Fig. 3
Cycling hypoxia-mediated Bcl-xL expression results in chemoresistance. a Verification of Bcl-xL knockdown by Tet-regulatable lentiviral knockdown system at the mRNA (a) and protein (b) levels. The lentiviral infected cells were treated for 48 h with Dox (0.04 μg/mL) to induce Bcl-xL knockdown. Error bars denote the standard deviation among triplicate experiments. *P < 0.05, **P < 0.01, ***P < 0.001 compared to no Dox treatment. Caspase-3 activity (c, d) and percentage of apoptotic cells (e, f) in U251 and U87 cells cultured in normoxia, uninterrupted (NiH) hypoxia (<1 % O2), and cycling (CyH) hypoxia (<1 % O2) with or without Bcl-xL knockdown in response to temozolomide (TMZ) treatment. Cells were pretreated for 48 h with Dox (0.04 μg/mL) to induce Bcl-xL knockdown and exposed to hypoxic stresses before TMZ treatment. Error bars denote the standard deviation among triplicate experiments. *P < 0.05, **P < 0.01, ***P < 0.001 compared to control without any treatment. #P < 0.05, ##P < 0.01 compared to normoxia with TMZ treatment