Ahmed Farid E
East Carolina University, Department of Radiation Oncology, LSB 014, Leo W Jenkins Cancer Center, The Brody School of Medicine, 600 Moye Blvd, LSB 003, Greenville, NC 27858, USA.
Expert Rev Mol Diagn. 2007 Sep;7(5):569-603. doi: 10.1586/14737159.7.5.569.
miRNAs, their involvement in cancer development and their potential to be robust biomarkers of diagnosis, staging, prognosis and response to therapy are reviewed. In small RNA animal biogenesis, miRNA genes in the nucleus are transcribed to generate long primary transcripts (pri-miRNAs), which are first cropped by RNase-III-type enzyme Drosha to release hairpin intermediates (pre-miRNAs) in the nucleus. Pre-miRNA is then exported to the cytoplasm by exportin-5. Following arrival in the cytoplasm, pre-miRNAs are subjected to the second processing step (dicing) to release the mature miRNA duplex, which is then separated: one strand becomes the mature miRNA and the other is degraded. These tiny miRNAs induce messenger degradation, translational repression or both. However, there is no evidence to demonstrate that these two mechanisms exist in the regulation of the same gene. Since a miRNA can target numerous mRNAs, often in combination with other miRNAs, these miRNAs operate a highly complex regulatory network. The specific function in most mammalian miRNAs is unknown. However, data suggest that miRNA genes, approximately 1% of all human genes, regulate protein production for 20-30% or more of all genes. miRNA expression profiles are effective for classifying solid and hematologic human cancers, and have shown great promise for early cancer detection. This is of great importance for effective treatment before the cells metastasize; therefore, tumors can be surgically resected. Computer-based prediction approaches of miRNAs and their targets, and biological validation techniques for ascertaining these predictions, currently play a central role in the discovery of miRNAs and in elucidating their function. Guidelines have been established for the identification and annotation of new miRNAs to distinguish them from other RNAs, especially siRNAs. These guidelines take into account factors such as transcript structure, conservation and processing, and a centralized, searchable database of all possible miRNA sequence information and annotation for humans and of more than 38 other species. Two approaches are used to characterize miRNAs: studying expression of known miRNAs by hybridization-based techniques (e.g., northern blots, RNase protection, primer extension, real-time, quantitative PCR and microarrays) or discovery of novel miRNAs molecules by cloning and sequencing. Owing to their adaptability and high throughput, microarrays may prove to be the preferred platform for whole-genome miRNA expression analysis.
本文综述了微小RNA（miRNA）及其在癌症发生发展中的作用，以及其作为诊断、分期、预后和治疗反应的可靠生物标志物的潜力。在小RNA动物生物合成过程中，细胞核中的miRNA基因转录生成较长的初级转录本（pri-miRNA），其首先被核糖核酸酶III型酶Drosha切割，在细胞核中释放出发夹状中间体（前体miRNA，pre-miRNA）。然后，pre-miRNA通过转运蛋白5输出到细胞质中。到达细胞质后，pre-miRNA经历第二步加工（切割）以释放成熟的miRNA双链体，随后双链体分离：其中一条链成为成熟的miRNA，另一条链则被降解。这些微小的miRNA可诱导信使RNA降解、翻译抑制或两者兼有。然而，尚无证据表明这两种机制存在于同一基因的调控中。由于一个miRNA通常可与其他miRNA联合靶向众多信使RNA，这些miRNA构成了一个高度复杂的调控网络。大多数哺乳动物miRNA的具体功能尚不清楚。然而，数据表明，miRNA基因约占人类所有基因的1%，却调控着所有基因中20%-30%或更多基因的蛋白质生成。miRNA表达谱可有效用于人类实体瘤和血液系统肿瘤的分类，并且在癌症早期检测方面显示出巨大潜力。这对于在细胞发生转移之前进行有效治疗至关重要；因此，肿瘤可通过手术切除。基于计算机的miRNA及其靶标的预测方法，以及用于确定这些预测的生物学验证技术，目前在miRNA的发现及其功能阐释中发挥着核心作用。已经建立了用于鉴定和注释新miRNA的指南，以将它们与其他RNA（尤其是小干扰RNA，siRNA）区分开来。这些指南考虑了转录本结构、保守性和加工等因素，以及一个集中的、可搜索的数据库，其中包含所有可能的人类miRNA序列信息和注释，以及38种以上其他物种的相关信息。有两种方法用于表征miRNA：通过基于杂交的技术（如Northern印迹、核糖核酸酶保护、引物延伸、实时定量PCR和微阵列）研究已知miRNA的表达，或通过克隆和测序发现新的miRNA分子。由于其适应性和高通量特性，微阵列可能被证明是全基因组miRNA表达分析的首选平台。
