Suppression of Hypoxia-Inducible Factor 1α (HIF-1α) by Tirapazamine Is Dependent on eIF2α Phosphorylation Rather Than the mTORC1/4E-BP1 Pathway
Figure 5
TPZ reduces HIF-1α protein only under hypoxic conditions, and its activity is independent of its topoisomerase II inhibition.
(A) HeLa cells were exposed to normoxic conditions for 4 h in the presence of TPZ. (B) Cells were treated with varying concentrations of TPZ for 4 h, as indicated, in the presence of the hypoxia-mimetic agent cobalt chloride (CoCl2). (C) HeLa cells were treated for 4 h in normoxia, hypoxia or with CoCl2 in the presence of TPZ at the indicated concentrations. (D) Cells were treated with 20 µM TPZ, 20 µM etoposide and 10 µM adriamycin for 4 h. (E) Topoisomerase IIα was knocked down using siRNA, as described in the Materials and Methods, followed by drug treatment (20 µM TPZ, 20 µM etoposide and 10 µM adriamycin). Proteins were detected by western-blot analysis.