In the human brain, microRNAs (miRNAs) from the microRNA-376 (miR-376) cluster undergo programmed "seed" sequence modifications by adenosine-to-inosine (A-to-I) editing. Emerging evidence suggests a link between impaired A-to-I editing and cancer, particularly in high-grade gliomas. We hypothesized that disruption of A-to-I editing alters expression of genes regulating glioma tumor phenotypes. By sequencing the miR-376 cluster, we show that the overall miRNA editing frequencies were reduced in human gliomas. Specifically in high-grade gliomas, miR-376a* accumulated entirely in an unedited form. Clinically, a significant correlation was found between accumulation of unedited miR-376a* and the extent of invasive tumor spread as measured by magnetic resonance imaging of patient brains. Using both in vitro and orthotopic xenograft mouse models, we demonstrated that the unedited miR-376a* promoted glioma cell migration and invasion, while the edited miR-376a* suppressed these features. The effects of the unedited miR-376a* were mediated by its sequence-dependent ability to target RAP2A and concomitant inability to target AMFR. Thus, the tumordependent introduction of a single base difference in the miR-376a* sequence dramatically alters the selection of its target genes and redirects its function from inhibiting to promoting glioma cell invasion. These findings uncover a new mechanism of miRNA deregulation and identify unedited miR-376a* as a potential therapeutic target in glioblastoma cells. IntroductionMicroRNAs (miRNAs) are short, noncoding RNAs that mediate post-transcriptional silencing of a set of target genes. The target gene specificity of each miRNA is dictated by sequence-dependent interaction between approximately 22-nt-long mature miRNAs, especially their 6-or 7-nucleotide "seed" sequences at the 5′ end, and the 3′ untranslated regions of mRNAs (1). It has been shown that the epigenetic process of adenosineto-inosine (A-to-I) editing of certain miRNAs can lead to a single base substitution in their seed sequence and generate variant "edited" mature miRNA species with target gene specificity drastically different from that of the unedited, genomically encoded miRNA (2). This was demonstrated for miR-376 cluster transcripts collected from normal human and mouse tissues. The miR-376 cluster encodes 4 primary miRNAs (primiRs), including pri-miR-376a1, -376a2, -376b, and -376c, that are processed to 5 distinct mature miRNAs, miR-376a, -376a*, -376a2-5p, -376b, and -376c. In the human brain, 9 adenosines within this miRNA cluster are subject to specific and high-level A-to-I RNA editing (2).In gliomas, the most frequent primary brain tumors, Alu repeats and several protein-coding substrates of adenosine deaminases acting on RNA (ADARs; a family of enzymes that mediate A-to-I editing of RNAs) have been found to be edited to lower than normal frequencies (3-5). Particularly in high-grade gliomas, glioblastoma multiforme (GBMs), emerging lines of evidence suggest a

Neurons and glia in the vertebrate central nervous system arise in temporally distinct, albeit overlapping, phases. Neurons are generated first followed by astrocytes and oligodendrocytes from common progenitor cells. Increasing evidence indicates that axon-derived signals spatiotemporally modulate oligodendrocyte maturation and myelin formation. Our previous observations demonstrate that F3/contactin is a functional ligand of Notch during oligodendrocyte maturation, revealing the existence of another group of Notch ligands. Here, we establish that NB-3, a member of the F3/contactin family, acts as a novel Notch ligand to participate in oligodendrocyte generation. NB-3 triggers nuclear translocation of the Notch intracellular domain and promotes oligodendrogliogenesis from progenitor cells and differentiation of oligodendrocyte precursor cells via Deltex1. In primary oligodendrocytes, NB-3 increases myelin-associated glycoprotein transcripts. Thus, the NB-3/Notch signaling pathway may prove to be a molecular handle to treat demyelinating diseases. Neural progenitor cells (NPCs)1 are self-renewing multipotent cells that can give rise to all types of neural cells, namely neurons, oligodendrocytes (OLs), and astrocytes. Increasing evidence suggests that this fate commitment of NPCs requires molecular cues provided by extracellular molecules and intrinsic signaling involving various transcription factors (1, 2). Our recent study (3) has demonstrated that the F3/Notch signaling pathway via Deltex1 (DTX1) promotes oligodendrocyte precursor cell (OPC) differentiation into oligodendrocytes (OLs) and up-regulates myelin-associated glycoprotein (MAG) expression in both primary OLs and OLN-93 cells, an OL cell line.

Mutations in the parkin gene, which encodes a ubiquitin ligase, are a major genetic cause of parkinsonism. Interestingly, parkin also plays a role in cancer as a putative tumor suppressor, and the gene is frequently targeted by deletion and inactivation in human malignant tumors. Here, we investigated a potential tumor suppressor role for parkin in gliomas. We found that parkin expression was dramatically reduced in glioma cells. Restoration of parkin expression promoted G 1 phase cell-cycle arrest and mitigated the proliferation rate of glioma cells in vitro and in vivo. Notably, parkin-expressing glioma cells showed a reduction in levels of cyclin D1, but not cyclin E, and a selective downregulation of Akt serine-473 phosphorylation and VEGF receptor levels. In accordance, cells derived from a parkin-null mouse model exhibited increased levels of cyclin D1, VEGF receptor, and Akt phosphorylation, and divided significantly faster when compared with wild-type cells, with suppression of these changes following parkin reintroduction. Clinically, analysis of parkin pathway activation was predictive for the survival outcome of patients with glioma. Taken together, our study provides mechanistic insight into the tumor suppressor function of parkin in brain tumors and suggests that measurement of parkin pathway activation may be used clinically as a prognostic tool in patients with brain tumor. Cancer Res; 72(10); 2543-53. Ó2012 AACR.