Induction of apoptosis and cell cycle arrest by a specific c-Jun NH2-terminal kinase (JNK) inhibitor, SP-600125, in gastrointestinal cancers

The c-Jun NH(2)-terminal kinase (JNK) is activated in several tumor cell lines. The aim of this study was to determine the effects of SP-600125, a specific JNK inhibitor, on the viability, apoptosis, cell cycle distribution of gastrointestinal cancer cells, and the potential anti-tumor mechanisms. Three gastric cancer cell lines, AGS, BCG-823 and MKN-45, and three colorectal cancer cell lines, SW1116, COLO205 and HT-29, were used. Cells were treated with SP-600125, and cell viability, apoptosis and cell cycle distribution, caspase-3 activity, expression of JNK and apoptosis related proteins were detected. SP-600125 inhibited cell proliferation by 10-80% for the different cell lines, and increased apoptosis by 1.5-4.5 folds for COLO205, BCG-823, MKN-45, AGS cells. Caspase-8 and caspase-3 were involved in the induction of apoptosis. SP-600125 caused G2/M cell cycle arrest and elevation of cyclin B1 and p27(kip). The differential response in cells to SP-600125 was associated with the basal level of phosphorylated JNK2. It is concluded that SP-600125 inhibits proliferation, induces apoptosis and causes cell cycle arrest in gastrointestinal cancer cells, indicating that JNK inhibitors have an anti-tumor effect and are potential therapeutic agents for cancers.     

Induction of p21CIP/WAF-1 and G2 arrest by ionizing irradiation impedes caspase-3-mediated apoptosis in human carcinoma cells

There is an ongoing controversy regarding the relevance of apoptosis induction by ionizing irradiation as compared with other end points including transient or permanent cell cycle arrest of damaged cells. Here, we show that such permanent cell cycle arrest and apoptosis represent two sides of the same coin. MCF-7 cells fail to express procaspase-3, which results in resistance to apoptosis induced by anticancer drugs. Conversely, restoration of procaspase-3 sensitizes MCF-7 cells to chemotherapeutics including epirubicine, etoposide and taxol. In contrast, irradiation does not trigger apoptotic cell death but results in prolonged arrest in the G2 phase of the cell division cycle regardless of procaspase-3 expression. This suggested that the propensity of MCF-7 cells to arrest at the G2 checkpoint results in resistance to apoptosis upon gamma-irradiation. This G2 arrest was associated with upregulation of p21CIP/WAF-1. Inhibition of DNA-damage-induced stress kinases and p21CIP/WAF-1 expression by caffeine abrogated G2 arrest and induced apoptosis of the irradiated cells in a caspase-3-dependent manner. Inhibition of cell cycle progression by adenoviral expression of the cyclin dependent kinase inhibitor p21CIP/WAF-1 prevented apoptosis upon caffeine treatment indicating that cell cycle progression, that is, G2-release, is required for induction of apoptosis. Likewise, cells homozygously deleted for p21CIP/WAF-1 (HCT116 p21-/-) display enhanced irradiation-induced apoptosis via a caspase-3-dependent mechanism. These data indicate that the disruption of G2 checkpoint control overcomes cell cycle arrest and resistance to gamma-irradiation-induced cell death. Thus, DNA damage may trigger a permanent G2 arrest as an initial inactivation step of tumor cells where the phenomenon of apoptosis is hidden unless cell cycle arrest is overcome. The efficient induction of apoptosis upon G2 release thereby depends on the propensity to activate the key executioner caspase-3. This finding is of crucial importance for the understanding of molecular steps underlying the efficacy of ionizing radiation to delete tumor cells.     

Downregulation of c-Jun expression and cell cycle regulatory molecules in acute myeloid leukemia cells upon CD44 ligation

