Abstract
The c-Myb oncoprotein is a DNA-binding transcription factor with a key role in early stages of hematopoiesis. To expand our knowledge of partners cooperating with c-Myb, we performed a yeast two-hybrid screening with full-length c-Myb as bait. Here, we report FLICE-associated huge protein (FLASH)/CASP8AP2 as a novel Myb-interacting protein. We show that FLASH interacts with the DNA-binding domain of c-Myb and enhances c-Myb-dependent reporter activity and expression of endogenous c-Myb target genes. Chromatin immunoprecipitation assays revealed that FLASH and c-Myb both associate with the MYC promoter region as well as with the intronic enhancer of the c-Myb target gene ADA. Furthermore, siRNA knock-down of FLASH or c-Myb both result in a reduction of MYC and ADA expression. The co-activator effect is mediated through the C-terminal part of FLASH, which binds c-Myb. The FLASH-induced enhancement is comparable with the increase seen with the c-Myb co-activator p300. We find FLASH localized in discrete nuclear speckles in several cell lines, co-localized with c-Myb in active RNA polymerase II foci. These results imply a novel molecular mechanism of regulation of c-Myb activity. We propose that c-Myb cooperates with FLASH in foci associated with active RNA polymerase II, leading to enhancement of Myb-dependent gene activation.
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Acknowledgements
We thank Elen Margrethe Brendeford and Oddmund Nordgaard for helpful assistance in parts of the work. We thank YK Jung, RJ Aguilera and D Livingston for providing the HA-FLASH construct, RAG-2 reporter and the p300 expression construct, respectively. We are grateful to V De Laurenzi for generous help with protocols and reagents. This work was supported by the Norwegian Research Council (ØD, OSG), including the FUGE program (OSG), and The Norwegian Cancer Society (TS, OSG).
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Alm-Kristiansen, A., Sæther, T., Matre, V. et al. FLASH acts as a co-activator of the transcription factor c-Myb and localizes to active RNA polymerase II foci. Oncogene 27, 4644–4656 (2008). https://doi.org/10.1038/onc.2008.105
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DOI: https://doi.org/10.1038/onc.2008.105
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