c-myb intron I protein binding and association with transcriptional activity in leukemic cells.
Specific binding of nuclear proteins to the region of transcriptional attenuation has been shown to modulate the expression of c-myb, a nuclear proto-oncogene preferentially expressed in lympho-hematopoietic cells. Here, it plays an important role in processes of differentiation and proliferation. The mechanism that regulates c-myb expression is not yet fully understood. The block of transcriptional elongation which has been mapped to a 1 kb region within murine intron 1 may represent one regulatory pathway. The DNA sequences containing the transcriptional pause site are well conserved between murine and human species, thus Implying similar transcription-control strategies. We compared the binding potential of nuclear extracts (from human fibroblasts and MOLT4 as well as murine NIH3T3- and 70Z/3B- cell lines) to oligonucleotide sequences previously shown to be target binding sites in the murine system. One complex containing a 70 D protein was found to be associated specifically with transcriptionally active leukemia cells. We performed transient expression studies with a CAT reporter construct containing this putative enhancer sequence and yielded significant CAT activity. We identified further a putative 20 kD repressor protein in transcriptionally silent cells and demonstrated that c-Jun is part of an ubiquitously present complex. Our results confirm the participation of intron 1 in transcriptional regulation of the c-myb gene (in mouse and human) and implicate multiple and complex regulatory mechanisms of activation during myelomonocytic differentiation and leukemic cell growth control.
Dooley
S
S
Institut für Humangenetik, Universität des Saarlandes, Homburg, Germany. hgsdoo@med-rz.uni-sb.de
Seib
T
T
Welter
C
C
Blin
N
N
D016475:3T3 Cells; D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D004273:DNA, Neoplasm / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000378:metabolism*; D015536:Down-Regulation; D006801:Humans; D007438:Introns; D015458:Leukemia, T-Cell / Q000378:metabolism*; D016393:Lymphoma, B-Cell / Q000378:metabolism*; D051379:Mice; D008969:Molecular Sequence Data; D009841:Oligonucleotides / Q000378:metabolism; D000090063:Proto-Oncogene Mas; D011518:Proto-Oncogene Proteins / Q000235:genetics* / Q000378:metabolism*; D020598:Proto-Oncogene Proteins c-myb; D012689:Sequence Homology, Nucleic Acid; D015534:Trans-Activators / Q000235:genetics* / Q000378:metabolism*; D018808:Transcription Factor AP-1 / Q000378:metabolism; D014157:Transcription Factors; D014158:Transcription, Genetic / Q000502:physiology*
D004273:DNA, Neoplasm; D004268:DNA-Binding Proteins; C490430:Hivep2 protein, mouse; C000715470:MAS1 protein, human; D009841:Oligonucleotides; D000090063:Proto-Oncogene Mas; D011518:Proto-Oncogene Proteins; D020598:Proto-Oncogene Proteins c-myb; D015534:Trans-Activators; D018808:Transcription Factor AP-1; D014157:Transcription Factors; C077171:HIVEP2 protein, human