Extracellular ATP reduces tumor sphere growth and cancer stem cell population in glioblastoma cells
Glioblastoma is the most aggressive tumor in the CNS and is characterized by having a cancer stem cell (CSC) subpopulation essential for tumor survival. The purinergic system plays an important role in glioma growth, since adenosine triphosphate (ATP) can induce proliferation of glioma cells, and alteration in extracellular ATP degradation by the use of exogenous nucleotidases dramatically alters the size of gliomas in rats. The aim of this work was to characterize the effect of the purinergic system on glioma CSCs. Human U87 glioma cultures presented tumor spheres that express the markers of glioma cancer stem cells CD133, Oct-4, and Nanog. Messenger RNA of several purinergic receptors were differently expressed in spheres when compared to a cell monolayer not containing spheres. Treatment of human gliomas U87 or U343 as well as rat C6 gliomas with 100 μM of ATP reduced the number of tumor spheres when grown in neural stem cell medium supplemented with epidermal growth factor and basic fibroblast growth factor. Moreover, ATP caused a decline in the number of spheres observed in culture in a dose-dependent manner. ATP also reduces the expression of Nanog, as determined by flow cytometry, as well as CD133 and Oct-4, as analyzed by flow cytometry and RT-PCR in U87 cells. The differential expression of purinergic receptor in tumor spheres when compared to adherent cells and the effect of ATP in reducing tumor spheres suggest that the purinergic system affects CSC biology and that ATP may be a potential agonist for differentiation therapy.
KeywordsGlioma Cancer stem cells CD133 Purinergic system ATP
Cancer stem cell
Calcium-calmodulin-dependent kinase II
Fibroblast growth factor
Epidermal growth factor
The present research was supported by grants from Brazilian funding agencies FAPERGS (Procoredes III 06/1376.0 and Pronex 10/0044-3) and CNPq (420036/2005-9). PL, ESV, DGF. and GL are recipient of CNPq fellowships.
Conflict of interest
We declare that we have no conflict of interest.
- 6.Diehn M, Cho RW, Lobo NA, Kalisky T, Dorie MJ, Kulp AN, Qian D, Lam JS, Ailles LE, Wong M, Joshua B, Kaplan MJ, Wapnir I, Dirbas FM, Somlo G, Garberoglio C, Paz B, Shen J, Lau SK, Quake SR, Brown JM, Weissman IL, Clarke MF (2009) Association of reactive oxygen species levels and radioresistance in cancer stem cells. Nature 458(7239):780–783PubMedCrossRefGoogle Scholar
- 10.Beier D, Rohrl S, Pillai DR, Schwarz S, Kunz-Schughart LA, Leukel P, Proescholdt M, Brawanski A, Bogdahn U, Trampe-Kieslich A, Giebel B, Wischhusen J, Reifenberger G, Hau P, Beier CP (2008) Temozolomide preferentially depletes cancer stem cells in glioblastoma. Cancer Res 68(14):5706–5715PubMedCrossRefGoogle Scholar
- 16.Resende RR, Majumder P, Gomes KN, Britto LR, Ulrich H (2007) P19 embryonal carcinoma cells as in vitro model for studying purinergic receptor expression and modulation of N-methyl-d-aspartate-glutamate and acetylcholine receptors during neuronal differentiation. Neuroscience 146(3):1169–1181PubMedCrossRefGoogle Scholar
- 27.Ouafik L, Sauze S, Boudouresque F, Chinot O, Delfino C, Fina F, Vuaroqueaux V, Dussert C, Palmari J, Dufour H, Grisoli F, Casellas P, Brunner N, Martin PM (2002) Neutralization of adrenomedullin inhibits the growth of human glioblastoma cell lines in vitro and suppresses tumor xenograft growth in vivo. Am J Pathol 160(4):1279–1292PubMedCrossRefGoogle Scholar
- 30.Chiou SH, Wang ML, Chou YT, Chen CJ, Hong CF, Hsieh WJ, Chang HT, Chen YS, Lin TW, Hsu HS, Wu CW (2010) Coexpression of Oct4 and Nanog enhances malignancy in lung adenocarcinoma by inducing cancer stem cell-like properties and epithelial–mesenchymal transdifferentiation. Cancer Res 70(24):10433–10444PubMedCrossRefGoogle Scholar