A review on microRNAs’ function, detection and evaluation methods, expression dysregulation mechanisms and possible applications in clinical phase as diagnostic, prognostic and therapeutic biomarkers of lung cancer patients

MicroRNAs are small endogenous single-stranded non-protein-coding RNAs that often act as negative gene regulators at post-transcriptional level. These molecules actively participate in a wide variety of cellular events, and are involved in pathogenesis of different malignancies, e.g. lung cancer. With a heterogeneous nature, non-small cell lung cancer comprises more than 80% of lung cancer cases. As of recent, expression profile of non-protein-coding RNAs have been considered in various normal and morbid tissues, and possible roles of microRNAs in gene regulation have been speculated. Functionally, a growing body of evidence categorizes these molecules as “oncomiRs” and “tumor suppressive RNAs.” Through high through-put screening of genome, it has been demonstrated that the expression pattern of specific microRNAs is associated with the outcome of non-small cell lung cancer. Furthermore, quantitative gene expression assessment has revealed that microRNAs with a high expression level in the normal lung often become down-regulated in lung tumors, indicating their possible role as tumor suppressive microRNAs. On the contrary, another group of microRNAs was found to be up-regulated in lung cancer tissues, hence, the name “oncomiR”. In this article, we will have a review on introduction, synthesis, and processing of microRNAs, and their importance in normal and abnormal cells, normal and cancerous lung tissue, and mechanisms involved in expression dysregulations, function, definition methods, and ultimately, application of these molecules as biomarker in clinic.