title: The scavenging of superoxide radicals promotes apoptosis induced by a novel cell-permeable fusion protein, sTRAIL:FeSOD, in tumor necrosis factor-related apoptosis-inducing ligand-resistant leukemia cells.
abstract: BACKGROUND
  Many cancer cells develop resistance to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptosis, necessitating combination with chemotherapy, and normal cells manifest side effects due to the combined treatment regimen of TRAIL and chemotherapeutic drugs. A novel cancer therapy utilizing TRAIL is thus urgently needed.
  
  
  RESULTS
  In this study, we exploited TRAIL receptor-mediated endocytosis for the first time to produce a cell-permeable molecule, soluble forms of recombinant TRAIL:iron superoxide dismutase (sTRAIL:FeSOD), which possesses sTRAIL-induced apoptotic ability and FeSOD antioxidant activity. The FeSOD component was rapidly introduced into the cell by sTRAIL and intracellular superoxide radical (O2-), which have been implicated as potential modulators of apoptosis in cancer cells, was eliminated, resulting in a highly reduced cellular environment. The decrease in cellular O2-, which was accompanied by a brief accumulation of H2O2 and downregulation of phosphorylated Akt (p-Akt) and cellular FLICE-inhibitory protein, sensitized K562 leukemia cells and human promyelocytic leukemia (HL-60) cells to TRAIL-induced apoptosis. The low H2O2 levels protected human LO2 hepatocytes from sTRAIL:FeSOD-induced apoptosis despite downregulation of p-Akt. We also obtained evidence that the lack of response to sTRAIL:FeSOD in normal T cells occurred because sTRAIL:FeSOD shows much stronger shifts of redox state in erythroleukemia (K562) and HL-60 cells compared to that in normal T cells. K562 and HL-60 cells underwent sTRAIL:FeSOD-induced apoptosis without the dysfunction of mitochondria.
  
  
  CONCLUSIONS
  The fusion protein overcomes the inability of FeSOD to permeate the cell membrane, exhibits synergistic apoptotic effects on K562 and HL-60 cells and demonstrates minimal toxicity to normal T cells and the normal liver cell line LO2, indicating its potential value for the treatment of leukemia.
authors.affiliation: Institute of Biochemistry, College of Life Sciences, Zijingang campus, Room 345, Zhejiang University, Hangzhou, PR China.
authors.forename: Hongyun
authors.initials: H
authors.lastname: Tang
authors.forename: Yong
authors.initials: Y
authors.lastname: Qin
authors.forename: Jianyong
authors.initials: J
authors.lastname: Li
authors.forename: Xingguo
authors.initials: X
authors.lastname: Gong
mesh_terms: D017209:Apoptosis / Q000187:drug effects; D018922:HL-60 Cells; D006801:Humans; D006861:Hydrogen Peroxide / Q000378:metabolism; D020014:K562 Cells; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D053220:Receptors, TNF-Related Apoptosis-Inducing Ligand / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000494:pharmacology*; D013482:Superoxide Dismutase / Q000494:pharmacology*; D013481:Superoxides / Q000378:metabolism*; D053221:TNF-Related Apoptosis-Inducing Ligand / Q000494:pharmacology*; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*
chemical_list: D053220:Receptors, TNF-Related Apoptosis-Inducing Ligand; D011993:Recombinant Fusion Proteins; D053221:TNF-Related Apoptosis-Inducing Ligand; C105190:TNFRSF10A protein, human; D014409:Tumor Necrosis Factor-alpha; D013481:Superoxides; D006861:Hydrogen Peroxide; D013482:Superoxide Dismutase; D051057:Proto-Oncogene Proteins c-akt