Missing Links in Epithelial-Mesenchymal Transition: Long Non-Coding RNAs Enter the Arena.

Cancer metastasis occurs through a series of sequential steps, which involves dissemination of tumor cells from a primary site and colonization in distant tissues. To promote the invasion-metastasis cascade, carcinoma cells usually initiate a cell-biological program called epithelial-mesenchymal transition (EMT), which is orchestrated by a set of master regulators, including TGF-β, Snail, ZEB and Twist families. The biological activities of these molecules are tightly regulated by a variety of cell-intrinsic pathways as well as extracellular cues. Recently, accumulating evidence indicates that long non-coding RNAs (lncRNAs) represent some of the most differentially expressed transcripts between primary and metastatic cancers. LncRNAs including MALAT1, HOTAIR, H19, LncRNA-ATB, and LincRNA-ROR have been reported to be involved in the process of EMT, mainly through cross-talking with master regulators of EMT. Thus, understanding the different and precise molecular mechanisms by which functional lncRNAs switch EMT on and off is important for opening up new avenues in lncRNA-directed diagnosis, prognosis, and therapeutic intervention against cancer.