Long non-coding RNAs in cancer

Long non-coding RNAs (lncRNAs) are a group of RNA transcripts that exceed 200 nt in length, yet lack significant open reading frames (ORFs) [1][2][3][4].In contrast to small non-coding RNAs (ncRNAs), such as microRNAs (miR-NAs) [4-23], small interfering RNAs (siRNAs) [24][25][26][27][28][29][30][31] and transfer RNAs (tRNAs) [32][33][34], there are thousands of lncRNA genes discovered during the past three years in the human genome and most of their functions remain elusive.The long nucleotide chain of lncRNAs can either form a complex spatial structure and interact with protein factors, or provide a large segment for the concurrent binding of many molecules that collectively participate in genomic imprinting, X-chromosome silencing, chromosome modification, intranuclear transport, transcriptional activation and interference, thereby regulating cell growth, differentiation, development, senescence and death [35].Accumulating evidence supports that lncRNAs participate in many physiological processes by modulating gene expression at the epigenetic, transcriptional and posttranscriptional levels.LncRNAs regulate gene expression at the epigenetic level through DNA methylation or demethyl-