In the present study, we investigated the mechanism of CD44 ligation with the anti-CD44 monoclonal antibody A3D8 to inhibit the proliferation of human acute myeloid leukemia (AML) cells. The effects of A3D8 on myeloid cells were associated with specific disruption of cell cycle events and induction of G0/G1 arrest. Induction of G0/G1 arrest was accompanied by an increase in the expression of p21, attenuation of pRb phosphorylation and associated with decreased Cdk2 and Cdk4 kinase activities. Since c-Jun is an important regulator of proliferation and cell cycle progression, we analysed its role in A3D8-mediated growth arrest. We observed that A3D8 treatment of AML patient blasts and HL60/U937 cells led to the downregulation of c-Jun expression at mRNA and protein level. Transient transfection studies showed the inhibition of c-jun promoter activity by A3D8, involving both AP-1 sites. Furthermore, A3D8 treatment caused a decrease in JNK protein expression and a decrease in the level of phosphorylated c-Jun. Ectopic overexpression of c-Jun in HL60 cells was able to induce proliferation and prevent the antiproliferative effects of A3D8. In summary, these data identify an important functional role of c-Jun in the induction of cell cycle arrest and proliferation arrest of myeloid leukemia cells because of the ligation of the cell surface adhesion receptor CD44 by anti-CD44 antibody. Moreover, targeting of G1 regulatory proteins and the resulting induction of G1 arrest by A3D8 may provide new insights into antiproliferative and differentiation therapy of AML.     

Anesthetic pentobarbital inhibits proliferation and migration of malignant glioma cells

Malignant gliomas are common and aggressive brain tumors in adults. The rapid proliferation and diffuse brain migration are main obstacles to successful treatment. Here we show that pentobarbital, a central depressant introduced clinically a century ago, is capable of suppressing proliferation and migration of C6 malignant glioma cells in a concentration-dependent manner. Pentobarbital also leads to a G1 phase cell cycle arrest accompanied by suppressed G1 cell cycle regulatory proteins Cyclin D1, Cyclin D3, CDK2 and phosphorylated Rb. In addition, noticeable morphological changes and interrupted α-tubulin microtubule assembly are induced by pentobarbital exposure. Intracellular signal pathways involved in the effect of pentobarbital is concerned with inactivation of ERK, c-Jun and Akt. Together, these findings suggest anti-proliferation and anti-migration effects of pentobarbital on malignant gliomas, most likely by arresting cell cycle and interfering microtubule. ERK, c-Jun MAPK and PI3K/Akt are possible signaling pathways involved.     

Cell cycle arrest mediated by a pyridopyrimidine is not abrogated by over-expression of Bcl-2 and cyclin D1

Inhibition of cyclin dependent kinases (Cdks) is of pivotal importance in tumor cell biology as these kinases are the drivers of cell proliferation. This inhibition can be achieved either by naturally occurring biological proteins or by small molecule compounds. They cause cell cycle arrest and/or apoptosis depending upon the specificity and efficacy of the inhibitor in question. We have reported earlier that specific pyridopyrimidines (novel Cdk inhibitors) cause cell cycle arrest in mink lung epithelial cells and the arrest is abrogated by over-expression of Cdk4. In contrast, we show here that one of these inhibitors effectively maintains cell cycle arrest in a leukemic or a breast cancer cell line even after the respective cells over-express an oncogene, either Bcl-2 or cyclin D1. However, in the leukemic cells, Bcl-2 over-expression suppresses apoptosis induced by the pyridopyrimidine. Thus, novel Cdk inhibitors can prove to be useful chemical genetics tools for understanding the underlying mechanisms of growth arrest and/or apoptosis in normal versus tumor cells. This could also lead to the development of improved inhibitors of cell proliferation.     

C-Jun modulates apoptosis but not terminal cell differentiation in murine erythroleukemia cells.

The proto-oncogene c-Jun has been implicated in the control of cell proliferation and differentiation and more recently in the regulation of apoptosis. We have previously reported the involvement of c-Jun in the erythroid differentiation block in murine erythroleukemia (MEL) cells. As reported here, we investigated the role of c-Jun in the regulation of terminal differentiation and apoptosis of MEL cells by studying different stable transfectant clones containing c-jun constructs in sense or antisense orientation. c-Jun did not prevent cell growth arrest in G0/G1 and p21 induction that are normally associated with terminal differentiation induced by DMSO treatment, suggesting that c-Jun may uncouple phenotypic differentiation and terminal cell division in the MEL cell system. Spontaneous apoptosis was accelerated in c-jun expressing MEL cells before and after DMSO treatment. Moreover, c-Jun sensitized apoptosis induced by various drugs. Drug-induced apoptosis was associated with c-Jun N-terminal kinase (JNK) activation and c-Jun N-terminal phosphorylation (JNP). In contrast, overexpression of c-jun delayed apoptosis in serum-starved cells, indicating that c-Jun may reduce or accelerate apoptosis in MEL cells depending on the nature of the apoptotic stimulus. These results suggest that the proto-oncogene c-Jun may modulate differentiation and apoptosis of leukemic cells.     

