Loss of the bcl-2 phosphorylation loop domain increases resistance of human leukemia cells (U937) to paclitaxel-mediated mitochondrial dysfunction and apoptosis.
The impact of ectopic expression of an N-terminal phosphorylation loop deletant Bcl-2 protein (Bcl-2Delta32-80) on the response of U937 monoblastic leukemia cells to paclitaxel was examined. In contrast to recent findings in HL-60 cells (Fang et al., Cancer Res. 58, 3202, 1998), U937 cells overexpressing Bcl-2Delta32-80 were significantly more resistant than those overexpressing full-length protein to caspase-3 and -9 activation, PARP degradation, and apoptosis induced by paclitaxel (500 nM; 18 h). Bcl-2Delta32-80 was also more effective than its full-length counterpart in opposing paclitaxel-mediated mitochondrial dysfunction, e.g., loss of mitochondrial membrane potential (Deltapsim) and cytochrome c release into the cytoplasm. Enhanced resistance of U937/Bcl-2Delta32-80 cells to paclitaxel was observed primarily in the G2M population. Together, these findings demonstrate that deletion of the Bcl-2 phosphorylation loop domain increases resistance of U937 leukemia cells to paclitaxel-mediated mitochondrial damage and apoptosis and suggest that factors other than, or in addition to, phosphorylation contribute to Bcl-2-related cytoprotectivity against paclitaxel in this model system.
Wang
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Department of Medicine, Virginia Commonwealth University, Richmond, Virginia, 23298, USA.
Wang
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Boise
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Dent
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Grant
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D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects*; D020169:Caspases / Q000378:metabolism; D002453:Cell Cycle / Q000187:drug effects; D002999:Clone Cells; D003574:Cytochrome c Group / Q000378:metabolism; D053938:DNA Fragmentation / Q000187:drug effects; D004351:Drug Resistance / Q000235:genetics; D004789:Enzyme Activation; D006801:Humans; D008564:Membrane Potentials / Q000187:drug effects; D008928:Mitochondria / Q000187:drug effects*; D017239:Paclitaxel / Q000494:pharmacology*; D010766:Phosphorylation; D011506:Proteins / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics* / Q000378:metabolism; D014162:Transfection; D020298:U937 Cells
D000972:Antineoplastic Agents, Phytogenic; D003574:Cytochrome c Group; D011506:Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D020169:Caspases; D017239:Paclitaxel