Bcl-2 slows in vitro breast cancer growth despite its antiapoptotic effect.
BACKGROUND
Although the Bcl-2 protein promotes tumor cell survival by blocking programmed cell death (apoptosis), Bcl-2 expression has been associated with favorable prognostic indicators in breast cancer. We hypothesize that despite its antiapoptotic effects, Bcl-2 slows tumor cell proliferation.


METHODS
Bcl-2-negative breast cancer cells (SKBr3) were transfected with the bcl-2 gene (Bcl2-1 clone, low expression; Bcl2-2 clone, high expression) or plasmid control (Neo). Cell cycle distribution and kinetics were analyzed using bivariate flow cytometry (PI staining and pulse BrdU uptake). Cells were treated for 72 h with doxorubicin (100 ng/ml) or vehicle (0.01% DMSO) and assayed for cytosolic DNA with diphenylamine to measure apoptosis.


RESULTS
Cell counting showed increased doubling time in the Bcl-2-expressing clones Bcl2-1 and Bcl2-2 (Bcl-2(+)) relative to the Bcl-2-nonexpressing lines SKBr3 and Neo (Bcl-2(-)). Cell cycle analysis showed a decreased S phase fraction in Bcl-2(+) cells. Pulse BrdU uptake showed an increased G1/G0 fraction in Bcl-2(+) cells. Doxorubicin-induced apoptosis occurred in Bcl-2(-) but not in Bcl-2(+) cell lines.


CONCLUSIONS
Despite antiapoptotic effects favoring tumor survival, Bcl-2 prolongs cell cycle. Decreased tumor proliferation may account for the association of Bcl-2 expression with a favorable outcome in breast cancer, even though Bcl-2 may mediate chemoresistance in some patients.
Department of Surgery, University of Washington, Seattle 98195, USA.
K
K
Knowlton
M
M
Mancini
S
S
Creason
C
C
Morales
D
D
Hockenbery
B O
BO
Anderson
D000230:Adenocarcinoma / Q000235:genetics*; D000903:Antibiotics, Antineoplastic / Q000494:pharmacology; D000963:Antimetabolites; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology*; D001943:Breast Neoplasms / Q000235:genetics*; D001973:Bromodeoxyuridine; D002453:Cell Cycle / Q000187:drug effects / Q000502:physiology; D004317:Doxorubicin / Q000494:pharmacology; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000502:physiology*; D014162:Transfection; D014407:Tumor Cells, Cultured / Q000378:metabolism
D000903:Antibiotics, Antineoplastic; D000963:Antimetabolites; D019253:Proto-Oncogene Proteins c-bcl-2; D004317:Doxorubicin; D001973:Bromodeoxyuridine