title: FLASH acts as a co-activator of the transcription factor c-Myb and localizes to active RNA polymerase II foci.
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.
authors.affiliation: Department of Molecular Biosciences, University of Oslo, Oslo, Norway.
authors.forename: A H
authors.initials: AH
authors.lastname: Alm-Kristiansen
authors.forename: T
authors.initials: T
authors.lastname: Saether
authors.forename: V
authors.initials: V
authors.lastname: Matre
authors.forename: S
authors.initials: S
authors.lastname: Gilfillan
authors.forename: O
authors.initials: O
authors.lastname: Dahle
authors.forename: O S
authors.initials: OS
authors.lastname: Gabrielsen
mesh_terms: D000818:Animals; D051017:Apoptosis Regulatory Proteins / Q000737:chemistry / Q000378:metabolism* / Q000502:physiology*; D019556:COS Cells; D002135:Calcium-Binding Proteins / Q000737:chemistry / Q000378:metabolism* / Q000502:physiology*; D002467:Cell Nucleus / Q000378:metabolism; D002478:Cells, Cultured; D002522:Chlorocebus aethiops; D006801:Humans; D020014:K562 Cells; D051379:Mice; D041681:NIH 3T3 Cells; D011485:Protein Binding; D017434:Protein Structure, Tertiary / Q000502:physiology; D020598:Proto-Oncogene Proteins c-myb / Q000737:chemistry / Q000378:metabolism* / Q000502:physiology; D012319:RNA Polymerase II / Q000378:metabolism*; D014018:Tissue Distribution; D015534:Trans-Activators / Q000502:physiology; D014157:Transcription Factors / Q000502:physiology; D015533:Transcriptional Activation / Q000502:physiology
chemical_list: D051017:Apoptosis Regulatory Proteins; C485604:CASP8AP2 protein, human; D002135:Calcium-Binding Proteins; D020598:Proto-Oncogene Proteins c-myb; D015534:Trans-Activators; D014157:Transcription Factors; D012319:RNA Polymerase II