels in curcumin-treated p53^+/+ and p53^−/− HCT-116 cells suggested that curcumin caused apoptosis. In addition, exposure to curcumin resulted in superoxide anion production and phosphorylation of oxidative stress proteins in p53^+/+ and p53^−/− HCT-116 cells. Collectively, our results indicate that, despite p53 upregulation and activation, curcumin-induced apoptosis in colon cancer cells was independent of p53 status and involved oxidative stress. Curcumin may therefore have therapeutic potential in the management of colon cancer, especially in tumors that are resistant to conventional chemotherapy due to defects in p53 expression or function.     

p53凋亡刺激蛋白2对饥饿诱导的大肠癌HCT116 p53+/+细胞凋亡、周期和自噬的影响

目的 探讨p53凋亡刺激蛋白2(ASPP2)对饥饿诱导的大肠癌HCT116 p53+/+(p53野生型)细胞凋亡、周期和自噬的影响.方法 实验分6组:①对照组;②绿色荧光蛋白腺病毒(rAd-GFP)感染组;③ASPP2腺病毒(rAd-ASPP2)感染组;④饥饿处理组;⑤rAd-GFP+饥饿组;⑥rAd-ASPP2+饥饿组.利用rAd-ASPP2感染使细胞过表达ASPP2基因.无血清培养基培养24h诱导凋亡、自噬和细胞周期改变.钙黄绿素(Calcein)/碘化丙啶(PI)吸收试验观察各组细胞调亡水平.细胞转染红色荧光蛋白标记的CFP-Lc3自噬质粒,荧光显微镜下观察各组细胞自噬水平.流式细胞术观察细胞周期改变.组间比较采用单因素方差分析进行统计学分析.结果 ASPP2过表达显著促进了饥饿诱导的细胞凋亡、自噬及G2-M期阻滞,各组细胞的凋亡率为:rAd-GFP+饥饿组10.00％±1.42％,rAd-ASPP2+饥饿组18.44％ ±2.06％(q=9.548,P=0.000);各组细胞的自噬发生率为:rAd-GFP+饥饿组35.00％±5.34％,rAd-ASPP2+饥饿组57.61％ ±6.06％(q=7.657,P=0.000).但无饥饿诱导时ASPP2过表达使G0-G1、G2-M期都发生阻滞.结论 ASPP2过表达促进饥饿诱导的大肠癌HCT116 p53+/+细胞凋亡和自噬,显著改变细胞周期进程.     

p53 Status does not affect photodynamic cell killing induced by hypericin

Purpose: Given that p53 is a tumor suppressor that plays a central role in the cellular response to DNA damage and that more than 50% of all cancers have mutated p53, the wider utility of photodynamic therapy (PDT) in the treatment of cancer will depend on an understanding of whether p53 status modulates response to PDT. In this study, we investigated the photosensitivity of isogenic cell lines that differ only in their p53 status to PDT using hypericin as the photosensitizer. Methods: Acute (MTT) and chronic (clonogenic) cytotoxic assays were performed on two osteosarcoma cell-lines (U2OS and U2OS+p53DD) that are isogenic except that the latter expresses dominant negative p53. The inducible expression of p53 was determined on western blots. Uptake of hypericin, cell cycle profile analysis, measurement of membrane phosphatidylserine externalization and changes in mitochondrial membrane potential were investigated using flow cytometry. Results: Hypericin uptake was observed to be equivalent in U2OS and U2OS+p53DD cells. There were no significant differences in cell killing between these cell-lines in both the MTT and clonogenic assays (IC₅₀ of 0.4 μg/ml from MTT assay). p53 expression did not increase up to 24 h after PDT treatment in both cell lines. There were also no significant differences in the cell-cycle arrest profiles and timing of onset of apoptosis. Conclusions: Taken together, these results suggest that the status of p53 may not be important in PDT-mediated cell killing or induction of apoptosis. By extension, these results imply that PDT may be used with equal efficacy for the treatment of p53-positive and -negative tumors.     

