title: Topoisomerase IIβ mediates the resistance of glioblastoma stem cells to replication stress-inducing drugs.
abstract: BACKGROUND
  Glioblastoma stem cells (GSC) have been extensively recognized as a plausible cause of glioblastoma resistance to therapy and recurrence resulting in high glioblastoma mortality. Abnormalities in the DNA repair pathways might be responsible for the inability of the currently used chemotherapeutics to eliminate the (GSC) subpopulation.
  
  
  METHODS
  In this work, we compared the expression of sixty DNA repair related genes between primary glioblastoma cell cultures and the glioblastoma enriched stem cell primary cultures. MTT test was used to analyze the effect of selected drugs and immunofluorescence to evaluate the load of DNA damage.
  
  
  RESULTS
  We found several differentially expressed genes and we identified topoisomerase IIβ (Top2β) as the gene with highest up-regulation in GSC. Also among the tested cell lines the expression of Top2β was the highest in NCH421k cells, a well-characterized glioblastoma cell line with all the stemness characteristics. On the other hand, Top2β expression markedly decreased upon the induction of differentiation by all trans-retinoic acid. Depletion of Top2β increased the sensitivity of NCH421k cells to replication stress inducing drugs, such as cisplatin, methyl-methanesulfonate, hydrogen peroxide, and temozolomide. Consistently, we found an increased load of DNA damage and increased Chk1 activation upon Top2β depletion in NCH421k cells.
  
  
  CONCLUSIONS
  We suggest that Top2β may represent a new target for gene therapy in glioblastoma. In addition, the other genes that we found to be up-regulated in GSC versus glioblastoma primary cells should be further investigated as glioblastoma theranostics.
authors.affiliation: Structural Biology Laboratory, Elettra-Sincrotrone Trieste, Strada Statale 14-km 163, 5, Basovizza, 34149 Trieste, Italy.
authors.forename: Saša
authors.identifier: 0000-0003-4272-3058
authors.initials: S
authors.lastname: Kenig
authors.affiliation: Structural Biology Laboratory, Elettra-Sincrotrone Trieste, Strada Statale 14-km 163, 5, Basovizza, 34149 Trieste, Italy.
authors.forename: Valentina
authors.initials: V
authors.lastname: Faoro
authors.affiliation: Department of Medical and Biological Sciences, University of Udine, Piazzale Kolbe 4, 33100 Udine, Italy.
authors.forename: Evgenia
authors.initials: E
authors.lastname: Bourkoula
authors.affiliation: Department of Genetic Toxicology and Cancer Biology, National Institute of Biology, Večna pot 111, 1000 Ljubljana, Slovenia.
authors.forename: Neža
authors.initials: N
authors.lastname: Podergajs
authors.affiliation: Neurosurgery Unit, Department of Neurosciences, Santa Maria della Misericordia University Hospital, Piazzale Santa Maria della Misericordia, 15, Udine, Italy.
authors.forename: Tamara
authors.initials: T
authors.lastname: Ius
authors.affiliation: Neurosurgery Unit, Department of Neurosciences, Santa Maria della Misericordia University Hospital, Piazzale Santa Maria della Misericordia, 15, Udine, Italy.
authors.forename: Marco
authors.initials: M
authors.lastname: Vindigni
authors.affiliation: Neurosurgery Unit, Department of Neurosciences, Santa Maria della Misericordia University Hospital, Piazzale Santa Maria della Misericordia, 15, Udine, Italy.
authors.forename: Miran
authors.initials: M
authors.lastname: Skrap
authors.affiliation: Department of Genetic Toxicology and Cancer Biology, National Institute of Biology, Večna pot 111, 1000 Ljubljana, Slovenia ; Faculty of Chemistry and Chemical Engineering, University of Ljubljana, Večna pot 113, 1000 Ljubljana, Slovenia.
authors.forename: Tamara
authors.initials: T
authors.lastname: Lah
authors.affiliation: Department of Medical and Biological Sciences, University of Udine, Piazzale Kolbe 4, 33100 Udine, Italy.
authors.forename: Daniela
authors.initials: D
authors.lastname: Cesselli
authors.affiliation: Structural Biology Laboratory, Elettra-Sincrotrone Trieste, Strada Statale 14-km 163, 5, Basovizza, 34149 Trieste, Italy.
authors.forename: Paola
authors.initials: P
authors.lastname: Storici
authors.affiliation: Structural Biology Laboratory, Elettra-Sincrotrone Trieste, Strada Statale 14-km 163, 5, Basovizza, 34149 Trieste, Italy ; Edward A. Doisy Department of Biochemistry and Molecular Biology, Saint Louis University School of Medicine, St. Louis, MO USA.
authors.forename: Alessandro
authors.initials: A
authors.lastname: Vindigni
keywords: Drug resistance; Glioblastoma stem cells; Glioma; Replication stress; Theranostic markers; Topoisomerase IIβ