Cellular studies of MrDb (DDX18)

Helicases are present in viruses, prokaryotes, and eukaryotes, and several of them have been linked to human diseases. Here we study the role of one putative DEAD-box RNA helicase, MrDb (DDX18), in tumor cells. We show that MrDb is a nucleolar protein ubiquitously expressed in tumor cells and that it is more abundantly expressed in proliferating cells. Inhibition of MrDb with dominant negative mutant or a shRNA reduces tumor cell proliferation without inducing a cell cycle arrest or apoptosis. These findings suggest that MrDb is important for cell proliferation and that its inhibition could prevent tumor cell proliferation.     

Inhibition of the mitogen activated protein kinase pathway potentiates radiation-induced cell killing via cell cycle arrest at the G2/M transition and independently of increased signaling by the JNK/c-Jun pathway

The ability of low dose ionizing radiation (2 Gy) to modulate the activities of the mitogen activated protein kinase (MAPK) and c-Jun NH2-terminal kinase (JNK1) cascades in human monocytic leukemia (U937/pREP4) cells and in cells over-expressing dominant negative c-Jun (TAM67) (U937/TAM67) was investigated. Radiation exposure caused prolonged ( approximately 1 h) MAPK activations in U937 cells. In contrast, low dose irradiation weakly modulated JNK1 activity in these cells. Inhibition of the MAPK pathway by use of the specific MEK1/2 inhibitor (10 microM PD98059) in both U937/pREP4 and U937/TAM67 cells prior to radiation exposure permitted strong prolonged radiation-induced activations of JNK1. Expression of TAM67 decreased the ability of radiation to cause apoptosis compared to control transfected cells. However, combined MEK1/2 inhibition and radiation exposure in both cell types caused a large decrease in suspension culture growth and a large increase in apoptosis, when compared to either treatment alone. Reduced proliferation after combined irradiation and PD98059 treatment in both cell types correlated with prolonged cell cycle arrest in G2/M phase. Prolonged growth arrest was abolished when MEK1/2 inhibitor was removed 6 h following irradiation, which was associated with a reduction in apoptosis. The ability of MEK1/2 inhibition to cause prolonged G2/M growth arrest was reduced in U937 cells stably transfected with a p21Cip-1/WAF1 antisense construct (U937/p21AS). This data correlated with an enhancement of radiation-induced apoptosis and a reduced ability of MEK1/2 inhibition to potentiate apoptosis. Collectively our data demonstrate that inhibition of MEK1/2 function increases the radiation sensitivity of U937 cells, independently of c-Jun function, and decreases the ability of these cells to recover from the radiation-induced G2/M cell cycle checkpoint arrest. In addition, our data also demonstrate that the ability of MEK1/2 inhibition to potentiate radiation-induced cell death in U937 cells in part requires an ability of cells to express low levels of p21Cip-1/WAF1.     

TSA对人肝癌细胞SMMC-7721的抑制作用及其机制

目的:研究去乙酰化转移酶抑制剂TSA对肝癌细胞SMMC-7721的作用及其机理。方法:利用细胞计数,流式细胞仪分析细胞凋亡及细胞周期,Tunel试验研究TSA对肝癌细胞SMMC-7721的作用;利用western研究TSA对肝癌细胞蛋白表达的影响。结果:TSA可明显抑制肝癌细胞SMMC-7721的生长,并可诱导细胞凋亡。可阻滞肝癌细胞SMMC-7721细胞周期于G0/G1期。可增加p53,p21,bax等基因的表达,降低BCL-2的表达。结论:去乙酰化转移酶抑制剂TSA可明显抑制肝癌细胞SMMC-7721的生长并诱导其凋亡,其主要通过调控一些肿瘤相关基因的表达起作用。     

