Guanine content of precursor microRNA’s terminal loop and its association with cancer

MicroRNAs (miRNAs) are small noncoding segments of RNA that negatively regulate gene expression at the post-transcriptional level and fine-tune gene functions. Several lines of evidence suggest that terminal loops (TLs) of miRNAs are important features determining their processing efficiency. A global repression in miRNAs expression in different types of human tumors, after exposure to cigarette-smoke (CS), or to the hormone estrogen, was shown to be associated with guanine (G) enrichment in the TLs of their precursors. In this review we summarize the results that show the relation of TLs G content to the regulation of miRNA maturation and function, suggest a new G-dependent miRNA-related model of carcinogenesis, and specify several dietary phytochemicals that can be used for its prevention.