The Role of Ago2 in microRNA Biogenesis: An Investigation of miR-21

Research into the biology of microRNAs (miRNA) continues to expand rapidly. As a result, their abundance and importance in cellular regulation and disease states, also continues to grow and they are considered master regulators. Despite this greater understanding, key mechanisms regulating global miRNA transcription have remained elusive. This paper addresses a critical issue regarding regulation of miRNA expression. Here, we describe and biochemically characterize a universal regulatory complex that directly binds miRNA genetic loci and regulates transcription of miRNA genes. In addition, our preliminary results provide evidence that miRNA-induced Ago2 binding can result in positive post-transcriptional regulation of many important primary miRNAs. Using chromatin immuno-precipitation (ChIP) assays, our results demonstrate that the human miRNA binding protein Argonaute 2 (Ago2) associates with endogenous promoter DNA from each of the important human miRNA genes investigated to date. Additionally, our data shows a robust, direct interaction between mature miR-21 directed Ago2 and a miR-21 promoter DNA sequence.