小檗碱通过调控IGF-1R信号通路抑制食管癌细胞增殖和诱导细胞凋亡的实验

目的 检测小檗碱对食管癌细胞增殖、周期和凋亡的影响,并探讨其作用机制。 方法 MTT法检测细胞的增殖抑制作用;碘化丙啶（Propidium iodide, PI）染色法检测细胞周期进程;Annexin V-FITC和PI双染法结合流式细胞技术检测小檗碱的凋亡诱导作用;Western blot技术检测小檗碱对胰岛素样生长因子1受体（IGF-1R）的活化及下游主要信号分子AKT和p44/42MAPK（ERK）磷酸化水平的影响。结果 小檗碱在体外可浓度依赖性地抑制四种食管癌细胞系的增殖,且其IC50值与细胞表面IGF-1R的表达水平呈负相关。小檗碱可使细胞阻滞在G₂/M期。细胞凋亡实验结果显示,小檗碱可浓度依赖性地诱导食管癌细胞发生凋亡,并且在相同浓度下KYSE450细胞（IGF-1R高表达）的凋亡率显著高于KYSE150细胞（IGF-1R低表达）。Western blot结果显示,小檗碱处理可显著抑制IGF-1R的磷酸化,并抑制AKT和ERK的活化,且抑制作用随着小檗碱浓度的增加而增强。结论 小檗碱可通过对IGF-1R及其介导的下游信号通路的调控来发挥抑制食管癌细胞增殖、阻断细胞周期进程以及诱导食管癌细胞凋亡的作用。     

三氧化二砷诱导Raji细胞凋亡与Survivin基因关系的研究

Objective:To investigate the apoptosis induction by arsenic trioxide (As2O3) in Raji cells and its correlation with cell cycle arrest and expression of the Survivin gene.Methods:After Raji cells were treated with As2O3 in different concentrations (1,2,4 and 8 μM),for 24,48 and 72 h,respectively,and cell proliferation was tested by MTT assay.Apoptosis was observed with electron microscope end DNA electrophoresis.The distribution of cell cycles and cell apoptosis were detected by flow cytometry.Expression of the Survivin gene was determined by real-time quantitative RT-PCR.Results:As2O3 (1-8 μM) inhibited Raji cells growth effectively in a dose- and time-dependent manner.As2O3 at 2-8μM could induce cell apoptosis and cell cycle arrest.However,As2O3 (1 μM) inhibited Raji proliferation only by cell cycle arrest,without any symptoms of cell apoptosis.At the same time,Survivin gene expression was down-regulated after the treatment.Conclusion:As2O3 could induce substantial proliferation inhibition,cell cycle arrest and apoptosis in Raji cell.Cell cycle arrest might be a reason why apoptosis occurs.As2O3 can markedly down-regulate expression of the Survivin gene in a dose- and timedependent manner.The down-regulated Survivin gene might be leading to cell apoptosis by As2O3.     

宫颈癌组织和细胞中PAGE4的表达及其对癌细胞增殖、凋亡和迁移的影响北大核心

目的:探究前列腺相关基因4(prostate-related gene 4,PAGE4)在宫颈癌组织和细胞中的表达及其对癌细胞增殖、凋亡和迁移的影响。方法:根据前期组学结果,已筛选出宫颈癌中显著差异表达的基因PAGE4。IHC和RT-qPCR检测PAGE4在宫颈癌组织和细胞中的水平。构建并验证PAGE4过表达载体,随后转染宫颈癌SiHa和HeLa细胞系,运用CCK-8实验、克隆形成实验、流式细胞术、划痕愈合实验、Transwell迁移实验和Western blotting探究PAGE4对宫颈癌细胞增殖、细胞周期、凋亡、迁移和上皮间质转化的影响。应用STRING数据库预测PAGE4的潜在互作分子c-Jun,RT-qPCR检测其在过表达PAGE4的宫颈癌细胞系中的水平。通过沉默c-Jun和回复实验初步探究c-Jun在PAGE4介导的宫颈癌细胞转移中的作用。结果:测序结果表明PAGE4在宫颈癌组织中表达明显下调,倍数约为457倍。PAGE4在宫颈癌组织及细胞系中均呈低表达。与对照组相比,过表达PAGE4组细胞增殖、细胞周期以及凋亡无明显差异,但细胞迁移明显减弱,E-cadherin蛋白表达上调且Vimentin蛋白表达下调。c-Jun逆转过表达PAGE4对宫颈癌细胞迁移和上皮间质转化的影响。结论:过表达PAGE4能抑制宫颈癌细胞的迁移和上皮间质转化,其机制可能与c-Jun相关。总之,PAGE4可能在宫颈癌的转移中起一定作用,PAGE4有望成为抑制肿瘤转移的新靶点。     

