Sequence Analyses of Oncogenic and Tumor Suppressive miRNAs in Cancers
Published on: 2014-02-25
MicroRNAs (miRNAs) are small (∼25 nucleotides) noncoding RNA molecules thought to play an important role in regulating gene expression. Knowledge of the biological functions of most miRNAs is still limited, but these miRNAs are thought to regulate the gene expression in various diseases. In this paper, the sequences of oncogenic and tumor suppressive miRNAs in human cancers are examined from the viewpoint of up- and down-regulation. Oncogenic miRNAs are involved in the overexpression/ upregulation of cancers, whereas tumor suppressive miRNAs are involved in the underexpression/downregulation of cancers. The oncogenic and tumor suppressive miRNA sequences were first collected from miRBase based on the relations between miRNAs and various cancers in the literature. Statistical analysis of the positional nucleotide occurrence features of miRNAs revealed differences between the positional nucleotide occurrences of oncogenic and tumor suppressive miRNAs. A miRNA gene-silencing score was then defined on the basis of the higher and lower levels of the statistical significances of positional nucleotides. Since the miRNA scores were closely related to miRNA frequencies, a method using the scores and nucleotide frequencies to distinguish whether a new miRNA is oncogenic or tumor suppressive is proposed.