title: Loss of mitochondrial membrane potential and caspase activation enhance apoptosis in irradiated K562 cells treated with herbimycin A.
abstract: OBJECTIVE
  We previously reported that herbimycin A (HMA) alters the mode of cell death of K562 cells induced by radiation and enhanced their radiosensitivity. In the present study, we explored the apoptosis-inducing activity of HMA and the fundamental mechanism via which it regulates radiation-induced cell death.
  
  
  METHODS
  Chronic myelogenous leukemia (CML) cell line K562 was used. For X-irradiation and drug treatment, cells were plated at approximately 2x10(5) cells/ml. Exponentially growing cells were treated with 10 Gy of X-ray using a 6-MeV X-ray machine at a dose rate of 200-300 cGy/min. The cells were treated with 0.25 microM HMA immediately after irradiation and HMA remained for the entire culture period. The modes of cell death were discriminated by morphological changes, analysis of cell cycle, analysis of the mitochondrial events, and the expression of apoptosis-related proteins.
  
  
  RESULTS
  Our data demonstrates that radiation induced a significant time-dependent increase of cell death and failed to sustain a prolonged G2 arrest in K562 cells. Radiation-induced cell death caused the accumulation of cyclinB1 and weak nuclear fragmentation, suggesting a mitotic catastrophe. This mitotic catastrophe was dependent upon the mitochondrial permeability transition pore (PTP) opening and was independent of caspase-3. In contrast, K562 cells treated with radiation and HMA had an accelerated cell death and induced a p53-independent apoptosis. This apoptotic pathway was dependent upon an initial hyperpolarization of the mitochondrial inner membrane, following the release of cytochrome c and subsequent caspase-3 activation.
  
  
  CONCLUSIONS
  Two mechanisms of radiation-induced cell death in K562 cells, mitotic catastrophe and apoptosis, are regulated through distinct pathways, mitochondria and caspase-independent and -dependent, respectively. The findings of this study may provide new insights into improving the efficiency of radiotherapy in CML patients.
authors.affiliation: Research Supporting Center for Medical Science (BK21 Program), College of Medicine, Dong-A University, Busan, Korea.
authors.forename: Wol-Soon
authors.initials: WS
authors.lastname: Jo
authors.forename: Min-Ho
authors.initials: MH
authors.lastname: Jeong
authors.forename: Young-Hee
authors.initials: YH
authors.lastname: Jin
authors.forename: Ji-Yeon
authors.initials: JY
authors.lastname: Jang
authors.forename: Byung-Hyouk
authors.initials: BH
authors.lastname: Nam
authors.forename: Seok-Hyun
authors.initials: SH
authors.lastname: Son
authors.forename: Sun-Seob
authors.initials: SS
authors.lastname: Choi
authors.forename: Young-Hyun
authors.initials: YH
authors.lastname: Yoo
authors.forename: Chi-Dug
authors.initials: CD
authors.lastname: Kang
authors.forename: Jae-Dong
authors.initials: JD
authors.lastname: Lee
authors.forename: Soo-Jin
authors.initials: SJ
authors.lastname: Jeong
mesh_terms: D017209:Apoptosis / Q000528:radiation effects*; D016227:Benzoquinones; D020169:Caspases / Q000378:metabolism*; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D016195:G2 Phase; D006801:Humans; D047029:Lactams, Macrocyclic; D015464:Leukemia, Myelogenous, Chronic, BCR-ABL Positive / Q000473:pathology*; D008564:Membrane Potentials; D051336:Mitochondrial Membranes / Q000502:physiology*; D008938:Mitosis / Q000502:physiology / Q000528:radiation effects; D011809:Quinones / Q000494:pharmacology*; D017828:Rifabutin / Q000031:analogs & derivatives; D014407:Tumor Cells, Cultured; D014965:X-Rays
chemical_list: D016227:Benzoquinones; D004791:Enzyme Inhibitors; D047029:Lactams, Macrocyclic; D011809:Quinones; D017828:Rifabutin; C020754:herbimycin; D020169:Caspases