Abstract
BackgroundGlioblastoma 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.MethodsIn 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.ResultsWe 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.ConclusionWe 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.Electronic supplementary materialThe online version of this article (doi:10.1186/s12935-016-0339-9) contains supplementary material, which is available to authorized users.
Highlights
Glioblastoma stem cells (GSC) have been extensively recognized as a plausible cause of glioblastoma resistance to therapy and recurrence resulting in high glioblastoma mortality
We show that the depletion of topoisomerase IIbeta (Top2β) in glioma stem cells leads to increased sensitivity to a panel of replication stress-inducing drugs
Glioma stem cell line NCH421k was obtained from CLS cell lines service and grown as floating neurospheres in DMEM/F12 medium supplemented with 0.25 % BSA, 1 % ITS, 20 ng/mL epidermal growth factor (EGF) and 20 ng/mL basic fibroblast growth factor
Summary
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. DNA repair pathways were extensively studied in carcinogenesis [12], because defects in these pathways enable tumor cells to accumulate mutations that enhance their proliferation and survival in the complex host tissue microenvironment. Cancer cells that maintain functional DNA repair pathways might be able to survive chemotherapy and/or radiation. The relevance of intrinsic DNA repair efficacy as a resistance mechanism of glioma stem cells remains elusive
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