The Enigma of miRNA Regulation in Cancer

MicroRNAs (miRNAs or miRs) are small 19-22 nucleotide long, noncoding, singlestranded, and multifunctional RNAs that regulate a diverse assortment of gene and protein functions that impact on a vast network of pathways. Lin-4, a noncoding transcript discovered in 1993 and named miRNA, initiated the exploration of research into these intriguing molecules identified in almost all organisms. miRNAs interfere with translation or posttranscriptional regulation of their target gene and regulate multiple biological actions exerted by these target genes. In cancer, they function as both oncogenes and tumor suppressor genes displaying differential activity in various cellular contexts. Although the role of miRNAs on target gene functions has been extensively investigated, less is currently known about the upstream regulatory molecules that regulate miRNAs. This chapter focuses on the factors and processes involved in miRNA regulation.