title: Activation of the phosphorylation of ATM contributes to radioresistance of glioma stem cells.
abstract: Ionizing radiation (IR) is currently the most efficient therapy available for malignant glioma. Unfortunately, this strategy is palliative due to the characteristics of radioresistance of malignant glioma. The aim of our study was to compare glioma stem cells (GSCs) with glioma cells (GCs) to determine whether GSCs are responsible for the radioresistance phenotype and to elucidate whether cell cycle checkpoint proteins are responsible for the radioresistance of GSCs. In this study, CD133 (a marker of brain cancer stem cells) and nestin were co-expressed in GSCs isolated from GCs. The percent of CD133+ cells in GSCs and GCs were >80 and <2%, respectively. Significantly more GSCs survived following 2, 4, 6 and 8 Gy IR than GCs. IR kills cancer cells primarily through DNA double-strand breaks (DSBs). The neutral comet assay is often used to intuitively show the level of DSBs. Significantly fewer GSCs showed DNA damage than GCs following 2 Gy IR. This demonstrated that GSCs are more resistant to in vitro radiation than GCs. Furthermore, activated ataxia telangiectasia mutated (ATM) is essential for the activation of downstream effector kinases, such as checkpoint kinase 2 (Chk2) and p53 which mainly contribute to the proper regulation of IR-induced arrest in the G1 phase. DNA damage induced by IR potently initiated activation of phosphorylation of the ATM, p53 and Chk2 checkpoint proteins. Activation of the phosphorylation of these checkpoint proteins was significantly higher in the GSCs compared to GCs. We found that inhibition of ATM activation induced cell cycle checkpoint defects and increased the rate of apoptosis of GSCs following IR. Our results suggest that GSCs were more resistant to radiation compared to GCs due to high expression of phosphorylated cell cycle checkpoint proteins, and inhibition of ATM could significantly reduce the radioresistance of GSCs and GCs. ATM may represent a source of radioresistance in GSCs and a target of improved radiosensitivity of GSCs.
authors.affiliation: Chongqing Cancer Institute, Chongqing 400030, P.R. China.
authors.forename: Wei
authors.initials: W
authors.lastname: Zhou
authors.forename: Mao
authors.initials: M
authors.lastname: Sun
authors.forename: Guang-Hui
authors.initials: GH
authors.lastname: Li
authors.forename: Yong-Zhong
authors.initials: YZ
authors.lastname: Wu
authors.forename: Ying
authors.initials: Y
authors.lastname: Wang
authors.forename: Fu
authors.initials: F
authors.lastname: Jin
authors.forename: Yun-Yun
authors.initials: YY
authors.lastname: Zhang
authors.forename: Li
authors.initials: L
authors.lastname: Yang
authors.forename: Dong-Lin
authors.initials: DL
authors.lastname: Wang
mesh_terms: D000071916:AC133 Antigen; D000818:Animals; D015703:Antigens, CD / Q000096:biosynthesis; D017209:Apoptosis / Q000528:radiation effects; D064007:Ataxia Telangiectasia Mutated Proteins / Q000378:metabolism* / Q000528:radiation effects; D002454:Cell Differentiation / Q000528:radiation effects; D045744:Cell Line, Tumor; D016543:Central Nervous System Neoplasms / Q000378:metabolism / Q000532:radiotherapy*; D064447:Checkpoint Kinase 2 / Q000378:metabolism; D053903:DNA Breaks, Double-Stranded / Q000528:radiation effects; D004260:DNA Repair; D004307:Dose-Response Relationship, Radiation; D004789:Enzyme Activation / Q000528:radiation effects; D005910:Glioma / Q000378:metabolism / Q000532:radiotherapy*; D006023:Glycoproteins / Q000096:biosynthesis; D006801:Humans; D051379:Mice; D008807:Mice, Inbred BALB C; D008819:Mice, Nude; D014411:Neoplastic Stem Cells / Q000378:metabolism* / Q000528:radiation effects*; D064231:Nestin / Q000096:biosynthesis; D010455:Peptides; D010766:Phosphorylation / Q000528:radiation effects; D011836:Radiation Tolerance; D011839:Radiation, Ionizing; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism
chemical_list: D000071916:AC133 Antigen; D015703:Antigens, CD; D006023:Glycoproteins; C577484:NES protein, human; D064231:Nestin; C000606023:PROM1 protein, human; D010455:Peptides; C000606024:Prom1 protein, mouse; D016159:Tumor Suppressor Protein p53; D064447:Checkpoint Kinase 2; C576324:ATM protein, human; D064007:Ataxia Telangiectasia Mutated Proteins