Competition for XPO5 binding between Dicer mRNA, pre-miRNA and viral RNA regulates human Dicer levels.

MicroRNAs (miRNAs) are a class of small, noncoding RNAs that function by regulating gene expression post-transcriptionally. Alterations in miRNA expression can strongly influence cellular physiology. Here we demonstrated cross-regulation between two components of the RNA interference (RNAi) machinery in human cells. Inhibition of exportin-5, the karyopherin responsible for pre-miRNA export, downregulated expression of Dicer, the RNase III required for pre-miRNA maturation. This effect was post-transcriptional and resulted from an increased nuclear localization of Dicer mRNA. In vitro assays and cellular RNA immunoprecipitation experiments showed that exportin-5 interacted directly with Dicer mRNA. Titration of exportin-5 by overexpression of either pre-miRNA or the adenoviral VA1 RNA resulted in loss of Dicer mRNA-exportin-5 interaction and reduction of Dicer level. This saturation also occurred during adenoviral infection and enhanced viral replication. Our study reveals an important cross-regulatory mechanism between pre-miRNA or viral small RNAs and Dicer through exportin-5.