Synthesis of Bcl-2 in response to anthracycline treatment may contribute to an apoptosis-resistant phenotype in leukemic cell lines.
BACKGROUND
Some forms of chemoresistance in leukemia may start from failure of tumour cells to successfully undergo apoptosis and Bcl-2 may play a role in this defect. Therefore, we evaluated the Bcl-2 content and synthesis in relation with the apoptotic potential in leukemic cell lines after anthracycline treatment.


METHODS
U937, HL60, and K562 cells and their drug resistant (DR) variants were treated with varying concentrations of Idarubicin (IDA). Apoptosis was evaluated by fluorescence microscopy after acridine orange staining. Bcl-2 and Bax content were evaluated either by flow cytometry after indirect immunolabelling or by Western blot.


RESULTS
High Bcl-2 contents were not related to a poor ability to undergo apoptosis in U937, HL60, K562 and their DR variants. IDA induced a concentration-dependent increase in Bcl-2 content in all cell lines as long as they do not perform apoptosis. Enhanced Bcl-2 expression was inhibited by cycloheximide, actinomycin D, or antisense oligonucleotide directed against bcl-2 mRNA. Bcl-2 expression was also increased in the resistant U937 variant after serum deprivation or C2-ceramide treatment. The synthesis of Bcl-2 led to an increased Bcl-2/Bax ratio solely in the cells with an apoptosis-resistance phenotype.


CONCLUSIONS
These data suggest that exposure to IDA induces Bcl-2 expression in leukemic cell lines, and that this mechanism could contribute to apoptosis resistance and participate in the acquisition of chemoresistance. They also confirm that the evolution of the Bcl-2/Bax ratio reflects apoptotic ability better than the steady state level of Bcl-2 expression.
Durrieu
F
F
Laboratoire Universitaire d'Hématologie, Université Victor Segalen, Bordeaux, France.
Belaud-Rotureau
M A
MA
Lacombe
F
F
Dumain
P
P
Reiffers
J
J
Boisseau
M R
MR
Bernard
P
P
Belloc
F
F
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000235:genetics; D000903:Antibiotics, Antineoplastic / Q000494:pharmacology / Q000627:therapeutic use*; D017209:Apoptosis / Q000187:drug effects* / Q000235:genetics; D002455:Cell Division / Q000187:drug effects; D002518:Ceramides / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D019008:Drug Resistance, Neoplasm / Q000235:genetics; D005434:Flow Cytometry; D005786:Gene Expression Regulation; D018922:HL-60 Cells; D006801:Humans; D015255:Idarubicin / Q000009:adverse effects / Q000494:pharmacology / Q000627:therapeutic use*; D020014:K562 Cells; D007951:Leukemia, Myeloid / Q000188:drug therapy* / Q000235:genetics / Q000473:pathology*; D010641:Phenotype; D011518:Proto-Oncogene Proteins / Q000096:biosynthesis; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000096:biosynthesis* / Q000235:genetics / Q000502:physiology*; D020298:U937 Cells; D051028:bcl-2-Associated X Protein
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000903:Antibiotics, Antineoplastic; C494826:BAX protein, human; D002518:Ceramides; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D051028:bcl-2-Associated X Protein; D015255:Idarubicin