title: Increase in the ratio of mitochondrial Bax/Bcl-XL induces Bax activation in human leukemic K562 cell line.
abstract: The p53- and Bcl-2-negative leukemic K562 cell line showed resistant to DNA damage-induced Bax activation and apoptosis. The constitutive balanced ratio of Bax/Bcl-XL in K562 mitochondria allowed the formation of active Bax and cytochrome c release from mitochondria in the presence of a BH3-only protein, tBid, in a cell-free system. Bax transfection led to Bax undergoing a conformational change, translocation to mitochondria and homo-oligomerization but not apoptosis in the K562 cell line. After treatment with UV light, while Bcl-XL but not Bax translocated to mitochondria in K562, both Bax and Bcl-XL translocated to mitochondria in the Bax stable transfectant K/Bax cells. The increased ratio of Bax/Bcl-XL in K/Bax mitochondria led to an increased conformationally changed Bax, formation of the homo-multimer of Bax-Bax, and a reduced hetero-dimerization of Bax-Bcl-XL. Increased proportion of active Bax was accompanied with increased percentage of apoptosis. We therefore demonstrate that direct increase in the ratio of mitochondrial Bax/Bcl-XL can induce Bax activation in the p53- and Bcl-2-negative leukemic cells. Increased Bcl-XL translocation and failure in Bax translocation from cytosol to mitochondria play important roles in preventing Bax activation.
authors.affiliation: Department of Haematology, Barts and The London Queen Mary's School of Medicine and Dentistry, University of London, London, UK.
authors.forename: F-T
authors.initials: FT
authors.lastname: Liu
authors.forename: L K
authors.initials: LK
authors.lastname: Goff
authors.forename: J-H
authors.initials: JH
authors.lastname: Hao
authors.forename: A C
authors.initials: AC
authors.lastname: Newland
authors.forename: L
authors.initials: L
authors.lastname: Jia
mesh_terms: D017209:Apoptosis; D051023:BH3 Interacting Domain Death Agonist Protein; D002352:Carrier Proteins; D003574:Cytochrome c Group / Q000378:metabolism; D006801:Humans; D020014:K562 Cells; D007700:Kinetics; D008928:Mitochondria / Q000737:chemistry* / Q000378:metabolism* / Q000502:physiology; D011487:Protein Conformation; D021381:Protein Transport; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000737:chemistry / Q000378:metabolism* / Q000528:radiation effects; D014162:Transfection; D014466:Ultraviolet Rays; D051028:bcl-2-Associated X Protein; D051020:bcl-X Protein
chemical_list: C494826:BAX protein, human; C494811:BCL2L1 protein, human; D051023:BH3 Interacting Domain Death Agonist Protein; C494814:BID protein, human; D002352:Carrier Proteins; D003574:Cytochrome c Group; D019253:Proto-Oncogene Proteins c-bcl-2; D051028:bcl-2-Associated X Protein; D051020:bcl-X Protein