Titolo della tesi: Molecular characterization of patient-derived glioblastoma stem-like cells to identify innovative therapeutic approaches for the management of glioblastoma
Glioblastoma (GBM) is the most common and lethal primary brain tumor in adults. Increasing studies have confirmed that GBM stem-like cells (GSCs) play a key role in the GBM initiation and progression, tumor recurrence and resistance to radiotherapy and chemotherapy. Accordingly, it is important to focus on cellular and molecular characterization of GSCs to develop more effective therapies for treatment of GBM patients. Investigating miRNA expression profile by microarray platform in a collection of patient-derived GSCs, we observed that the expression of miRNAs, from a large cluster on chromosome 14q32 were downregulated, compared to normal neural stem cells. This cluster locates within the imprinted chromosomal region, named DLK1-DIO3 locus. Besides miRNAs, RT-PCR analysis showed that other genes (DLK1 and DIO3) and non-coding RNAs (SNORD113-1, SNORD114-1, MEG3 and MEG8 lncRNAs) contained in this locus were downregulated in GSCs and GBM tissues compared to normal neural stem cells and normal brain, respectively. Of note, Kaplan-Meier analysis revealed that the expression of the lncRNAs, MEG3 and MEG8, was correlated with GBM patient overall survival. MLPA analysis and methylation profiles obtained with the Illumina array 450k have demonstrated that aberrant methylation may contribute to the downregulation of MEG3 in GBM. Moreover, VPA treatments in vitro and in vivo showed that other epigenetic alterations, such as histone acetylation, could be implicated in MEG3 silencing. MEG3 restoration and knockdown affected proliferation, colony formation ability and migration of GSCs in vitro. In addition, MEG3 restoration significantly reduced the tumor growth and the degree of brain invasion in vivo supporting the involvement of MEG3 as tumor suppressor in GBM tumorigenesis. Gene expression and Reverse-Phase Protein Arrays (RPPA) analysis showed that cellular processes affected by MEG3 and the main mediators of its tumor suppression function are genes involved in cell adhesion and epithelial-mesenchymal transition (EMT) pathways.