Altered sensitivity to retinoid-induced apoptosis associated with changes in the subcellular distribution of Bcl-2

Exp Cell Res. 1997 Jun 15;233(2):281-7. doi: 10.1006/excr.1997.3594.


In the acute promyelocytic leukemia cell line NB4, Bcl-2 downregulation occurred as a late event of retinoid-induced differentiation. In the maturation-resistant NB4-R1 subclone, retinoids failed to downregulate Bcl-2 even in the situation of apoptosis massively induced by pan-agonists and RXR-selective agonists. We observed that NB4 and NB4-R1 cells differed with respect to the intracellular localization of Bcl-2 which showed a perinuclear localization in NB4-R1 cells, while Bax was broadly expressed in the cytoplasm and to only a minor extent in the perinuclear area. Therefore, the distinct intracellular localization of Bcl-2 and Bax was in general nonoverlapping. Bcl-2 remained massively expressed until cell disruption. Bax was not significantly upregulated in cells committed to death. However, Bax localization changed from a diffuse pattern to concentrate in few specific cytoplasmic area at a stage preceding the formation of apoptotic bodies. A human Bcl-2 transgene was transiently overexpressed in NB4-R1 cells which showed increased resistance to apoptosis induced by retinoids. Stably transfected clones of NB4-R1 cells showed an increased expression of Bcl-2 and a marked resistance to apoptosis. Interestingly, the overexpression of Bcl-2 restored a pattern of uniform Bcl-2 labeling in the cytoplasm and, remarkably, the colocalization of Bcl-2 with Bax. This work demonstrates that the ability of retinoid-induced cells to undergo apoptosis depends on the level of expression and the functional interaction between Bcl-2 and Bax.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Apoptosis* / drug effects
  • Cell Compartmentation
  • Humans
  • Leukemia, Promyelocytic, Acute / drug therapy*
  • Leukemia, Promyelocytic, Acute / pathology
  • Proto-Oncogene Proteins / metabolism
  • Proto-Oncogene Proteins c-bcl-2 / metabolism*
  • Retinoids / pharmacology*
  • Transfection
  • Tumor Cells, Cultured
  • bcl-2-Associated X Protein


  • BAX protein, human
  • Proto-Oncogene Proteins
  • Proto-Oncogene Proteins c-bcl-2
  • Retinoids
  • bcl-2-Associated X Protein