microRNAs Downregulation in Cancer is Associated with Guanine Enrichment in the Terminal Loop Sequences of their Precursors

摘要

Background: microRNAs (miRNAs) are small noncoding segments of RNA that negativelyregulate gene expression at the post-transcriptional level and fine-tune gene functions. A globalrepression in miRNA expression is a phenomenon observed in different types of cancer. In this studywe aimed to reveal a possible association of miRNAs downregulation in cancer, with the guanine (G)content in the terminal loop (TL) sequences of their precursors.Methods: Lists of most significantly downregulated miRNAs in different tumor types, obtained frompreviously published microarray experiments, were selected for bioinformatics analysis. The completeprecursor, TL, and mature miRNA sequences, were analyzed for evaluation of nucleotide compositionand motif enrichment.Results: Herein, we show an association of miRNAs downregulation in cancer, with G enrichment inthe TL sequences of their precursors. High G (and GG) content was mostly found in repressed miRNAsof breast, lung and ovary cancers, predominantly in poorly differentiated tumors. The mature sequencesof repressed miRNAs had significantly low G content and were enriched with an ACA motif.Conclusion: This study suggests a new link between G enrichment of precursor miRNAs TLs andcarcinogenesis, and the possible association of specific sequence motifs with the regulation of theirexpression.