Exploration of oncogenic or tumor-suppressive microRNAs in oral cancer.

在过去的几年里，microRNAs （miRNAs）在分子生物学中掀起了一场革命，并在致癌作用中发挥了关键作用。它们已经在不同的肿瘤类型中被发现，表明不同的mirna组通常在不同的癌症中被解除调控。为了确定口腔鳞状细胞癌（OSCC）特异性的miRNA特征，我们首先在18个OSCC细胞系和永活的口腔角质形成细胞系RT7中检测了148个miRNA的表达谱。与RT7相比，54个mirna（36.5%）在OSCC细胞系中频繁下调表达（< 0.5倍表达，占18个细胞系的66.7%）。在这54种mirna中，我们进一步分析了其中的4种mirna。即位于CpG岛周围的miR-34b、miR-137、miR-193a和miR-203，以鉴定通过异常DNA甲基化沉默的肿瘤抑制mirna。在缺乏这四个基因表达的OSCC细胞中，5-aza-2′-脱氧胞苷处理后，这四个基因的表达得以恢复。此外，在OSCC细胞系中，这四种mirna的表达水平与其DNA甲基化状态呈负相关。在配对正常口腔黏膜的OSCC原发肿瘤中，miR-137和miR-193a通过肿瘤特异性高甲基化下调miRNA表达的频率高于miR-34b和miR- 203。此外，将miR-137或miR-193a异位转染到缺乏表达的OSCC细胞系中，细胞生长明显降低，CDK6或E2F6的翻译分别下调。综上所述，我们的研究结果清楚地表明，miR-137和miR-193a是在口腔癌发生过程中表观遗传沉默的肿瘤抑制mirna。

In the last few years, microRNAs (miRNAs) have started a revolution in molecular biology and emerged as key players in the carcinogenesis. They have been identified in various tumor types, showing that different sets of miRNAs are usually deregulated in different cancers. To identify the miRNA signature that was specific for oral squamous cell carcinoma (OSCC), we first examined expression profiles of 148 miRNAs in a panel of 18 OSCC cell lines and the immortalized oral keratinocyte line RT7 as a control. As compared with RT7, the expression of 54 miRNAs(36.5%) was frequently down-regulated in OSCC lines(< 0.5-fold expression, 〓 66.7% of 18 lines). Among these 54 miRNAs, we further analyzed four of these miRNAs. i.e., miR-34b, miR-137, miR-193a, and miR-203, located around CpG islands, to identify tumor-suppressive miRNAs silenced through aberrant DNA methylation. The expression of those four genes was restored by treatment with 5-aza-2'-deoxycytidine in OSCC cells lacking their expression. In addition, expression levels of the four miRNAs were inversely correlated with their DNA methylation status in the OSCC lines. In primary tumors of OSCC with paired normal oral mucosa, down-regulation of miRNA expression through tumor-specific hypermethylation was more frequently observed for miR-137 and miR-193a than for miR-34b and miR 203. Moreover, the ectopic transfection of miR-137 or miR-193a into OSCC lines lacking their expressions significantly reduced cell growth, with down-regulation of the translation of CDK6 or E2F6, respectively. Taken together, our results clearly demonstrate that miR-137 and miR-193a are tumor-suppressor miRNAs epigenetically silenced during oral carcinogenesis.