Akhtar M, Cheng Y, Magno R M, Ashktorab H, Smoot D T, Meltzer S J, Wilson K T
Department of Medicine, University of Maryland School of Medicine and Veterans Affairs Maryland Health Care System, Baltimore 21201, USA.
Cancer Res. 2001 Mar 15;61(6):2399-403.
Cyclooxygenase (COX)-2, the inducible form of the rate-limiting enzyme for prostaglandin synthesis, is up-regulated in gastrointestinal cancers and is a key mediator of epithelial cell growth. Helicobacter pylori is causally linked to gastric cancer. In H. pylori gastritis, COX-2 expression localizes to the subepithelial region, with variable levels in the epithelium. In contrast, in gastric cancer, COX-2 strongly predominates in the epithelium, suggesting that the transition to consistent epithelial COX-2 overexpression may be a critical molecular event in gastric carcinogenesis. Because aberrant promoter methylation inhibits expression of a variety of genes in gastrointestinal cancers, we sought to determine whether methylation of the COX-2 promoter could regulate the response to H. pylori in gastric epithelial cells. We assessed COX-2 expression and promoter methylation status in six gastric epithelial cell lines. In all four of the cell lines that exhibited basal expression of COX-2 and a significant increase in expression in response to H. pylori, the COX-2 promoter was unmethylated, whereas in the two cell lines that did not express COX-2, the COX-2 promoter was methylated. Treatment of COX-2-methylated cells with the demethylating agent 5-azacytidine had a modest effect on COX-2 expression, but when 5-azacytidine-treated cells were subsequently stimulated with H. pylori, there was a significant, 5-10-fold enhancement of both COX-2 mRNA and protein expression and release of the COX-2 product, prostaglandin E2. In contrast, in COX-2-expressing cell lines that were unmethylated at the COX-2 promoter, 5-azacytidine had no effect on H. pylori-stimulated COX-2 expression. These findings suggest that loss of COX-2 methylation may facilitate COX-2 expression and promote gastric carcinogenesis associated with H. pylori infection.
环氧化酶（COX）-2是前列腺素合成限速酶的诱导型，在胃肠道癌症中上调，是上皮细胞生长的关键介质。幽门螺杆菌与胃癌有因果关系。在幽门螺杆菌胃炎中，COX-2表达定位于上皮下区域，上皮中的水平各不相同。相比之下，在胃癌中，COX-2在上皮中占主导地位，这表明向一致的上皮COX-2过表达的转变可能是胃癌发生中的关键分子事件。由于异常的启动子甲基化会抑制胃肠道癌症中多种基因的表达，我们试图确定COX-2启动子的甲基化是否能调节胃上皮细胞对幽门螺杆菌的反应。我们评估了六种胃上皮细胞系中COX-2的表达和启动子甲基化状态。在所有四个表现出COX-2基础表达且对幽门螺杆菌刺激后表达显著增加的细胞系中，COX-2启动子未甲基化，而在两个不表达COX-2的细胞系中，COX-2启动子甲基化。用去甲基化剂5-氮杂胞苷处理COX-2甲基化的细胞对COX-2表达有适度影响，但当用幽门螺杆菌刺激经5-氮杂胞苷处理的细胞后，COX-2 mRNA和蛋白表达以及COX-2产物前列腺素E2的释放均显著增强了5至10倍。相比之下，在COX-2启动子未甲基化的COX-2表达细胞系中，5-氮杂胞苷对幽门螺杆菌刺激的COX-2表达没有影响。这些发现表明，COX-2甲基化的缺失可能促进COX-2表达，并促进与幽门螺杆菌感染相关的胃癌发生。
