食管癌新鲜肿瘤组织中MT-3基因CpG岛甲基化的临床意义

The Clinical Significance of Methylation of the CpG Island in the MT-3 Gene in Fresh Esophageal Cancer Tissues

目的:金属硫蛋白(metallothionein,MT)-3不仅具有其它MT共有的细胞解毒功能,还有很强的生长抑制活性,是目前所知唯一一个具有独特生理功能的MT亚型。本研究旨在明确MT-3基因CpG岛在食管癌组织中的甲基化状况及其临床意义。方法:选取2005年5月至7月河北医科大学第四医院胸外科食管癌手术治疗患者68例,其中男49例,女19例;年龄42～76岁;其中食管上段癌6例,中段癌46例,下段癌16例。国际TNM分期:Ⅰ期3例,ⅡA期13例,ⅡB期29例,Ⅲ期22例,Ⅳ期1例。组织学分级:高分化癌8例,中分化癌54例,低分化癌6例。全组患者均为鳞状细胞癌,且随访满30个月。取其新鲜手术标本及切缘正常组织,提取组织DNA及RNA,应用重亚硫酸钠处理限制性酶切图谱分析研究其MT-3基因的甲基化情况;应用实时RT-PCR技术,研究其MT-3mRNA的表达情况,然后与各临床病理参数及随访资料进行比较。结果:全组患者共11例(16.2%)肿瘤组织发现MT-3基因甲基化,而所有患者的上或下切缘的正常组织均未检测到甲基化。存在和不存在甲基化的肿瘤组织中MT-3mRNA的表达水平分别为2.54±1.11和5.13±1.86(P=0.027)。MT-3基因甲基化与TNM分期(P=0.031)、淋巴结转移情况(P=0.001)及术后生存时间(P=0.037)有关,而与患者的性别、肿瘤部位、组织分化程度及肿瘤侵犯深度均无关(P均>0.05)。结论:食管癌组织MT-3基因的甲基化影响该基因的表达水平,此事件易发生于肿瘤晚期患者,与淋巴结转移及预后较差相关。

Objective： To investigate the methylation of a CpG island in the MT-3 gene in tissues of esophageal cancer and its clinical significance. Methods： A total of 68 patients with esophageal cancer who underwent surgery between May and July 2005 were analyzed. There were 49 males and 19 females, ranging from 42 to 76 years old. The numbers of cases of esophageal cancer in the upper, middle, and lower part of the esophagus were 6, 46, and 16, respectively. There were 3 stage Ⅰ cases, 13 stage IIA cases, 29 stage liB cases, 22 stage Ⅲ cases, and 1 stage Ⅳ case. Eight cases were well differentiated, 54 cases were moderately differentiated, and 6 cases were poorly differentiated. All of the patients suffered from squamous cell carcinoma and were followed up for more than 30 months. Samples of tumor and normal margin tissues were collected. DNA and RNA were extracted from these tissues. Combined bisulfite restriction analysis （COBRA） was employed to investigate the status of MT-3 methylation. Real-time RT-PCR was used to detect the levels of MT-3 mRNA expression. The results of COBRA and RT-PCR, clinicopathologic parameters, and follow-up data were analyzed. Results： MT-3 methylation was found in 16.2% （11/68） of the tumor tissues. However, no methylation was detected in the normal tissues from the upper or lower margin. The expression of MT3 mRNA in methylat- ed and unmethylated tumor tissues was 2.54± 1.11 and 5.13± 1.86, respectively （P=-0.027）. MT-3 methylation was correlated with TNM stage, lymph node metastasis, and survival time but was not correlated with gender, tumor localization, differentiation grade or tumor depth. Conclusion： Methylation of the MT-3 gene can impact its mRNA expression in esophageal cancer, especially in advanced esophageal cancer. Methylation of the MT-3 gene is correlated with lymph node metastasis and implies poor prognosis.