Non-coding RNAs and cancer: microRNAs and beyond

Non-coding RNAs were previously thought to have little importance because they are not directly translated into a protein like their coding counterparts. However, it was recently found that non-coding RNAs do in fact have a much bigger role than previously thought. They are involved in cancer predisposition, development and progression. MicroRNAs, very short non-coding RNAs, are abnormally expressed in cancer and some harbor mutations that affect expression levels. MicroRNA alterations have been observed in all forms of cancer that have been researched to the current date. MicroRNAs are also located in cancer- associated genomic regions, which have been previously shown to affect gene expression leading to the activation or inhibition of cancer growth. Single-nucleotide polymorphisms within microRNAs can predispose someone to cancer. MicroRNAs have been shown to target both tumor suppressors, inhibiting cancer development, as well as oncogenes, stimulating cancer development. Some microRNAs can switch between these two functions and behave as a tumor suppressor at one time and an oncogene at another time. MicroRNAs can be used for diagnostic purposes as well as prognostic evaluations. Outside of microRNAs, ultraconserved genes, another group of non-coding RNAs, also express differently in cancer patients. Large intervening non-coding RNAs, specifically one termed HOTAIR, have been quantified in very high levels in cancer cells and have been implicated in metastasis. Further research into noncoding RNAs may allow for the development of therapies that will target non-coding RNAs creating better treatment options for cancer patients, improving their prognosis. This review discusses the most current discoveries about non-coding RNAs, revealing their associations with cancer.