组蛋白去乙酰化酶抑制剂SAHA抑制乳腺癌细胞MDA-MB-435增殖及促凋亡的作用机制

目的 观察组蛋白去乙酰化酶抑制剂SAHA对人乳腺癌细胞系MDA-MB-435增殖、凋亡等的作用及其相关分子机制。方法 不同浓度的SAHA作用于MDA-MB-435细胞后,采用MTT、流式细胞分析、Western blot、荧光定量PCR等方法检测细胞增殖、凋亡、周期阻滞情况及相关蛋白及mRNA表达。 结果 MTT检测结果表明SAHA可呈剂量依赖性抑制细胞增殖,流式细胞分析发现SAHA可导致G2/M期周期阻滞、线粒体膜电位下降、活性氧（ROS）产生并发生早期凋亡。同时,SAHA可下调周期蛋白cyclinB、活化p38-MAPK及JNK,抑制p53的表达且可能不是通过PI3K通路、P38 MAPK通路、ERK1/2通路和NF-κB 、JNK通路起作用。结论 SAHA能抑制MDA-MB-435细胞增殖,诱导其周期阻滞及早期凋亡,活化细胞内相关增殖分子,可作为乳腺癌潜在的候选药物。     

PRKAA1 Promotes Proliferation and Inhibits Apoptosis of Gastric Cancer Cells Through Activating JNK1 and Akt Pathways

PRKAA1 (protein kinase AMP-activated catalytic subunit 1) is a catalytic subunit of AMP-activated protein kinase (AMPK), which plays a key role in regulating cellular energy metabolism through phosphorylation, and genetic variations in the PRKAA1 have been found to be associated with gastric cancer risk. However, the effect and underlying molecular mechanism of PRKAA1 on gastric cancer tumorigenesis, especially the proliferation and apoptosis, are not fully understood. Our data showed that PRKAA1 is highly expressed in BGC- 823 and MKN45 cells and is expressed low in SGC-7901 and MGC-803 cells in comparison with the other gastric cancer cells. PRKAA1 downregulation by shRNA or treatment of AMPK inhibitor compound C significantly inhibited proliferation as well as promoted cell cycle arrest and apoptosis of BGC-823 and MKN45 cells. Moreover, the expression of PCNA and Bcl-2 and the activity of JNK1 and Akt signaling were also reduced in BGC-823 and MKN45 cells after PRKAA1 downregulation. In vivo experiments demonstrated that tumor growth in nude mice was significantly inhibited after PRKAA1 silencing. Importantly, inactivation of JNK1 or Akt signaling pathway significantly inhibited PRKAA1 overexpression-induced increased cell proliferation and decreased cell apoptosis in MGC-803 cells. In conclusion, our findings suggest that PRKAA1 increases proliferation and restrains apoptosis of gastric cancer cells through activating JNK1 and Akt pathways.     

吲哚美辛诱导肝癌HepG2细胞凋亡及其对cyclin E蛋白表达的影响

目的　观察吲哚美辛诱导肝癌 Hep G2细胞凋亡 ,及其对 cyclin E蛋白的影响。方法　采用 MTT比色法观察吲哚美辛对肝癌 Hep G2细胞增殖的影响 ;采用流式细胞仪检测吲哚美辛对 Hep G2细胞周期分布的影响 ,同时结合透射电子显微镜观察吲哚美辛诱导肝癌 Hep G2细胞凋亡的作用 ;免疫细胞化学方法观察吲哚美辛对Hep G2细胞周期调控蛋白 cyclin E的影响。结果　吲哚美辛可抑制肝癌 Hep G2细胞的增殖 ,诱导其凋亡 ,改变细胞周期分布 ,使 G0 /G1 期细胞比例增高 ,S期比例降低 ,同时还可使 cyclin E蛋白表达下降。上述作用具有剂量和时间依赖性 (P<0 .0 5 )。结论　吲哚美辛可诱导肝癌 Hep G2细胞凋亡 ,改变细胞周期分布 ,影响细胞周期调控蛋白表达 ,从而抑制细胞增殖。     

