Abstract
miRNAs play key roles in the nervous system, where they mark distinct developmental stages. Accordingly, dysregulation of miRNA expression may have profound effects on neuronal physiology and pathology, including cancer. Among the neuronal miRNAs, miR-9 was shown to be upregulated during in vitro neuronal differentiation and downregulated in 50% of primary neuroblastoma tumors, suggesting a potential function as an oncosuppressor gene. In this study we characterized the promoter and the transcriptional regulation of the miR-9-2 gene during neuronal differentiation. We found that, despite its localization inside an exon of a putative host-gene, miR-9-2 is expressed as an independent unit with the promoter located in the upstream intron. By promoter fusion and mutational analyses, together with RNAi and Chromatin immunoprecipitation assays, we demonstrated that the concerted action of the master transcriptional factors RE1-silencing transcription factor (REST) and cAMP-response element binding protein (CREB) on miR-9-2 promoter induces miRNA expression during differentiation. We showed that the repressor REST inhibits the activity of the miR-9-2 promoter in undifferentiated neuroblastoma cells, whereas REST dismissal and phosphorylation of CREB trigger transcription in differentiating cells. Finally, a regulatory feed-back mechanism, in which the reciprocal action of miR-9 and REST may be relevant for the maintenance of the neuronal differentiation program, is shown.