Expression profile of MicroRNA: An Emerging Hallmark of Cancer

MicroRNA (miRNAs), a class of small, endogenous non-coding RNA molecules of about 21-24 nucleotides in length, have unraveled a new modulatory network of RNAs that form an additional level of posttranscriptional gene regulation by targeting messenger RNAs (mRNAs). These miRNAs possess the ability to regulate gene expression by modulating the stability of mRNAs, controlling their translation rates, and consequently regulating protein synthesis. Substantial experimental evidence established the involvement of miRNAs in most biological processes like growth, differentiation, development, and metabolism in mammals including humans. An aberrant expression of miRNAs has been implicated in several pathologies, including cancer. The association of miRNAs with tumor growth, development, and metastasis depicts their potential as effective diagnostic and prognostic biomarkers. Furthermore, exploitation of the role of different miRNAs as oncogenes or tumor suppressors has aided in designing several miRNA-based therapeutic approaches for treating cancer patients whose clinical trials are underway. In this review, we aim to summarize the biogenesis of miRNAs and the dysregulations in these pathways that result in various pathologies and in some cases, resistance to drug treatment. We provide a detailed review of the miRNA expression signatures in different cancers along with their diagnostic and prognostic utility. Furthermore, we elaborate on the potential employment of miRNAs to enhance cancer cell apoptosis, regress tumor progression and even overcome miRNA-induced drug resistance.