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

在过去的几年里，microRNAs（miRNAs）已经开始了分子生物学的革命，并成为癌症发生的关键参与者。它们已在各种肿瘤类型中被鉴定，表明不同的miRNA组通常在不同的癌症中失调。为了鉴定口腔鳞状细胞癌（OSCC）特异性的miRNA特征，我们首先检测了18个OSCC细胞系和作为对照的永生化口腔角质形成细胞系RT 7中148个miRNA的表达谱。与RT 7相比，54个（36.5%）miRNAs在OSCC细胞系中表达频繁下调（< 0.5倍，占18个细胞系的66.7%）。在这54个miRNAs中，我们进一步分析了其中的4个miRNAs。也就是说，miR-34 b、miR-137、miR-193 a和miR-203，位于CpG岛周围，以鉴定通过异常DNA甲基化沉默的肿瘤抑制性miRNA。在缺乏这四种基因表达的OSCC细胞中，用5-氮杂-2 '-脱氧胞苷处理可以恢复这四种基因的表达。此外，在OSCC细胞系中，四种miRNAs的表达水平与其DNA甲基化状态呈负相关。在具有配对正常口腔粘膜的原发性OSCC肿瘤中，通过肿瘤特异性高甲基化，miR-137和miR-193 a的miRNA表达下调比miR-34 b和miR 203更常见。此外，将miR-137或miR-193 a异位转染到缺乏其表达的OSCC细胞系中显著降低了细胞生长，分别下调了CDK 6或E2 F6的翻译。综上所述，我们的结果清楚地表明，miR-137和miR-193 a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.