Increase in the ratio of mitochondrial Bax/Bcl-XL induces Bax activation in human leukemic K562 cell line

Apoptosis. 2004 May;9(3):377-84. doi: 10.1023/b:appt.0000025815.78761.5c.


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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Apoptosis
  • BH3 Interacting Domain Death Agonist Protein
  • Carrier Proteins
  • Cytochrome c Group / metabolism
  • Humans
  • K562 Cells
  • Kinetics
  • Mitochondria / chemistry*
  • Mitochondria / metabolism*
  • Mitochondria / physiology
  • Protein Conformation
  • Protein Transport
  • Proto-Oncogene Proteins c-bcl-2 / chemistry
  • Proto-Oncogene Proteins c-bcl-2 / metabolism*
  • Proto-Oncogene Proteins c-bcl-2 / radiation effects
  • Transfection
  • Ultraviolet Rays
  • bcl-2-Associated X Protein
  • bcl-X Protein


  • BAX protein, human
  • BCL2L1 protein, human
  • BH3 Interacting Domain Death Agonist Protein
  • BID protein, human
  • Carrier Proteins
  • Cytochrome c Group
  • Proto-Oncogene Proteins c-bcl-2
  • bcl-2-Associated X Protein
  • bcl-X Protein