Doxorubicin induces apoptosis in Jurkat cells by mitochondria-dependent and mitochondria-independent mechanisms under normoxic and hypoxic conditions

In this study, we investigated the molecular mechanism of doxorubicin (dxr)-induced cytotoxicity on Jurkat cells - a model cell of human acute lymphoblastic leukemia - under normoxic (20% O2) and hypoxic (5% O2) conditions. Using in-cell western analysis, immunofluorescence, flow cytometry analysis, and biochemical inhibitors, we evaluated several oxidative stress (OS) and cell death markers. It was found that dxr (5-100 μmol/l) induced apoptosis by OS mechanisms involving DNA fragmentation (8-48%), loss of mitochondrial membrane potential (ΔΨm, 33-92%), and H2O2 production (15-42%) under normoxia. In addition, dxr (10 μmol/l) induced activation and/or nuclei translocation of NF-κB (6.6, 1.6-fold increase), p53 (4.3, 3.1 f), c-Jun (9.5, 5.0 f), apoptosis-inducing factor (AIF) (1.9, 3.9 f), caspase-3 (3.7, 1.9 f), overexpression of Parkin (2.1, 1.2 f)/PINK-1 (2.1 f) proteins, and reduced DJ-1 levels by half compared with untreated cells under normoxia, according to immunofluorescence and in-cell western analysis, respectively. In contrast, dxr (10 μmol/l) could not induce apoptosis in Jurkat cells under hypoxia. Effectively, dxr significantly reduced DNA fragmentation (6%), expression levels of cell death (e.g. p53, c-Jun, caspase-3, AIF), and OS (e.g. Parkin) markers, whereas it increased ΔΨm, hypoxia-inducible factor 1-α (HIF-1α, 3.1, 2.3 f), NF-κB (6.8, 2.0 f), and DJ-1 (1.3, 1.0 f) levels. This investigation suggests that dxr might efficiently eliminate acute lymphoblastic leukemia cells by OS-induced apoptosis under normoxic conditions through a minimal completeness of cell death signaling (i.e. mitochondria-caspase-3/AIF-dependent pathways) and through a direct DNA damage process. However, hypoxic conditions may reduce the effectiveness of dxr toxicity.