Hypoxia-inducible factor 1α regulates chemoresistance of glioma cells in hypoxia environment: A preliminary study

Abstract

Objective To confirm that hypoxia can induce reverse differentiation of glioma cells or maintain the stemness of glioma cells, leading to chemotherapeutic resistance and to explore its mechanism by in vitro studies. Methods U87 and GL261 cells were considered as glioma cells line in this study. CD133+ CD15+ Nestin+ and CD133-CD15-Nestin- glioma cells were sorted through magnetic activated cell sorting and cultured in normoxia and hypoxia environments. CD133+ CD15+ Nestin+ and CD133-CD15-Nestin- glioma cells were cultured in hypoxia to detect the expressions of CD133, CD15, Nestin and hypoxia-inducible factor (HIF) 1α by Western blot and immunofluorescence assay. Cell apoptosis and half maximal inhibitory concentration (IC50) values were assessed after temozolomide (TMZ) treatment. HIF1α knocked-out glioma cells were cultured in hypoxia and the expressions of CD133, CD15 and Nestin were determined by Western blot. Besides, we compared cells apoptosis rate and IC50 values after TMZ treatment between HIF1α knocked-out glioma cells and control group. Results GL261 CD133+ CD15+ Nestin+ cells showed lower cells apoptosis and higher IC50 value compared with Gl261 CD133-CD15-Nestin- cells after TMZ treatment (both P<0.05). The results of Western blot showed that the expression levels of CD133, CD15, Nestin and HIF1α in CD133+ CD15+ Nestin+ and CD133-CD15-Nestin- U87 cells in hypoxia were higher than those in control group cultured in normoxia, which were barely expressed in the latter (all P<0.05). There were lower cells apoptosis and higher IC50 value after TMZ treatment in hypoxia in CD133+ CD15+ Nestin+ and CD133-CD15-Nestin- U87 and GL261 glioma cells (all P<0.05). The expressions of CD133, CD15 and Nestin were decreased in HIF1α knocked-out glioma cells compared with those in cells without knocking out HIF1α. Higher cells apoptosis rate and lower IC50 value were reported for HIF1α knocked-out glioma cells after TMZ treatment (all P<0.05). Conclusion Hypoxia could induce chemotherapy resistance by maintaining the stemness of glioma stem cells or promoting the reverse differentiation of normally differentiated glioma cells. Key words: Glioma; Cell hypoxia; Hypoxia-inducible factor 1, alpha subunit; Chemoresistance