MicroRNA-mediated down-regulation of NKG2D ligands contributes to glioma immune escape
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Paula Codo1, Michael Weller1, Gunter Meister2, Emese Szabo1, Alexander Steinle3, Marietta Wolter4, Guido Reifenberger4 and Patrick Roth1
1 Laboratory of Molecular Neuro-Oncology, Department of Neurology, University Hospital Zurich, Switzerland
2 Department of Biochemistry I, University of Regensburg, Germany
3 Institute for Molecular Medicine, University of Frankfurt, Germany
4 Department of Neuropathology, Heinrich Heine University Düsseldorf and German Cancer Consortium (DKTK), partner site Essen/Düsseldorf, Germany
Patrick Roth, email:
Keywords: glioma, immune escape, NKG2D, miRNA
Received: June 19, 2014 Accepted: July 31, 2014 Published: July 31, 2014
Malignant gliomas are intrinsic brain tumors with a dismal prognosis. They are well-adapted to hypoxic conditions and poorly immunogenic. NKG2D is one of the major activating receptors of natural killer (NK) cells and binds to several ligands (NKG2DL).
Here we evaluated the impact of miRNA on the expression of NKG2DL in glioma cells including stem-like glioma cells. Three of the candidate miRNA predicted to target NKG2DL were expressed in various glioma cell lines as well as in glioblastomas in vivo: miR-20a, miR-93 and miR-106b. LNA inhibitor-mediated miRNA silencing up-regulated cell surface NKG2DL expression, which translated into increased susceptibility to NK cell-mediated lysis. This effect was reversed by neutralizing NKG2D antibodies, confirming that enhanced lysis upon miRNA silencing was mediated through the NKG2D system. Hypoxia, a hallmark of glioblastomas in vivo, down-regulated the expression of NKG2DL on glioma cells, associated with reduced susceptibility to NK cell-mediated lysis. This process, however, was not mediated through any of the examined miRNA. Accordingly, both hypoxia and the expression of miRNA targeting NKG2DL may contribute to the immune evasion of glioma cells at the level of the NKG2D recognition pathway. Targeting miRNA may therefore represent a novel approach to increase the immunogenicity of glioblastoma.
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