MicroRNA-146a Inhibits Glioma Development by Targeting Notch1

Abstract

Dysregulated epidermal growth factor receptor (EGFR) signaling through either genomic amplification or dominant-active mutation (EGFR vIII ), in combination with the dual inactivation of INK4A/ARF and PTEN, is a leading cause of gliomagenesis. Our global expression analysis for microRNAs revealed that EGFR activation induces miR-146a expression, which is further potentiated by inactivation of PTEN. Unexpectedly, overexpression of miR-146a attenuates the proliferation, migration, and tumorigenic potential of Ink4a/Arf ؊/؊ Pten ؊/؊ Egfr vIII murine astrocytes. Its ectopic expression also inhibits the glioma development of a human glioblastoma cell line in an orthotopic xenograft model. Such an inhibitory function of miR-146a on gliomas is largely through downregulation of Notch1, which plays a key role in neural stem cell maintenance and is a direct target of miR-146a. Accordingly, miR-146a modulates neural stem cell proliferation and differentiation and reduces the formation and migration of glioma stem-like cells. Conversely, knockdown of miR-146a by microRNA sponge upregulates Notch1 and promotes tumorigenesis of malignant astrocytes. These findings indicate that, in response to oncogenic cues, miR-146a is induced as a negative-feedback mechanism to restrict tumor growth by repressing Notch1. Our results provide novel insights into the signaling pathways that link neural stem cells to gliomagenesis and may lead to new strategies for treating brain tumors.Gliomas are the most frequently observed brain tumors, with glioblastoma multiforme (GBM) being the most common and aggressive form in adults (35). Despite major therapeutic improvements made by combining neurosurgery, chemotherapy, and radiotherapy, the prognosis and survival rate for patients with GBM is still extremely poor (7). The deadly nature of GBM originates from explosive growth and invasive behavior, which are fueled by dysregulation of multiple signaling pathways. Epidermal growth factor receptor (EGFR) activation, in cooperation with loss of tumor suppressor functions, such as mutations in Ink4a/Arf and Pten genes, constitutes a lesion signature for GBM (4). Such dysregulated genetic pathways are sufficient to transform neural stem cells (NSCs) or astrocytes into cancer stem-like cells. This gives rise to highgrade malignant gliomas with a pathological phenotype resembling human GBM (5, 59). However, the downstream events underlying these genetic dysregulations in gliomagenic cells have not been fully elucidated.MicroRNAs are 20-to 22-nucleotide noncoding RNA molecules that have emerged as key players in controlling NSC self-renewal and differentiation (11,57). Aberrant expression of miRNAs, such as miR-21, miR-124, and miR-137, is linked to glioma formation (49). miR-199b-5p and miR-34a impair cancer stem-like cells through the negative regulation of several components of the Notch pathway in brain tumors (18,21). The Notch pathway is an evolutionarily conserved signaling pathway that plays an important role in neurogenesis (3, 10, 23). Upon bindi...

Thymosin β4 Up-regulation of MicroRNA-146a Promotes Oligodendrocyte Differentiation and Suppression of the Toll-like Proinflammatory Pathway

“…Overexpression of miR-146a up to at least 35-fold was required for endotoxin tolerance (44). Transfection of miR-146a was also employed previously for tumor suppression in glioma (45). Lentiviral miR-146a transfection showed a 26-fold increase of wild-type miR-146a and attenuated the proliferation, migration, and tumorigenic potential of Ink4a/ Arf_/_ Pten_/_EgfrvIII murine astrocytes.…”

MiR-663, a microRNA targeting p21WAF1/CIP1, promotes the proliferation and tumorigenesis of nasopharyngeal carcinoma

“…Artificial miRNA decoys termed 'miRNA sponges' were recently introduced as a long-term inhibitor that can stably block the function of miRNAs in cell lines and transgenic organisms (Ebert et al, 2007). This approach has proved to be a useful tool to probe miRNA functions in a variety of experimental systems, such as models of breast cancer and glioma (Valastyan et al, 2009;Mei et al, 2011). In the present experimental model, we structured a miR-663 sponge to block miR-663 stably in NPC cells in a stronger way than with LNA, in accordance with the report by Ebert et al (2007) Therefore, we speculate that 'miRNA sponges' can be used as a powerful tool to investigate the functions of miRNAs and as a potential therapeutic strategy by targeting miRNAs.…”

Role of Krüppel-Like Factor 4 in Neurogenesis and Radial Neuronal Migration in the Developing Cerebral Cortex

“…The sense strands that have cloning sites for the two shRNA constructs are GAT CCC CAC CTA TAC CAA GAG TTC TCA TTT CAA GAG AAT GAG AAC TCT TGG TAT AGG TTT TTT A and GAT CCC CGC GTG AGG AAC TCT CTC ACA TTT CAA GAG AAT GTG AGA GAG TTC CTC ACG CTT TTT A. To make lentivirus, Klf4 cDNA was inserted into the lentiviral vector CS-CDF-CG-PRE, which also expresses GFP under the control of an IRES. Lentiviruses were produced as previously described (25).…”