Abstract
Bcr-abl signals for leukemogenesis of chronic myeloid leukemia (CML) and activates ras. Since the function of promyelocytic leukemia protein (pml) is provoked by ras to promote apoptosis and senescence in untransformed cells, the function is probably masked in CML. Imatinib specifically inhibits bcr-abl and induces apoptosis of CML cells. As reported previously, p53(wild) CML was more resistant to imatinib than that lacking p53. Here, we searched for an imatinib-induced p53 independent proapoptotic mechanism. We found imatinib up-regulated phosphorylation of p38 mitogen-activated protein kinase (MAPK), checkpoint kinase 2 (chk2) and transactivation-competent (TA) p73; expression of pml and bax; formation of PML-nuclear body (NB); and co-localization of TAp73/PML-NB in p53-nonfunctioning K562 and p53(mutant) Meg-01 CML cells, but not in BCR-ABL(-) HL60 cells. In K562 cells, with short interfering RNAs (siRNAs), knockdown of pml led to dephosphorylation of TAp73. Knockdown of either pml or TAp73 abolished the imatinib-induced apoptosis. Inhibition of p38 MAPK with SB203580 led to dephosphorylation of TAp73, abolishment of TAp73/PML-NB co-localization, and the subsequent apoptosis. Conversely, interferon alpha-2a (IFNalpha), which increased phosphrylated TAp73 and TAp73/PML-NB co-localization, increased additively apoptosis with imatinib. The imatinib-induced TAp73/PML-NB co-localization was accompanied by co-immpunoprecipitation of TAp73 with pml. The imatinib-induced co-localization was also found in primary CML cells from 3 of 6 patients, including 2 with p53(mutant) and one with p53(wild). A novel p53-independent proapoptotic mechanism using p38 MAPK /pml/TAp73 axis with a step processing at PML-NB and probably with chk2 and bax being involved is hereby evident in some imatinib-treated CML cells.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Apoptosis / drug effects*
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Apoptosis / physiology
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Benzamides
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Blotting, Western
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Caspase Inhibitors
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Caspases / metabolism
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Cell Nucleus / metabolism*
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Checkpoint Kinase 2
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DNA-Binding Proteins / antagonists & inhibitors
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DNA-Binding Proteins / genetics
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DNA-Binding Proteins / metabolism*
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Drug Resistance, Neoplasm
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HL-60 Cells
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Humans
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Imatinib Mesylate
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Immunoprecipitation
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Interferon-alpha / metabolism
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K562 Cells
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Leukemia, Myelogenous, Chronic, BCR-ABL Positive / drug therapy
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Leukemia, Myelogenous, Chronic, BCR-ABL Positive / metabolism
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Leukemia, Myelogenous, Chronic, BCR-ABL Positive / pathology*
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Nuclear Proteins / antagonists & inhibitors
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Nuclear Proteins / genetics
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Nuclear Proteins / metabolism*
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Phosphorylation / drug effects
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Piperazines / pharmacology*
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Promyelocytic Leukemia Protein
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Protein Kinase Inhibitors / pharmacology
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Protein Serine-Threonine Kinases / metabolism
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Protein-Tyrosine Kinases / antagonists & inhibitors
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Pyrimidines / pharmacology*
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RNA, Small Interfering / pharmacology
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Transcription Factors / genetics
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Transcription Factors / metabolism*
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Tumor Suppressor Protein p53 / genetics
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Tumor Suppressor Protein p53 / metabolism*
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Tumor Suppressor Proteins / antagonists & inhibitors
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Tumor Suppressor Proteins / genetics
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Tumor Suppressor Proteins / metabolism*
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bcl-2-Associated X Protein / metabolism
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p38 Mitogen-Activated Protein Kinases / antagonists & inhibitors
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p38 Mitogen-Activated Protein Kinases / metabolism
Substances
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BAX protein, human
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Benzamides
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Caspase Inhibitors
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DNA-Binding Proteins
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Interferon-alpha
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Nuclear Proteins
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Piperazines
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Promyelocytic Leukemia Protein
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Protein Kinase Inhibitors
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Pyrimidines
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RNA, Small Interfering
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TP53 protein, human
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Transcription Factors
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Tumor Suppressor Protein p53
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Tumor Suppressor Proteins
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bcl-2-Associated X Protein
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PML protein, human
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Imatinib Mesylate
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Checkpoint Kinase 2
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Protein-Tyrosine Kinases
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CHEK2 protein, human
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Protein Serine-Threonine Kinases
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p38 Mitogen-Activated Protein Kinases
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Caspases