Resveratrol induces colon tumor cell apoptosis independently of p53 and precede by epithelial differentiation, mitochondrial proliferation and membrane potential collapse.

Resveratrol, a polyphenol present in wine and grapes, can inhibit tumor cell growth in vitro and tumorigenesis in vivo. Some of its effects have been linked to activation of the p53 tumor suppressor; however, p53 is frequently mutated in tumors, particularly in the common and often therapy-resistant colon cancers. Using the human wild-type p53-expressing HCT116 colon carcinoma cell line and HCT116 cells with both p53 alleles inactivated by homologous recombination, we show in the current study that resveratrol at concentrations comparable to those found in some foods can induce apoptosis independently of p53. The cell death is primarily mitochondria-mediated and not receptor-mediated. No cells survived in cultures continuously exposed to 100 microM resveratrol for 120 hr. When compared with 5-FU, resveratrol stimulated p53 accumulation and activity only weakly and with delayed kinetics and neither the increased levels nor the activity affected apoptosis detectably. The apoptosis agonist Bax was overproduced in response to resveratrol regardless of p53 status, yet the kinetics of Bax expression were influenced by p53. Remarkably, apoptosis was preceded by mitochondrial proliferation and signs of epithelial differentiation. Thus, resveratrol triggers a p53-independent apoptotic pathway in HCT116 cells that may be linked to differentiation.     

p21(Waf1/Cip1) and p53 are downstream effectors of protein kinase C delta in tumor suppression and differentiation in human colon cancer cells

We have previously demonstrated that the delta isoform of protein kinase C (PKCdelta) is importantly involved in cell growth inhibition and tumor suppression in colon cancer cells. To investigate further the activity and mechanism of action of PKCdelta, we have retrovirally transduced a PKCdelta cDNA in HCT116 human colon cancer cells. PKCdelta-overexpressing cells (HCT116/PKCdelta) were growth-inhibited, showed marked morphologic changes and underwent multinucleation and phenotypic changes characteristic of mitotic catastrophe. Compared to controls, HCT116/PKCdelta cells showed a highly attenuated tumorigenic profile and poor anchorage-independent growth. In addition, transfected cells established junction-coordinated intercellular communications, expressed cell surface microvilli and overexpressed the colon differentiation marker alkaline phosphatase. HCT116/PKCdelta cells also produced the 89 kDa, carboxy-terminal catalytic domain of PARP. In HCT116/PKCdelta cells, p21(Waf1/Cip1) and p53 were transiently upregulated for 48 hr after PKCdelta transduction. In a p21 null subline of HCT116 cells (HCT116/p21null), overexpression of PKCdelta did not affect tumorigenicity or differentiation, indicating that p21 is essential for the antitumorigenic activity of PKCdelta. Similarly, overexpression of PKCdelta caused no significant phenotypic changes in HCT116/E6 cells, an HCT116 subline in which the p53 protein is downregulated by the human papillomavirus E6 gene product. We conclude that overexpression of PKCdelta in human colon cancer cells induces multiple antineoplastic effects that depend on the activities of p21(Waf1/Cip1) and p53.     

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.     

Securin depletion sensitizes human colon cancer cells to fisetin-induced apoptosis

Securin is highly-expressed in various tumors including those of the colon. In this study, the role of securin in the anticancer effects of fisetin on human colon cancer cells was investigated. Fisetin-induced apoptosis in HCT116 cells as indicated by TUNEL assay, Annexin V-FITC/PI double staining, Ser15-phosphorylation of p53, and cleavages of procaspase-3 and PARP. These effects were enhanced in HCT116 securin-null cells or in wild-type cells in which securin was knockdown by siRNA, but attenuated when wild-type or non-degradable securin was reconstituted. Moreover, fisetin did not induce apoptosis in HCT116 p53-null and HT-29 p53-mutant cells. Knockdown of securin in HCT116 p53-null cells potentiated fisetin-induced cytotoxicity by induction of apoptosis. Our results provide the first evidence to support that securin depletion sensitizes human colon cancer cells to fisetin-induced apoptosis.     

