DNA methyltransferase expression and DNA hypermethylation in human hepatocellular carcinoma

Aberrant DNA methylation and increased expression of DNA methyltransferases (DNMTs) are features of tumor cells. To investigate roles for DNMTs during hepatocarcinogenesis, we examined DNMT expression at both the mRNA and protein level in hepatocellular carcinomas (HCCs) and paired non-neoplastic liver tissues, along with measuring the DNA methylation status of five tumor suppressor genes. Expression of DNMT1, DNMT3a and DNMT3b mRNA was detected in 33.3, 59.3, and 55.6% of HCCs and 40.7, 22.2, and 0% of non-neoplastic liver tissues, respectively. DNMT1 and DNMT3a were immunoreactive in 100 and 48% of HCCs and 52 and 0% of non-neoplastic liver tissues. The DNMT3a mRNA expression profile showed significant correlation with its immunoreactivity (P=0.022). DNA methylation status of five tumor suppressor genes, HIC-1, p16, RASSF1A, p53, and RB1 was detected in 85.2, 48.1, 44.4, 22.2, and 0% of HCCs, respectively. There was no significant correlation between DNMT mRNA expression and DNA methylation (P>0.05). DNMT immunoreactivity was also not associated with DNA methylation except HIC-1 (P=0.036) and p53 methylation (P=0.009). Despite the lack of correlation between DNA methylation status and DNMT expression, the frequency of hypermethylation of tumor suppressor genes remained relatively high in HCCs, suggesting that regional DNA hypermethylation is involved in hepatocarcinogenesis and that there may be other mechanisms for increasing DNA methylation.     

Mutation of p53 gene in hepatocellular carcinoma cell lines with HBX DNA

It has been known that the incidence of p53 mutation is very rare in HBX-positive primary human hepatocellular carcinoma (HCC) tissues. The frequency of p53 mutation, however, in established cell lines with integrated HBV DNA and/or HBX has not been well studied. To know p53 mutational frequency, and to investigate whether the presence of HBX DNA sequence correlates with the absence of p53 mutation in the established HCC cell lines, we studied the p53 mutation and the presence of HBX sequence in 12 recently characterized HCC cell lines. As a result, all 12 (100%) lines showed mutation in the p53 gene. Three (25%) cell lines had transversion of codon 215 while no mutation of codon 249 was found. In contrast with previous reports, although HBX DNA was present in 11 cell lines, p53 mutation had occurred, indicating that the presence of HBX viral DNA does not correlate with a lack of p53 mutation in established HCC cell lines. Our results suggest that the frequency of p53 mutation is extremely high even in HBX DNA positive HCC cell lines. © 1996 Wiley-Liss, Inc.     

Paclitaxel shows cytotoxic activity in human hepatocellular carcinoma cell lines

Paclitaxel stabilizes microtubules with inhibition of mitotic spindle formation and has been found effective in several solid cancers. To test whether paclitaxel could be cytotoxic in human HCC cell lines, we used established HuH-7 and HepG2 cell lines. Changes in cell number, DNA synthesis rates and cell viability were determined. We tested whether paclitaxel-treated cells underwent apoptosis, microtubular reorganization, and cell cycle restriction. Studies also examined whether chemosensitization with verapamil enhanced the antitumor activity of paclitaxel. The cell viability was impaired at greater than 0.01 microM paclitaxel concentrations (LD50, 0.8 microM), with flow cytometry indicating accumulation of cells in G2/M, and immunostaining showing polymerized microtubules with characteristic banding patterns. This G2/M restriction was further characterized by flow cytometry, which revealed cyclin A and cdc2 kinase accumulation in paclitaxel-treated cells. Exposure to paclitaxel decreased [3H]thymidine incorporation into DNA in cells at 24 h but this significantly increased at 72 h, most likely due to DNA repair mechanisms related to cell cycle restriction. The cell death was via both apoptotic and non-apoptotic mechanisms. Finally, co-administration of the chemosensitizer verapamil in doses as little as 1 microM increased the antitumor efficacy of paclitaxel by up to five-fold and changed the LD50 of paclitaxel to 0.1 microM. The findings indicate that paclitaxel is cytotoxic to cultured hepatocellular carcinoma cells. Clinical studies of paclitaxel in patients with hepatocellular carcinoma may help determine additional therapies.     

