Constitutive expression of ectopic c-Myc delays glucocorticoid-evoked apoptosis of human leukemic CEM-C7 cells.
Sensitivity to glucocorticoid (GC)-evoked apoptosis in lymphoid cell lines correlates closely with GC-mediated suppression of c-Myc expression. To establish a functional role for c-Myc in GC-mediated apoptosis, we have stably expressed MycER(TM), the human c-Myc protein fused to the modified ligand-binding domain of the murine estrogen receptor alpha, in GC-sensitive CEM-C7-14 cells. In CEM-C7-14 cells, MycER(TM) constitutively imparts c-Myc functions. Cells expressing MycER(TM) (C7-MycER(TM)) exhibited a marked reduction in cell death after 72 h in 100 nM dexamethasone (Dex), with 10-20-fold more viable cells when compared to the parental CEM-C7-14 clone. General GC responsiveness was not compromised, as evidenced by Dex-mediated suppression of endogenous c-Myc and cyclin D3, and induction of c-Jun and the glucocorticoid receptor. MycER(TM) also blunted Dex-mediated upregulation of p27(kipI) and suppression of the Myc target p53. In comparison to parental CEM-C7-14 cells, Dex-evoked DNA strand breaks were negligible and caspase activation was delayed, but the extent of G1 cell cycle arrest was similar in C7-MycER(TM) cells. Myc-ER(TM) did not result in permanent, complete resistance to GC however, and the GC-treated cells eventually died, indicative of redundant or interactive mechanisms in the GC-evoked lytic response of lymphoid cells. Our results emphasize the importance of c-Myc suppression in GC-evoked apoptosis of CEM-C7-14 cells.
Medh
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Department of Human Biological Chemistry and Genetics, The University of Texas Medical Branch, Galveston, Texas, TX-77555-0645, USA. rmedh@utmb.edu
Wang
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A
Zhou
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Thompson
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D018931:Antineoplastic Agents, Hormonal / Q000494:pharmacology*; D017209:Apoptosis; D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D050976:Basic-Leucine Zipper Transcription Factors; D001708:Biopterins / Q000031:analogs & derivatives* / Q000494:pharmacology; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism; D018797:Cell Cycle Proteins / Q000096:biosynthesis / Q000235:genetics; D002999:Clone Cells; D050760:Cyclin-Dependent Kinase Inhibitor p27; D004249:DNA Damage; D004268:DNA-Binding Proteins / Q000378:metabolism; D003907:Dexamethasone / Q000494:pharmacology*; D047628:Estrogen Receptor alpha; D016193:G1 Phase / Q000187:drug effects; D005938:Glucocorticoids / Q000494:pharmacology*; D006801:Humans; D007945:Leukemia, Lymphoid / Q000378:metabolism / Q000473:pathology*; D016271:Proto-Oncogene Proteins c-myc / Q000235:genetics / Q000378:metabolism* / Q000502:physiology*; D011960:Receptors, Estrogen / Q000235:genetics; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D014157:Transcription Factors; D014162:Transfection; D014407:Tumor Cells, Cultured; D025521:Tumor Suppressor Proteins
D018931:Antineoplastic Agents, Hormonal; D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D050976:Basic-Leucine Zipper Transcription Factors; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D047628:Estrogen Receptor alpha; D005938:Glucocorticoids; C499330:MAX protein, human; C067850:Myc associated factor X; D016271:Proto-Oncogene Proteins c-myc; D011960:Receptors, Estrogen; D011993:Recombinant Fusion Proteins; D014157:Transcription Factors; D025521:Tumor Suppressor Proteins; D050760:Cyclin-Dependent Kinase Inhibitor p27; D001708:Biopterins; D003907:Dexamethasone; C505407:CASP3 protein, human; D053148:Caspase 3; D020169:Caspases; C003402:sapropterin