Mitochondrial p53 phosphorylation induces Bak-mediated and caspase-independent cell death

Chemoresistance in cancer has previously been attributed to gene mutations or deficiency. Caspase mutations or Bax deficiency can lead to resistance to cancer drugs. We recently demonstrated that Bak initiates a caspase/Bax-independent cell death pathway. We show that Plumbagin (PL) (5-hydroxy-2-methyl-1,4-napthoquinone), a medicinal plant-derived naphthoquinone that is known to have anti-tumor activity in a variety of models, induces caspase-independent cell death in HCT116 Bax knockout (KO) or MCF-7 Bax knockdown (KD) cells that express wild-type (WT) Bak. The re-expression of Bax in HCT116 Bax KO cells fails to enhance the PL-induced cell death. Additionally, Bak knockdown by shRNA efficiently attenuates PL-induced cell death. These results suggest that PL-induced cell death depends primarily on Bak, not Bax, in these cells. Further experimentation demonstrated that p53 Ser15 phosphorylation and mitochondrial translocation mediated Bak activation and subsequent cell death. Knockdown of p53 or a p53 Ser15 mutant significantly inhibited p53 mitochondrial translocation and cell death. Furthermore, we found that Akt mediated p53 phosphorylation and the subsequent mitochondrial accumulation. Taken together, our data elaborate the role of Bak in caspase/Bax-independent cell death and suggest that PL may be an effective agent for overcoming chemoresistance in cancer cells with dysfunctional caspases.     

In vivo evaluation of the role of DNp73alpha protein in regulating the p53-dependent apoptotic pathway after treatment with cytotoxic drugs

The amino terminus truncated p73 isoform, DeltaNp73alpha, shows dominant negative behavior toward TAp73 and wild-type p53, and has oncogenic potential. By contrast, we recently showed that in HCT116 clones forced expression of DeltaNp73alpha did not increase in vitro cellular resistance to anticancer agents. The purpose of this study was to characterize in vivo models and to investigate the functional interaction between the DeltaNp73alpha isoform and the p53 pathway. Human colon carcinoma HCT116 clones expressing inducible DeltaNp73alpha (HCT116/DN3, HCT116/DN14) and HCT116/8a (transfected with the mock empty vector), transplanted in immunodeficient nude mice, were used to study the antitumor activity of cis-diammine-dichloro-platinum (cDDP) (4 mg/kg, i.v., q7d x 3) and Doxorubicin (DX) (7.5 mg/kg, i.v., q7d x 3), with or without tetracycline-induced DeltaNp73alpha overexpression. DeltaNp73alpha expression was confirmed by RT-PCR, immunoblotting and immunohistochemical analysis. DeltaNp73alpha subcellular localization after DX treatment was checked by an immunofluorescence assay. Western blot was used to analyze p53, p21, Bax, Bcl-2 and p53AIP1 expression. DeltaNp73alpha overexpression did not modify the antitumor activity of either DX or cDDP in xenograft models. DX reduced DeltaNp73alpha protein expression, without affecting its nuclear localization. p53, p21, Bax and p53AIP1 protein expression increased and Bcl-2 decreased in HCT116 clone derived tumors 24 hr after DX exposure, independently of the presence of DeltaNp73alpha. Overexpression of DeltaNp73alpha does not affect tumor growth in vivo, does not increase the resistance of established tumors to anticancer agents and does not antagonize p53 apoptotic functions.     

茯苓酸通过调控AKT/MDM2/p53通路影响结直肠癌HCT116细胞的恶性生物学行为

目的：探究茯苓酸（PA）是否通过AKT/MDM2/p53通路影响结直肠癌HCT116细胞的恶性生物学行为。方法：常规培养HCT116细胞,并将其分为对照组、MK-2206(AKT抑制剂)组、PA低浓度（PA-L）组、PA高浓度（PA-H）组、PA-H+SC79(AKT激活剂)组。CCK-8法、细胞克隆形成实验、流式细胞术、Transwell、qPCR法和WB法实验分别检测各组HCT116细胞的增殖活力,克隆形成能力,细胞凋亡,迁移、侵袭能力,E-cadherin、N-cadherin和vimentin mRNA表达以及AKT/MDM2/p53通路相关蛋白的表达。结果：PA可明显抑制HCT116细胞的增殖活力（P<0.05）、克隆形成能力（P<0.05）、迁移和侵袭能力（P<0.05）,诱导其凋亡（P<0.05）,抑制N-cadherin、vimentin mRNA的表达（P<0.05）,促进E-cadherin mRNA的表达（P<0.05）,抑制AKT、MDM2的磷酸化水平（P<0.05）,促进p53蛋白的表达（P<0.05）;AKT抑...     

