Physiologic Oxygen Concentration Enhances the Stem-Like Properties of CD133+ Human Glioblastoma Cells In vitro

Abstract

In vitro investigations of tumor stem-like cells (TSC) isolated from human glioblastoma (GB) surgical specimens have been done primarily at an atmospheric oxygen level of 20%. To determine whether an oxygen level more consistent with in situ conditions affects their stem cell–like characteristics, we compared GB TSCs grown under conditions of 20% and 7% oxygen. Growing CD133+ cells sorted from three GB neurosphere cultures at 7% O2 reduced their doubling time and increased the self-renewal potential as reflected by clonogenicity. Furthermore, at 7% oxygen, the cultures exhibited an enhanced capacity to differentiate along both the glial and neuronal pathways. As compared with 20%, growth at 7% oxygen resulted in an increase in the expression levels of the neural stem cell markers CD133 and nestin as well as the stem cell markers Oct4 and Sox2. In addition, whereas hypoxia inducible factor 1α was not affected in CD133+ TSCs grown at 7% O2, hypoxia-inducible factor 2α was expressed at higher levels as compared with 20% oxygen. Gene expression profiles generated by microarray analysis revealed that reducing oxygen level to 7% resulted in the up-regulation and down-regulation of a significant number of genes, with more than 140 being commonly affected among the three CD133+ cultures. Furthermore, Gene Ontology categories up-regulated at 7% oxygen included those associated with stem cells or GB TSCs. Thus, the data presented indicate that growth at the more physiologically relevant oxygen level of 7% enhances the stem cell–like phenotype of CD133+ GB cells.

Hydrogen Peroxide Promotes Epithelial to Mesenchymal Transition and Stemness in Human Malignant Mesothelioma Cells

“…Recent studies have suggest that cancer stem cells of several tumor types have similar redox patterns to normal stem cells (Kobayashi et al, 2012). Consistent with the present study, hypoxia enhances the expression of stemness genes such as Sox2 and Oct4 in glioblastoma (McCord et al, 2009). Furthermore, it has been shown that HIF-1α interacts with Notch under hypoxic conditions to maintain a stem cell phenotype and Notch signaling is enhanced by hypoxia (Gustafsson et al, 2005).…”

Cancer stem cells in glioblastoma—molecular signaling and therapeutic targeting

“…While brain tumor stem cells have been linked to a perivascular niche, we have found an additional enrichment of GSCs around necrotic regions that often display hypoxic condition . Several groups have found that restricted oxygen promotes a GSC phenotype (McCord et al, 2009;Soeda et al, 2009). Our group also found that restricted oxygen conditions increase expression of GSC markers and the indicators of self-renewal, suggesting that the state of cancer stem cell may be plastic and that microenvironmental conditions can promote the acquisition of a stem cell-like phenotype (Heddleston et al, , 2010.…”

“…Interestingly, HIF-1α and HIF-2α specifically controlled VEGF expression in GSCs in a nonredundant manner ). In addition, hypoxia can promote the expansion of GSC fraction and regulate expression of stem cell markers McCord et al, 2009;Soeda et al, 2009). Thus, hypoxia may enhance tumor progression and therapeutic resistance through its promotion of a cancer stem cell phenotype and induction of VEGF and other pro-angiogenic factors.…”

miR-495 is upregulated by E12/E47 in breast cancer stem cells, and promotes oncogenesis and hypoxia resistance via downregulation of E-cadherin and REDD1

“…In MDA-MB-231 cells, miR-495 upregulation hindered REDD1 induction and allowed cells to proliferate continuously in a hypoxic environment (Figure 4). Short-term (48 h) culture in hypoxia has been shown to expand the sub-population of cells expressing CSC marker CD133 (Soeda et al, 2009), and to enhance the stem-like phenotypes (McCord et al, 2009). Although most studies have focused on the roles of hypoxia-inducible factors in inducing CSC phenotypes and conferring tumorigenic potential (Covello et al, 2006;Heddleston et al, 2009), our data, in contrast, demonstrate the role of miR-495 promoting cell proliferation in hypoxia.…”