bcl-2 protein downregulation is not required for differentiation of multidrug resistant HL60 leukemia cells.
Parental and multidrug resistant HL60 leukemia cell lines were used to study coupling of expression of apoptotic/cytostatic (bcl-2, bax, bclxL, p21/Waf1, and c-myc) genes during differentiation. The multidrug resistant HL60 cell line, HL60/ADR, was less sensitive than parental cells to cytostatic activity of low (0.4-2 ng/ml) doses of PMA. However, during treatment with standard differentiating doses of PMA (10 ng/ml), no difference between the two cell lines in cytostasis and differentiation was found. Downregulation of c-myc and upregulation of p21/Waf1 proteins showed the same time-course in both cell lines. The bcl-2 mRNA was rapidly downregulated while bax and bclxL gene expression was not altered in both differentiating HL60 and HL60/ADR cells. Significant downregulation of bcl-2 protein occurred only in parental HL60 cells. In HL60/ADR, despite rapid cessation of bcl-2 protein synthesis, almost no change in steady-state bcl-2 protein level was found. The lack of bcl-2 protein downregulation was a result of the prolonged half-life of this protein in HL60/ADR cells. Thus, although downregulation of bcl-2 mRNA is coupled to differentiation, actual loss of bcl-2 protein is not required for accomplishment of the differentiation program.
Blagosklonny
M V
MV
Clinical Pharmacology Branch, National Cancer Institute, NIH, Bethesda, MD 20892, USA.
Alvarez
M
M
Fojo
A
A
Neckers
L M
LM
D015153:Blotting, Western; D002454:Cell Differentiation / Q000187:drug effects; D015536:Down-Regulation; D018432:Drug Resistance, Multiple; D019008:Drug Resistance, Neoplasm; D016259:Genes, myc; D018922:HL-60 Cells / Q000187:drug effects / Q000473:pathology*; D006207:Half-Life; D006801:Humans; D015473:Leukemia, Promyelocytic, Acute / Q000235:genetics / Q000473:pathology; D015689:Oncogene Protein p21(ras) / Q000235:genetics; D016133:Polymerase Chain Reaction; D011518:Proto-Oncogene Proteins / Q000235:genetics*; D019253:Proto-Oncogene Proteins c-bcl-2; D016271:Proto-Oncogene Proteins c-myc / Q000235:genetics; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D051028:bcl-2-Associated X Protein
C494826:BAX protein, human; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D016271:Proto-Oncogene Proteins c-myc; D051028:bcl-2-Associated X Protein; D015689:Oncogene Protein p21(ras); D013755:Tetradecanoylphorbol Acetate