Paclitaxel sensitivity correlates with P53 status and DNA fragmentation, but not G2/M accumulation

Purpose: The antitumor agent paclitaxel (Taxol®) has been shown to arrest cells in mitosis through microtubule stabilization and to induce apoptosis. The tumor suppressor gene p53 is implicated in the regulation of cell cycle checkpoints and can mediate apoptotic cell death. Although initial studies demonstrated that various DNA-damaging agents can induce p53, more recent studies have also shown p53 induction following nonDNA–damaging agents, including paclitaxel. We investigated the influence of p53 abrogation on paclitaxel-induced cell kill and correlated the extent of mitotic arrest and DNA fragmentation by paclitaxel with the drug’s cytotoxic effect.

Materials and Methods: The parental human colorectal carcinoma cell line (RKO) with wild-type p53 alleles, and two transfected RKO cell lines with inactivated p53 (RKO.p53.13 with transfected mutant p53 and RC 10.3 with HPV-16-derived E6 gene) were exposed to graded doses of paclitaxel (1–100 nM) for 24-h intervals. The functional status of p53 in cells was assessed by thymidine and BrdU incorporation following exposure to ionizing radiation (4 Gy). Reproductive integrity following paclitaxel treatment was assessed by clonogenic assay. Immunolabeling and microscopic evaluation were used to assess mitotic accumulation and micronucleation. Apoptosis was assayed using DNA fragmentation analyses.

Results: A 4-fold increase in paclitaxel sensitivity was observed among RKO cells deficient in p53 function compared with wild-type RKO cells (IC 50: 4 nM, 1 nM, 1nM for RKO, RKO.p53.13, RC 10.3, respectively). The increased cytotoxic effect in RKO cells with inactive p53 correlated with an increased propensity towards micronucleation and DNA fragmentation following paclitaxel treatment. However, no significant difference in peak mitotic accumulation was observed among RKO cells with functional or abrogated p53.

Conclusions: RKO cells lacking functional p53 demonstrate significantly enhanced sensitivity to paclitaxel compared with that of wild-type RKO cells. This response corresponded with increased micronucleation and DNA fragmentation in cells deficient in p53 function. Although previous published reports of enhanced paclitaxel sensitivity in p53-deficient cells correlated this finding with increased G2/M arrest, we did not observe any significant correlation between paclitaxel-induced cell kill and the degree of mitotic arrest. Our data suggest that apoptosis is the predominant mechanism of paclitaxel cytotoxicity in RKO cells and is likely mediated by a p53-independent process.     

Crystal structure of a p53 core tetramer bound to DNA

The tumor suppressor p53 regulates downstream genes in response to many cellular stresses and is frequently mutated in human cancers. Here, we report the use of a crosslinking strategy to trap a tetrameric p53 DNA-binding domain (p53DBD) bound to DNA and the X-ray crystal structure of the protein/DNA complex. The structure reveals that two p53DBD dimers bind to B form DNA with no relative twist and that a p53 tetramer can bind to DNA without introducing significant DNA bending. The numerous dimer-dimer interactions involve several strictly conserved residues, thus suggesting a molecular basis for p53DBD-DNA binding cooperativity. Surface residue conservation of the p53DBD tetramer bound to DNA highlights possible regions of other p53 domain or p53 cofactor interactions.     

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.     

15-lipoxygenase-1 activates tumor suppressor p53 independent of enzymatic activity

15-LOX-1 and its metabolites are involved in colorectal cancer. Recently, we reported that 15-LOX-1 overexpression in HCT-116 human colorectal cancer cells inhibited cell growth by induction of p53 phosphorylation (4). To determine whether the 15-LOX-1 protein or its metabolites are responsible for phosphorylation of p53 in HCT-116 cells, we used HCT-116 cells that expressed a mutant 15-LOX-1. The mutant 15-LOX-1 enzyme, with a substitution of Leu at residue His361, was devoid of enzymatic activity. HCT-116 cells transiently transfected with either native or mutant 15-LOX-1 showed an increase in p53 phosphorylation and an increase in the expression of downstream genes. Thus, 15-LOX-1 induces p53 phosphorylation independent of enzymatic activity. Treatment of A549 human lung carcinoma cells with IL-4 increased the expression of 15-LOX-1 and also increased the expression of downstream targets of p53. This confirmed that the activation of p53 was also observed in wild-type cells expressing physiological 15-LOX-1. Immunoprecipitation experiments revealed that 15-LOX-1 interacts with, and binds to, DNA-dependent protein kinase (DNA-PK). The binding of 15-LOX-1 to DNA-PK caused an approximate 3.0-fold enhancement in kinase activity, resulting in increased p53 phosphorylation at Ser15. Knockdown of DNA-PK by small interfering RNA (siRNA) significantly reduced p53 phosphorylation. Furthermore, confocal microscopy demonstrated a colocalization of 15-LOX and DNA-PK in the cells. We propose that the 15-LOX-1 protein binds to DNA-PK, increasing its kinase activity and results in downstream activation of the tumor suppressor p53, thus revealing a new mechanism by which lipoxygenases (LOX) may influence the phenotype of tumor cells.     

