Department of Pharmacy, College of Pharmacy, Seoul National University, Seoul, Korea.
Lab Invest. 2011 Nov;91(11):1652-67. doi: 10.1038/labinvest.2011.117. Epub 2011 Aug 15.
The tight junction (TJ) protein claudin-4 is aberrantly upregulated in gastric cancer, but its clinical significance and the molecular mechanisms underlying claudin-4 overexpression in gastric cancer remain unclear. Here, we investigated its roles and epigenetic mechanisms regulating CLDN4 expression in gastric cancer. We show that increased membranous expression of claudin-4 in gastric carcinoma is associated with better patient prognosis, whereas cytoplasmic claudin-4 expression did not show a significant association with prognosis. Consistent with the correlation of increased membranous claudin-4 with favorable clinicopathological factors, claudin-4 overexpression inhibited the migration and invasion of gastric cancer cells; in contrast, it did not affect cell growth. Claudin-4 expression also increased the barrier function of TJs. Claudin-4 upregulation was strongly correlated with DNA hypomethylation in both gastric tissues and gastric cancer cells. Moreover, CLDN4 expression was repressed in normal gastric tissues in association with bivalent histone modifications, and loss of repressive histone methylations and gain of active histone modifications were associated with CLDN4 overexpression in gastric cancer cells. Interestingly, CLDN4 repression could be markedly derepressed by combined treatments that simultaneously target both histone modifications and DNA demethylation in CLDN4-hypermethylated cells, whereas concomitant changes in histone methylations and acetylations are required for CLDN4 induction in CLDN4-repressed cells with low DNA methylation. Taken together, this study reveals that membranous claudin-4 expression is associated with gastric cancer progression and that it is an independent positive prognosis marker in gastric carcinoma. Furthermore, our findings suggest that epigenetic derepression may be a possible mechanism underlying CLDN4 overexpression in gastric cancer and that claudin-4 may have potential as a promising target for the treatment of gastric cancer.
紧密连接（TJ）蛋白 Claudin-4 在胃癌中异常上调，但 Claudin-4 在胃癌中过表达的临床意义和分子机制尚不清楚。在这里，我们研究了其在胃癌中的作用和表观遗传机制调节 CLDN4 表达。我们表明，胃癌中 Claudin-4 膜表达的增加与患者预后较好相关，而 Claudin-4 细胞质表达与预后无显著相关性。与膜 Claudin-4 与有利的临床病理因素相关的相关性一致，Claudin-4 过表达抑制了胃癌细胞的迁移和侵袭；相反，它不会影响细胞生长。Claudin-4 表达还增加了 TJ 的屏障功能。Claudin-4 的上调与胃组织和胃癌细胞中的 DNA 低甲基化强烈相关。此外，CLDN4 表达与双价组蛋白修饰相关，在正常胃组织中被抑制，并且抑制性组蛋白甲基化的丧失和活性组蛋白修饰的获得与胃癌细胞中 CLDN4 的过表达相关。有趣的是，CLDN4 的抑制可以通过同时针对 CLDN4 高甲基化细胞中的组蛋白修饰和 DNA 去甲基化的联合治疗显著解除，而在 CLDN4 低甲基化的抑制细胞中诱导 CLDN4 需要同时改变组蛋白甲基化和乙酰化。总之，这项研究表明，膜 Claudin-4 的表达与胃癌的进展相关，并且是胃癌中独立的阳性预后标志物。此外，我们的发现表明，表观遗传去抑制可能是 Claudin-4 在胃癌中过表达的一种可能机制，Claudin-4 可能具有作为治疗胃癌的有前途的靶标的潜力。
