Relevance of transcription regulator MED13 in response of brain tumour cells to the alkylation therapy
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Glioblastoma multiforme (GBM) is the most frequent and aggressive brain tumour in adults, defined with poor survival, high tumour heterogeneity, and lack of effective treatments. Despite the increasing knowledge in molecular mechanisms of GBM, treatment options remain challenging due to remarkable intertumoral and intratumoral heterogeneity. Isolation and characterization of glioblastoma stem cells (GSCs) from patient tumours can provide insight for effective, subtype-specific treatments. Standard treatment for GBM includes surgery, radiotherapy, and chemotherapy. Alkylating agent temozolomide (TMZ) is the most frequently used chemotherapeutic drug in GBM treatment. However, many tumours develop resistance to treatment and recur.Alterations in many transcriptional regulators have been detected in Grade III gliomas and Grade IV GBM. Mediator complex is one such evolutionary conserved transcriptional regulator, which is composed of multiple subunits and a cyclin-dependent kinase module (CDK). Mediator complex conveys signals between transcription factors and basal transcription machinery, thus regulating transcription both positively and negatively. Alterations of Mediator subunits have been detected in different cancers including breast, prostate, and lung. Unpublished findings from our laboratory indicate that besides in transcription, MED13 plays a decisive role in survival upon TMZ exposure. In this thesis, the impact of Mediator complex subunit (MED13) on the response to treatment with alkylating drugs and the migration capacity was investigated in glioblastoma stem cells and cerebral organoids. To determine the function of MED13, G144 glioblastoma stem cells lacking MED13 were generated by using CRISPR-Cas9 engineering, and the response of G144 MED13 knock-out (KO) cells to alkylating drugs TMZ and methyl methanesulfonate (MMS) were investigated. G144 MED13 KO cells showed increased survival upon alkylating treatment. The migration potential of G144 MED13 KO cells was also analysed with neurosphere migration assay and visualized with immunofluorescence by using glioblastoma stem cell markers OLIG2 and NESTIN. G144 MED13 KO cells displayed higher migration potential than G144 wild type cells.In summary, the findings of this thesis indicate that loss of MED13 drives resistance against alkylating agent TMZ and promotes cell migration. To which extent MED13 influences survival of GBM cells to TMZ treatment and promotes migration of GBM cells remain unknown.