DNA damage inducible-gene expression following platinum treatment in human ovarian carcinoma cell lines

 Repair of cisplatin-damaged DNA was investigated in a human ovarian carcinoma cell line (2008) and its cisplatin-resistant variant (C13^*) using a host-cell reactivation (HCR) assay. The HCR of cisplatin-damaged adenovirus (Ad) was not significantly different in C13^* cells compared to 2008 cells. The cisplatin concentrations required to reduce the amount of viral DNA replicated to 50% were 0.12±0.02 μM and 0.10±0.01 μM after 48 h of repair in 2008 and C13^* cells respectively. Similarly, the cisplatin concentration required to reduce the expression of a reporter gene inserted in the viral DNA was not significantly altered in C13^* cells compared to the parental line (IC₅₀ values were 0.28±0.04 μM in 2008 cells and 0.17±0.06 μM in C13^* cells after 48 h of repair). Pretreatment of the cells with cisplatin, immediately prior to Ad infection, did not significantly alter the HCR of cisplatin-damaged Ad in either cell type. In addition, a cisplatin-sensitive variant derived from the C13^* cells, namely the RH4 cells, did not differ significantly from either the 2008 or C13^* cells in their ability to reactivate cisplatin-damaged Ad. Furthermore, a component of the nucleotide excision repair (NER) pathway, DNA polymerase α, was investigated using the competitive inhibitor aphidicolin. The combination of cisplatin and aphidicolin resulted in similar synergistic growth inhibition in both the 2008 and C13^* cells providing additional support to the HCR results which suggest that enhanced NER is not responsible for the cisplatin resistance in C13^* cells. Received: 21 April 1995/Accepted: 9 October 1995     

Aberrant DNA methyltransferase 1 expression in clear cell renal cell carcinoma development and progression

Objective： To better understand the contribution of dysregulated DNA methyltransferase 1 （DNMT1） expression to the progression and biology of clear cell renal cell carcinoma （ccRCC）. Methods： We examined the differences in the expression of DNMT1 in 89 ecRCC and 22 normal tissue samples by immunohistochemistry. In addition, changes in cell viability, apoptosis, colony formation and invading ability of ccRCC cell lines （786-0 and Caki-1） were assessed after transfection with DNMT1 siRNA. Results： We found DNMT1 protein was significantly higher expressed in ccRCC than that of in no-tumor tissues （56.2% and 27.3%, respectively, P=0.018）. The expression of DNMT1 was strongly associated with ccRCC tumor size, tumor pathology stage, histological grading, lymph node metastasis, vascular invasion, recurrence and prognosis. Moreover, knockdown of DNMT1 expression significantly inhibited ccRCC cell viability, induced apoptosis, decreased colony formation and invading ability. Conclusions： Expression of DNMTI protein is increased in ccRCC tissues, and DNMT1 expression is associated with poor prognosis of patients. Experiments in vitro further showed DNMT1 played an essential role in proliferation and invasion of renal cancer cells. Moreover, targeting this enzyme could be a promising strategy for treating ccRCC, as evidenced by inhibited cell viability, increased apoptosis, decreased colony formation and invading ability.     

三氧化二砷对人类肝癌细胞株端粒酶活性的影响

目的观察中药砒霜的主要成分——三氧化二砷(As2O3)对人类肝癌细胞株的端粒酶活性的影响,深入探讨As2O3注射液的抗肝癌作用机制。方法采用端粒重复序列扩增法(TRAP)结合聚丙烯酰胺凝胶电泳(PAGE)银染法,检测不同浓度和作用时间的As2O3对人类肝癌细胞株SMMC-7721和QGY-7703以及对人类正常肝细胞株L-02端粒酶活性的影响。结果人类正常肝细胞株L-02端粒酶活性为阴性,人肝癌细胞株SMMC-7721和QGY-7703端粒酶活性为阳性。不同浓度的As2O3作用24小时时对肝癌细胞株端粒酶活性未见明显抑制,而浓度20μg/ml和40μg/ml的As2O3作用48小时时可完全抑制其端粒酶活性,浓度为8、10、20和40μg/ml的As2O3作用72小时时可完全抑制其端粒酶活性。结论As2O3能够显著地选择性抑制人类肝癌细胞株端粒酶活性,且这种抑制作用呈现出典型的剂量相关性和时间依赖性。这可能是As2O3抗肿瘤作用的重要机制之一;同时提示As2O3注射液可能是一种优良的和具有临床实用价值的端粒酶抑制剂。     

Decrease of DNA methyltransferase 1 expression relative to cell proliferation in transitional cell carcinoma

