Noncoding RNAs: Different roles in tumorigenesis

A major portion of the mammalian genome is transcribed to produce large numbers of noncoding RNAs (ncRNAs). During the past decade, the discovery of small RNAs, including the microRNAs (miRNA) and small interfering RNAs (siRNA), has led to important advances in biology. The breadth of the ncRNA field of study has substantially expanded and many recent results have revealed a range of functions that can be attributed to the miRNAs and other ncRNAs. For example, H19 RNA, HOTAIR RNA, transcribed ultraconserved regions (T-UCRs), natural antisense RNA, transfer RNA and mitochondrial noncoding RNA have been suggested to play important roles in cancers and other diseases as well as in diverse cellular processes. In this review, we focus on the current status of several classes of ncRNAs associated with cancer with the emphasis on those that are not microRNAs.