The nuclear DICER-circular RNA complex drives the deregulation of the glioblastoma cell microRNAome.

The assortment of cellular microRNAs ("microRNAome") is a vital readout of cellular homeostasis, but the mechanisms that regulate the microRNAome are poorly understood. The microRNAome of glioblastoma is substantially down-regulated in comparison to the normal brain. Here, we find malfunction of the posttranscriptional maturation of the glioblastoma microRNAome and link it to aberrant nuclear localization of DICER, the major enzymatic complex responsible for microRNA maturation. Analysis of DICER's nuclear interactome reveals the presence of an RNA binding protein, RBM3, and of a circular RNA, , within the complex. Targeting of this complex by knockdown of results in the restoration of cytosolic localization of DICER and widespread derepression of the microRNAome, leading to transcriptome-wide rearrangements that mitigate the tumorigenicity of glioblastoma cells in vitro and in vivo with correlation to favorable outcomes in patients with glioblastoma. These findings uncover the mechanistic foundation of microRNAome deregulation in malignant cells.