In many common cancers such as transitional cell carcinoma (TCC), specific genes are hypermethylated, whereas overall DNA methylation is diminished. Genome-wide DNA hypomethylation mostly affects repetitive sequences such as LINE-1 retrotransposons. Methylation of these sequences depends on adequate expression of DNA methyltransferase I (DNMT1) during DNA replication. Therefore, DNMT1 expression relative to proliferation was investigated in TCC cell lines and tissue as well as in renal carcinoma (RCC) cell lines, which also display hypomethylation, as indicated by decreased LINE-1 methylation. Cultured normal uroepithelial cells or normal bladder tissue served as controls. In all tumor cell lines, DNMT1 mRNA as well as protein was decreased relative to the DNA replication factor PCNA, and DNA hypomethylation was present. However, the extents of hypomethylation and DNMT1 downregulation did not correlate. Reporter gene assays showed that the differences in DNMT1 expression between normal and tumor cells were not established at the level of DNMT1 promoter regulation. Diminished DNMT1:PCNA mRNA ratios were also found in 28/45 TCC tissues but did not correlate with the extent of DNA hypomethylation. In addition, expression of the presumed de novo methyltransferases DNMT3A and DNMT3B mRNAs was investigated. DNMT3B overexpression was observed in about half of all high-stage TCC (DNMT3B vs. tumor stage, chi(2): p = 0.03), whereas overexpression of DNMT3A was rarer and less pronounced. Expression of DNMT3A and DNMT3B in most RCC lines was higher than in TCC lines. Our data indicate that DNMT1 expression does not increase adequately with cell proliferation in bladder cancer. This relative downregulation probably contributes to hypomethylation of repetitive DNA but does not determine its extent alone.     

不同转移潜能人肝癌细胞系的基因表达分析

目的：比较不同转移潜能人肝癌细胞系的基因表达谱,寻找与癌转移相关的基因表达改变。方法：采用基因芯片技术,比较遗传背景相同但转移力有明显差异的两个细胞系MHCC97－L和HCCLM3,分析其基因表达谱的差异。结果：在1626个候选基因中,筛选出25个差异表达基因。HCCLM3与MHCC97－L相比,表达上调的基因有8个,包括细胞增生基因E25、信号传导基因NKK6和免疫相关基因SP40,40等;下调的有17个,包括细胞周期调控基因Rb2、信号传导基因PKCβ2和错配修复基因hMSH2等。结论：肝癌转移是多基因作用的综合结果,筛选的基因对预测转移和抗转移干预措施可能有指导意义。     

DNA 甲基化抑制剂对肿瘤细胞中核糖核酸酶抑制因子表达下调的影响

背景与目的:人核糖核酸酶抑制因子 (ribonucleasE-inhibitor, RI) RI能有效抑制血管生成因子诱导的血管形成及某些可移植性实体瘤在动物体内的生长.然而, RI抗肿瘤的分子机制还未完全阐明.许多抑癌基因通过启动子区域异常的甲基化而使表达缺失,去甲基化抑制能使其表达恢复.为了进一步了解 RI的功能以及探讨 RI与肿瘤发生的关系,本实验拟研究甲基化抑制剂 5-aza-2′-deoxycytidinE-(5-Aza-CdR)对肿瘤细胞中 RI表达的影响.方法:用 5-Aza-CdR作用人乳腺癌细胞系 MCF-7、人胃癌细胞系 BGC-823、人的前列腺癌细胞系 DU-145和人结肠癌细胞系 HT-29.通过 RT PCR,蛋白免疫印迹法( Western blot) ,免疫荧光( immunofluorescence)和免疫细胞化学( immunocytochemistry)技术分析 RI基因的表达.结果:与对照组比较, 5-Aza-CdR能显著提高 RI基因在 MCF-7、 BGC-823和 DU 145细胞中的表达, RT PCR检测结果分别为 37.2%、 46.0%和 32.4%, Western blot检测结果分别为 26.4%、 20.9%和 24.4%( P< 0.01);但对 HT-29细胞没有明显的影响.结论: RI基因可能与胃癌、前列腺癌和乳腺癌的发生有关.     

Increased expression of IL-6 mRNA in hepatocellular carcinoma cell lines correlates with biological characteristics

Background & aims: IL-6 has been implicated in both virus-associated and diethylnitrosamine-induced hepatocellular carcinomas (HCCs). Generally it is produced by immune cells such as Kupffer cells inthe liver. To understand mechanisms by which IL-6 might participate in the genesis of HCCs, the production of IL-6 by cell lines under different conditions was examined to determine inducing factors Methods: Expression of IL-6 mRNA in both hepatoma cell lines and a normal liver cell line L-02 was measured by quantitative RT-PCR. Biological molecules including liposome, dsRNA and cell debris were used to stimulate IL-6 mRNA expression in HepG2 cells and inhibition was effected by RNAi. Proliferation was assessed by MTT and clone formation and migration was determined by scratch assay. Results: All of the HCC cell lines observed expressed IL-6 mRNA, including HepG2, Bel-7402(7402), MHCC-97H and SMMC-7721.Normal liver cell line L-02 also expressed IL-6 mRNA. SiRNA to IL-6 specifically knockdowned IL-6 mRNA expression in HepG2, and liposome, dsRNA and cell debris increased it. Both proliferation and migration of HepG2 cells were related to the level of IL-6 HepG2 expressed. Conclusion: Both normal liver cell line and HCC cell lines can produce IL-6 so that Kupffer cells are noit the only source of the cytokine in the liver well as other immune cells. That the fact that HCC cells reacted to stimulation of biological molecules such as liposome, dsRNA or cell debris with increasing production of IL-6 indicates that the cytokine might play an important role not only in the period of tumor initiation but progression and recurrence as well.     

