Glioblastoma cancer-stem like cells (GSCs) display marked resistance to ionizing radiation (IR), a standard of care for glioblastoma patients. Mechanisms underpinning radio-resistance of GSCs remain largely unknown. Chromatin state and the accessibility of DNA lesions to DNA repair machineries are crucial for the maintenance of genomic stability. Understanding the functional impact of chromatin remodeling on DNA repair in GSCs may lay the foundation for advancing the efficacy of radio-sensitizing therapies. Here, we present the results of a high-content siRNA microscopy screen, revealing the transcriptional elongation factor SPT6 to be critical for the genomic stability and self-renewal of GSCs. Mechanistically, SPT6 transcriptionally up-regulates BRCA1 and thereby drives an error-free DNA repair in GSCs. SPT6 loss impairs the self-renewal, genomic stability and tumor initiating capacity of GSCs. Collectively, our results provide mechanistic insights into how SPT6 regulates DNA repair and identify SPT6 as a putative therapeutic target in glioblastoma.

Biotech Research and Innovation Centre Faculty of Health and Medical Sciences University of Copenhagen Ole Maaløes Vej 5 Copenhagen DK 2200 Denmark

Brain Tumor Biology Danish Cancer Society Research Center Strandboulevarden 49 Copenhagen DK 2100 Denmark

Department of Clinical and Molecular Pathology Faculty of Medicine and Dentistry Palacky University Hnevotinska 3 Olomouc 77515 Czech Republic

Department of Computational and RNA Biology Department of Biology University of Copenhagen Ole Maaløes Vej 5 Copenhagen DK 2200 Denmark

Department of Drug Design and Pharmacology Copenhagen University Jagtvej 160 Copenhagen DK 2100 Denmark

Department of Neurosurgery Copenhagen University Hospital Blegdamsvej 9 Copenhagen DK 2100 Denmark

Division of Genome Biology Department of Medical Biochemistry and Biophysics Science for Life Laboratory Karolinska Institute Scheeles vag 2 Stockholm 17177 Sweden

Genome Integrity Unit Danish Cancer Society Research Center Strandboulevarden 49 Copenhagen DK 2100 Denmark

University Hospital Olomouc Hnevotinska 3 Olomouc 77515 Czech Republic

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