Guanine content of microRNAs is associated with their tumor suppressive and oncogenic roles in lung and breast cancers

BACKGROUND: microRNAs (miRNAs, miRs) are small noncoding RNAs that negatively regulate gene expression at the post-transcriptional level and fine-tune gene functions. A global repression of miRNAs expression in different types of human tumors, after exposure to cigarette-smoke, or to the hormone estrogen, have been shown to be associated with guanine (G) enrichment in the terminal loops (TLs) of their precursors. METHODS: we integrated the G content of miRNA mature forms and precursor miRNA TLs with their described function in the literature, using the PubMed database. Gene Ontology term analysis was used to describe the pathways in which the G-enriched miRNA targets are involved. RESULTS: herein we show an association between the relative G enrichment of precursor miRNAs' TLs and their tendency to act as tumor suppressor miRs in human lung and breast cancers. Another association was observed between the high G content of the miRNAs 5-mature forms and their tendency to act as oncomiRs. CONCLUSION: the results support previous findings showing that the G sequence content is an important feature determining miRNA expression and function, and opens the way for future cancer investigations in this direction.