Identifikation von microRNA-Markern der Glioblastoma progression

As a highly invasive and progressive tumor, GBM ranks among the most lethal cancers. MiRNAs, as small regulators of posttranscriptional gene expression, are associated with aberrant intracellular signaling pathways that characterize GBM biology. Recurrent, progressive GBM is hardly treatable due to limited therapeutic options and the rapid acquaintance of radiation- and chemotherapy resistance. These relapses are often mediated by GSCs, a small but highly influential fraction of tumor cells with pluripotent properties. Identifying mediators of GBM progression, GCS maintenance, and underlying dysregulated signaling pathways is essential for developing new therapeutic strategies. This thesis investigated the role of miRNAs in GBM progression by identifying miRNAs of GSC maintenance and by exploring signaling pathways downregulating miR-181a-5p, a tumor suppressor miRNA in GBM. The membrane-anchored ADAM8 induces the transcription of pro-invasive and angiogenic oncogenes by initiating intracellular signaling pathways. In this context, the first study uncovered a new regulatory network implementing miR-181a-5p downregulation by ADAM8-induced MAPK and STAT3 signaling. In ADAM8-deficient U87 cells, miR-181a-5p was significantly upregulated. Notably, the overexpression of miR-181a-5p extended to the EV cargo. The cytoplasmatic domain of ADAM8 accelerates MAPK and STAT3 signaling, thereby silencing miR-181a-5p transcription. Furthermore, transiently overexpressed miR-181a-5p reduced proliferation and MMP9 expression by targeting MAPK pathway kinases, highlighting this miRNA's tumor- suppressive properties, and introducing a complex regulatory miR-181a- 5p/MAPK/MMP9 loop. In tissue specimens ADAM8 and MMP9 were overexpressed, their levels were strikingly correlated, while miR-181a-5p was downregulated. Analysis of patient-serum-derived EVs revealed reduced miR-181a-5p levels in recurrent glioblastoma proposing miR-181a-5p as a potential biomarker of GBM progression. The second study explored the miRNA profiles of GSCs and their corresponding differentiated cell states, aiming to uncover regulatory miRNAs of GSC maintenance. Upon in-vitro differentiation of well-characterized GSCs into astrocytic tumor cells, 31 dysregulated miRNAs were uncovered by conducting a miRNA PCR array. Combing literature research and bioinformatic analyses, four miRNAs, miR-425-5p, miR-223-3p, let-7a-5p, and miR-17-5p, were introduced as putative mediators of GSC fate. Since target prediction analysis revealed that PTEN and GFAP mRNAs display authentic binding sites for miR-425-5p, and validating experiments confirmed miR-425-5p overexpression in all GSC lines, this onco-miRNA was selected for further investigations. Indeed, GFAP and PTEN expression decreased upon miR-425-5p overexpression in 25 one primary patient-derived GBM cell line, highlighting a potential role of this onco- miRNA in GSC survival and GBM progression. A distinctive miRNA profile is linked to core features of GBM like invasion, therapeutic resistance, and phenotype plasticity. Thereby, altered expressions of numerous miRNAs, including miR-425-5p and miR-181-5p, are associated with GBM progression and discussed as future biomarkers of GBM recurrence.