v-Myb mediates cooperation of a cell-specific enhancer with the mim-1 promoter.
The oncogenic transcription factor v-Myb disrupts myelomonocytic differentiation and transforms myelomonocytic cells by deregulating the expression of specific target genes. One of these genes, the chicken mim-1 gene, is activated by Myb exclusively in myelomonocytic cells and, therefore, has been an interesting model system to study how Myb activates a target in a lineage-specific manner. Previous work has suggested that Myb activates mim-1 by cooperating with CCAAT box/enhancer binding protein beta (C/EBPbeta) or other C/EBP transcription factors at the mim-1 promoter. We have now identified and characterized a powerful Myb-dependent enhancer located 2 kb upstream of the mim-1 promoter. The enhancer is preferentially active in myelomonocytic cells, confers Myb responsiveness onto a heterologous promoter, and dramatically increases Myb responsiveness of the mim-1 promoter. Chromatin immunoprecipitation demonstrates that v-Myb and C/EBPbeta are bound to the enhancer in v-Myb-transformed cells; furthermore, cooperation of the enhancer with the mim-1 promoter is greatly stimulated by C/EBPbeta and p300. Taken together, our results show that the regulation of mim-1 expression by v-Myb is more complex than previously assumed and involves two distinct regions of the mim-1 gene. A major function of v-Myb (in addition to its role at the mim-1 promoter) apparently is to activate the mim-1 enhancer and, together with C/EBPbeta and p300, facilitate its cooperation with the promoter. Interestingly, our work also shows that the v-Myb protein encoded by avian myeloblastosis virus is defective in this function, suggesting an explanation for why primary avian myeloblastosis virus-transformed myeloblasts do not express the mim-1 gene.
Chayka
Olesya
O
Institut für Biochemie, Westfälische-Wilhelms-Universität Münster, Wilhelm-Klemm-Strasse 2, D-48149 Münster, Germany.
Kintscher
Jörg
J
Braas
Daniel
D
Klempnauer
Karl-Heinz
KH
D000123:Acetyltransferases / Q000235:genetics*; D000818:Animals; D001483:Base Sequence; D022782:CCAAT-Enhancer-Binding Protein-beta / Q000378:metabolism; D002460:Cell Line; D002461:Cell Line, Transformed; D019070:Cell Lineage; D002645:Chickens; D002843:Chromatin / Q000378:metabolism; D047369:Chromatin Immunoprecipitation; D004252:DNA Mutational Analysis; D004742:Enhancer Elements, Genetic; D005786:Gene Expression Regulation; D017930:Genes, Reporter; D005822:Genetic Vectors; D047468:Immunoprecipitation; D008156:Luciferases / Q000378:metabolism; D008264:Macrophages / Q000378:metabolism; D008957:Models, Genetic; D008969:Molecular Sequence Data; D020626:Oncogene Proteins v-myb / Q000378:metabolism / Q000502:physiology*; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D015533:Transcriptional Activation; D014162:Transfection
D022782:CCAAT-Enhancer-Binding Protein-beta; D002843:Chromatin; D020626:Oncogene Proteins v-myb; D008156:Luciferases; D000123:Acetyltransferases; C077509:mim-1 protein, Gallus gallus