DNA异常甲基化在肿瘤中的作用

DNA甲基化与肿瘤有密切的联系,DNA甲基化状态改变是致癌的一个关键因素,是抑癌基因失活的方式之一。本文对相关基因甲基化与肿瘤发生,肿瘤的早期诊断、预后判断及治疗的关系进行了阐述。     

肺鳞癌、腺癌中p14 ARF基因启动子区甲基化及蛋白表达的研究

背景与目的 p14^ARF基因是新近发现的抑癌基因，其异常表达与多种人类肿瘤发生有关，启动子区异常甲基化作为p14^ARF基因失活的重要形式可能参与了肿瘤的发生。本研究通过检测肺鳞癌、腺癌中p14^ARF启动子区甲基化状态和蛋白表达，探讨p14^ARF启动子区甲基化与肺癌的关系。方法 通过免疫组织化学（IHC）、甲基化特异性PCR（MSP）和相关限制性内切酶PCR（RF-PCR）方法，检测40例肺鳞癌、腺癌组织中p14^ARF启动子区甲基化状态和蛋白表达水平。结果 癌组织及癌旁正常组织中p14^ARF启动子区甲基化阳性率分别为17．5％（7／40）和2．5％（1／40）（P-0．025）。RE-PCR检测结果相同。癌组织及癌旁正常组织中p14^ARF蛋白阳性率分别为70．0％（28／40）和95．0％（38／40）（P-0．003）。p14^ARF基因启动子区甲基化和蛋白表达均与肿瘤分期、组织类型、分化程度、淋巴结转移等临床病理特征无明显关系（P＜0．05）。p14^ARF启动子区甲基化与蛋白表达呈负相关（r=-0．56，P=0．001）。结论 启动子区甲基化是p14^ARF基因失活的重要机制。p14^ARF启动子区异常甲基化可能参与了非小细胞肺癌的发生，是肺癌发生过程的早期事件。     

Syk基因甲基化和肝癌术后复发转移关系的研究

目的 探讨肝癌组织Syk基因启动子甲基化改变的特点,及其与肝癌术后复发转移的关系.方法 采用甲基化特异性PCR方法检测Syk基因启动子甲基化情况,结合随访结果,探讨Syk基因启动子甲基化和肝癌术后复发转移的关系.结果 在64例肝癌组织标本中,有19例检测到Syk基因启动子甲基化,发生率为29.7%;在对应癌周正常肝组织中,只有2例检测到Syk基因启动子甲基化,发生率为3.1%.癌组织Syk基因启动子甲基化发生率显著增高（P〈0.005）.在19例癌组织检测到Syk基因启动子甲基化的肝癌患者中,有14例术后发生癌复发转移,发生率为73.7%;在45例癌组织未检测到Syk基因启动子甲基化的肝癌患者中,只有19例术后发生癌复发转移,发生率为42.2%.癌组织检测到Syk基因启动子甲基化的肝癌患者术后复发转移发生率显著增高（P〈0.05）.结论 Syk基因启动子甲基化可能是肝癌发生发展过程中重要的机制之一.肝癌组织Syk基因启动子甲基化可能是预测患者术后复发转移潜在的生物标记物.     

DNA甲基化抑制剂诱导Kasumi-1细胞分化和凋亡作用

目的：探讨DNA甲基化抑制剂5—氮—2′—脱氧胞苷(5—Aza—CdR)体外诱导Kasumi-1细胞分化和凋亡作用。方法：应用MTT比色法观察5—Aza—CdR对细胞的生长抑制作用，普通光学显微镜观察细胞形态和结构改变，流式细胞术检测髓系分化抗原的表达，DNA凝胶电泳分析细胞凋亡。结果：5—Aza—CdR明显抑制Kasumi-1细胞的生长，半数抑制浓度(IC50)约为0.65μmol/L。5—Aza—CdR可诱导Kasumi-1细胞髓系分化抗原CDllb和CDl3表达增加。5—Aza—CdR诱导Kasumi-1细胞凋亡。用5—Aza—CdR处理后的细胞出现单核细胞样分化和凋亡细胞形态改变。结论：5--氮—2′—脱氧胞苷抑制Kasumi-1细胞生长，并能诱导细胞部分分化与凋亡。     

