Causes and consequences of MicroRNA dysregulation

It is currently well recognized that microRNA deregulation is a hallmark of human cancer, and an aberrant expression of these tiny regulatory RNA molecules in several cell types is not just a random association, but it also plays a causal role in different steps of the tumorigenic process, from the initiation and development to progression toward the acquisition of a metastatic phenotype.Different regulatory mechanisms can control microRNA expression at a genetic or epigenetic level as well as involve the biogenesis machinery or the recruitment of specific transcription factors. The tumorigenic process implies a substantial alteration of these mechanisms, thus disrupting the equilibrium within the cell and leading to a global change in microRNA expression, with loss of oncosuppressor microRNAs and overexpression of oncomiRNAs.We review the main mechanisms regulating microRNAs and the consequences of their aberrant expression in cancer, with a glance at the possible implications at a clinical point of viw.