MicroRNA-138 promotes acquired alkylator resistance in glioblastoma by targeting the Bcl-2-interacting mediator BIM

Abstract

// Nina Stojcheva 1, 2 , Gennadi Schechtmann 3 , Steffen Sass 4 , Patrick Roth 1, 2 , Ana-Maria Florea 3 , Anja Stefanski 5 , Kai Stühler 5 , Marietta Wolter 3 , Nikola S. Müller 4 , Fabian J. Theis 4, 6 , Michael Weller 1, 2 , Guido Reifenberger 3, 7 , Caroline Happold 1, 2 1 Laboratory of Molecular Neuro-Oncology, Department of Neurology, University Hospital and University of Zurich, Zurich, Switzerland 2 Neuroscience Center Zurich, University of Zurich, Zurich, Switzerland 3 Department of Neuropathology, Heinrich Heine University Düsseldorf, Düsseldorf, Germany 4 Institute of Computational Biology, Helmholtz Center Munich, German Research Center for Environmental Health, Neuherberg, Germany 5 Molecular Proteomics Laboratory, Biological and Medical Research Center (BMFZ), Heinrich Heine University Düsseldorf, Düsseldorf, Germany 6 Department of Mathematics, Technische Universität München, Garching, Germany 7 German Cancer Consortium (DKTK), German Cancer Research Center (DKFZ) Heidelberg, partner site Essen/Düsseldorf, Germany Correspondence to: Caroline Happold, e-mail: caroline.happold@usz.ch Keywords: chemoresistance, temozolomide, glioblastoma, miR-138, BIM Received: December 11, 2015      Accepted: January 26, 2016      Published: February 12, 2016 ABSTRACT Glioblastoma is the most aggressive brain tumor in adults with a median survival below 12 months in population-based studies. The main reason for tumor recurrence and progression is constitutive or acquired resistance to the standard of care of surgical resection followed by radiotherapy with concomitant and adjuvant temozolomide (TMZ/RT→TMZ). Here, we investigated the role of microRNA (miRNA) alterations as mediators of alkylator resistance in glioblastoma cells. Using microarray-based miRNA expression profiling of parental and TMZ-resistant cultures of three human glioma cell lines, we identified a set of differentially expressed miRNA candidates. From these, we selected miR-138 for further functional analyses as this miRNA was not only upregulated in TMZ-resistant versus parental cells, but also showed increased expression in vivo in recurrent glioblastoma tissue samples after TMZ/RT→TMZ treatment. Transient transfection of miR-138 mimics in glioma cells with low basal miR-138 expression increased glioma cell proliferation. Moreover, miR-138 overexpression increased TMZ resistance in long-term glioblastoma cell lines and glioma initiating cell cultures. The apoptosis regulator BIM was identified as a direct target of miR-138, and its silencing mediated the induced TMZ resistance phenotype. Altered sensitivity to apoptosis played only a minor role in this resistance mechanism. Instead, we identified the induction of autophagy to be regulated downstream of the miR-138/BIM axis and to promote cell survival following TMZ exposure. Our data thus define miR-138 as a glioblastoma cell survival-promoting miRNA associated with resistance to TMZ therapy in vitro and with tumor progression in vivo .