乙型肝炎病毒感染后表型不一致的单卵孪生子基因组CpG岛甲基化谱差异分析

目的进行乙型肝炎病毒感染后表型不一致的单卵孪生子基因组CpG岛甲基化谱差异分析,以发现可能的差异甲基化基因。方法采用改良甲基化间区位点扩增技术,根据人基因组CpG岛甲基化位点的两种主要碱基组合,-CGCG-和-CCGG-,用3种不同的酶切组合（SmaⅠ—XmaⅠ、HpaⅡ-MspⅠ、BssHⅡ—PauⅠ／BsePⅠ）,同时采用Personal Molecular Imager FX分子成像系统及放射自显影相结合的方法,经Quantity One 4．4．0凝胶图像分析软件进行差异条带分析,分离回收差异甲基化条带并克隆人T载体,阳性克隆进行测序,将测序结果进行BLAST分析,初步了解与乙型肝炎病毒感染后表型不一致的单卵孪生子相关的差异甲基化基因情况。结果在一对表型一致的单卵孪生子间基因组CpG岛甲基化分析显示条带几乎相同,而在另一对表型一致以及一对表型不一致的单卵孪生子之间均存在差异甲基化条带,前者差异甲基化条带数目少于后者,将得到的差异甲基化条带克隆人T载体,目前测序分析得到4个可能与乙型肝炎病毒感染后表型不一致的单卵孪生子相关的差异甲基化基因。结论乙型肝炎病毒感染后表型不一致的单卵孪生子间基因组CpG岛甲基化水平有差异,其对疾病表型的影响及机制尚需后续深入研究。     

Aberrant p16 methylation is a biomarker for tobacco exposure in cervical squamous cell carcinogenesis

OBJECTIVE: The purpose of this study was to determine the association between active tobacco exposure and aberrant p16 promoter methylation in primary cervical squamous cell cancer and high-grade squamous cervical dysplasia. STUDY DESIGN: p16 methylation-specific polymerase chain reaction was performed on DNA that was extracted from 60 cervical cancers, 30 high-grade dysplasia specimens, and 78 normal cervical cytologic specimens. Patient data were obtained by medical record review or were collected prospectively. RESULTS: Aberrant p16 methylation was significantly higher in squamous cell cervical cancers (61%) than in squamous high-grade dysplasia (20%) or normal cytologic specimens (7.5%). Approximately one half the women with squamous cancer and one half of the women with high-grade dysplasia were active smokers. Aberrant p16 methylation was associated with active tobacco use in patients with squamous carcinoma (odds ratio, 20.6; 95% CI, 3.6-118; P<.001) and high-grade dysplasia (odds ratio, 4.57; 95% CI, 1.63-12.78; P=.002). CONCLUSION: Aberrant p16 methylation is associated strongly with active tobacco use in squamous cell cervical cancers and high-grade dysplasia.     

Methylation of tumor suppressor gene p16 and prognosis of epithelial ovarian cancer