Induction of apoptosis in hepatocellular carcinoma cell lines by emodin.

Previous experiments have shown that emodin is highly active in suppressing the proliferation of several tumor cell lines. However, it is not clear that emodin can induce growth inhibition of hepatoma cells. We have found that emodin induces apoptotic responses in the human hepatocellular carcinoma cell lines (HCC) Mahlavu, PLC/PRF/5 and HepG2. The addition of emodin to these three cell lines led to inhibition of growth in a time- and dose-dependent manner. Emodin generated reactive oxygen species (ROS) in these cells which brought about a reduction of the intracellular mitochondrial transmembrane potential (DeltaPsim), followed by the activation of caspase-9 and caspase-3, leading to DNA fragmentation and apoptosis. Our findings demonstrate that ROS and the resulting oxidative stress play a pivotal role in apoptosis. Preincubation of hepatoma cell lines with the hydrogen peroxide-scavenging enzyme, catalase (CAT) and cyclosporin A (CsA), partially inhibited apoptosis. These results demonstrate that enhancement of generation of ROS, DeltaPsim disruption and caspase activation may be involved in the apoptotic pathway induced by emodin.     

DNA甲基转移酶1在子宫颈病变组织和子宫颈癌细胞中的异常表达及其意义

 目的　探讨DNA甲基转移酶1（DNMT1）在子宫颈病变组织和子宫颈癌细胞中的异常表达及其意义。方法　选择经病理学确诊的子宫颈鳞状细胞癌（SCC）患者80例、子宫颈上皮内瘤样变（CIN）患者105例（CINⅠ 52例,CINⅡ／Ⅲ 53例）和子宫颈正常（NC）者53名,收集其手术或活组织检查子宫颈组织标本。选择子宫颈癌Caski细胞（HPV16阳性）和C33A细胞（HPV阴性）进行体外实验。分别采用Western blot和实时荧光聚合酶链反应（qRT-PCR）法检测子宫颈组织和细胞中DNMT1蛋白和mRNA的表达。结果　DNMT1蛋白和mRNA的表达水平在CIN及SCC组织中均较NC组织高,差异均有统计学意义（F＝110.57,P＜0.001;F＝2.68,P＝0.048）;随着子宫颈病变程度的加重,DNMT1蛋白表达水平呈逐渐上升趋势（χ2趋势＝50.80,P＜0.001）,但DNMT1 mRNA的表达在调整子宫颈癌相关因素后,未显示相同趋势（χ2趋势＝3.63,P＞0.05）。Caski 细胞DNMT1蛋白和mRNA的表达水平均较C33A细胞高,特别是mRNA的表达水平差异有统计学意义（t＝7.134,P＝0.002）。结论　DNMT1蛋白和mRNA高表达均是导致子宫颈癌和癌前病变发生的危险因素,HPV16感染与DNMT1转录功能异常对子宫颈癌的发生可能有协同效应。     

Functional diversity of DNA methyltransferase inhibitors in human cancer cell lines

DNA methyltransferase inhibitors represent promising new drugs for cancer therapies. The first of these compounds (5-azacytidine, Vidaza) has recently been approved as an antitumor agent, and others are presently in various stages of their preclinical or clinical development. Most of the archetypal inhibitors have been established and characterized in different experimental systems, which has thus far precluded their direct comparison. We have now established defined experimental conditions that allowed a comparative analysis of the six most widely known DNA methyltransferase inhibitors: 5-azacytidine (5-aza-CR), 5-aza-2'-deoxycytidine (5-aza-CdR), zebularine, procaine, (-)-epigallocatechin-3-gallate (EGCG), and RG108. Of these, 5-aza-CR, 5-aza-CdR, zebularine, and EGCG were found to exhibit significant cytotoxicity in human cancer cell lines. 5-aza-CdR and EGCG were also found to be genotoxic, as evidenced by the induction of micronuclei. In addition, 5-aza-CR, 5-aza-CdR, zebularine, and RG108 caused concentration-dependent demethylation of genomic DNA, whereas procaine and EGCG failed to induce significant effects. Finally, the experiments in cancer cell lines were complemented by a cell-free in vitro assay with purified recombinant DNA methyltransferase, which indicated that RG108 is the only drug capable of direct enzyme inhibition. These results show a substantial diversity in the molecular activities of DNA methyltransferase inhibitors and provide valuable insights into the developmental potential of individual drugs.