Bcl-2-independent Bcr-Abl-mediated resistance to apoptosis: protection is correlated with up regulation of Bcl-xL.
Bcr - Abl is the molecule responsible for both the transformation phenotype and the resistance to chemotherapeutic drugs found in chronic myelogenous leukemia (CML) cells. Wild-type HL-60, a transformed pro-myelocytic cell line, is very susceptible to apoptosis-inducing agents. We show here that expression of Bcr - Abl in HL-60 cells rendered them extremely resistant to apoptosis induced by a wide variety of agents. The anti-apoptotic effect of Bcr - Abl was found to be independent of the phase of the cell cycle. Treatment with antisense oligonucleotides directed to bcr decreased the expression of the ectopic bcr - abl and restored susceptibility to apoptosis. Double mutations affecting the autophosphorylation site and the phosphotyrosine-binding motif (FLVRES) have been previously shown to impair the transforming activity of Bcr - Abl in fibroblasts and hematopoietic cells, however HL-60 cells expressing this double mutant molecule exhibited the same level of resistance to apoptosis as those expressing the wild-type Bcr - Abl. Interestingly, wild type and mutant Bcr - Abl induced in HL-60 cells a dramatic down regulation of Bcl-2 and increased the levels of Bcl-xL. The level of Bax did not change in response to the presence of Bcr - Abl. Antisense oligonucleotides targeted to bcl-x downregulated the expression of Bcl-x, and increased the susceptibility of HL-60. Bcr - Abl cells to staurosporine. Importantly, HL-60 cells overexpressing Bcl-xL showed higher expression of Bcl-xL but lower resistance to apoptosis when compared to HL-60. Bcr - Abl cells. The results described here show that Bcr - Abl is a powerful mammalian anti-apoptotic molecule and can act independently of Bcl-2. Bcl-xL, however, seems to participate in part in Bcr - Abl-mediated resistance to apoptosis in HL-60 cells.
Amarante-Mendes
G P
GP
Division of Cellular Immunology, La Jolla Institute for Allergy and Immunology, San Diego, California 92121, USA.
McGahon
A J
AJ
Nishioka
W K
WK
Afar
D E
DE
Witte
O N
ON
Green
D R
DR
D017209:Apoptosis; D018432:Drug Resistance, Multiple / Q000235:genetics; D016044:Fusion Proteins, bcr-abl / Q000235:genetics / Q000378:metabolism*; D018922:HL-60 Cells; D006801:Humans; D016376:Oligonucleotides, Antisense / Q000494:pharmacology; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism*; D015854:Up-Regulation; D051020:bcl-X Protein
C494811:BCL2L1 protein, human; D016376:Oligonucleotides, Antisense; D019253:Proto-Oncogene Proteins c-bcl-2; D051020:bcl-X Protein; D016044:Fusion Proteins, bcr-abl