(ac) GSC-enriched NS cell lines isolated from four patient tumors (C, D, G and I) were kept in SCM medium or allowed to differentiate as adherent GBM cells for at least 15 days in FCS medium. (a) Phase-contrast photomicrographs of NS or GBM-differentiated cells. Unique magnification: 10, scale bar: 6m. anti-apoptotic protein survivin and we showed that its specific downregulation led to the blockade of the IR-induced plasticity. Completely, these results shown that irradiation could regulate GBM cell dedifferentiation via a survivin-dependent pathway. Targeting the mechanisms associated with IR-induced plasticity will likely contribute to the development of some innovating pharmacological strategies for an improved radiosensitization of these aggressive brain cancers. Radiotherapy is, following medical resection and associated with Temozolomide, the platinum standard treatment for glioblastoma (GBM). However, actually after the association of surgery and combined chemo/radiotherapy, these invasive and resistant tumors almost systematically recur, having a median overall survival of 14 weeks.1It is now established that GBM are some very heterogeneous tumors related to most of the stable cancers.2Recent studies highlighted the presence of a subpopulation of self-renewing and pluripotent GBM stem-like cells (GSCs), also called GBM-initiating cells, among the tumor. These GSC are characterized by their ability to self-renewin vitro(neurospheres (NS) formation) andin vivo, their higher manifestation of neural stem cell (NSC) markers (i.e., Olig2, Nestin or A2B5) and stem cell transcription factors (SCTF, i.e., Sox2, Nanog, Gli1 or Oct4), Rabbit polyclonal to STAT2.The protein encoded by this gene is a member of the STAT protein family.In response to cytokines and growth factors, STAT family members are phosphorylated by the receptor associated kinases, and then form homo-or heterodimers that translocate to the cell nucleus where they act as transcription activators.In response to interferon (IFN), this protein forms a complex with STAT1 and IFN regulatory factor family protein p48 (ISGF3G), in which this protein acts as a transactivator, but lacks the ability to bind DNA directly.Transcription adaptor P300/CBP (EP300/CREBBP) has been shown to interact specifically with this protein, which is thought to be involved in the process of blocking IFN-alpha response by adenovirus. their pluripotent aptitude to differentiate into neurons, PCI-34051 astrocytes or oligodendrocytes and their high tumorigenic potentialin vivoin mice.3,4In addition, the presence of these GSC may explain the high GBM recurrence rate, as they were shown to be extremely tumorigenic and radioresistant.3,5,6 Several radioresistance mechanisms have been recognized in these GSC. Most of them are in favor of a clonal selection process through the GSC intrinsic resistance to ionizing radiation (IR)-induced cell death,7,8supported by a better effectiveness of DNA-damage restoration systems,6,9,10a higher level of anti-apoptotic11,12or pro-survival factors13,14,15and a sustained manifestation of pluripotency maintenance factors such as Notch1,16TGF,17,18Sonic hedgehog (SonicHH),19STAT320or Wnt.21Besides this, the influence of the microenvironment could also participate in radioresistance,17,22as hypoxia, which is a well-known element of radioresistance,23,24acidic extracellular pH25and nitric oxide26,27were shown to be involved in GSC stemness preservation. However, several studies possess put forward the hypothesis that GBM-differentiated cells may be able to dedifferentiate toward a stem-like state when submitted to appropriate stimuli7and then contribute to increase the tumor stem cell pool. This assumption was supported by PCI-34051 studies showing that hypoxic conditions, hepatocyte growth element or Temozolomide could induce such a trend in GBM cells.23,28,29Of note, hypoxia was previously shown to induce a similar reprogramming in breast cancer30and neuroblastoma cells,31and our group showed that IR can PCI-34051 stabilize HIF1(hypoxia-inducible factor 1) and activate the connected hypoxic pathways in GBM.32,33This dedifferentiation process was also demonstratedin vivoin murine neurons and astrocytes through the expression of GBM-associated oncogenes.34In line with this, recent works showed that IRs were able to induce at short term the expression of stem markers (such as Sox2, Nestin and CD133) in GBM,35without PCI-34051 studying the presence of a potential dedifferentiation process. In result, we hypothesized that plasticity may occur after radiotherapy in resistant remaining GBM cells. The present study was designed to analyze the long-term effects of radiotherapy within the phenotypic and molecular status of GBM cells isolated from several patient resections and to find out whether or not these cells can dedifferentiate toward a stem-like phenotype in response to IR. Our present data display in human main GBM patient cell lines that a subtoxic IR dose can induce at long term the overexpression of a large panel of stem markers in GBM cells, a potentiation of their NS-forming capacity and an exacerbated tumorigenesis in nude mice, indicating an IR-induced dedifferentiation process. We have also recognized the inhibitor of apoptosis protein (IAP) survivin as an important regulator of this IR-induced plasticity. In conclusion, we showed here for the first time that radiotherapy is able to sustain a phenotype shift toward stemness in GBM, which.