Long noncoding RNAs and their link to cancer

The central dogma of molecular biology, developed from the study of simple organisms such as Escherichia coli, has up until recently been that RNA functions mainly as an information intermediate between a DNA sequence (gene), localized in the cell nucleus, serving as a template for the transcription of messenger RNAs, which in turn translocate into the cytoplasm and act as blueprints for the translation of their encoded proteins. There are a number of classes of non-protein coding RNAs (ncRNAs) which are essential for gene expression to function. The specific number of ncRNAs within the human genome is unknown. ncRNAs are classified on the basis of their size. Transcripts shorter than 200 nucleotides, referred to as ncRNAs, which group includes miRNAs, siRNAs, piRNAs, etc, have been extensively studied. Whilst transcripts with a length ranging between 200 nt up to 100 kilobases, referred to as lncRNAs, make up the second group, and are recently receiving growing concerns. LncRNAs play important roles in a variety of biological processes, regulating physiological functions of organisms, including epigenetic control of gene regulation, transcription and post-transcription, affecting various aspects of cellular homeostasis, including proliferation, survival, migration and genomic stability. LncRNAs are also capable of tuning gene expression and impact cellular signalling cascades, play crucial roles in promoterspecific gene regulation, and X-chromosome inactivation. Furthermore, it has been reported that lncRNAs interact with DNA, RNA, and/or protein molecules, and regulate chromatin organisation, transcriptional and post-transcriptional regulation. Consequently, they are differentially expressed in tumours, and they are directly linked to the transformation of healthy cells into tumour cells. As a result of their key functions in a wide range of biological processes, lncRNAs are becoming rising stars in biology and medicine, possessing potential active roles in various oncologic diseases, representing a gold mine of potential new biomarkers and drug targets.