Natural withanolide withaferin A induces apoptosis in uveal melanoma cells by suppression of Akt and c-MET activation

Uveal melanoma (UM) is the most common primary intraocular malignancy in adults. While effective therapy exists for the primary tumor, there is a lack of effective treatment for metastatic disease currently. Natural withanolide withaferin A (WA) has shown efficacy in cancers demonstrating upregulation of pro-survival pathways. The purpose of the present study is to investigate the effect of WA as a potential therapeutic agent for UM in vitro as well as in vivo. UM cells were treated with WA and several cell-based assays, such as MTS, trypan blue exclusion assay, clonogenic, wound healing, cell cycle shift, annexin V/propidium iodide, and Western blot, were performed. In vivo experiments utilized the 92.1 cells in a xenograft murine model. WA inhibits cell proliferation of uveal melanoma cells with an IC50 of 0.90, 1.66, and 2.42 μM for OMM2.3, 92.1, and MEL290 cells, respectively. Flow cytometry analysis demonstrates G2/M cell cycle arrest and apoptosis at 1 μM WA in treated cells. WA induced apoptosis partly through the suppression of c-Met, Akt, and Raf-1 signaling activation. In vivo studies using WA reduced tumor growth in 100% of animals (p = 0.015). Our observation indicates that WA is a potent drug that inhibits cell proliferation, shifts cell cycle arrest, and induces apoptosis in multiple UM cell lines in vitro. WA-mediated apoptosis in UM cells is partly mediated though the suppression of c-Met and Akt activation. WA significantly decreases UM tumor growth in vivo and justifies further evaluation of this drug for the treatment of metastatic uveal melanoma.     

Different contribution of apoptosis to the antiproliferative effects of diosgenin and other plant steroids,hecogenin and tigogenin,on human 1547 osteosarcoma cells

Regulation of growth arrest and apoptosis are, in part, controlled by the tumor suppressor p53 after its phosphorylation which causes a determinant role in its functional activation. Moreover, PPAR regulate many functions such as proliferation and apoptosis. We compared the biological activity of diosgenin with hecogenin and tigogenin, plant steroids structurally close to diosgenin, on proliferation rate, cell cycle distribution and apoptosis in human 1547 osteosarcoma cells. We found that all three molecules have an antiproliferative effect but gel shift analysis demonstrated that none of the plant steroids transactivated PPAR in human 1547 osteosarcoma cells whereas these molecules induced NF-kappaB binding to DNA. Although these plant steroids have a very close structure, only diosgenin caused a cell cycle arrest associated with strong apoptosis. This biological action seems correlated with a large increase of p53 protein expression. This fact was showed by immunofluorescence analysis which confirmed that diosgenin strongly enhanced the activation of p53 in contrast to hecogenin and tigogenin actions.     

Notch-dependent cell cycle arrest and apoptosis in mouse embryonic fibroblasts lacking Fbxw7

The F-box protein Fbxw7 mediates the ubiquitylation and consequent degradation of proteins that regulate cell cycle progression, including cyclin E, c-Myc, c-Jun and Notch. Moreover, certain human cancer cell lines harbor loss-of-function mutations in FBXW7 that result in excessive accumulation of Fbxw7 substrates, implicating Fbxw7 in tumor suppression. To elucidate the physiological function of Fbxw7, we conditionally ablated Fbxw7 in mouse embryonic fibroblasts (MEFs). Unexpectedly, loss of Fbxw7 induced cell cycle arrest and apoptosis that were accompanied by abnormal accumulation of the intracellular domain of Notch1 (NICD1). Forced expression of NICD1 in wild-type MEFs recapitulated the phenotype of the Fbxw7-deficient (Fbxw7(Delta/Delta)) MEFs. Conversely, deletion of Rbpj normalized the phenotype of Fbxw7(Delta/Delta) MEFs, indicating that this phenotype is dependent on the Notch1-RBP-J signaling pathway. Deletion of the p53 gene prevented cell cycle arrest but not the induction of apoptosis in Fbxw7(Delta/Delta) cells. These observations suggest that Fbxw7 does not function as an oncosuppressor in MEFs. Instead, it promotes cell cycle progression and cell survival through degradation of Notch1, with loss of Fbxw7 resulting in NICD1 accumulation, cell cycle arrest and apoptosis.