涎腺腺样囊性癌DNA甲基转移酶与抑癌基因甲基化

Expression of DNA methyltransferases in salivary adenoid cystic carcinoma and its association with the CpG islands methylation of tumor suppressor genes

目的通过对DNA甲基转移酶(DNMT)在涎腺腺样囊性癌(ACC)中表达的检测,分析DNMT与ACC抑癌基因甲基化、生物学行为的相关性,探讨DNMT在ACC发生、发展中的作用。方法对60例ACC临床病理标本进行DNMT1、DNMT3b的免疫组化染色,显微镜观察,将观察结果与p16、RASSF1A、DAPK、MGMT、E-cadherin多个抑癌基因的甲基化状况、病理分级、临床分期进行比较,应用Fisher确切概率法进行统计学分析。结果①DNMT1在ACC中的阳性表达程度明显高于DNMT3b的阳性表达(P<0．01)。②DNMT1阳性表达随发生甲基化的抑癌基因个数的增加而增加,DNMT1高、低表达组与抑癌基因高、低甲基化组之间差异有统计学意义(P<0．05),与RASSF1A基因的甲基化呈相关性(P<0．01)。③DNMT1的阳性表达程度与ACC病理分级(P<0．05)、临床分期(P< 0．01)呈正相关,实性成分越多、分期越晚,表达越高。④未发现DNMT3b与抑癌基因的甲基化状况、病理分级、临床分期间的相关性。结论DNMT1可能是ACC体内对维持抑癌基因甲基化起主导作用的甲基化酶,与RASSF1A基因的甲基化、ACC病理分级、临床分期有相关性,在ACC的发生、发展中扮演着重要角色,有可能作为肿瘤预后的评估指标之一。

Objective To investigate the role of DNA methyhransferases （DNMT） in carcinogenesis and development of salivary adenoid cystic carcinoma （ACC） by detection the expression of DNMT in ACC and to assess its correlation to methylation of tumor suppressor genes and biological behavior of ACC. Methods The protein expression of DNMT1 and DNMT3b were examined by immunohistochemistry in paraffin-embedded tissues of ACC from 60 patients. The association between the positive staining of DNMT1 and DNMT3b microscopically and the CpG islands methylation status of some tumor suppressor genes, tumor grade and stage was apalysed by Fisher exact test. Results The number of DNMT1 positive cells was much more than that of DNMT3b （ P 〈 0.01 ）. The positive expression of DNMT1 was increased concomitantly to the amounts of methylation of tumor suppressor genes occurred in ACC and was significantly correlated to the methylation status of RASSF1A （P 〈 0. 01 ）. A difference was found between the more and less methylation of tumor suppressor genes group （ P 〈 0.05 ） The increased positive expression of DNMT1 correlated to the tumor grade （P 〈0. 05） and stage （P 〈0. 01 ）. It was much more expressed in the lower grade or more advanced stage cases. The correlation between the expression of DNMT3b and the methylation of tumor suppressor genes, tumor grade and stage was not found. Conclusions DNMT1 may play an important role in the maintenance of methylation of tumor suppressor genes in ACC and was related correlated to the methylation of RASSF1 A, tumor grade and stage, which implied that DNMT1 may contribute to the carcinogenesis and development of ACC and was likely to be a molecular marker for evaluating the prognosis of patients with ACC.