Role, function and regulation of human Dicer

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The molecular mechanisms regulating the expression of mammalian genomes is more complex than previously thought, with the recent discovery of gene regulatory processes based on small non-coding RNA species, such as microRNAs. Expressed in almost all living eukaryotes, microRNAs act in concert to regulate ~60% of the genes in humans, suggesting that every biochemical and cellular processes may be under microRNA control in our body! In humans, microRNAs are generated by the ribonuclease III Dicer, a large enzyme that we discovered and characterized initially in its recombinant form. Strategically positioned at the nuclear/cytoplasmic interface, Dicer would accept its microRNA precursor (pre-microRNA) substrate of nuclear origin from the transporter Exportin-5, recognize it via its central PIWI/Argonaute/Zwille (PAZ) domain and release microRNAs through the concerted action of its RNase IIIa and IIIb motifs. Despite its central importance in microRNA biogenesis, the cellular context in which Dicer functions in RNA silencing still remains poorly understood. In this proposal, we wish to address that issue by elucidating the protein interaction network of human Dicer and characterizing the interaction between human Dicer and cellular protein candidates that are very likely to modulate various aspects of Dicer, such as its intracellular localization, stability, processivity, trafficking and ability to interact with other proteins. Expected to clarify the mechanisms regulating the human genome, our findings may provide a better understanding of the cellular role, function and regulation of the microRNA-generating enzyme Dicer. This is a prerequisite for eventually identifying genetic diseases possibly linked to alterations in Dicer function or caused by malfunctioning of the microRNA pathway.