DNMT3a plays a role in switches between doxorubicin‐induced senescence and apoptosis of colorectal cancer cells

The DNA‐damaging drug doxorubicin (Dox) induces cell senescence at concentrations significantly lower than those required for induction of apoptosis. At low Dox concentrations, tumor suppressor p53 is activated, which enhances the expression of p21^Waf1/Cip1 (p21). At high concentrations, Dox activates p53 leading to apoptosis without enhancing p21 expression. The underlying mechanisms and factors that govern the differential effects of Dox in inducing senescence and apoptosis are unclear. Here, we report that the DNA methyltransferase (DNMT) DNMT3a was upregulated by Dox especially at concentrations that induced apoptosis in HCT116 colorectal cancer cells, and this process was regulated by p53. Meanwhile, p21 expression was significantly upregulated at senescence‐inducing concentrations and kept low on treatment with apoptosis‐inducing concentrations of Dox. The differential expression of DNMT3a and p21 in response to Dox suggests that DNMT3a may be a key factor in switches between Dox‐induced senescence and apoptosis. Moreover, when DNMT3a was silenced, treatment of HCT116 cells with apoptosis‐inducing concentration of Dox increased the percentage of cells undergoing senescence, accompanied by upregulation of p21. Contrarily, senescence‐inducing concentration of Dox promoted apoptosis rate, and p21 expression was repressed. Surprisingly, no changes in DNA methylation status at p21 promoter were detected at either ranges of Dox, although DNMT3a and HDAC1 were recruited to p21 promoter at apoptosis‐inducing Dox concentration, where they were present in the same complex. Overall, these data demonstrate that DNMT3a impacts the expression of p21 and plays a role in determining the Dox‐induced senescence and apoptosis in HCT116 cells.     

Oncogenic WIP1 phosphatase attenuates the DNA damage response and sensitizes p53 mutant Jurkat cells to apoptosis

Wild-type (wt) p53-induced phosphatase 1 (Wip1), encoded by the protein phosphatase, Mg²⁺/Mn²⁺ dependent 1D (PPM1D) gene, is a serine/threonine phosphatase induced upon genotoxic stress in a p53-dependent manner. Wip1/PPM1D is frequently overexpressed, amplified and mutated in human solid tumors harboring wt p53 and is thus currently recognized as an oncogene. Oncogenic Wip1 dampens cellular stress responses, such as cell cycle checkpoints, apoptosis and senescence, and consequently increases resistance to anticancer therapeutics. Targeting Wip1 has emerged as a therapeutic strategy for tumors harboring wt p53. However, little is known about the efficacy of Wip1-targeted therapies in tumors lacking p53. The present study aimed to investigate the potential role of oncogenic Wip1 in p53 mutant (mt) Jurkat cells. In the present study, it was demonstrated that p53 mt Jurkat cells exhibited PPM1D/Wip1 gene amplification and expressed relatively high levels of Wip1, as confirmed by gene copy number and RNA expression analysis. In addition, Jurkat cells underwent G2 cell cycle arrest, apoptotic cell death and senescence in response to etoposide and doxorubicin, although the phosphorylation levels of DNA damage response (DDR) elements, including ataxia-telangiectasia mutated, ataxia-telangiestasia and Rad3-related, checkpoint kinase (Chk)1 and Chk2 were significantly low. Accordingly, the targeting of Wip1 phosphatase by RNA interference increased the phosphorylation of DDR elements, but decreased the rate of apoptosis in response to etoposide or doxorubicin in Jurkat cells. The induction of senescence or cell cycle arrest was not affected by the knockdown of Wip1. The results suggest that increased Wip1 expression enhances the apoptotic sensitivity of Jurkat cells in response to chemotherapeutic agents by attenuating DDR signaling. The present study highlights the possible pro-apoptotic role of Wip1 in a p53 mt T-cell acute lymphoblastic leukemia cell line. The data suggest the careful consideration of future treatment strategies aiming to manipulate or target Wip1 in human cancers lacking p53.     

