Altered sensitivity to retinoid-induced apoptosis associated with changes in the subcellular distribution of Bcl-2.
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.
Bruel
A
A
INSERM U-301, Centre G. Hayem, Hôpital Saint-Louis, Paris, France.
Karsenty
E
E
Schmid
M
M
McDonnell
T J
TJ
Lanotte
M
M
D017209:Apoptosis / Q000187:drug effects; D002451:Cell Compartmentation; D006801:Humans; D015473:Leukemia, Promyelocytic, Acute / Q000188:drug therapy* / Q000473:pathology; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism*; D012176:Retinoids / Q000494:pharmacology*; D014162:Transfection; D014407:Tumor Cells, Cultured; D051028:bcl-2-Associated X Protein
C494826:BAX protein, human; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D012176:Retinoids; D051028:bcl-2-Associated X Protein