The chromatin remodeling factor Mi-2alpha acts as a novel co-activator for human c-Myb.
The c-Myb protein belongs to a group of early hematopoietic transcription factors that are important for progenitor generation and proliferation. These factors have been hypothesized to participate in establishing chromatin patterns specific for hematopoietic genes. In a two-hybrid screening we identified the chromatin remodeling factor Mi-2alpha as an interaction partner for human c-Myb. The main interacting domains were mapped to the N-terminal region of Mi-2alpha and the DNA-binding domain of c-Myb. Surprisingly, functional analysis revealed that Mi-2alpha, previously studied as a subunit in the NuRD co-repressor complex, enhanced c-Myb-dependent reporter activation. Consistently, knock-down of endogenous Mi-2alpha in c-Myb-expressing K562 cells, led to down-regulation of the c-Myb target genes NMU and ADA. When wild-type and helicase-dead Mi-2alpha were compared, the Myb-Mi-2alpha co-activation appeared to be independent of the ATPase/DNA helicase activity of Mi-2alpha. The rationale for the unexpected co-activator function seems to lie in a dual function of Mi-2alpha, by which this factor is able to repress transcription in a helicase-dependent and activate in a helicase-independent fashion, as revealed by Gal4-tethering experiments. Interestingly, desumoylation of c-Myb potentiated the Myb-Mi-2alpha transactivational co-operation, as did co-transfection with p300.
Saether
Thomas
T
Department of Molecular Biosciences, University of Oslo, Oslo, Norway.
Berge
Tone
T
Ledsaak
Marit
M
Matre
Vilborg
V
Alm-Kristiansen
Anne Hege
AH
Dahle
Oyvind
O
Aubry
Florence
F
Gabrielsen
Odd Stokke
OS
D000251:Adenosine Triphosphatases / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D019556:COS Cells; D002478:Cells, Cultured; D002522:Chlorocebus aethiops; D042002:Chromatin Assembly and Disassembly; D004265:DNA Helicases / Q000235:genetics / Q000378:metabolism*; D050881:E1A-Associated p300 Protein / Q000235:genetics / Q000378:metabolism; D017930:Genes, Reporter; D006801:Humans; D020014:K562 Cells; D056245:Mi-2 Nucleosome Remodeling and Deacetylase Complex; D011401:Promoter Regions, Genetic; D020598:Proto-Oncogene Proteins c-myb / Q000235:genetics / Q000378:metabolism*; D025842:SUMO-1 Protein / Q000378:metabolism; D015534:Trans-Activators; D014158:Transcription, Genetic; D015533:Transcriptional Activation; D014162:Transfection; D020798:Two-Hybrid System Techniques
D020598:Proto-Oncogene Proteins c-myb; D025842:SUMO-1 Protein; D015534:Trans-Activators; D050881:E1A-Associated p300 Protein; C494360:EP300 protein, human; D056245:Mi-2 Nucleosome Remodeling and Deacetylase Complex; D000251:Adenosine Triphosphatases; D004265:DNA Helicases; C115322:CHD3 protein, human