A novel role for GSK3 beta as a modulator of Drosha microprocessor activity and MicroRNA biogenesis

摘要

Regulation of microRNA (miR) biogenesis is complex and stringently controlled. Here, we identify the kinase GSK3 beta as an important modulator of miR biogenesis at Microprocessor level. Repression of GSK3 beta activity reduces Drosha activity toward primiRs, leading to accumulation of unprocessed primiRs and reduction of pre-miRs and mature miRs without altering levels or cellular localisation of miR biogenesis proteins. Conversely, GSK3 beta activation increases Drosha activity and mature miR accumulation. GSK3 beta achieves this through promoting Drosha: cofactor and Drosha: pri-miR interactions: it binds to DGCR8 and p72 in the Microprocessor, an effect dependent upon presence of RNA. Indeed, GSK3 beta itself can immunoprecipitate pri-miRs, suggesting possible RNA-binding capacity. Kinase assays identify the mechanism for GSK3 beta-enhanced Drosha activity, which requires GSK3 beta nuclear localisation, as phosphorylation of Drosha at S-300 and/or S-302; confirmed by enhanced Drosha activity and association with cofactors, and increased abundance of mature miRs in the presence of phospho-mimic Drosha. Functional implications of GSK3 beta-enhanced miR biogenesis are illustrated by increased levels of GSK3 beta-upregulated miR targets following GSK3 beta inhibition. These data, the first to link GSK3 beta with the miR cascade in humans, highlight a novel probiogenesis role for GSK3 beta in increasing miR biogenesis as a component of the Microprocessor complex with wide-ranging functional consequences.