Regulation of miRNA biogenesis as an integrated component of growth factor signaling.

Transcriptional control of microRNAs (miRNA) by cell signaling pathways, especially in the context of growth factor regulation, is a widely recognized phenomenon with broad-reaching implications. However, several recent studies indicate that not just transcription, but also processing of miRNAs is subject to regulation as part of an integrated physiological response to various stimuli and environmental changes. The canonical miRNA biogenesis pathway; sequential steps of nucleolytic cleavage by the RNase III enzymes Drosha and Dicer, are emerging regulatory hubs for the modulation of miRNA expression as part of both physiological and pathological responses. In this article we use well-characterized growth-factor signaling pathways such as transforming growth factor-β (TGF-β), Protein Kinase B (PKB, also known as Akt) and extracellular-signal-regulated kinase (ERK) to illustrate how basic cell signaling pathways modulate the activities of these components of the miRNA biogenesis pathway to achieve optimal miRNA expression patterns.