Potential epigenetic players: non-coding RNAs
Contrary to the central dogma which states that RNA is the messenger between genes and the proteins they encode, ncRNAs have emerged as major transcriptional units that do not encode proteins, but have many different functions, one being regulation of gene expression [24, 25]. Only 2% of the genome is transcribed and the remainder are ncRNAs [15]. NcRNAs have been found to influence all aspects of cancer biology as shown in Figure 1 [26]. There is a broad spectrum of functions that ncRNAs perform in the cell from transcriptional regulation to interacting with target proteins and mRNAs in the cytoplasm [27]. Some act at the site of transcription to regulate transcription and gene structure, while others play diverse functions away from the site of transcription in regulating other processes in the cell [27, 28]. Similar to protein-coding genes, ncRNAs have to be tightly regulated to protect the integrity of a normal cell. There are two main groups of ncRNAs- short ncRNAs that are 200 nts. The short ncRNAs are further broken down into three major classes: miRNA, short-interfering RNA (siRNA), and piwi-interacting RNA (piRNA).
As mentioned previously, abundantly expressed miRNA are approximately 21-23 nts in length and arise from coding and non-coding genomic regions. miRNA negatively
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Dysregulation of non-coding RNAs has been established in numerous types of cancers including colon cancer [33], hepatocellular carcinoma [34], melanoma [35], and breast cancer [36]. Aberrant expression of these non-coding RNAs can be associated with increased tumorigenesis on one hand and inhibition of proliferation on the other. As a result of altered expressions of non-coding RNAs in the majority of cancer models that exists, new biomarkers and targets can be identified to aid in the progression of treatment for all