Members of the nuclear factor kappa B family transactivate the murine c-myb gene.
Expression of the c-myb proto-oncogene is primarily detected in normal tissue and tumor cell lines of immature hematopoietic origin, and the down-regulation of c-myb expression is associated with hematopoietic maturation. Cell lines that represent mature, differentiated hematopoietic cell types contain 10-100-fold less c-myb mRNA than immature hematopoietic cell types. Differences in steady-state c-myb mRNA levels appear to be primarily maintained by a conditional block to transcription elongation that occurs in the first intron of the gene. The block to transcription elongation has been mapped, using nuclear run-on analysis, to a region of DNA sequence that is highly conserved between mouse and man. Two sets of DNA-protein interactions, flanking the site of the block to transcription elongation, were detected that exhibited DNA-binding activities that strongly correlated with low steady-state c-myb mRNA levels. Several criteria demonstrated that members of the nuclear factor kappa B (NF-kappa B) family of transcription factors were involved in the DNA-protein interactions identified in these two sets. Surprisingly, cotransfection experiments demonstrated that coexpression of members of the NF-kappa B family, specifically p50 with p65 and p65 with c-Rel, transactivated a c-myb/chloramphenicol acetyltransferase reporter construct that contained 5'-flanking sequences, exon I, intron I, and exon II of the c-myb gene. Transactivation by these heterodimer combinations was dependent on regions of the c-myb first intron containing the NF-kappa B-binding sites. These findings suggest that NF-kappa B family members may be involved in either modifying the efficiency of transcription attenuation or acting as an enhancer-like activity to increase transcription initiation. Thus, the regulation of c-myb transcription may be quite complex, and members of the NF-kappa B family likely play an important role in this regulation.
Toth
C R
CR
Department of Microbiology and Immunology, University of Virginia, Charlottesville 22903, USA.
Hostutler
R F
RF
Baldwin
A S
AS
Bender
T P
TP
D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism; D017124:Conserved Sequence; D004247:DNA / Q000737:chemistry / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000096:biosynthesis / Q000378:metabolism; D005091:Exons; D005786:Gene Expression Regulation; D007438:Introns; D016393:Lymphoma, B-Cell; D051379:Mice; D008969:Molecular Sequence Data; D016328:NF-kappa B / Q000378:metabolism*; D009838:Oligodeoxyribonucleotides; D009857:Oncogenes; D011401:Promoter Regions, Genetic; D011518:Proto-Oncogene Proteins / Q000096:biosynthesis*; D020598:Proto-Oncogene Proteins c-myb; D011519:Proto-Oncogenes; D015183:Restriction Mapping; D012689:Sequence Homology, Nucleic Acid; D014158:Transcription, Genetic; D014407:Tumor Cells, Cultured
D004268:DNA-Binding Proteins; D016328:NF-kappa B; D009838:Oligodeoxyribonucleotides; D011518:Proto-Oncogene Proteins; D020598:Proto-Oncogene Proteins c-myb; D004247:DNA