miR-138-5p induces aggressive traits by targeting Trp53 expression in murine melanoma cells,and correlates with poor prognosis of melanoma patients

Deregulation of miRNAs contributes to the development of distinct cancer types, including melanoma, an aggressive form of skin cancer characterized by high metastatic potential and poor prognosis. The expression of a set of 580 miRNAs was investigated in a model of murine melanoma progression, comprising non-metastatic (4C11-) and metastatic melanoma (4C11+) cells. A significant increase in miR-138-5p expression was found in the metastatic 4C11+ melanoma cells compared to 4C11-, which prompted us to investigate its role in melanoma aggressiveness. Functional assays, including anoikis resistance, colony formation, collective migration, serum-deprived growth capacity, as well as in vivo tumor growth and experimental metastasis were performed in 4C11- cells stably overexpressing miR-138-5p. miR-138-5p induced an aggressive phenotype in mouse melanoma cell lines leading to increased proliferation, migration and cell viability under stress conditions. Moreover, by overexpressing miR-138-5p, low-growing and non-metastatic 4C11- cells became highly proliferative and metastatic in vivo, similar to the metastatic 4C11+ cells. Luciferase reporter analysis identified the tumor suppressor Trp53 as a direct target of miR-138-5p. Using data sets from independent melanoma cohorts, miR-138-5p and P53 expression were also found deregulated in human melanoma samples, with their levels negatively and positively correlated with prognosis, respectively. Our data shows that the overexpression of miR-138-5p contributes to melanoma metastasis through the direct suppression of Trp53.     

褪黑素对小鼠肝癌H22细胞抗增殖和促凋亡的p53依赖性机制研究

背景与目的：本室已经证明了褪黑素(melatonin,MLT)对小鼠肝癌H22细胞的生长具有抑制作用,本研究旨在探讨其机理。方法：(1)建立荷瘤小鼠模型并给予褪黑素处理,取肿瘤组织进行p53、cyclin E水平的免疫组化分析;(2)不同浓度褪黑素体外培养小鼠肝癌H22细胞,采用流式细胞技术(flow cytometry,FCM)检测细胞周期分布和凋亡率;免疫组化法分析培养细胞的p53和cyclin E的蛋白水平;采用RT-PCR方法检测Fas mRNA的水平。结果：(1)FCM显示褪黑素可引起H22细胞G0／G1期比例升高,从75．24％上升至85．46%,同时细胞凋亡增多,从5．07％升至12．77％;(2)褪黑素作用后p53水平较对照组增高42．5％(培养细胞)和19．5%(肿瘤组织),而cyclin E的水平则降低31．7％(培养细胞)和39．9％(肿瘤组织);(3)RT-PCR结果显示Fas mRNA水平增高44、2％。结论：MLT通过阻滞细胞周期和诱导细胞凋亡抑制H22细胞增殖。其机理可能是通过p53抑制下游的cyclin E的表达,阻止细胞进入S期;同时又通过p53上调Fas表达,从而诱导细胞凋亡。     

p53/bcl-2与放疗诱导的宫颈癌细胞凋亡关系的研究

目的探讨宫颈癌放疗过程中,放疗诱导的细胞凋亡与p53、bcl-2的相关性.方法选择未经治疗的宫颈癌病人20例为实验对象,搜集分割放疗前后宫颈癌组织标本,用TDT-mediated dUTP-biotin nick end labeling(TUNEL)方法检测凋亡细胞;采用单克隆抗体免疫组化ABC法检测细胞凋亡相关基因p53、bcl-2的蛋白表达水平.结果(1)在宫颈癌放疗前后,细胞凋亡阳性率和平均凋亡指数分别为25%和0.11%、75%和2.8%,放疗前后有显著差异(P＜0.001);(2)放疗后p53蛋白表达显著减少,bcl-2蛋白无显著变化;(3)放疗前后,p53基因的表达与细胞凋亡呈有意义的相关性变化.结论放射治疗诱导了宫颈癌细胞凋亡的发生,并与凋亡调节基因p53及其表达呈间接有关.