Zhang Kun, Yao Hang-Ping, Wang Ming-Hai
Laboratory of Cancer Biology and Therapeutics, First Affiliated Hospital, Zhejiang University School of Medicine, Hangzhou 310003, People's Republic of China.
Carcinogenesis. 2008 Mar;29(3):552-9. doi: 10.1093/carcin/bgn003. Epub 2008 Jan 19.
Claudins are integral membrane proteins essential in tight junction formation and function. Altered expression of claudins has been implicated in epithelial malignant transformation. We report here that activation of recepteur d'origine nantais (RON) differentially regulates tight junction function and claudin expression. In Martin-Darby canine kidney (MDCK) cells, macrophage-stimulating protein-induced RON activation or expression of constitutively active variant RON160 significantly disrupted cellular tight junctions and reduced transepithelial electrical resistance. These changes were featured by diminished claudin-1 expression and redistribution of claudin-3 and -4 into cytoplasmic compartments. The inhibition of claudin-1 was also seen in breast cancer T-47D cells. By analyzing the signaling events, we found that activation of the extracellular signal-regulated kinase 1/2 pathway is required for RON-mediated inhibition of claudin-1 expression and redistribution of claudin-3 and -4. Results from luciferase reporter assays showed that inhibition is acted at the transcriptional levels because RON activation decreases claudin-1 promoter activities and increases transcriptional repressor Snail-1 expression. Functional analysis further revealed that reduced claudin-1 expression is linked to increased motilities of MDCK and T-47D cells as evident in cell migration and wound-healing assays. Forced expression of claudin-1 prevented RON-mediated cell migration and restored cell morphologies to their original epithelial appearance. In conclusion, RON activation differentially regulates claudin expression in epithelial cells. Inhibition of claudin-1 expression may represent a novel mechanism that contributes to RON-mediated invasive activities, leading to increased tumor malignancy.
闭合蛋白是紧密连接形成和功能所必需的整合膜蛋白。闭合蛋白表达的改变与上皮细胞恶性转化有关。我们在此报告，源自南特的受体（RON）的激活差异性地调节紧密连接功能和闭合蛋白表达。在犬肾上皮细胞（MDCK）中，巨噬细胞刺激蛋白诱导的RON激活或组成型活性变体RON160的表达显著破坏细胞紧密连接并降低跨上皮电阻。这些变化的特征是闭合蛋白-1表达减少以及闭合蛋白-3和-4重新分布到细胞质区室中。在乳腺癌T-47D细胞中也观察到了闭合蛋白-1的抑制。通过分析信号转导事件，我们发现细胞外信号调节激酶1/2途径的激活是RON介导的闭合蛋白-1表达抑制以及闭合蛋白-3和-4重新分布所必需的。荧光素酶报告基因检测结果表明，这种抑制作用发生在转录水平，因为RON激活会降低闭合蛋白-1启动子活性并增加转录抑制因子Snail-1的表达。功能分析进一步表明，闭合蛋白-1表达的降低与MDCK和T-47D细胞运动性增加有关，这在细胞迁移和伤口愈合试验中很明显。强制表达闭合蛋白-1可阻止RON介导的细胞迁移，并使细胞形态恢复到原来的上皮外观。总之，RON激活差异性地调节上皮细胞中的闭合蛋白表达。抑制闭合蛋白-1的表达可能代表了一种新机制，有助于RON介导的侵袭活性，导致肿瘤恶性程度增加。
