Yu Jun, Leung Wai K, Lee Tin-Lap, Tse Pete C H, To Ka Fai, Sung Joseph J Y
Department of Medicine and Therapeutics, Prince of Wales Hospital, The Chinese University of Hong Kong, Shatin, Hong Kong, PR China.
Int J Oncol. 2003 May;22(5):1025-31.
Overexpression of cyclooxygenase-2 (COX-2) is associated with loss of apoptosis, enhancement of proliferation and tumorigenesis. The role of promoter methylation in the transcriptional silencing of cox-2 gene in human gastric cancer is less determined. We investigated 5 gastric cancer cell lines and 58 primary gastric carcinomas for the presence of promoter hypermethylation in cox-2 gene. Combined methylation-specific polymerase chain reaction analysis and bisulfite sequencing analysis revealed that the cox-2 promoter was methylated in 2 of the gastric cancer cell lines. Treatment with 5-aza-2'-deoxycytidine, a DNA methyltransferase inhibitor, induced COX-2 expression in the methylated gastric cancer cell line. Among the 58 primary gastric cancers, hypermethylation was detected in 25 (43.1%) cases. However, none of the normal gastric tissues showed methylation in cox-2. Promoter hypermethylation was associated with loss of protein expression as determined by immunostaining (p=0.005). Our results indicate that hypermethylation of the CpG island in the cox-2 gene is a major mechanism that mediates transcriptional silencing in a subset of gastric cancers. Thus, gastric cancers with methylation in cox-2 may not be good candidates for treatment with specific COX-2 inhibitors.
环氧化酶-2（COX-2）的过表达与细胞凋亡丧失、增殖增强及肿瘤发生相关。启动子甲基化在人类胃癌中COX-2基因转录沉默中的作用尚不完全明确。我们研究了5种胃癌细胞系和58例原发性胃癌中COX-2基因启动子高甲基化的情况。甲基化特异性聚合酶链反应分析和亚硫酸氢盐测序分析显示，2种胃癌细胞系中COX-2启动子发生了甲基化。用DNA甲基转移酶抑制剂5-氮杂-2'-脱氧胞苷处理后，甲基化的胃癌细胞系中COX-2表达上调。在58例原发性胃癌中，25例（43.1%）检测到高甲基化。然而，正常胃组织中均未检测到COX-2甲基化。免疫染色结果显示，启动子高甲基化与蛋白表达缺失相关（p=0.005）。我们的结果表明，COX-2基因中CpG岛的高甲基化是介导一部分胃癌转录沉默的主要机制。因此，COX-2发生甲基化的胃癌可能不是特异性COX-2抑制剂治疗的理想候选对象。
