A far upstream element stimulates c-myc expression in undifferentiated leukemia cells.
A sensitive exonuclease assay revealed multiple sites for interaction, in vitro, of sequence specific factors with c-myc upstream elements. At one site, more than 1500 base pairs upstream of the c-myc promoter P1, binding activity was lost as dimethyl sulfoxide (Me2SO) induced shut-off of c-myc expression in HL-60 and U-937 leukemia cells. The disappearance of other specific binding activities was not noted. In addition, the binding activity was noted to be cell-line specific. The sequence binding the Me2SO-regulated factor was precisely located allowing confirmation of the temporal pattern of regulation by electrophoretic mobility shift analysis. Because the binding activity was most abundant before the decrease of c-myc expression during differentiation, it was inferred that the far upstream element (FUSE) served a positive role, potentiating c-myc expression. A 4-base pair deletion which eliminated binding to FUSE also reduced expression of a transfected, chimeric c-myc-CAT gene in untreated, but not in Me2SO-treated U-937 cells. FUSE and its binding protein may contribute to cell line- and differentiation-specific modes of c-myc regulation.
Laboratory of Pathology, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892.
M I
MI
Avigan
B
B
Strober
D
D
Levens
D001483:Base Sequence; D002454:Cell Differentiation; D004268:DNA-Binding Proteins / Q000502:physiology*; D004121:Dimethyl Sulfoxide / Q000494:pharmacology; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D066298:In Vitro Techniques; D007951:Leukemia, Myeloid / Q000235:genetics / Q000473:pathology; D008969:Molecular Sequence Data; D009841:Oligonucleotides; D016271:Proto-Oncogene Proteins c-myc / Q000235:genetics*; D011519:Proto-Oncogenes; D012045:Regulatory Sequences, Nucleic Acid; D015183:Restriction Mapping; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014407:Tumor Cells, Cultured
D004268:DNA-Binding Proteins; D009841:Oligonucleotides; D016271:Proto-Oncogene Proteins c-myc; D013755:Tetradecanoylphorbol Acetate; D004121:Dimethyl Sulfoxide