Global microRNA downregulation: all roads lead to estrogen

MicroRNAs (miRNAs) are small noncoding segments of RNA, that negatively regulate gene expression at the post-transcriptional level and fine-tune gene functions. A widespread repression in miRNA expression was observed in different types of human tumors, and after exposure to cigarette-smoke, or to the hormone estrogen. The association of miRNAs downregulation in cancer, and after estrogen treatment, with guanine (Gua) enrichment in the terminal loop sequences of their precursors, suggests a possible link between estrogen-related miRNA-Gua adducts formation and carcinogenesis.