OBJECTIVE: Methylation of p16 promoter was evaluated in ovarian cancer to determine the role of p16 methylation in ovarian cancer prognosis. METHODS: Two hundred and forty-nine patients with primary epithelial ovarian cancer were selected for the study; these patients were followed for a median of 31 months. Genomic DNA extracted from fresh frozen tumor tissues were treated with sodium bisulfite and were analyzed for p16 methylation using methylation-specific PCR (MSP). Cox regression survival analysis was performed to examine the associations of p16 methylation with progression-free and overall survivals. RESULTS: Of the 249 patients, 100 (40%) were tested positive for p16 promoter methylation. The status of p16 methylation did not change significantly with patient age, disease stage, histological grade, residual tumor size, and debulking results, although p16 methylation seemed to occur more often in patients with advanced diseases or aggressive tumors. Compared to those without p16 methylation, patients with p16 methylation had significantly higher risk for disease progression (P = 0.01). The relative risk for progression was 1.69 (95% CI: 1.12-2.54), and the association remained statistically significant (RR = 1.54, 95% CI: 1.01-2.34) after adjusting for clinical and pathological variables. The risk for death was also higher in methylation positive patients than in methylation negative patients (RR = 1.33, 95% CI: 0.88-2.00), but the difference was not statistically significant. CONCLUSION: The study suggests that promoter methylation in the p16 gene is associated with ovarian cancer progression, and evaluation of p16 methylation may have values in predicting ovarian cancer prognosis.     

5-AZA-2'-deoxycytidine (5-AZA-CdR): a demethylating agent affecting development and reproductive capacity

The objective was to evaluate the effects of 5-AZA-2'-deoxycytidine (5-AZA-CdR) on postnatal development and reproductive capacity. Pregnant mice were administered 1 mg kg-1 5-AZA-CdR at gestation day 10. The body weights of F1 control and treated (in uterine-exposed) pups were recorded. To evaluate the reproductive capacity, 5-AZA-CdR F1 males and females were mated with control mice. The presence of plugs and the number of pregnancies were recorded. The 5-AZA-CdR F1 male mice were killed. Total body, testes and epididymis weights were recorded. Spermatid head counting, histological analyses and serum testosterone levels were performed. Body weights of 5-AZA-CdR F1 mice were statistically lower than controls (P < 0.01), with the females more strongly affected (P < 0.05). Male mating capacity appeared to be more adversely affected. Mating of 5-AZA-CdR F1 males with control females resulted in a lower pregnancy rate compared with control mating groups (P < 0.01). Gross testicular and epididymis weights were lower in 5-AZA-CdR F1 mice (P < 0.01). However, testicular and epididymis weights in these mice were higher than controls when correlated to body weight (P < 0.01). In 5-AZA-CdR F1 male mice, all measured reproductive parameters, including total number of spermatid heads per testis, are significantly lower (P < 0.01) than the controls except for the number of spermatid heads per milligram of testis.     

氯化镉诱发16HBE细胞恶性转化不同阶段P16基因甲基化研究

目的对氯化镉（CdCl2）诱发16HBE细胞系恶性转化不同阶段P16基因启动子区甲基化状况进行研究，探讨镉的表遗传致癌机制。方法从各组CdCl2恶性转化不同阶段及接种裸鼠成瘤的16HBE细胞中提取全基因组DNA，采取甲基化特异性PCR法（Methylation—specific PCR，MSP）检测该基因组P16基因启动子区的甲基化状况，与非转化的16HBE对照细胞进行比较，并用去甲基化因子5-Azac（5-Aza-2＇deoxycytidine）处理有异常甲基化的细胞。结果CdCl2恶性转化及接种裸鼠成瘤的16HBE细胞P16抑癌基因启动子区CpG岛存在异常高甲基化现象，且随着细胞恶性程度的增加，甲基化现象有明显升高的趋势，同时发现有异常高甲基化的细胞经去甲基化处理后甲基化现象消失。结论P16基因启动子区的高甲基化导致抑癌基因表达关闭，无法正常发挥细胞增殖周期对细胞分裂和生长的负调控，造成细胞周期失控而导致无限制地细胞增殖，这可能是氯化镉诱导16HBE细胞恶性转化及接种裸鼠成瘤的一种表遗传致癌作用。研究结果可部分解释镉化合物的细胞转化作用及其可能的表遗传致癌机制，以及进一步对甲基化的表型逆转和药物治疗研究提供了重要依据。