Emodin-Provoked Oxidative Stress Induces Apoptosis in Human Colon Cancer HCT116 Cells through a p53-Mitochondrial Apoptotic Pathway

Emodin, a natural anthraquinone isolated from the traditional Chinese medicine Radix rhizoma Rhei, can induce apoptosis in many kinds of cancer cells. This study demonstrated that emodin induces apoptosis in human colon cancer HCT116 cells by provoking oxidative stress, which subsequently triggers a p53-mitochondrial apoptotic pathway. Emodin induced mitochondrial transmembrane potential loss, increase in Bax and decrease in Bcl-2 expression and mitochondrial translocation and release of cytochrome c to cytosol in HCT116 cells. In response to emodin-treatment, ROS increased rapidly, and subsequently p53 was overexpressed. Pretreatment with the antioxidant NAC diminished apoptosis and p53 overexpression induced by emodin. Transfecting p53 siRNA also attenuated apoptosis induced by emodin, Bax expression and mitochondrial translocation being reduced compared to treatment with emodin alone. Taken together, these results indicate that ROS is a trigger of emodin-induced apoptosis in HCT116 cells, and p53 expression increases under oxidative stress, leading toBax-mediated mitochondrial apoptosis.     

Association of JNK1 with p21waf1 and p53: modulation of JNK1 activity

Exposure of mammalian cells to genotoxic stress results in activation of the c-jun amino-terminal kinase (JNK)-stress-activated protein kinase (SAPK) pathway and induction of DNA repair enzymes and cell cycle-regulatory proteins such as p53 and p21waf1. The p53 tumor suppressor protein transmits signals that activate p21waf1 gene expression. The p21waf1 protein then restricts cell-cycle progression, thereby allowing time for DNA repair to occur. In this study, we investigated the effects of modulation of the level of wild-type and mutant p53 protein on basal JNK1 activity in the A1-5 rat fibroblast cell line. This cell line contains a p53 gene coding for a temperature-sensitive p53 protein, which allows us to regulate the relative level of wild-type and mutant p53 protein produced in cells. Using the immune complex kinase assay to measure JNK1 activity, we demonstrated that cells expressing the wild-type-conformation p53 protein (when grown at 32.5 degrees C) exhibited a very low level of JNK1 activity. When cells were grown at 37 degrees C or 39 degrees C to express predominantly mutant p53 protein, basal level of JNK1 activity was significantly higher than at 32.5 degrees C. We also demonstrated protein-protein interactions between the p53, p21waf1, and JNK1 proteins in this cell line. Both wild-type p53 protein (expressed at 32.5 degrees C) and mutant p53(val135) protein (expressed at 37 degrees C and 39 degrees C) were present in immunocomplexes of JNK1 protein. Under conditions where wild-type p53 protein was present to induce p21waf1 expression (at 32.5 degrees C), a higher level of p21waf1 protein was also detected in the JNK1 immunocomplexes than in those at 37 degrees C and 39 degrees C. We next investigated the effect that co-association of p53 protein and p21waf1 protein would have on JNK1 activity. We measured basal levels of JNK1 activity in cells expressing wild-type p53 and p21waf1, or in p21waf1-null cells, and demonstrated that cells expressing both p53 and p21waf1 proteins exhibited an approximately threefold lower basal level of JNK1 activity when compared with p21waf1-null cells. To confirm that p21waf1 protein expression in cells resulted in reduced JNK1 activity, we transfected p21waf1-/- cells with a p21waf1 expression vector. We observed that JNK1 activity was inhibited after exogenous p21waf1 protein was expressed in these cells. Our results provide evidence for modulation of the JNK1 pathway by p53 and p21waf1 proteins and support the hypothesis that modulation of JNK1 activity occurred through protein-protein interactions between JNK1, p53, and p21waf1 proteins.